New Zealand is a unique case in that the attic air systems are the #1 selling ventilation system. In America and Europe the true HRV or ERV system is preferred whilst the PPV systems are banned because of the danger they represent during a house fire where smoke in the roof space is then pushed back into sleeping areas.
The condensation problem is a simple one, it is allowing high humidity air to cool onto a cold surface: two actions are required to fix this.
1) Remove the built up human caused high humidity air from the house (technically the removal of high absolute or latent humidity)
2) Replace it with drier air
How?
Bring in outdoor air.
Outdoor airs Absolute or total humidity measured by weight is almost always lower than indoor humidity.
At 25% RH and 20C the surface temperature of a surface (say aluminium window frames) is minus 11 and considering the air inside also can keep the frame a bit warmer the outdoor air temperature needs to be almost arctic conditions.
Quite different if no ventilation was present.
Typical new house w=that is not ventilated would have say a minimum overnight temp of 15C and a RH of 50% in these conditions the aluminium frame or glass only needs to reach 4C for moisture to occur so if we have a frost condensation is very likely.
In rooms where the bedroom door is kept closed and breathing increases humidity it can condensate on even mild winter nights
HRV has fans bringing in outdoor air at contolled rates
The result is that the air coming into the house is dryer and thus stopping that dreaded condensation
All areas where moisture is a problem requires ventilation if you don’t have a flow through of air how can it be removed and replaced.
Keeping the air warm in the house is very important as if we bring air into a house that is kept as the same temperature as outdoors no lowering of RH will occur
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You talk about PPV systems being illegal in USA and Canada. They are not. In fact, roughly a third of ventilation systems sold over there are PPV systems. It all depends on humidity levels for that region. If you take air from outside in a high humidity environnment, you will increase the RH inside. So high humidity areas use PPV systems because the air in your attic/roof is drier and typically warmer than outside. HRV (Marc Ellis) is the NO. 1 selling system in NZ and Australia for a reason. This article is written by “Cleanair HRV” who account for under 1% of sales in NZ. Which means for you that you can ignore their opinion. HRV (Mark Ellis) is award winning everything and designed for NZ climates. Please Deon, next time you post some rubbish, check it out first. Thanks
well maybe you should do something of your own! and put the story straight…