Tips for buying air-conditioners
[edit] Basic Information
Air conditioners (refrigerated coolers) are the least energy efficient of all cooling systems, and have high purchase and running costs. Air conditioners provide cooling or, if they are a reverse cycle model, both heating and cooling from the one unit. When buying a new air conditioner consider the type of air conditioner, size, and purchase and running costs. Simple energy saving measures such as closing windows and external doors can keep running costs down. There are two common types of air conditioners: room, or window, air conditioners and central air conditioners. A compromise between the two types of systems is provided by ductless, mini-split air conditioners.
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[edit] Room Air Conditioner
Room or window air conditioners cool rooms rather than an entire home or business. Providing cooling when needed, they are less expensive to operate than central units, even though their efficiency is generally lower. A room air conditioner's efficiency is measured by the energy efficiency ratio (EER). The EER is the ratio of the cooling capacity (in British thermal units [Btu] per hour) to the power input (in watts). The higher the EER rating, the more efficient the air conditioner. US appliance standards require room air conditioners built after January 1, 1990, to have an energy efficiency ratio (EER) of 8.0 or greater. Look for an EER of 10 or higher.
A smaller aircon unit running for an extended period operates more efficiently and is more effective at dehumidifying than a large unit that cycles on and off too frequently. Moreover, frequent turning on and off cause early failure.
[edit] Central Air Conditioner
Central air conditioners are more efficient than room air conditioners. In addition, they are out of the way, quiet, and convenient to operate. If you are considering adding central air conditioning to your home, the deciding factor may be the need for ductwork. The "lifespan" of a central air conditioner is about 15 to 20 years.
There is two configurations of a centralized air conditioning system you can choose from: the split system or a package system. A split system includes an outdoor metal cabinet, which contains the condenser and compressor, and an indoor cabinet that contains the evaporator coil. The outdoor cabinet is located next to the home and the evaporator coil is located inside the home, above or near the air handling unit (furnace or blower). The indoor components may be located in a crawlspace, basement, attic or closet. In split systems, the outdoor and indoor units must be properly matched to achieve the rated efficiency.
In a single-package system, all of the mechanical parts are housed in one cabinet, typically located outside the house. Air supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors.
Central air conditioners are rated according to their seasonal energy efficiency ratio (SEER). SEER indicates the relative amount of energy needed to provide a specific cooling output. The minimum SEER allowed today is 13. Higher SEER means greater savings. ENERGY STAR qualified units have 13 or higher ratings.
[edit] Mini-split System
The third type, the ductless, mini split-system air-conditioners (mini splits), like the central system, have two main components: an outdoor compressor/condenser, and an indoor air-handling unit. A conduit, which houses the power cable, refrigerant tubing, suction tubing, and a condensate drain, links the outdoor and indoor units. It uses a wall or ceiling-mounted blower to deliver cool air to a room. Since mini splits have no ducts, they avoid the energy losses associated with ductwork of central forced air systems. Duct losses can account for more than 30% of energy consumption for space conditioning. The primary disadvantage of mini splits is their cost. Such systems cost about $1,500-$2,000 per ton (12,000 Btu per hour) of cooling capacity. This is about 30% more than central systems (not including ductwork) and may cost twice as much as window units of similar capacity.
[edit] Evaporative System
A fourth type exists, evaporative systems are sometimes also referred to as a "swamp cooler". Evaporative systems tend to use less energy than split or ducted systems, however, unlike split or ducted systems they consume water to provide cooling. It is not advisable to use this system in highly humid environment. In using this system, you will need to make sure you leave some windows open to allow air to flow in and out of the house, otherwise it is possible for condensation to form inside the house as a result of the elevated indoor humidity.
[edit] Portable Air Conditioning
Another option is the portable air conditioning. They are usually small in capacity, and may be either refrigerated or evaporative. Normally the only installation they require is to be plugged into an electrical outlet - if this is the case, they can be used without needing a licensed contractor to install them.
[edit] Zoning
Zoning allows you to designate specific temperature zones in multiple areas in your home. It also enhances airflow in individual zones allowing your system to more efficiently clean the air and exchange stale air. And, if used properly, a zoned system also has been shown to reduce energy use by 25 percent to 30 percent because it can deliver just the right amount of conditioned air to the areas of the home that need it. The components needed to have zoned heating and cooling typically require electronic zone dampers to be installed inline with the ductwork, a zone control panel and thermostats for each zone.
[edit] Cooling Capacity and Efficiency
The total cooling capacity consists of two components. The major component is the sensible cooling capacity, which is the energy equivalent of the temperature change of the air that flows across the airconditioner, while the second component is the latent cooling effect or dehumidification effect, which is determined by the amount of moisture removed from the conditioned space. The latter component is expressed as litres of moisture removed per hour. One kg of moisture removed per hour equates to a latent cooling capacity of 683 Watts. The output of an airconditioner depends on the motor efficiency, the compressor efficiency, the evaporator and condenser design and heat transfer properties, relative size of the evaporator and condenser, air flow design over the evaporator and condenser, fan efficiency and size, control system etc.
The cooling capacity of window air conditioners is measured in British Thermal Units or BTUs. The air BTU rating refers to the cooling power of the product. It is critical that the capacity of a room air conditioner be the right size for the room being cooled. An improperly-sized air conditioner can result in a cold, clammy environment or an inadequately cooled room.
It is important to select an air conditioner with an output capacity to suit your particular cooling or heating needs: Over-sizing can result in frequent cycling (turning on and off), which is inefficient, expensive and increases wear and tear. It can also result in cooling with limited humidity reduction. An undersized air conditioner will not provide adequate cooling or heating.
[edit] Tips
| Room Size (sq. ft.) | BTU | |
|---|---|---|
| 100-150 | 5,050–5,250 | |
| 150-250 | 6,000-6,300 | |
| 300-400 | 8,000-8,900 | |
| 400-450 | 9,900-10,500 | |
| 450-550 | 11,600-12,000 | |
| 550-700 | 13,700-14,300 | |
| 700-1,050 | 17,600-18,450 | |
| 1,200-1,600 | 22,900-25,200 |
- Before you buy, measure the square footage of the room or rooms to be cooled. If an exact match of cooling capacity is not possible, it is preferable to select a unit which is slightly undersize in BTUs, rather than oversize. See the table above from GE to see how much BTU applies to you. This table is based on an 8-ft. ceiling height. Size requirements will vary based on other factors. (See tips below.)
- Rooms that are connected by permanently open entryways wider than five feet ought to be considered as one room and their square footage should be combined.
- If the area to be cooled includes a kitchen, add an additional capacity of 4000 BTU/hr.
- If the room is heavily shaded, reduce capacity by 10 percent.
- If the room is very sunny, increase capacity by 10 percent.
- If more than two people regularly occupy the room, add 600 BTUs for each additional person.
- Consider where you install the unit. If you are mounting an air conditioner near the corner of a room, look for a unit that can send the airflow in the right direction.
- When sizing larger living areas, it is usually better to use at least two air conditioners rather than one large unit. Doing so offers better air distribution which reduces the likelihood of hot and cold spots.
- Ask a North American Technician Excellence (NATE)-certified technician to perform a Manual J analysis, the industry’s term for the standardized equation for sizing an air conditioning system. To properly size a system for a home, trained technicians will use an equation that factors the home’s age, the number and quality of its windows, how well it is insulated, how many stories it has, its total square footage, and local energy rates. For Australians, visit thislocator.
- ENERGY STAR qualified room air conditioners use at least 10% less energy than standard models. Additionally, ENERGY STAR qualified room air conditioners often include more features, such as timers, digital displays, remote controls, and directional vents.
- Select energy-efficient equipment and look for high Annual Fuel Utilization Efficiency (AFUE) ratings and the Seasonal Energy Efficiency Ratio (SEER). The national minimums are 78% AFUE and 13 SEER. (However, see here for a critical view of AFUE ratings).
- Air conditioner outputs are measured in kilowatts (kW), which is stated on the Energy Rating label. (For Australian consumers) As an approximate guide for sizing a room unit, allow 125 Watts (0.125 kW) per square metre of floor area to be cooled in living areas, and 80 Watts (0.08kW) per square metre of floor area in bedrooms. These estimates depend on the climate and the efficiency of your house design (orientation, glazing and insulation levels).
- Central air conditioners that are performance certified bear the AHRI Performance Certified® mark and are listed in the AHRI Directory of Certified Product Performance. The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) uses an independent, third party laboratory to certify a manufacture’s efficiency claims.
- Other Features to Look For When Buying an Air Conditioner:
- A thermal expansion valve and a high-temperature rating (EER) greater than 11.6, for high-efficiency operation when the weather is at its hottest
- A variable speed air handler for new ventilation systems
- A unit that operates quietly. Presence of sound-dampening features such as vibration isolation for the compressor and insulation.
- Multi-speed fans.
- A fan-only switch, so you can use the unit for nighttime ventilation to substantially reduce air-conditioning costs
- A fan control known as "Power Thrust" or "Super Thrust" that can send cooled air far into the room.
- An automatic-delay fan switch to turn off the fan a few minutes after the compressor turns off.
- A filter check light to remind you to check the filter after a predetermined number of operating hours
- A filter that slides out easily for regular cleaning
- A unit that can direct its airflow in the desired direction for your room layout.
- Logically arranged controls.
- Programmable timer and thermostat controls. Set your air conditioner at the highest temperature setting at which you still feel cool enough, 25ºC is usually adequate. Each 1°C increase of the thermostat setting will save about 10% on your energy usage.
- 'Set-back' and 'sleep' modes that automatically adjust thermostat settings
- Economy settings
- A scroll, or two-speed, compressor. This new compressor design have fewer moving parts and may therefore break down less often than the older, reciprocating type.
- Adjustable and rotating louvresreference needed
- Inverter technology. Models with inverters respond to the changing cooling/heating needs of a room. A variable-speed motor, or a two-stage central air conditioners consume less electricity than standard motors.
- Movement sensors, which reduce power and energy usage when the room is unoccupied.
[edit] Recycling
(US) For recycling your old unit, visit this page of the US Dept of Energy or the National Recycling Coalition locator powered by Earth911.com. Or visit this page for offers and rebates in buying new Energy Star units.
[edit] Manufacturers
Visit various distributors offerings of air conditioners:
- Carrier
- Friedrich
- Haier and their commercial air conditioners.
- GE
- LG
- Panasonic
- Samsung
- Sharp
- Whirlpool
- Sanyo
- Aire-flo
- AirEase
- Airwell-Fedders North America, Inc.
[edit] References
Home Energy Saver EnergyStar Room Air Conditioner GEAppliances.com Air-Conditioning, Heating and Refrigeration Institute EnergyRating.gov.au
