Balanced heat recovery ventilation - the case for "reversed" flow
We moved into our present home 3 years ago and have a counterflow heat recovery system. I am not happy so started to study this subject and our installation issues because we want to have a better setup in a new and smaller house that we are building.
The documentation that I've come accross recommends is an extract of the stale air in the living areas (sometimes bathrooms, toilet(s) and laundry get included but normally not done here) then goes to a heat exchanger and next gets discarded outside. Similarly the fresh air goes through the heat exchanger and gets supplied to bedrooms and living areas.
The problem with this (imho) is several fold:
- if the HRV is situation in the ceiling on a single level building (as normal here in New Zealand) and there is a fire then smoke gets distributed to all rooms in the building and the inhabitants of the home are quickly overcome
- colder air is supplied in different places, often exactly in a spot where one can feel it (above the bed, above a desk in front of the window etc)
- if there is a fireplace in the house and the doors to the other rooms are closed and there is only a single stale air extraction (often in the living area close to the heater / stove) then the living area will experience negative pressure resulting in backdraft through the fireplace (even more so with backdraft dampers in the kitchen extract fan)
- the polluted air is not extracted most of the time at the place of pollution (!) Normally inhabitants of a house spend most of their time ... in bed (!)
If the flow is reversed, i.e. have a single supply of fresh air in the living/kitchen area and the stale air is extracted from living area (furthest from kitchen) and bedrooms then surely this would result in better air quality? Especially if one is to leave either the bedroom doors open (I am retired and only live with my wife in the 3 bedroom home where one spare bedroom will be a home office and the other is for the occasional guests) or when bedroom doors are closed have the window in the bedrooms slightly open. The overpressure in the living /kitchen will at such time that the doors are closed simply escape through the kitchen extract fan (backdraft damper will be opened by the over pressure).
I am making the installation in our new building in such a way that I can just swap two ducts and reverse the flow. The fans are external to the heat exchanger and we'll be using S&P silent fans with an oversized aluminum counterflow core and I will be balancing the flows. The total thoughput will be controlled by a timer, 20 min on, 40min off and have boost on at dinner times. I intend to tailor the 20/40 min to an optimum flow by measuring the CO2 levels in the home.
Am I missing something in this reasoning :anyone: , please comment since New Zealand has only 4 Million people and there is just not enough knowledge to go around and have a decent discussion on this interesting subject.
Many thanks in advance, AM.