Retired air tightness technician Trevor Clark this month explains what energy exchange is and steps you can take in your household to improve ventilation.

When we get hot and sweaty during a walk, we open the jacket to let air in to remove the moist warm air around our body - this is the exchange of air, to allow the moist warm air out and fresh air into and around our bodies.

In energy terms this exchange of air also means that the energy used to warm the air inside the building can now be lost to the outside as we expel the warm moist air from our homes via an extractor fan.

While just exchanging air is good for our Indoor Air Quality (IAQ) it comes with an energy cost.

Air is a Mass Transfer Medium; and while both the outgoing and incoming air holds energy the outgoing stale air holds more energy than the incoming fresh air.

We could accept that the fresh air required heating and pay the utility bill, but with energy costs now rising substantially, we could also use a system that will either: recover most of the energy, or reclaim all of the energy plus some more.

Heat Recovery or Heat Reclaim Ventilation Terms?

There is a misunderstanding about these two terms, which potentially mean similar things.

To my mind recovery means to ‘take back’ what was ‘lost’ while to reclaim means to ‘restore to a previous natural state’.

As long as the two air streams are kept separated there should be no contamination to either air stream. But we need to keep contaminants out of the system so we use filters to keep the equipment and ducting clean.

Before getting into the different types of ventilation systems available it is important that any ventilation system includes at least one filter. This should be provided on the fresh air intake to prevent contaminants from outside entering the ventilation system and clogging the energy exchange coils or transfer plates within the unit.

Fresh air outside and the stale air inside contain ‘contaminants’ (particulates which include dusts, fumes, mists, aerosols, and fibres) which for improved IAQ is removed with filters.

While it may not be as important to filter the stale air from our dwellings it may be a requirement for industry to filter their air so it does not get into nearby dwellings.

It may also have other filters that remove contaminates from the return air flow from around the building, this to stop contaminants from being re-circulated again and again.

These filters are generally made from fibres which are treated so as not to release the fibres themselves into the circulating air flow.

Different grades of filter are available and the grade used depends on both the contaminants likely to be found within the building and to what level of contamination is acceptable. For example in an operating theatre we may expect the filters to remove bacteria which in a domestic home would be unreasonable to expect.

No matter which filter is used regular maintenance is required to either clean or replace these filter mediums to prevent the contaminants getting into the air stream as the filters become full and reduce air flow.