[Bldg-sim] PSZ HP undercooling and questionable reheat energy

Derek Whitehead Derek.Whitehead at rwdi.com
Wed Dec 19 10:24:05 PST 2007


Hello,
 
I hope someone in the user community can help me with a modelling
problem. I have created a PSZ HP system in eQUEST 3.60, build 5210 and
assigned a zone. The system is scheduled to operate 24/7 and to maintain
a zone temperature between 70F and 73F. 100% outdoor air is supplied to
the zone. The location is in Saudia Arabia (quite hot and humid). I have
set the max. humidity to 50%. The system is autosized with a sizing
ratio of 1.15 and a design day is used.
 
Hourly reports suggest to me that the system is operating rather
strangely. Cooling occurs most hours to dehumidify, but often doesn't
provide adequate cooling or dehumidification for several hours middays.
At these times, return humidity ratios creep up and zone temperatures
rise (sometimes over 100F). One might think that the cooling capacity is
inadequate, but the system PLR is reported as well below 1.0 at these
times. Has anyone else experienced this? Is there a bug in this system
type?

Another issue of concern is that reheat is provided by refrigerant hot
gas, but a significant amount of electrical energy for reheat is
reported. Why would this add any additional work on the compressor? Or
is there something else I'm missing?

Thanks
Derek
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