Free cooling
Encyclopedia
Free cooling is an economical method of using low external air temperatures to assist in chilling water, which can then be used for industrial process, or air conditioning
systems in green data centers.
When the ambient air temperature drops to a set temperature, a modulating valve allows all or part of the chilled water to by-pass an existing chiller and run through the Free Cooling system, which uses less power and uses the lower ambient air temperature to cool the water in the system.
This can be achieved by installing an air blast cooler with any existing chiller or on its own.
During low ambients a processor can by-pass an existing chiller giving energy savings of up to 75%, without compromising cooling requirements.
in winter months, large commercial buildings’ interior spaces may need cooling, even while perimeter spaces may need heating. Free cooling is the production of chilled water without the use of a chiller
, and can be used generally in the late fall, winter and early spring, in the Northern Hemisphere. Free cooling is not entirely free since the chiller is still operational.
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
systems in green data centers.
When the ambient air temperature drops to a set temperature, a modulating valve allows all or part of the chilled water to by-pass an existing chiller and run through the Free Cooling system, which uses less power and uses the lower ambient air temperature to cool the water in the system.
This can be achieved by installing an air blast cooler with any existing chiller or on its own.
During low ambients a processor can by-pass an existing chiller giving energy savings of up to 75%, without compromising cooling requirements.
Free Cooling in HVAC
In HVACHVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
in winter months, large commercial buildings’ interior spaces may need cooling, even while perimeter spaces may need heating. Free cooling is the production of chilled water without the use of a chiller
Chiller
A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.-Use in air conditioning:...
, and can be used generally in the late fall, winter and early spring, in the Northern Hemisphere. Free cooling is not entirely free since the chiller is still operational.
Methods of Free Cooling
Assuming that the system can utilize free cooling, there are three ways to use free cooling:- Strainer Cycle - The cooling towerCooling towerCooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...
water can be directly linked into the flow through the chilled waterChilled waterChilled water is a commodity often used to cool a building's air and equipment, especially in situations where many individual rooms must be controlled separately, such as a hotel...
circuit. If the cooling towerCooling towerCooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...
is open then a strainer is required to eliminate any debris that could accumulate within the tower. The cost savings are associated with the limited use of the water chillerChillerA chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.-Use in air conditioning:...
energy There is an increased risk of corrosion using this method. - Plate and Frame Heat exchanger - A heat exchangerHeat exchangerA heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
, will transfer heat directly from the chilled water loop to the cooling towerCooling towerCooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...
loop. The exchanger keeps the cooling tower water separate from the coolant flowing through the cooling coils. The chiller water is thus pre-cooled. An energy savings is due reduced chiller loading and thus a reduction in energy consumption. There is an increase in cost due to the pump need to compensate for the pressure differences. - Refrigeration Migration - A valve arrangement within the water chillerChillerA chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.-Use in air conditioning:...
opens a direct path between the condenserCondenserCondenser may refer to:*Condenser , a device or unit used to condense vapor into liquid. More specific articles on some types include:*Air coil used in HVAC refrigeration systems...
and the evaporatorEvaporatorAn evaporator is a device used to turn the liquid form of some chemical into its gaseous form. For example, an evaporator is used in an air conditioning system to allow the compressed cooling chemical to evaporate from liquid to gas, absorbing heat in the process.-Uses:As stated above, an...
. The relatively warm fluid in the chiller loop vaporizes the refrigerant, and the energy is carried directly to the condenser, where it is cooled and condensed by the water from the cooling tower. This method is driven by the idea that the refrigerant tends to move towards the coldest point in a refrigeration circuit. The cost savings associated with this method are due to the compressor’s inactivity, since the blower, fans, and pumps are all operational
Limitations
Freezing can be difficult to avoid once the cooling tower water temperature gets below 39 °F. Another limitation is the temperature difference across the heat exchanger. A heat exchanger that has a very low temperature difference across can become economically unrealistic. The economics of the heat exchanger allow for a minimum free cooling water temperature of about 41 °F.Sources
There are four main sources of natural cooling energy- Deep seawater
- High-altitude coldness
- Night-time coldness
- Subterranean geothermal energy