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Why the internal temperature of the model started from a value close to the setpoint temperature, rather than starting from room temperature like a real-world scenario. [closed]

asked 2023-04-03 03:17:59 -0500

Zakaria's avatar

updated 2023-04-05 00:34:19 -0500

I have a question that troubles me a lot and I would like to have some clarification on it.

Let's imagine that we have a freezer in the real world, which has been stopped at t=0. The internal temperature would be around room temperature. At t≠0, the freezer starts running, so the internal temperature drops to the desired temperature, and then it stabilizes due to on/off cycles of the compressor.

It is not the same case in EnergyPlus. I ran a freezer model and the temperature started from a value close to the desired temperature, as if the refrigeration system was already working.

Any explanation as to why EnergyPlus is doing this?

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Closed for the following reason the question is answered, right answer was accepted by Zakaria
close date 2024-01-28 06:36:16.583453

Comments

For which E+ application/model: walking-in freezer? refrigerated warehouse? As suggested previously by Aaron Boranian here, I don't think E+ outputs "freezer" temperatures at runtime. How did you manage to track these temperatures? My understanding is that E+ product refrigeration models assume ~continuous operation. Sure, there are restocking schedule inputs, yet unlike what you're describing.

Denis Bourgeois's avatar Denis Bourgeois  ( 2023-04-04 14:04:07 -0500 )edit

I was talking about a refrigerated warehouse, but after thinking about it, I concluded that in the real case, the refrigeration system in the warehouse is already runing, and then you add the products to the warehouse. So it is normal that the temperature starts from a the desired point.

Zakaria's avatar Zakaria  ( 2023-04-05 01:19:06 -0500 )edit

OK. Thanks for clarifying. You could summarize your observations as an answer to your own question.

Denis Bourgeois's avatar Denis Bourgeois  ( 2023-04-05 05:57:03 -0500 )edit

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answered 2024-01-28 06:22:58 -0500

Zakaria's avatar

updated 2024-01-28 06:41:12 -0500

I've done some digging and discovered that EnergyPlus conducts a series of preliminary checks, known as warm-up tests, prior to initiating the specified run-period simulation.

In these warm-up tests, the initial settings are configured with surface temperatures at 23°C and zone humidity ratios matched to the outdoor humidity ratio. The system then continuously repeats the environmental conditions of the first day until it either meets the convergence tolerance values for loads and temperature as outlined in the building object or it hits the pre-set maximum number of warm-up days, which defaults to a minimum of 6 days and a maximum of 25 days.

And you can report the simulation data during the warmup period using the **ReportDetailedWarmupConvergence** and **ReportDuringWarmup** in **Output:Diagnostics** object.

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Asked: 2023-04-03 03:17:59 -0500

Seen: 110 times

Last updated: Jan 28