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# HOT WATER COIL

Member Posts: 3
I HAVE A LARGE COMMERCIAL AIR HANDLE WITH A HOT WATER  HEATING COIL. THE UNIT IS APPROX. 40 YEARS OLD.  NO ID NUMBERS.  ALL I  KNOW IS THE TON-AGE OF THE COOLING SYSTEM . HOW CAN I ESTIMATE THE OUTPUT OF THE HEATING COIL.  THANKS FOR ANY HELP  FRED

• Member Posts: 2,144
Hot Water Coil

I would look up coils in the"replacement coil manufactuers" catalog.You will need l x w x d x h. Also tube size ,fins per inch, water temp in/out and air temp in/out and how many passes the water goes thru the coil
• Member Posts: 1,380
Try This...

Use the sensible heat formula, which will get you very very close. Here goes...

With the blower operating, determine the temperature of the air before and after the coil to establish your delta-T across the coil. Next you need to determine the air volume through the coil. You will need a velometer for this. To get an accurate reading of the velocity, you will need to take a traverse, which is basically the average of multiple air velocity readings. The third thing you need to know is the area of the coil, or the duct, in square feet. I know this all sounds complicated, but it's very straightforward.

Now that you have the area, velocity and the delta-T across the coil, your heat output can be found by:

Qs = 1.08 x velocity (feet/min) x Area (Square feet) x delta T

Have fun and let us know how you make out!
• Member Posts: 2,397
Re: the btu formula

Eugene, should he also set his water temp from boiler to what he would like to size new coil to. Maybe 150 inlet water temp. Then take his delta t as outputs if I remember right are not linear?
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