Fresh and Healthy Indoor Air
Fresh air is constantly supplied to all living areas. The same air volume is extracted as stale, moisture-laden air from kitchen and bathrooms. The key point is that the air being introduced is fresh air taken from the outside, and not stale air from the attic or other parts of the house. This distinguishes genuine Heat Recovery Ventilation from other ventilation technologies. Although air filtration is normally unnecessary, optional air filters (e.g. for pollens, hay fever allergens or odours) are available. Heat Recovery Ventilation systems are designed to ventilate homes at a rate recommended in NZ Standard 4303 "Ventilation for Acceptable Indoor Air Quality" i.e. one air change every three hours.
Saving Heat Energy
In the heat exchanger the incoming fresh air is warmed up by heat transferred from the exhaust air extracted from the home. Depending on the heat exchanger model you choose, between 67 and 95 percent of the heat energy is recovered from the extracted air and so ventilation heat loss is enormously reduced.
Due to the heat exchanger the system pays back its cost by recovering up to five times more energy than the energy consumed by the two fans.
Example:
For a room temperature of 20°C and an outside temperature of 0°C, a heat exchanger with 75% efficiency will warm up the intake air to about 15°C, using the heat energy of the exhaust air. Additional heat sources in the house are only required to warm up the incoming air from 15°C to 20°C.
Reducing Condensation Problems
The HRV system reduces condensation problems by providing adequate ventilation for the whole house. Outside air is very dry in winter. Even though the relative humidity outside can sometimes be very high, cold air has a small intake capacity for water vapour. By warming up cold, fresh air in the heat exchanger and by additional space heating, the relative humidity of the supplied air drops, which results in a high intake capacity for water vapour in the air. Moisture generated in the house can be absorbed by the air and extracted through the ventilation system. The colder it gets outside, the better the HRV system will dehumidify the indoor environment.
Heat Recovery Ventilation in Summer
For air-conditioned homes, the HRV recovers and recycles ?cooled energy?, saving summer energy costs. If your home is not air conditioned, and your lifestyle is to have windows open in summer, switch the HRV OFF. Optional automatic controls are available.
Combining an HRV with a Ducted Heating / Air Conditioning System
HRV systems may often be combined with existing or new ducted heating or air conditioning systems. Systems can be Heat Pump Air Con, Gas, Diesel, or Hot Water. Heating system fans may need to operate continuously operate depending on the air-flow resistance of the heating system.
Importance of Building Airtightness
Infiltration due to air leakages in the building envelope cause additional ventilation heat loss without heat exchange, which can exceed the scheduled ventilation heat loss of the HRV system, especially when using very efficient heat exchangers. For example, 2.5 m3 cold outdoor air coming through air leakages cause the same ventilation heat loss as 10 m3 pre-heated fresh air coming through a heat exchanger with 75% efficiency.
In buildings with poor airtightness the ventilation heat loss is therefore mainly affected by air leakages. Improving the airtightness of the building envelope will reduce ventilation heat loss considerably and optimize the performance of your HRV system.
Beware of Imitations!
Before you decide on a ventilation system, make sure it brings in outdoor air and not roof space air!
NZ Standard 4303 "Ventilation for Acceptable Indoor Air Quality" requires outdoor air for ventilation. Roof space air is not outdoor air. It may be polluted by dust, loose insulation fibres and biological contaminants, which are a potential health risk when inhaled. Biological contaminants will accumulate on air filters; most allergens pass through even the best air filters. Inspect your roof space through the manhole. Decide yourself, what you want to breath - fresh or polluted air.
Besides, attic fans pressurize the home and force warm, damp air into wall and other cavities, where it may cause mould/mildew problems and structural rot as a result of condensation. The fans may cost "cents to run", but what is the cost of the warm air forced out of your home? An electric 1 kW heater to replace that heat, running 24 hrs a day, will add $130 to your monthly power bill (18 cents per kWh).
The Cleanaire HRV is supported by an extensive Warranty (2 pages)
Find out more:
"Print version"
"How to identify a genuine Heat Recovery Ventilation system."
"Common sense reasons why roofspace air should never be used to ventilate the living space of a home."
"Is it possible to dehumidify your house by ventilating with cold, humid air?"
"Cleanaire HRV Brochure"
"Cleanaire HRV Technical Info Sheet"
Negawatt prides itself on its independence. We do not sell just one product. Instead, we carefully analyze the needs of a home and recommend only the measures that will produce the best results - from a health perspective, and in cost/benefit terms. We will advise you with the selection of the HRV, design the ducting/ air distribution system to suit your home and arrange a detailed quotation for a complete installation.
Contact Negawatt for a quote and more information.
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