Heat recovery ventilation (also known as a heat exchanger, air exchanger or air-to-air exchanger) is a ventilation system that employs a counter-flow heat exchanger between the inbound and outbound air flow.  HRV provides fresh air and improved climate control, while also saving energy by reducing the heating (or cooling) requirements.

Ground Source Heat Pumps are an example of an earth-to-air heat exchanger.  Energy recovery ventilators (ERVs) are closely related, however ERVs also transfer the humidity level of the exhaust air to the intake air.

AIR TO AIR HEAT EXCHANGER - HRV USING CONDENSING UNITS

HRVs and ERVs can be stand-alone Condensing units - 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 a fan.  When used with 'central' HVAC systems, then the system would be of the 'forced-air' type.

TYPES OF HEAT EXCHANGERS

There are a number of heat exchangers used in HRV devices

Cross flow heat exchanger up to 60% efficient (passive)

Counter current heat exchanger up to 99% efficient (passive)

Rotary heat exchanger (motorised)

Heat pipes / thin multiple heat wires

The air coming into the heat exchanger should be at least 0°C. Otherwise humidity in the outgoing air may condense, freeze and block the heat exchanger.

A high enough incoming air temperature can also be achieved by recirculating some of the exhaust air (causing loss of air quality) when required, or by using a very small (1 kW) heat pump to warm the inlet air above freezing before it enters the HRV. (The 'cold' side of this heatpump is situated in the warm air outlet.)

ADVANTAGES OF CONDENSING UNITS

Within the busy commercial sector strict guidelines are put on the ventilation requirements of a building.

Whatever the property, restaurant, leisure facilities, student/key worker accommodation, etc a controlled ventilation system is required to operate in a continual quiet, energy efficient manner.

Without the generally higher costs incurred for full air-conditioning, a Heat Recovery Ventilation system will provide full filtered fresh air and extract air ventilation, where necessary, with an option for additional cooling.  As the Heat Recovery ventilation system recovers 60-70% of the heat within the extracted air during the colder winter months ventilation is provided in an energy efficient manner.

A Central Extract System provides the necessary extraction minimising breakout points and electrical connections.