What is Air-Conditioning?

Air conditioning for buildings falls into two types, comfort air conditioning, sometimes referred to as comfort cooling and close-control air conditioning. Both types comprise control of temperature, with or without heating, but always with cooling, plus ventilation and air filtration. The quality of filtration and ventilation can vary to suit ones requirement or budget, but cooling is always an integral part and is necessary where a build up of heat inside a building will otherwise cause discomfort to occupants or damage to property. UK weather is often very humid; indeed our rainfall is renowned world-wide. It is the amount of water vapour in the air, which when coupled with warm air temperatures can make most humans very uncomfortable. That hot sticky feeling; lethargy sets in; clothing become uncomfortable. Cooling not only reduces the air temperature, it also reduces the relative humidity and this is what provides a comfortable atmosphere.

• Air-Conditioning applications for various building types are quite different and may be categorized as:

• Low-Rise Residential buildings, including single family houses, duplexes, and small apartment buildings

• High-Rise Residential buildings, such as tall dormitories and apartment blocks

• Commercial buildings, which are built for commerce, including offices, malls, shopping centers, restaurants, etc

• Institutional buildings, which includes hospitals, governmental, academic and so on Industrial spaces where thermal comfort of workers is desired

Three Main Types
Equipment and systems generally fall into three main types, all-air, all-water and all-refrigerant, however, in every case; refrigerant is used as the final cooling source or medium. Most systems these days are also referred to as air cooled, as opposed to water cooled. That is, the final rejection of heat to external atmosphere is via air, using a dry coil and fans. Water-cooled systems use a cooling tower and if this is not properly maintained can lead to problems with Legionella or Legionnaires disease.

All-Air Systems
All-air systems transfer cooled or heated air from a central plant via ducting, distributing air through a series of grilles or diffusers to the room or rooms being served. It normally comprises the cheapest equipment cost, but is not necessarily easy or cheap to install in a building due to the size of ducting required and the cost to install. It can be a problem to control temperature properly, and the system may be energy inefficient. All-air is generally rated in second place compared to other systems in relation to the amount of energy used to achieve the desired result.

All-Water Systems
Water based systems use a single chiller plant or chiller plus boiler to produce water which is then pumped around a building to, most commonly, fan coil units; a fan blows air over a coil containing the water, which then cools or heats the room air. The heat rejected from the room to the water is then pumped back to the chiller unit where it is rejected by a condenser to external air. The water is then chilled or heated again and pumped back to the room units This type of system is generally the most expensive to install and own, and is classed as the least energy efficient in terms of transfer of energy.

Refrigerant Systems
Refrigerant based systems, often referred to as DX (Direct Expansion), are by far the most efficient, cheapest and most energy efficient form of air conditioning and generally operate split or multi-split systems. Split means that there is a room or area mounted unit, generally a fan coil and an external unit, a condensing unit or heat pump. Refrigerant is pumped around connecting pipework from the compressor in the condensing unit to the room unit (evaporator) where it expands causing a refrigeration effect; the room air is blown across the coil causing cooling.
The refrigerant carrying the rejected room heat is pumped back to the outdoor unit where it is condensed, giving off the heat to outside air via a dry coil and fan. The refrigerant is then compressed into liquid again by the compressor and the cycle continues.

What Is Refrigerant?
There is often a lot of media attention given to refrigerants, most of the attention being alarmist, but the truth of the matter is that refrigerants have to be used for cooling. The most common refrigerants now in use for air conditioning are R22 and R407C. Refrigerants only damage the ozone layer or atmosphere if they are released.
There are now strict controls on the handling, use, and release of refrigerants, so you should ensure that you employ a reputable organisation to install or service your air conditioning.

Commercial Systems and equipment are as applied generally for business users or organisations, however, some residential systems can also be used for commercial applications.

Domestic System Benefits

• Air-Conditioning not only cools, it also heats, dehumidifies, ventilates and filters the air

• Air-Conditioning creates a relaxed and pleasant atmosphere in which to rest, play, and work

• Air-Conditioning  provides ventilation and air filtration, which improves air quality

• Air-Conditioning systems can be unobtrusive and quiet in operation.

• Air-Conditioning  can provide total control of cooling and heating at the touch of a button

• Air-Conditioning removes humidity, lets you sleep peacefully, no more hot, sticky, uncomfortable nights

• Air-Conditioning allows you to keep windows closed in the summer, improves security and cuts down on external noise nuisance

• Air-Conditioning  can remove dust and pollen by the addition of special filters

Commercial Installations
In a workplace, if it becomes too hot then staff efficiency will be health concerns as in extreme temperatures there is a risk of serious fatigue or heat stroke. Whilst British legislation does not set a maximum working temperature, it is interesting that the World Health Organisation recommends a maximum air temperature of 75°F/24°C for workers to work comfortably.

Uncomfortable levels of heat are more likely to cause accidents because it lowers concentration levels. Putting aside the health and safety implications of having a hot working environment, by installing air conditioning the workplace becomes a much nicer place to spend a considerable part of one’s day-to-day life. The high heat gains and expense of replacing burnt out computer equipment makes reliable server room air conditioning an essential requirement. Although widely debated, it is recommended that a server room temperature should be maintained at around  C and between 40-50% relative humidity.

Arguably, the most popular systems for medium to large commercial projects are now VRV or VRF systems, these are modular heat pump or condensing units connected to a number of room mounted fan coil units. The systems use copper pipework distribution systems to connect all the components. Refrigerant is used to provide both cooling and heating and electricity is used as the power source. These systems are inherently very reliable and very efficient and provide extremely economical running and owning costs because the capacity of each system is matched to the load by varying the refrigerant volume (VRV) or flow (VRF). VRV/VRF systems provide year round heating or cooling if required, so you do not need a boiler and radiators if a heat pump is used.

Many options are available with various means of controlling, both locally, centrally and remote, you can have cooling only, cooling and heating or heat recovery. Heat recovery can be used in some buildings to reduce fuel consumption by recovering waste heat from zones that need cooling to others that may simultaneously require heating.

Split systems can serve single rooms or areas, either cooling only or heat pumps.
Multi-split systems effectively are smaller versions of VRV and VRF and can be designed to serve up to 7 small rooms or areas.

Chilled water fan coil systems use a central water chiller providing chilled water to any number of room mounted fan coil units. Heat pumps are also available but more commonly 2-pipe systems only provide cooling as heating is dealt with by an existing heating system, or 4-pipe where a boiler is used to also supply hot water to the same room fan coil units.

Variable water temperature (VWT) systems have a common two pipe water distribution system to which are connected room or zone mounted terminal units (effectively a fan coil unit but also with a refrigeration compressor) that are heat pumps. The central plant comprises a cooling tower or other heat rejection device plus a water boiler. The temperature of the water circuit is adjusted by the central plant to suit prevailing conditions and the terminal units then adjust the required heating or cooling to suit the room requirements.

XS Engineering can provide a complete design service including power supply requirements, cable specifications/calculations and drawings. As we do not sell any air-conditioning units ourselves, you can be assured that our advice will be completely impartial.