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Old 06-29-2009, 12:16 PM   #1
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Capacity loss with line size


I came across the table below in the Service Manual for Goodman heatpumps. I have a new 5 ton unit awaiting a lineset install. I have a 7/8" set with a 20-25 foot effective run. My reading from the table is that all units from 42000 BTUH and up really need a 1 1/8" suction line to avoid a substantial loss in capacity. Especially mine which--extrapolated out--would have its capacity reduced to 95% with a 7/8" line.

The 36000 BTUH systems fall off the most if a 3/4" line is used.

The spec sheet for my particular unit indicates use of a 7/8" line up to 50' effective run. The installation manual says to definitely add a 7/8" to 1 1/8" adapter at the compressor end, without mentioning the specs.

My system is rated at 16 SEER. I suppose a reduction in capacity might also mean a reduction in SEER to 15, if the same electric power draw applies.

Anyone have any comments on this?



Quote:
Table 4 lists multiplier values to recalculate system-cooling
capacity as a function of a systemís equivalent line length (as
calculated from the suction line) and the selected suction
tube size. Table 5 lists the equivalent length gained from


adding bends to the suction line.
Properly size the suction

line to minimize capacity loss.




TABLE 4. CAPACITY MULTIPLIERS AS A FUNCTION OF

SUCTION LINE SIZE & EQUIVALENT LENGTH







Nominal____Vapor____EQUIVALENT LINE LENGTH (FT)
capacity______line
BTUH__________Diam.(in)____50_____75____100____125 ____150
__________________________________________________ ____________



18,000________3/4_________.99____.97____.96____.95____.95


24,000________3/4__________1_____.99____.99____.98____.97

30,000________3/4_________.98____.97____.96____.95____.94

36,000________3/4_________.93____.90____.86____.83____.79
______________7/8_________.98____.96____.94____.92____.90

42,000________3/4_________.93____.90____.87____.83____.80
______________7/8_________.97____.96____.94____.93____.92
____________1-1/8__________1______1_____.99____.99____.98

48,000________3/4_________.90____.86____.82____.78____N/R
______________7/8_________.96____.94____.93____.91____.89
____________1-1/8__________1______1_____.99____.99____.98

60,000________7/8_________.93____.91____.89____.86____.84
____________1-1/8_________.99____.98____.98____.97____.97


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Last edited by Einride; 06-30-2009 at 07:01 AM. Reason: Fix spacing on table headings
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Old 06-29-2009, 04:10 PM   #2
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Capacity loss with line size


You will get better than a 95% multiplier for the 7/8" vapor line with a 25 foot lineset (the extrapolation is not linear). So your "16" SEER may only be reduced to 15.5 SEER. You're going to have more losses elsewhere in a typical system (coil matching, air handler matching, ductwork, filters, etc). If you can change out the lineset, by all means so so, but I wouldn't lose any sleep over it if you can't.

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