fuel savings math

dhghm

I am putting together a proposal for oil savings for boiler and domestic hot water savings the following is my projected savings does this math and savings sound plausable. 140 reduced to 120 degree water temp.(domestic hot water) 1 btu = 1 pound of water 1 degree f / 1 gallon water = 8.33 lbs. / 8.33 btu to raise 1 gal.1 degree f rise / 8.33 btu x 20 gallons per day(estimated per person use)1 degree f rise /166.6 btu per person-per day 1 degree f rise/3,332 btu per person -per day - 20 degree f rise/1,999,200 btu (300 apartment units-600 people estimate)20 degree f rise /1,999,200 btu @100 % eff./299,800 btu 15%eff. loss (85% eff system) / 2,299,080 btu per day waste / btu/gal.#2 fuel oil = 140,000 / 2,299,080 divided by 140,000 = 16.42 gals a day wasted / 16.42 x 365 days a year = 5,994.03 gallons. / 5,994.03 x $1.50 per gallon (estimate) = $8,991.04 per year waste Thanks for checking

John@Reliable_10

Be very careful when quoteing this................

Be very careful when quoting fuel savings in dollars. You will look foolish if it doesn’t happen. So many things can go wrong when you state savings. Like a new baby in house, or someone retires and is now home all day, kids start taking 3 showers a day just to name a few. PS where can you buy $1.50 oil today, because I really need some?

jerry scharf_3

I don't agree with that math

Hi,

There are a few cases to be sorted out.

For somone running how water down the drain, the numbers are as you say.

If you are talking about people taking showers/tubs/washing hands, they have a preferred water temperature. If you deliver 140F water, they will turn the hot ware down and the cold water up compared to 120F water.

There are standby and delivery losses that increase with hotter water, but they are not in the range you computed.

So you have to pull out your favorite divining method and decide how much falls into each category.

jerry

Chuck Shaw_4

Showers

I understand what you are saying, however, in Massachusetts, and I am sure elsewhere, showers are required to use a pressure balanced anti-scald valve. The temperature must be limited to 112 F. So, if the water is at 120 or at 140 or even 180, it will still be mixed below your "new temp". So, they may use 20 gallons at 120, or 15 gallons of 140 or 5 gallons of 180 (just using numbers here, no math involved).

You now have a certain number of gallons of cold street water coming in, that you have to reheat. Once you heat your initial stored capacity, you are only heating what is used.

Also, if you use a hotter storage temp, and mix down for delivery to the fixtures, you will have an effective larger capacity, so, you might be able to use a smaller tank, which is most likely less money to purchase.

I am also very careful about quoting $$$$ savings, I can see nothing good coming from doing that, in the long term.

Just some things to think about

Chuck Shaw

Constantin

You're not going to save that much...

... like others have correctly pointed out, the DWH BTU load isn't going to go down significantly just because you reduce the storage temperature by 20°F. The standby loss difference for the piping will amount to something, but not that much....

No, if you're serious about reducing the energy used for DWH consumption, propose a GXFTechnology heat exchanger instead. These use the warm water coming down the DWV pipes to pre-heat the water going into the indirect hot water tank. That's where you're going to see the kind of payback you're calculating above because you can obviate up to 40 degrees of temperature rise.