22-12-2012, 05:12 PM
A Report Prepared for Urban Green Council by Steven Winter Associates April 2011
1A Report Prepared.pdf (Size: 3.26 MB / Downloads: 25)
ABSTRACT
This study examines the impact on thermal performance of building
envelope penetrations associated with distributed heating, ventilating, and
air conditioning (HVAC) equipment such as window air conditioners (ACs),
sleeved ACs, and packaged terminal air conditioners and heat pumps (PTACs
and PTHPs). Physical testing of sixteen di!erent AC and PTAC units in eleven
buildings revealed that the infiltration losses through leaks and poorly-fitting
installations are far greater than might be expected, and that the leakage
area associated with the average unit in this sample was six square inches,
the size of the rectangle on the cover of this report. Extrapolated to the New
York City residential housing stock, this corresponds to a hole equal to 60%
of a city block. The associated heating losses are estimated to cost in the
neighborhood of $150 million per year in excess fuel use, and result in the
emission of around 400,000 tons of CO# annually – about 1% of the city’s
annual total. In some individual buildings, the estimated average cost of fuel
to make up for winter thermal losses is comparable to the cost of electric
energy used in the summer for cooling.
The study finds the primary cause of the leakage to be a lack of long-term
integrity in the installation kits for window ACs and poor fit and sealing for
sleeved units and PTACs, especially in retrofit and replacement situations.
The causes of this poor performance start with the Energy E"ciency Ratio
(EER) standard, which measures cooling performance but provides no
constraints that would encourage designs incorporating e"cient air sealing.
Other causes include split incentives, where the building owner may supply
the equipment but the resident pays the electric bill, or the resident makes
the installation, but the building supplies the heat. Poor understanding of
cost e!ectiveness plays a role, since residents will often purchase a less
expensive window AC to either use in or replace a sleeve AC, with worse fit,
greater infiltration, and greater electric and fuel costs in either case.
Finally, the study evaluates a variety of o!-the-shelf products that can
reduce infiltration and thermal losses, in some cases dramatically, and
describes various alternative technologies that appear practical but have
not yet been widely deployed or, in some cases, developed. Innovations
in operations and maintenance, including improved installation kits,
are found to o!er the most immediate benefits, while development of
suitable split systems to minimize wall penetrations o!er the possibility of
greater improvement long-term. These proposals were integrated into the
recommendations of the Advisory Committee, which follow the study.
INTRODUCTION
This paper presents the findings of our work on the
impact of room air conditioners (ACs) on building
envelope performance and details the basic design
considerations of room air conditioners, the human
factors in their application, the negative impacts on
building envelope e"ciency, and the possible solutions
to those e!ects, both available and proposed.
We use “room air conditioner” as an umbrella term
here to describe three types of cooling systems:
window-mounted (“window AC”), through-the-wall
(“sleeve AC”), and packaged terminal systems such
as packaged terminal heat pumps and packaged
terminal air conditioners (“PTHPs” and “PTACs”). All
constitute a permanent or semi-permanent penetration
through the building envelope. The infrared image of
a multi-family building with through-the-wall sleeves
shown in Figure 1 qualitatively illustrates the nature of
the problem. This image was taken during winter from
the exterior of a building. The red and orange colors
indicate warmer exterior surface temperatures and
areas of concentrated heat loss.
A room air conditioner’s Energy E"ciency Ratio (EER)
rating is the sole industry standard used to compare the
e"ciency of di!erent units. It allows a simple way for
building owners, designers, and consumers to distinguish
between units of di!erent cost and design. Still, as we
discuss below, since this rating applies only to cooling
performance, it falls far short of properly characterizing
the total energy impact of room air conditioners for a
number of reasons.
WINDOW AIR CONDITIONERS
Window air conditioners are extremely common in
all types of housing. They can be installed in doublehung,
single-hung or casement windows. In multifamily
buildings, they may be installed by residents or
maintenance sta! and are typically not installed in all of
the rooms. The units themselves are usually purchased
by residents. However, in some cases where the building
owner pays the apartment electricity bill, an owner may
provide, install, and maintain window air conditioners as
part of an additional service charge. Typical dimensions
for window air conditioners range from 11 to 18 inches
in height, 18 to 26 inches in width, and 15 to 30 inches
in depth. On the exterior, where they protrude from
the building facade, they have louvers on three sides
to allow air to flow through the outdoor coil section
when operated during the summer. Manufacturers
usually include window gasket seals and adhesive
foams with the unit to prevent air leakage via unsealed
joints around the unit perimeter and the window frame.
With double-hung windows, accordion panels can be
installed and adjusted accordingly when the window
frame is significantly wider than the unit itself. Separate
installation kits are available for horizontal sliding and
casement windows. In NYC multi-family buildings, it
is very typical for window air conditioners to be left
in place year-round, since 1) winter storage space is
usually not available, 2) residents typically do not pay
for heat, and 3) no one enjoys lifting the units out of
windows. Air-leakage pathways exist both through and
around the window AC units. In double-hung windows,
the installation of a window unit also results in a gap
between the two sashes (red arrow in Figure 3).
THE ROOM AIR CONDITIONER
MARKETPLACE
There are major di!erences in the way that room air
conditioners are marketed and purchased. PTACs are
in a separate class altogether in this respect, in that
the decision for their inclusion in the building is made
early in the design process. Their e"ciency is a design
decision made by a developer or designer and not by
an individual resident. They are not easily or cheaply
retrofitted into existing buildings. Window and sleeve
units are most often purchased by individual tenants and
lend a more direct comparison. In terms of cost, sleeve
units are much more expensive due to design factors
and the comparatively smaller volume of units produced
annually. For example, a typical Friedrich 8,000 Btu per
hour window unit costs approximately $200, while an
equivalent sleeve unit from the same company costs
about $400. To sell window air conditioners, major
appliance manufacturers are often paired with big-box
retailers in order to corner large segments of the market
(e.g. LG with The Home Depot, GE with Wal-Mart and
Frigidaire with Lowes). These major manufacturers and
retailers market the air conditioner units less like HVAC
equipment and more like convenience appliances. Their
lowest-price models sell for less than $100 and come
with very little in the way of support.