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Why is my minimum setpoint not met?

asked 2021-06-10 00:28:19 -0500

Wolfgang Kaiser gravatar image

Hi all,

I have a dual thermostat 15 and 25 but my zone never reaches 15 despite having Alaska as my region. It always goes back up around 16 and 17. Why does this happen?

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answered 2021-06-10 09:25:43 -0500

Sounds like there is not enough load leaving your zone to take the zone temperature below the heating thermostat setpoint (15 C in this case), which is the only time your heating equipment will come on and maintain that setpoint.

This is very common in interior zones since significant natural cooling really only happens in the perimeter zones of a building. If this is a perimeter zone, you should look at your window size and material properties, as well as infiltration and other zone loads (people, electric equipment and lights). The balance between those parameters are probably such that they are offsetting each other. For example, let's say your windows are providing -1000 W, but your internal loads are 1200 W, which will cause your zone temperature to go up despite the temperature outside.

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answered 2021-06-10 01:14:24 -0500

Keigo gravatar image

15 for heating and 25 for cooling? If so, the result is reasonable. Between 15 and 25 is a deadband (uncontrolled range). If 15 for cooling and 25 for heating, you should avoid such settings. You should see such an error message.

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@Keigo well without the controlled zone, the zone temperature even reaches -23 but now I have these and the room is heated up at around 16 before its temperature reached 15. Why is that so?

Wolfgang Kaiser gravatar image Wolfgang Kaiser  ( 2021-06-10 06:12:34 -0500 )edit

@Wolfgang Kaiser so, your problem is overheat, right? What is your HVAC system? Autosize or manual input? If you could share your IDF file, I will check it in details.

Keigo gravatar image Keigo  ( 2021-06-10 06:46:29 -0500 )edit

No, it's actually not overheated it's just it does not come down to 15 and starts heating right at 16 instead of15. Sure, I will try to upload the file.

Wolfgang Kaiser gravatar image Wolfgang Kaiser  ( 2021-06-10 07:50:56 -0500 )edit

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Asked: 2021-06-10 00:28:19 -0500

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Last updated: Jun 10