Heat Recovery Ventilation – Increasing Energy Costs
The effect of continual increasing energy costs has provoked efficient building designs.
The previous generations happily cranked up the thermostat when they felt chilly. Once heating costs went through the roof, we all started looking for ways to save, and with up to 40 percent of our heating dollar going to air infiltration and drafts, sealing up all the gaps seemed like the next best option to reduce the high heating bills.
Over time, older buildings began to refurbish with new, tight windows and doors, insulation and vapour-barrier improvements. New structures were designed to be air tight, and builders became familiar with the new materials and skills needed to meet market demand and updated regulations. Buildings were finally becoming thermally efficient.
It turns out that the infiltrating drafts had a role in the ecosystem — they provided ventilation and the fresh air that we need to breathe.
Life inside today’s tight office or apartment building generates both moisture and pollutants. The moisture comes from every activity even including breathing. At excessive levels, moisture condenses on windows, can cause structural deterioration, and become breeding grounds for mould, mildew, fungi, dust mites and bacteria. Unsightly black spots appear indicating mildew growth. Mould spores and dust easily become airborne and circulate freely, possibly causing a range of symptoms and allergic reactions.
In addition to excessive moisture, new buildings products can give off gases that are adverse to your comfort and good health and even breathing can add to the problem when carbon dioxide reaches excessive levels. All these produce the stale air syndrome.
Standards for Ventilation
The Building Code of Australia (BCA) states that for the purpose of ventilation, an openable window or similar aperture is required to be at least 5% of the floor space in that particular area. The Australian Standard AS 1668.2 ‘Mechanical ventilation for acceptable indoor air quality’ also applies. Failure to comply with these standards could result in ‘sick building syndrome’.
Mostly, sick buildings are the result of a build-up of moisture and mould created by inefficiencies with air conditioning and ventilation. Living and working in such an environment can lead to eye, nose, throat and skin problems, or hypersensitivity.
There are partial solutions to the indoor air-quality problem. For example, an electrostatic filter installed in an airconditioning system will reduce airborne contaminants, but it won’t help with moisture, stale air or gaseous pollutants. Exhaust fans can remove excess moisture in the kitchen, and wet areas, but this creates negative pressure inside the building and as they extract air out, the resultant vacuum slowly draws air into and through the building structure, bringing with it odours, dust and contaminants.
The solution is to create balanced ventilation. This can be achieved with one fan exhausting the stale, polluted air out of the house while another fan replaces it with filtered fresh air.
Ventilation with Heat Recovery
A heat recovery ventilator (HRV) works on this balanced ventilation system, with the addition of also recovering the energy latent in the air. In winter, the heat in the outgoing stale air is transferred to warm up the fresh air through the use of a unique heat-exchange core. This core transfers heat from the outgoing stream to the incoming stream in the same way that a radiator in a car transfers heat from the engine’s coolant to the outside air. It’s composed of a series of narrow alternating passages through which incoming and outgoing airstreams flow. As the streams move through, heat is transferred from the warm side of each passage to the cold, while the airstreams never mix.
Depending on the model, Heat Recovery equipment can recover up to 75 percent of the heat in the outgoing airstream, making this a better option for the budget than opening a few windows. Also just as effective in the summer months, it will remove heat from the incoming fresh air and transfer it to stale air-conditioned exhaust air, reducing the load on your air-conditioning system.
Heat recovery is the ideal solution for any tight, moisture-prone building, replacing humid indoor polluted air with dry, filtered, pre conditioned fresh air.