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New heat pumps cool well but we need heat

12 years ago

It is time to replace our heat pump, even though it is only 30-years old and still works. It is a 4-ton Westinghouse Hi/Re/Li HP048D. We bought it from a Boeing engineer who recommended it for the unique valving that gave good efficiency at low temperature. He early on replaced a leaky outdoor coil and a bad valve and for the last 25 years all I have had to do was replace the motor capacitor, and the power contactor, which probably died because of the bad capacitor. But Westinghouse unique parts are long gone, and the $1,500 tax rebate will not be around much longer.

We live in a 2,400 square foot house near Seattle with tall trees to the south so we practically never use air conditioning (nor do we have much luck with tomatoes). During the coldest 4-5 months we use about 60 kWh per day in excess of our power usage the rest of the year. At $.10 per kWh it is painful, but not out of line for an old house that is impossible to seal well.

Given our need for heat, not cooling, I am not happy with what I see in modern heat pumps. Detailed performance data are painful to acquire, but what I have seen suggest they have been engineered for cooling, not heating performance.

Here are the published heating performance of our Westinghouse Hi/Re/Li HP048D versus a Trane XL16i (2nd stage) with a 4TEE air handler, both with 1,600 CFM 70 degree indoor air:

At 17 degrees outside:

Westinghouse: 4.40 KW in; 35,000 BTU out; COP = 2.33

Trane: 2.94 KW in; 27,600 BTU out; COP = 2.94

At 47 degrees outside:

Westinghouse: 5.80 KW in; 56,000 BTU out; COP = 2.83

Trane: 3.29 KW in; 43,000 BTU out; COP = 3.29

The newer unit is more efficient, but it will give us about 20% less heat at low temp. I interpret this to mean more time with the backup heat strips sucking up electricity. I haven not tried to analyze it, but suspect the net result will be a higher heating bill.

My first thought was to move up to a 5 ton unit, but our ducts are inaccessible and really do not seem to support more than about 1,600 CFM air flow, rather than the 2,000 CFM most 5 ton units expect. Switching the Westinghouse fan between slow and fast settings yielded hardly any change in measured air velocity. My understanding is that lower than spec airflow is likely to reduce compressor life.

I am not totally locked into the XL16i, but it seemed to have one of the better heat output numbers, plus good HSPF and COP. And during those hours when we can tolerate the 25-30% lower output of the 1st Stage, our long-suffering neighbors (their patio is very close to our heat pump) will appreciate the resulting lower noise level.

Are there better solutions than the 4-ton XL16i? Do any other brands or models give us better heat output given our airflow limitations? Manufacturer websites seem to be all fluff and provide appallingly little real data. And most heat pump salesmen seem to go blank when I try to explain what I am looking for.

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