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Sizing-day run period failed to achieve the setpoint

asked 2018-12-12 03:17:17 -0600

zahro gravatar image

updated 2018-12-12 08:55:30 -0600

Hello, I am learning to use Energy Plus as a sizing software to calculate my HVAC system cooling capacity. I defined the constant temperature for the setpoint schedule in my design-day and scheduled setpoint for the annual simulation to reduce the unmet hours when the AC was turned off. I defined it using the schedule:compact feature in energy plus, as described in the image below.

image description

I did the sizing run period in the model, but when I looked into it, the temperature was not reaching the setpoint that I set.

image description

What I understand is that the result from sizing run period would be used as the baseline to calculate the component capacity. Do I make some mistake in the model input so it could not reach the setpoint temperature in sizing period? I worried that this condition would make my equipment sizing undersized because it could not reach the setpoint. Is that correct or not?

This is my sizing:zone definition for the model. image description

I would be happy if someone could give me some recommendation or clarification regarding my problem.

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answered 2018-12-14 16:28:20 -0600

You are correct that the sizing period simulations are the basis for the sizing calculations. Without a description of the HVAC system, it's hard to say for sure why the system isn't maintaining setpoint. Check the system description (especially setpoint managers and schedules) to make sure the system is controlling to the same supply temperatures specified in the sizing objects.

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I figured out the reason why my model could not achieve the setpoint during sizing calculation. Because I have an office building, the HVAC system has a system operation schedule based on the office operational hour. When I put the HVAC always on for the sizing calculation, it can achieve the setpoint all time during sizing calculation. Am I doing right for this?

zahro gravatar imagezahro ( 2018-12-19 03:23:12 -0600 )edit

I also want to check, is there any difference between HVAC sizing period and annual weather period, that we need to be careful about, other than the setpoint schedule and system operation schedule? Thank you

zahro gravatar imagezahro ( 2018-12-19 03:24:26 -0600 )edit

Make sure that every schedule is appropriate for the WinterDesignDay and SummerDesignDay day types. Common design practice is to turn off all internal gains (lights, people, equipment) for sizing heating, but these should all be active when sizing for cooling (usually same as a normal weekday, unless the building has special events that should be allowed for in the sizing). Also, note that the standard winter design days in the ddy files have zero solar (clearness = 0).

MJWitte gravatar imageMJWitte ( 2018-12-20 12:05:28 -0600 )edit

Thank you very much for the explanation

zahro gravatar imagezahro ( 2019-01-03 02:25:46 -0600 )edit

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Asked: 2018-12-12 03:17:17 -0600

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Last updated: Dec 14 '18