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VAV system but costant air flow rate

asked 2017-05-23 11:05:40 -0500

PaoloMassaroni gravatar image

updated 2017-07-24 09:07:43 -0500

Hi, i can't understand why the rooftop with variable volume fans is always constat with the outdoor air and the design airflow rate i defined in E+. I suppose the first one should be remain constant, while the second should change depending on the cooling/heating load. Where am i getting wrong with the model?Thank you.

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answered 2017-05-26 14:21:34 -0500

kpp gravatar image

It is hard to say without looking at the idf file but the first possibility that comes to my mind is oversized RTU. If the RTU is oversized then the system will run at minimum airflow condition. In such case, the RTU will provide a constant supply airflow rate.

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Yes, you are right, the Rooftop unit can be a bit oversized, but the airflow rate (mixed air) is constant on a value greater than the min (OA rate). So i dont' t know why it never modulate the flow rate.

PaoloMassaroni gravatar imagePaoloMassaroni ( 2017-06-01 09:58:57 -0500 )edit
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answered 2017-05-30 06:07:48 -0500

Have you checked the controls in your Controller:OutdoorAir, often this can be set incorrectly causing issues with your flow rates, also check the flow rates in your fans, have you autosized or put in actual values? How are you checking your air flow rates, are you looking at the nodes on each object or just the final flow rate into the space?

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Hi, i set min and max air flow rate in Fan:Variable. Also the controller is correct, where i defined the outside air flow rate. The result is a constant OA flow rate and a constant Mixed air flow rate. I understand why the OA is fixed, as i want to have that min quanitity, whereas i don't understand the mixed one that is constant all year long in a value set by E+.

PaoloMassaroni gravatar imagePaoloMassaroni ( 2017-06-01 09:58:57 -0500 )edit

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Asked: 2017-05-23 11:05:40 -0500

Seen: 863 times

Last updated: May 30 '17