I have 4 air handling units and all of their air is being exhausted to
the same exhaust manifold. I have a heat recovery glycol run around coil
in that exhaust stream of air, and the glycol is returning that heat to
only one of the four air handling units.
Is there any way to model this? I have heat recovery turned on for just
the one unit that the heat is being returned to, but this doesn't
account for the other 3 units' exhaust air. Thanks for all of your help!
Amanda E. Martz, EIT, LEED AP
I specified the max airflow the unit is designed for, but it might not
see all of this exhaust air at any given point. I would rather it size
itself based on what exhaust it calculates. It's hard to tell what it's
doing with the information it has and what I give it.
Also, I'm not sure what to do with the pump power for the glycol loop. I
don't have the glycol loop included in the model as a circulation loop
because its MBH varies depending on time of year, but I need to include
that power somewhere.
Amanda,
To simulate heat recovery from multiple air handler exhaust streams to
one air handler outside air stream, you could try to account for it by
modeling heat recovery in one unit only and increasing the heat
exchanger effectiveness. eQUEST allows you to enter a number greater
than 1.0 for ERV-SENSIBLE-EFF, but when I tried it the program gave me a
caution message and changed it to 0.9. You will have to do a
hand/spreadsheet calculation to determine what the actual effectiveness
might be. The 2008 ASHRAE Handbook - HVAC Systems and Equipment, Chapter
25 is one resource.
To account for the pump power, add it as ERV power (ERV-HX-KW in the
Heat Recovery 2 tab).
Regards,
William Bishop, PE, BEMP, LEED(r) AP