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A Jargon free outline of what an air conditioning system comprises of, the
type of systems available, what they look like, and some considerations

Unfortunately an air conditioning system isn't something you can pick up off the shelf & plug in (Unless its a simple portable solution you require).  There are many different types of systems and it requires a specialist installer to find the right solution for the type of premises and how those premises are used.  A room full of people and computers requires a greater cooling capacity than one used for display of inorganic products.  A room with large windows facing south requires a greater capacity than north facing with small windows, depending on the other uses of that room of course. Every factor has to be taken into account to arrive at the optimum cooling and/or heating capacity.  If the equipment capacity is too small then the units may be operating at their maximum limits the majority of the time and this leads to greater component wear, higher maintenance and possibly early component failure. If the capacity is greater than needed it will be an unnecessary expense.  The details here are designed to give the newcomer a basic insight into air conditioning


Heating & Cooling or Just Cooling?

The modern office would use the air conditioning for both whereas a computer room might require cooling only.  Both systems operate on a thermostat and a unit with heating and cooling can maintain a constant pre-set temperature.  A cooling only unit can maintain a pre-set temperature providing this can be achieved through cooling.  If the room becomes too cold it can not provide heat

The Systems

The smaller system is called a Split System and consists of one indoor unit and one outdoor which  are connected via copper pipes, which carry pressurised refrigerant gasses, and electrical wiring.  This system suits a small installation to one or a few offices/rooms. For a larger requirement there are the Multi Systems which enable more than one indoor unit to be connected to one outdoor unit.  A ducted unit can be used when the indoor unit is sited away from the room/office it serves, and the hot/cold air is fed to the room via flexible or rigid ducting, terminating at an outlet in the actual room which is covered by a grill.  These units can have single or multiple outlets

Indoor Unit Types

The indoor units are designed to fit into a suspended ceiling, under a ceiling, on a wall, or floor standing and the type chosen is largely dependant on the room & furniture layout, and ceiling design. The styles vary between the manufacturers but the pictures provide examples of these main types

Ceiling Cassettes Wall Mounted Unit Under Ceiling Units
Under Ceiling or Wall Mounted
Floor Standing Unit

Outdoor Units

These have to be literally sited outdoors or in a location where there is free external natural air-flow.  Common locations are on a flat roof (Providing it will take the weight), bolted to an external wall, or at ground level in a compound or cage.  They can not be sited near a source of polluted air.  The aesthetics of the building, potential for vandalism, safety of the public, distance from the indoor units, and the weight of the units all have to be considered when choosing the outdoor unit location.  The Holiday Inn and Other Installs pages on this site show photographs of larger multi systems

Single Split System

Large Multi System

Multi System


There are a variety of options for controlling the systems and these include wired controllers fixed to a wall either near the unit or for convenience of use.  Infrared controllers provide even greater flexibility although there is more potential for damage or loss by the user.  Central controllers enable a large system to be controlled from a central point and this is useful for such as hotels.  Central controllers can be combined with individual room controllers which enable the unit to be controlled from within the same room or from a remote distance.  The controllers provide a variety of features which include temperature settings, cooling or heating only, humidity, fan only, and timing facilities
Central Controller Group Controller for
multiple units
Infrared Room Controllers


In Cooling mode, the indoor unit produces water and this needs to be drained away.  A gravity drain is used where possible which entails a pvc pipe being routed from the unit into the nearest drain e.g. a nearby sink drainage pipe, or through the wall and into a drainage stack.  Sometimes the nearest drain is above the actual unit or it might be unsightly to have a pipe running from the unit down the interior wall.  In that situation a pump is fitted which pumps the water through the drain pipe regardless of the angle


The cooling and heating capacity is measured in kilowatts and the same cabinet size can be obtained in various different capacities.  The capacity required is calculated from such factors as the size of the room, the usage of that room, the location of the room which affects heat gain or loss and a number of other similar factors.  It is well worth considering the future as if an office has only 2 people and 2 computers at the moment, could  it be that as your company grows the office might eventually have 10 people and 10 computers?  A Reception area may need greater cooling or heating capacity than a similar sized room elsewhere if the door is constantly being opened letting in either cold or warm air

Portable Units (Our Portable Range will be available for on line purchase soon)

This type of unit is self contained and can be bought off the shelf and operational within minutes.  It is not as efficient as the separate indoor/outdoor type but it does offer immediate relief for the odd hot day.  One consideration is that most units expel water and therefore either the water container has to be emptied on a regular basis, or the flexible drain outlet has to be positioned over such as a sink. New models are coming to the market which evaporate the water instead of the regular emptying but obviously this vapour is still expelled to the room.  Some units are unable to draw external air and can only merely re-process the air within the room.  Other types have a flexible duct inlet that can be used to introduce natural air from outside.  Such a duct may require a window to be open slightly.  If your cooling needs are infrequent then this is a solution you might consider.  Units are available for heating and cooling or if you want cooling only and don't want the space taken up in the winter then you might consider hiring when the need arises


The systems should have a maintenance visit approximately twice per year depending on usage.  A dusty environment may need more maintenance whereas a cooling system only used in the hot summer months may need less.  The systems have refrigerant gas and the amount of gas and the pressure it is operating under need to be checked to ensure there are no leakages or some other fault which is causing a lack of pressure which will reduce the efficiency of the system.  The indoor units have filters fitted which collect dust and bacteria from the air.  If the filters are not cleaned regularly they can begin to emit dust and bacteria into the atmosphere instead of capturing it.  It is part of the system warranty that the maintenance is carried out by a competent industry professional and you will be offered a package that includes this during the initial installation

Prices & Manufacturers

There are various manufacturers to choose from and price range varies between them as does specification. The most expensive isn't always necessary e.g. greater noise levels from cheaper units are usually not a problem in an unmanned room.  There's no point in paying for features you won't use or don't need e.g. hospital filter specification isn't necessary for most rooms.  Cabinet designs for indoor and outdoor units vary between manufacturers and some offer ultra slim-line, some require less void depth for ceiling cassettes therefore your choice may be limited due to your specific needs.  Styles of indoor unit types are not dissimilar between the manufacturers but if style is particularly important then it may come down to pure looks. If you want information on a particular manufacturer then they all have internet sites.  The technical information may or may not mean a great deal depending on you having any expertise in this field, but you can see what the various styles look like including when fitted, and there's a wealth of information on decibel noise level, filtration and everything else if you wish to do some of your own homework.  AlterTherm has no allegiance to any particular manufacturer and we look to design the system which best fits your needs within your budget and you'll find us happy to work with you to achieve that aim including answering any questions, and providing any details necessary



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