Heat recovery ventilation
To help develop this article, click 'Edit this article' above.
Ventilation is necessary in buildings to remove ‘stale’ internal air and replace it with ‘fresh’ outside air. This helps to:
- Moderate internal temperatures.
- Reduce the accumulation of moisture, odours and other gases that can build up during occupied periods.
- Create air movement which improves the comfort of occupants.
Very broadly, ventilation can be ‘natural’ or ‘mechanical’.
- Mechanical (or ‘forced’) ventilation tends to be driven by fans.
- Natural ventilation is driven by ‘natural’ pressure differences from one part of the building to another.
Ventilation has become increasingly important because of the tendency to ‘seal’ modern buildings. However the process of extracting internal air, which may have been conditioned, and replacing it with air that has not is inherently wasteful.
This can be mitigated by heat recovery, the process of collecting and re-using heat that would otherwise be lost, which can help to reduce energy consumption, reducing running costs and carbon emissions.
Heat recovery ventilation (HRV or ventilation heat recovery (VHR) or mechanical ventilation heat recovery (MVHR)) uses a heat exchanger to recover heat from extract air, that would otherwise be rejected to the outside, and uses this heat to pre-heat the ‘fresh’ supply air. Very efficient heat exchangers can recover as much as 98% of the ‘waste’ heat.
Typically heat recovery ventilation works by transferring heat between the incoming and outgoing air streams by blowing them in opposite directions between adjacent flat plates in air-to-air heat exchangers. Heat is absorbed by the plates from the 'hot' air on one side and released to the 'cold' air on the other. Cellular heat exchangers, which can achieve greater efficiency, drive the incoming and outgoing heat through adjacent square tubes, increasing the heat transfer surface area.
Air to ground and air to water heat exchangers use the earth or water as a heat exchange body by blowing air through tubes surrounded by earth or water.
Heat can also be recovered from other processes and components, such as refrigeration units and chiller units, boilers, power generation plant, plant cooling systems, hot liquid effluents and high-temperature exhaust gasses. Recovered heat can also be used for drying processes, power generation, pre-heating combustion air for furnaces or boilers and so on.
 Related articles on Designing Buildings Wiki.
- Air conditioning.
- Air handling unit.
- Chiller unit.
- District energy.
- Geothermal pile foundations.
- Heat pump.
- Heat recovery.
- Mechanical ventilation.
- Thermal labyrinths.
- Variable refrigerant flow.
 External references
- Heat recovery: A guide to key systems and applications.
- How to implement heat recovery in heating, air conditioning and ventilation systems.
- The Future of Heating: Meeting the Challenge.
- The potential for recovering and using surplus heat from industry.
- Harvesting energy: body heat to warm buildings
Featured articles and news
What is liquidation and how does it apply to contractors in the construction industry?
Scrutiny is placed on Carillion's controversial 2013 decision to extend subcontractor payment terms to 120 days.
RSHP unveil their involvement in a boundary crossing which will provide a new entry point into Hong Kong.
With PFI currently under the spotlight due to Carillion, this introductory article explains what they are.
Estimates suggest that up to 30,000 small firms could be at risk of non-payment as a result of Carillion's collapse.
Sir Oliver Letwin to lead an independent review into the delays in the delivery of housing.
As Carillion collapses, read our article explaining insolvency in the construction industry.
43,000 jobs at risk as Carillion declares insolvency..
1961 saw the publication of three important books about urban design that remain relevant today.
Next week the planning fee increases by 20% and new fees are introduced.
How the transformative power of BIM and other digital technologies can be used to gain a competitive edge.