Calculating Cooling Needs for Wine Cellar

For those of you building your own cellars (or at least thinking about it), I’m adding some documents to help guide you in calculating cooling needs.

First is a spreadsheet that lets you calculate your BTU needs, or at least approximate them.

https://www.dropbox.com/s/4ic366ysrw271tv/BTU%20Calculator.xlsx

(can’t upload here so link to Dropbox)

This may need a bit of explanation.

For “height and width” it should be obvious–that’s the dimensions of each wall (this assumes a rectangle). For ceiling and floor, use the length/width dimensions. All that really matters is that the two numbers when multiplied equal the square footage of that wall/floor/ceiling. Keep in mind that the “door wall” should omit the square feet for the door, and that should be entered separately.

Ambient temperature should be the highest typical temperature that will be on the other side of the wall. Because this has my figures in it (which you can replace after downloading) you can see I determined my basement doesn’t rise above 76 degrees. The room above it may rise to 82 if the AC is turned to its lowest point.

Note in the lower left you can set your preferred cellar temperature, which I put at 55. If you want it lower (or higher) that will affect the BTUs you need.

For the floor, I used ground temperatures, which I’ll explain how to calculate in the next post. (Here it is 67, which is the maximum soil temperature at that depth in Washington DC)

The temperature delta multiplied by square feet of space is what determines your heat gain (delta and BTU are both calculated for you).

Finally, enter the R value for the given wall. That depends on the amount of insulation provided by the wall, door, or flooring.

This all results in a total BTU need, which is the maximum you should need for your space. Most of the time you’ll need much less, because the temperature delta will be much smaller in the winter for example. The total BTU need can tell you the approximate size of AC that you need, and how often you can expect it to run.

Next up is a sheet that helps you calculate the average ground temperature in your location. This is important to figure out what kind of “heat” your floor will give off if you’re building a cellar in your, well, cellar.

Find your location to determine your average ground temperature.
GroundTemps.pdf (40.7 KB)

Finally, use this chart of variation in temperature to determine how much the ground temperature at your basement depth is likely to vary throughout the year. As you might expect, the deeper your basement the lower the variation in ground temperature.

In conjunction with the average temperature you can determine the approximate maximum ground temperature under your basement slab. That can help in calculating heat gain and thus cooling needs for your cellar.
groundtemps-variation.pdf (48.7 KB)

Wow, thanks Andrew, great resources!
Still looking at my temps in the new cellar to see what I need to do but thus far have been in the low 60s so may need to pick up a unit.

Andrew, I just tried your calculator and changed the #s for a room 8x10x8 and came up with 1200 BTU’s. Typical sizing calculators will account for lighting (3.4 BTU per watt) and human (600 BTU per person) loading.
From experience I can assure you that the current parameters will lead to undersized systems. Also keep in mind that adding a through the wall system will increase indoor ambients affecting the metrics, most systems will not achieve the BTU rating and ratings fall as ambients rise.
In the real world that 8x10x8 room will need closer to 4000 BTU’s.

Proceed with caution. $.02

Chris - I’m happy to adjust the spreadsheet so no one is misled or undersizes their cooling, but when you talk about sizing for humans and lighting, does that apply to a wine cellar? I could certainly understand the need for “loading” in a regular living area, but does that translate to what is essentially a closet?

In my case, the lights are on only when I’m in the cellar, and I’m only in the cellar for short periods of time. So while I may put ~800BTU into the cellar when I’m there, that’s for 10 minutes out of a typical day.

I have gone through this myself and agree that your numbers make sense. However you will find that if you don’t account for those other factors you will be outside the range of every manufacturers recommended sizing. If you undersize you will have trouble maintaining set point, humidity and a short life expectancy.

The calculator is a continuous load and you need overhead to pull down and real world factors, people, lights, infiltration, etc.

If I were building a system for that room it would be 1/5-1/4 HP and have a capacity of 2000-2500 BTU.

Do you have a document that lists Tulsa, OK? I see Oklahoma City listed. Tulsa is 100+ miles further north and east and a different growing zone (cooler), so not sure how much temps vary. I’ve reviewed data from the statewide organization that provides weather and ground temp data for agricultural purposes and I guesstimated the mean is about 58-59. Similar to Wichita. Any idea of how to confirm that data?

I pulled that off the web somewhere when I was doing the research. I think for these purposes the best you can get is a guesstimate.