Modelling heat loss from an outdoor heated pool using tools/inputs intended for basements

asked 2022-11-09 20:42:01 -0500

willyJohan
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updated 2022-11-17 10:59:19 -0500

I'm hoping to model the impact different levels of insulation would have on heat loss from an in-ground pool.

I'm thinking this is basically just a basement with water instead of air and plan to model it as such.

I'm wondering if there is a way to account for the difference between air and water when modelling convective heat transfer as i assume this will be the major issue with this model.

Also curious to hear folks' general thoughts on how best to model heat transfer from an in-ground pool.

Thanks in advance.

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As an experiment, I modified the "ZoneCoupledKivaBasement.idf" example file, removing the ground floor zone, making the basement ceiling adiabatic, extended the wall and floor insulation to the full extent of those surfaces and updated other various inputs to be more pool like. I then ran few different insulation levels and compared the results to a pool with the same properties modelled using NRCan's Enerpool tool. The results were very similar for R12 (34 GJ vs 35 GJ) and a bit different for no insulation (57 GJ vs 66 GJ). However, I have no idea which result is more accurate.

willyJohan ( 2022-11-11 14:18:50 -0500 )edit

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answered 2022-11-18 04:13:04 -0500

Jim Dirkes
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A pool is indeed a basement as far as conduction through its walls is concerned. The pool water temperature is the "room" temperature setpoint, so it's normally around 80F / 27C - a bit higher than is typical for rooms. My preference for accuracy would be KIVA, but I'm pretty sure that conduction is the small part of your heating load...

The majority of the heating load will be caused by evaporation, especially when pool walls are insulated. This is true even more so for an outdoor pool. I have used the Shah method for calculating evaporation for both pool locations, then applied the evaporation load to a water heater as an EnergyPlus "OtherEquipment" object as the load. I am confident it's a reasonable approach, but am unaware of any pool studies which compare predicted performance against actual performance.

ps, E+ has a swimming pool object that I have not used, but should be worth investigating.

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Thanks Jim. I am specifically looking a the impact of insulation, so the relative impact overall is less important to me. Any thoughts on how to account for the different convective heat transfer coefficient of water vs air and (what i assume will be) the higher U-value of interior surface films? Can these be specified by the user somewhere? Also, the E+ pool object is for indoor pools only and seems to be more about modelling surface heat transfer than Wall/floor conduction.

willyJohan ( 2022-11-18 13:51:09 -0500 )edit

For a wall, the impact of the "air film", which contribute to the overall U-value, is greater/lesser depending on air speed adjacent to the wall. Water would be the rough equivalent of a strong wind.

I have not paid attention to that air film value in E+, largely because any insulation at all has an order of magnitude higher impact (and a few other reasons). Since the air film R-value becomes smaller at higher air speeds (check the values in the ASHRAE Fundamentals handbook), you might consider reducing the R-value for the pool wall slightly to "fudge" the impact.

Jim Dirkes ( 2022-11-18 15:13:18 -0500 )edit

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answered 2022-11-30 17:31:30 -0500

willyJohan
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updated 2022-11-30 17:42:57 -0500

I've decided to just go with EnerpoolPro which allows the user to report all the hourly outputs necessary for any sort of analysis. I wish I understood better what was going on under the hood but if its good enough for Canada its good enough for me, not exactly the answer to my original question but though I'd add it here in case anyone else needs to do a similar analysis.

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Modelling heat loss from an outdoor heated pool using tools/inputs intended for basements

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Modelling heat loss from an outdoor heated pool using tools/inputs intended for basements