Hi,
?
I model a PSZ system with exhaust air heat recovery. I set the static pressures of supply/exhaust fans as zero in ERV tab. Therefore, the fan energy is the same with or without ERV. However, there is an increasing cooling load in?the cooling model. I changed the hourly report and?didn't find the reason.?Any suggestions are highly appreciated.
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Thanks
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Shaojie?
ERV with increasing cooling load
Oct 27, 2008
Shaojie,
Check to make sure that you are not recovering heat during hours that
you can be using the economizer. Choose the Control Sequences:
Operation: "When Minimum OA" so that the heat recovery device will only
operate when you cannot benefit from free cooling.
Michael L. Kingsley, PhD, PE, LEED AP
Gary,
A dual enthalpy type economizer would be recommended rather than a dry
bulb type. In either case the number of econmizer hours would be less
for a warm/humid climate than for a temperate northern climate. My
response to Shaojie was aimed at trying to troubleshoot why his cooling
load increased with the heat recovery. Extra fan heat doesn't seem to
be the cause because fan energy consumption was forced to not increase
with the heat recovery.
Best Regards,
Michael L. Kingsley, PhD, PE, LEED AP
Hi,
?
Thanks a lot for all your replies. I changed the following settings and solved the problem.
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Control Sequences Operation:?when minimum OA
Make air temperature cotrol: Mixed?Air Reset
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Best,
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Shaojie
I'm wondering whether the Mixed Air Reset will really be implemented in the real system? How big difference the air temperature control strategy will make?
Xiaobing
The eQUEST default for temperature control is FLOAT whereby the heat
recovery device aims to maximize heat recovery for all ambient
conditions. This leads to heat recovery when economizer free cooling
would be preferable.
With "Mixed Air Reset", the device is modulated, either by bypassing air
or by modulating the heat exchanger (slowing the wheel), to maintain the
mixed air temperature at the mixed air temperature setpoint -- which is
typically the supply air temperature setpoint less a couple of degrees
for fan pick-up. This is definitely a common building automation system
strategy.
my 2 cents..
I can attest first hand to having witnessed ERV systems operating in a
"FLOAT" mode that were using chilled water for cooling on a 50-degree day
because heat recovery increased SAT to ~67F and they then proceeded to cool
SA back down to 55F.
I believe equest folks made the ERV default "FLOAT" so that people would at
least stop and think about the fact that an improperly designed ERV system
will actually increase energy use.
Michael Tillou, PE, LEED