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Hvac Basics
HVAC systems provide heating, ventilation, and air conditioning to ensure human comfort and allow occupation of spaces under adverse conditions. Proper load calculations and equipment selection are important for efficiency. HVAC transfers heat via conduction, convection, and radiation. Psychrometrics deals with air temperature and humidity. Common HVAC equipment includes fans, filters, compressors, furnaces, and air distribution components. Various system types include rooftop units, split systems, heat pumps, and geothermal. Controls manage temperature, airflow, and equipment operation.
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Hvac Basics
- 1. 1 HVAC - Basics(IAQ)
- 2. HVAC • Heating, Ventilationand Air Conditioning • Provides comfort for people • Allows humans to exist under adverse conditions.
- 3. Comfort • Comfort isprimary intent of HVAC systems. • Productivity • Building Durability • Health • Mold
- 4. Load Calculations • Heatingand Cooling • Accuracy important! • Design conditions • Building shell load • R, U value • Internal load • Ventilation load • Infiltration • Occupancy schedules
- 5. Heat Transfer • Conduction •Convection • Radiation • Resistance (R-Value) • U = 1 / R • Q = U x A x ∆T U-Value is the rate of heat flow in Btu/h through a one ft2 area when one side is 1o F warmer
- 6. The amount ofsolar heat energy allowed to pass through a window Example: SHGC = 0.40 Allows 40% through and turns 60% away Solar Heat Gain Coefficient
- 7. Psychrometrics • Dry bulbtemp. • Wet bulb temp. • Humidity • Dew point • Moisture content • Heating • Cooling • Humidify • De-Humidify Psychrometric Chart
- 8.
- 9. Basic HVAC Equipment •Fans / Blowers • Furnace / Heating unit • Filters • Compressor • Condensing units • Evaporator (cooling coil) • Control System • Air Distribution System
- 11. System Types andCommon Terms • Packaged Rooftop Unit • Split System • Heat Pump • Geothermal • Air to Air • Hydronic (water) • PTAC / PTHP Constant Volume Variable Volume Indoor Air Quality Direct Expansion
- 12.
- 13. FURNACE A/C UNIT Ductwork Heating and Cooling Equipment Temperature& Humidity Controls Split System
- 14. Heat Pump • Operateon simple refrigeration cycle • Reversing the cycle provides heating • Temperature limitations • Air to air • Water source • Geothermal • Lake coupled
- 15. Geothermal Heat PumpSystems
- 16. Variable Air Volume TT Variable Speed Return Fan ReturnAir Return Ducts Zone Thermostat Reheat Coil VAV Box Supply DuctsVariable Speed Supply Fan Filters CoolCoilw/TempReset HeatCoilw/Temp Reset HVAC-16
- 17. Terminal Units Variable volume: Parallel Constantvolume: Series
- 18. Hydronic systems • Pumps •Piping • Valves
- 19. Control Devices • Thermostats –Manual – Programmable • Optimum Start • DDC Systems • Variable Speed Drives • Automatic Valves and Dampers • Outdoor Sensors
- 20. Major Equipment • Chillers •Boilers • Cooling Towers
- 21.
- 22. Economizers Free cooling source:When available, use cool outdoor air instead of mechanically cooled air. 55 o F 80 o F Minimum supply of outside air Normal Operation Outside air dampers are positioned to provide the minimum outside air Economizer Operation Outside air dampers are fully open. Maximum outside air is provided 80 o F 55 o F and up 85% outside air 85% exhaust HVAC-22
- 23. Zoning and Economizers •Economizers provide “free cooling” when outdoor conditions are optimal • Proper orientation & zoning yields comfort & efficiency N S W ECore HVAC-23
- 24. Air Distribution • Ductwork –Metal – Flexible – Duct board • Grilles, Louvers, & Registers • Dampers – Shut off – Fire – Smoke • Sealants • Supports
- 25.
- 26. Additional Equipment • EnergyRecovery Units • Desiccant Systems
- 27. Additional Equipment • HeatExchangers • Humidifiers • Silencers
- 28. Mechanical Dehumidification Return airis mixed with ventilation air Cold coil condenses moisture Heat is added back (electric or gas) so that room air is not over cooled- Reheat Filter
- 29. Historical Minimum Ventilation ) 0 10 20 30 40 50 60 70 1835 1842 1849 1856 1863 1870 1877 1884 1891 1898 1905 1912 1919 1926 1933 1940 1947 1954 1961 1968 1975 1982 1989 1996 Tredgold 1836 Nightengale 1865 Billings 1895 Flugge 1905 Yaglou 1938 ASHRAE 62-73 ASHRAE62-81 Smoking 62-81 ASH- RAE 62-89 Smoking 62-89 Rates (cfm/person)
- 30. Improved Ventilation Effectiveness •Mechanically provide filtered and dehumidified outdoor air to the breathing space • Vary ventilation based on the number of occupants and process loads - changes in occupancy can be measured by CO2 sensors • Consider designs that separate ventilation and space conditioning • Utilize heat recovery systems to reduce system size and ventilation energy costs
- 31. Improved Ventilation Effectiveness •Effective mixing of ventilation air within space • Net positive pressure in the southeast; exhaust from appropriate spaces • Provide clean outdoor air, avoid: – loading docks – exhaust vents – plumbing stacks – waste collection – stagnant water
- 32. Additional Information /Resources • ASHRAE – The American Society of Heating, Refrigerating and Air-Conditioning Engineers – www.ashrae.org • Geothermal heat pump consortium www.geoexchange.org • www.buildingscience.com • www.energycodes.gov
Editor's Notes
- #6 1. Conduction is the transfer of heat through matter. 2. Convection is heat disbursement of heat through space, imagine ice at the top of the drink disbursing cold throughout the drink. (forced air systems) 3. Radiation is heat moving away in waves of energy from a heated object. 4. Consider the R-value of the structure. 5. Consider the U-value of windows.
- #7 Solar Heat Gain Coefficient (SHGC) The glazing’s effectiveness in rejecting solar heat gain. Part of a system for rating window performance used by the National Fenestration Rating Council (NFRC) Gradually replacing shading coefficient (SC) in product literature and design standards convert SC to SHGC by multiplying the SC value by 0.87
- #10 Picture: heat gun view of a blower Picture: Typical blower fans
- #14 An HVAC system consists of a heating and/or cooling source, a distribution system (e.g. ductwork or hot/chilled water piping) and temperature controls.
- #15 Lake coupled systems are run to a sufficient body of water, and the coils are submerged in the water. The coils are wrapped in overlapping circles. The coils must be submerged at least 8ft to prevent freezing.
- #19 Hydronic – the oldest system, using steam or cold water driven through pipes to produce conditioning. This system often used in commercial buildings via radiators.
- #20 Optimum start – sensors on the outside of the building monitor the exterior temperature. The HVAC system starts up at the optimal time to ensure that the building temperature has reach the desired level at the time the occupants arrive. DDC systems - Direct Digital Control – measure supply air temperature, mixed air temperature, return air temperature, outside air and outside humidity. This automated system economizes energy use by activity adjusting output in response to changing conditions. Variable Speed Drives – control the ac power supplied to fans, blowers and other devices to optimize power usage during varying heating and cooling loads. By reducing the power supplied to a fan by 15 – 20% the system can reduce power usage by 30%
- #25 1. duct board is a fiber-glass based ductwork. It is self insulated with a R-value of 4.3 for a typical 1” thick board, reduces noise, reduce air leakage and is mold and condensation resistant. 2. Allow for dispersion of air from the HVAC system 3. Dampers allow for cutting off of air supply to unused rooms, fire dampers close in case of fire exposure to prevent the supply air from fueling the fire. 4. It is important to seal connections of components. 5. Properly spaced supports prevent the ductwork from sagging or falling. A sagging section of ductwork could cause connections to lose proper seal thereby lowering the efficiency of the entire system.
- #26 Plenum is the enclosed space. This slide is attempting to illustrate how poorly sealed soffits, ceilings and units contribute poor quality air into ventilation systems.
- #28 Left: Humidifier. This is a steam power humidifier. The coil inside (barely visible) heats the water in the reservoir and the steam enters the air flow. The humidifier in this picture is intended for heat pumps and furnaces. Upper Right: Heat exchanger. The heat exchanger is comprised of tubes that are filed with a liquid, often water, a water-glycol solution, steam, or a refrigerant. The air is forced through the unit. The cooled or heated tubes affect the temperature of the air. Chillers are slightly different then heat exchangers. As the air travels through, latent moisture condenses on the chiller coils and the condensation must be collected and expedited to prevent mold growth. Lower Right: This is a silencer. The supply air enters in one slot and exits through the other. Inside, the pathway is made of acoustical fill that helps silence the air as it travels. Typically they are bonded fibers to prevent the fibers from entering the airstream as it moves through the unit. These devices are used to silence the operations in areas where there is excess noise. These devices can be used in the supply runs and return runs.
- #30 This chart is showing that in the progression of mechanical ventilation with respect to the amount of air being forced through the system.
- #31 1. Ventilator 2. Vary ventilation – With more occupants, there is need for more fresh air to offset increased CO2 levels. 3. This allows for you to ventilate without running the conditioner, for example in times of pleasant outdoor temperatures such as the spring or fall. 4. Heat recovery systems are ventilation devices where the incoming air passes through a box and is affected by the exhausted air. The air flows are not mixed. The exhausted air is conditioned, and by passing through the device, 60 to 80 percent of the temperature is transferred to the incoming air. This preconditions the air before it enters the conditioning cycle. * Note* - Open windows and bath fans are not adequate forms of ventilation!
- #32 1. This can be achieved by having the ventilation in conjunction with the duct systems, or through ceiling fans. 2. Positive pressure in the southeast to combat humid air infiltration. Do exhaust right next to an air intake, operable windows, or door ways. 3. These places all increase the likelihood of drawling in contaminated or undesirable air in to the building.