What sort of system should I buy?
SPLIT SYSTEMS.
The most common form is a split system with an indoor unit and an outdoor unit coupled together with two pipes and a communication and supply cable. They are simple systems and can be installed in less than a day. The indoor (cooling) coil is designed to do one room only so if you are thinking of getting a larger sized unit to do two rooms do not waste your money you will have one room at 21C and the other at 31C. If you wish to do more than one room you will need a multi head unit (one out door unit running two to four indoor units). These units have an inverter which varies the speed of the A/C compressor to suit the load from the indoor units. Advantages are One (albeit larger) electrical supply required for the outdoor unit. Disadvantages are one fault in the outdoor unit and all indoor units are out of service. A much more complex pipe run and therefore, has the potential for more leaks. Repairs out of warranty are more expensive. A large compressor is running a small load when only one indoor unit is required. They are made to recirculate room air and their is no allowance for fresh air.
Single indoor unit systems for each room means only one smaller system runs per room cooling and will be cheaper to run. Breakdowns only affect one room. Out of warranty repairs are less complex and cheaper. One common problem of both is that indoor units need to be installed on outside walls so that the unit can naturally drain the condensate to outside. Units generally should be installed on the centre of the wall for even air flow. Units installed on inner walls will require a small water pump to drain the water through the ceiling space to outside or directly on to the roof. The filter should be cleaned once a month and the evaporator with a foam cleaner every twelve months at least. The outdoor unit should be installed on a wall out of direct sunlight with plenty of ventilation preferably away from soil and dust.
DUCTED SYSTEMS
Ducted systems are more commonly used in commercial buildings or larger houses where rooms are extremely large or multiple rooms are cooled at the same timeand are generally considered uneconomical in the smaller sizes. They are more expensive to install and maintain. Ducts are usually round flexible or rectangular sheet metal and insulated. They should be coated in tropical climates with a mould and fungus inhibitor which also helps with odour control. These systems can modulate a certain amount of fresh air into the building to prevent stale air. The fresh air can be set at a constant air quantity or can be modulated with a CO2 monitor for more efficient operation. The fresh air duct can also be modulated by temperature to take advantage of cooler night time temperatures in temperate areas allowing for less outdoor unit operation and greater efficiency gains (often referred to as an economiser). Ducted systems generally allow for more sophisticated air filtration and therefore can deliver a better overall indoor air quality than a standard split system. Air return will be required in each room either by ceiling return or appropriately sized door or wall vents. Where possible the ceiling space can be utilised as a return air plenum which saves money on running multiple return air ducts to each room. Each varying room load is controlled by an adjustable air volume damper and a separate room thermostat strategically located. More efficient systems have electronically controlled variable air volume dampers (VAVs) which help decrease energy costs. Zone control can be installed to isolate areas that are not being used. Supply air registers are round square or rectangular and are strategically place to prevent dead air pockets. Slot diffusers are often required above large glass areas with a high solar load. A higher amount of maintenance is required due to the ductwork, filtration and extra complexity and therefore higher maintenance costs.