Use the following learning
objectives to focus your study while reading this month’s
ARCHITECTURAL RECORD / AIA Continuing Education article.
After reading this article, you will be able to:
the difference between types of heat pumps.
2. Describe how a heat pump works.
3. Discuss solutions to using
heat pumps in cold climates.
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 its 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 theyve 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 thats a bit like making
buildings into giant toastersresistance 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.