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    Everything You Need To Know About Air Conditioning Units

    Air Conditioning Units Guide

    What are air conditioners?

    Air conditioners are machines that take in and alter or treat the air around them - usually operating within an enclosed indoor zone or environment - before recirculating or expelling it for the benefit of users in that area.

    Any such machine installed as part of a broader HVAC (heating, ventilation and air-conditioning) system might technically qualify as an air conditioning unit. In everyday usage, however, the terms ‘air conditioner’, ‘air con’ or ‘AC’ almost always signify a unit designed to rapidly chill excessively warm air, helping to create a more comfortable living or working environment for people in the immediate vicinity.

    In this guide, we’ll look at some of the key definitions, functions and varieties of air conditioners available on the UK market, and identify the sorts of roles they most commonly fill across a broad range of homes and offices today.

    Who invented auto air conditioning?

    Although the sleek, powerful, user-friendly air conditioners we’re all familiar with in the 21st century continue to evolve even now, the origins of modern climate control units and techniques actually lie much further back than most people might realise.

    In fact, two early but very significant steps were taken in the development of A/C technology as long ago as the mid-1800s:

    • British chemist, physicist and inventor Michael Faraday - best known as the inventor of the Faraday Cage, a technology for blocking and dissipating electric fields that we still use widely today - was among the first to discover that air could be chilled using compressed and liquidised ammonia.
    • Following on from this breakthrough, Philippines physician Dr John Gorrie developed Faraday’s idea of using compression forces to reduce the temperature. He went one step further and actually came up with a workable compression-based system for creating ice, which he used to cool rooms in a Florida hospital.

    After this, the earliest versions of the modern air con unit we’d recognise today were later prototyped by US inventor Willis Carrier in 1902. Tasked with solving an ambient humidity issue for a Brooklyn printworks, he took the (then relatively recent) concept of mechanical refrigeration, and developed a machine that worked along similar lines - but with a strictly HVAC/thermal management focus, as the problem demanded.

    Carrier’s inspired solution was a device that funnelled the warm, moist air of the printworks through a series of copper coils filled with cold water. As it wafted over these coils, the air cooled quickly enough to deposit much of its moisture on the exposed metal pipework as condensation, exiting at far lower temperatures (and significantly drier) than it had gone in.

    It would still be another four or five years before the generic name ‘air conditioner’ was coined, and of course, those earliest bespoke creations were hardly practical: bulky, loud, and prohibitively expensive. However, Carrier felt the idea had much broader potential, and stuck with it. The eventual result was an establishment of his pioneering Carrier Air Conditioning Company of America.

    In 1933, it was under this same catchy branding that the first belt-driven, mechanically controlled evaporator coil AC units began to roll off the production line in America. Nearly a century later - innumerable tweaks and improvements to the basic formula notwithstanding - many of Carrier’s basic innovations are still central to the quiet, compact, sensor-driven and energy-efficient units we rely on today.

    How air conditioners work

    While we’re all familiar with what an air con unit does (for the purposes of this guide, we’ll refer broadly to machines designed for cooling), fewer of us could confidently describe what’s going on under the hood.

    You can dive to frightening depths in researching the precise scientific formulae involved at each stage of the process, of course. For more of a general skim, though, here’s a simplified breakdown of the key steps a modern air conditioning system goes through in order to keep you cool:

    1. A thermostat sets the temperature you want to achieve in a given space, and ambient sensors communicate with the A/C unit, automatically starting or pausing the mechanical cooling process.
    2. When requested, the air conditioner sucks in warm air from the room through a (somewhat confusingly named) blower motor - essentially a series of powerful fans - and channels it over a network of hollow, sealed metal coils.
    3. These closed coils contain refrigerant compounds; chemicals that can easily be forced to change states from a liquid to a gas. This phase conversion process is endothermic, meaning it naturally absorbs heat, and so the metal coils quickly lose warmth to it.
    4. As air passes over the coils, it too drops in temperature as this ongoing phase conversion continues to pull in heat. Moisture in the air is also deposited on the coils as condensation at this stage and drained off.
    5. Because there’s a finite amount of refrigerant contained in the coils, the liquid-to-gas state change will eventually need to be reversed, so that the cycle can keep running. To achieve this, a compressor in the A/C system kicks in, forcing the vaporised refrigerant back into liquid form.
    6. As you’d expect, reversing the phase conversion process also reverses the outcome. It becomes an exothermic process, meaning it expels heat; the opposite of the desired effect. For this reason, the compressor is usually located on an exterior roof or wall - warm air generated at this stage is directed away from the immediate area, which why you’ll often feel a warm draft from exterior vents around air-conditioned buildings.
    7. These processes are, in effect, looped continuously while the A/C unit is working, with the resulting cold/warm air streams being directed into/outside the building. Indoor cooling can, therefore, continue for as long as necessary to reach the temperature on the thermostat.

    Types of air conditioning units

    Given the variety of home/work environments air con units are deployed in, and the diverse range of temperatures and humidities they’re expected to maintain in various locations, it’s no surprise that there’s a wide selection of AC units and system configurations designed and sold by suppliers worldwide.

    Many of them also pack in some fairly major additional features and functions alongside their basic cooling properties. In this section, we’ll give an overview of a few key types to look out for.

    Split wall-mounted units

    Split AC units are a popular method of physically separating out the two main ‘stages’ of an air conditioner’s work. They’re installed in two parts; an indoor unit and an outdoor unit. The former contains the blower and cooling coil, while the latter houses the condenser coils, compressor, capillary tubing and so on.

    A split unit AC is therefore much easier to install in most settings, as there’s no complex or invasive ductwork system that needs to be run through the interior of a building to divert out the warm air - that part of the transfer is already happening outside. Additionally, this division of labour tends to mean that a split unit air conditioner runs more quietly for those inside the premises.

    It also allows for hooking up multiple intake units to a single outside processing unit, which leads to greatly increased efficiency over time. The main drawback of a split unit is that the initial buy-in cost is usually heftier, although lower energy bills will usually see this more than recouped in the long-run.

    Single portable units

    Single portable AC units offer all kinds of flexibility bonuses - as the name implies, they can freely be moved from room to room as and when needed. However, the main caveat here is that you’ll need to have a way of venting them directly to the outside in any/all locations you wish to use them. Usually, this will mean finding a suitable window, although patio doors or even pet doors would technically work just as well in many cases.

    It should be noted that most portable air conditioners still aren’t exactly easy to move - they can be extremely heavy, even if they’re wheeled - and that they’ll also need to be manually emptied of water on a fairly regular basis, (they’ll automatically shut down when full). They’re very handy for short-term fixes, but are only ever really suitable for cooling one room at a time; if you need air conditioning over a wider area, then other options will likely prove more efficient.

    Units with dehumidifiers

    Combination air conditioner-dehumidifier units are also common, which isn’t surprising - the two types of machine perform almost identical functions in terms of removing moisture from the air, and they do it using much the same methods as each other. What tends to differ wildly is how the waste products get dealt with.

    While air conditioners channel warm air outside the room or building they’re trying to cool, dehumidifiers usually churn it back out in the immediate vicinity. Similarly, the moisture removed by air con units (as a natural consequence of the heat transfer process) is often automatically drained away to the outside too - dehumidifiers, meanwhile, tend to rely on their owner manually emptying an integrated bucket system every so often.

    Units that combine both functions can, therefore, err one side or the other - in most cases, the more cost-effective combo AC units with dehumidifiers will require more manual input to keep them ticking over. Pricier models will often be able to direct moisture outside automatically, provided you’re able to create the necessary ducting routes to allow for that.

    Units with heaters

    Combined air conditioning and heating units might sound like a bit of a contradiction in terms at first - and in many ways they are, but that’s sort of the point. As we’ve outlined in previous sections of this guide, the mechanics of how an AC unit works means that heat is always going to be generated somewhere as a natural part of the process. In a cooling-only scenario, that heat will need to be channelled away from the area as efficiently as possible.

    In more changeable climates, though, users will often have very different temperature requirements at different times of the year. That’s where a portable air conditioner-heater might come in handy: the only real difference with these sorts of units is that the heat pump can effectively be reversed. At the flick of a switch, users can instruct these versatile machines to direct warm air created at one end of the phase conversion process back into the room, instead of always to the outside

    Uses for air conditioning units

    While the core mechanics of all AC units are always fairly uniform and predictable, air con uses themselves are almost as diverse as the many makes and models of conditioner available to buy. For example

    Domestic use

    In many countries around the world, domestic air conditioning units represent by far the biggest sector of the overall AC market. This may not be the case in the UK, for obvious reasons - we tend to be more concerned with trying to stay warm than anything else.

    However, for the brief month or two each year when it can be nice to have the air around the house feeling a little fresher and less stifling, portable air con units for short-term domestic use are always a popular choice.


    Air conditioners for garages are useful for freshening up the general fug of auto fumes, gardening products, cleaning chemicals and DIY essentials that can linger in these small, multi-use spaces. Various sorts of combo units (such as AC with dehumidifiers or heaters) can really help to stabilise the overall ambience and humidity in what is often a highly changeable environment.

    Smaller portable ductless air con units for occasional or seasonal use are becoming increasingly popular in domestic garages, especially with growing numbers of people looking to make better use of their entire living space for home office, leisure or storage purposes.


    Conservatory air conditioning units can be a real bonus at almost any time of year - these ever-changing environments, often built in relatively exposed locations around the exterior of British homes to ‘bring the outdoors in’, can swelter in summer but feel far too chilly for comfort at many other times of the year.

    Air con units for conservatories can really help to stabilise and control this sort of environment, transforming an otherwise gloomy or oppressively humid garden room into somewhere relaxing to sit all year round.

    Commercial use

    Commercial air conditioning can take on a great diversity of forms and functions. In many cases, just as with domestic versions, it will chiefly be about keeping individuals comfortable, productive and happy. However, there are also some slightly more specialised roles played by popular AC setups in a variety of industries and sectors.


    Depending on what the pervading air quality and the ambient temperature is like in any given business or workplace, office air conditioners could be an absolute must for achieving a content and motivated workforce. Industrial building-wide AC systems are commonplace in many types of an office environment, but portable office air conditioners might well be an equally viable option if you’re renting a workspace, or in any other circumstance where it’d be overly expensive and impractical to install a large-scale plumbed and hardwired system on a budget.


    Cavernous spaces, polished surfaces and a lack of direct access to purer air from outside can mean that many intensive retail environments quickly start to feel too hot, stuffy, chilly or stale. Retail air conditioning can help enormously to lift the general atmosphere inside a busy, high footfall showroom or shop floor space, which can quickly translate into tangible benefits for staff, customers and turnover alike.

    Server Rooms

    Air conditioning units for server rooms can play a crucial role in keeping vital hardware ticking over at optimal temperatures and humidity levels. Precise climate control for server racks and storage facilities is something of a delicate science, and one that’s rightly taken very seriously across the IT industry, and server room AC is therefore regarded almost as a separate, specialised branch of the HVAC buying industry.

    For further guidance on this or any other aspect of planning and costing an air conditioning purchase for home or work, please feel free to contact a member of our expert support team any time.

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