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By Charles Linn, FAIA

This article is also available for Continuing Education credit here.

When David Shaw got a $400 electric bill in 1995, he was inspired. He had recently retired from his job as compressor designer and refrigeration engineer at the Carrier Corporation, and had moved into a New Britain, Connecticut, condominium that was heated and cooled by an air-source heat pump. “It worked great,” he says, “except when it got cold. The air-conditioning industry never developed a heat pump that could heat a home when it is really cold outside.” So, Shaw set up an R&D lab, Shaw Engineering Associates, and started developing the heat pump that could.

Everyone loves the idea of heat pumps, because it’s as if they give us something for nothing. Conventional air-source models heat or cool using thermal energy that is naturally present in the air, and their cousins, geothermal heat pumps, tap the heat that is present in earth or water. These devices “compress” this energy to yield temperatures required to condition interior space. Air-source types are commonly used to condition homes and small commercial buildings in the southern part of the U.S. and in many parts of the world. Yet they’ve always been very expensive to use where ambient outdoor temperatures begin to approach and go below freezing and, as the map indicates, that leaves most of the U.S. out in the cold. The reason for this is that as temperatures fall, heat pumps become less and less efficient. So, most use electric-resistance heating as a backup when a severe cold snap occurs. But that’s a bit like making buildings into giant toasters—resistance heating is not only terrible from an efficiency standpoint, but when hundreds of thousands of resistance heaters go online at the same time, electric utilities experience peak-loading. Their distribution systems are taxed, they must bring extra power plants online to meet demand, and they pay dearly to buy power from other utilities. Utility companies build these costs into their retail customers’ base rates.

 

Platts E Source expects that the low-temperature heat pump will be competitive with conventional heat pumps and central air in Zones 1 and 2. In Zone 3, utility companies would likely have to provide consumers with incentives to get them to make the switch. Image: Courtesy Platts E Source

The absence of viable low-temperature air-source heat-pump (LTHP) technology has left the geothermal heat pump as the only practical alternative for people who wish to use heat pumps in cold climates. The first-costs for these systems is higher than it is for fossil-fueled heaters because they are complex, and the systems that draw heat from natural sources can be difficult to install. Payback periods for them can be reasonable, but many urban and suburban sites are unsuitable because they lack either the real estate needed for ground loops or sources of water.