Re: [EnergyPlus_Support] Re: Heating Coil and Cooling Coil are running simultaneously!?!?

You place a setpoint usually on the outlet node of the AHU. Depending on which setpointmanager you use to place the setpoint, the setpoint could dynamically change to best meet the load in the zone. Often both coils look at this same setpoint together with their relative entering air temperatures: based on this information each independant coil controller will actuate to best try and achieve the air setpoint that you placed on the AHU outlet (which may change dynamically the value to achieve).

Therefore if the setpoint the AHU outlet (at a timestep) was 13 deg C (because the zone needed cooling, because some equipment has turned on), the heating coil entering air temperature was 10 deg C from cold outside air, and the cooling coil entering air is 16 deg C (for any number of reasons), then both coils will operate.

Mit freundlichen GrÃ¼Ã?en- Sent from my iPhone (excuse the brevity)

i. A.

Jean Marais

b.i.g. bechtold

Tel. +49 30 6706662-23

On 18.12.2013, at 11:16, "hisham.rashrash" <hisham.rashrash@xxxxxxxxx> wrote:

Dear all,
Regarding this warning 'In HVACTemplate:System:VAV "VAV" the Heating Coil Design Setpoint is greater than the Cooling Coil Design Setpoint. This may cause the heating coil and cooling coil to operate simultaneously. Check results carefully and adjust controls if needed.'

Please, can anyone explain how this HVACTemplate:System:VAV works? I feel lost in questions, like:
Should heating and cooling coils run independently of each others and only depend on thermal zones thermostats? Then, what if two thermostats provided contradicting signals: a request for heating and another for cooling?
And in case there are no contradicting signals, why there is a possibility both coils are running together when heating coil setpoint is higher than cooling coil setpoint? Is there some 'invisible' thermostat E+ object between these two coils?

Maybe my questions are too basic, but I really need help here.

Thank you very much.

Hisham

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "hisham.rashrash" <hisham.rashrash@...> wrote:
>
> Dear all,
>
> I got this warning:
>
> Program Version,EnergyPlus-Windows-64 8.1.0.008, YMD=2013.12.17 17:18,IDD_Version 8.1.0.008
> ** Warning ** Output:PreprocessorMessage="ExpandObjects" has the following Warning conditions:
> ** ~~~ ** Warning: In HVACTemplate:System:VAV "VAV" the Heating Coil Design Setpoint
> ** ~~~ ** is greater than the Cooling Coil Design Setpoint. This may cause the
> ** ~~~ ** heating coil and cooling coil to operate simultaneously. Check results
> ** ~~~ ** carefully and adjust controls if needed.
>
> It seems like EnergyPlus puts a thermostat between coils? why should they run at the same time?
>
> Please advise.
>

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