Posted by Larry on April 11, 2001 at 07:57:55:

In Reply to: Ours, and most other plants, posted by MikeH on March 27, 2001 at 01:25:36:

: use just such a heat exchanger for preheating incoming make-up water.

I've decided to recommend that, but I'm trying to figure out the energy savings (for payback analysis).

The boiler is used to heat a water pit up to 140 degrees and they are currently heating freshwater (from approx 65degrees)

I want to use a flat plate heat exchanger (for the area tradeoff) for make up that will utilize approx. 110 degrees for the make up.

(all temps are in degrees F)

In trying to find the mass flow rate, I used the fact that they use 5 million gallons a month, which is approx. 115.7 gall/min and

15.464 cubic ft/min (which is the volumetric flow rate).

To find the energy savings, I think I should use the equation:

Q=(eff. of ht. exchanger)*mdot*Cp(TempH - TempC)

in order to find the differences in using 65F and the additional 110F for makeup.

But I'm not sure if that's the equation I should use or even how to use it without knowing the velocity or area.

Please tell me where I should go from here...