air exchanger/dehumidifier

In winter the warm air inside is a lot dryer than the outside air.

You have single panel windows (I suspect) and they bring the surface below the dew point = condensation.

solution = a dehumdifier, which is a cold plate device to remove water from the airr. Now your windows do that

Leaks around the windows draws the condensation to the glass. Caulk but on the other hand getting your home tooo air tight could be harmful also.

You need to explore the home ventilation aspect of home building. Some fresh air is a must for a home.

A friend of mine recently built a house using some relatively up-to-date technology. It's very well insulated and has underfloor heating. He fitted a system of air exchange that involved a heat exchanger in his loft. I don't think he included dehumidification. The heat exchanger was a rotating drum type and I know he had noise problems on account of poor balance. Basically it used the upper floor ceilings as a sound board. I haven't heard him comment on condensation. I don't know what winter weather is like where you are but are you sure your windows offer enough of a thermal barrier? Obviously condensation only occurrs on surfaces which are cold relative to the air in contact with them.

It is most unlikely to be caused by your heating system, unless it is actually losing water! Or the exhaust is emptying into the house!!

You should check that water loss somewhere is not compounding the problem....that outside water is not being sucked into the brickwork for example....

Have you measured the humidity in the house?, for comfort it should be more than 30% and less than 55% is my personal take. 40-50 % is usually about right. Less humidity and you will be drinking all the time and more will cause more condensation.

Use an accurate unit, the cheap wall units are just not accurate enough.....the wet bulb/dry bulb are the most accurate and the cheapest of the accurate ones I believe!! Its made of wood, looks like a rattle and has twin thermometer on it! Only one gets wet!!

1) A possible reason for condensation is cold window glass, you should have double glazing at least. The windows should also catch any condensation and bring it outside though tiny channels. Window frames must be properly made not to bring cold into the house from outside, some are not made well. Do they get very cold inside when its cold outside? If yes, change them out....

2) Badly insulated walls, or heat conducting materials that reach from outside to inside in the wall, will bring the temperature from outside into the house....

3) An AC or dehumidifier can be used in winter to remove humidity, but of course you have the electricity costs as well.

4) Do you change the air out regularly, humans actually give up a lot of moisture each day into the air. You should change the air out. There are units which while exchanging out air, remove the heat from the exhausted air to warm up the fresh....

5) Get someone with a special heat loss machine working like a Video camera that "spots" heat (I have not a clue what they are called in English!)to come and look at your house from outside, especially in the winter, he will help you track down heat loss (which also translates to "Cold in"), which will cause extra condensation.....

If all else fails, stop everyone breathing or perspiring in the house !!! (Joke!)

Thanks for the comments so far. I probably should have provided more details in my initial post so going on the principle of better late than never, here goes:

1) We live in an area classified as a rain forest and receive very little direct sun light.

2) We have double paned vinyl windows whose average size is 5' by 5'.

3) The exterior walls are 2x6 construction with proper insulation and poly sealing.

4) We do have a dehumidifier and the humidity reading can be as high as 70% but averages about 60% in the winter.

5) the hydronic floor has been operating well for 3.5 years with never a drop in pressure (suggesting there probably isn't a leak).

6) We do not have air circulation in our house other than several ceiling fans and do not change air from the exterior to the interior (and vise versa).

This last point is the reason for the original post. I'm interesting in hearing about what this community would recommend as a quality air exchanger and dehumidifier that can be installed, preferably plumbed through my attic.

Andy Germany has a good suggestion that I may simply have to get a contractor out to test my house...

You wrote:-

Andy Germany has a good suggestion that I may simply have to get a contractor out to test my house...

I think then you will learn a hell of a lot more, plus as a professional person working in your area, he might have already fixed similar problems elsewhere.....you could profit!!

Even if you do the actual work yourself, it could save you a lot of time and time is money!!

Best wishes.

what is the water table like? high and at average temperature, so it can be used to supply water circulated through a couple of car radiators in series with a small pump. You then have a fan that blows the air throuh the two rads in series in counter current style. This would be the cheapest way and would use the lower water temperature instead of grid power for most of the work.

A filter would be needed on the input

I understand your problem having lived in a similar climate. The condensation on the windows is a sign of a tightly sealed home without adequate ventilation. The windows at a lower R value than the walls are the natural place for condensation. I have a Venmar heat exchanger in my hydronically heated home and am very pleased with it. The unit has a HEPA filter for the incoming air so even in my inner city home there is very little dust.

I think the solution is removal of water. They live in a rain forest ~= 100% humidity, so outside air would not be much less humd than inside air. Out side air at 10C 100% RH will be about ~75% RH at 20C, this will have a dew point of 10C

They need to do a water balance. Add up all the water evaporating things in the house. People, plants and cooking, pets etc. These will add water to the air. You need to remove more than this to reduce your humidity. At some point you will redice it below the dew point for air in contact with the windows and condensation will cease. Do not forget the water from a concrete pad the house is on(unless covered with plastic).

Counter current vents that conserve heat can be used for air exchange

Oliver--

I am not familiar with the Venmar brand, but understand the technology well. In addition to transferring the heat energy from between the incoming and outgoing air streams, they also transfer the moisture (latent heat) between the two air streams. Usually this is with a wheel whose honeycombed air passages are coated with a hygroscopic (desiccant) material. The problems with these units are in three areas--1) the mechanical components (fans, motors, bearings, belts) to move the air, 2) the air leakage and cross-mixing that can occur where the wheel moves between the two air streams, and 3) corrosion from condensation.

I believe that there side-by-side tests of different units have been published, but don't remember where. The manufacturer should give you performance ratings for their unit, along with a warranty of some type.

Since you have no duct work, installation of the unit will be more difficult than normal. Frequently it is done so the most humid sources of air are the ones being exhausted, and the incoming air is in locations where drafts will not be noticed.

--JMM

Thanks for your input, JMUELLER.

Since you're well versed in the technology I hope you don't mind if I ask you a couple more questions?

I assume you probably agree that some kind of air exchange/circulation should be installed in my house since none exists right now (other than opening a window a two)?

You identified 3 critical areas in your post. In your experience, what are reputable companies offering in the way of warranties in these areas? The Venmar unit has a 2 year warranty.

Thanks for the info about a comparison study being done. I'll try to find it on the internet.

Any other info you can provide would be greatly appreciated.

Thanks again.

Oliver--

I try to be a generalist and am interested in many topics which often connect to some degree or another. The last time I studied air/air heat exchangers in depth was about 4-5 years ago, so it is possible for others to be more current than I am and that some of my knowledge is out of date. Thats the disclaimer part...

I re-read all the posts. You say you have a dehumidifier already and have family members with allergy problems. You have not mentioned indoor allergies or other concerns about air quality other than the condensation on the 2x glazed windows. If dehumidification is not sufficient and you believe that the air is poor (residual odors are a good hint), I would agree that an air-air heat exchanger is desirable. If you are exhausting warm humid air in the winter time when the incoming air stream is colder than the dew point of the outgoing air stream, you will have condensation inside the unit, so it must be provided with some form of drain connection and be made from materials that are resistant to rust. If you have exhaust ductwork in the attic (above the conditioned space), it is possible for the inside of this ductwork to become cool enough to have condensation inside the ducts. Good sealing, good insulation, and even constructing them from non-corroding materials with a slope to drain may all be necessary. Putting the ductwork within the conditioned space is generally better. One way to retrofit this is to build soffits just inside the bedrooms off the hallway and put ductwork there; another is to drop the ceiling of the hallway about 4-6" and use the area above as an exhaust plenum. (The wiring for lights and smoke alarms can be a problem. If you turn the framing lumber on its side, you can have even less height taken out of the hallway ceiling.)

My memory is that a 2-year warranty is a good one (at least 5-years ago). One other person wrote that he had a Venmar unit with HEPA filtering on the incoming air and was very pleased. That sounds like a good recommendation to me.

I liked the suggestion from Andy Germany, to talk with local people. Sometimes finding a contractor who is sufficiently open to alternative approaches or "edge of his/her known world" type of thinking is difficult. Another person mentioned doing a "water balance" on the house--in other words, looking at all the sources of indoor moisture and seeing if they could be changed, controlled, or locally vented outside. Even an informal one can help--often overlooked areas are showers and indoor-vented dryers.

One question back to you--how much water are you removing each day from your dehumidifier, and does it have an automatic drain so it does not shut-off when its pan gets full?

--JMM

Thanks again for all your input, jmueller.

I've done more research and taken everyone's advise into consideration. I contacted all the local plumbing and heating suppliers in our city. Oddly, only one place had someone who knew anything about HRVs. He mentioned that because ventilation is not a building code requirement in our province, not many people opt to install a system when their heating source is either baseboard electric or radiant. As a result, there's not a lot of demand and therefore not a lot of discussion about ventilation. Once again, odd.

The dehumidifier we have is a department store one aimed at being used one room at a time. I think it's a good quality one and can accumulate several litres of water in a day. It does have a drain but we simply empty the reservoir each day. The main problem with the unit is its noise. We can't use it at night when most of the humidity seems to occur (at least in our bedrooms).

Air quality seems fine but due to the lack of air movement, cooking smells can last a while in the house.

My research showed that some companies are now offering lifetime warranties on heat exchange cores and 5 year warranties on parts on some HRVs. I think that's pretty good. I still have some questions pending with a couple of manufacturers regarding ducting and specific product features and can post a summary of all I've learned in the near future.

Regarding the ducting question: I've seen some manufacturers recommending insulated flex pipe to connect the HRV to the outdoor air but rigid pipe throughout the rest of the system. I assume this has something to do with minimizing air restriction and leaving places for moisture, dust and lint to accumulate. If this isn't the case, why couldn't I run insulated flex pipe throughout the entire system? If it is the case, and I don't want to lower ceilings or build bulk heads, couldn't I just run the rigid pipes through the attic and cover them with insulation bats?

If you're talking about avoiding thin corrugated flexible type trunking but dont't want to bother with the kind of tin ducting used in commercial buildings, my guess is that for your airflow requirements you could consider push-fit or solvent glued drainpipe. Plenty economical and easy to fit. If the dia is a bit small it would be cheap enuff to double-up (parallel feeds to larger rooms? I suppose at worst you might have to fabricate some sort of weird manifold.