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Posted by HeatPro on July 04, 2006 at 13:19:17:
In Reply to: Re-Calc: cut flow rates by 50% for 1/2" pipe limits posted by Eiclher on July 04, 2006 at 11:45:33:
Nope. - still applying the incorrect idea to the calculations.
"1.6 gpm max flow rate for a 1/2" pipe ."
a. You won't be having the full flow in the 1/2 pipe unless you force it to do so with too powerful a pump for your needs.
b. You still don't have the heat calculation of the entire house as a standard to start with. If the house load is 150,000 btuh, you have too little floor area to do the job. 2250 sq ft times 30 btuh max is 67,500 btuh, so the boiler needs 6.8 gpm @ 20 degree F drop. You will have the boiler at half load all the time until you turn on another load like an indirect water heater, jacuzzi or pool exchanger that you haven't mentioned yet.
c. I have no idea why you would think you could 'get away' with 2 gpm at any head for the entire house.
d, The instructions for the Knight say to use a boiler subloop with its own circulator on a main loop with its own circulator. You take your chances in performance AND warrantee when you don't follow manufacturer instructions. Your existing 1/6th horse circulator does the job with the NO head boiler already there, which proves the point of little need for a high-head pump, UNLESS you don't follow the manufacturer installation guide.
e. The tables made in the 1940's by Professor Warren Harris in Chicago include els and valves for 'normal' installations and have proven adequate for residential systems over theat time. Ordinary straight power conversions don't work as they don't include Reynolds numbers and pipe surface compensations. There are more sophisticated calculations in the ASHRAE guides.
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