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Can EnergyPlus simulate the temperature variation inside a walk-in cooler/freezer when using the Refrigeration:Walkin model?

asked 2022-11-09 16:24:39 -0500

Zakaria's avatar

updated 2022-11-12 06:56:51 -0500

I am trying to simulate a walk-in freezer in EnergyPlus using the Refrigeration:Walkin model and see how the internal temperature of the walk-in freezer evolves.

I used the example of the SupermarketDetailed in the E+ documentation (without modifications), where a walk-in freezer was simulated to better understand how the Walkin model works. The cold room freezer was placed in the "backroom" zone and characterized by an operating temperature of -2.2°C;

I set the Backroom Zone air temperature as an output, expecting it to be the temperature inside the walk-in freezer and below zero. However, I was surprised to find that the temperature was above zero (between 19.7 and 20.7°C).

So my question is: can we track the temperature variation inside the freezer? In other words, can the Refrigeration:Walkin model calculate the temperature variation inside a Walk-in freezer?

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@Zakaria can you try to attach your image again? It looks like it didn't work correctly the first time.

Aaron Boranian's avatar Aaron Boranian  ( 2022-11-11 09:53:14 -0500 )edit

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answered 2022-11-12 17:16:51 -0500

If you're looking for those specific outputs (air temperature inside the walk-in freezer and temperature of stored product within the walk-in freezer), then it doesn't look like EnergyPlus calculates this. For any object type, you can review their list of possible output variables that can be plotted on a time-series bases in the Input Output Reference. The Refrigeration:WalkIn object type's list of output variables does not include either of these variables that you're looking for.

For some further research, the Engineering Reference documentation is a good place to review calculations, assumptions, and other details for various simulation processes used by EnergyPlus. For the walk-in refrigeration, it doesn't explicitly state it, but it seems that EnergyPlus assumes that the air inside the walk-in freezer is at a constant temperature (the rated operating temperature input). The Engineering Reference section doesn't mention product within the walk-in freezer, but there is a restocking schedule input that sets a Watt of refrigeration load imposed on the system caused by stocking the walk-in with product warmer than the operating temperature. So again, it seems that EnergyPlus assumes that the product temperature is constant (likely also the operating temperature input).

The Engineering Reference does say that the walk-in freezer model is based on the ASHRAE load model, and provides the following reference:

  • Gosney, W.B., Olama, G.A.-L. 1975. Heat and Enthalpy Gains through Cold Room Doorways, Proceedings of the Institute of Refrigeration, vol. 72, pp 31-41
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answered 2022-11-10 17:08:54 -0500

I think you are misinterpreting the zone input for the Refrigeration:Walkin object. As the documentation states, it specifies the zone (or zones) adjacent to the walkin, in order to capture the heat transfer between the walkin and the adjacent zone(s). It does not define a zone that is comprised of the walkin.

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Thank you so much for your comment, it was very helpful. And yes, it is what I concluded from my deep research in the documentation. E+ can perform 4 main functions.

 1. Calculate the electric consumption of walk-in coolers;
 2. Determine the impact of refrigerated cases and walk-in coolers on zone cooling and dehumidification loads;
 3. Calculate the electric consumption and COP of the compressor;
 4. Determine the total amount of heat rejected by the compressor rack’s condenser;
Zakaria's avatar Zakaria  ( 2022-11-12 07:40:45 -0500 )edit

I am new to EnergyPlus and am trying to simulate a walk-in freezer and get both the temperature fluctuations inside the freezer and of the stored product as an output. I am wondering if you know how to perform this type of simulation. I would be grateful if you could help me. Thank you in advance.

Zakaria's avatar Zakaria  ( 2022-11-12 07:58:12 -0500 )edit

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Asked: 2022-11-09 16:24:39 -0500

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Last updated: Nov 12 '22