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How can I confirm that my model is working properly?

I was given a model that was fully operational.

So I removed the whole functional, yet obsolete, HVAC system and inserted a new one with ideal loads, for I need to know what are the exact loads that the building is experiencing and refurbish the envelope accordingly.

The thing now is that, after running my new model and comparing it with the former one, I seem to have loads that are around 4 to 7 times higher for each zone.

I mean, the former HVAC system was really poorly designed, but THAT poorly? It is also known that the building's envelope is terrible when it comes to thermal insulation.

Or is it likely that my new model isn't running properly?

sirYESsir's avatar
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sirYESsir
asked 2017-06-21 09:00:42 -0500
Julien Marrec's avatar
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Julien Marrec
updated 2017-06-26 15:49:09 -0500
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What do you mean by "loads"? Do you mean the total heating energy for the year? Or the Peak Heating rate?

Julien Marrec's avatar Julien Marrec (2017-06-26 15:53:46 -0500) edit
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I was referring to the total heating energy.

I also solved my problem already. It seems like I was comparing the sensible heating energy of the initial problem with the total heating energy of my new model, which included the internal gains.

So instead of having 4 to 7 times difference, I have 2 to 3 now. Solved!

sirYESsir's avatar sirYESsir (2017-07-05 09:50:28 -0500) edit
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1 Answer

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The original system likely had unmet hours - periods of time where the setpoint wasn't achieved. The ideal loads case will always meet setpoints resulting in higher heating or cooling loads. 4-7x more seems excessive, but checking how far off setpoint the original model was will tell you if that's legit.

ljbrackney's avatar
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ljbrackney
answered 2017-06-21 09:16:10 -0500
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Thank you for your answer, Ljbrackney.

In fact, my ideal system is having 1200 hours not met, against 4000 of the original one (out of 1 year).

  • Is this difference big enough to justify the differences in loads?
  • And is it normal that my ideal system is having unmet hours?
sirYESsir's avatar sirYESsir (2017-06-21 09:26:27 -0500) edit
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So 4x unmet hours - that could translate to the kind of load variation you're seeing. One of the E+ guys can chime in on your ideal air load unmet hours. My understanding is that ideal air loads should achieve setpoints with as much district heating or cooling as is needed, but I could be wrong.

ljbrackney's avatar ljbrackney (2017-06-21 09:47:09 -0500) edit
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Contrary to OpenStudio where the idealLoads is a checkbox, the EnergyPlus ZoneHVAC:IdealLoadsAirSystem can be customized quite heavily, including input for the heating/cooling limiting values, availability schedules for heating/cooling, etc. All of which can easily lead to 1000 unmet hours.

Julien Marrec's avatar Julien Marrec (2017-06-26 15:52:56 -0500) edit
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