Heat recovery is the collection and re-use of heat arising from any process that would otherwise be lost. The process might be inherent to a building, such as space heating, ventilation and so on, or could be something carried out as part of business activity, such as the use of ovens, furnaces and the like. Heat recovery can help to reduce the overall energy consumption of the process itself, or provide useful heat for other purposes.
Ventilation systems bring cool fresh air into a building using fans in Air Handling Units (AHUs). The AHUs also contain heating coils to allow the fresh air to be raised to the required temperature by the buildings boiler. The air continues to be heated by the occupants and equipment in the room and all this heat energy is lost when the air is extracted and dumped into the environment.
The addition of heat recovery means that some of the heat contained within the extract air can be recovered. The heat energy is passed into the incoming fresh air effectively pre-heating it and meaning the boiler needs to add less heat. The two air streams need not mix directly to allow the transfer of heat.
Sources of 'waste' heat
You're likely to have sources of 'waste' heat in your building whether you are in an office (e.g. from the heating or ventilation systems) or a factory (e.g. in an industrial drying process or compressed air system).
Waste heat from the following common sources often presents opportunities for cost-effective heat recovery:
- ventilation system extracts
- boiler flue gases
- boiler blowdown
- air compressors
- refrigeration plant
- high temperature exhaust gas streams from furnaces, kilns, ovens and dryers
- hot liquid effluents
- power generation plant
- process plant cooling systems.
Use the Heat recovery checklist (CTL142) to help you decide whether your building is likely to have any of these types of sources.
Improving the energy efficiency of heat generation
Where it's possible, the most cost-effective use of waste heat is usually to improve the energy efficiency of the heat generating process itself.
Common uses (or 'sinks') for recovered heat include:
- pre-heating combustion air for boilers, ovens, furnaces, and so on;
- pre-heating fresh air used to ventilate the building;
- hot water generation, including pre-heating boiler feed water;
- space heating;
- other industrial process heating/pre-heating;
- power generation.
In most cases, heat recovery is far more efficient when the heat source and heat sink are coincident - meaning they are physically close together and occur at the same time.
Refer to the Heat recovery overview guide (CTG057) for more information on the various types of heat recovery technology and techniques and how you can apply them to your business.
Further guidance on heat recovery systems
We have the following publications available for free download:
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