Heat recovery

Heat recovery ventilation (HRV), also known as mechanical ventilation heat recovery (MVHR), is an energy recovery ventilation system using equipment known as a heat recovery ventilator, heat exchanger, air exchanger, or air-to-air heat exchanger which employs a cross flow or counter-flow heat exchanger (countercurrent heat exchange) between the inbound and outbound air flow. HRV provides fresh air and improved climate control, while also saving energy by reducing heating (and cooling) requirements for many applications including vehicles.

Energy recovery ventilators (ERVs) are closely related, however ERVs also transfer the humidity level of the exhaust air to the intake air.

As building efficiency is improved with insulation and weather stripping, buildings are intentionally made more airtight, and consequently less well ventilated. HRV systems provide ventilation without the loss of heat or humidty, which could the stress on a building's heating, ventilating/ventilation, and air conditioning (HVAC) systems. HRV introduces fresh air to a building and improves climate control, whilst promoting efficient energy use.

UK building regulations require one air change every two hours (0.5 ACH). With traditional extract-only ventilation that means a house boiler would need to warm up a house-full of cold air 12 times a day.

HRVs and ERVs can be stand-alone devices that operate independently, or they can be built-in, or added to existing HVAC systems. For a small building in which nearly every room has an exterior wall, then the HRV/ERV device can be small and provide ventilation for a single room. A larger building would require either many small units, or a large central unit. The only requirements for the building are an air supply, either directly from an exterior wall or ducted to one, and an energy supply for air circulation, such as wind energy or electricity for fans and electronic control system. When used with 'central' HVAC systems, then the system would be of the 'forced-air' type.

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Wikipedia