Free cooling is an economical method of using low external air temperatures to assist in chilling water, which can then be used for industrial processes, or

air conditioning Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...

systems. The

chilled water Chilled 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. The chilled water can be supplied by a vendor, such as a public util ...

can either be used immediately or be stored for the short- or long-term. When outdoor temperatures are lower relative to indoor temperatures, this system utilizes the cool outdoor air as a free cooling source. In this manner, the system replaces the

chiller A chiller is a machine that removes heat from a liquid coolant via a vapor-compression, adsorption refrigeration, or absorption refrigeration cycles. This liquid can then be circulated through a heat exchanger to cool equipment, or another p ...

in traditional air conditioning systems while achieving the same cooling result. Such systems can be made for single buildings or district cooling networks.

Operation

For a human-powered version, see yakhchal. 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

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 ambient temperatures, an installation can by-pass an existing chiller giving

energy savings Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively (using less energy for continuous service) or changing one's behavior to use less service (f ...

of up to 75%, without compromising cooling requirements. In heating, ventilation, and air conditioning ( HVAC) in winter months, large commercial buildings interior spaces may need cooling, even while perimeter spaces may need heating.McQuiston, Faye C., Jerald D. Parker and Jeffrey D. Spitler. ''Heating, Ventilation, and Air Conditioning''. Hoboken: John Wiley & Sons, Inc., 2005. Free cooling is the production of chilled water without the use of a

, and can be used generally in the late fall, winter and early spring, in

temperate zone In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

s.Kelly, David W. "Free Cooling Considerations". ''Heating, Piping, Air Conditioning'' (1996): 51-57. Free cooling is not entirely free since the chiller is still operational.

Methods

Assuming that the system can utilize free cooling, there are three ways to use free cooling:

Strainer cycle

The

cooling tower A cooling tower is a device that rejects waste heat to the atmosphere through the cooling of a coolant stream, usually a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat an ...

water can be directly linked into the flow through the

circuit. If the cooling tower 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

energy. There is an increased risk of corrosion using this method.

Plate and frame heat exchanger

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...

will transfer heat directly from the chilled water loop to the cooling tower loop. The exchanger keeps the cooling tower water separate from the coolant flowing through the cooling coils. The chiller water is thus pre-cooled and the building is liquid cooled. An energy savings is due to reduced chiller loading and thus a reduction in energy consumption. There is an increase in cost due to the pump needing to compensate for the pressure differences.

Refrigeration migration

A valve arrangement within the water chiller opens a direct path between the condenser and the

evaporator An evaporator is a device used to turn the liquid form of a chemical substance, such as water, into a vapor. Uses Air conditioning and refrigeration Some air conditioners and refrigerators use a compressed liquid with a low boiling point, su ...

. 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.

Seasons

High ambient temperature

When the process return water temperature is equal to or lower than the ambient air temperature, free cooling is not suitable. The system's three way valve will bypass the free cooling heat exchanger and direct the fluid flow through the chillers to be cooled to the required set point temperature.

Mid-season operation

For mid-season operation, the water is partially cooled by the compressor and partially by the ambient temperatures. The percentage of free cooling achieved mid-season is dependent on seasonal temperatures although partial free cooling commences when the ambient air temperature is below the process return water temperature. The water is partially cooled through the free cooler, then flows through the chillers to achieve the required set point temperature.

Winter operation

In winter, when outdoor temperatures are low enough, the water is chilled solely by the free cooling coil. This allows the chillers' compressors to stop operating, saving significant amounts of energy. The only electrical power used in winter operation is for fan operation. This can be achieved once the ambient air temperature is to below the process supply water temperature.

Limitations

Freezing can occur once the ambient air temperature gets below . 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 .

Data centers and server rooms

Energy efficiency

Data centers account for 2% of the Global Electricity Consumption.

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

: In 2013, Chancellor

George Osborne George Gideon Oliver Osborne (born Gideon Oliver Osborne; 23 May 1971) is a former British politician and newspaper editor who served as Chancellor of the Exchequer from 2010 to 2016 and as First Secretary of State from 2015 to 2016 in the ...

agreed to make a concession for data centers to be exempt from Carbon Reduction Commitment (CRC) and allow them to produce their own Climate Change Agreement (CCA). This is also recognised by a new European Commission to reduce EU greenhouse gas emissions by 40% by 2030. Cooling data centers or server rooms requires a lot of energy, therefore free cooling can be an ideal solution to save energy.

Types

There are two free cooling options for a data center or server room with the first one being an integral free cooling coil or a chiller which works alongside a free cooler unit. Integral chillers are ideal for sites which have limited space and can offer high

energy efficiency Energy efficiency may refer to: * Energy efficiency (physics), the ratio between the useful output and input of an energy conversion process ** Electrical efficiency, useful power output per electrical power consumed ** Mechanical efficiency, a ra ...

levels. These units feature high quality components including scroll and screw compressors, axial fans, and three-way modulating valves. The other options is an independent free cooler that has a greater capacity for heat exchange, as it is sized to maximise efficiency which enables a larger area for the transfer of thermal energy. Independent free coolers have shown energy savings of up to 70%.

References

{{HVAC Heating, ventilation, and air conditioning