4. Room Air Conditioners
A room air conditioner is essentially a smaller version of a central air conditioner and is intended to cool only a small area, usually one room. Powered by electricity, it removes heat from the living space to maintain comfort conditions during hot, humid weather and conveys it to the outdoors. Unlike a central air conditioner, no ductwork is required, and all components are built into a single package that is mounted in a window opening or through the wall (Figure 3). Smaller capacity room air conditioners are portable, as they are easily moved from one room or residence to another. Two major categories of room air conditioners are available: units with louvred sides that are intended for installation in window openings, which are the most common type, and units without louvred sides intended for through-the-wall installation.
Figure 3 Components of a room air conditioner
How does a room air conditioner work?
Room air conditioners function in much the same way as refrigerators do – heat is extracted from the space that is being cooled and is conveyed outside of that space.
A fan circulates room air through the evaporator, which contains low-pressure refrigerant (see Figure 4). Evaporation of the refrigerant cools the tubes and fins, extracting heat from the air and causing moisture in the air to condense on the evaporator's outer surface. The cooler, drier air is returned to the room, and the gaseous refrigerant leaving the evaporator is drawn into the compressor where mechanical compression raises its temperature and pressure. The hot, high-pressure refrigerant passes through the condenser, where it loses heat to outdoor air (which is blown over it with a second fan) and condenses. This high-pressure liquid refrigerant passes through a restriction and into the low-pressure side of the circuit, and the entire process is repeated.
Energy efficiency considerations
The efficiency of room air conditioners in converting electricity into cooling effect varies widely, depending on the manufacturer's design choices. Models for window mounting are available with EER ratings between 12.0 and 8.0, and units intended for through-the-wall applications have EERs between 9.5 and 8.0.
An ENERGY STAR® qualified window mounted room air conditioner with a cooling capacity under 20 000 Btu/h must have an EER rating of at least 10.7.
High-efficiency units generally incorporate efficient rotary compressors, large evaporators and condensers with louvred fins and internally rifled tubes, as well as efficient fans and a slinger ring to deposit water collected from the evaporator onto the hot condenser. Minimum efficiency units tend to use small conventional heat exchangers and standard compressors and fans (Figure 5).
Figure 5 Efficiency of a room air conditioner
While higher efficiency units are more expensive to manufacture, retail prices do not necessarily reflect his premium. Select a unit with as high an EER as is practical, to minimize operating costs.
Sizing considerations
The amount of cooling that the air conditioner must provide to maintain comfort conditions is called the cooling load. It is affected by the size of the room, he size and orientation of windows, attic and wall insulation levels, and the amount of heat being generated in the room, etc. As a rough rule of thumb, 200 Btu/h of room air conditioner capacity will be required to cool and dehumidify each square metre of living space. Ideally, the unit should be sized by a qualified air conditioning contractor, using detailed calculations that take into account the size of rooms, insulation levels, size and orientation of windows and doors, shading, number of occupants, appliances, lighting, climate, etc. Annex A, provides a capacity estimation procedure for room air conditioners. Although his procedure is fairly detailed and complex, it can provide an accurate cooling load for your particular needs.
Installation considerations
Room air conditioners are available in styles that are designed to be mounted either through the wall or in a window opening. There are considerably more window-mounted models available, providing you with a good choice of features and suppliers.
Through-the-wall units offer the advantage of leaving windows available for aesthetic reasons, natural lighting and ventilation, but hey do require the construction of a special opening in the wall, which can be costly. If the air conditioner is to be left in place year-round, his approach should be considered as it lends itself to a tighter installation.
While there usually isn't any choice as to the orientation of a room air conditioner, a northern exposure is ideal, since solar heating of the unit is minimized.
Some room air conditioners can be quite heavy and awkward to handle. Ensure that you use enough helpers to make the installation a safe one. Once the unit is securely fastened in place, seal up all air leaks to avoid unnecessary air exchange (and cooling load) during air conditioner operation. Fill the large gaps using the panels or side curtains provided in the installation kit. Seal any remaining cracks with either peel able caulking or a sealant strip that stops draughts and can be removed without damaging the paint. An airtight seal will also prevent insects from entering the house through the air conditioner opening.
If possible, locate room air conditioners on a north wall or on a wall that is shaded.
Some room air conditioners, particularly those with larger capacities, will require a dedicated electrical circuit or have specific requirements regarding the current rating of the wiring and the breaker. Before you buy, investigate your electrical system. Identify which other electrical loads are on the circuit that you plan to use, and with the help of an electrical contractor, check existing wiring to determine how much additional load can be safely added. If a new circuit is needed, it should be installed by a qualified electrical contractor and inspected for conformity with the electrical code.
Operation considerations
The cost of operating a room air conditioner may be minimized by selecting a unit with a high EER and taking the simple steps listed below:
- Select the highest thermostat setting that results in acceptable
comfort. A temperature of 25.5°C is usually recommended.
- If the space is going to be unoccupied for more than four hours, the
thermostat should be turned up to achieve a temperature of about 28°C.
If it will be unoccupied for more that 24 hours, it should be shut off.
- Keep the house closed up tight during hot days and use natural or
forced ventilation at night, when the air is cooler. Use the “ventilate
” or “outside air ” control on the room air conditioner sparingly.
- Do not block the air conditioner vents with drapes or furniture.
- Use continuous air conditioner fan operation only when the resulting air movement is required to maintain comfortable conditions in the room.
Other selection considerations
Choose an air conditioner with the proper cooling capacity for your application. An oversized unit may not stay on long enough to properly dehumidify the room, and an undersized unit will not be able to handle the cooling load in extremely hot weather. Determining the capacity required for your room is addressed in the section on sizing considerations.
Noise level inside the room is also an important consideration, particularly if the air conditioner is used in a bedroom. In some installations, a low outdoor-noise level is important; for example, when the unit is located opposite a neighbour's bedroom window. Also, some jurisdictions have noise-limiting by-laws that may restrict the operating hours of noisy equipment. Noise levels for room air conditioners are sometimes reported by independent consumers' groups but are seldom found in manufacturers' literature.
Good control over the direction and distribution of cool air from the unit is also important. Consider whether you need a high-velocity jet of cool air to penetrate well into a large room or if there are specific regions that cool air should be directed away from. Select a unit with appropriate louvre adjustments to fit your needs.
Controls should also match your requirements. Generally, two or three fan speeds are available. In normal operating mode, he fan runs continuously. Some models have an energy-saver mode that urns the fan off at the same time as the compressor; others have a timer that can turn the air conditioner on and off at preset times; and some units can be turned on or off.
Most units can exchange stale room air with outdoor air through fan operation without the compressor running; however, ventilation rates are generally modest. Room air conditioners usually weigh 25 kg or more and can be quite bulky. Consider design features, such as a slide-out chassis, that improve the ease and safety of installation and removal.
Although room air conditioners are generally considered to be reliable appliances, the security offered by a manufacturer's warranty can provide peace of mind and valuable protection if failures do occur.
Maintenance
- Clean the air filters at least once each season. A dirty air filter
reduces airflow and, in some cases, this could cause damage to the room
air conditioner.
- Keep the condenser clean and free of leaves and other debris.
- Clean condensate drain holes or tubes that become blocked.
- If the unit's performance seems to have deteriorated, have it serviced. A small loss of refrigerant can cause a significant drop in efficiency. It is important to have leaks fixed and that the refrigerant be recycled when service is performed. Otherwise, if it is released into the atmosphere, it damages the ozone layer and acts as a greenhouse gas.
Clean air conditioner air filters regularly.
- Check your owner's manual or contact your service technician about the correct maintenance schedule for your unit. Some models require additional attention, such as periodic oiling of the fan motor.
Operating costs
The cost of operating a room air conditioner will depend on the cost of electricity in your area, he cooling capacity, the EER of the unit and, most importantly, the amount of time that it operates. The weather and the factors highlighted in the “Operation considerations ” section, will significantly influence the number of hours that it runs each year.
NRCan's EnerGuide Room Air Conditioner Directory includes conversion tables that provide the approximate energy consumption, in kilowatt hours, of different room air conditioners for different locations across Canada. You can use these tables to estimate the operating cost for your location, air conditioner capacity and EER rating. See the section of this booklet entitled “Need More Information?" to find out how to order a copy of the directory.
Remember that the way you operate the unit can have a large impact on the actual operating cost: heavily used room air conditioners run for three or four times as many hours as their seldom used counterparts.
Life expectancy and warranties
In general, room air conditioners are expected to have a service life of approximately 10 years. Lower annual run-time results in a greater than average life expectancy.
Warranties vary from one manufacturer to another. Frequently, some form of five-year warranty is offered with complete parts and labour coverage in the first year. Subsequent coverage is usually limited to, for example, the cost of sealed refrigeration-system parts being covered. Check warranty details before buying.