Heat Recovery Ventilation / HRV
Don't be fooled by a high pressure sales pitch on positive pressure ventilation systems. Most southern homes DO NOT HAVE RESIDUAL HEAT in the roof space.
Ventilate with a Balanced Pressure, Genuine Heat Recovery System
A balanced pressure ventilation system extracts the stale air from within your home - taking the moisture with it. At the same time, the same volume of fresh air from outside your home is brought into your home. These two air streams pass through a heat exchange core and as much heat as possible from the outgoing air is transferred to the incoming air. This effectively removes moisture and reduces the heating needs to maintain your homes warmth in winter.
There has been strong promotion of ventilation systems in New Zealand using so-called warm air from your roof-space. In the lower South Island while you may control condensation, there are several problems with this approach.
Some serious reasons why roof-space air just doesn't cut it
Beacon Study 2010 - forced air ventilation systems from roof-space air, see www.beaconpathway.co.nz:
- Natural ventilation rate was 90% of the homes capacity per hour for homes built prior to the 1960's. The NZ Standard requires just 35%.
- Cold and damp was not caused by a lack of ventilation but by a lack of insulation and heating, control of ground water, leaking vents and the use of gas heating.
- In winter (Christchurch) there was more moisture in the roof space than there was in the home, with the result that the ventilation systems increased the moisture levels during the day.
- At night homes are significantly cooled at night, resulting in heat losses and increased heating costs.
- During the day roof-space ventilation systems increased the moisture content in the home!
EECA Energywise - forced air systems do not comply with NZS4303:1990, see www.energywise.govt.nz/node/5112:
- Forced air / roof air systems do not comply with ventilation standard NZS4303:1990 and cannot be used to comply with the Building Codes Acceptable Solution for under-ventilated homes.
- University of Otago and BRANZ study in Dunedin (2008) found that there is little (if any) residual heat in the roof cavity of southern homes.
- Despite claims by some suppliers that their systems are akin to "placing a 1200 watt heater in every room", there is a complete lack of evidence that such systems offer any heat to your home.
- Roof space ventilator filters are unproven to prevent the entry of dust, vermin particles and insulation particles into your home.
In summary, there is a complete lack of evidence that roof-space ventilation systems provide any heat to homes in the South Island in winter.
Forced air (roof-space) ventilation systems are not very effective in removing moisture from a home - what they do is pick up the moisture from windows etc and retain it in the house air with only minimal actual removal as forced air leaves the home (along with the heat). Heat recovery systems pick up moisture and actively expel it from your home.
A genuine heat recovery ventilator must have an input fan, an exhaust fan and a heat exchange core - if it hasn't got these things then it is NOT A TRUE HEAT RECOVERY VENTILATOR (HRV).
Why balanced pressure fresh air?
Roof air is not fresh air. Fresh air ventilation systems such as Cleanaire, Smart-vent Synergy and Mitsubishi Lossnay comply with NZS4303:1990.
Positive pressure systems force air into the home and then it leaks out of gaps, taking heat with it. In newer homes the lack of air gaps works against this system. Moisture is picked up by the incoming air but may not always be expelled from your home.
Balanced systems replace the outgoing air with fresh air, recapturing as much of the latent heat as possible. This genuinely removes moisture from the home and also reduces heating requirements.
- Balanced pressure heat recovery ventilation systems are particularly suitable for homes in colder areas of the country, if they are already well heated and if they are reasonably airtight. (EECA)
- Warm (stale) air is extracted from your home and exhausted outside. The equivalent volume of fresh air is drawn into the home without many of the contaminant risks of roof-space air.
- Ventilation systems are also fitted with high grade filters with options to remove pollen or excess carbon.
- A level of heat from the outgoing air (up to 95% in the right conditions) is exchanged to the incoming fresh-air so that the nett loss of heat from your home is minimized.
If ventilation is a priority, fresh-air, true heat recovery ventilation is essential
Ventilation is not just about temperature and moisture control but about air health
The common practice overseas is to control ventilation systems not on temperature, but on air quality. These are optional control methods with our systems.
- The key health issue is carbon dioxide level. Carbon controllers automatically begin ventilation when carbon levels exceed 1000 parts per million. When levels are low (due to low occupancy) the ventilation system will turn off or reduce to a minimum operating level - saving on operation costs and unnecessary ventilation.
- If moisture is truly a problem, ventilation systems can also be controlled via humidity sensors. This is essential for systems fitted to swimming pool rooms.
- Remember that positive pressure, forced air systems do not necessarily expel moisture totally from the home, but may simply suspend moisture in the air (see the Beacon Study 2010 in Christchurch, above).
Heat Exchange Cores
Not all heat exchange cores are the same.
- Plastic crossflow exchange cores transfer heat efficiently and they do not allow moisture or odours to pass through the core. However, they do contain dioctyl phthalate - the stuff that makes plastics feel smooth and slightly oily. These compounds evaporate from the plastics as air passes over and these losses eventually cause the plastic to become brittle and break down. Because this will occur after about 6 - 7 years of exposure, warranties will expire at about 5 years. Any welding of the plastic accelerates this process which is why many plastics break at such junctions.
- Aluminium crossflow exchange cores are best. Being a metal they are very efficient in transferring heat. They do not suffer from the degradation incurred by plastics. The Cleanaire system uses an aluminium core and carries a full 12 year warranty - parts and labour!
- Parallel-flow exchange cores (usually plastic). Are considered to be very efficient but they have other problems. They are often linked to positive pressure systems - if you have any real heat in the roof space this will be fairly good news in winter. However, in summer these types of exchange core tend to overheat the home just when you might prefer it to be cooler.
- Treated paper exchangers offer high heat transfer efficiency but they are also susceptible to moisture and odour exchange. The warranties offered on these systems are around 5 years. Care needs to be taken regarding the particular situation where these type of exchange cores are to be used.
Fresh-Air True Heat Recovery Ventilation from Warm and Cool
At Warm and Cool be believe that if ventilation of your home is a high priority for you, then using a true heat recovery ventilation system is essential. Many of the forced-air roof space systems make claims regarding adding warmth and improving the health of your home which as the above information shows are highly dubious claims.
We can supply 3 brands of genuine fresh air, heat recovery ventilator to ensure that the best option can be tailor-made for your situation:
Cleanaire Heat Recovery Ventilators
The original HRV - manufactured in NZ for more than 25 years.
- 6 year general warranty
- 12 year warranty on the aluminium exchange core
- Achieves NZS4303:1990
- High quality F7 filtration
- Large capacity suits larger homes / systems - www.avonelectric.co.nz
Download Brochure:
SmartVent Home Ventilation Systems
- 5 year warranty
- Polymer (plastic) exchange core
- Achieves NZS4303:1990
- High quality F7 filtration
- Digital display control
- Compact unit suits standard homes / systems - www.smartvent.co.nz
Mitsubishi Electric - Lossnay Fresh Air Energy Recovery
- Plate separation - treated paper
- Achieves NZS4303:1990
- High quality F7 filtration
- Digital display control
- Large capacity suits larger homes / systems - www.lossnay.co.nz
HEX390 - Domestic Ventilation System with Heat Exchanger
- Simple to use controllers (automatic and manual options)
- Washable filters
- Acoustic ducting for quieter operation
- Modular kitset design for easy installation (unit fits through standard manhole)
- Custom units to suit special requirements
- Options: UV filter, F7 filter, heater, summer bypass kit, 'EC' fans (new technology, energy efficient & even quieter)
- 5 year warranty
- Made in New Zealand for New Zealand conditions -
home-ventilation.co.nz
Download Brochure:
To discuss Balanced Pressure, Genuine Heat Recovery Systems please contact us
