Heat Exchange Airflows

[tbedford]

I am balancing airflows (8000 cfm) across a heat pipe to reclaim heat from many parts of a school.
The manufacturer has installed identical blower/drive combinations with the same hosepower. Due to duct resistance, the supply airflows are significantly less the exhaust airflows. I do need to maitain a positive building pressure.
Do these airflows need to be similar in order to maintain maximum efficiency?
Thanks,

 

[atlas06]

Tbedford,
Have you noticed that no one answered your post? When you don't get a response, chances are that your question is not phrased properly, or not enough data.
You situation is not clear. And what does efficiency has to do with positive pressure in building? You are not likely to maintain a positive pressure if you exhaust more air than you are bringing in.
What kind of conditions are you trying to achieve, what are your actual airflows and temperatures? etc..

 

[tbedford]

thanks atlas06...

I didn't print more because I was looking for some general answers/ideas and I had only been to the site to get initial airflows.
However, I have two airhandlers with the same situation...

The manufacturer has provided a supply motor and a return motor of equal hosrepower. In addition the blower/drive combination are the same. The supply duct for each is rather convoluted with 11 hot water reheat coils. Total static resistance is in the order of 1.8"wc. The return duct is typical, short and large...TSP in the order of .6" wc. RLA for all motors is well below nameplate.

Design airflows are given at 5500 cfm, significantly less than I measured so I was wondering... why the disparity?

The heat exchanger in question is a heat pipe... with refrigerant in the tubes. I have obtained as much as 18F heat exchange from these coils in other buildings. The best I can do with the existing airflows is 6F.

Ther airhandlers were purchased separately by the school district and I am beginning to think there was a lack of commuincation between the duct designer and the equipment supplier. The equipment supplier perhaps was expecting long returns to pick up from many parts of the school. The duct designer was under pressure to keep costs down and now we have a waste of money.
Does the formula for load "Q=AUD" apply for heat exchange across these coils? The return is from common areas such as hallways; the return air dewpoint would not be affected by mosture to any great extent.

Hope this lowers a few eyebrows and raises a few more

Tom