Last edited 03 Aug 2021

Cooling systems for buildings


[edit] Introduction

It can be necessary to provide cooling to buildings during warm weather, or where there are significant thermal gains (such as solar gain, people and equipment). This cooling is sometimes referred to as comfort cooling. Cooling may also be necessary for refrigeration or for some industrial processes.

[edit] Passive cooling

Passive or 'natural' cooling can be provided by:

[edit] Natural ventilation

Removes warm internal air and replaces it with cooler external air. See Natural ventilation for more information.

[edit] Thermal mass

Can be used to even out variations in internal and external conditions, absorbing heat as temperatures rise and releasing it as they fall. See Thermal mass for more information

[edit] Evaporative cooling

Such as moisture evaporating from the surface of a building, or the inclusion of water features such as ponds. See Evaporative cooling for more information.

[edit] Other

Devices such as shading, reflective surfaces, insulation, green roofs, and so on, which while they do not in themselves provide cooling, do reduce thermal gains.

[edit] Active cooling

Active cooling can be provided by:

[edit] Earth-to-air heat exchanger (ground coupling)

This draws ventilation supply air through buried ducts or tubes (sometimes referred to as earth tubes). As the temperature of the ground below 3 m is practically constant, it can be use to substantially reduce ambient air temperature fluctuations, with the incoming air being heated in the winter and cooled in the summer.

See Earth-to-air heat exchanger for more information.

[edit] Open or closed loop water-to-air heat exchanger

This exploits the relatively stable temperature of the earth to provide water that can cool in the summer and heat in the winter.

See Ground energy options for more information.

[edit] Mechanical, or forced ventilation, driven by fans

This might be cooled below outside air temperature by the use of refrigerants, or by thermal mass, such as thermal labyrinths, or by night time purging.

See Mechanical ventilation for more information.

[edit] Chilled water

Chilled water is typically provided by chiller units using absorption refrigeration or compression refrigeration. It can then be used to provide cool air, in air handling units (to be ducted around the building), chilled beams, chilled ceilings, and so on. Chiller units use a refrigerant that boils at a low temperature and pressure, removing heat from the chilled water, and then condenses to release that heat, which is rejected to the outside (or recovered).

See Refrigerants for more information.

NB: The use of chilled water to cool the building fabric itself is sometimes described as 'active thermal mass'.

[edit] Refrigerants

Refrigerants can be used to provide cooling directly to spaces in variable refrigerant flow (VRF) systems. This is based on the flow of refrigerant between an external condensing unit and multiple internal evaporators (typically fan coil units).

See Variable refrigerant flow for more information.

[edit] Evaporative cooling

This can be provided by simple systems, such as misting fans and by spraying water over the roof of a building, or by more complex packaged units that draw hot, dry air through a continually dampened pad and supply cool, humid air to the building.

Indirect evaporative cooling can be provided by the incorporation of heat exchangers, by the use of cooling towers, or by spraying water over the cooling coils of conventional chiller units. Typically, evaporative cooling is best suited to hot, dry climates.

See Evaporative cooling for more information.

[edit] Ice

Ice can be used as an effective means of thermal storage, storing ‘coolth’ in colder parts of the day to provide cooling during warmer parts of the day.

See Thermal storage for cooling for more information.

Active cooling might be provided as part of a heating, ventilation and air conditioning system (HVAC) which may also include air filtration and humidity control. The cooling process itself can result in dehumidification, as cool air is less able to ‘hold’ moisture than warm air. The term air conditioning is sometimes taken to mean control over air temperature and humidity, rather than just temperature control in the case of comfort cooling.

NB: Direct evaporative cooling results in humidification of air.

NB: Night time purging, and ground coupling are sometimes considered to be passive, rather than active systems.

[edit] Definitions

'Cooling plant means that part of a cooling system that produces the supply of cooling
medium. It does not include means of distributing the cooling medium or the delivery of the cooling into the relevant zone. It may consist, for example, of a single chiller or a series of chillers.'

'Cooling system means the complete system that is installed to provide the comfort cooling to the space. It includes the cooling plant and the system by which the cooling medium effects cooling in the relevant zone and the associated controls. This will in some cases be a complete packaged air conditioner.'

Ref Non-domestic Building Services Compliance Guide For Scotland, 2015 Edition v1.1, published by the Scottish Government, Building Standards Division in April 2018.

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