[BLDG-SIM] Ventilation fan energy changes from PTAC to FC

Neuhauser, Ken Ken.Neuhauser at csgrp.com
Wed Nov 14 13:59:44 PST 2007


Greetings:

I think I've wrestled with this long enough and it's time to invoke the
collection of greater minds on this list service for help.  

I am using eQUEST models to compare scenarios and I find that changing
from a fan-coil system (two-pipe) to a PTAC system (with HW coil heating
using the same two-pipe loop) causes a 3 fold increase in ventilation
fan energy for this system.  This is distorting the energy use
projections between these two scenarios.

Is there a logical explanation for this?  I have run a number of
parametrics to try to isolate the cause for the difference in Vent Fan
energy.  The fan power parameters are the same.  Fan control and flow
parameters appear to be consistent.  The systems take outdoor air from
another system and the Vent Fan energy does not appreciably change for
that system.  For the real world, I would not expect to see a huge
change in fan energy if I change the cooling source from a chilled water
coil to a refrigerant coil.  What is happening in the model that I don't
understand?

Many thanks in advance to all who are able to give time and wisdom to
this.

Ken

Ken Neuhauser, M.Arch, MSc.Arch, LEED AP

Architectural Project Manager

Conservation Services Group, Inc.

40 Washington Street

Westborough, MA 01581

Ph. 508 836-9500 ext. 13226

Fax 508 836-3181

www.csgrp.com <http://www.csgrp.com/>    

 



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