HVAC sizing.

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flyinghigh Power-User Join Date: May 2008 Location: Arizona Posts: 355 Good Answers: 4	HVAC sizing. 06/21/2008 7:26 AM
	When sizing an HVAC unit and/or its ducting, do you add the frictional losses in both the return AND the supply, and compare the result to the inches-water-column capacity of the heat pump? IOW, if the return loss was 0.10"wc and the supply loss was 0.12"wc and your heat pump was rated at 0.3"wc, would you say that it would work, because 0.3"wc is greater than 0.22"wc?
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shogun7 Commentator Join Date: Dec 2005 Posts: 92 Good Answers: 5	#1 Re: HVAC sizing. 06/21/2008 9:46 PM
	yes!
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ChemP Member Join Date: Jun 2008 Posts: 6	#2 Re: HVAC sizing. 06/22/2008 1:44 AM
	yes it willl work , as it is a closed loop so the static head is nullified. But you should have cosidered pressure drops due to any strainers or control valves in the supply/return lines.As this will add to the total diff head. Regards ChemP
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flyinghigh Power-User Join Date: May 2008 Location: Arizona Posts: 355 Good Answers: 4	#3 In reply to #2 Re: HVAC sizing. 06/22/2008 5:48 AM
	The only strainer in the system would be the self-contained filter, which I assumed was taken into account by the manufacturer when he rated it at 0.3"wc. The only control valves would be the dampers in each duct, which I'm assuming cause minimal pressure drop when wide open.
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markar Power-User Join Date: Mar 2007 Location: Nothing sucks more than that moment during an argument when you realize you're wrong. Posts: 301 Good Answers: 22	#4 Re: HVAC sizing. 06/22/2008 8:55 AM
	The Manual "D" may address this or check out a Trane "Ductulator" Check out this site for reference material. www.acca.org __________________ You never know when it will strike, but there comes a moment when you know that you just aren't going to do anything productive for the rest of the day.
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CONWAYMECH Power-User Join Date: May 2006 Posts: 142 Good Answers: 3	#5 Re: HVAC sizing. 06/23/2008 7:40 AM
	GOOD GOD I CAN TELL FROM YOUR QUESTION YOU ARE NOT AN HVAC CONTRACTOR FROM NEW JERSEY. WHAT YOU HAVE DESCRIBED IS TSP AND YOU ARE RIGHT. INCIDENTALLY YOU ARE RUNNING THE STATIC ON THE SUPPLY ABOUT WHERE I WOULD RECCOMEND. IF YOU USE A "DUCULATOR" YOU CAN COMPARE THE VELOCITY TO THE RECCOMENDED 1000FPM ON RESIDENTIAL MAINS AND 600FPM ON THE BRANCHES. USE A VOLUME DAMPER AT THE TAKE OFFS AND SIZE THE BRANCHES FOR THE VOLUME AT 550-600 FPM AT THE MANUAL J VOLUME. RESULT LOW NOISE, EASY BALANCE AND IMPROVED COMFORT. PS TAKE THE RETURN AIR FROM LOW AND HIGH AND SUPPLY CAN ENTER AT ANY ELEVATION.
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flyinghigh Power-User Join Date: May 2008 Location: Arizona Posts: 355 Good Answers: 4	#6 In reply to #5 Re: HVAC sizing. 06/23/2008 9:41 AM
	Good morning, CONWAYTECH. One of these days I hope to get a Ductulator and a Manual J; in the meantime, my HVAC Prime software is showing 800 fpm in the mains, and 625 in the branch. The plan is for 2 main supply ducts, one of which has a branch; and 2 return ducts. All ducts have a damper, for ultimate control. The damper in the one main is downstream of the branch.
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ChemP (1); CONWAYMECH (1); flyinghigh (2); markar (1); shogun7 (1)

You might be interested in: HVAC Services, HVAC Controllers, HVAC Ductwork

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