High-Tech Air Conditioning: Costs and Benefits:
When considering the purchase of a new air
conditioning system or even the renovation of an
old one few consumers are able to determine what
is best for their home. The number of
manufacturers, the variety of components of a
system, the quality range of contractors and the
wide spread of cost estimates for installations
make for well founded consumer confusion.
Of primary importance is the separation of fact
from fiction about the "as installed"
efficiencies of the new equipment. The
efficiency of an air conditioning system is
rated on a scale called the Seasonal Energy
Efficiency Ratio. The SEER is a relative measure
of how much cooling you get from the electricity
the unit uses. The fact is that SEERs range from
a low of about six (typical for equipment
manufactured in the 1970s) to a high of around
14. The fiction is that you can expect to
achieve very high efficiencies when you retrofit
new equipment to older existing duct systems.
Before you buy a new compressor or condensing
unit for an older ducted system, investigate to
be sure they are compatible: too often a
combination of the two results in little or no
savings.
CONDENSING UNIT:
The expensive mechanical part of central air
conditioners is the outside condensing unit. It
generally lasts 8 to 14 years and tends to fail
when working hard in hot and humid worst
weather. When your air conditioner fails, you
can usually get it operating again by simply
replacing the condensing unit, or even just the
compressor in the condensing unit. Replacing a
compressor is usually the lowest cost
expenditure that will "fix "your unit but it
won't improve the efficiency.
At some point, consideration should be given to
spending extra money to buy high efficiency gear
to lessen your utility bills. Unfortunately,
however, the decision is complicated by the fact
that some gear will not work at its normal high
efficiency when installed as a single outside
piece or as part of a restrictive duct system.
You can often estimate your air conditioning
costs by subtracting your monthly winter
electric bills, provided you don't have electric
heat, from the monthly summer bills. If other
activities have been roughly the same, the
difference can probably be attributed to the
electric air conditioning, although you have to
make allowances for seasonal price variations.
Once you figure how much it costs to run your
air conditioning, you can determine your total
savings using more efficient gear by comparing
the Seasonal Energy Efficiency Ratios of the
existing gear with that of the planned
replacement gear. Your local dealer should have
a book which lists the SEER and date of
manufacture of most existing air conditioners by
serial number.
The SEER, as noted earlier, measures the amount
of cooling against the amount of electricity
consumed. A unit with a SEER of ten will use
half of the electricity of a unit with a SEER of
five. The wider the difference between the SEER
ratings of old and potential replacement
equipment the greater the savings.
SAVINGS EXAMPLE:
For example, if your old unit has a SEER rating
of five and you replace it with one rated at
ten, and you figure your AC usage at $500, your
new bill would be $250 ($500 X 5/10).
If your original AC figure was $1,000 and you
upgraded from a SEER of six to one of nine, then
your new bill would be $667 ($1,000 x 6/9).
Electric central air conditioners consist of an
outside unit, generally a compressor, a coil and
a fan all housed together and an inside coil
mounted within the ductwork of the forced air
heating system. A refrigerant continuously
circulates between the coils alternately
compressing to high pressure (and high
temperature) outside, and evaporating to low
pressure (and low temperature) inside.
The house duct system recirculates household air
over the inside coil where the air loses some
heat and humidity. As the circulating
refrigerant picks up the household heat energy,
it is moved to the outside coil and gets
compressed to high temperature where the
resulting heat is blown off to the outside air.
Newer equipment is more efficient primarily
because it utilizes better compressors, a larger
outside coil and a stronger fan to lower the
condenser temperature. This allows the system to
"move" heat efficiently with the same amount of
electricity.
REPLACEMENT GEAR:
As a practical matter, most old duct systems
will accommodate higherefficiency AC gear only
up to a SEER of about nine. Since the duct
modifications required to attain higher
efficiencies can easily cost upwards of $1,000,
the ultra high efficiency air conditioning
systems are most appropriate for new
construction where the duct systems can be
designed accordingly.
It is important that the flow of refrigerant
between the coils of air conditioning systems be
regulated and balanced properly. A thermostatic
expansion valve is critical on a highefficiency
system. Installing a highefficiency outside unit
without converting an inside coil with capillary
tubes to a coil with a thermostatic expansion
valve will most likely prevent the overall
system from achieving its optimum SEER rating.
Some older inside coils have thermostatic
expansion valves and will work well with a new
highefficiency outside unit, but it takes
careful measurement by a qualified contractor to
determine this.
The average upgrade in efficiency is from a SEER
rating of about six to one of about nine or
more. The net resulting reduction in air
conditioning utility consumption is about 35 to
40 percent. This computes to an average savings
of approximately $100 to $175 per season for a
1,200 to 1,500 sq. ft. house that is reasonably
tight and adequately insulated.
The available choices of replacement gear are:
1. Replace the compressor.
2. Replace the entire outside package with a
similar efficiency unit.
3. Replace the outside package with a high
efficiency unit.
4. Replace both the inside and outside units as
a balanced package.
In general, alternative 4 is the best way to
save money in the long run, although alternative
3 will bring the quickest payback if the
existing inside coil is well suited to a high
efficiency outside replacement unit; a relative
rarity.
INSTALLATION:
Following are some top of the scale estimates
for installing a balanced high quality system
(SEER of approximately nine) with the best
technicians. A ton of air conditioning is
equivalent to 12,000 British Thermal Units
(BTUs) and will cool approximately 500 sq. ft.
of living space if the house is reasonably tight
and insulated:
1. Two ton system $3,000 and up.
2. Three ton system $3,400 and up.
3. Four ton system $3,600 and up.
4. Five ton system $3,800 and up.
Keep in mind that a good job of installation
could very well depend on the time spent by the
mechanic doing the work. Cleanliness and
moisture control are important to the
equipment's duration, and shortcuts in the area
of cleaning, soldering and evacuation procedures
could leave you with a vulnerable system. Always
ask how long the installation will take and
remember: a good mechanic will take two days to
install a typical, well balanced air
conditioning system.
Have a quality contractor, who won't want the
hassles of installing and serving lower quality
equipment, choose the brand of equipment for
you. It is virtually impossible for the layman
to determine the quality of the gear offered.
The actual equipment of a high efficiency system
costs far less than the installation. The
installation cost tends to stay the same whether
the unit is small or large or even if a furnace
is installed at the same time. Since the
installation cost is the major expense that must
be paid back by the savings in utilities, it
makes good sense to amortize the installation
cost against a larger package installation.
The installation cost of a small, high
efficiency air conditioning package can be 50
percent of the total cost, while it might drop
to 20 to 25 percent of an air
conditioning/furnace package.
UNREALISTIC EXPECTATIONS:
Replacing an operating central air conditioner
with a high-efficiency unit would be difficult
to justify on utility savings alone, but it is
well considered once a unit quits. Get at least
three bids beforehand and try to lock in the
prices for a reasonable period of time. Don't
have unrealistic expectations about the most
powerful high efficiency units as these seem to
be in the province of new construction only.
WORTHWHILE INVESTMENTS:
In the event that repair of your air
conditioning system is being considered, here
are some extra cost items well worth the
investment:
Copper coils instead of aluminum ones. Repairing
pinholes or joints is practically impossible
with aluminum coils but relatively easy with
copper. The extra $100 or so in cost is easily
worth the increased life expectancy and enhanced
repair ability.
A thermostatic expansion valve vs. capillary
tubes. It takes a top quality technician to
service a unit properly with capillary tubes and
in the crush of demand for service during the
dog days, you won't be able to be so choosey.
A sight glass or "liquid eye." Mounted on the
liquid hose, the "eye" costs about $15 and makes
it easy to check for refrigerant deficiencies.
A "dryer." Also mounted on the liquid hose, this
part keeps the system protected from moisture
and promotes longer life. For around $20, it is
well worth it.