Enough Flow?


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Old 06-20-08, 10:58 AM
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Enough Flow?

Have a single 2.5 ton a/h v/s and a 2 ton compressor.

The fan speed is set at 350 cfm per ton or 700 cfm total.

This is a 1 1/2 storey house w/ 1,000 s/f down & 600 s/f up stairs.(Spray Foam Insulation)

To cool the upstairs, I have to all but close every supply duct damper that feeds the 1st. floor.---> 10 ea. 6" rigid pipe....( as a side note there are 3 ea. 8" return ducts on the 1st floor.)

Supply ducts feeding the upstairs (dampers wide open) are as follows--->2ea. 8" rigid pipe, approx. 40' in length...and approx. 5 ea. 90 degree fittings on each duct.......also 1ea. 6" rigid pipe going upstairs.

Upstairs there is 1ea. 10" return main trunk w/ 2ea. 8" pipe splitting off the main pulling air from the 2 bedrooms.

With dampers positioned as they are, I get a 3 degree differential between up & downstairs



My question is....With a educated guess (without doing a s/p test)with the 1st floor duct dampers being closed approx. 85 to 90% will this harm the system?


thanks for any response...
 

Last edited by Bpawb; 06-20-08 at 01:00 PM. Reason: sp.
  #2  
Old 06-20-08, 05:55 PM
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Oh I am sure its all good. Just so you can get a taste of whats happening go ahead and run as hard as you can for about a mile or two then stick a straw in your mouth and only breath thru your mouth and the straw and no cheating. Sounds good let it eat.
 
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Old 06-20-08, 08:14 PM
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No way would I do this! Sounds like just another bad install job. Have duct sized to meat heat load for 2nd floor.
 
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Old 06-21-08, 10:36 AM
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Not to mention that reducing air flow will ice up the indoor coil, further reducing air flow, possibly causing liquid return to the compressor. Which will kill it in short order. I'd open all the dampers first, then do a SP/cfm survey. Probably could up the airflow to 1000 cfm if the ducts can handle it. 400 cfm/Ton.
Tom
 
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Old 06-21-08, 06:34 PM
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Thanks for the replys !

Do you think if I opened all 10 of the 1st floor 6" supply dampers to approx 1/4 to 1/3 from fully closed position,

that I would increase the airflow enough that I would be safe as far as static pressure or any thing else goes
 
 

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