HEAT RECOVERY VENTILATION

Although it is not a full heating system in its own right, Heat Recovery Ventilation (HRV) can have a very significant bearing on the type of heating system that you install in your house. It should be looked on as part of an overall package that includes top-grade insulation and air circulation.

HRV has been in use for decades, especially in the colder countries of Scandinavia and Canada. Only in the last 10 years or so has it come into usage in Ireland, Britain and mainland Europe.

The system works as a result of an ingenious design that allows cool air and warm air to by-pass each other on their way in and out of the house without mingling; the warm air raises the temperature of the cool air which can then be used for space and water heating. But it only works if the home is exceptionally air-tight and has a very high level of insulation. It also needs a well-thought-out system of ducts within the house to transport the air.

So what is HRV? Heat Recovery Ventilation is a method of efficiently ventilating a house.

Ventilation:
Through a network of ducts fresh air is supplied continuously to every room in the house.
This fresh air is being filtered as it enters the house.

Meanwhile through a similar network of ducts the stale warm air is extracted from
every "wet" room in the house. (The "wet" rooms are the kitchen, utility, bathrooms,
toilets and shower rooms).

Heat Recovery:
Using a HRV machine up to 90% of the heat can be recovered from the extracted air and
transfered to the incoming fresh air. 
 

Cost (initial)

The availability of such a wide range of capacity and energy usage in heat exchangers makes it difficult to generalise about the capital cost. Reputable suppliers will give ball-park figures for different house sizes and conditions; experienced architects and specifiers will provide more detailed assessments.

Cost (running)

Keeping the heat inside your home will significantly reduce home-heating bills but the system is reliant on electricity to run it.

Cost (maintenance)

Attention needs to be paid to the regular replacement of air filters for both incoming and outgoing air. The SEI recommends that filters be changed every six months to 12 months. If an extractor hood in the kitchen is connected to the system, the high-quality filter needs to be cleaned or replaced at specified intervals.

Efficiency

In the context of this system, efficiency means the percentage of the heat that is transferred from the waste air being expelled to the fresh air being taken in. The SEI warns specifiers and designers to be wary of manufacturers who claim “extraordinary efficiency rates of 95% or higher” for their products. Brochures from the more reputable suppliers we have examined claim anything from 65% right up to 92%, with the main bulk of claims being around 70%.

Payback

Difficult to pin down the payback period because of the wide range of heat exchangers on the market.

New houses/Existing houses

This system is definitely more suited to new houses because of the vital requirements of an air-tight envelope around the house and a ducting system which should be planned and installed at a very early stage in the build.