ENERGY FOR A SUSTAINABLE WORLD - World Resources Institute

Detailed measurements in the late 1970s
revealed that obscure defects in houses' thermal
envelopes allow far greater heat losses
than were predicted by traditional heat-loss
models. Fortunately, auditing procedures aided
by instruments such as house pressurization
devices and infrared viewers now permit these
defects to be identified quickly. 28 Such audits
are much more costly than walk-through, noninstrumented
audits that many U.S. gas and
electric utilities offer. However, many of the
obscure defects discovered with instruments
can be corrected on-the-spot with low-cost
materials. When such improvements are made
at the time of the audit, the costly diagnostic
procedure becomes a very cost-effective way to
save significant amounts of energy, even in
houses with attic and wall insulation and storm
windows.
This "house doctor" concept was tested in
the Modular Retrofit Experiment by gas utilities
in New Jersey and New York in collaboration
with the Buildings Research Group at Princeton
University. In this experiment, a one-day,
two-person house doctor visit saved, on average,
19 percent of the gas use associated with
space heating. 29 Later conventional shellmodification
retrofits brought the total fuel
savings to an average of 30 percent, for an
average total investment of about $1,300. The
real rate of return on this investment, in fuel
costs savings, was nearly 20 percent. 30
The achievements demonstrated commercially
in the Modular Retrofit Experiment do not
represent all that can be done through shell
improvements in existing dwellings. One
reason is that energy-saving shell improvements
become more cost-effective when they
are accompanied by home improvements made
for reasons other than energy savings. For example,
if old windows are replaced to reduce
drafts, facilitate cleaning, or make a room more
pleasant, energy-saving windows are economically
attractive compared to conventional replacement
windows, even when replacement
windows cannot be justified on the basis of the
expected energy savings alone. Over the years,
there will be many opportunities to incorporate
new energy-saving features this way in typical
houses.
A second reason is that new technologies for
energy savings will continually be commercialized.
One experiment by Princeton University
researchers suggests the possibilities. These
researchers exploited unconventional retrofit
opportunities that brought about energy savings
of two thirds in a house regarded as
"thermally tight" by U.S. standards before it
was modified. 31
HEATING SYSTEMS FOR EXISTING HOUSES
The economics of efficient furnaces or heat
pumps tend to be much better in the replacement
market than in new housing because the
heat loads in the former are relatively large.
Even after major shell improvements, heating
requirements greatly exceed those in new
superinsulated houses. For example, if new
energy-efficient condensing gas furnaces were
introduced after the shell improvements were
made in the houses of the Modular Retrofit Experiment,
the fuel requirements for space
heating could be reduced to 44 percent rather
than only 70 percent of the pre-retrofit level.
Installing a new condensing furnace instead of
a new conventional furnace that costs $1,000
less would result in a 15-percent rate of return
on the extra investment. 32
Appliances in Industrialized and Developing
Countries. Water heating accounts for between
10 and 35 percent of residential energy use in
industrialized countries. In the United States
and Sweden, refrigeration accounts for one
fourth of residential electricity use. Lighting
typically accounts for about half as much electricity
use as refrigeration.
WATER HEATING Recently, gas-fired water
heaters that use only half as much fuel as conventional
units have become available, and the
most efficient new heat-pump water heaters
use only one third as much electricity as conventional
electric resistance units do. 33 55