Improving Efficiency In Heating And Cooling
The symposium “Methods and Effects of Improving Efficiency of Unitary Equipment to Meet New Energy Efficiency Requirements,” held at the 2002 American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Winter Meeting, discussed the cost and benefit tradeoffs of moving to 12- or 13-SEER equipment, and described an improved heat pump design and modulating blower/compressor strategies for comfort control.
LIFE-CYCLE COST IMPACTModerator Piotr Domanski, Ph.D., National Institute of Standards and Technology (NIST), introduced the first speaker, Gregory Rosenquist of Lawrence Berkeley National Laboratory, who talked about “Consumer Life-Cycle Cost Impact of Energy Efficiency Standards for Residential-Type Central Air Conditioners and Heat Pumps.”
Life-cycle calculation (LCC) is an analysis that Lawrence Berkeley conducted on a representative set of buildings for the Department of Energy (DOE). Rosenquist said that 90% of the equipment studied was residential, the remainder commercial.
For a typical split-system air conditioner, the baseline manufacturing cost for 10, 11, 12, and 13 SEER, he stated, was $394 in each case. For installed cost, markups were what varied as you moved up to 13 SEER.
Looking at operating expenses, there was a 1% increase in repair costs for 11-, 12-, and 13-SEER equipment. Maintenance did not vary as the efficiency level increased. The compressor failed on average in the 14th year.
Examining energy price trends, Rosenquist said to expect energy costs to flatten out over time after 2006.
In determining the percentage of consumers who would benefit from 12 vs. 10 SEER as opposed to 13 vs. 10 SEER, with 12 SEER there is an increase in cost of $344; with 13 SEER, cost increases by $530. Therefore, for 12 SEER, 51% of consumers see the LCC benefit; for 13 SEER, 45% see the LCC benefit.
He concluded that, for air conditioning units, research showed that 12 SEER looked good for consumers because most benefit, but 13 is not attractive because it negatively impacts consumers. For heat pumps, however, the research indicated that both 12 and 13 SEER look attractive.
MINIMIZING FROST IN HEAT PUMPSThe next speaker, John Richardson Jr., P.E., of the Tennessee Valley Authority (TVA), talked about a new development: “A Frostless Heat Pump.” He said that Oak Ridge National Laboratory approached TVA to see if a method could be devised to retard the growth of frost in air-source heat pumps cost effectively. Richardson emphasized that the new methodology is not frost-free.
Current solutions, he said, are to reduce supply airflow, add resistance heat, use variable speed, or apply a new refrigerant mix. All of these result in higher cost.
The new operational scheme adds a moderate amount of heat for a warmer supply air temperature, which serves to reduce defrosting by a factor of five, stated Richardson. And this was accomplished cost efficiently.
Showing sample photos of a conventional heat pump and one with the new technology, he pointed out that a conventional unit will frost up in a test chamber over time. After 90 min, the whole unit was shown covered with frost. After 90 min with the new technology, there was minimal frost on the unit.
He concluded that this project validated experimentally a technology that reduced defrost cycles and improved indoor comfort, and was also cost efficient.
MODULATING FOR COMFORTClark Hubbard, a professor at the University of Illinois, then discussed “Modulating Blower and Compressor Capacities for Efficient Comfort Control.” He said that there are two approaches for air conditioning:
1. Handle sensible and latent loads separately.
2. Modulate refrigerant flow.
The test unit was an R-410A system operating in a mild, humid baseline condition, which is a tough dehumidification application, Hubbard noted. The system was in a single-family residence, running with varying blower and compressor speeds.
A slower airflow means more air to move. Going from 500 to 200 cfm, system energy efficiency at 200 cfm provides only about an 8% improvement. However, there is a substantial comfort improvement, going from 61% to 57% rh.
When you reduce blower speed at normal compressor speed on hot days, the primary benefit is reduced indoor humidity. The energy savings are small.
When you reduce blower speed at low compressor speed on moderate days, you save energy. Airflow of 400 cfm saves the most energy.
He concluded that you can increase energy efficiency by reducing temperature lift, mainly on the high side. This requires a variable-speed blower to maintain comfort. Substantial energy savings are available, he said, but as a college professor, he doesn’t know what the cost is.
Publication date: 03/18/2002