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Re: [EnergyPlus_Support] How to control Supply air temperature for heating in VAV system


Two pointers:
1) the radiant system should have priority 1, not the VAV
2) make sure the system is sized on "Ventilation Rate" in the Sizing:System object and not "Sensible" as is the default.
Your VAV pulls its sizing from the sizing:zone object directly. So if your sizing:zone object does not use "flow/zone" instead of "designday" for the sizing method, then you still have to set a fixed limit on the maximum flowrate in the VAV object. However, for the coil in the VAV to size correctly, it is better to set the sizing method to  "flow/zone" in the sizing:zone object.
I believe also that the supply max temp from the VAV is pulled from the design supply air temperature for heating in the sizing:zone object, whereas the supply temp delivered to the VAV from the AHU is set in the sizing:system object.
Hopefully, if the program sees that the incomming hot air into the zone is limited, the radiators will size correctly to makeup the difference, however you should probably size them manually as you have the existing parameters.

Goodluck,

 The project I am doing is actually a existing building so I only need to use their design parameters to calculate the building energy. They controlled the supply air temperature to 31 C during heating so thats the reason I also want to do that. I tried to use the reverse control logic with minimum air flow rate set to zero, hoping it will use maximum air temperature all the time (31 C). But instead, I now see the SA temperature is even lower than before, and most of the heating load is on radiant side, even though DOAS is set as sequence 1 to meet the heating load and radiant system as 2. I am really confused what part I did wrong...


HJ



On 6/3/2014 5:12 PM, annie <mailto:anniemarston@xxxxxxxxxxx><mailto:anniemarston@xxxxxxxxxxx>anniemarston@xxxxxxxxxxx [EnergyPlus_Support] wrote:
>  
> If you have the size of your radiant system in correctly the program will be able to let you know if your fresh air will need to rise to such a high temperature. In the models for DOAS with radiators that I have done previously in equally cold climates as Chicago the radiant system is capable of meeting the heating needs of the building as long as the air handler is conditioning the air to ambient temperature. The advantage with this system of course is that a lot of energy is saved as you avoid a lot of reheat issues in the AHU. Regardless the simulation can calculate this for you if you program it correctly in the VAV component, the radiant component and in the equipment list and zone sizing components.
> Annie
> 
> To: <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx><mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx><mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>EnergyPlus_Support@xxxxxxxxxxxxxxx
> Date: Tue, 3 Jun 2014 16:51:42 -0400
> Subject: Re: [EnergyPlus_Support] How to control Supply air temperature for heating in VAV system
> 
>  
 Thanks. We do have a radiant system for heating and cooling. Since the winter in chicago is pretty cold, we need to heat up the outdoor air to 31 C otherwise the radiant system might not be able to provide enough heating for the room. So I added a reheat coil on there. I checked the I/O guide, seems like the reverse control might simulate this control logic most similiarly. Thanks again.
> 
> HJ
> 
> 
> 
> On 6/3/2014 4:29 PM, annie <mailto:anniemarston@xxxxxxxxxxx><mailto:anniemarston@xxxxxxxxxxx>anniemarston@xxxxxxxxxxx [EnergyPlus_Support] wrote:
>>  
>> The VAV component takes care of this, you have two settings, you can either have a steady temperature with varying air flow until maximum air flow then the temperature will increase to meet the conditions of your thermostat, or you can have minimum air flow with increasing temperature until the temperature is at the maximum then the air flow will increase to meet the conditions of your thermostat. You will need to open the input output reference guide (I/O reference guide), which is in the help menu in E+. Find your VAV component name in the contents and click on it to take you to information about the component. It will explain how you control the VAV component to make this happen.
>> A side note, a dedicated outdoor air system would normally have a constant flow so in that case the supply air temperature would need to fluctuate at the reheat coil in order to condition the room, that or you would deliver the air at ambient temperature and condition the room through another component, in which case you can get rid of your reheat coil and put a setpoint temperature on the heating coil in your air handling unit.
>> I hope this helps.
>> Annie
>> 
>> To: <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx><mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>EnergyPlus_Support@xxxxxxxxxxxxxxx
>> From: <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx><mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>EnergyPlus_Support@xxxxxxxxxxxxxxx
>> Date: Tue, 3 Jun 2014 16:11:44 -0400
>> Subject: Re: [EnergyPlus_Support] How to control Supply air temperature for heating in VAV system
>> 
>>  
 Thanks Annie. But in a real building control system, a VAV usually have fixed supply air temperature and so that it can vary the air flow rate the meet the load right? Our company use Trace most of the time and it can fix the supply air temperature, so when compared to E+, the DOAS system seems to be off by a lot and I think the reason is becuase E+ fluctuate the supply air temperature. Is there any work around that I can do in energyplus so that I can fix the SA temperature?
>> 
>> Thanks
>> 
>> HJ
>> 
>> 
>> 
>> On 6/3/2014 4:07 PM, annie <mailto:anniemarston@xxxxxxxxxxx><mailto:anniemarston@xxxxxxxxxxx>anniemarston@xxxxxxxxxxx [EnergyPlus_Support] wrote:
>>>  
>>> The temperature out of the reheat coil is controlled by EnergyPlus, information from zone sizing and the thermostat let E+ decide what temperature should be coming off the reheat  coil to condition the space. In other words you should not to put a setpoint on here, just make sure your thermostats are correct for the space. for more information you can look up the VAV component in the input output reference guide. Lots of lovely information in there for you!
>>> Annie
>>> 
>>> To: <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx><mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>EnergyPlus_Support@xxxxxxxxxxxxxxx
>>> From: <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx><mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>EnergyPlus_Support@xxxxxxxxxxxxxxx
>>> Date: Tue, 3 Jun 2014 15:59:49 -0400
>>> Subject: Re: [EnergyPlus_Support] How to control Supply air temperature for heating in VAV system
>>> 
>>>  
 Correction. When I use setpointmanage:singlezone:heating to set the supply air temperature to 40 C after reheat coil, it seems it does nothing to the supply air temperature.
>>> 
>>> 
>>> 
>>> On 6/3/2014 3:22 PM, HJ <mailto:wanghaojie630@xxxxxxxxx><mailto:wanghaojie630@xxxxxxxxx>wanghaojie630@xxxxxxxxx [EnergyPlus_Support] wrote:
>>>>  
 I built a VAV system through open studio. I am able to fix the Supply
>>>> air temperature for cooling by putting a setpoint manager before reheat
>>>> coil. However, I dont know how should I control the supply air
>>>> temperature for heating. When I put a setpoint manager after the reheat,
>>>> the air temperature will be forced to that value no matter heating or
>>>> cooling...
>>>> 
>>>> Thanks,
>>>> 
>>>> HJ
>>>> 
>>> 
>>> 
>> 
>> 
> 
> 





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