Dear Colleagues,
I would like to hear about your work arounds for Air Handling Units with unbalanced Supply and Extract volumerates pertaining to heat recovery.
We specify the heat recovery device with sensible and latent efficiencies at both 100% Design Flow Rate and at 75% Design Flow Rate. I believe the model expects both Supply and Extract to be equal for this input, because the model has a way to modify the efficiencies when imbalances occur in upto 50%.
So I believe the correct way to specify the characteristics of the heat recovery device is as if it is balanced, once at 100% and once at 75% with both supply and extract rates equal.
Alternatively, I could be wrong and one needs to specify it with worse efficiencies of the heat exchanger at unbalanced air flows, meaning the supply is at 100% but often the exhaust is at somewhere between 100 and 50% of the supply rate.
When I then reduce the supply to 75% of the design flow rate, should I specify the exhaust reduced by 25% as well...or at least by the same volume flow rate?
In real systems I might supply a conference room with variable supply rates and a toilet where the exhaust from the toilets is seperate, hence causing the imbalance.
Looking forward to your opinions,
Jean