What capacity rating should be used for sizing ductless heat pump?
The easily obtainable heating capacity information for ductless heat pumps are generally listed as Btu/h at 47 degrees and Btu/h at 17 degrees. These don’t appear to line up with the expanded capacity charts which can (sometimes) be found with some digging on manufacturers websites. Let’s look at the Fujitsue ASU9RLS3:
It’s capacity is readily reported as:
7,0000 Btu/h @ 17 degrees
12,000 Btu/h @ 47 degrees
However, if I look up the expanded heating capacity chart, it reports the Total Capacity as (assuming 70 degrees indoor temperature):
16,000Btu/h @ 14 degrees (the closest on the chart to 17 degrees)
22,000Btu/h @ 47 degrees
Both of these numbers are significantly higher than what is indicated on the spec sheets from suppliers.
In some previous posts about sizing, I recall Dana Dorsett specifically referencing these charts when sizing and using the Total Capacity numbers. What is the difference here and which numbers should I use for sizing?
Manual J calls for 16,000 Btu/h. 15 degrees is design temp.
If I go by first set of numbers, the 9RLS3 is too small and even the 15RLS3 won’t be enough.
If I go by the expanded capacity chart and Total Capacity number, the 9RLS3 would be more than enough.
What am I missing? Thanks in advance.
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