Is SEER Driving HSPF Down for Heat Pumps?

I enjoyed the “SEER Ratings Challenged” article and Mike Murphy’s editorial “Efficiency Gaining Ground, Again” in the July 23 issue. These were of specific interest because of my involvement in the marketing of heat pumps in colder climates for over 20 years.

In Nebraska, with averages of 6,500 heating degree days and 1,000 cooling degree days annually, SEER is certainly important, but HSPF is even more important from a total energy-savings perspective. We have over 20,000 satisfied heat pump owners in our service area who derive the bulk of their annual energy savings in the heating mode.

SEER seems to have been the marketing focus from an efficiency perspective. However, we are beginning to see that when heat pump efficiencies approach the 15 SEER level, there is a potential that the HSPF will actually begin to decline.

The integrated performance curves for some heat pumps in this category drop off more quickly than those of comparable heat pumps with a lower SEER. That results in higher thermal balance points and a heat pump system that must switch to its secondary heating source at a higher ambient condition in order to meet the load of the home.

The end result is lower overall energy savings, particularly in those instances where the heat pump is dual fuel and the secondary energy source is more expensive per Btu.

In visiting with various HVAC dealers and manufacturers, it appears that in the quest for higher SEER, HSPF can be reduced. Manufacturers are designing for lower system pressures to lower work load on the compressor, which in turn lowers wattage and discharge pressures while raising efficiencies.

That’s great on the cooling side, but in heating, lower discharge pressures and temperatures reduce heating capacity.

Pressure and temperature can’t be increased without increasing watts and thereby decreasing efficiency.

Ultimately, matching the heat pump and indoor coil takes on additional significance from a perspective of specifying equipment that gives the homeowner the best combination of both heating and cooling efficiency. And in colder climate environments, that might mean selecting a lower SEER to deliver a higher HSPF, greater energy savings, and overall efficiency.

Our review of this issue has been nothing more than cursory to date, but we do see a trend developing. Energy efficiency is important to all of us in the HVAC industry in providing customer value.

That is equally important within the electric utility industry, as is optimizing the utilization of generation resources and making the most effective use of limited natural resources.

I suspect there are a number of utilities that would appreciate a national look at the relationship between SEER and HSPF.

Dave Swett
Omaha Public Power District
Omaha, Neb.

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Publication date:08/06/2007