Like so many powerful innovations, central air conditioning is easy to take for granted. The cool, dry air that whispers unceasingly from wall and ceiling registers can lull us into a false sense of security. Then an electric bill arrives, or the system starts to falter. Suddenly we realize that basic maintenance was called for--just cleaning the air filter would have cut cooling costs 5 to 15 percent. Or perhaps it's time to replace an old and inefficient central air conditioner. There are a number of options to consider, including high-efficiency systems that can reduce electrical cooling costs 20 to 30 percent. Here's a crash course in the mechanical system that helps you keep your cool when temperatures start to climb. Conventional central air systems graft into a house that has ducts for forced-air heating. The hot and noisy portion of the cooling system, the compressor-condenser, is located outside. The cool and quiet component, the evaporator coil, is located inside, above the furnace blower.

Cool, dry air is distributed; warm, humid air returns to be cooled and dried.%" align="center" style="padding:2px;border-right:1px solid #ccc;">%" align="center" style="padding:2px;border-right:1px solid #ccc;">%" align="left" style="padding:2px;border-right:1px solid #ccc;">Houses heated with boilers lack ducts to distribute cooled air. They can be centrally cooled with mini-duct systems in which an evaporator coil, fan and trunk duct are located in the attic. Cooled, high-velocity air is piped from the trunk duct through flexible, insulated plastic ducts.>A ductless split system is the answer for many homes that are not centrally cooled or that need more cooling after an addition is built. The compressor-condenser serves one or more evaporator coil fan units installed on the inside walls of the house.The Refrigeration CycleMechanical, chemical and thermal energy act together in your central air-conditioning system to cool and dehumidify indoor air. Warm liquid refrigerant is driven under high pressure toward the evaporator coil.2.

Near the evaporator, the liquid flows through a metering device that functions like a garden-hose nozzle. It converts the warm, high-pressure liquid into warm, low-pressure droplets.3. As the droplets enter the evaporator coil they begin to cool, and the droplets are transformed into cold vapor.4. A fan blows warm, humid indoor air over the cold coil. Moisture in the air condenses and drips off the coil into a pan to be drained or pumped away. The gas in the coil warms as it removes heat from the indoor air.5. When the compressor turns on, it draws the warm gas toward its suction port. The gas enters as a warm vapor and leaves hot and at high pressure. Now it enters the condenser, and as it makes its way through the labyrinth of tubing, it gives up its heat to air moved by the condenser fan. The gas condenses into a warm liquid ready to repeat the cycle. The Lennox SunSource is a heat pump with a solar assist. Its condenser fan motor draws power from a 190-watt photo­voltaic panel, a $3000 add-on.

The high-efficiency heat pump itself costs $4000 to $7500, depending on the installation. The equipment runs the refrigeration cycle in reverse for winter heating, so it achieves energy gains year-round, not just in the summer cooling cycle, accelerating the energy payback of the photo­voltaics. european style ac unitsIn most cases the solar panel is installed in a sunny location, either on the roof or the side of the house. home air conditioning unit ukWiring then runs from the panel to the fan motor.ac unit making water noiseEquipment CheckThe best way to ensure a steady flow of cool, dry air this summer is to do a little basic maintenance this spring."The key to maintenance is air flow," according to PM contributor Pat Porzio, a heating-cooling contractor and mechanical engineer.

Ensure that air can move freely through the compressor-condenser by using a shop vacuum to remove grass clippings, leaves, dryer lint and any dust discharged from a central vacuum system. If the equipment is near a dryer vent, check it weekly.Clean dirty compressor-condenser fins using specialized foaming cleaner, sold at supply houses and on the Web. Don't use household cleaners, which can cause corrosion. Rinse the fins with a garden-hose nozzle pointed down, not horizontally, to avoid blasting dirt into the equipment. .+ Check the air filter monthly and replace it when necessary.+ Keep the thermostat set at 78 F.+ Seal leaky ducts with mastic and tape to prevent loss of cooled air and infiltration of dust and dirt into the duct system.+ Seal gaps around the home that allow cool air to escape.+ Open vents that were closed during the winter. Recently, we have received a few questions about the advantages and disadvantages of replacing an older R-22 outdoor unit (partial replacement) versus replacing the whole system (indoor and outdoor components). 

Since R-22 refrigerant and related equipment is being phased out over the next few years as part of the Montreal Protocol regulations to reduce the effect on atmospheric ozone, the decision about whether to stay with R-22 or jump to a new system with R410A is causing some confusion among HVAC consumers.  This is becoming a very common situation and there is really no right or wrong answer as it depends on your particular needs and your personal preferences.  We’ve compiled a few considerations and suggestions for reference. Replacing an R-22 compressor or the outdoor unit (which contains the compressor) is a good, low cost way to get your A/C  system running again without changing the indoor system (which contains the cooling coil, the blower and often is integrated with a gas furnace or other heating system).  This approach can save some money,  if the indoor components are still in good shape and you can find the R-22 outdoor replacement parts along with the R-22 refrigerant.

Many people have decided to do this and many contractors support this approach.  We think this repair will continue to be a viable, low cost repair option, at least through 2016 and maybe longer – as long as parts are available. Some other low cost replacement options should be emerging even after the R-22 availability dwindles.  Many R-22 indoor coils built since 2006 were designed to be compatible with R-410A, which means a homeowner can keep the indoor equipment but upgrade to a newer outdoor unit and metering device. There are some extra parts and steps involved but it should still be lower cost than a total system replacement. Unfortunately, just like with the R-22 outdoor replacement option mentioned above, the overall efficiency of the system typically will not improve when only the outdoor equipment is replaced. For people who are willing to pay a little more, some new, high efficiency retrofits are becoming available in the market.  These should help satisfy homeowners who want the low cost replacement but would also like to reduce their energy bills or address some comfort issues like humidity control, nighttime temperature swings or sound and air quality.