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[EnergyPlus_Support] Economizer/Heat recovery operation



Dear all,

I'm trying to simulate a constant flow system with generic heat
exchanger and an air side economizer. As I get it from "Input-Output
reference" pg. 1023 (PDF pg. 1060), when all other user definable
limits are satisfied, the economizer has the following control:

Cond.1)"Outside Air (OA) Temperature" >= "Mixed Air (MA) temp. set
point" --> Maximum outside air flow

Cond.2)"OA Temperature" < "MA temp. set point" --> Modulated outside
air flow in order to meet "MA temp. set point".

Regarding heat recovery/economizer operation. If I choose ECONOMIZER
or BYPASS in CONTROLLER:OUTSIDE AIR without any other limit, heat
recovery will always be bypassed.

My system. After satisfying all the other limits, I need my economizer
to always modulate OA flow, from minimum to maximum, in order to meet
"MA temp. set point". That is, independently of OA Temp./MA Temp.
relationship. The economizer should "know" that it was OFF, once the
OA flow was set to a minimum, allowing heat recovery to operate.

Is there any way of doing this? Has I see it, we can play around with
"all the other limits" but not with Cond.1 and Cond.2 . Is this right?

I know I could try to work with the weather file, and try controlling
this operation with TEMPERATURE LIMIT and TEMPERATURE LOWER LIMIT.
That could be an option, but it would be great have E+ controlling
this automatically, and on the other hand this model is to be used in
very different climates.

By the way, this model is always in cooling mode (very high internal
loads) and I'm controlling zone temperature in deadband. Deadband
control is also behaving a bit strange. My system insists on keeping
the zone's cooling set point temperature when it could be just keeping
the zone inside the deadband range. This means that, at times, MA
temp. is suitable to keep the zone in the deadband range and is also
in the acceptable supply air temperature range, but the system insists
on heating the air a bit to keep the zone's cooling set point
temperature. To make it a bit clearer:

Zone deadband thermostat: 19-23ºC
Mixed air temperature: 19.9ºC
Supply air temperature range:16-28ºC
Heating Coil Outlet temperature: 22.6ºC
Resulting zone temperature: 23ºC (when it could be kept at around
without the additional heating 21ºC)

Sorry for the long and maybe not so clear problem explanation. Thank
you very much for all your help. Best regards,
Alexandre






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