Q. & A.s ‑‑‑ SCI.
& TECH. –
Q: To save on cooling
costs, is it recommended to shut the air-conditioner vents in rooms that are
unused and closed?
A: If designed
correctly, the air delivery system in your house has been sized according to
the flow requirements of the unit and each room. Closing off vents can create a
pressure imbalance within the system that can reduce the effectiveness of your
cooling system. By closing off registers, the increased pressure within the
ducts can also cause increased duct leakage.
Q: Can I allow the upstairs
to heat up even more during the day and cool the downstairs less at night?
A: Anytime you
increase the temperature on your thermostat, you save money. When a unit first
turns on, it takes seven to 10 minutes of continuous operation to reach maximum
efficiency. The longer it runs after reaching peak efficiency, the better it is
for the unit. When you return home at night and the unit is forced to run
longer to bring the temperature down, it is running at peak efficiency. If you
are on the SRP Time-of-Use™ Price Plan,
and run your unit during the off-peak period, you'll be taking advantage of
lower-priced electricity.
Q: Is it more energy
efficient for the air conditioner to come on for short bursts of cooling
(running for five to seven minutes at a time) or to come on and stay on for
longer periods? How about the wear and tear on the unit as well?
A: A heat pump's
job is two-fold. Not only does it remove the heat from your home, it also must
remove the moisture from the inside air in order for you to feel comfortable.
When the unit first turns on, it will take about seven to 10 minutes for the
unit to get to its peak efficiency and remove the moisture from your home. By
allowing a unit to run five to seven minutes, you're not getting the most out
of the system. The starting and stopping is also hard on the system.
Q: Should I leave interior
doors open or closed during heating and cooling?
A: Because the
air-conditioning systems in our homes are closed-loop system, they are designed
to move a specific amount of air throughout the house. Closing bedroom doors
causes the air pressure in those rooms to increase. The air-conditioning unit
pushes air in but cannot get it back out, which causes the unit to force
conditioned air out of the bedroom under the door and through cracks or leak
around the windows, wall plates and ceiling fixtures and draw in hot attic or
outside air through similar cracks and leaks in the rest of the house.
Q: We are new to Arizona
and are wondering how to configure our air conditioning for summer. We have two
units, one upstairs and one down. How do you recommend we set them up for
comfort and energy savings? Should they be set on different temperatures? Do we
redo the settings at night? What temperatures do you recommend?
A: Because heat
rises and extra heat gain exists on the second floor because of the windows and
attic, the upper level will require more cooling than the lower level. To
maintain a constant temperature in your home, set each thermostat at the same
temperature. However, to reduce energy costs, you can maintain a comfortable
temperature on the floor you are occupying. If you're not using the upstairs,
set the second-floor thermostat a couple of degrees higher. Reverse the process
at night when you're upstairs.
Q: Is it better to set the
thermostat to a high temperature (85° to 90°) while at work all day and cool
the house (two-story, approximately 3,200 square feet) when you get home to a
comfortable temperature (approximately 80°), or to keep the thermostat just a degree
or two higher during the day so that the cooling unit doesn't have to work as
hard during peak hours to cool the house?
A: You will save
money anytime you can increase the temperature on your thermostat and cause the
unit not to run. The old myth that says you will spend more energy bringing the
temperature back down than you would have spent just leaving the thermostat
alone is just that, a myth.
Q: Does setting the fan
switch on my thermostat to the "on" position cause air imbalances in
my home?
A: Assuming there
are no interior doors closed in the home, there should be no air imbalance
caused by running the air-handler fan. However, in typical Phoenix
construction, with a central air-conditioner return, you can get significant
pressure imbalances when interior doors are closed. Because the door undercuts
are not large enough to allow for sufficient free flow of air, it is common to
create imbalances.
Q: If all things are equal,
is it better to set your thermostat at a certain temperature all the time or
use a programmable thermostat in conjunction with the Time-of-Use Price Plan?
A: Using a
programmable thermostat to control the operation of your air conditioner will
provide you the greatest savings on the Time-of-Use Price Plan. Not only will
scheduled operating schemes reduce the unit's operating time during on-peak
periods, but they also will increase the run time of the unit during off-peak
periods, and this increased run time will allow the air-conditioning unit to
run more efficiently.
Q: I want to replace our
thermostat with a programmable one. Which do you recommend?
A: Rather than
selecting a certain brand, make sure you select the right programmable thermostat
for your system. There are different models for single-stage heat pumps,
multistage heat pumps, straight air conditioning, air conditioning with gas
heat, etc. Ask your service contractor what type of system you have and what
model thermostat you need. After you know what model to get, determine your
programming requirements:
- 5-2 programming maintains two temperature schedules — one for weekdays and one for weekends.
- 5-1-1 programming provides the added flexibility of setting different programs for Saturday and Sunday.
- Seven-day programming lets you have different settings for every day of the week.
Q: I am buying a new air
conditioner and have the option of purchasing a system that uses R-22 or a
system that uses R-410A refrigerant. Will R-22 refrigerant be available in the
future?
A: Even though
R-22 will not be manufactured after 2010, the supply will last well beyond the
life of a new system installed today. The efficiency of the two products is
similar. However, R-22 tends to be more stable. R-410A is a mixture of
refrigerants that has to have the proper amount of each to be efficient. Any
leaks in the system could cause an imbalance and reduce the efficiency of the
refrigerant.
Q: What size air
conditioner should I install on my 2,000-square-foot house?
A: It is important
that new or replacement equipment not be sized by "rule of thumb" or
by the existing equipment. The only accurate way to determine the correct
capacity of heating and air-conditioning equipment for your home is to have a
heat-load calculation performed on your home. This will give your dealer the
heat gain and heat loss design data for your home. These figures can then be
used to select the appropriately sized cooling or heating system for your home
based on equipment performance data: The SRP Certified Contractor Program
connects SRP customers with heating and cooling contractors that are able to
perform Manual J calculations, which will determine the correct sizing for a
new air conditioner or heat pump.
Q: Could you please let me
know what SRP recommends on how many tons of air conditioning you should have
per square footage of home?
A: It is important
to make sure your new unit is properly sized. The best way to determine the
proper size is to request an evaluation by an SRP Certified Contractor.
SRP Certified Contractors perform Manual J or equivalent load calculations on
installations of replacement and new heat pumps. A Manual J calculation
determines the size of the air-conditioning unit required for your home.
Q: We have a heat pump that
was installed in 1998. When installed, the thermostat was set to take into
account a 1° temperature difference (more frequent cycling on/off of unit).
We've recently been trying a 2° temperature difference (less frequent cycling
on/off). Which is best for the most efficient operation of our heat pump?
A: When a unit
first turns on, it typically takes about seven to 10 minutes of continuous operation
before it reaches the steady state and highest efficiency. The longer the unit
runs after it reaches its steady state, the longer the unit will be operating
at its peak efficiency. Anytime you can reduce the number of cycles and
increase the run time, you will save money and increase the comfort level of
your home.
Q: Does the design of new
residential heat pumps cause lights to flicker in the house?
A: New
high-efficient heat pumps often cause lights in homes to flicker. The motors
used in high-efficiency heat pumps draw more in-rush current (amps) when they
first start (compared with older, less efficient units). This will cause the
voltage to drop at your service panel for a fraction of a second. This can
sometimes be observed as flicker (dimming of the lights).
Q: With the
commercialization of variable-speed heat pumps, have the benefits of a
programmable thermostat been reduced or eliminated? It seems to me that with
variable-speed equipment, the correct operating strategy would be to set the
thermostat at one setting and let the unit choose its own speed instead of
using a "set up, set down" strategy that could cause the unit to run
at high speed more of the time.
A: You would get
better humidity control by setting the thermostat and leaving it. However, if
the contractor oversizes the unit, there may still be a reason to set the
temperature higher while you are away. Correct system sizing still has to be
the No. 1 issue, and then nearly everything else will fall into place.
Q: Do high-efficiency
filters harm my air-conditioning system?
A: The use of
high-efficiency filters won't necessarily harm your air conditioner; however,
they can cause the unit to pull hot attic air into the ductwork, reducing the
overall efficiency of the system. By adding a high-efficiency filter to your
system, you add resistance to the air moving across the filter. Because the fan
in your system is rated to move a certain amount of air, it will get this air
from anywhere it can. If the added resistance of the filter makes it easier to
draw air into the ducts through leaks in the ductwork, then it will do so.
Aside from the added resistance of
a high-efficiency filter, this scenario is exactly why it is so important to
replace your filters on a regular basis. As the filter becomes dirty, the resistance
increases and the unit begins to pull more and more air in through the leaks in
the ductwork. If your ducts are tight and in good shape, the use of a
high-efficiency filter is fine. However, to avoid possible airflow problems, I
recommend the 3/4-inch to 1-inch pleated filter that usually costs $4 to $6.
Q: I have never changed my
filters. Every time I check them, they look like the day I bought them. Is that
good? My house is 2,400 square feet, and my electric bill is subnormal.
A: Never having to
change your filters is unusual, especially with Arizona's fine dust. If you are
using very inexpensive filters, they may be too loose to catch any of the fine
dust. This allows the dust to accumulate on the unit's evaporator coil, which
could cause problems down the road. I recommend trying the 1-inch pleated
filter (typically $4 to $6). More expensive filters may be too restrictive and
could cause problems for your air conditioning unit.
Q: How do I balance the air
being supplied to each room of my house?
A: The only
accurate way of determining how to set your supply registers is to have a contractor
complete a load calculation on your house. As part of this process, the
calculation software will identify how much air should be delivered to each
room. Once this is known, the contractor will measure and adjust the amount of
air being delivered at each register. The "do-it-yourself" approach
is to experiment with different settings over the course of a couple weeks
until you get an even comfort level throughout the house.
Q: Are there advantages to
shading your outside air-conditioning unit if you provide for proper air
circulation?
A: Shading the
coils of an air-conditioning unit has the potential to modestly reduce energy
demand. However, improper shading techniques can result in a net increase in
energy consumption by blocking proper airflow or trapping radiant heat. In many
cases, a simpler approach is to plant trees strategically around a building to
reduce indoor cooling loads or pursue other, more surefire air-conditioning
efficiency upgrades.
Q: My landscapers built a
three-sided wall around my ground air-conditioning unit in the backyard, and I
am concerned that there may be restricted airflow to the unit. The wall is made
of concrete block covered with stucco and painted on the outside. It is as tall
as the unit and surrounds it on three sides. There is a break of about 24 inches
on one side, and the wall is built about eight to 12 inches from the unit
itself. How will this affect the life of the unit, cost to run, etc.? What
options do you suggest to vent the wall ,or should I totally remove it?
A: The outdoor
unit must be positioned a minimum of 12 inches from any wall or surrounding
shrubbery to ensure adequate airflow. A 30-inch clearance must be provided in
front of the control box (access panels) and any other side requiring service
access to meet National Electrical Code. The top discharge area must be
unrestricted for at least 5 feet above the unit.
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