How to size and select an Air Conditioning System.

Introduction – types of machine and running costs.

What types of machine are available?

Common terms to describe features within an AC system.

What capacity is required for my application?

Types of indoor air conditioner cassette available.

What is involved with installing a true single split Air Conditioning System.

Manufacturer Table.

Introduction.
The information here is to provide a general guide on selection and installation and an indication of what items to lookout for when considering selecting a suitable contractor or undertaking a suitable DIY air conditioning unit, there are many types of air conditioning unit on the market offering many features , in addition there are many different brands do not be fooled by thinking if they look the same on the outside they are internally they could be worlds apart in technology, reliability and performance.
This information is based on our experience over many years at GT Mechanical Services and if you would like any further advice please contact Gerald Seager you can visit our website @
www.gt-mechanical.co.uk or alternatively email on gerald.seager@ymail.com we are always happy to assist where we can.

What types of machine are available?

Mobile Air Con. units
these are usually free standing with a short 6”hose to be passed through a window or door these items serve a purpose for spot cooling but very uneconomical to run for any length of time or within a large open area, the main reason they are so expensive is due to using a 13 amp three pin plug this limits the current they can draw on single phase which in turn limits the compressor size and the fact you pass a hose through an aperture means there is normally a large gap to allow the air within the environment to be displaced, in short they are far from ideal and rarely provide a satisfactory solution to peoples cooling requirements and require constant attention.

Fixed
These are permanently fixed into position with an indoor evaporative cassette drawing heat from the room when the gas with the circuit is allowed to expand with the fan coil, coupled with a suitable outdoor condensing unit which compresses the gas back to a liquid and expels the unwanted heat to the outside air, these systems allow for the air within the environment to be controlled without needing to leave windows and doors open during the operation of the device, these air conditioning systems are usually called single split systems, in addition to the energy saving over mobile units these systems also tend to make much less noise and vibration.

Common terms to describe features within an AC system.

Fixed Speed
This means the compressor runs at a constant fixed speed and typical costs forty percent more to run than an Inverter driven unit of the same size
Inverter
This is a general term within the industry to describe the use of a speed control drive on the compressor within the outdoor condensing unit allowing it to run only at the speed required to serve the exact energy requirement at that moment i.e. when the room being cooled is near the required temperature and only a fraction of the systems overall capacity is required.
Single Split
This is the term for an air conditioning system which has one outdoor condensing unit supplying one indoor cassette, sizes range from 1.8Kw through to typically 14Kw
Multi Split
This is the term used for an air conditioning system which has one outdoor condensing unit supplying more than one indoor cassette; these can work out a little more expensive when only a few indoor units are required over single split, but when considering location and visual impact on the external elevations of a property can still be advantageous.
Heat Pumps
This term is used to describe a machine which can reverse the gas cycle and heat a location by recovering heat from outside even on the coldest days
VRF/VRF
This is used to describe large industrial packed units with one outdoor condensing unit coupled to many indoor cassettes.
BTU’s
This is a term for a British Standard Unit of energy (it is the energy required to lift the temperature of one pound of water by one degree).
Kw
This is another expression of energy 1000 watts per hour/1Kw there are approx 3500BTU’s in a Kw so the conversion is easy divide BTU’s by 3500 and you will have a rough ideal of capacity.
ECA
Enhanced Capital Allowance government scheme for approved energy efficient AC systems allowing the total machine and installation cost to be claimed against the financial year.

What capacity is required for my application?

There are a few simple rules which allow you to get a rough idea of the size and type of machine which is required, this allows you to get an idea before you move forward with any purchase if the unit you select is too small the machine will fail you when you need it most on the hottest days, and if to big the location will suffer large uncontrollable thermal swings and cost more to run, to get a rough idea without the technical mind melt we use the following for a rough indication.
New build well insulated construction    115 to 125 watts per square meter.
Older more traditional construction         130 to 150 watts per square meter.
Additional allowances must be made for rooms with many large windows, conservatories or a location which sees direct sunlight for long durations.

Types of indoor air conditioner cassette available.
High Wall.
Mounted at high wall level usually a small rectangular unit.
Low Wall.
Mounted at low level and similar in appearance to small night storage heater.
Ceiling suspended cassette.
This item is used in most offices and shops as it is more expensive than a high wall (approx 40% more) and is mounted flush within suspended ceilings with four way discharge louvers.
Below Ceiling Cassette
This item is mounted below a solid ceiling when there is not enough void to mount the unit above they are also sometimes also called mouth organs due to their general appearance?
Ducted Above Ceiling Unit
This system is a fan coil cased in an insulated manifold mounted within a ceiling void allowing the installer to duct the conditioned air through grilles and louvers into the desired areas this systems offers the least visual impact, but has a down side as theses air con systems are a little more expensive due to the need for more consumable parts and more involved install process.

What is involved installing an Air Conditioning System?

In short unless you installing a push fit DIY product (not recommended) quite a lot more than you imagine see the general schedule of installation below, if the work is done correctly by an experienced engineer this looks quite simple and this is where many people watching fall foul and think it is just a few pipes and bit of flex and might be tempted to have a go, must add at this stage suppliers do not help as some mislead customers into thinking machines are DIY when they are not, a good indicator of this is ask them to explain how to commission the item in question, or better still send you details if it involves purging refrigerant you are being sold something you will almost certainly not be able to install or commission further more will not operate for long without fault.
Also intentionally releasing HCFC or CFC refrigerant gas is strictly against the law and can carry large penalties and should be reported to DEFRA or REFCOM see links on our main page.

What Involved.
1)Identify locations for indoor and outdoor unit taking into account the manufacturesspace and location requirements.
2)Ensure pipe work distance and pipe work head levels are not exceeded.
3)Mount indoor unit using suitable materials for example uni strut and studding.
4)Mount outdoor cassette on suitable brackets if wall mounted or firm base.
5)Decide your pipe work interconnecting cable and condensate drain route and method of fixing example cable tray surface mount or trunking etc.
6)Once all above is mounted connect your insulated copper pipe using suitable flairingtool and make off the electrical terminations ensuring not to mix the cores as this could cause damage in parts greater machine is worth.
7)Pressure text the gas circuit using only dried nitrogen to a suitable pressure for the type of gas to be contained with it, be aware modern gases use much high pressures than traditional ones.
8)Connect the condensate removal drain this is the hose used to allow the moisture removed from of the air by the indoor unit to drain away, if the machine is on aninternal wall or water requires lifting away a pump might be required (this must be fused by installer).
9)Once the pressure test has been completed and it is established there are not leaks the pipe work can be evacuated using a suitable pump, the system will normally require a vacuum being held in the circuit for at least three hours of not less than 2 Torr but you should try and achieve around 0.5 minimum, as the engineers GT Mechanical know if the system will not go down this far there is a good chance there is a leak within the installation which will result in a gas leak fault within the first few months of operation.
10)Once the pipe work has been evacuated the gas must be released into the circuit from the outdoor  condensing unit without any air being allowed to enter at any time failure to ensure this will reduce the machines performance and lifespan dramatically.
11)Install suitable mains feed usually to the outdoor unit.
12)Test electrical Installation.
13)Commission system in line with manufactures requirements.
14)Test condensate removal drain for correct operation.

If the above is done well you have a good reliable installation if not best not start in the first place as if done poorly will result in nothing but problem after problem.

Manufacturer Table.
At GT Mechanical Services we would recommended you aim as high up this list as your budget can afford the top few being the preferred option, and ideally on the ECA anything else can be a big false economy with regard to running costs.
Daikin.                                               
Mitsubishi Electric                            
Mitsubishi Heavy Industries.           
Hitachi                                                           
Panasonic                                                      
Toshiba
Carrier
IMI
Marstair
Fujitsu
Samsung
York
Sanyo
Vent Axia
Airflow
Airwell           
Gree               
Another good indication is to visit www.eca.gov.uk  and check the item you are considering is on the register if not you cannot claim the full capital cost of the machine within the first year and also cost you a lot more to run than one that is, should save you more than the total initial purchase over lifetime of A/C System.