This is Part Two of my Air-Conditioning series. This part will focus on the various types of air-conditioners on the residential market. My previous post explained some basics of AC, and efficiency ratings.
Window Units
The old-fashioned wall-banger is probably the most familiar type of air-conditioning. A metal box containing compressors, coils, fans, and refrigerant is placed through a wall or a window. The unit can both cool and dehumidify a room, but will have difficulty providing comfort in a large space.
A major drawback to these types of units is the noise. These units are loud. They are also not especially efficient. A window unit will tend to be less efficient than ductless or central systems. If not properly sealed, the air-conditioner will let outside air seep into the home through the space around the unit. This warm and humid outside air forces the air-conditioner to work harder to keep the room cool.
Another major drawback to window systems is the electrical connection. Window units are plugged into standard wall outlets. An air-conditioner requires a lot of electricity, and need to be plugged into a dedicated outlet, with nothing else on the circuit. However, in older homes with scarce wall outlets, air-conditioners end up on the same circuits as lamps, televisions, and computers. This can quickly become a fire hazard.
Window AC units are tried and true technology. They are not particularly efficient, nor are they particularly effective. They are, however, cheap to buy and easy to use.
Portable Units
Portable units are the newest iteration of the unitary air-conditioner. These units only require a small hose to extend outside the home to allow the unit to exhaust heat. Portable units are easy to move from room to room (hence the name), and do not require the installation effort of a window AC.
Electrical connections are again an important issue with these units. Some of the larger units can draw up to 12 amps. This is the maximum amount of load you can put on a standard 15 A residential circuit. If you plug the unit into the same outlet as other appliances, you risk tripping the breaker, or worse – an electrical fire. Any AC unit, window or portable, should be plugged into its own outlet with nothing else on the circuit. A quick way to test the circuit is to manually trip the breaker. If the only thing that doesn’t have power is the air-conditioner, it’s on a dedicated circuit.
Drainage is a factor to consider with these units. Window AC units allow condensate water to drip outside the building. A portable AC unit will typically have a reservoir that must be drained regularly to allow for effective dehumidification. As my previous post stated, dehumidifying the air is just as important as lowering the air temperature when it comes to residential cooling.
Like window units, these ACs are not terribly efficient, with EERs ranging from 8 to 11. Both window and portable units require an EER of greater than 10.8 to qualify for an Energy Star rating.
Ductless Units
Ductless air-conditioners (sometimes called ductless splits, or split-systems) are becoming the most popular form of air-conditioning in New Brunswick. They are easy to install in existing homes and becoming cheaper every year. One or more indoor units are placed inside the house. Refrigerant lines are run from the indoor unit to a condenser unit outside. Both the indoor and outdoor units require separate electrical feeds.
The popularity of ductless units is driven by the ease of installation. No new ductwork is required, and no major interior preparation is needed. The biggest challenge in most homes is finding a suitable location for the outdoor unit. Ductless systems work best when the distance between the indoor and outdoor units is minimal. Of course, the best place inside a house for the unit rarely lines up perfectly with the best place outside the home for the condenser.
Another challenge for ductless units is finding enough capacity in the home’s electrical system. Older homes may not have spare capacity in the electrical panel to feed the new system. Homes heated by oil usually have smaller electrical entrances, and unknowing homeowners may find out that their electrical system is already maxed out when it comes time to install the new air-conditioner. It’s worthwhile to have an electrician review your existing electrical system if you’re unsure whether your home can handle the increased electrical consumption of an air-conditioner.
A big plus for ductless systems is that they can also act as heat pumps during heating season. Not all ductless units are heat pumps, so it is important to specifically seek out a ductless heat pump if you want to use the unit for heating during winter. I’ve written a similar post on heat pumps here. Modern units can generally provide heat down to temperatures of about -15°C. Beyond that your home’s main form of heat will be used.
To qualify for an Energy-Star rating, a ductless air-conditioner must have a EER equal or greater than 12, and a SEER equal or greater than 14.5
Central Units
“Central air” is the full meal deal of air-conditioning. A blower unit inside a building blows air across a coil full of cold refrigerant. The coil cools the air and removes humidity. The cool, dry air is then delivered through ducts to various parts of the home. A thermostat in a central location in the home controls the system, and keeps the temperature inside the house below a set temperature.
A central AC system will be much more efficient that a window or portable unit. The central system also eliminates the need to hang a large piece of cooling equipment in your living room or bed room as required by a split system. Central systems also come with air filters that can control the amount of allergens in a home.
Central AC is easiest to install when a home is being built. Ducts can be run between floor joists and in other convenient areas. Flooring and drywall can be coordinated with air outlets and inlets. Retrofits are possible, but may require ceiling modifications, opening walls, or cutting floors. The amount of work required to install a central system into an existing house is the main driving factor in the popularity of ductless split systems. If you already have a furnace that heats your home with hot air, installing central air conditioning can be as easy as placing a coil in the furnace duct and running refrigerant lines to an outdoor condenser.
In our climate, central AC is generally linked with the home’s main form of heat. This can take the form of a gas, oil, or electric furnace, or a heat pump. The home’s thermostat will have a “HEAT-COOL” toggle switch that allows the homeowner to switch the central system from heating to cooling as needed over the course of a year.
Central systems require an EER equal or greater than 11, and a SEER equal or greater than 14 to qualify for an Energy Star rating.
It’s hard to say which type of air-conditioning system is “best”. A central AC is a great solution, but not if you have to tear down a basement ceiling to install ducts. A ductless AC is perfect unless your home is walled off into many rooms. Many factors will affect your choice of equipment. Portable and window units are cheap solutions that can effectively and simply cool a room, while central and ductless systems are more efficient but also more complex. If you’re considering buying a larger system, it’s likely worthwhile to take the time to speak to several local contractors to decide what’s best for you.
