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How to run HVAC system in open-loop (manual air flow rate control)?

asked 2020-01-02 22:00:13 -0500

Rohit gravatar image

I am an electrical engineer trying to develop a thermal model for zone as shown in equation below:

<math> Tindoor(t+1) = a1Tindoor(t) + a2Toutdoor(t) + a3Qcooling(t) + a4 </math>


<math> Qcooling(t) = <dot>m</dot>air-flowcair(Tsupply - Tindoor) </math>

To get the constants (<math> a1, a2, a3, and a4 </math>), I need to keep the <math> Tsupply </math> constant and independently control <math> <dot>m</dot>air-flow</math> i.e. airflow rate set-points to the zones.

By reading the Engineering reference and other answers on this portal, I understand that I have to use

    1. AirTerminal:SingleDuct:Uncontrolled terminal for individual zones
    2. A constant fan / constant volume zone conditioning component to control the flow and a setpoint manager to control the temperature of the air flowing into the space.

However, I keep getting many errors (such as Thermostat needed for zone even though the terminal is uncontrolled).

Are there any example IDF cases that I can refer or any place where I can get detailed instructions. Thanks.

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Why are you using a constant fan / constant volume zone conditioning component if you want to vary the airflow rate? I would think that you would want a variable speed fan with a constant discharge temperature and a VAV box without a reheat coil.

You need a thermostat in the zone so EnergyPlus knows how to vary the airflow rate (i.e. it needs to know Tindoor(t) like in your equation above).

anchapin gravatar imageanchapin ( 2020-01-06 07:55:23 -0500 )edit

Thanks for the suggestion, I will try with the variable speed fan with constant discharge temperature.

I will add the Thermostat to the zone, but I want to manually control air flow rate. That is why I was using the uncontrolled terminal. Any suggestions on how to manage this issue.

Rohit gravatar imageRohit ( 2020-01-06 20:44:38 -0500 )edit

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answered 2020-01-07 08:00:20 -0500

If you would like to manually control the air flow rate, I would suggest checking out the suggestions in the following three unmethours posts which uses EMS to manually adjust airflow. I think that's the only way to do what you want.

  1. Overriding fan mass air flow in EMS
  2. How to overwrite the terminal box airflow
  3. How to set VAV mass flow rates by EMS?
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Asked: 2020-01-02 22:00:13 -0500

Seen: 375 times

Last updated: Jan 07