indirect DHW BTU demand?

CC.Rob

perfect. thanks.

CC.Rob

indirect DHW BTU demand?

Is there a simple means to estimate the BTU demand of an indirect water heater? Say 40 gallon unit like AO White, Burnham Alliance? See much on first hour ratings, but seem to draw a blank on finding simple demand. Thanks.

Brad White_9

If you know your GPH

of hot water (Fixture Units/Hunter's Curve or whatever demand rate method you choose):

GPH x 8.34 x Delta-T = BTUH

Delta-T is (outlet temperature minus inlet temperature)

GPH x 8.34 converts gallons per hour to lbs. per hour.
The temperature rise (another variable you dictate) goes directly to BTU's.

Beyond that you can figure a known jacket loss in degrees per hour to top off the calculation.

First hour rating of course is the tank volume plus input as a steady state, starting with a hot tank (you knew this of course). The numbers you figure will likely vary because in actual practice the first hour is diluted by incoming water. The rating values do not always take that into account so the above is the way to cross-check.

Hope this helps.

Brad

Brad White_9

Remember though

what you and I have been figuring is net input to the unit. Actual fuel usage should be derived by dividing by the efficiency of your supplying boiler plant (e.g.: 0.85 for 85% efficiency).

Good Luck.

Brad