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Engineering plant facilities 04 mechanics hvac


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Plant Manufacturing and Building Facilities Engineering

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Engineering plant facilities 04 mechanics hvac

  1. 1. L | C | LOGISTICS PLANT MANUFACTURING AND BUILDING FACILITIES EQUIPMENT Engineering-Book ENGINEERING FUNDAMENTALS AND HOW IT WORKS MECHANICS HVAC September 2014 Supply Chain Manufacturing & DC Facilities Logistics Operations Planning Management Expertise in Process Engineering Optimization Solutions & Industrial Engineering Projects Management
  2. 2. Thermal comfort Conditions/variables that contribute to making space comfortable for its occupants Human comfort ● Dry-bulb temperature ● Humidity ● Air movement ● Fresh air ● Clean air ● Noise level ● Adequate lighting ● Proper furniture and work surfaces ● …… Air-conditioning systems: providing thermal comfort Mechanics HVAC
  3. 3. radiation convection hot water conduction cool air warm air Air-conditioning is a process of heat transfer ● Types of heat  Sensible heat results in a change of dry-bulb temperature.  Latent heat is associated with the addition or removal of moisture, or phase change, for example water converted to steam. ● Quantity & quality of heat  Heat energy cannot be destroyed  Heat always flows from a higher temperature substance to a lower temperature substance ● How is heat being transferred?  Convection, Conduction, Radiation  Working fluid: water and air 100oC sensible heat latent heat 30oC 100oC 100oC Mechanics HVAC
  4. 4. Mechanics HVAC Air property and Psychometric process ● Parameters of the air  dry-bulb / wet-bulb / dew point temperature, relative humidity, etc ● Process of air-conditioning A B A B comfort zone dry-bulb temperature humidity ratio 21.2ƒC 26.7ƒC
  5. 5. Mechanics HVAC Central HVAC system ● Chiller plant  Chillers  Cooling tower  Pumps ● Water system  Water distribution  Pipes & accessories ● Air system  Air handling units  Air distribution  Terminal… ● Instrument & controls ● ……
  6. 6. Mechanics HVAC Type of water chillers ● Chemical absorption  Heat source needed -- steam, hot water, etc. ● Vapor-compression  Electrical power needed to drive the compressors ● Air-cooled or Water-cooled
  7. 7. Mechanics HVAC Chiller plant schematics ● Condenser water ● Chiller water  Primary–Secondary flow system  Primary–only flow system
  8. 8. Mechanics HVAC Chiller plant operation ● Sequencing Too fast response causes: • system unstable, waste energy • unnecessary wear & tear on mechanical components  Turn-on / turn-off to meet the demand ● Parameters to be monitored  Temperature, flow rate, capacity, motor current, etc ● System timers: to prevent frequent on/off of equipment  Confirm the demand before starting the next unit  Staging timer to prevent more units from starting  Minimum period required to run a unit prior to turning it off
  9. 9. Chiller in operation  The compressor compresses the refrigerant gas. Raising its temperature and pressure.  The hot gas dissipates its heat to condenser water, and condenses into liquid at high pressure.  The high-pressure refrigerant liquid flows through the expansion device (valve or orifice); its pressure and temperature are lowered down.  Chilled water flows through the evaporator and cooled down by the cold refrigerant; vaporized refrigerant gas is returned to the compressor again. Chiller Mechanics HVAC
  10. 10. Refrigeration cycle Common Refrigerants used in chillers R134a, R123, R132, R139 R134a R123 Atmospheric pressure Temperature Presure Chillers operate at different pressure with different refrigerant Mechanics HVAC
  11. 11. Refrigeration cycle Compressor & Expansion device: refrigerant heated up/cooled down Low-pressure/temp refrigerant absorb heat from chilled water High-pressure/temp refrigerant release heat to condenser water Mechanics HVAC
  12. 12. Mechanics HVAC Compressor The main function of the compressor is to increase pressure/temperature of refrigerant. The core components of a centrifugal compressor is the impeller. Rotation of the impeller creates a low pressure at the volute which draws in refrigerant vapor and accelerates it. The pressure and temperature of refrigerant is increased by centrifugal acceleration.
  13. 13. Condenser A shell & tube heat exchanger. Refrigerant is cooled down by condenser water from cooling towers. tt nnaarreeggiirrff eeRR tt nnaarreeggiirrff eeRR CWS/R in the tubes CHWS/R in the tubes Mechanics HVAC
  14. 14. Mechanics HVAC Evaporator A shell & tube heat-exchanger. Chilled water is cooled down by refrigerant.
  15. 15. Mechanics HVAC Expansion device To maintain the pressure difference between Condenser (high pressure) and Evaporator (low pressure). Pressure drop occurs when high- pressure refrigerant liquid flows through the expansion device. Pressure drop creates a small portion of liquid to flash, and reduces the remaining refrigerant to evaporator temperature.
  16. 16. Operation log ● Review daily operation log is necessary ● Important parameters  Evaporator and Condenser refrigerant pressure  CHWS/R and CWS/R temperature  Oil pressure and level  Motor current, winding temperature, etc • Vibration • …… Review operation parameters for early alert of problems Mechanics HVAC
  17. 17. Maintenance tasks ● Mechanical, electrical and controls  Visual inspection, check for leakage  Tighten electrical/controls terminals  Safety interlocks, etc ● Follow recommendations from the manufactures  Change of oil and oil filters  Oil analysis  Check shaft alignment  Replace shaft seal  Inspect purge system  …… ● Good practices  Maintain good quality of water treatment  Cleaning of Condenser tubes  …… If applicable Mechanics HVAC
  18. 18. Static Pressure Friction Flow Velocity pressure Discharge Suction Impeller Basics ● Pressure, friction and flow ● Water pumps  Increase pressure of the water and move it from one point to another  Centrifugal pumps are commonly used in HVAC systems ● Centrifugal pumps  Rotating impeller creates centrifugal force and a pressure difference across the impeller. Mechanics HVAC
  19. 19. Pumps, pipes and accessories ● Pump components  Impeller, shaft & seal, bearing, casing, etc. ● Piping and accessories  Typical installation  Valves, strainer, flexible connection, pressure gauges, thermometers, etc. Globe valve Check valve Pressure gauge Thermometer Flexible connection Strainer Pump Pressure gauge Thermometer Gate valve Mechanics HVAC
  20. 20. Mechanics HVAC Operation and maintenance ● Important parameters  Suction & discharge pressure, flow, vibration, bearing temperature, motor KW, ● NPSH (Net Positive Suction Head) and cavitations  Suction pressure to be maintained. ● Parallel operation Single pump performance curve System curve Parallel pump performance curve Single pump operating point etc Parallel pump operating point
  21. 21. Operation and maintenance ● Common breakdown  Mechanical seal failure  Excessive vibrations  Pump rubbing or seizure  Inadequate performance (flow rate, head developed, power consumption)  Leaking casing ● Main areas of maintenance  Lubrication  Seal replacement  Shaft alignment Laser alignment Mechanics HVAC
  22. 22. Basics ● Function of cooling towers  When warm water flows through the tower, heat is absorbed by air and the remaining water is cooled, through evaporation of a small percentage of the total water flow. ● Type of cooling towers  Natural draft, mechanical draft  Forced draft, induced draft  Counter-flow, cross-flow Release heat from HVAC system to surrounding air Forced draft, counter flow Induced draft, counter flow Induced draft, cross flow Mechanics HVAC
  23. 23. Mechanics HVAC Components ● Fill ● Structure, frame, casing ● Fan, motor and drive ● Hot water distribution ● Cold water basin ● Make-up water
  24. 24. Operation and Maintenance ● Air side  Motor, shaft, gearbox, fan ● Water side  Fill  Hot & cold water basin/nozzle  Make-up water, drain, overflow  Water treatment • Corrosion, scaling, bacteria ● Structural integrity  Structure  casing Follow O & M checklist Mechanics HVAC
  25. 25. Mechanics HVAC Fan basics ● Types of fans  Centrifugal fan – Forward and Backward curved  Axial fan – positive discharge head ● Fan system components  Impeller, motor, drive, ducts, damper, air-conditioning equipment. Air Axial fan Forward curve Backward curve Centrifugal fan Air Air Air Air
  26. 26. Mechanics HVAC Maintenance of fans ● Common problems  Belt drive wear, rupture, noisy, etc  Bearing wear, noisy, high temperature  Dirty fan blades  … ● Common maintenance tasks  Regular inspection of all components  Bearing maintenance: lubrication, replacement  Belt tightening and replacement  Cleaning
  27. 27. Air distribution, ducts & accessories ● Equipment ● Ducts  Rectangular, Round, flexible  VAV box (variable air volume)  Dampers ● Terminals  Supply air diffuser  Return air grills Damper Ducts Diffusers Mechanics HVAC
  28. 28. Configuration of AHUs ● Functions of AHUs  Conditions the air and distributes it to various spaces.  Fresh air and re-circulation air are often mixed and conditioned. ● Components  Casing, Cooling/dehumidification coil, Heating coil, Humidifier, Filters.  Controls – temperature/humidity, fan speed, interlock, etc.  Fan, motor, drive  Modular design Typical arrangement Mechanics HVAC
  29. 29. Operation and Maintenance ● Monitoring operation conditions  Supply/return air temperature  Filter condition and pressure-drop  Supply/return water temperature  Strainer pressure-drop  Functioning of controls -- sensors, actuators, interlock, etc  Drain pipes operation  Moving parts – motor, fan, drive ● Maintenance tasks  Water side  Air side  Motor/fan/drive  Controls Maintain good performance of equipment: 1. Review operation log sheets 2. Follow maintenance checklist Mechanics HVAC
  30. 30. 33333333333333333330000000000000000000 Basic functions of control systems ● To maintain environment conditions in the space:  Temperature  Humidity  Air distribution  Indoor air quality ● Components of control systems  Sensor  Controller  Actuator + damper/valve, etc The controller compares the temperature of the air leaving coil to the setting, and adjusts the valve to meet the setting. Mechanics HVAC
  31. 31. Maintenance of control systems ● Common issues:  Damage of electronic components/device  Loosening of damper linkage fastenings  Loosening of control wiring connections ● Planned maintenance:  Re-calibration  Functioning test Control valve not closed…when AHU stopped Mechanics HVAC
  32. 32. Mechanics HVAC The float valve maintains the constant level of the liquid in the flooded evaporator irrespective of the pressure and the temperature inside it The float of the low side float valve is placed in the evaporator, which is at low pressure The construction and the working of the low side refrigeration float valve are similar to the float valve used in the water tank used for maintaining the level of the liquid In the water tank the float keeps floating inside on the water and its arm is connected to the water connection When the level of the water drops down the arm of the float valve moves to open the water connection and allows the flow of the water to the tank When the tank gets filled the float rises up and the arm closes the water connection The float valve in the refrigeration plant also works in a similar manner
  33. 33. Mechanics HVAC The valve assembly of the low side float valve comprises of the hollow ball, a float arm, needle valve and the seat The valve seat and the needle forms the orifice opening of the valve that provides the throttling effect to the refrigerant passing through it and through which the regulated amount of the refrigerant can pass The valve seat and the needle are located inside the chamber of the float valve which is connected to the evaporator The hollow ball or float floats on the refrigerant inside the evaporator and moves up and down as per the level of the liquid The hollow ball is connected to the needle and valve seat via the float arm Thus as the ball moves up and down the float arm also moves that allows for the opening or the closing of the orifice.
  34. 34. Mechanics HVAC When the level of the refrigerant drops inside the evaporator due to high refrigeration load the float moves down, this allows for the opening of the orifice of the valve increasing the flow of the refrigerant When the sufficient amount of refrigerant enters the evaporator the level of the float rises due to which moves the float valve closes The movement of the float and the opening of the float valve is in accordance to the refrigeration load on the evaporator High Side Float Valve While in the low side float valve the float chamber is placed in the evaporator on low pressure side, in the high pressure side float valve and the float chamber is placed on the high pressure side between the condenser and the evaporator In low side float valve the valve opens as the level of the refrigerant drops in the evaporator, but in high side float valve the valve opens when the level of the refrigerant increases in the chamber
  35. 35. Mechanics HVAC The refrigerant condensed in the condenser moves to the chamber of the high pressure float valve As the level of the refrigerant rises the float ball moves up and opens the float valve that allows for the passage of the refrigerant through needle valve The level of the refrigerant would rise in float chamber when more refrigerant is coming from the condenser that means there is more load on the plant Thus when there is higher load on the plant there is increase in the flow of the refrigerant through the float valve The level of the refrigerant coming from the condenser reduces when there is less load on the plant When the level of the refrigerant drops down the orifice of the needle valve closes, thus reducing the flow of the refrigerant through it The high side float valves are usually used with the centrifugal refrigeration plants.
  36. 36. Mechanics HVAC Capillary tube used as the throttling device in the domestic refrigerators, deep freezers, water coolers and air conditioners When the refrigerant leaves the condenser and enters the capillary tube its pressure drops down suddenly due to very small diameter of the capillary In capillary the fall in pressure of the refrigerant takes place not due to the orifice but due to the small opening of the capillary The decrease in pressure of the refrigerant through the capillary depends on the diameter of the capillary and the length of the capillary Smaller is the diameter and more is the length of the capillary more is the drop in pressure of the refrigerant as it passes through it In the normal working conditions of the refrigeration plant there is drop in pressure of the refrigerant across the capillary but when the plant stops the refrigerant pressure across the two sides of the capillary equalize
  37. 37. Mechanics HVAC Due to this reason when the compressor restarts there won’t be much load on it. Also, due to this reason one cannot over-charge the refrigeration system with the refrigerant and no receiver is used The capillary tube is non-adjustable device that cannot control the flow of the refrigerant through it as one can do in the automatic throttling valve Due to this the refrigerant flow through the capillary changes as the surrounding conditions changes. For instance as the condenser pressure increases due to high atmospheric pressure and the evaporator pressure reduces due to lesser refrigeration load the flow of the refrigerant through the capillary changes Thus the capillary tube is designed for certain ambient conditions. However, if it is selected properly, it can work reasonably well over a wide range of conditions The length of the capillary of particular diameter required for the refrigeration applications cannot be found by fixed formula rather it is calculated by the empirical calculations Some approximate length required for certain application is found out and it is then corrected by the experiments
  38. 38. Mechanics HVAC When the refrigerant leaves the condenser and enters the capillary tube its pressure drops down suddenly due to very small diameter of the capillary In capillary the fall in pressure of the refrigerant takes place not due to the orifice but due to the small opening of the capillary The decrease in pressure of the refrigerant through the capillary depends on the diameter of the capillary and the length of the capillary Smaller is the diameter and more is the length of the capillary more is the drop in pressure of the refrigerant as it passes through it The capillary tube limits the maximum amount of the refrigerant that can be charged in the refrigeration system due to which the receiver is not required in these systems When the refrigeration plant stops the pressure across the capillary tube becomes same and also along the whole refrigeration cycle the pressure is constant This means that when the plant is stopped the pressure at the suction and discharge side of the compressor are same
  39. 39. Mechanics HVAC Thus when the compressor is restarted there is not much load on it since it does not have to overcome very high pressures Due to this the compressor motor of smaller torque can be selected for driving the compressor, thus reducing the cost of the compressor When the fresh refrigerant is charged into the refrigerator or the deep freezers, the capillary of the system should also be changed This is because when the machine is stopped some oil particles may clog the capillary as the refrigerant leaks to the atmosphere
  40. 40. Mechanics HVAC Accumulator is a small hollow cylindrical shape vessel made of copper It is fitted between the evaporator and the compressor of the refrigeration system towards the suction side of the compressor Sometimes the refrigerant leaving the evaporator carries liquid particles These particles get separated in the accumulator The liquid refrigerant collected in the accumulator slowly gets vaporized and is then sucked by the compressor The accumulator also prevents the flooding of the liquid refrigerant to the compressor when the load on the evaporator drops down drastically
  41. 41. Mechanics HVAC Simple ones are made from fiberglass or polyester, and allow for the passage of air but trap large particles of dust These filters are often placed in front of fans because the large particles of dust can accumulate over time and eventually clog up the machinery. These basic filters serve no real protection, but they do protect the machinery from burning out Some types of filter can be washed and reused, but the majority of them are meant to be thrown away after they become too dirty to use anymore. Then they are simply replaced with a new one They do nothing against harmful moulds and bacteria. They are equally useless against airborne viruses
  42. 42. Mechanics HVAC Another form of air filtration system is the needle ionizer and the plate ionizer, also known as Electrostatic Precipitators. These devices use electricity to filter out all of the smoke and dust out of the air Plate ionizers use electricity to give the incoming air a static charge The air then is passed through a series of metal “plates” that contain the opposite charge of the air surrounding it This causes all of those charged particles to be attracted to the plates, and in this way the air is effectively purified Needle ionizers use high voltage electricity to create negative electrons These electrons run up the length of a pointed spike, or needle, where they stream into the air and attract oxygen molecules At this point, they become negative ions. Negative ions occur naturally in the air we breathe, and they are quite harmless. These negative ions attach themselves to airborne particles When enough negative ions attach to a particle, it gets too heavy to float in the air and drops to the ground
  43. 43. Mechanics HVAC An inverter in an air conditioner is used to control the speed of the compressor motor to drive variable refrigerant flow in an air conditioning system to regulate the conditioned-space temperature. By contrast, traditional air conditioners regulate temperature by using a compressor that is periodically either working at maximum capacity or switched off entirely. Inverter-equipped air conditioners have a variable-frequency drive that incorporates an adjustable electrical inverter to control the speed of the motor and thus the compressor and cooling output The variable-frequency drive uses a rectifier to convert the incoming alternating current (AC) to direct current (DC) and then uses pulse-width modulation in an electrical inverter to produce AC of a desired frequency. The variable frequency AC drives a brushless motor or an induction motor. As the speed of an induction motor is proportional to the frequency of the AC, the compressor can now run at different speeds A microcontroller can then sample the current ambient air temperature and adjust the speed of the compressor appropriately. Eliminating stop-start cycles increases efficiency
  44. 44. Mechanics HVAC Variable-frequency drive (VFD) (also termed adjustable-frequency drive, variable-speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage. Where process conditions demand adjustment of flow from a pump or fan, varying the speed of the drive may save energy compared with other techniques for flow control.
  45. 45. Mechanics HVAC An adjustable speed drive can often provide smoother operation compared to an alternative fixed speed mode of operation For example, When fixed speed pumps are used, the pumps are set to start when the level of the liquid in the reaches some high point and stop when the level has been reduced to a low point Cycling the pumps on and off results in frequent high surges of electric current to start the motors that results in electromagnetic and thermal stresses in the motors and power control equipment, the pumps and pipes are subjected to mechanical and hydraulic stresses When adjustable speed drives are used, the pumps operate continuously at a speed that increases as the level increases This matches the outflow to the average inflow and provides a much smoother operation of the process
  46. 46. Mechanics HVAC The variable frequency drive controls the speed of compressor motor The compressor is specifically designed to run at different motor speeds to modulate cooling output Variable speed operation requires an appropriate compressor for full speed operation and a special compressor lubrication system Proper oil management is a critical requirement to ensure compressor lifetime Proper oil management provides proper lubrication for scroll set at low speed and prevents excess oil from being injected into the circuit when operating at full speed Inverter compressor: uses an external variable frequency drive - to control the speed of compressor. The refrigerant flow rate is changed by the change in the speed of compressor. The turndown ratio depends on the system configuration and manufacturer. It modulates from 15 or 25% up to 100% at full capacity with a single inverter from 12 to 100% with a hybrid tandem
  47. 47. Mechanics HVAC Importance of the inverter drive: The compressor and drive need to be qualified to work together and for dedicated applications The drive modulates the compressor speed and prevents it from operating out of the compressor operating limits The inverter frequency drives need to use algorithms developed specifically for heating, ventilation and air conditioning (HVAC) or for refrigeration They ensure that the system will run within the application constraints The drive can also manage other devices such as oil injection valves or multiple compressors. As the compressor rotational speed changes, the amount of refrigerant — and oil — flowing through the compressor increases or decreases The drive ensures that the compressor and bearings are optimally lubricated at all compressor speeds
  48. 48. Mechanics HVAC AC Motor The AC electric motor used in a VFD system is a three-phase induction motor. Some types of single-phase motors can be used, but three-phase motors are usually preferred, and are the most economical motor choice Controller The VFD controller is a solid state power electronics conversion system consisting of three distinct sub-systems: a rectifier bridge converter, a direct current (DC) link, and an inverter. Voltage-source inverter (VSI) drives are by far the most common type of drives. Most drives are AC-AC drives in that they convert AC line input to AC inverter output. The most basic rectifier converter for the VSI drive is configured as a three-phase, six-pulse, full-wave diode bridge. In a VSI drive, the DC link consists of a capacitor which smoothes out the converter's DC output ripple and provides a stiff input to the inverter. This filtered DC voltage is converted to quasi-sinusoidal AC voltage output using the inverter's active switching elements. VSI drives provide higher power factor and lower harmonic distortion than phase-controlled current-source inverter (CSI) and load-commutated inverter (LCI) drives (see 'Generic topologies' sub-section below). The drive controller can also be configured as a phase converter having single-phase converter input and three-phase inverter output
  49. 49. Mechanics HVAC VRF / VRV technology—basic principle: Air conditioning removes heat from the space to be cooled by pushing refrigerant through a cycle The cycle comprises four elements common to all HVAC systems, based on the fluid dynamics When a refrigerant expands, it becomes cooler; When it is compressed, it becomes warmer; Changing phases from fluid to gas or back again adds to the cooling/warming effect The system is composed of a compressor, a condensing unit, a metering device (or expansion valve), and an evaporator or heat sink.
  50. 50. Mechanics HVAC Window units, pack all the elements of the cycle into one small device the hot side being on the outside the cool part facing the space to be cooled. Split-system units split the hot side of the cycle (placed outside the building) from the cold side (placed inside the building) Cool air is often transferred from the evaporator to many different rooms by an air-handling unit, which distributes the conditioned air through a series of ducts
  51. 51. Mechanics HVAC Direct expansion (DX) system The “hot” part of the cycle starts at the compressor, which compresses refrigerant vapor and turns it into a high-temperature gas The refrigerant then goes through a condensing unit, a series of coils in which the gas loses heat and becomes liquid The “cold” part of the cycle begins as the liquid refrigerant passes through the metering device, which causes a drop in pressure The refrigerant then goes through the evaporator (another series of coils) In the process of evaporating it absorbs heat from the surrounding area Producing a cooling effect that is dissipated through fans After completing the cycle, the refrigerant goes back to the compressor in its initial low-pressure, gaseous state
  52. 52. Mechanics HVAC Industry standards set limits on the length of piping running between the condenser and the evaporator in DX systems. When the needs of a particular project exceed such limits, chilled water systems are often used as an alternative In chilled water systems water is cooled by a regular refrigeration system and then circulated through ducts to air handlers throughout the building Because there is no limit to the permitted length of water pipes, these systems are often used to cool large buildings or entire campuses Chilling is often cycled at night to take advantage of off-peak energy rates
  53. 53. Mechanics HVAC DX systems configurations vary among the types of air-conditioning systems available, but always one condensing unit to one evaporator once a condensing unit is connected to an evaporator inside the building, providing cool air to several spaces requires either ductwork or additional condensing units and evaporators Not so with VRF systems, in which one condensing unit can be connected to multiple evaporators, each individually controllable by its user Similar to the more conventional ductless multi-split systems, which can also connect one outdoor section to several evaporators
  54. 54. Mechanics HVAC Multi-split systems, like DX systems, turn on and off depending on whether the room to be cooled is too warm or not warm enough VRF systems are different VRF systems constantly modulate the amount of refrigerant being sent to each evaporator By operating at varying speeds, VRF units work only at the needed rate, which is how they consume less energy than on/off systems, even if they run more frequently Less likely candidates to benefit from VRF technology are large open volumes, such as gyms, theaters, or sanctuaries These building types often fail to maximize the potential of the system, which is ideal for areas with different zones
  55. 55. Mechanics HVAC VRF systems offer an energy-efficient solution that provides considerable flexibility But, as with any other HVAC system, their cost-effectiveness and usefulness need to be evaluated on a building-by-building basis VRF systems are a good option for buildings with varying loads and different zone structures such as hotels, schools, and office buildings where individual users want to have control over the temperature in their areas. VRF systems tend to have greater piping length allowances than DX systems and use copper piping with small diameters, which makes them suitable for buildings with low-ceiling spaces
  56. 56. Mechanics HVAC VRF systems with one evaporator in every single room may be more costly initially, but the installation might require less ductwork In a different arrangement, several spaces might share a nearby evaporator The smaller footprint of VRF equipment can also reduce costs; the system eliminates the need to have mechanical rooms, so useable space is given back to the client Concerning outside air ventilation, can turn into a hurdle, because VRF units may require a separate ventilation system Especially in hot and humid climates or when dealing with high occupancy areas. Major manufacturers do generally offer outside air processing solutions that can be tied into the same control systems used for VRF units
  57. 57. Mechanics HVAC A fan coil unit (FCU) is a simple device consisting of a heating or cooling coil and fan. Typically a fan coil unit is not connected to ductwork, and is used to control the temperature in the space where it is installed, or serve multiple spaces. It is controlled either by a manual on/off switch or by thermostat. Due to their simplicity, fan coil units are more economical to install than ducted or central heating systems with air handling units. However, they can be noisy because the fan is within the same space. A concealed fan coil unit will typically be installed within an accessible ceiling void or services zone. The return air grille and supply air diffuser, typically set flush into the ceiling, will be ducted to and from the fan coil unit and thus allows a great degree of flexibility for locating the grilles to suit the ceiling layout and/or the partition layout within a space. It is quite common for the return air not to be ducted and to use the ceiling void as a return air plenum.
  58. 58. Mechanics HVAC The centrifugal fan has a moving component (called an impeller) that consists of a central shaft about which a set of blades, or ribs, are positioned Centrifugal fans blow air at right angles to the intake of the fan, and spin the air outwards to the outlet (by deflection and centrifugal force) The impeller rotates, causing air to enter the fan near the shaft and move perpendicularly from the shaft to the opening in the scroll-shaped fan casing A centrifugal fan produces more pressure for a given air volume One phenomenon particular to the cross-flow fan is that, as the blades rotate, the local air incidence angle changes The result is that in certain positions the blades act as compressors (pressure increase), while at other azimuthal locations the blades act as turbines (pressure decrease)
  59. 59. Mechanics HVAC The cross-flow or tangential fan, is usually long in relation to the diameter, so the flow approximately remains two-dimensional away from the ends The CFF uses an impeller with forward curved blades, placed in a housing consisting of a rear wall and vortex wall. Unlike radial machines, the main flow moves transversely across the impeller, passing the blading twice The flow within a cross-flow fan may be broken up into three distinct regions: a vortex region near the fan discharge, called an eccentric vortex, the through-flow region, and a paddling region directly opposite Both the vortex and paddling regions are dissipative, and as a result, only a portion of the impeller imparts usable work on the flow. The cross-flow fan, or transverse fan, is thus a two-stage partial admission machine. The popularity of the cross-flow fan in the HVAC industry comes from its compactness, shape, quiet operation, and ability to provide high pressure coefficient. Effectively a rectangular fan in terms of inlet and outlet geometry, the diameter readily scales to fit the available space, and the length is adjustable to meet flow rate requirements for the particular application
  60. 60. Valves measure and control flow They operate either with linear force or with torque, which is rotary Linear valve types (operating with force) include: Gate valves, Knife Gate valves, Globe valves, Diaphragm Valves, Pinch valves, Slide Gate valves and Rising Stem Ball valves Rotary valve types (operating with torque) include: Ball valves, Plug valves and Butterfly valves Actuators provide the muscle that creates the force or torque to operate the valves, by opening, closing or modulating Without the actuator, the valve is useless Mechanics HVAC
  61. 61. Mechanics HVAC What is an Air-Cooled Chiller? Air-cooled chillers are refrigeration devices of a sort They utilize a process of evaporation and condensation within a closed system to chill the surrounding air Typically, such devices are used for large industrial purposes, as they are more energy efficient than traditional freon-powered refrigerators It is a common misconception that air-cooled chillers do not use water. What the name actually means is that no water is used to absorb waste heat from the chiller's closed system
  62. 62. Mechanics HVAC Structure An air-cooled chiller is a closed system It starts with a device called an evaporator It has a shell of tubes surrounding a central chamber The tubes surround whatever item or material is meant to be cooled by the chiller The central chamber of the evaporator then connects with a compressor The compressor connects with a condenser, which then connects back to the evaporator
  63. 63. Mechanics HVAC How Do Air-Cooled Chillers Work? The process starts with the evaporator, which contains a liquid refrigerant The refrigerant radiates out cold to the surrounding tubes filled with water The water is chilled and pumped through a circuit, absorbing heat from whatever items the chiller is meant to cool When the water has finally reached a high enough temperature, it radiates the heat back at the refrigerant in the evaporator, causing it to turn into vapor The vapor passes through a pipe into the compressor, which, compresses the vapor into a smaller space, putting it under high pressure and heat This superheated vaporized refrigerant is then pumped through a condenser The condenser is a series of air-cooled vanes, similar to those in a car's radiator The vapor gives off its heat into the air and then condenses back into a liquid The liquid flows back into the evaporator to repeat the chilling process
  64. 64. Mechanics HVAC Operation Chillers send heat from air to water by circulating chilled water to air handlers, or devices used to condition and circulate air during the HVAC process This water is sent back to the evaporator side of the chiller Heat then passes from the water to freon, a liquid refrigerant Freon exits the evaporator in the form of a cold vapor This vapor enters the compressor in the chiller and is pressurized, or compressed, converting the cold vapor to a heated vapor As the heated vapor enters the chiller's condenser side, heat is transferred from the freon and is passed to a cooling tower, where it is removed through evaporation
  65. 65. Mechanics HVAC Efficiency •Chiller efficiency refers to the electricity amount needed to generate one cooling ton •Tons are measured in kilowatts per ton (kw/ton) •When commissioned, chillers are designated with a specific kw/ton efficiency rating Applications •Chillers are utilized in such applications as mechanical maintenance and water chemistry • Chillers are often used to determine mechanical lubrication levels, liquid refrigerant levels, and meter and gauge calibrations
  66. 66. Mechanics HVAC Air Cooled Vs. Water Cooled Chillers | Centrifugal Chiller Compressors . Conventional thinking has been that water cooled chillers are more efficient than air cooled chillers If we only look at compressor costs, this may be true However, using state-of-the-art technology with centrifugal compressors and variable speed control, air-cooled chillers are often the better choice It is important to look at the total operating costs involved with the chillers, not just the compressor costs. Cooling tower operating costs should be added. It includes the tower fan, water and sewer costs, chemical costs and pumping costs; process pumps and recirculation pumps
  67. 67. The illustration compares the operating cost of an air cooled variable speed centrifugal chiller versus a water cooled screw chiller This comparison is based upon a 140 ton load, $.07/kwh electrical costs, $5.00/1000 gallon water and sewer costs and 6,000 hrs/year operation. Mechanics HVAC
  68. 68. Mechanics HVAC A heat pump is a device that provides heat energy from a source of heat to a destination called a "heat sink" While air conditioners and freezers are familiar examples of heat pumps, the term "heat pump" is more general and applies to many HVAC devices used for space heating or space cooling When a heat pump is used for heating, it employs the same basic refrigeration-type cycle used by an air conditioner or a refrigerator, but in the opposite direction - releasing heat into the air-conditioned space rather than the surrounding environment In this use, heat pumps generally draw heat from the cooler external air or from the ground A simple stylized diagram of a heat pump's vapor-compression refrigeration cycle: 1) condenser, 2) expansion valve, 3) evaporator, 4) compressor Operating principles Mechanical heat pumps exploit the physical properties of a volatile evaporating and condensing fluid known as a refrigerant. The heat pump compresses the refrigerant to make it hotter on the side to be warmed, and releases the pressure at the side where heat is absorbed.
  69. 69. Mechanics HVAC The working fluid, in its gaseous state, is pressurized and circulated through the system by a compressor. On the discharge side of the compressor, now hot and highly pressurized vapor is cooled in a heat exchanger, called a condenser, until it condenses into a high pressure, moderate temperature liquid The condensed refrigerant then passes through a pressure-lowering device also called a metering device. This may be an expansion valve, capillary tube, or possibly a work-extracting device such as a turbine The low pressure liquid refrigerant then enters another heat exchanger, the evaporator, in which the fluid absorbs heat and boils. The refrigerant then returns to the compressor and the cycle is repeated Insulation is used to reduce the work and energy required to achieve a low enough temperature in the space to be cooled
  70. 70. Mechanics HVAC It is essential that the refrigerant reaches a sufficiently high temperature, when compressed, to release heat through the "hot" heat exchanger (the condenser). Similarly, the fluid must reach a sufficiently low temperature when allowed to expand, or else heat cannot flow from the ambient cold region into the fluid in the cold heat exchanger (the evaporator). In particular, the pressure difference must be great enough for the fluid to condense at the hot side and still evaporate in the lower pressure region at the cold side. The greater the temperature difference, the greater the required pressure difference, and consequently the more energy needed to compress the fluid. Thus, as with all heat pumps, the coefficient of performance (amount of thermal energy moved per unit of input work required) decreases with increasing temperature difference.
  71. 71. Mechanics HVAC Heat transport Heat is typically transported through engineered heating or cooling systems by using a flowing gas or liquid Air is sometimes used, but quickly becomes impractical under many circumstances because it requires large ducts to transfer relatively small amounts of heat In systems using refrigerant, this working fluid can also be used to transport heat a considerable distance, though this can become impractical because of increased risk of expensive refrigerant leakage When large amounts of heat are to be transported, water is typically used, often supplemented with antifreeze, corrosion inhibitors, and other additives
  72. 72. Mechanics HVAC Refrigerants R-12 (dichlorodifluoromethane) replacement refrigerant is the hydro fluorocarbon (HFC) known as R- 134a (1,1,1,2-tetrafluoroethane) Heat pumps using R-134a are not as efficient as those using R-12 and therefore, more energy is required to operate. Other substances such as liquid R-717 ammonia are widely used in large-scale systems, or occasionally the less corrosive but more flammable propane or butane, can also be used. Since 2001, carbon dioxide, R-744, has been used, utilizing the transcritical cycle, although it requires much higher working pressures.
  73. 73. Mechanics HVAC In residential and commercial applications, the hydro chlorofluorocarbon (HCFC) R-22 is still widely used, however, HFC R-410A does not deplete the ozone layer and is being used more frequently. Hydrogen, helium, nitrogen, or plain air is used in the Stirling cycle, providing the maximum number of options in environmentally friendly gases. More recent refrigerators use R600A which is isobutane, and does not deplete the ozone and is friendly to the environment Dimethyl ether (DME) is also gaining popularity as a refrigerant
  74. 74. Mechanics HVAC One observation is that while current "best practice" heat pumps (ground source system, operating between 0 °C and 35 °C) have a typical COP around 4, no better than 5, the maximum achievable is 8.8 because of fundamental Carnot cycle limits This means that in the coming decades, the energy efficiency of top-end heat pumps could at least double. Cranking up efficiency requires the development of a better gas compressor, fitting HVAC machines with larger heat exchangers with slower gas flows, and solving internal lubrication problems resulting from slower gas flow. Depending on the working fluid, the expansion stage can be important also. Work done by the expanding fluid cools it and is available to replace some of the input power. (An evaporating liquid is cooled by free expansion through a small hole, but an ideal gas is not.)
  75. 75. Mechanics HVAC SEER Seasonal energy efficiency ratio SEER = EER ÷ 0.9 SEER = BTU ÷ (W·h) coefficient of performance (COP) SEER = COP × 3.792 SEER = (BTU / h) ÷ W Energy Efficiency Ratio (EER) EER = COP × 3.413 where "W" is the average electrical power in Watts, and (BTU/h) is the rated cooling power For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, would consume 5000/10 = 500 Watts of power on average The electrical energy consumed per year can be calculated as the average power multiplied by the annual operating time: 500 W × 1000 h = 500,000 W·h = 500 kWh Assuming 1000 hours of operation during a typical cooling season (i.e., 8 hours per day for 125 days per year). 5000 BTU/h × 1000 h = 5,000,000 BTU Then, for a SEER of 10, the annual electrical energy usage would be: 5,000,000 BTU ÷ 10 = 500,000 W·h = 500 kWh
  76. 76. Mechanics HVAC
  77. 77. Mechanics HVAC Regular AHU maintenance system should include the following: •Coil Cleaning •Coil Treatment •Filtration Maintenance •Damper Maintenance •System Fan, Bearing & Belt Inspection / Maintenance •Air Intake Inspections •Cabinet & Supply Duct Inspection While there are different methods for coil cleaning, high pressure power washing is the most effective way to handle condenser and evaporator coil cleaning Damp, moist and humid areas present an ideal environment for mold growth. This type of microbial growth on the HVAC coils poses a cleaning challenge due to the fact that this material is quite sticky, creating a bio-film that seemingly ‘cements' particulate matter to the growing microorganism.
  78. 78. Mechanics HVAC For proper AHU maintenance service when coil cleaning, it is essential that an effective cleaning solution is used and that it is allowed ample time to do its job on the coils before being rinsed off. This includes not just the evaporator & condenser coils, but anywhere microbial growth may be growing on related metal surfaces Use of antimicrobial treatments can be an effective way to curtail mold/bacterial growth by disrupting the mold spore reproductive cycle One suggestion is that after a thorough coil cleaning the entire air handling unit should be treated This will help ensure all metal surfaces stay free of mold/bacterial growth until the next scheduled cleaning.
  79. 79. Mechanics HVAC Basic system maintenance is ensuring your AHU systems filter is replaced regularly, depending on the dirt/particulate load. This may mean every month for very heavy loads, or less frequently, perhaps once every six months It's not just dust and dirt that filters capture. Anything airborne including small insects, organic fibers, etc. can be caught in filters. Keep in mind that these various particulates, especially if they are organic, can be a source for mold growth and mold spores, depending on the type of filter used Also ensure your system's filter has the right capacity. The type of filter can impact the indoor air quality as well, with certain filter fabrics like cotton or other synthetics which help boost filtration and particulate matter capture. This increases the overall filtration efficiency and ultimately your system's effectiveness When dampers aren't cleaned and well lubricated, they get sticky & stuck. When this happens the HVAC unit can overload the cooling coil with too much hot outside air, or rob the unit of free cooling potential if the dampers are stuck in the closed position
  80. 80. Mechanics HVAC Inspecting the AHU unit fan, bearings and belts for dirt and dust buildup, along with regular cleaning of the fan and blades will help keep your commercial AHU air duct cleaning system's efficiency and air flow operating at optimal levels Conventional greased ball bearings should include checking for under or over-greasing, which can be damaging proper belt alignment (helps avoid lateral wear) proper belt tension (avoiding rapid wear and torque loss due to belt slippage on the pulley wheels) In addition, look for belts that are overly tight. This can lead to bearing and/or belt early failure due to the increased belt tension which puts an excessive load on the motor and fan shaft bearings Inspecting the Cabinet & Supply Duct look for an air leaks in the cabinet and supply duct Mold spores can be sucked into the commercial ventilation system. This can lead to further system contamination and indoor air quality issues
  81. 81. Mechanics HVAC A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another The media may be separated by a solid wall to prevent mixing or they may be in direct contact They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air
  82. 82. Mechanics HVAC Countercurrent flow - almost full transfer. In countercurrent flow, the two flows move in opposite directions. Two tubes have a liquid flowing in opposite directions, transferring a property from one tube to the other For example this could be transferring heat from a hot flow of liquid to a cold one The counter-current exchange system can maintain a nearly constant gradient between the two flows over their entire length of contact With a sufficiently long length and a sufficiently low flow rate this can result in almost all of the property transferred So, for example, in the case of heat exchange, the exiting liquid will be almost as hot or cold as the original incoming liquid's heat / cold
  83. 83. Mechanics HVAC For maximum heat transfer, the average specific heat capacity and the mass flow rate must be the same for each stream If the two flows are not equal, for example if heat is being transferred from water to air or vice-versa, then, similar to concurrent exchange systems, a variation in the gradient is expected because of a buildup of the property not being transferred properly Heat capacity, or thermal capacity, is a measurable physical quantity; it's the ratio of the heat added or subtracted to an object to the resulting temperature change. The SI unit of heat capacity is joule per Kelvin, and the dimensional form is M1L2T−2Θ−1 Volumetric heat capacity (VHC), describes the ability of a given volume of a substance to store internal energy while undergoing a given temperature change, but without undergoing a phase transition VHC is a 'per unit volume' measure of the relationship between thermal energy and temperature of a material, while the specific heat is a 'per unit mass' measure If given a specific heat value of a substance, one can convert it to the VHC by multiplying the specific heat by the density of the substance
  84. 84. Mechanics HVAC Heat transfer occurs at a higher rate across materials of high thermal conductivity than across materials of low thermal conductivity Correspondingly materials of high thermal conductivity are widely used in heat sink applications and materials of low thermal conductivity are used as thermal insulation Thermal conductivity of materials is temperature dependent. The reciprocal of thermal conductivity is called thermal resistivity Ceramic coatings with low thermal conductivities are used on exhaust systems to prevent heat from reaching sensitive components Air and other gases are generally good insulators, in the absence of convection. Many insulating materials function by having a large number of gas-filled pockets which prevent large-scale convection An object's heat capacity (symbol C) is defined as the ratio of the amount of heat energy transferred to an object and the resulting increase in temperature of the object
  85. 85. Heat Capacity Ratio for various gases[1][2] Temp. Gas γ Temp. Gas γ Temp. Gas γ −181°C H2 1.597 200°C Dry Air 1.398 20°C NO 1.400 −76°C 1.453 400°C 1.393 20°C N2O 1.310 20°C 1.410 1000°C 1.365 −181°C N2 1.470 100°C 1.404 2000°C 1.088 15°C 1.404 400°C 1.387 0°C CO2 1.310 20°C Cl2 1.340 1000°C 1.358 20°C 1.300 −115°C CH4 1.410 2000°C 1.318 100°C 1.281 −74°C 1.350 20°C He 1.660 400°C 1.235 20°C 1.320 20°C H2O 1.330 1000°C 1.195 15°C NH3 1.310 100°C 1.324 20°C CO 1.400 19°C Ne 1.640 200°C 1.310 −181°C O2 1.450 19°C Xe 1.660 −180°C Ar 1.760 −76°C 1.415 19°C Kr 1.680 20°C 1.670 20°C 1.400 15°C SO2 1.290 0°C Dry Air 1.403 100°C 1.399 360°C Hg 1.670 20°C 1.400 200°C 1.397 15°C C2H6 1.220 100°C 1.401 400°C 1.394 16°C C3H8 1.130 Carnot's heat engine In this diagram, abcd is a cylindrical vessel, cd is a movable piston, and A and B are constant– temperature bodies The vessel may be placed in contact with either body or removed from both (as it is here) Mechanics HVAC
  86. 86. Carnot's theorem is a formal statement of this fact: No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between the same reservoirs Mechanics HVAC is the work done by the system (energy exiting the system as work), is the heat put into the system (heat energy entering the system), is the absolute temperature of the cold reservoir, and is the absolute temperature of the hot reservoir. Carnot realized that in reality it is not possible to build a thermodynamically reversible engine, so real heat engines are less efficient than indicated by Equation (1) Although Carnot's cycle is an idealization, the expression of Carnot efficiency is still useful. Consider the average temperatures,
  87. 87. Mechanics HVAC Different measurements of heat capacity can therefore be performed, most commonly either at constant pressure or at constant volume Measurements under constant pressure produce larger values than those at constant volume because the constant pressure values also include heat energy that is used to do work to expand the substance against the constant pressure as its temperature increases This difference is particularly notable in gases where values under constant pressure are typically 30% to 66.7% greater than those at constant volume Hence the heat capacity ratio of gases is typically between 1.3 and 1.67
  88. 88. Mechanics HVAC To understand this relation, consider the following thought experiment. A closed pneumatic cylinder contains air The piston is locked The pressure inside is equal to atmospheric pressure This cylinder is heated to a certain target temperature Since the piston cannot move, the volume is constant The temperature and pressure will rise When the target temperature is reached, the heating is stopped The amount of energy added equals: , with representing the change in temperature The piston is now freed and moves outwards, stopping as the pressure inside the chamber equilibrates to atmospheric pressure
  89. 89. Mechanics HVAC We are free to assume the expansion happens fast enough to occur without exchange of heat (adiabatic expansion) Doing this work, air inside the cylinder will cool to below the target temperature To return to the target temperature (still with a free piston), the air must be heated This extra heat amounts to about 40% more than the previous amount added In this example, the amount of heat added with a locked piston is proportional to whereas the total amount of heat added is proportional to . Therefore, the heat capacity ratio in this example is 1.4
  90. 90. Mechanics HVAC Another way of understanding the difference between and is that applies if work is done to the system which causes a change in volume (e.g. by moving a piston so as to compress the contents of a cylinder), or if work is done by the system which changes its temperature (e.g. heating the gas in a cylinder to cause a piston to move)
  91. 91. Mechanics HVAC There are three primary classifications of heat exchangers according to their flow arrangement In counter-flow heat exchangers the fluids enter the exchanger from opposite ends The counter current design is the most efficient, in that it can transfer the most heat from the heat (transfer) medium due to the fact that the average temperature difference along any unit length is greater In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger For efficiency, heat exchangers are designed to maximize the surface area of the wall between the two fluids, while minimizing resistance to fluid flow through the exchanger The exchanger's performance can also be affected by the addition of fins or corrugations in one or both directions, which increase surface area and may channel fluid flow or induce turbulence
  92. 92. Mechanics HVAC The plate heat exchanger, is composed of multiple, thin, slightly separated plates that have very large surface areas and fluid flow passages for heat transfer This stacked-plate arrangement can be more effective, in a given space, than the shell and tube heat exchanger Online monitoring of commercial heat exchangers is done by tracking the overall heat transfer coefficient. The overall heat transfer coefficient tends to decline over time due to fouling U=Q/AΔTlm By periodically calculating the overall heat transfer coefficient from exchanger flow rates and temperatures, can estimate when cleaning the heat exchanger is economically attractive
  93. 93. Mechanics HVAC Temperature Glycol -45°C (-50°F) to 121°C (250° °C °F Vol% -7 20 12 -12 10 20 -18 0 24 -23 -10 28 -29 -20 30 -34 -30 33 <-40 <-40 35 Recommended Range Heat transfer fluids, propylene glycol is mainly used to reduce the freezing point of the liquid, thus preventing the cooling system and the engine from corrosion, overheating and freezing In burst protection liquids, propylene glycol, with its inherently high boiling point, lowers vapor pressure: When fluids freeze they expand in volume, which can cause pipes or other containment vessels to rupture When a water-glycol mixture becomes colder, it retains its flow ability and does not create added pressure in pipes or vessels. This makes it an ideal solution for burst protection in pipe and containment systems Applications include pipes and tubes
  94. 94. Boiling point at atmospheric pressure 14.7 psia, 1 bar abs Freezing Point at atmospheric pressure 14.7 psia, 1 bar abs Refrigerant Name No. (oF) Centigr (oF) Centigr R-22 Monochlorodifluoromethane3) -41.3 (40.72) -256 (160.00) R-134a Tetrafluoroethane6) -15 (26.11) -142 (96.67) R-404a R125(44%)/R143a(52%)/R134a(4 %) -55.4 (48.56) - R-717 Ammonia -28 (33.33) -107.9 (77.72) Freezing, the process of changing a liquid into a solid by cooling below a certain temperature called the freezing point The freezing point is the temperature at which the liquid and solid forms of a substance are in equilibrium (balance) At this point, if heat is neither added nor taken away, the liquid will not change into a solid, nor the solid into a liquid. Thus, the freezing point and the melting point of a substance are the same A heat exchanger is used for more efficient heat transfer or to dissipate heat One common example of a heat exchanger is a car's radiator, in which the hot coolant fluid is cooled by the flow of air over the radiator's surface Mechanics HVAC
  95. 95. Mechanics HVAC About 80 calories of heat are required to convert a gram of ice into water. Conversely, water liberates about 80 calories of heat per gram into the air when it freezes This heat is called the heat of fusion, or latent heat. The temperature of both the ice and the water from melting ice is 32 F., or 0 C The freezing point of a substance often determines how it can be used. Ethyl alcohol, for example, freezes at -179 F. (-117 C.), mercury at -38 F. (-39 C.) A familiar example of changing the freezing point of a liquid by adding another substance is the use of antifreeze. Automobile radiators are commonly protected against freezing during winter by adding ethylene glycol or other antifreezes to the water to lower its freezing point Most substances contract and become denser upon freezing, but water expands and becomes less dense. It is this expansion that causes pipes and bottles to crack when their contents freeze, and rocks to split open when water freezes in their crevices. Icebergs and blocks of ice float in water because they are less dense than the water from which they were frozen
  96. 96. The fundamental principle in freeze-drying is sublimation, the shift from a solid directly into a gas. Like evaporation, sublimation occurs when a molecule gains enough energy to break free from the molecules around it Water will sublime from a solid (ice) to a gas (vapor) when the molecules have enough energy to break free but the conditions aren't right for a liquid to form. Mechanics HVAC You can see from the chart that water can take a liquid form at sea level (where pressure is equal to 1 atm) if the temperature is in between the sea level freezing point (32 degrees Fahrenheit or 0 degrees Celsius) and the sea level boiling point (212 F or 100 C) But if you increase the temperature above 32 F while keeping the atmospheric pressure below .06 atmospheres (ATM), the water is warm enough to thaw, but there isn't enough pressure for a liquid to form. It becomes a gas
  97. 97. With most machines, you place the material to be preserved onto the shelves when it is still unfrozen When you seal the chamber and begin the process, the machine runs the compressors to lower the temperature in the chamber The material is frozen solid, which separates the water from everything around it, on a molecular level, even though the water is still present The machine turns on the vacuum pump to force air out of the chamber, lowering the atmospheric pressure below .06 ATM Mechanics HVAC The heating units apply a small amount of heat to the shelves, causing the ice to change phase. Since the pressure is so low, the ice turns directly into water vapor The water vapor flows out of the freeze-drying chamber, past the freezing coil. The water vapor condenses onto the freezing coil in solid ice form, in the same way water condenses as frost on a cold day This continues for many hours (even days) while the material gradually dries out. The process takes so long because overheating the material can significantly change the composition and structure
  98. 98. 1. Basics of HVAC control system ● Function of control system ● Basic control loop ● Sensor ● Controller ● Actuator, valves and dampers 1. Control fundamentals ● Set point, control variable, input/output ● Control modes - Two-position control - Floating control - Modulating control 3. Typical application ● Usual application of subsystems ● Examples: - Discharge temperature control - Static pressure control - Ventilation control - Chilled water system control - Fan pressure optimization 4. O&M of control system ● Common operation procedures and checkout items ● Common maintenance procedures and issues Mechanics HVAC
  99. 99. Mechanics HVAC Function of control system An HVAC control system operates the system and equipment (chillers, pumps, fans, AHUs, boilers, etc.) to maintain a comfortable environment, Inclusive of temperature, humidity, pressure and ventilation etc.
  100. 100. Function of control system Control loop Classification Description Ventilation Basic Coordinates operation of the outdoor, return, and exhaust air dampers to maintain the proper amount of ventilation air. Better Measures and controls the volume of outdoor air to provide the proper mix of outdoor and return air under varying indoor conditions Cooling Chiller control Maintains chiller discharge water at preset temperature or resets temperature according to demand. Cooling tower control Controls cooling tower fans to provide the coolest water practical under existing wet bulb temperature conditions. Coil control Adjusts chilled water flow to maintain temperature. Direct expansion (DX) control Cycles compressor or DX coil solenoid valves to maintain temperature. If compressor is unloading type, cylinders are unloaded as required to maintain temperature. Fan Basic Turns on supply and return fans during occupied periods and cycles them as required during unoccupied periods. Better Adjusts fan volumes to maintain proper duct and space pressures. Reduces system operating cost and improves performance (essential for variable air volume systems). Heating Coil control Adjusts water or steam flow or electric heat to maintain temperature. Boiler control Operates burner to maintain proper discharge steam pressure or water temperature. For maximum efficiency in a hot water system, water temperature should be reset as a function of demand or outdoor temperature. Mechanics HVAC
  101. 101. Mechanics HVAC Basic control loop  The intent of this control, as an example, is to maintain a desired supply air temperature.  It is called a control loop because information flows in a circle • The senor measures the temperature and the signal is sent to the controller where the actual value is compared to the setting • The controller then makes control decision to adjust position of the valve; this then has an effect on the current temperature.
  102. 102. Basics of HVAC control system Temperature sensor Dew-point sensor Differential pressure sensor Flow sensor Sensors  Components & functions • Sensing element, Transducer, Transmitter  Standard signals of transmission • 0 ~ 10V, 4 ~ 20mA, Pulse, Free contact  Typical sensors in HVAC application • Temperature sensor • Humidity or dew-point sensor • Pressure/differential pressure sensor • Velocity/flow sensor • Others: various gas detectors
  103. 103. Basics of HVAC control system Controller  Controller provides a signal to the controlled device in response to feed back from the sensor.  Controller could be a hardware device in a simple application or a software function in a large system, for example DDC or PLC/field bus Examples of controllers DDDDCC wwiitthh cceennttrraalliizzeedd ccoonnttrroolllleerr aanndd hhaarrddwwiirriinngg EExxaammppllee ooff uuss ssyysstteemm
  104. 104. Basics of HVAC control system Actuators, valves and dampers  An actuator responds to the output signal from a controller and provides the mechanical action to operate the control device – usually a valve or damper.  Types of actuators • Electrical, Pneumatic, Hydraulic, etc  Characteristics of valves • Equal percentage is suitable for continuous volume control
  105. 105. Control fundamentals Set point, Control variable, Input/output  Set point is the desired condition of a variable that is to be maintained, such as room temperature  Control variable is the actual process value being sensed  Input/output signal to/from the controller • Digital input: fan status (on/off), dirty filter • Digital output: start/stop fan or pump, open/close damper • Analog input: temperature, pressure, airflow • Analog output: control valve or damper position
  106. 106. Control fundamentals Control mode  Controllers maintain the process value at the desired set point, through output signal to the controlled device.  The output signal is a function of the difference between the control variable and the set point.  The action that the controller takes is called control mode or control logic, of which there are three basic types: • Two-position control • Floating control • Modulating control
  107. 107. Control fundamentals Two-position (on/off)  Applies to systems that have only 2 states, for example On/Off of equipment, Close/Open of solenoid valves, etc  Balancing between frequent start/stop of equipment and tighter tolerance of the control variables
  108. 108. Control fundamentals Floating control  Similar to two-position control but not limited to two states. The controller has three modes – Open/Idle/Close  A modulating-type controlled device is needed, typically a valve or damper driven by a slow moving bi-directional actuator More stable control: smaller variation on process and less cycling…
  109. 109. Control fundamentals Modulating control  PID (proportional – integral – derivative) algorithm has been widely applied for majority of the industrial processes .  Best tuning of PID parameters depends on a clear understanding of behavior of the process responding to the changes; fortunately there are lots of techniques helpful for selecting appropriate values. Loop tuning is some what of an art and is usually done empirically by trial-and-error……
  110. 110. Typical applications Usual application of subsystems  System start/stop control  Air filter section control  Mixed air section control  Cooling/heating coil control  Dehumidification/humidification control  Air distribution control  Fan capacity modulation and static pressure control  Terminal units control  Pumping systems control  Chilled water system control  Boiler plant control  Etc…
  111. 111. Typical applications Example: discharge temperature control  The controller compares the measured temperature to the set point  The valve is adjusted to change chilled water flow rate through the coil to achieve the set point.
  112. 112. Typical applications Example: static pressure control  The controller compares the measured static pressure to the set point  Capacity of the supply fan is adjusted to maintain the static pressure and deliver required air volume to the space. Common methods to modulate fan capacity • Inlet vanes control • Fan speed control • Discharge damper control • Variable pitch blade control
  113. 113. Typical applications Example: ventilation control  Fresh air (outdoor air) entering the AHU is monitored and compared to the desired value  The controller compares the difference and adjusts the damper to bring in the proper amount of fresh air. Acceptable IAQ……
  114. 114. Typical applications Example: chiller water system control  Control strategy inclusive of sequencing and staging is defined to respond to load change and equipment failure  Heat-load, as an example of load indicator, is calculated on-line based on measured supply/return temperature and flow rate  The controller determines operation of ancillary equipment based on pre-defined philosophy for specific situation.
  115. 115. Typical applications Example: fan pressure optimization  Each VAV terminal unit is positioned based on individual demand  Positions of all dampers are monitored, and the control system re-sets its set point so that at least one damper is near fully open Beneficial to energy efficiency
  116. 116. O&M of control system O&M is required for control system  Control systems & devices are made of components with highly complex mechanisms, circuits and/or software  Proper operation is required to assure functioning of the control systems. The devices must be commissioned, programmed, and adjusted to incorporate with M&E equipment  Proper maintenance is required to maintain reliability of the devices to provide operation as designed. Maintenance should be carefully planned and carried out properly
  117. 117. O&M of control system Operation procedures usually include  Initial set-up of control components in the system  Operational checkout of control system  Functional checkout of control system Common checkout items for a elect. control system  Power supply • Verify requirement, supply installation, wiring inter-connection, etc  Controller • Verify parameters set-up, calibration, signal transmission, etc  Controlled devices • Verify input/feedback signals, motion linkage, limit switches, valve/damper positioning, etc
  118. 118. sodexo. c1o1m8 O&M of control system Maintenance procedures usually include  Routine maintenance • Re-calibration, functioning test, tightening connections, cleaning, etc  Breakdown maintenance • Rectification, repair or replace damaged parts Common issues  Loosening of Damper Linkage Fastenings  Loosening of Control Wiring Connections  Damaged due to vibration, wear and tear, etc
  119. 119. Content 1. Basic of Refrigeration 2. Servicing valves and gauges 3. Fundamentals of servicing ● Using proper tools and techniques ● Basic rules of refrigerant piping ● Maintaining cleanliness ● Brazing tubes ● De-contamination ● Leak detection 1. Standard operation design data ● Air-cooled packaged units ● Water-cooled packaged units 5. Safety precautions ● Pump down ● Evacuation ● Charging refrigerant ● Compressor replacement ● Condenser cleaning
  120. 120. Definitions of Heat First of all, did you know that there is no such thing as cold? You can describe something as cold and everyone will know what you mean, but cold really only means that something contains less heat than something else. The definition of refrigeration is the removal and relocation of heat.
  121. 121. Definitions of Heat So if something is to be refrigerated, it is to have heat removed from it. Let us take an example: If you have a warm can of drink at say 25°C and you would prefer to drink it at 15°C, you could place it in your fridge for a while, heat would somehow be removed from it, and you could eventually enjoy a less warm drink. But lets say you placed that 15ºC pop in the freezer for a while and when you removed it, it was at 5ºC. Even "cold" objects have heat content that can be reduced to a state of "less heat content". The limit to this process would be to remove all heat from an object. This would occur if an object was cooled to Absolute Zero which is -460 ºF or -273 ºC. They come close to creating this temperature under laboratory conditions and strange things like electrical superconductivity occur.
  122. 122. Energy Units There are many domains where there is the notion of energy but there are also many units to express it. The Si unit is the joules (J) but there several other units:  Electron volt. We use this unit for the energy gained by a single electron – 1 eV = 1.60217646 × 10-19 J  Kilowatt hour. We often find the kilowatt hour in electric utilities – 1 kWh = 3.6 MJ  Calorie. We use this unit for heat, it is the pre-Si unit – 1 cal = 4.182 J  Kilo-calorie or large calorie. As the calorie, it is the pre-Si unit – 1 Cal = 1 kcal = 4182 J  British thermal unit is for steam generation, heating or air conditioning – 1 Btu = 1054.35 J
  123. 123. Defining Heat Sensible heat When an object is heated, its temperature rises as heat is added. The increase in heat is called sensible heat. Similarly, when heat is removed from an object and its temperature falls, the heat removed is also called sensible heat. Heat that causes a change in temperature in an object is called sensible heat.
  124. 124. Defining Heat Latent heat All pure substances in nature are able to change their state. Solids can become liquids (ice to water) and liquids can become gases (water to vapor) but changes such as these require the addition or removal of heat. The heat that causes these changes is called latent heat. Latent heat however, does not affect the temperature of a substance. The heat added to keep the water boiling is latent heat. Heat that causes a change of state with no change in temperature is called latent heat.
  125. 125. Dynamics of Heat Phase changes Transitions between solid, liquid and gas phases typically involve large amounts of energy. If heat were added at a constant rate to a mass of ice to take it through its phase changes to liquid water, the heat is called the latent heat of fusion. If heat were added at a constant rate to liquid water to take it through its phase changes to steam, the heat is called latent heat of vaporization. Superheat occurs when all the phase changes have been completed and the temperature rises in proportion to the heat energy added.
  126. 126. Definition of Heat Superheat What is superheat? Superheat refers to the number of degrees a vapor is above its saturation temperature (boiling point) at a particular pressure. How do I measure superheat? Superheat is determined by taking the low side pressure gauge reading, converting that pressure to temperature using a PT chart, and then subtracting that temperature from the actual temperature measured (using an accurate thermometer or thermocouple) at the same point the pressure was taken.
  127. 127. Refrigerants A refrigerant is a chemical that is used to provide cooling in a heat transfer system. Chlorofluorocarbons (CFCs) This refrigerant contains: Chlorine, Fluorine and Carbon. Positive points: non-toxic, non-flammable, and non-reactive with other chemical compounds. Negative points: Chlorine atom is a catalyst for ozone depletion.
  128. 128. Refrigerants Hydrochlorofluorocarbons (HCFCs) This refrigerant contains: Hydrogen, Chlorine, Fluorine, and Carbon. Positive points: energy-efficient, low-in-toxicity, cost effective and can be used safely. Negative points: HCFCs are greenhouse gases, despite their very low atmospheric concentrations. Hydrofluorocarbons (HFC's). This refrigerant contains: Hydrogen, Fluorine, and Carbon. Positive points: do not contain any ozone depleting Chlorine. Negative points: targets of the Kyoto-Protocol because of an activity in an entirely different realm of greenhouse gases.
  129. 129. Refrigerants Ozone Depletion Potential (ODP) The ozone layer is damaged by the catalytic action of chlorine and bromine in compounds, which reduce ozone to oxygen when exposed to UV light at low temperatures. The ODP of a compound is shown as an CFC-11 equivalent (ODP of CFC-11 = 1). Global Warming Potential (GWP) The greenhouse effect arises from the capacity of materials in the atmosphere the heat emitted by the Earth back onto the Earth. The direct GWP of a compound is shown as a CO2 equivalent (GWP of CO2 = 1)
  130. 130. Pressure Temperature Charts
  131. 131. Refrigeration Circuit
  132. 132. Refrigeration Circuit
  133. 133. Refrigeration Cycle
  134. 134. System Components
  135. 135. Subcooling What is meant by subcooling? Subcooling is the condition where the liquid refrigerant is colder than the minimum temperature (saturation temperature) required to keep it from boiling and, hence, change from the liquid to a gas phase. The amount of subcooling, at a given condition, is the difference between its saturation temperature and the actual liquid refrigerant temperature.
  136. 136. Subcooling Why is subcooling desirable? Subcooling is desirable for several reasons:  You pump less refrigerant through the system to maintain the refrigerated temperature you want. This reduces the amount of time that the compressor must run to maintain the temperature. The amount of capacity boost which you get with each degree of subcooling varies with the refrigerant being used.  It prevents the liquid refrigerant from changing to a gas before it gets to the evaporator. Pressure drops in the liquid piping and vertical risers can reduce the refrigerant pressure to the point where it will boil or "flash" in the liquid line. This change of phase causes the refrigerant to absorb heat before it reaches the evaporator.
  137. 137. Superheat settings Why is it important to know the superheat of a system? Superheat gives an indication if the amount of refrigerant flowing into the evaporator is appropriate for the load. If the superheat is too high, then not enough refrigerant is being fed resulting in poor refrigeration and excess energy use. If the superheat is too low, then too much refrigerant is being fed possibly resulting in liquid getting back to the compressor and causing compressor damage.
  138. 138. Superheat settings Superheat? The superheat should be checked whenever any of the following takes place: • System appears not to be refrigerating properly. • Compressor is replaced. • TXV is replaced. • Refrigerant is changed or added to the system. Note: The superheat should be checked with the system running at a full-load, steady-state condition. How do I change the superheat? Turning the adjustment stem on the TXV changes the superheat. • Clockwise - increases the superheat. • Counterclockwise - decreases the superheat
  139. 139. Chilling & Freezing Process Heat energy is transferred by temperature difference. The coldest point of a refrigeration system is the evaporator, called the evaporation temperature. The temperature of the surface of an evaporator is almost the temperature of the boiling refrigerant liquid within it. Examples: If a coldstore is required to be at a temperature of +5°C, then the temperature of the evaporator surface needs to be colder and typically minus -3°C. If a frozen food coldstore is required to be at minus - 25°C, the evaporator temperature is likely to be at minus -32°C. This temperature gradient is necessary for all steps in the chilling and freezing process.
  140. 140. Chilling & Freezing Process Another practical case: If a spiral freezer is required to freeze product quickly to a deep temperature of -25°C typically an air temperature needs to be -35°C, and the evaporator temperature needs to be even colder, likely to be -40°C. Air temperatures and product temperatures will tend to converge only during light refrigeration demand. Freezing and chilling times are dependent on two properties: 1. The weight of the product – heat energy contained is in direct proportion to the weight. 2. The size of the product – thicker product takes time for the temperature to penetrate.
  141. 141. Super heat and the TX Valve
  142. 142. Servicing Valves and Gauges System service valves Almost all refrigeration and air conditioning systems have service valves for operational checking and maintenance access.
  143. 143. Servicing Valves and Gauges Service gauge manifold Important tool used for checking system pressures, charging refrigerant, evacuating the system, purging non-condensable and adding oil, etc
  144. 144. Carry out service properly Use proper tools / techniques
  145. 145. Carry out service properly Minimize contamination  Air and water/moisture can cause corrosion, copper plating, acid formation, sludge, and other harmful reactions Basic rules of refrigerant piping  Drying -- make sure no moisture in the pipes  Cleaning -- make sure no dirt in the pipes  Air tight -- make sure no leakage of refrigerant  Constraint on piping/equipment arrangement • Max allowable piping length/height for split type • Oil return An example of proper riser to prevent oil from being trapped in the horizontal portion of the pipe.
  146. 146. Maintaining Cleanliness Materials handling  Use only copper tubing especially cleaned and dehydrated for refrigeration usage.  Soft copper tubing is available in rolls with the ends sealed, and hard drawn tubing is available capped and dehydrated.  Keep the tubing capped or sealed until ready for installation, and reseal any tubing returned to storage
  147. 147. Maintaining Cleanliness Care must be taken during service or installation  Use only refrigeration grade copper tubing; properly sealed to keep tubing clean and dry.  Pass an inert gas (N2 usually ) through the tubing when brazing tubes.  Evacuate the system if exposed to the environment during service.  Replace the filter-drier each time the system is opened for service.  Do not leave filter-driers open to the atmosphere.
  148. 148. Refrigerant pipe flushing Flushing removes foreign particles from the inside of pipes by means of gas pressure Mount a pressure regulator on the N2 cylinder; connect the charge line to the pipes Open the main valve of the N2 cylinder, and adjust the pressure regulator to 0.5 MPa. Flushing Maintaining Cleanliness
  149. 149. Brazing tubes Tubing should be cleaned and burnished bright before brazing. Particular attention should be given to preventing metal particles or abrasive material from entering the tubing Follow soldering procedures: Cut the tubing to length and remove the burrs. Clean the joint area with sandpaper. Clean inside the fitting. Use sandpaper or wire brush.
  150. 150. Brazing tubes . Apply flux to the inside of the fitting. Apply flux to the outside of the tubing. Assemble the fitting onto the tubing. Obtain proper tip for the torch and light it. Adjust the flame for the soldering being done.
  151. 151. Brazing tubes Apply heat to the joint. When solder can be melted by the heat of the copper (not the torch), apply solder so it flows around the joint. Clean the joint of excess solder and cool it quickly
  152. 152. Brazing tubes Prevention of oxidation during brazing  Oxidization layer is formed on the inside surface of the pipe during brazing if no preventive measure  Supply N2 (Nitrogen) into the pipe to replace the air during brazing Oxidation can cause clogging of solenoid valve, capillary tube, accumulator's oil return or compressor's internal oil inlet, etc.
  153. 153. De-contamination Drying is needed in case of leakage at water-refrigerant heat-exchangers  The system is dried by decontamination, evacuation, and driers.  Transfer refrigerant into a separate storage tank. Parts of the system may have to be disassembled and the water drained from system low points.  Perform decontamination before re-installation of compressors. After reassembly, dry the compressor further by passing N2 through the system and by heating and evacuation. Using internal heat, by circulating warmed water on the water side of water-cooled equipment, is preferred.  Drying may take an extended period and require frequent changes of the vacuum pump oil; filter-driers need to be changed often.
  154. 154. Leak Detection Leak test is a critical process for installation, trouble-shooting or repair.  Leakage results in loss of the refrigerant charge, reduces equipment capacity, and allows air & moisture to enter the system and can cause major breakdown.  Methods • Bubble test using water/soap solution • Pressure test using nitrogen • Electronic leak detector
  155. 155. Pump down If leakage is found to be minor and on the low side: Pump-down is necessary before carrying out the repairs. If leakage is found on the high side: Removal of all the refrigerant is required.
  156. 156. Evacuation Purpose  Needed whenever the system is exposed for prolonged periods to atmospheric air, or if the system is contaminated and removal of the refrigerant charge is necessary  The only effective way of removing air and moisture to required low level prior to charging refrigerant Methods  Perform leak test before evacuation  Utilize vacuum pump
  157. 157. Charging Refrigerant Methods  Vapor charging  Liquid charging Determine proper amount  Weighing the Charge  Using A Sight Glass  Using A Liquid Level Indicator  Checking operational parameters
  158. 158. Compressor Replacement Possible causes of a hermetic compressor motor burn-out  Prolonged operation at high discharge pressures and temperatures  Excessive motor starting  Fluctuating voltage  Shortage of refrigerant charge  Shortage of oil in the compressor  …… The system must be cleaned thoroughly to remove all contaminants. Or, a repeat burnout will likely occur !
  159. 159. Compressor Replacement Applicable for positive-displacement hermetic compressors only
  160. 160. Compressor Replacement Applicable for positive-displacement hermetic compressors only
  161. 161. Condenser Cleaning Water-cooled condenser: scaling and corrosion  Water treatment must be carried out properly  Scaling could be removed manually or through chemical clean carried out by qualified specialists  Chemical handling procedure and EHS requirement must be followed
  162. 162. Standard Operation Design Data Air-cooled packaged unit  Based on piping length of 5m and level difference of 0m  Outdoor air temp. 35˚C DB, Indoor air temp. 27˚CDB/19.5˚C WB Standard design value, R22 system
  163. 163. sodexo. c1o6m3 Standard Operation Design Data Standard design value, R22 system Water-cooled packaged unit  Based on tower water temperature 32˚C / 37˚C  Indoor air temp. 27˚CDB/19.5˚C WB
  164. 164. Safety Precautions Safety precautions  Wear proper PPE to protect eyes and to prevent direct contact of refrigerant with the skin which can cause burns, especially when charging or discharging refrigerant.  Make sure that the service cylinder is not over filled.  Do not expose cylinders to direct sunlight, or other heat sources.  Avoid discharge near naked flames.  Avoid direct contact with refrigerant/oil solutions from hermetic systems in the case of motor burn-out, which can be very acidic.  Always perform vapor charge from low-pressure side.  Always check that the refrigerant is correct for the system being charged.  Ensure that the working area is well ventilated. Breathing apparatus should be at hand in case of ammonia system
  165. 165. Ammonia Systems
  166. 166. What is Ammonia ? Ammonia is made up of one atom of nitrogen and three atoms of hydrogen, with the chemical symbol NH3. Ammonia is a key element in the nitrogen cycle. Ammonia can be found in water, soil, and air, and is a source of much needed nitrogen for plants and animals. In fact, ammonia is among the most abundant gasses in the environment.
  167. 167. What is Ammonia ? Ammonia is the refrigerant with the demonstrably best thermodynamic properties. Ammonia is also unbeatable in ecological terms: • no ozone depletion potential • no global warming potential (ODP and GWP = 0) • a favourable energy consumption to load balance thanks to the high COP of ammonia systems.
  168. 168. Refrigerants Ozone Depletion Potential (ODP) The ozone layer is damaged by the catalytic action of chlorine and bromine in compounds, which reduce ozone to oxygen when exposed to UV light at low temperatures. The ODP of a compound is shown as an CFC-11 equivalent (ODP of CFC-11 = 1). Global Warming Potential (GWP) The greenhouse effect arises from the capacity of materials in the atmosphere the heat emitted by the Earth back onto the Earth. The direct GWP of a compound is shown as a CO2 equivalent (GWP of CO2 = 1)
  169. 169. Ammonia as a Refrigerant Ammonia is an efficient refrigerant used in food processing and preservation. Ammonia has desirable characteristics: • corrosive • hazardous • irritating odor Ammonia is difficult to ignite and will not support combustion after the ignition source is withdrawn. Restrictions on chlorine and fluorine containing refrigerants have focused attention on ammonia to emerge as one of the widely used refrigerants that, when released to the atmosphere, do not contribute to ozone depletion and global warming. in large quantities.
  170. 170. What is Ammonia ? Ammonia is extremely soluble in water, it chemically combines with water to form ammonium hydroxide. Household ammonia is a diluted water solution containing 5 to 10 % ammonia. On the other hand, anhydrous ammonia (without water) is essentially pure (over 99%) ammonia. Preserving the purity of the ammonia is essential to ensure proper function of the refrigeration system.
  171. 171. Ammonia as a Refrigerant In industrial systems with capacities exceeding 500 kW, ammonia is simply unsurpassed in terms of energy and cost efficiency.
  172. 172. Ammonia Systems Ammonia is one alternative refrigerant for new and existing refrigerating and air-conditioning systems. Ammonia has  a low boiling point (-28°F at 0 psig)  an ozone depletion potential (ODP) of 0.00 when released to atmosphere  a high latent heat of vaporization (9 times greater than R-12)  the atmosphere does not directly contribute to global warming These characteristics result in a highly energy-efficient refrigerant with minimal environmental problems.
  173. 173. Ammonia Refrigeration Systems Ammonia Refrigeration Systems – Ways They Differ In a Direct Expansion halocarbon unit, oil is continuously returned to the compressor. Oil is not returned to the compressor in ammonia refrigeration systems but is instead drained out of the system periodically.
  174. 174. Ammonia Refrigeration Systems Ammonia Refrigeration Systems – Ways They Differ Oils used in ammonia refrigeration systems are essentially insoluble in NH3 (some slight solubility exists at high pressures); oil is heavier than liquid ammonia, making it easy to drain out. On the other hand, oil solubility is absolutely essential with the halocarbons in order to facilitate oil return. Paraffinic-based oils are commonly used with ammonia. These oils do a good job of cleaning out old welding slag and dirt. Oil, once drained from the system, is no longer usable.
  175. 175. Chiller Water System Lube Oil System The machines we are looking at are oil flooded compressors. These machines require large amounts of lube oil to:  provide sealing between the rotor lobes and the casing  provide sealing between the male and female lobes where the compression occurs.  for lubrication of the bearings and shaft seals  reduce the heat of compression in the machine.
  176. 176. Chiller Water System Quick overview of the mechanism The lube oil system on a screw compressor is a closed loop system. The oil is injected into the machine in several places. The main oil injection port feeds the rotors directly with smaller lines feeding various points on the machine for seals and bearings. Once the oil is injected, passages within the machine will drain all the bearing and seal oil into the rotors where it combines with the gas. The gas and oil mixture is then discharged out of the machine. The oil that is injected must be removed from the gas down stream of the compressor.
  177. 177. Chiller Water System Oil separator A separate oil separator vessel is required to remove this oil from the gas. This vessel can be either vertical or horizontal in design. The vessel will require coalescing type elements to remove as much oil as possible. The oil separator also acts as a reservoir for the lube oil system. The lube oil will flow from the bottom of the separator, through an oil cooler where it is cooled from discharge temperature down to 140-160ºF, through an oil filter and then back to the machine.
  178. 178. Chiller Water System Lube oil pumps Depending on the compressor manufacturer and the operating conditions, some machines require lube oil pumps to circulate the oil. Other manufacturers will use the differential pressure from discharge to suction to move the oil around the system.
  179. 179. Chiller Water System The oil cooling The oil cooling can be done using two different methods. The direct cooling method simply uses a section in the after cooler to cool the oil using the ambient air. The indirect method cools the oil in a shell and tube or plate and frame cooler. A water/glycol mixture is pumped through the other side of the exchanger and then circulated through a section in the gas after cooler. This method requires an additional exchanger and water pump.