Laundromat Gas Allocation Percentage

[Howard]

Was doing some cost analysis today using very detailed numbers from my card system along with utility bills and was very surprised to find (for my store atleast) that the old rule of thumb of 50% of gas used for hotwater and 50% for drying clothing does not even come close to applying.

I made serveral assumptions. First I assumed that customers used Hot water for 75% of the washes and warm for 20% with only 5% of washes being done in cold. Next I assumed that on average I was heating incoming water from 50 degrees to 125 degrees as a year-round average. Lastly I assumed that my water heating system had an overall efficiency of transfering heat from BTUs of natural gas burned to the water of 90% (units rated at 95%). When all this was said and done I came up with 25% of the purchased gas being used for water heating and 75% being used for a combination of drying and heating the store (winter-time).

Anyone else have similar experience???

[azkid]

I ran the numbers with a formula from a old thread on this topic on this board or coinwash 1-2 years ago now. My assumptions were a little different - I assumed I was heating the water from 70F and I have no furnace to worry about (Arizona). I came out to within 5% of the 50/50 figure.

I don't think the 50/50 swag is supposed to include heat loads, but I could be wrong. Anyhow, for my store it's accurate enough.

[Howard]

Well you are in a much warmer climate, so maybe heating from 70 is valid - but it still seems kind of high. Are you saying that your cold tapwater is 70 degrees?

I felt in most accurate to throw the space heating load in with the dryers for the reason that the heat only runs a portion of the year, and when there is much of any business the heat does not even run as heat loss from the dryers pretty much heat the store.

I am quite confident in my engineering calculations to come up with the water heating demand.

[azkid]

I think the cold tap is about that here in the summer at least. Another significant difference is that I only used 80% efficiency for my HW heaters (they're about 10 years old). After running the calculations, I think I ended up with something like 45/55 (HW vs dryers). I used my actual billed useage amounts, so I'm confident about my numbers also (of course the assumed hot water selection percentages are a factor too, but I think I was close to yours).