Heat rejection
Contents |
[edit] Introduction
Waste heat can be produced by any process that uses energy. In buildings, this might include:
- Heating, ventilation and air-conditioning systems (HVAC).
- Refrigeration.
- Machinery, equipment and industrial processes.
Where this waste heat is at a low-temperature, it may have limited useful capacity for work and so it may be rejected to the environment. However, if it is suitable for use in another process, a portion of heat that would otherwise be wasted might be reused. This is known as heat recovery.
Heat rejection methods include, air cooing, evaporative cooling, and ground coupling.
[edit] Air cooling
Air cooling can be as simple as using mechanical or natural ventilation to reject excess heat to the outside.
Typically in heating, ventilation and air-conditioning systems, air cooling rejects heat to the outside air by circulating 'outside' air over coils containing 'hot' fluid returning from the building. Heat is transferred from the coil to the air which is then rejected to the outside. See cooling for more information.
[edit] Evaporative cooling
When water evaporates, it absorbs significant amounts of heat energy (latent heat), which produces a cooling effect in its surroundings.
Direct evaporative coolers (sometimes referred to as sump coolers, swamp coolers, or desert coolers) draw hot, dry air through a continually dampened pad and supply cool, humid air.
Indirect evaporative cooling can be achieved by using a heat exchanger to cool supply air, by spraying water over the cooling coils of a conventional chiller or by cooling towers.
Cooling towers reject heat through the evaporation of water in a moving air stream within the cooling tower. The temperature and humidity of the air stream increases through contact with the warm water, and this air is then discharged. The cooled water is collected at the bottom of the tower. This process can achieve lower temperatures than air-cooled heat rejection systems. See Cooling towers for more information.
[edit] Ground coupling
Earth-to-air heat exchangers draw air through buried ducts or tubes (sometimes referred to as earth tubes). As the temperature of the ground below 3m is practically constant, it can be used to substantially reduce air temperatures. See Earth-to-air heat exchanger for more information.
Open or closed loop water to air heat exchangers, similarly exploit the relatively stable temperature of the earth to provide cool water. See Ground energy options for more information.
[edit] Heat recovery
Heat recovery is the process of collecting and re-using heat that would otherwise be lost. This can help reduce the energy consumption of the process or the heat can be used elsewhere, reducing running costs and carbon emissions. See Heat recovery for more information.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
STEM ambassadors needed for ICE CityZen award.
Digital gaming competition for UK students aged 16 to 18.
Heritage protection in England vs Australia.
Fire doors and the Fire Door Inspection Scheme.
Three-quarters of fire doors fail inspections
UN International Day for Biological Diversity, May 22.
The role of geoparks, biospheres and world heritage sites.
BSRIA conference 2022, June 23.
Just one month to go ! Find out more here.
Restoring Broadbent’s Bath House
A new gallery for the University of Huddersfield.
Corruption in the construction industry.
What will it take to stop it ?
To celebrate world bee day 2022 !
Just one month until the changes to part L come into effect.
Not forgetting part F and the new part overheating part O.
Heat Pump demand rises by one quarter.
As energy prices jump up in cost.
With people in the UK from Ukraine.
Industry leader Steve Murray takes on role.
An abundant and versatile building material.
How overheating complicates ending gas in the UK.
600,000 heat pump installations targeted per year by 2028.
Cost planning, control and related articles on DB.
Helping prevent those unwanted outcomes.
ICE debate Public transport - post pandemic.
How has transport changed due to Covid-19 ?
Cross-ventilation in buildings. Do you have it ?
Will you need it ? after June 15 and the new Part O ?
Share your knowledge with the industry.
Create an account and write the first of many articles.
The green jobs delivery group.
CIAT commentary after the first meeting.
Liverpool's world heritage site status
Who is to blame?
Research recommends focussing on portfolio success rather than project success.