Heat Pump, Ventilation and Airconditioning System.pdf

Unit- 3:
Heat Pump, Ventilation and
Air-Conditioning Systems
Ankur Sachdeva
AP (ME)
KIET Group of Institutions

What is a Heat Pump?
• A heat pump uses technology similar to that found in a refrigerator or an air
conditioner.
• It extracts heat from a source, such as the surrounding air, geothermal
energy stored in the ground, or nearby sources of water or waste heat from a
factory. It then amplifies and transfers the heat to where it is needed.
• The output of energy in the form of heat is normally several times greater
than that required to power the heat pump, normally in the form of
electricity.
• For example, the coefficient of performance (COP) for a typical household
heat pump is around four, i.e. the energy output is four times greater than
the electrical energy used to run it.
Ankur Sachdeva, KIET Group of Institutions

Heat Pump (Contd..)
• The heat pump itself consists of a compressor, which moves a
refrigerant through a refrigeration cycle, and a heat exchanger, which
extracts heat from the source.
• The heat is then passed on to a heat sink through another heat
exchanger.
• In industry, heat pumps are used to deliver hot air, water, or steam, or
to directly heat materials.
• Large‐scale heat pumps in commercial or industrial applications or in
district heating networks require higher input temperatures than in
residential applications, which can be sourced from the waste heat of
industrial processes, data centers, or wastewater.

Heat Pump Cycles
The heating cycle of a heat pump works by taking heat in from
air outside, warming it up further, and using this warm air to
heat indoor air. It does so by the following process:
1. Liquid refrigerant absorbs heat in the "evaporator" from the
outdoor air, turning it into a gas.
2. The refrigerant is put through a "compressor", which raises
the pressure of the gas, increasing its temperature.
3. The hot gas flows through "condenser coils" inside the space
to be heated, and since it is at a higher temperature than this
space, it transfers heat to the room and condenses back into a
liquid.
4. The liquid finally flows back through a valve that reduces its
pressure in order to cool it down so it can repeat the cycle.

Heat Pump Cycles (Contd..)
• The cooling cycle of a heat pump is used to cool a space
by removing heat from it and expelling it to another area,
usually to the outdoors for air conditioning or to the
room for a refrigerator.
• To do this, the "evaporator" and "condenser coils" switch
roles and the flow of refrigerant is reversed:
1. The cold refrigerant absorbs heat from the hotter room in
the evaporator, so the room will cool down.
2. It is then put through the compressor to increase its
temperature.
3. It passes through the condenser coils, and transfers this
heat to the outside air.
4. It then expands in order to decrease its pressure and cool
down to below the room's temperature to repeat the
cycle.

Decentralized Heating Systems
• Decentralized heating systems are essentially the inverse of the centralized
alternatives.
• Instead of having a single unit that distributes heat to the whole house, there are
individualized units that control the heating within a single room or location.
• Decentralized heating systems allow individual control of the temperature in
different areas of a building as needed.
• This ensures that heating costs are kept to a minimum.
• These systems are often very practical in the context of large commercial spaces.
• When dealing with massive square footage, it can be financially impractical to
keep the entire space heated to a consistent temperature.

Industrial Heat Pump
• A heat pump is a device that can increase the temperature of a waste-heat source
to a temperature where the waste heat becomes useful.
• The waste heat can then replace purchased energy and reduce energy costs.
However, the increase in temperature is not achieved without cost.
• A heat pump requires an external mechanical- or thermal-energy source. The
goal is to design a system in which the benefits of using the heat-pumped waste
heat exceed the cost of driving the heat pump.
• Industrial heat pumps are big-scale devices that capture heat from a variety of
sources, mainly sea-, river- and industrial wastewater, and repurpose it for other
uses.
• Heat pumps can distribute heat and cold to a variety of end-users, including
district heating and cooling.
• They can also make use of renewable electricity generation by converting it into
heat and cold, which can then be stored.

Industrial Heat Pump
• Heat pumps have become increasingly important in the world as a technology to improve energy efficiency
and reduce CO2 emissions.
• In particular industrial heat pumps (IHPs) offer various opportunities to all types of manufacturing processes
and operations.
• IHPs are using waste process heat as the heat source, deliver heat at higher temperature for use in industrial
processes, heating or preheating, or for space heating and cooling in industry.
• They can significantly reduce fossil fuel consumption and greenhouse gas emissions in drying, washing,
evaporation and distillation processes in a variety of applications.
• Industries that can benefit from this technology include food and beverage processing, forest products,
textiles, and chemicals.
• The introduction of heat pumps with operating temperature below 100 °C is in many cases considered to be
easy, however, higher temperature application still require additional R&D activities for the development of
high temperature heat pumps, integration of heat pumps into industrial processes and development of high
temperature, environmentally sound refrigerants

Types of Industrial Heat Pumps
• Closed-Cycle Mechanical Heat Pumps use mechanical compression of a working fluid to achieve
temperature lift. The working fluid is typically a common refrigerant. Most common mechanical
drives are suitable for heat-pump use; examples include electric motors, steam turbines,
combustion engines, and combustion turbines.
• Open-Cycle Mechanical Vapor Compression (MVC) Heat Pumps use a mechanical compressor
to increase the pressure of waste vapor. Typically used in evaporators, the working fluid is water
vapor. MVC heat pumps are considered to be open cycle because the working fluid is a process
stream. Most common mechanical drives are suitable for heat-pump use; examples include electric
motors, steam turbines, combustion engines, and combustion turbines.

Types of Industrial Heat Pumps
• Open-Cycle Thermocompression Heat Pumps use energy in high-pressure motive steam to
increase the pressure of waste vapor using a jet-ejector device. Typically used in evaporators, the
working fluid is steam. As with the MVC Heat Pump, thermocompression heat pumps are open
cycle.
• Closed-Cycle Absorption Heat Pumps use a two-component working fluid and the principles of
boiling-point elevation and heat of absorption to achieve temperature lift and to deliver heat at
higher temperatures. The operating principle is the same as that used in steam-heated absorption
chillers that use a Lithium Bromide/water mixture as their working fluid.

Applications of Industrial Heat Pumps

What is Ventilation?
• Ventilation is the process by which ‘clean’ air (normally outdoor air) is intentionally provided to a
space and stale air is removed.
• This may be accomplished by either natural or mechanical means.
• Building ventilation has three basic elements:
1) Ventilation rate — the amount of outdoor air that is provided into the space, and the quality of
the outdoor air;
2) Airflow direction — the overall airflow direction in a building, which should be from clean
zones to dirty zones; and
3) Air distribution or airflow pattern — the external air should be delivered to each part of the
space in an efficient manner and the airborne pollutants generated in each part of the space
should also be removed in an efficient manner.

Purpose of Ventilation
a) To provide oxygen: The oxygen concentration is 21% by volume in atmospheric air. It should not fall below
15% under any circumstances whatsoever. The metabolic oxygen requirement of individuals varies between
0.03 m3/hr for very light work to 0.15 m3/hr for very heavy work.
b) To remove carbon dioxide: The CO2 concentration in atmospheric air is 0.03% by volume. It should not be
allowed to rise above 5% under any circumstance. For CO2 dilution, a minimum fresh air flow of 0.2 cmm per
sedentary adult is recommended. In spaces of heavy activity and smoking, 0.7 to 1.1 cmm per person is required.
0.42 cmm of fresh air per person is used as a design standard.
(c) To remove odours: 0.42 cmm of fresh air per person is required to remove body odours. The actual air
requirement depends on room size and level of activity.
(d) To remove heat and humidity: Removal of body heat and moisture addition by ventilation is the controlling
factor. The ventilation requirement can be determined from the room’s sensible and latent heat generation rates
using the following equation:
(e) To dilute toxicity: This is required when toxic and hazardous fumes/particles are being generated in the
space.

Air Infiltration and Exfiltration
• In addition to intentional ventilation, air inevitably enters a building by the process of ‘air
infiltration’.
• Air infiltration is the uncontrolled flow of air into a space through adventitious or unintentional gaps
and cracks in the building envelope.
• The corresponding loss of air from an enclosed space is termed ‘exfiltration’.
• The rate of air infiltration is dependent on the porosity of the building shell and the magnitude of the
natural driving forces of wind and temperature.
• Vents and other openings incorporated into a building as part of ventilation design can also become
routes for unintentional air flow when the pressures acting across such openings are dominated by
weather conditions rather than intentionally (e.g. mechanically) induced driving forces.
• Air infiltration not only adds to the quantity of air entering the building but may also distort the
intended airflow pattern to the detriment of overall indoor air quality and comfort.
• Moreover, infiltration can result in inferior performance, excessive energy consumption, an inability
to provide adequate heating (or cooling), and drastically impaired performance from heat recovery
devices.

Types of Ventilation
1) Natural ventilation:
• It is the ventilation of a building with outside air without using fans or other mechanical systems. It
can be via operable windows, louvers, or trickle vents when spaces are small and the architecture
permits.
• ASHRAE defined Natural ventilation as the flow of air through open windows, doors, grilles, and
other planned building envelope penetrations, and as being driven by natural and/or artificially
produced pressure differentials.
• Natural ventilation is caused by two natural forces: pressure differences caused by the wind
blowing around the building (wind-driven ventilation) and temperature variations (‘stack effect’
ventilation).
• In more complex schemes, warm air is allowed to rise and flow out of high building openings to
the outside (stack effect), causing cool outside air to be drawn into low building openings.
• Natural ventilation schemes can use very little energy, but care must be taken to ensure comfort.
• In warm or humid climates, maintaining thermal comfort solely via natural ventilation might not be
possible.

Types of Natural Ventilation
.
• The windows can only be opened on one side of the room. The amount of fresh air coming into the room
is limited by single-sided ventilation.
• Windows in two or more façades can create cross-ventilation in the room. The ventilation is powered
primarily by wind, which creates differences in air pressure on the facades in which the vents are located.
• Stack ventilation occurs when there is a height difference between windows – i.e. between façade and
roof windows. This type of ventilation is primarily driven by warm air rising to the top, whereby it
creates a pressure difference which drives the ventilation

Mechanical Ventilation
• Mechanical ventilation is a method of forced or induced ventilation by using mechanical air
handling systems, commonly called HVAC systems.
• These systems utilize fans installed in air ducts or directly in windows or walls. The fans exhaust
the polluted air to the ambient and supply clean air into the room.
• Different types of mechanical ventilation are available, which can be used for various purposes.
• The type of mechanical ventilation depends upon the climate, level, and types of pollutants.
• For example, in hot and humid climates, it may be necessary to minimize or prevent intrusion
rather than interstitial compaction (which, when hot and humid air penetrates a wall, ceiling, or
floor from inside a building with a cold surface encounters) prevent. In these cases, a positive-
pressure mechanical ventilation system is often used.
• Conversely, in cold climates, exfiltration should be avoided, and negative pressure ventilation
should be used to prevent intermediate condensation. A negative pressure system is often used for a
room with locally produced pollutants, such as a bathroom, toilet, or kitchen.

Types of Mechanical Ventilation
1. Exhaust-Only Ventilation System:
• Exhaust-only ventilation is a one-sided system that typically relies on
bathroom and kitchen fans to get rid of stale air but does not provide any
dedicated source of fresh air.
• To make up for the lost air, the house draws outside air through leaks in
the floors and walls (this is called “makeup air”)
• The principle of working of this system is based on depressurizing the
building. It often does not have any particular component to pull outside
air into the room.
• By decreasing the indoor air pressure below the outdoor air pressure, the
outside air will enter the room through leakages in walls and windows.
• The exhaust ventilation system is suitable for cold climates. If we
employ this system in warm and humid summers, the reduced pressure
may draw moisture into the building and wall cavities, where it may
cause moisture damage because of condensation.

Types of Mechanical Ventilation (Contd…)
2. Supply-Only Ventilation System:
• The supply ventilation system employs a fan to pressurize the
inside air and force outside air into the building.
• The polluted air in the rooms escapes through exhaust fan ducts
and possible leaks in the building envelope.
• This type of mechanical ventilation allows better control of the
entering air in comparison with exhaust ventilation.
• By pressurizing the house, supply ventilation reduces the chance
of pollutants entering the room and inhibits back drafting of
combustion gases produced in fireplaces and other applications.
• They also allow the air entering the house to be dehumidified and
filtered to remove dust.
• The supply ventilation system shows better performance in hot
and mixed climates since pressurizing the inside air may result
in some moisture difficulties in cold winters.

Types of Mechanical Ventilation (Contd…)
• Another type of mechanical ventilation system is a balanced
ventilation type.
• The properly designed balance ventilation system neither
depressurizes the indoor air, like exhaust ventilation nor
pressurizes it, such as supply ventilation.
• Even the ventilation system introduces fresh outside air and
exhaust polluted inside air in approximately equal quantities.
• This system often utilizes two duct systems and two fans to do its
job well. If supply and exhaust vents are placed in appropriate
positions, the balanced ventilation system facilitates the proper
distribution of clean air.
• A typical balanced air conditioning system is designed to provide
fresh air to the bedrooms and living rooms, where people spend
most of the time.
• It removes air from places where most moisture and pollutants are
generated, such as the kitchen, bathroom, and laundry room as
well.

Tunnel Ventilation
• Road tunnels have been used for more than two centuries around the world to allow road transport
to avoid natural and human-made obstacles such as rivers, mountain ranges, and dense urban areas.
• Road tunnels provide for reduced travel times and improved connectivity of the road network, but
their enclosed environment means that some form of ventilation is often required to maintain a safe
environment within the tunnel.
• Road tunnels can be uni-directional, meaning traffic within the tunnel moves only in one direction.
Usually, two uni-directional tunnels will run side by side to allow for bi-directional traffic flow.
Alternatively, road tunnels can be bi-directional, meaning traffic travels in both directions, sharing
a common road space.
• Road tunnels create an enclosed space around vehicles where emissions from the vehicles can
build up to unacceptable levels without an engineered ventilation system to replace natural surface
air flows.
• For tunnels up to around 500m in length the natural airflow through the tunnel driven by the
movement of vehicles (the ‘piston-effect’) is normally adequate to manage in-tunnel air quality,
and forced ventilation is not required.
• For longer tunnels forced ventilation in the form of fans may be required at times to ensure that air
flow rates are sufficient to maintain in-tunnel air quality to required levels.

Tunnel Ventilation
• The basic principle of tunnel ventilation is the dilution of vehicle emissions by providing fresh air
and then removing the exhaust air from the tunnel.
• The exhaust air can be removed via a portal (a location where the tunnel carriageway opens up to
the surrounding environment), via a ventilation outlet (such as a stack), or via a combination
of both.
• The amount of a given pollutant that is produced in a tunnel per unit time is determined by
calculating the total number of vehicles in the tunnel multiplied by the emission rate of each
vehicle.
• In terms of ventilation design, the total number of motor vehicles in a tunnel at any one time is
primarily determined by the tunnel length, the traffic density, and the traffic speed.
• The emission rate of a vehicle is dependent on speed and additionally, vehicle type, vehicle
age, vehicle condition, traffic conditions, and road gradient.

Types of Tunnel Ventilation
• Longitudinal ventilation in its simplest form comprises of fresh air introduced within the entry
portal and exhaust air expelled out of the exit portal.
• The pollution level increases along the tunnel because this is the direction of air flow, and vehicles
continue to generate emissions as they pass from one end to the other.
•

Types of Tunnel Ventilation
• Transverse ventilation works on the same principle of dilution and removal as longitudinal
ventilation, but the supply of fresh air and the removal of exhaust air occurs across the tunnel
(ie transversely).
• This system requires two ducts along the length of the tunnel, one for the supply of fresh air and one
for exhausting polluted air. These ducts can be located both at a high level or low level in the tunnel,
or one at a low level and one at a high level.

Mine Ventilation
• Mine ventilation is the process of supplying sufficient fresh air to the underground mining ventilation
system and working to achieve the purpose of ensuring proper distribution, use, and controlling of the
air that returns to the surface as contaminated air.
• Mine ventilation is very important because underground mining operations are often fraught with a lot
of dangers as tunneling through the earth presents the miners with an unfamiliar environment and
several issues that affect the health as well as safety of the workers.
• A lack of ventilation could result in fatalities because of exposure to dust that is generated from
underground coal mining activities.
• A good mine ventilation system should achieve the following objectives:
• Dilute and remove poisonous gases like NO2, SO2, CO and CO2.
• Removes dusts and noxious gases.
• Regulate the temperature in the mine.
• Remove gases from diesel engines, explosives and orebodies.
• Ensures proper breathing of the workers.
• Ensures there is sufficient ventilation flow, regardless of weather or season.
• Helps efficiently clear blast fumes, particularly when mine is not occupied.

Airconditioning System
• It is a system for controlling the humidity, ventilation, and temperature in a building or vehicle,
typically to maintain a cool atmosphere in warm conditions.

Role of Thermal Distribution System
in Airconditioning
• An air-conditioning system consists of an air conditioning plant and thermal
distribution system.
• Air, water, or refrigerant are used as media for transferring energy from the air
conditioning plant to the conditioned space.
• A thermal distribution system is required to circulate the media between the
conditioned space and the A/C plant.
• Another important function of the thermal distribution system is to introduce the
required amount of fresh air for ventilation.

Selection of an Airconditioning System
• Capacity, performance, and spatial requirements.
• Initial and Running costs.
• Required system reliability and flexibility.
• Maintainability.
• Architectural constraints.
The relative importance of the above factors varies from building owner to owner
and may vary from project to project

Classification of Airconditioning Systems
• The air conditioning system may be broadly classified as follows:
a) According to the purpose
(i) Comfort air conditioning system.
(ii) Industrial air conditioning system.
b) According to a season of the year
(i) Winter air conditioning system.
(ii) Summer air conditioning system.
(iii) Year-round air conditioning system.
c) According to the arrangement of equipment
(i) Unitary air conditioning system
(ii) Central air conditioning system.

According to the purpose
Comfort Airconditioning
• In comfort air conditioning, the air is brought to the required dry bulb temperature and relative
humidity for human health, comfort, and efficiency.
• If sufficient data of the required is not available, then it is assumed to be 21°C dry bulb temperature
and 50% relative humidity.
• Ex. In homes, offices, shops, restaurants, theatres, hospitals, schools, etc. are using air-conditioning
systems to give comfort to people.
Industrial Airconditioning
• In the industrial air conditioning system, the inside dry bulb temperature and relative humidity of
the air are kept constant for the working of the machine and for the manufacturing process.
• Textile mills, Paper mills, Machine part manufacturing plants, toolrooms, Photographic, etc. are
using this type of air-conditioning system.

According to the season of year
• In winter air conditioning system, the air is burnt and heated,
which is generally followed by humidification.
• The outside air flows through a damper and mixes with the
recirculated air. The mixed air passes through a filter to remove
the dirt, dust and impurities.
• The air now passes through a preheat coil to prevent the possible
freezing of water and to control the evaporation of water in the
humidity.
• After that, the air is made to pass through a reheat coil to bring the
air to the designed dry bulb temperature.
• Now, the conditioned air is supplied to the conditioned space by a
fan.
• From the conditioned space, a part of the air is exhausted to the
atmosphere by the exhaust fans.
• The remaining part of the used air is again conditioned and this
will repeat again and again.
Winter Airconditioning System

• In this system, the air is cooled and generally dehumidified.
• The outside air flows through the damper and mixed with recirculated air (which is
obtained from the conditioned space).
• The mixed air passes through a filter to remove the dirt, dust and impurities.
• The air now passes through a cooling coil. The coil has a temperature much below the
required dry bulb temperature of the air in the conditioned space.
• The cooled air passes through a perforated membrane and loses its moisture in the
condensed from which is collected in the sump.
• After that, the air is made to pass through a heating coil which heats the air slowly. This is
done to bring the air to the designed dry bulb temperature and relative humidity.
• Now the conditioned air is supplied to the conditioned space by a fan. From conditioned
space, a part of the used air is rejected to the atmosphere by the exhaust fan.
• The remaining air is again conditioned and this repeated for again and again. The outside
air is sucked and made to mix with recirculated air to make for the loss of conditioned air
through exhaust fan from the conditioned space.
Summer Airconditioning System

Schematic of Summer Airconditioning System

• In year-round air conditioning system, it should have
equipment for both the summer and winter air
conditioning.
• In year-round air conditioning system, the outside air
flows through the damper and mixed with the
recirculated air.
• The mixed air passes through a filter to remove dirt,
dust and impurities.
• In summer air conditioning system, the cooling by
operates to cool the air to the desired valve.
• The dehumidification is obtained by operating the
cooling coil at a lower temperature than the dew point
temperature.
• In winter air conditioning system, the cooling coil is
made inoperative and the heating coil operates to heat
the air. The spray type humidifier is also used in the dry
season to humidify the air
Year Round Airconditioning System

Unitary Air Conditioner
• Unitary refrigerant-based systems consist of several separate air conditioning units with
individual refrigeration systems.
• These systems are factory assembled and tested as per standard specifications, and are available
in the form of package units of varying capacity and type.
• Each package consists of refrigeration and/or heating units with fans, filters, controls etc.
• Depending upon the requirement these are available in the form of window air conditioners, split
air conditioners, Vertical Packaged Units, etc.
• Depending upon the capacity, unitary refrigerant-based systems are available as single units
which cater to a single conditioned space, or multiple units for several conditioned spaces.

Window/Room Air Conditioner Unit
• A typical window-type, room air conditioner is
available in cooling capacities varying from about 0.3
TR to about 3.0 TR.
• As the name implies, these units are normally mounted
either in the window sill or through the wall.
• As shown in the figure, this type of unit consists of
single package which includes the cooling and
dehumidification coil, condenser coil, a hermetic
compressor, expansion device (capillary tube),
condenser fan, evaporator fan, room air filter and
controls.
• A drain tray is provided at the bottom to take care of
the condensate water.
• Both evaporator and condensers are plate fin-and-tube,
forced convection type coil.

Vertical Packed Units or PTAC systems
• These type of air conditioners are bigger in the capacity of 5 to 20TR and are
adjacent to the space to be conditioned.
• This unit is very useful for conditioning the air of a restaurant, bank or small
office.
• PTAC systems are also known as wall split air conditioning systems or ductless
systems.
• These PTAC systems which are widely used in hotels have two separate units,
the evaporative unit on the interior and the condensing unit on the exterior, with
tubing passes through the wall and connects them together.
• This minimizes the interior system footprint and allows each room to be
adjacent independently.
• PTAC system may be adapted to provide heating in cold weather, either directly
by using an electric strip, gas or other heaters, or by reversing the refrigerant
flow to heat the interior and draw heat from the exterior air, converting the air
into a heat pump.
• While room air conditioning provides maximum flexibility when cooling rooms
it is generally more expensive than a central air conditioning system.

Central Air Conditioning
• A central air conditioning system is a type of air conditioning system that uses a network of ducts to cool and dehumidify
the air in an entire building or home.
• It is often used in larger homes, commercial buildings, and other facilities where individual room air conditioning units
are not practical or cost-effective.
• In central air conditioning, air, water, or both are used as working fluids to produce the required heating and/or cooling,
and therefore based on working fluids, central air conditioning systems can be classified into three groups:
1. All-air systems: In these systems, air is used as working fluid for heating and/or cooling purposes.
2. All-water (hydronic) systems: In these systems, water is used as a working fluid for heating and/or cooling purposes.
3. Air-water systems: In these systems, both air and water are used as working fluids for producing heating and cooling
purposes.

All Air Systems
• In these systems, air alone is used as a
working fluid to produce
• cooling or heating in air-conditioned zones;
• besides that air is responsible for controlling
the zones’ humidity level and
• providing the required ventilation to air-
conditioned zones.
• In addition, in all-air systems, air is used
for aromatizing purposes.
• Therefore, only air as working fluid is
responsible for providing comfort, i.e.,
cooling, heating, controlling of humidity
and ventilation odor, and thus these
systems are called all-air systems.

Components of All Air Systems
Air handling unit (AHU)
• Air handling unit can be considered as the heart of all-air systems since cooling and heating take
place in the air handling unit.
• It also mixes the outside air after being purified with the return air, then the necessary psychometric
processes are carried out.
• The air conditioner is then expelled or withdrawn to the place to be airconditioned. These units are
used for capacities exceeding 100,000 CFM (50 m3 /s) air.
The main components of the air handling unit are:
• Supply fan: Centrifugal fan type is used to provide the conditioned air to various zones.
• Fan motor: An electric motor is used to provide the rotating motion to the supply fan.
• Cooling coil: Coil placed in AHU where cold water from the chiller is circulating in medium- and
large-capacity AHU or expanded refrigerant in small-capacity AHU.

Components of AHU

Components of All Air Systems (Contd…)
• Filters: Filters or strainers are placed at the early air path in AHU. Filter type used may depend on application type.
• Mixing box: It is place where fresh air is mixed with zone return air or with fresh conditioned air. Mixing processes
are performed to obtain the desired air temperature and humidity or to maintain energy-efficient performance.
• Dampers: Dampers are used to control the amount and direction of air before or after conditioning is performed.
• Heating coil: Coil placed in AHU where hot liquid or vapor water from boilers is circulating.
• Preheating coil: Preheating coil is placed at AHU entrance before cooling and heating coils. The task of preheating
coil in hot days is to reduce the entering fresh air’s relative humidity, thus preventing possibly the condensation of
water vapor on cooling coil, hence preventing frost formation on the cold coil. In addition, preheater coil will
prevent the freezing of water inside the coils in cold days.
• Humidifier: It is a system which is responsible for increasing the humidity in the conditioned zone. Humidifiers are
usually used in cold days where maintaining hot climate is desired; however this will accompany low-humidity
levels, and thus the use of humidifier becomes essential to maintain the comfort edge. Humidifier can provide
humidity either as hot vapor or water spray. The first one is more preferable particularly in healthcare applications as
hot vapor will prevent the growth of biological organisms such as bacteria or algae besides hot vapor compared to
the water spray. Besides that hot vapor is more preferable as provided humidity will have higher temperature and
thus will not reduce the conditioned hot air provided to the zones.

Components of All Air Systems (Contd…)
• Centrifugal pumps:
• Centrifugal pumps are used for cooling and heating air processes.
• They are used to maintain the pumping cycle of hot water from boilers to the heating or preheating coils and back to
the boiler and/or the pumping cycle of cold water from the chiller or cooling tower to the cooling coil in AHU and
back to the chiller or cooling tower.
• Control systems:
• Control systems can vary from simple control systems to advanced control systems that use the latest technologies
such as programmable logic controllers.
• Usually, controllers are used to control the temperatures and humidity of the supply air to the zones.
• It also controls the damper systems in the AHU.
• Moreover, advanced control systems can even control the fan rotation and thus the rate of air supplied to the zone
based on the required temperature in the zone and zone exit damper.
• In such systems, a pressure sensor connected to the control system will be placed in the air duct, and as attaining the
required temperature in the zone, dampers will get closer increasing the duct-sensed pressure through which the fan
connected to the control system will reduce its speed and thus maintain energy-efficient performance.
• Casing: Casing is a kind of AHU cover that includes all the above AHU components.

Blow-through and Draw-through
AHUs
• In the blow-through units, supply air fan
forces or pushes the air through the cooling
coil to reduce the increase of supplied air
temperature due to friction, and thus air can
be cooled before being supplied to the
various zones.
• In draw-through units, the supply fan is
placed after the cooling coil, heating coil,
filter, and humidifier, and thus air is pulled
by the supply fan. This system is commonly
used as filters and coils which require small
air speeds and larger ducts than large speeds
and small ducts through the fan. The only
disadvantage of this system is that the fan
sound can travel with supply air to the
conditioned zones.

Advantages of All Air Systems
• All air systems offer the greatest potential for energy conservation by utilizing the
outdoor air effectively.
• It is possible to maintain the temperature and relative humidity of the conditioned
space within 0.15˚C and 0.5% respectively.
• Using dual duct system, it is possible to provide simultaneous cooling and heating.
• It is possible to provide good room air distribution and ventilation under all
conditions of load.
• Noise in the conditioned space can be minimized by locating the power plant
away.

Disadvantages of All Air Systems
• They occupy more space and thus reduce the available floor space in the
buildings. It could be difficult to provide air conditioning in high-rise buildings
with the plant on the ground floor or basement due to space constraints.
• Retrofitting may not always be possible due to the space requirements.
• Balancing of air in large and particularly with variable air volume systems could
be difficult.

Applications of All Air Systems
• All air systems can be used in both comfort as well as industrial air conditioning
systems.
• They are especially suited to buildings that require individual control of multiple
zones, such as office buildings, classrooms, laboratories, hospitals, hotels, ships,
etc.
• They are also used extensively in applications that require very close control of the
conditions in the conditioned space such as clean rooms, computer rooms,
operation theatres, research facilities, etc.

All Water Systems
• In all-water systems, water is used as a
working fluid for providing heating and
cooling.
• Water is pumped to the fan coil unit
located in the zone which is to be
conditioned.
• And then the fan coil unit will use the zone
air or sometimes outdoor air for cooling or
heating purposes.
• If outdoor air is used with the fan coil
units, then a separate air duct system will
be introduced to the structure of the
building

All Water Systems

Advantages of All Water Systems
• Occupies considerably less space, hence can be easily retrofitted.
• Although central system, individual room control is possible easily.
• Since the temperature of hot water required for space heating is small, it is
possible to use solar or waste heat for winter heating.
• Simultaneous cooling and heating is possible with 4-pipe systems.

Disadvantages of All Water Systems
• Requires higher maintenance compared to all air systems, particularly in the
conditioned space.
• Draining of condensate water may be messy and may also create health problems
if water stagnates in the drain tray.
• It is difficult to ensure the required ventilation.
• Control of humidity, particularly during summer is difficult using chilled water
control valves.

Applications of All Water Systems
• All water systems using fan coil units are most suitable in buildings requiring
individual room control, such as
• Hotels,
• Apartment buildings, and
• Office buildings.

Air Water Systems
In these systems, both air and water produce heating
and cooling effects.
Usually, induction or fan coil units can be used in air-
water systems.
Induction unit systems in air-water central air
conditioners are used in building of multi-surrounding
rooms such as offices, hotels, hospital patient rooms, as
well as apartments.
These systems are used where higher thermal loads are
present.
In addition, these systems are suitable where some
rooms require cooling, while the next other rooms
require heating.
Besides that, these systems are suitable for buildings
such as skyscrapers where the spaces are limited.

Advantages of Air-Water Systems
• Individual room control is possible in an economic manner using room
thermostats, which control either the secondary water flow rate or secondary air or
both.
• It is possible to provide simultaneous cooling and heating using primary air and
secondary water.
• Space requirement is reduced, as the amount of primary air is less than that of an
all air systems.
• Positive ventilation can be ensured under all conditions.
• The cooling coil in the conditioned space is dry, thereby problems of drainage of
condensate water and possibility of bacterial growth is eliminated.

Disadvantages of Air-Water Systems
• Operation and control are complicated due to the need for handling and
controlling both the primary air and secondary water,
• In general, these systems are limited to perimeter zones.
• The secondary water coils in the conditioned space can become dirty if the quality
of filters used in the room units is not good.
• Since a constant amount of primary air is supplied to conditioned space, and room
control is only through the control of room cooling /heating coils, shutting down
the supply of primary air to unoccupied space is not possible.
• If there is abnormally high latent heat load on the building, then condensation may
take place on the cooling coil of secondary water.
• Initial cost could be high compared to all air systems.

Applications of Air-Water Systems
• These systems are mainly used in exterior buildings with large sensible loads and
where close control of humidity in the conditioned space is not required.
• These systems are thus used in
• Hospitals
• Schools,
• Hotels
• Apartments, and

DX Airconditioning system
• The refrigerant enters the DX cooling coils,
where it absorbs the heat from the air and
transforms to a gas.
• The refrigerant then moves into the
condenser located outside, where the heat is
released.
• An expansion valve exists between the
evaporator and the condenser to help
facilitate the changes in the pressure and
temperature of the refrigerant as it moves
through this cooling process.
• A compressor drives the refrigerant through
its journey, and the entire DX cooling system
offers a closed loop solution.

DX Airconditioning system
• A direct expansion or DX cooling system is a type
of air-conditioning system that removes heat from
a space through evaporation and condensation of a
refrigerant.
• The refrigerant absorbs the heat in the air, such as
the heat generated by IT equipment in a network
closet or other IT space, and then ultimately rejects
the heat outdoors.
• This is possible because the refrigerant boils below
room temperature, and is condensed back to a
liquid by transferring the heat to outdoor air or
water through a heat exchanger.
• In a DX cooling system, the evaporator is placed
inside the space to be cooled.

Advantages of Unitary Refrigerant
based Systems
• Individual room control is simple and inexpensive.
• Each conditioned space has individual air distribution with simple adjustment by the occupants.
• Performance of the system is guaranteed by the manufacturer.
• System installation is simple and takes very less time.
• Operation of the system is simple and there is no need of a trained operator..
• Initial cost is normally low compared to central systems.
• Retrofitting is easy as the required floor space is small.

Disadvantages of Unitary Refrigerant
based Systems
• As the components are selected and matched by the manufacturer, the system is less flexible in
terms of airflow rate, condenser, and evaporator sizes.
• Power consumption per TR could be higher compared to central systems.
• Close control of space humidity is generally difficult.
• Noise level in the conditioned space could be higher.
• Limited ventilation capabilities.
• Systems are generally designed to meet the appliance standards, rather than the building standards.
• May not be appealing aesthetically.
• The space temperature may experience a swing if on-off control is used as in room air conditioners.
• Limited options for controlling room air distribution.
• Equipment life is relatively short.

Applications of Unitary Refrigerant
based Systems
• Unitary refrigerant based systems are used where stringent control of conditioned space,
temperature and humidity is not required and where the initial cost should be low with a small lead
time.
• These systems can be used for air conditioning individual rooms to large office buildings,
classrooms, shopping centres, nursing homes, etc..
• These systems are especially suited for existing building with a limitation on available floor space
for air conditioning systems.

Central Airconditioning Vs Unitary Airconditioning

Heat Pump, Ventilation and Airconditioning System.pdf

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