Residential air conditioning unit efficiency
Energy efficient central air conditioning
Installing an efficient residential air conditioning unit might be the biggest energy saving thing you do for your home. Of course, in my home town of Toronto, where summers are not too extreme, it is possible to live without any air conditioning, as I explain in my Summer energy saving tips. Even if you know you need central air, it's helpful to read those summer tips for ideas on how to rely more on passive cooling opportunities than on expensive AC.
But assuming that a residential air conditioning unit is a necessity for you (or a luxury you're willing to pay for), you might as well get the most mileage out of your air conditioning system. So turn your residential air conditioning unit into an energy efficient central air conditioning system - whether by maintaining it properly, relocating a poorly placed compressor air conditioner unit, or, if it's time to buy a new air conditioner unit, choosing the most efficient residential air conditioning unit possible.
Remember to check my Home air conditioning problems page if you feel your existing residential air conditioning unit isn't performing as efficiently as you think it should.
Make your home energy efficient first
Before you go out and buy the most energy saving residential air conditioning unit you can find, do everything you can to reduce the amount of air and heat that can pass between the inside and outside of your home. It is better to convert an old, poorly insulated, leaky home into a very well-insulated, airtight home, and then buy a mid-efficiency residential air conditioning unit, than to install the most energy saving residential air conditioning unit on the market in a sieve. Not only will this save on cooling costs, but if you heat during winter it will cut your heating costs as well.
Vintage AC unit
Photo by Rob Ireton, via FLICKR
Buy the right-sized air conditioner unit
For a central residential air conditioning unit, you should hire an HVAC contractor to do an on-site inspection of your house and any existing forced-air heating/cooling system, so that they can determine the correct size for your residential air conditioning unit. As with window air conditioners, there is no benefit to buying an oversized residential air conditioning unit. An oversized air conditioner unit will cycle on and off more frequently, reducing its efficiency, increasing wear on its parts, and shortening its life. As well, the indoor temperature will fluctuate more than with a correctly sized air conditioner unit.
Buy the most efficient unit you can afford
What are the chances that your electricity rates will drop over the next twenty years? Pretty slim. But it is fairly likely that they will rise, even considerably. With ever increasing electrical demand, and with the most popular US source, coal, likely to become more expensive once we put an appropriate price on its greenhouse gas emissions, electricity costs could easily double or triple in the next decade. Protect yourself by buying the most energy efficient residential air conditioning unit you can.
Two companies in particular are near the top of the list in terms of efficiency. The Nordyne air conditioner with its ultra-quiet iQ Drive techology offers air conditioners with an SEER rating between 21 and 24.5, and is sold under well-known brands such as Maytag, Frigidaire, and Westinghouse. The Trane AC unit is another popular, very efficient air conditioner with an SEER of up to 19.5. Both the Trane and Nordyne systems are substantially higher than the minimum ENERGY STAR SEER requirement of 14.5.
Hire the right HVAC contractor - when buying a new unit
As with any major home renovation, you need to hire an air conditioning system contractor who will do an outstanding job sizing your residential air conditioning unit. Your contractor should help you choose the right manufacturer and model of condenser and evaporator (not just whatever they happen to have in stock), should provide a schedule of when the parts will be ready and when the installation will be done, should be willing to dismantle, remove, and dispose of any old equipment that is no longer needed, and should provide a written warranty as well as an optional service extension.
Newer AC unit
Photo by barkingmoose, via FLICKR
Below are some recommendations on how to find the right contractor. You don't have to follow all the recommendations - most people don't, as it's quite time consuming - but remember that you'll be spending several thousand dollars on your residential air conditioning unit (in combined installation, operation and maintenance costs) over the lifetime of the air conditioner unit, so any time you invest in carefully choosing a good contractor will pay big dividends later.
First, before you call any contractors, make a list of possible contractors:
- Ask friends and neighbors for a recommendation.
- Make note of any AC contractor vans you see driving through your neighborhood or parked during an installation.
- Figure out what manufacturers you would like to consider for your residential air conditioning unit. Then find the local dealers for each manufacturer, using their website or a phone call.
To figure out what manufacturers you would like to consider:
- Do a rough estimate of the BTU capacity your air conditioner unit will need, using the chart for window AC units. Use the US ENERGY STAR or Canadian Office of Energy Efficiency websites to find residential air conditioning units of that BTU capacity, and look for the most efficient air conditioner units in that range. Look for an EER rating of 12 or higher if possible. (Some air conditioners provide an SEER rating as well as, or instead of, an EER rating. To convert between SEER and EER, see my conversion formulas at Air conditioner ratings.)
- Use magazine or online resources such as Consumers Reports to compare the quality of the products made by different residential air conditioning unit manufacturers.
Once you have a list of possible contractors:
- Ask friends and neighbors if they have dealt with any contractor on your list. If they have (for instance if they gave you a recommendation), ask to see their installed system, as well as the paperwork that was provided at installation, to judge for yourself the quality of the installation.
- Do a web search on the contractor name and see if any discussions come up on the quality of their work
- Contact your local Better Business Bureau to find out if any complaints have been lodged against them.
Then, for each contractor you identify, conduct a phone interview. (Remember, you're the boss!)
- Knowing what you know about the most energy efficient residential air conditioning unit for your house size (based on the research you did above), ask the contractor what systems they recommend. Casually mention the manufacturers you found had the highest energy efficiency ratings (and perhaps a couple big brands that didn't), and see how well their responses match your research. Remember that an energy efficiency rating does not mean the residential air conditioning unit is top quality, so listen for any indication of quality problems with a manufacturer's products. A thorough knowledge on the contractor's part of the features and flaws of different residential air conditioning units is a good sign. Also, their knowledge may convince you not to buy a particular manufacturer's product based on their experience with product quality.
- Ask them for energy efficiency advice. Tell them you want to cool your home using as little electricity as possible, and ask them what they recommend. Compare what they say with what you've researched. Some contractors are very knowledgeable about the energy efficiency side of their business; others are not. Your research before the interview should help you tell the difference. Avoid contractors who don't seem to understand energy efficiency very well, or who claim that there's not much difference in operating costs between the most efficient models and ones with a lower initial sticker price.
- Ask them what professional organizations they belong to. Reputable air conditioning system contractors in the US and Canada should belong to an organization such as the Sheet Metal and Air Conditioning Contractors National Association or the Air Conditioning Contractors of America.
- Ask them what insurance they carry and what licensing their company and their technicians have.
- Ask them how they size the system. If they suggest they will just use the existing system to determine the capacity of the new system, stay away from them. They should be doing a thorough load calculation to determine your system's capacity. How do they know the existing system is properly sized?
- Ask them what the process is for buying a residential air conditioning unit: how long does it take for a typical unit (of the brands you're considering) to be available for installation, how long does installation take, how will payments be handled, what warranty is provided, what service extensions are available for the air conditioner unit at what cost.
- If you're impressed with the interview up to this point, you may want to ask for customer references, or you may wait until they come to your home to do their detailed capacity sizing and cost estimate. You should also consider visiting their shop facility or showroom.
- Remember that every interaction you have with a company is a reflection of how they will perform as your energy saving air conditioning system installer. If they are not prompt and courteous and helpful at any point in the selection process, they may behave similarly during the estimate, the installation, or afterwards when you start to have problems. Stick with true professionals.
The phone interviews should help you narrow your contractor list down to three or four at most. Arrange for them to come on separate days, and keep their names straight when they come! During their on-site visit, follow them around and observe what they are doing. Afterwards, follow up with any questions you have that aren't answered. Among the questions you should ensure you ask are:
- If new ductwork is required, what duct sizing technique did they use? If ductwork is already present, did they determine if its size is adequate? If so, ask them to show you the calculations and explain the methodology.
- If new ductwork is required for upstairs rooms, is the ductwork going to be installed in the attic? This is to be avoided if possible. If it cannot be avoided, the contractor's plan should include a high-R-value insulation around the attic ductwork.
- How will existing or new ductwork be tested for leaks, and how will it be sealed? Make sure testing and sealing is part of your quote even if you are simply installing a new air conditioner unit into an existing forced air system (furnace or AC system).
- Has the sizing of space required for the system taken into account clearances needed around the indoor unit (evaporator) to perform maintenance and cleaning, or to change air filters? If your unit will be located in a narrow room, will there be enough clearance to get around it in case you need to?
- Has the design incorporated a sealable opening that can be used to access the coils for cleaning and inspection?
- What are the options for where to locate the condenser unit? Do the options take into account (A) the importance of good airflow around the unit, (B) your or your neighbors' peace and quiet (keep units as far as possible from neighbors' bedroom windows), (C) the importance of shade around the unit, which will increase its efficiency?
- If this is a new residential air conditioning unit (no existing cooling or heating system is installed), where will the thermostat be located? Is the location out of sunlight and away from any heat source?
- If this is a replacement for the air conditioning system in an existing forced air unit, will the old evaporator coils be removed? You should not reuse the old coils. You may save some money but you will pay for it in reduced efficiency and potential increased maintenance costs. Also make sure the new evaporator coils exactly match what is required for the condenser unit.
- If you do not have a programmable thermostat, will the new system include one? Insist on this as you will save a lot on cooling with a programmable thermostat.
- What will the contractor do to verify the installation was done correctly? Will the same person do the installation as perform the verification? Will the verification include measuring the charge level and ensuring it is right where it should be according to the manufacturer's guidance? Will air flow be checked?
You should also ask them to demonstrate to you that their sizing of the BTU capacity required for your residential air conditioning unit is well thought out. An oversized or undersized system will cost you a lot more in the long run. Their calculation should take into account the following factors:
- The area (in square feet or meters) of your home. Have them show you how they calculated it, and verify afterwards with similar calculations of your own.
- The orientation of your house - are there south facing walls (there may not be if you live in townhouse or semi-detached house), are the south-facing walls shaded, is the south facing wall longer or shorter than the east/west walls, etc.
- The layout of windows: how many on south-facing walls, how big they are, what energy saving window coverings they may have
- The insulation levels in your walls and attic
- The level of weatherproofing and sealing of air leaks
- The condition of any existing ductwork that will be used, in terms of both its dimensions and any air leaks (although presumably the contractor will try to fix those leaks where possible.
Boost your unit's efficiency with an Aircosaver
You may be able to turn your existing residential air conditioning unit into a more energy saving air conditioner using a controller such as the Aircon energy saver, a small device you can install yourself, or have installed by your air conditioning system contractor. The Aircosaver monitors the operation of your air conditioner unit and attempts to detect thermodynamic saturation, which is the point at which the compressor has cooled the refrigerant more than necessary to provide the desired cooling. In a normal cooling cycle, the compressor works full-time so that the temperature decrease of the air exiting the unit trends steadily downward. However the efficiency of the compressor decreases as the refrigerant gets colder. The Aircosaver detects this decrease in efficiency and shuts off the compressor for short periods (but not short enough to cause short cycling). The air conditioning system can still bring a room down to the desired temperature in the same amount of time, however the intervals when the compressor is switched off mean the temperature may rise slightly at times as it drops to the desired temperature.
Remember that because thermostats have a range between the temperature at which they engage the air conditioning system and the temperature at which they shut off, you will always have a cycling between a steadily rising temperature in the room, when the unit is off, and a steadily dropping temperature, when the unit is in cooling mode.
For more information on the Aircosaver, see their website at www.aircosaver.com.
Hire the right service technician to service your existing unit
Most air conditioning technicians are competent and well-trained. However, a technician who lacks training, takes short cuts, or makes mistakes, can cost you money in the form of higher electricity bills (because the air conditioner unit is not operating optimally) or further service calls when the unit malfunctions as a result of poor maintenance. You should ensure that your technician performs all of the following tasks, and uses a maintenance checklist to show that each task was done (and, for tasks involving a test or measurement, what the result of the test or measurement was):
- Check for any signs of refrigerant leakage using a leak detector
- Check the refrigerant charge and ensure it matches the manufacturer's specifications
- Capture any excess refrigerant for safe and legal disposal (it is illegal to release it into the atmosphere)
- Inspect all electric terminals for proper connections and coverings
- Measure evaporator coil airflow and ensure it is adequate (low air flow decreases efficiency)
- Ensure all motors are adequately oiled and free of dust build-up
- Test the unit's startup control sequence is operating properly
- Check all belts for tightness and wear, replace any that are loose or frayed
- Test central AC ductwork for any leaks or areas with high heat exposure
- Ensure that the air conditioner unit cannot operate while the heating unit is in operation
- Verify that the thermostat current temperature reading is correct
- Verify that the air conditioner unit starts when the thermostat is set slightly lower than the current indoor temperature
Keep the central AC filter clean
Check the air filter on your residential air conditioning unit frequently through the heating season, especially if there are sources of dust or animal hair within your home (some common sources are a smoggy city; a renovation project or woodworking shop in or near your house; a shedding dog or cat). Clogged air filters restrict airflow through the unit, which means the compressor may be doing as much work while cooling less air. As well, on some units air may bypass the filter if it becomes too clogged up, which means dusty air will flow directly onto the evaporator coil, which will then operate less efficiently as the dust will restrict heat exchange between the refrigerant and the air being vented.
You can buy
air conditioner filters
Inspect your filter monthly. If you use the thin filters with cardboard border, they should typically be changed monthly. For fanfold filters (such as AprilAire) you may not need to change them more than once a year, but you should still check them every month or two to ensure they aren't clogged up.
Keep the condensate drain clear
Central air conditioner units extract humidity from the indoor air and drain it through a condensate drain. The drain channels inside the air conditioner unit may become clogged, particularly if the condenser is located near a dust source. You can unblock these drain channels by pushing a stiff wire through them. Clogged drain channels mean your unit cannot extract humidity from the indoor air, which will make the air feel warmer, and will also cause increased moisture and the risk of increased mold or mildew which may discolor walls, floor coverings and furniture, and may pose health risks. For more information on reducing moisture in the home see Energy efficient dehumidifiers.
Keep the outdoor unit clean
In winter (if you have one), cover the outdoor condenser unit with the cover that came with it, or purchase one through your HVAC contractor. This will keep the unit dry and free of the debris (dust, leaves, insects, dirt, and so on) that will otherwise pile up inside it and around its fins. But remember to take the cover off before you start using the unit, or you could cause serious damage to the unit.
During the air conditioning season, check the condenser regularly for any debris or dust on the fins. Blow or vacuum it away. Also make sure nothing is leaning against the fins as this will both restrict airflow and may bend the fins, leading to reduced efficiency of the heat exchange in the area where the fins are damaged. If your fins are bent, you may be able to fix them using a fin comb, which can be purchased from an air conditioning system installer or wholesaler.
Make sure the condenser unit is located well away from any permanent or seasonal sources of dust or lint, such as dryer vents, lawn mower, gravel roads, workshop vents, and so on.
Seal and insulate your ductwork
Leaks in ductwork can account for up to a 25% increase in your air conditioning system costs. Wherever possible, check for and seal any such leaks using duct tape, or if necessary replacing sections of ductwork. You can also cover exposed (or temporarily exposed) ductwork in a duct wrap in areas where you don't want the cooling (or heating) from the duct to transfer into the area where the ductwork is exposed.
For attic ductwork (which you would probably only have if your central air comes out of ceiling vents), make sure there is plenty of insulation around the ductwork. Attics can reach temperatures up to 150F (66C) during the day, and the cool air in an uninsulated attic duct will warm to a temperature well beyond comfort before it even makes it into an upstairs room.
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