[bldg-sim] Too capacity in AHU's?

[Turner, Stephen]

Pedro,
I am not certain, but I suspect that the large cooling capacity is for dehumidification of (outdoor) air at design wet bulb temperatures, in addition to the sensible load.  If the energy recovery is anything but an enthalpy wheel, it is unlikely to provide any latent capacity.  So the energy recovery may not help dehumidify, and the air may need to be "wrung out" with the large cooling capacity, and then reheated -- hopefully not with primary energy!  I realize this may raise more questions than it answers, but I thought I'd contribute this thought anyway.
Regards,
Stephen Turner
Mechanical Engineer, Brown University, 401 255 9897

-----Original Message-----
From: bldg-sim at gard.com [mailto:bldg-sim at gard.com] On Behalf Of Pedro Rodrigo
Sent: Thursday, September 01, 2005 11:56 AM
To: bldg-sim at gard.com
Subject: [bldg-sim] Too capacity in AHU's?

Hi all.
We have developed a TRNSYS building model of a real yet existing building in Jaen (Spain) in order to study different ways to operate the HVAC systems for improving energy efficiency. We are now working in the summer mode (cooling) that is much more important due to Jaen climate.
The HVAC systems are divided in two groups: first, several AHUs that provide a constant volume of conditioned outside air at 21ºC; second, each room has its own fancoil units so that when a user goes into a room, he turns on the fancoils to get the confort temperature.
We have tried to turn off the AHU's coils so that the ventilating air is now entering at the outside temperature minus some degrees due to the effect of energy recovery equipment. The model shows that the fancoil units still have enough capacity to provide the confort temperature in the occupied rooms. The unoccupied rooms are now hotter so that the mean temperature in the building has increased. This means that the energy comsuption has decreased.
It seems to be very simple but we have no experience about. Do you think there could be any problems by operating the system in this way? Why have the designers installed a so big amount of capacity in the AHUs?
Thanks for your suggestions,
Regards,


Pedro Manuel Rodrigo Cruz
University of Jaen, Spain


		
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