"Air exchange" units

Hi,
Does anyone have experience of extraction fans that use the heat from the outgoing air to warm the in-coming air? I read about this approach to reduce the possibility of condensation in houses where they were insulated and glazed tight as a drum but the lack of air circulation with the outside was causing damp / condensation problems.
I have found a sutiable unit a CES in Whetstone London, and I only have a one bedroom flat - but I just want to know if anyone has use done successfully in any domestic situation?
My thinking behind fitting such a device, rather than a conventional extractor is that any incming air would probably be colder than the expelled air and the classic argument is the condensation occurs at lower levels of "water saturation" when the temperature of the air drops. Hence I want the in-coming replacement air to be heated , if possible
Thanks
Clive
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yes fitted one a few years ago in a domestic bedroom, seems to have done the trick with the condensation and mould on the walls.
Drilling a 6in hole through the double brick wall was tiring tho (even with a diamond core bit)

Prob works as well as an extractor - but if warm are is sucked out it has to be replaced somehow (i.e with cold air from outside) this would increase heating costs. The heat exchange system goes some way to reduce these heat losses. Your point is theorecticall valid tho.
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John wrote:

Commonly used here, for the last 10 to 15 years, in a climate slightly colder and with a much longer winter than the UK; they are in fact mandatory in any house constructed to meet R2000 standard; which means heavily insulated tightly sealed. Both my daughters houses have them. They run continuously (probably 15 watts or so?) blowing air in and out through a core with many square centimetres/inches of surface area. Water condenses from the moister/warmer outgoing stale air and runs down a small tube to a drain or container. Typical cost is IIRC about the equivalent of 500 to 600 quid for the basic unit for, say a three bedroom 1500 to 2000 sq. foot house. Then installation is needed with in ceiling ducting to and from various discreet ceiling outlets in most rooms. Probably cost about 1000 pounds total for a typical installation in new home construction. More difficult to add later; also difficult to retrofit insulation and vapour barriers to meet anything close to R2000 after home has been built. Our 1970s home is not so equipped; we know it is somewhat more leaky than an R2000 and therefore more expensive to heat but we but have no problems with stale air, mould etc. during a long heating season. In all/most homes including R2000s there are also specific 'exhaust' fans, not connected to the 'Air exchanger' which are run for shorter periods in bathrooms, toilets and kitchen/cooking areas at discretion of residents. Air exchangers appear to work well; however one son in law has found his unit caused drafts and so has a) slowed the fan and b) partially screened some of the vents. Neither of the homes has had any dampness, mould or mildew problems and it does seem to take care of smoke from perfumed candles. (Never could see the point of burning several pounds/kilograms of hydrocarbons inside a house except during an emergency/power failure!). The 'Air exchangers' also referred to as heat exchangers are claimed to be 80% efficient in reclaiming heat that would otherwise be lost outside. I personally doubt that high a percentage, over the range of temperatures we encounter. Units require cleaning at least twice a year depending on how dusty is your house, pets etc. I would say that they are absolutely essential in a well sealed home; despite the heat loss they may engender. If I was ever building again I would definitely include an Air Exchanger and probably other technology for health and conservation of energy. Whether they are necessary in a one bedroom flat? I guess we don't sleep with the window open these days? Might be an unnecessarily expensive solution though, if all that is required is a bit of ventilation to change the room air every few hours and avoid condensation? Terry.
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I have 2 such systems one in my current place ... and one in the new build that is coming to the end. Both work are MHRV (Mechanical heat Recovery & Ventilation) ... suck air from rooms with moisture or smells. ... utility, kitchen, wc's bathroom ... plus over hob extract a swell.
This goes via filters into centrifugal fans pushing the air through large plastic heat exchanger in the loft (aprox 1.5m x 0.6 x 0.6) ... and is then expelled outside through a tile vent.
Incoming air comes in through filters through the exchanger into a separate fan unit, and then through sound dampers before being distributed to all other rooms.
In summer you flick a switch downstairs and it operates a bypass unit .. taking heat exchanger out of the loop.
I have been running this system 24 Hr. a day for more then 20 yrs ..... no faults, and the only problem is that if it close to freezing or below the incoming air is too cold and I have turned it off .... probably only 3 or 4 nights in 20 years.
In the kitchen there is a 0-2 Hr boost that doubles extract in kitchen and cuts it by half elsewhere, in the lounge there is a 0-4Hr boost switch that does the same for supply air. This system is made by Greenwood Airvac.
In my new build the design has moved on ... the ducts are flexible aluminium rather than plastic, fully insulated. The incoming air goes through a 4 stage filter process then via an electrostatic filter which will take out particles at the micron level (smoke dust, pollen etc.)
The heat exchanger has an electric pre-heater in the event of incoming air being too cold, I also have a LPHWB (Low pressure hot water battery) this is like a car rad with a 225mm pipe through it ... the heating system hot water is circulated through this and therefore anytime the heating is 'on' it will a also warm incoming air. (I may think up a temp differential circuit to control this in the future via a simple 2 port valve.)
The extract & supply is similar to before, the big benefit of the new system is the greatly increased efficiency of the heat exchanger - now an aluminium cross flow device, the fans are variable speed low current consumption devices.
It also has an addition (or will have when I install it) of an air conditioning unit, not big enough to provide full air-con, but it can drop incoming temp by several degrees and dehumidify the air.
The system this time is supplied by Villavent http://www.villavent.co.uk /
They did the CAD design, I did the install. They also supplied the central vacuum cleaner system.
I was so pleased with the system in current place that I had to have it in the new build, it also allowed me to meet building regs ventilation requirements without having to fit damn ugly trickle vents.
Rick
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clive snipped-for-privacy@yahoo.com (Clive Long,UK) wrote in message

I have 2 such systems one in my current place ... and one in the new build that is coming to the end. Both work are MHRV (Mechanical heat Recovery & Ventilation) ... suck air from rooms with moisture or smells. ... utility, kitchen, wc's bathroom ... plus over hob extract a swell.
This goes via filters into centrifugal fans pushing the air through large plastic heat exchanger in the loft (aprox 1.5m x 0.6 x 0.6) ... and is then expelled outside through a tile vent.
Incoming air comes in through filters through the exchanger into a separate fan unit, and then through sound dampers before being distributed to all other rooms.
In summer you flick a switch downstairs and it operates a bypass unit .. taking heat exchanger out of the loop.
I have been running this system 24 Hr. a day for more then 20 yrs ..... no faults, and the only problem is that if it close to freezing or below the incoming air is too cold and I have turned it off .... probably only 3 or 4 nights in 20 years.
In the kitchen there is a 0-2 Hr boost that doubles extract in kitchen and cuts it by half elsewhere, in the lounge there is a 0-4Hr boost switch that does the same for supply air. This system is made by Greenwood Airvac.
In my new build the design has moved on ... the ducts are flexible aluminium rather than plastic, fully insulated. The incoming air goes through a 4 stage filter process then via an electrostatic filter which will take out particles at the micron level (smoke dust, pollen etc.)
The heat exchanger has an electric pre-heater in the event of incoming air being too cold, I also have a LPHWB (Low pressure hot water battery) this is like a car rad with a 225mm pipe through it ... the heating system hot water is circulated through this and therefore anytime the heating is 'on' it will a also warm incoming air. (I may think up a temp differential circuit to control this in the future via a simple 2 port valve.)
The extract & supply is similar to before, the big benefit of the new system is the greatly increased efficiency of the heat exchanger - now an aluminium cross flow device, the fans are variable speed low current consumption devices.
It also has an addition (or will have when I install it) of an air conditioning unit, not big enough to provide full air-con, but it can drop incoming temp by several degrees and dehumidify the air.
The system this time is supplied by Villavent http://www.villavent.co.uk /
They did the CAD design, I did the install. They also supplied the central vacuum cleaner system.
I was so pleased with the system in current place that I had to have it in the new build, it also allowed me to meet building regs ventilation requirements without having to fit damn ugly trickle vents.
Rick
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