Zedman: HVAC stuff

[kurtdesign1]

Here's a piece of equipment that I'm intrigued by. Being Canadian, do you have any more seasoned experience with this, Zed? I've been installing ERVs (and previously HRVs) for years but I've never seen or done anything without its own mechanical air handler. What say you?

http://www.hoyme.com/index.php?option=c ... &Itemid=64

[Zedman05]

Yes, we have these here. Basically the same as an HRV. Warms up incoming fresh air so there is not such a temp difference to overcome when heating. As you most likely already know, that extremely cold air coming in is dense, and therefore accounts for a greater duct volume once heated. With it warming before hitting the ductwork, you lose the possibility of it having a condensing issue from moisture and also keeps the static pressure at more of a normal rate on your return side.
I think the only issue with this is the fact that yes, you don't have a fan inside moving the air, but will it cause a lack of static pressure in ductwork already installed enough to lose airflow in those farther areas of the house ? If this was installed at the same time as the furnace, I would think it is a nifty idea, but if you go into a house and throw one in, it looks to be removing some of that needed cfm to atmosphere. If your furnace is size to, lets say 1600 cfm, and that is keeping it nice and warm around the house, if you added this equipment are you going to lose that velocity to the farther rooms and thus cause them to be coler as they will now have reduced flow ? You could opt for a new 2000 cfm furnace to account for some loss, but you would have to sell the home owner on this idea.
Witha typical hrv, this is all kept in check.

Cigar F^iend

[kurtdesign1]

Yes, we have these here. Basically the same as an HRV. Warms up incoming fresh air so there is not such a temp difference to overcome when heating. As you most likely already know, that extremely cold air coming in is dense, and therefore accounts for a greater duct volume once heated. With it warming before hitting the ductwork, you lose the possibility of it having a condensing issue from moisture and also keeps the static pressure at more of a normal rate on your return side.
I think the only issue with this is the fact that yes, you don't have a fan inside moving the air, but will it cause a lack of static pressure in ductwork already installed enough to lose airflow in those farther areas of the house ? If this was installed at the same time as the furnace, I would think it is a nifty idea, but if you go into a house and throw one in, it looks to be removing some of that needed cfm to atmosphere. If your furnace is size to, lets say 1600 cfm, and that is keeping it nice and warm around the house, if you added this equipment are you going to lose that velocity to the farther rooms and thus cause them to be coler as they will now have reduced flow ? You could opt for a new 2000 cfm furnace to account for some loss, but you would have to sell the home owner on this idea.
Witha typical hrv, this is all kept in check.

Cigar F^iend

Great insite. Thank you. How do you calc sizes of your systems? We use Elite's software (Manual J, mainly).

[Zedman05]

The furnace/air handler will have a model number which will correlate to the cfm the blower is rated for.

Cigar F^iend

[Zedman05]

As for duct sizing, if that is what you are asking for, you would just need what you most likely have talked about; a program to calculate the volume of air the duct sizing will move.
You can always push higher volumes through ductwork, but it comes at a price: 1- blower static capabilities. This is where you need to product info from the manufacturer as they will tell you what the highest static that fan was meant to push against is. 2- noise. When the volume goes up, so does the whistling noise from your registers. When working in a residential setting, you can only go so high before people get annoyed with how loud the air coming from the supply registers is. You may also start to get a slight whistle as the sudden air pressure drop out of siad supply register causes that whistling at the choke point: just before register.
When I upgrade furnaces for people, the first thing they say is " wow, that furnace moves a lot more air and that air is louder".

Always remember to calculate air volumes based on maximum as AC works on the blower running at it's highest speed tap, whereas in the winter in heat mode, a blower will only run at med/med-high. Just a helpful reminder, but I am sure you already know these things as you have been doing it for a while

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