Comparison between Comparison between the different types of the different types of the Air conditioning the Air conditioning

systemssystems

Air cooled systemsAir cooled systems 1- Air cooled systems (2-piece) 1- Air cooled systems (2-piece)

This type of system is often referred to as a DX system This type of system is often referred to as a DX system or split system. The “DX” designation stands for direct or split system. The “DX” designation stands for direct expansion and although this term often refers to an air expansion and although this term often refers to an air cooled system, in fact any system that uses refrigerant andcooled system, in fact any system that uses refrigerant and an evaporator coil can be called a DX system.an evaporator coil can be called a DX system. Refrigerant circulates between the indoor and outdoor Refrigerant circulates between the indoor and outdoor components in pipes called refrigerant lines. Heat from thecomponents in pipes called refrigerant lines. Heat from the IT environment is “pumped” to the outdoor environment IT environment is “pumped” to the outdoor environment using this circulating flow of refrigerant. using this circulating flow of refrigerant.

The outdoor unit The indoor unit

Advantages:Advantages:• • Lowest overall costLowest overall cost• • Easiest to maintainEasiest to maintain

Disadvantages:Disadvantages:• • Refrigerant piping must be installed in the field. Only Refrigerant piping must be installed in the field. Only properly engineered piping systems that carefully properly engineered piping systems that carefully

consider consider the distance and change in height between the IT and the distance and change in height between the IT and outdoor environments will deliver reliable outdoor environments will deliver reliable

performance.performance.

• • Refrigerant piping cannot be run long distances Refrigerant piping cannot be run long distances reliably reliably

and economically.and economically.

• • Multiple computer room air conditioners cannot be Multiple computer room air conditioners cannot be attached to a single air cooled condenser.attached to a single air cooled condenser.

Usually Used:Usually Used:• • In wiring closets, computer rooms and small-to-In wiring closets, computer rooms and small-to-

medium data centers with moderate availability medium data centers with moderate availability requirements. requirements.

Air cooled self-contained systems (1-piece)Air cooled self-contained systems (1-piece)

Self-contained systems locate all the components of the Self-contained systems locate all the components of the refrigeration cycle in one enclosure that is usually found in refrigeration cycle in one enclosure that is usually found in

the the IT environment. Heat exits the self-contained system as a IT environment. Heat exits the self-contained system as a stream of hot (about 120°F [49°C]) air called exhaust air. This stream of hot (about 120°F [49°C]) air called exhaust air. This stream of hot air must be routed away from the IT room to stream of hot air must be routed away from the IT room to the outdoors or into an unconditioned space to ensure proper the outdoors or into an unconditioned space to ensure proper cooling of computer equipment. If mounted above a drop cooling of computer equipment. If mounted above a drop ceiling and not using condenser air inlet or outlet ducts, the ceiling and not using condenser air inlet or outlet ducts, the hot exhaust air from the condensing coil can be rejected hot exhaust air from the condensing coil can be rejected directly into the drop ceiling area. directly into the drop ceiling area.

The building’s air conditioning system must have The building’s air conditioning system must have available available

capacity to handle this additional heat load. Air that is capacity to handle this additional heat load. Air that is drawn through the condensing coil (becoming exhaust air) drawn through the condensing coil (becoming exhaust air) should also be supplied from outside the computer room. should also be supplied from outside the computer room. This will avoid creating a vacuum in the room that would This will avoid creating a vacuum in the room that would allow warmer, unconditioned air to enter. Self-contained allow warmer, unconditioned air to enter. Self-contained indoor systems are usually limited in capacity (up to 15kW) indoor systems are usually limited in capacity (up to 15kW) because of the additional space required to house all the because of the additional space required to house all the refrigeration cycle components and the large air ducts refrigeration cycle components and the large air ducts required to manage exhaust air. Self-contained systems required to manage exhaust air. Self-contained systems that mount outdoors on a building roof can be much larger that mount outdoors on a building roof can be much larger in capacity but are not commonly used for precision in capacity but are not commonly used for precision

cooling cooling applications.applications.

Advantages:Advantages: • • Indoor self-contained systems have the lowest Indoor self-contained systems have the lowest

installation cost. There is nothing to install on the installation cost. There is nothing to install on the roof or outside the building.roof or outside the building.

• • All refrigeration cycle components are contained All refrigeration cycle components are contained inside one unit as a factory-sealed and tested inside one unit as a factory-sealed and tested system for highest reliability.system for highest reliability.

Disadvantages:Disadvantages:• • Less heat removal capacity per unit compared to Less heat removal capacity per unit compared to

other configurations.other configurations.• • Air routed into and out of the IT environment for Air routed into and out of the IT environment for

the condensing coil usually requires ductwork the condensing coil usually requires ductwork and/or dropped ceiling. and/or dropped ceiling.

. .

Usually Used:Usually Used:• • In wiring closets, laboratory environments and In wiring closets, laboratory environments and

computer rooms with moderate availability computer rooms with moderate availability requirements. Sometimes used to fix hot spots in requirements. Sometimes used to fix hot spots in data centers.data centers.

Glycol cooled systemsGlycol cooled systems

This type of system locates all refrigeration cycle This type of system locates all refrigeration cycle components in one enclosure (like a self-contained system) components in one enclosure (like a self-contained system) but replaces the bulky condensing coil with a much smaller but replaces the bulky condensing coil with a much smaller heat exchanger shown in Figure 3. The heat exchanger heat exchanger shown in Figure 3. The heat exchanger uses flowing glycol (a mixture of water and ethylene glycol, uses flowing glycol (a mixture of water and ethylene glycol, similar to automobile anti-freeze) to collect heat from the similar to automobile anti-freeze) to collect heat from the refrigerant and transport it away from the IT environment. refrigerant and transport it away from the IT environment. Heat exchangers and glycol pipes are always smaller than Heat exchangers and glycol pipes are always smaller than condensing coils (2-piece air cooled systems) and condensing coils (2-piece air cooled systems) and condenser air ducts (self contained air cooled systems) condenser air ducts (self contained air cooled systems) because the glycol mixture has the capability to collect and because the glycol mixture has the capability to collect and transport much more heat than air doestransport much more heat than air does

The glycol flows via pipes to an outdoor-mounted The glycol flows via pipes to an outdoor-mounted device device

called a fluid cooler. Heat is rejected to the outside called a fluid cooler. Heat is rejected to the outside atmosphere as fans force outdoor air through the atmosphere as fans force outdoor air through the

warm warm glycol-filled coil in the fluid cooler. A pump package glycol-filled coil in the fluid cooler. A pump package

(pump, (pump, motor and protective enclosure) is used to circulate motor and protective enclosure) is used to circulate

the the glycol in its loop to and from the computer room air glycol in its loop to and from the computer room air conditioner and fluid cooler. conditioner and fluid cooler.

Advantages:Advantages:

• • The entire refrigeration cycle is contained inside the The entire refrigeration cycle is contained inside the computer room air conditioning unit as a factory-sealed and computer room air conditioning unit as a factory-sealed and tested system for highest reliability with the same floor space tested system for highest reliability with the same floor space requirement as a two piece air cooled system.requirement as a two piece air cooled system.

► Glycol pipes can run much longer distances than Glycol pipes can run much longer distances than refrigerant lines (air cooled system) and can service refrigerant lines (air cooled system) and can service several computer room air conditioning units from one fluidseveral computer room air conditioning units from one fluid cooler and pump package.cooler and pump package.► In cold locations, the glycol within the fluid cooler can be In cold locations, the glycol within the fluid cooler can be cooled so much (below 50°F [10°C]) that it can bypass thecooled so much (below 50°F [10°C]) that it can bypass the heat exchanger in the CRAC unit and flow directly to a heat exchanger in the CRAC unit and flow directly to a specially installed economizer coil. specially installed economizer coil.

Under these conditions, the refrigeration cycle is turned Under these conditions, the refrigeration cycle is turned off off

and the air that flows through the economizer coil, now and the air that flows through the economizer coil, now filled with cold flowing glycol, cools the IT environment. filled with cold flowing glycol, cools the IT environment. This process is known as “free cooling” and provides This process is known as “free cooling” and provides excellent operating cost reductions when used. excellent operating cost reductions when used.

Disadvantages:Disadvantages: • • Additional required components (pump package, Additional required components (pump package, valves) raise capital and installation costs when valves) raise capital and installation costs when

compared compared with air cooled DX systems.with air cooled DX systems.• • Maintenance of glycol volume and quality within the Maintenance of glycol volume and quality within the system is required.system is required.• • Introduces an additional source of liquid into the IT Introduces an additional source of liquid into the IT environment.environment.

► Usually Used:Usually Used:► In computer rooms and small-to-medium data In computer rooms and small-to-medium data

centers with moderate availability requirements. centers with moderate availability requirements.

Water cooled systemsWater cooled systemsWater cooled systems are similar to glycol cooled Water cooled systems are similar to glycol cooled

systems systems in that all refrigeration cycle components are located in that all refrigeration cycle components are located

insideinside the computer room air conditioner. However, there are the computer room air conditioner. However, there are two important differences between a glycol cooled two important differences between a glycol cooled

system system and a water cooled system:and a water cooled system:• • A water (also called condenser water) loop is usedA water (also called condenser water) loop is used instead of glycol to collect and transport heat away frominstead of glycol to collect and transport heat away from the IT environment.the IT environment.• • Heat is rejected to the outside atmosphere via a coolingHeat is rejected to the outside atmosphere via a cooling tower instead of a fluid cooler. tower instead of a fluid cooler.

A cooling tower rejects heat from the IT room to the A cooling tower rejects heat from the IT room to the outdoor environment by spraying warm condenser wateroutdoor environment by spraying warm condenser water onto sponge-like material (called fill) at the top of the onto sponge-like material (called fill) at the top of the tower. The water spreads out and some of it evaporatestower. The water spreads out and some of it evaporates away as it drips and flows to the bottom of the coolingaway as it drips and flows to the bottom of the cooling tower (a fan is used to help speed up the evaporation bytower (a fan is used to help speed up the evaporation by drawing air through the fill material). In the same drawing air through the fill material). In the same manner as the human body is cooled by the evaporationmanner as the human body is cooled by the evaporation of sweat, the small amount of water that evaporates of sweat, the small amount of water that evaporates from the cooling tower serves to lower the temperature from the cooling tower serves to lower the temperature of the remaining water. The cooler water at the bottom of of the remaining water. The cooler water at the bottom of the tower is collected and sent back into the condenser the tower is collected and sent back into the condenser water loop via a pump package. water loop via a pump package.

Condenser water loops and cooling towers are Condenser water loops and cooling towers are usually usually

not installed solely for the use of water cooled not installed solely for the use of water cooled computer computer

room air conditioning systems. They are usually room air conditioning systems. They are usually part of a part of a

larger system and may also be used to reject heat larger system and may also be used to reject heat from from

the building’s comfort air conditioning system (for the building’s comfort air conditioning system (for cooling cooling

people) and water chillers (water chillers are people) and water chillers (water chillers are explained in explained in

the next section). the next section).

Advantages:Advantages:

► All refrigeration cycle components are contained insideAll refrigeration cycle components are contained inside the computer room air conditioning unit as a factory-the computer room air conditioning unit as a factory-sealed and tested system for highest reliability.sealed and tested system for highest reliability.

► Condenser water piping loops are easily run long Condenser water piping loops are easily run long distances and almost always service many computer room distances and almost always service many computer room air conditioning units and other devices from one coolingair conditioning units and other devices from one cooling tower.tower.► In leased IT environments, usage of the building’s In leased IT environments, usage of the building’s condenser water is generally less expensive than chilledcondenser water is generally less expensive than chilled water (chilled water is explained in the next section).water (chilled water is explained in the next section).

Disadvantages:Disadvantages:► High initial cost for cooling tower, pump, and piping High initial cost for cooling tower, pump, and piping systems.systems.

Very high maintenance costs due to frequent cleaning Very high maintenance costs due to frequent cleaning andand

water treatment requirements. water treatment requirements. Introduces an additional source of liquid into the IT Introduces an additional source of liquid into the IT environment. A non-dedicated cooling tower (one environment. A non-dedicated cooling tower (one

used toused to cool the entire building) may be less reliable then a cool the entire building) may be less reliable then a

coolingcooling tower dedicated to the Computer Room Air tower dedicated to the Computer Room Air

Conditioner.Conditioner.

Usually Used:Usually Used:• • In conjunction with other building systems in small, In conjunction with other building systems in small, medium and large data centers with moderate to-highmedium and large data centers with moderate to-highavailability requirements. availability requirements.

Absorption cooling systemsAbsorption cooling systemsAdvantages and Comparison of Vapor Absorption Advantages and Comparison of Vapor Absorption

Refrigeration over Vapor Compression RefrigerationRefrigeration over Vapor Compression RefrigerationHere are of the comparisons and advantages of absorptionHere are of the comparisons and advantages of absorption refrigeration system over vapor compression refrigeration refrigeration system over vapor compression refrigeration system:system: 1) Method of compression of the refrigerant: One of the1) Method of compression of the refrigerant: One of the most important parts of any refrigeration cycle is the most important parts of any refrigeration cycle is the compression of the refrigerant since all the further compression of the refrigerant since all the further Operations depend on it. In the vapor compression Operations depend on it. In the vapor compression refrigeration system ,the compression of the refrigerant is refrigeration system ,the compression of the refrigerant is done by compressor which can be of reciprocating, rotating done by compressor which can be of reciprocating, rotating or centrifugal type. or centrifugal type.

In the vapor absorption refrigeration system, the In the vapor absorption refrigeration system, the compressioncompression

of the refrigerant is done by absorption of the refrigerant of the refrigerant is done by absorption of the refrigerant byby

the absorbent. As the refrigerant is absorbed, it getsthe absorbent. As the refrigerant is absorbed, it gets converted from the vapor state to liquid state so its volumeconverted from the vapor state to liquid state so its volume reduces.reduces.

2) Power consumption devices: In the vapor compression2) Power consumption devices: In the vapor compression cycle the compressor is the major power consuming devicecycle the compressor is the major power consuming device while in the vapor absorption cycle the pump used for while in the vapor absorption cycle the pump used for pumping refrigerant-absorbent solution is the major powerpumping refrigerant-absorbent solution is the major power consuming device.consuming device.

3) The amount of power required: The compressor of 3) The amount of power required: The compressor of thethe

vapor compression cycle requires large quantities of vapor compression cycle requires large quantities of powerpower

for its operation and it increases as the size of the for its operation and it increases as the size of the refrigeration system increases. In case of the vaporrefrigeration system increases. In case of the vapor absorption refrigeration system, the pump requires absorption refrigeration system, the pump requires

veryvery small amount of power and it remains almost the small amount of power and it remains almost the

same (orsame (or may increase slightly) even for higher capacities of may increase slightly) even for higher capacities of refrigeration. Thus the power consumed by the vaporrefrigeration. Thus the power consumed by the vapor absorption refrigeration system is much more than absorption refrigeration system is much more than

thatthat required by the vapor compression system.required by the vapor compression system.

4) Type of energy required: The vapor absorption 4) Type of energy required: The vapor absorption system system

runs mainly on the waste or the extra heat in the runs mainly on the waste or the extra heat in the plant.plant.

Thus one can utilize the extra steam from the boiler, Thus one can utilize the extra steam from the boiler, oror

generate extra steam for the purpose and also use generate extra steam for the purpose and also use the hotthe hot

available water. Similarly the waste heat from the available water. Similarly the waste heat from the diesel diesel

engine, hot water from the solar water heater, etc. engine, hot water from the solar water heater, etc. can can

also be utilized. In case of the vapor compression also be utilized. In case of the vapor compression refrigeration system, the compressor can be run by refrigeration system, the compressor can be run by

electric electric power supply only; no other types of energy can be power supply only; no other types of energy can be

utilized utilized in these systems.in these systems.

5) Running cost: The vapor compression refrigeration 5) Running cost: The vapor compression refrigeration system can run only on electric power, and they requiresystem can run only on electric power, and they require large amount of power. These days the electric power haslarge amount of power. These days the electric power has become very expensive, hence the running cost of the become very expensive, hence the running cost of the vapor compression refrigeration system is very high. Invapor compression refrigeration system is very high. In case of the absorption refrigeration system only small case of the absorption refrigeration system only small pump requires electric power and it is quite low. In most of pump requires electric power and it is quite low. In most of the process industries, where the absorption refrigeration isthe process industries, where the absorption refrigeration is used, there is some extra steam available from the boiler,used, there is some extra steam available from the boiler, which can be used for running the system. Thus in which can be used for running the system. Thus in absorption refrigeration system no extra power in the pureabsorption refrigeration system no extra power in the pure electric form is required and the energy that would have electric form is required and the energy that would have otherwise gone wasted is utilized in the plant. Thus theotherwise gone wasted is utilized in the plant. Thus the running cost of the absorption refrigeration system is running cost of the absorption refrigeration system is much lesser than the vapor compression system. much lesser than the vapor compression system.

6) Foundations required and noise: The compressor of 6) Foundations required and noise: The compressor of thethe

vapor compression system is operated at very high vapor compression system is operated at very high speedsspeeds

and it makes lots of vibrations and noise. It also and it makes lots of vibrations and noise. It also requiresrequires

very strong foundation so that it can remain intact very strong foundation so that it can remain intact underunder

vibrations and high pressures of the refrigerant. In thevibrations and high pressures of the refrigerant. In the absorption refrigeration system there are no major absorption refrigeration system there are no major

movingmoving parts hence they don’t vibrate, don’t make noise and parts hence they don’t vibrate, don’t make noise and

alsoalso don’t require heavy foundations. The absorptiondon’t require heavy foundations. The absorption refrigeration systems operate silently. refrigeration systems operate silently.

7) Maintenance: Compressor is the crucial part of the7) Maintenance: Compressor is the crucial part of the vapor compression cycle, and it has number of moving vapor compression cycle, and it has number of moving parts. It is very important to do the thorough lubrication ofparts. It is very important to do the thorough lubrication of the compressor and also keep checking it regularly for anythe compressor and also keep checking it regularly for any defects. The compressor also requires changing of thedefects. The compressor also requires changing of the piston, piston rings, cylinder liner etc. from time-to-time.piston, piston rings, cylinder liner etc. from time-to-time. Thus the vapor compression system requires lots ofThus the vapor compression system requires lots of maintenance. Failure of compressor can be very expensive at maintenance. Failure of compressor can be very expensive at times as the suction and the discharge valve of the times as the suction and the discharge valve of the

compressor compressor are very expensive. Even the motor of the compressor is very are very expensive. Even the motor of the compressor is very heavy and expensive. The compressor also requires cooling, heavy and expensive. The compressor also requires cooling, for which special pump is required to pump the water from for which special pump is required to pump the water from

the the cooling tower to the compressor. Since there are number of cooling tower to the compressor. Since there are number of moving parts of the compressor that move at very fast speed moving parts of the compressor that move at very fast speed some or the other failure occurs regularly. In the absorption some or the other failure occurs regularly. In the absorption

refrigeration system the only moving part is the small pumprefrigeration system the only moving part is the small pump that fails rarely. Thus the maintenance required by the vaporthat fails rarely. Thus the maintenance required by the vapor compression system is much more than that required by the compression system is much more than that required by the vapor absorption system. vapor absorption system.

8) Capacity control of the system: In the vapor compression 8) Capacity control of the system: In the vapor compression cycle the capacity control of the system is done from the cycle the capacity control of the system is done from the compressor and in most of the cases stepwise capacity controlcompressor and in most of the cases stepwise capacity control is obtained. In case of the absorption refrigeration system it is is obtained. In case of the absorption refrigeration system it is possible to obtain step less capacity control and zero capacity possible to obtain step less capacity control and zero capacity when there is no load on the system. Though these days when there is no load on the system. Though these days compressors with step less capacity control are available, but compressors with step less capacity control are available, but they will consume lots of power even if there is zero load on they will consume lots of power even if there is zero load on the refrigeration system. In absorption system, when there is the refrigeration system. In absorption system, when there is zero load the power consumption is almost zero. zero load the power consumption is almost zero.

9) Type of refrigerant used and its cost: In ammonia-9) Type of refrigerant used and its cost: In ammonia-water absorption refrigeration system, ammonia is usedwater absorption refrigeration system, ammonia is used as the refrigerant, which is easily and cheaply available.as the refrigerant, which is easily and cheaply available. In lithium bromide system, water is used as the In lithium bromide system, water is used as the refrigerant, which is also available cheaply and easily. Inrefrigerant, which is also available cheaply and easily. In case of the vapor compression refrigeration system case of the vapor compression refrigeration system halocarbons are used as the refrigerants, which are veryhalocarbons are used as the refrigerants, which are very expensive.expensive.10) Leakage of the refrigerant: In the absorption 10) Leakage of the refrigerant: In the absorption refrigeration system there are no (or very few) leakagesrefrigeration system there are no (or very few) leakages of the refrigerant and the refrigerant itself is very cheap.of the refrigerant and the refrigerant itself is very cheap. Thus there are almost zero refrigerant recharging costs.Thus there are almost zero refrigerant recharging costs. In case of the vapor compression systems there are lots In case of the vapor compression systems there are lots of leakages of the refrigerant thus regular recharge of of leakages of the refrigerant thus regular recharge of the refrigerant is required which is very expensive.the refrigerant is required which is very expensive.

11) Greenhouse effect: Most of the halocarbon 11) Greenhouse effect: Most of the halocarbon refrigerantsrefrigerants

used in the compression refrigeration system used in the compression refrigeration system produces produces

greenhouse effect. As per the Montreal Protocol, their greenhouse effect. As per the Montreal Protocol, their use use

has to stop completely by the year 2020. In the has to stop completely by the year 2020. In the absorption absorption

refrigeration system no refrigerant produces the refrigeration system no refrigerant produces the green housegreen house

effect, so their use won’t be stopped in future.effect, so their use won’t be stopped in future.

Disadvantages of Absorption Refrigeration over Disadvantages of Absorption Refrigeration over Vapor Compression Refrigeration Cycle:-Vapor Compression Refrigeration Cycle:-

1)1) Initial capital cost: Though the running cost of the Initial capital cost: Though the running cost of the Absorption refrigeration system is much lesser than the vapor Absorption refrigeration system is much lesser than the vapor compression system, its initial capital cost is much higher.compression system, its initial capital cost is much higher. 2) Corrosive nature of lithium bromide: In the lithium bromide2) Corrosive nature of lithium bromide: In the lithium bromide absorption refrigeration system, lithium bromide is corrosive inabsorption refrigeration system, lithium bromide is corrosive in nature, which reduces the overall life of the system. In case ofnature, which reduces the overall life of the system. In case of the ammonia system, ammonia is corrosive to copper. In the the ammonia system, ammonia is corrosive to copper. In the vapor compression system copper is used with the halocarbonvapor compression system copper is used with the halocarbon refrigerants and they are quite safe thus ensuring long life of refrigerants and they are quite safe thus ensuring long life of the refrigeration system. As such the vapor compression the refrigeration system. As such the vapor compression

system system with reciprocating or centrifugal compressor has longer life thanwith reciprocating or centrifugal compressor has longer life than the lithium bromide absorption refrigeration system. the lithium bromide absorption refrigeration system.

4) Coefficient of Performance (COP):4) Coefficient of Performance (COP):

The coefficient of performance of the absorptionThe coefficient of performance of the absorption refrigeration systems is very low compared to the vaporrefrigeration systems is very low compared to the vapor compression systems. For instance, the COP of the twocompression systems. For instance, the COP of the two stage lithium bromide system is about 1.1, while that of stage lithium bromide system is about 1.1, while that of the vapor compression system used for the air conditioning the vapor compression system used for the air conditioning applications it is about 4 to 5.Thus the absorption applications it is about 4 to 5.Thus the absorption refrigeration system becomes competitive only if the ratio ofrefrigeration system becomes competitive only if the ratio of the electricity to fuel (oil, gas or coal used to generate thethe electricity to fuel (oil, gas or coal used to generate the steam in the boiler) becomes more than four. If this ratio issteam in the boiler) becomes more than four. If this ratio is lesser there are chances that excess fuel would be requiredlesser there are chances that excess fuel would be required to generate the steam. However, if there is excess steam in to generate the steam. However, if there is excess steam in the industry, this ratio may not be given importance. the industry, this ratio may not be given importance.

5) Higher heat rejection:5) Higher heat rejection:

In the absorption refrigeration heat has to be rejected In the absorption refrigeration heat has to be rejected from number of parts like condenser, absorber, analyzer, from number of parts like condenser, absorber, analyzer, rectifier etc. thus heat rejection factor for absorption rectifier etc. thus heat rejection factor for absorption refrigeration system is high and it can be around 2.5. In refrigeration system is high and it can be around 2.5. In the compression refrigeration system the heat is given up the compression refrigeration system the heat is given up only from the condenser, so it heat rejection factor is small, only from the condenser, so it heat rejection factor is small, which is about 1.2. Thus the cooling tower and pump which is about 1.2. Thus the cooling tower and pump capacities for pumping the cooling water have to be higher capacities for pumping the cooling water have to be higher in case of the absorption refrigeration system, which leads in case of the absorption refrigeration system, which leads to increase in the running cost of the system.to increase in the running cost of the system.

Variable Refrigerant FlowVariable Refrigerant Flow► A VRF system is a direct expansion (DX) HVAC systemA VRF system is a direct expansion (DX) HVAC system consisting of at least one variable capacity compressor consisting of at least one variable capacity compressor connected to two or more independently-controllable fan connected to two or more independently-controllable fan coil units on a single refrigerant piping network. Most VRF coil units on a single refrigerant piping network. Most VRF systems available today also include a variety of indoor systems available today also include a variety of indoor units including: ducted units, wall-mounted units, and units including: ducted units, wall-mounted units, and cassette-type units that will fit into a standard 2- x 2-ft cassette-type units that will fit into a standard 2- x 2-ft ceiling grid. ceiling grid.

VRF systems generally include proprietary controls VRF systems generally include proprietary controls systems that modulate fans, compressors, and systems that modulate fans, compressors, and

electronic electronic expansion valves to ensure the highest efficiency of expansion valves to ensure the highest efficiency of

the the system. These controls systems can also include system. These controls systems can also include

advanced advanced features such as remote monitoring (through a features such as remote monitoring (through a

building building network or over the internet), BMS interface network or over the internet), BMS interface

modules, and modules, and central control systems capable of handling up to central control systems capable of handling up to

2,000 2,000 indoor units.indoor units.

Multi-splits include multiple indoor units connected to a Multi-splits include multiple indoor units connected to a single single

outdoor unit. Ductless products are fundamentally outdoor unit. Ductless products are fundamentally different different

from ducted systems in that heat is transferred to or from from ducted systems in that heat is transferred to or from the the

space directly by circulating refrigerant to indoor units space directly by circulating refrigerant to indoor units (evaporators or condensers) located near or within the (evaporators or condensers) located near or within the conditioned space. (When the indoor units are in the conditioned space. (When the indoor units are in the

cooling cooling mode they act as evaporators and when they are in the mode they act as evaporators and when they are in the

heating heating mode they act as condensers) In contrast, conventional mode they act as condensers) In contrast, conventional

ducted ducted systems transfer heat from the space to the refrigerant by systems transfer heat from the space to the refrigerant by circulating air (inducted systems) or water (in chillers) circulating air (inducted systems) or water (in chillers) throughout the building.throughout the building.

Advantages of VRF and Multi-Split SystemsAdvantages of VRF and Multi-Split Systems► Good part load performance due to multiple compressor Good part load performance due to multiple compressor and variable speed compressor systems permitting and variable speed compressor systems permitting capacity modulation to serve 7% to 100% of the cooling capacity modulation to serve 7% to 100% of the cooling or heating load. Many hours of HVAC system operation or heating load. Many hours of HVAC system operation are spent between 30% and 70% of maximum capacity are spent between 30% and 70% of maximum capacity where the VRF system efficiency is high (Roth 2002).where the VRF system efficiency is high (Roth 2002).• • Good zone control, saving by not conditioning Good zone control, saving by not conditioning unoccupied zones and by providing capability to condition unoccupied zones and by providing capability to condition single zones off hours at a reasonable cost. Figure 3 shows single zones off hours at a reasonable cost. Figure 3 shows how VRF systems can provide zone control, including how VRF systems can provide zone control, including simultaneous heating and cooling.simultaneous heating and cooling.

► Heat recovery is readily accomplished with the refrigerant Heat recovery is readily accomplished with the refrigerant when some of the indoor units are heating and some of the when some of the indoor units are heating and some of the units are cooling. According to one manufacturer’s publishedunits are cooling. According to one manufacturer’s publisheddata, if a 50% demand for full cooling and a 50% demand for data, if a 50% demand for full cooling and a 50% demand for full heating exist, in the heat recovery mode the compressor full heating exist, in the heat recovery mode the compressor would only be 48% loaded (Inman, 2007).would only be 48% loaded (Inman, 2007).• • Duct losses are confined to the ventilation air which is Duct losses are confined to the ventilation air which is normally about 1/5th of the air flow of a ducted system normally about 1/5th of the air flow of a ducted system circulating and conditioning both the ventilation air and thecirculating and conditioning both the ventilation air and therecirculated air. (Since ducts are often in unconditioned recirculated air. (Since ducts are often in unconditioned spaces, duct losses may not contribute to building space spaces, duct losses may not contribute to building space conditioning).conditioning).

► Refrigerant is used directly as both the working fluid andRefrigerant is used directly as both the working fluid and the heat transfer fluid tending to make the VRF system the heat transfer fluid tending to make the VRF system more efficient than systems that use air or water as a more efficient than systems that use air or water as a secondary heat transfer fluid for delivering heating or secondary heat transfer fluid for delivering heating or cooling.cooling.• • The use of R-410Aand other features such a variable The use of R-410Aand other features such a variable speed compressors, multiple speed fans and blowers, speed compressors, multiple speed fans and blowers, refrigerant circuitry, electronic expansion valves and refrigerant circuitry, electronic expansion valves and advanced controls contributes to enhanced low advanced controls contributes to enhanced low temperature performance that can avoid or minimize thetemperature performance that can avoid or minimize the► need for supplementary heat in many U.S. climates.need for supplementary heat in many U.S. climates.

► Better comfort. Since the system can be modulated to Better comfort. Since the system can be modulated to follow the load, units can remain running to maintain follow the load, units can remain running to maintain temperature within narrow limits, assuring a comfortable temperature within narrow limits, assuring a comfortable Temperature envelope.Temperature envelope.• • Low noise levels. Levels are 24 dBA for the indoor unit Low noise levels. Levels are 24 dBA for the indoor unit and 56 dBA for the outdoor unit (Siddens, 2007).and 56 dBA for the outdoor unit (Siddens, 2007).• • Flexible and quick installation. Only a small (3” or so)Flexible and quick installation. Only a small (3” or so) opening is needed for the refrigerant piping.opening is needed for the refrigerant piping.• • Low-profile, low space requirements and light weight Low-profile, low space requirements and light weight make units easier to fit into tight spaces and to avoid make units easier to fit into tight spaces and to avoid obtrusive terminal units that could spoil the esthetics of a obtrusive terminal units that could spoil the esthetics of a

space.space.

► Claimed low maintenance and high reliability. AlthoughClaimed low maintenance and high reliability. Although the large amount of refrigerant piping and numbers of the large amount of refrigerant piping and numbers of connections is a concern to U.S. specifiers and connections is a concern to U.S. specifiers and installers, manufacturers claim low maintenance costsinstallers, manufacturers claim low maintenance costs and a record of reliability. Maintenance consists of and a record of reliability. Maintenance consists of changing filters and cleaning coils.changing filters and cleaning coils.• • Modularity allows easy apportioning of energy costs Modularity allows easy apportioning of energy costs among tenants or operations.among tenants or operations.► Increased useful building space is enabled by reducing Increased useful building space is enabled by reducing floor to floor height (12” ceiling void vs. 20”) and floor to floor height (12” ceiling void vs. 20”) and eliminating the need for a machine room.eliminating the need for a machine room.• • Avoids the need for an on-site, trained operator as might Avoids the need for an on-site, trained operator as might

be desirable with a large chiller based system.be desirable with a large chiller based system.

Disadvantages of VRF and Multi-Split Systems:-Disadvantages of VRF and Multi-Split Systems:-

► Less economizer cycle benefit may occur with the smaller Less economizer cycle benefit may occur with the smaller ventilation system since the ducting is sized just for ventilation system since the ducting is sized just for ventilation.ventilation.• • Use of supplementary heat may be required for quick Use of supplementary heat may be required for quick recovery from night setback. This can be avoided to a great recovery from night setback. This can be avoided to a great extent by providing sufficient time to allow the heat pump extent by providing sufficient time to allow the heat pump Cycle to be used with the compressors running at maximum Cycle to be used with the compressors running at maximum capacity to provide morning warm up.capacity to provide morning warm up.• • Use of backup strip heat for space heating in cold weather Use of backup strip heat for space heating in cold weather would be a detriment to the efficiency of the system. would be a detriment to the efficiency of the system. However, as indicated above in the list of advantages, However, as indicated above in the list of advantages,

speedspeedvariation and other features help increase the heat pump variation and other features help increase the heat pump capacity to offset some of the vapor compression cycle capacity to offset some of the vapor compression cycle degradation with lower temperatures. This can avoid ordegradation with lower temperatures. This can avoid orminimize the need for backup heat. Integrated gas heating minimize the need for backup heat. Integrated gas heating systems are not available as yet as a dual fuel option.systems are not available as yet as a dual fuel option.

► It may be less economical to provide high efficiencyIt may be less economical to provide high efficiency components (such as fans, or filter systems) for many components (such as fans, or filter systems) for many decentralized indoor units compared to the efficiency decentralized indoor units compared to the efficiency of these systems when installed in a single larger of these systems when installed in a single larger centralized system.centralized system.► The need for a separate ventilation system to satisfy The need for a separate ventilation system to satisfy code requirements for delivery of outside air offsets code requirements for delivery of outside air offsets some of the retrofit advantages of the VRF system.some of the retrofit advantages of the VRF system.• • Each VRF indoor unit should be supplied with Each VRF indoor unit should be supplied with

condensatecondensate drain that needs to have access to a water collection drain that needs to have access to a water collection system.system.

- Long refrigerant runs and large numbers of - Long refrigerant runs and large numbers of connections connections

could result in refrigerant leakage that could be could result in refrigerant leakage that could be significant, significant,

causing safety issues and repair difficulties. One VRFcausing safety issues and repair difficulties. One VRFmanufacturer cautions not to install an air conditioner in manufacturer cautions not to install an air conditioner in

a a room where the limit density will be exceeded if room where the limit density will be exceeded if

refrigerant refrigerant leaks. They assert that the refrigerant (R410A) used by leaks. They assert that the refrigerant (R410A) used by

thisthissystem is itself a safe refrigerant; however, if for some system is itself a safe refrigerant; however, if for some reason the refrigerant leaks and the limit density is reason the refrigerant leaks and the limit density is exceeded, there is a risk of injury to persons due to a exceeded, there is a risk of injury to persons due to a

lack lack of oxygen.of oxygen.

► Oil return (and refrigerant positioning) could be Oil return (and refrigerant positioning) could be an issue an issue

but many systems employ special oil retrieving but many systems employ special oil retrieving modes modes

that are periodically, automatically activated to that are periodically, automatically activated to flush oil flush oil

(or refrigerant liquid) out of any locations where it (or refrigerant liquid) out of any locations where it has has

accumulated.accumulated.

► Installed costs are highly dependent on the application, Installed costs are highly dependent on the application, construction and layout of the building and whether the construction and layout of the building and whether the installation is new or retrofit. Lack of familiarity with the installation is new or retrofit. Lack of familiarity with the technology in the U.S. will add to VRF costs. Total costs for technology in the U.S. will add to VRF costs. Total costs for VRF systems are likely to be about 5% to 20% higher than VRF systems are likely to be about 5% to 20% higher than chilled water systems of similar capacity (Roth 2002).chilled water systems of similar capacity (Roth 2002).

► One manufacturer provided verbal information that VRF One manufacturer provided verbal information that VRF systems cost about 30% to 50% more than equivalent systems cost about 30% to 50% more than equivalent capacity single package ducted systems with a SEER of 13 capacity single package ducted systems with a SEER of 13 to 14. And that VRF systems cost more than twice as much to 14. And that VRF systems cost more than twice as much as packaged terminal units. This information is interesting as packaged terminal units. This information is interesting but not as important as the comparisons of VRF and chiller but not as important as the comparisons of VRF and chiller systems if VRF manufacturers position their product as a systems if VRF manufacturers position their product as a chiller alternative.chiller alternative.

Eng.Mohamed Abou YahiaEng.Mohamed Abou Yahia++201100800213201100800213