How to connect an Air Exchanger to my ducts

[phreaq]

I live in a corner unit loft, with concrete floors, ceiling and walls. The two inside walls are covered with drywall, and the two outside walls have mostly large windows on them.

During the winter months, I get excessive water on the windows and door (its a glass door). So much so in fact, that on very cold days, the water actually freezes at the bottom of the doorway.

The windows aren't the most efficient, but they are double pane, with steel framing.

I believe the problem is I am not circulating the air and think an air exchanger with a HRV will help.

I have looked at a few models, and seen how they hook up to 'conventional' duct work, but mines a little different. The loft is only about 750 sq ft, and is essentially open concept, with half walls creating 'rooms' (the ceiling in about 11' high). There is a single furnace, laid on its side, hanging from the ceiling. The output of the furnace connects to a round duct which tees off and provides a total of 3 vents. The 'cold air intake' doesn't really exist, and the bottom of the furnace is wide open, where the filter is.

Since I don't have any cool air intakes, how do I connect an air exchanger with hrv?

Here's a couple of pics

thanks in advance,

phreaq
Has anyone seen my brain today? (^_^)

http://www.phreaq.net

 

[tombmech]

You may or may not have a humidity problem within the space. However, normal practice is for perimeter heating to "wash" windows with the airflow. This keeps the air temperature in the immediate vicinity higher than the dewpoint, and reduces the chance of condensation or ice formation in extreme circumstances.

Pursuing a heat recovery system may not be the best direction. More airflow may help, but mostly if directed at the poorly insulated surfaces (double pane construction doesn't mean good resistance in and of itself).

 

[phreaq]

thanks tombmech,

If a heat recovery system is not the best direction, what is?

as for the "wash" statement, not sure I follow. I have thought it odd that the duct work is on the opposite side of the windows, is that what you mean?

I do have a de-humidifier, and basically have it running all the time.

 

[quark]

I remember looking those pictures one year back and sorry to know that your last winter was also bad. Can't you put trace heaters to your door (like they do for cold room doors near the frame)?

 

[phreaq]

yup, I'm still having problems

I'm not sure what trace heaters are, or how they are applied. The glass door and windows have metal framing, which mounts to the brick, the bottom of the door is in contact (via a rubber seal) with the Terrazzo flooring.

 

[macmet]

What about replacing one of your ceiling lights with a decent fan to increase flow?

 

[phreaq]

actually it is a seeing fan, hard to tell in the photo. I also have one in the back bedroom.

 

[tombmech]

Yes - "washing" the windows with airflow means that perimeter diffusers are often placed with the idea that the airflow clings along the ceiling and then gently curves down the wall. This "bathes" the wall in constant airflow, and focuses the conditioning capacity at the source of the load - the perimeter walls.

I believe quark's idea is about heat trace tape - similar to a car's rear-window defroster. Unfortunately, this may be difficult to achieve on a residential basis. Heat trace tape is often used for freeze protection of piping, but it is not really appropriate for an entire window. You could apply automotive defrosters, but conversion to 12 VDC would be needed without an expensive, custom product

The suspicion still remains - there is a great chance that your humidity is too high. The classic case usually involves heating with no means of exchanging drier, outside air with the air in the space. There is nothing to dehumidify the inside air. Without the simplest draft and infiltration, RH will continue to climb until the dewpoint is higher than the surface temperature of the windows and door, hence, condensation and frost result.

 

[phreaq]

I should say "ceiling fan" I could never figure out how to edit these posts.

also, the ceiling fans are on pretty much 24/7.

 

[phreaq]

what if I were to extend the ducting where the vents are, so they are closer to the windows?

and, back to the original question how do I hook up the air exchanger when I have no cold air returns.

 

[tombmech]

The vents should be closer to the windows (at least a reasonable number of them). That seems counter-intuitive, but it's best.

Before you do a lot of work, though, it might be better to get some real data. Tell us the temperature and humidity values in your space when this condensation and frost occurs. If your problem is bad enough, it may be better to focus on putting an outdoor intake connection on your furnace.

BTW, the heat recovery does nothing by itself to control humidity. It may allow you to bring in outside air to dry out the space with less of a penalty. That is because with a heat recovery HX, you can "temper" the outside air by heating it with waste heat. So your furnace doesn't see as much added load. There are heat recovery systems that work on moisture, but nothing's available on a small scale such as this (I think).

Your primary problem is humidity. It may be that your humidity is within an acceptable range, and your windows and door still attain too cold a surface temperature. There are things that can alleviate that somewhat (our previous suggestions), but you may still have too much moisture.

 

[Assumptions]

Just happened upon this post and have to comment. I have no expertise nor experience in HVAC other than living in a cold climate.

Looking at the pictures and reading the comments it has not been stated whether there is a fresh air intake for combustion. If not there shoud be one for safety.

It is not stated if there is an exhaust for the combusted fuel? I presume there is.

If possible a fresh air intake should be considered, as with high humidity your insulation could be getting wet and even freezing.

Just though I would throw in my two cents to be sure that safety aspects weren't being overlooked.

 

[IRstuff]

Fundamentally, if you have high condensation on the inside panes, your double paned windows have failed, particularly if you're actually getting freezing temperatures on the inside.

You might see about replacing the windows and door with newer stuff. Or, it might be possible to rework the existing windows and door back to their factory specs.

Most of the other stuff discussed above address the ultimate symptomology of a breach of your thermal barriers, but the correct solution is to fix the thermal barriers.

TTFN

 

[friartuck]

go to nuairegroup in the uk. They have a division called Homevent and make special units made just for this situation.

I have specd 'drimaster' and it has cured every damp problem that I ever came across.

A HRV unit would also do the job.

Friar Tuck of Sherwood

 

[tombmech]

A properly constructed double pane window has a good thermal resistence, but it is not infinite. If the outside temperature and heat transfer is great enough (wind, shading, etc.), and the inside air is humid enough, condensation will form - period.

I have seen condensation form on walls, carpet, and furnishings - the humidity was so bad. In one case the space was brand new, had the latest energy-savings construction, and was air conditioned. Yet, the units were way oversized, so the coils never got into their dehumidification range. The humidity continued to rise until mold was growing on the books and paper in the book shelves.

That was in a hot and humid climate, but there are also stories of wet houses in Alaska - especially the tight and energy efficient ones.

 

[phreaq]

Hey guys, thanks a LOT for all your comments. I truly appreciate it.

There is a fresh air and exhaust pipe for the furnace, looks like a 4" dia pipe that makes it way up thru the building.

I have figured out another trend too. We use this loft as our 'cottage' and as such aren't there everyday. When we get there after a few days absence, the place is all dry. It only starts getting damp when the furnace and people are there.

Also, tying back to what "tombmech" was saying about the "washing" effect, I don't actually have hot air blowing on the windows (see pic below).

So, since I have no hot air blowing on the windows, and outside temps can go to below -15C (plus wind chill if that affects windows), wouldn't it make sense that the windows would start to condense water?

So does that mean I should move the vents towards the window?

 

[SAK9]

The easy solution is to raise the temperature of the window panes by having the air flow directed onto them.Rerunning the duct closer to the windows would help achieve this and get rid of the condensation problems.

In well sealed houses there is moisture build up from people and cooking.This explains why dampness sets in only when the house is occupied.Try keeping a table lamp with a 100w bulb shining onto the windows (a few inches from the window)and it would be clear to you!

 

[walkes]

Phreaq, Do you have washroom exhaust fans in your space or is there just an operable window? Showers, breathing and general space use will contribute to your humidity problems.

Some thoughts:

1) You could install electric baseboards below the windows to get the window washing effect.
2) Provide branch ducts where the grilles are located to extend to the perimeter to blow down the windows. (may cause drafts however).
3) Add a residential HRV unit (venmar, vanee, lifebreath to name a few). A plenum could be added to the return side of the furnace to connect the HRV, or the HRV could discharge in the proximity of the return intake. The HRV would be controlled by a space humidistat.

 

[phreaq]

Hey SAK9,

I just went for breakfast, and left a 60W bulb on one of the windows, who has 100W anymore and it cleared the area up.

walkes,

I do have a bathroom fan, and a kitchen fan, and when I leave I have them running while I'm away.

As for your suggestions;

1. I hate the concept of electricity heating windows. Especially since my windows are 84" high, for a total of 37' feet long!

2. This sounds like a plan, but wasn't sure if it would work, but it seems most of you guys are in agreeance. As for the 'drafts', what would cause that?

3. If all else fails, I'll get a HRV.

 

[macmet]

If you do decide to branch off and carry the air over to the window - which I think is also the best idea - I know you can get inline duct fans for cheap.

I set up a 10' exhaust, 5" dia, for <$80. I just went and bought the first things I found to.

Good luck, it's an interesting home project.