- if the outdoor temperature is below the ahu (or the HR recovery)
setpoint temperature, then the HR modulates its bypass damper to
regulate the supply air temperature (correct operation)
- if the outdoor temperature rises above our setpoint temperature, then
the bypass damper of the HR closes and all the air passes through the
HR, leading to a overheating of the air.
I am aware of the fact that one could use the economizer to bypass the HR, however there are many problems with that manoeuver:
1 - controlling the AHU operation solely on the outdoor air temperature
is sometimes not possible (e.g. when we're using a "warmest" setpoint to
acclimatize a room, so using schedules will always limit my control;
2 - not all AHU have economizer operation (aka recirculation). In
Europe, most of the AHU operate with 100% outside air, meaning that if I
am adding an economizer to control my HR I'm adultering my HVAC
simulation.
My question is then why there is no way to control the heating battery
and the HR simultaneously from one AHU. This problem becomes serious
when no cooling battery is available: the indoor conditions become
unbearable with overheating during the wintertime. Briefly, one should
be able to have the HR totally bypassed when the outdoor temperature is
above the setpoint temperature. Then, there is still the HR for cooling
mode but that's very easy to control: on if the outdoor air temperature
is higher than the exhaust air. The only option I see is to add a
profile to the HR that turns it on and off depending on the outdoor air
temperature but, again, then I'm limited in my supply air temperature
control.
Has any of us ever had this problem before? Any suggestion on how to fix? Could anyone also explain me the reasoning behind the actual HR control?
Thanks,
Pedro
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