Hello Users,
I have a packaged (Heating: Gas-Fired, Cooling: DX) air handling unit with
VAV boxes in the zones. The cooling coil control for the AHU is Zone reset.
I have noticed an odd behavior in the cooling side when I model an exhaust
air heat recovery as follow:
The cooling energy increase from 67.7MBTU to 132MBTU when I include 70%
exhaust air heat recovery which doesn't physically make sense to me.
When I change the cooling coil control to Outdoor air reset the results
change as follow:
The above scenario makes sense in a way that both the heating and cooling
energy decreased by incorporating exhaust air heat recovery.
I appreciate any explanation on the strange behavior of scenario I
Best Regards,
Ahmed Azhari, B.Eng., LEEDR AP
Your cooling loads are so small, I suspect there is some kind of net
effect (sometimes smaller, sometimes greater loads) happening. For
example, if your ERV is sensible only, perhaps the increase in latent
loads is more than offsetting your sensible savings. Can't tell without
knowing more about your system and your weather data. Take a look at
your hourly "savings" for clues.
Glenn
I have found an explanation:
Look your air system.
If your cooling system is installed before the heat exchanger you will cool the air and then heat it. So you will need much more energy than without HE. So change the position of the HE in the system. In theory that can be the problem but I don?t have experience with complex energy systems on eQUEST.
example summer day
outdoor air ... 30?C
Cross the cooling system 20?C --->delta T=10?C
cross the HE system 25?C
Without HE
outdoor air ... 30?C
Cross the cooling system 25?C --->delta T=5?C
Mateo de Guadalfajara.
Mateo de Guadalfajara Pinilla
mateo_mw at hotmail.com
Engineer Energy systems and construction Student
Looking for a job :)
Date: Mon, 17 May 2010 11:55:04 -0400
Hi Ahmed, not knowing the details of your system and model, but in
general by having an ERV, your system may not be able to take advantage
of the free cooling when outdoor air temperatures are below your return
air temperature and there is cooling demand. It seems from your numbers
that free cooling could be available for many days during the year.
During the cooling season, and unless it is bypassed, your ERV may be
preheating cool before it enters the space.
Regards,
Bassam