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An air conditioner is basically a refrigerator without the insulated box. An air conditioner is doing exactly the same thing as your fridge, except it dumps the heat it takes out of the controlled area and dumps it outdoors instead of in your kitchen. To understand what goes on in the system, let's start where the "freon" gas enters the compressor located typically in the outside part of the unit.
As the Refrigerant gas enters the compressor, it squeezes this freon gas that has just absorbed heat from the indoor air, causing it to become extremely hot. This is just like what happens near the end of a bicycle pump when you push the handle down. The air being compressed into the end of the pump will get hot, because all the heat that the air inside it contained, is squeezed into an area that is many times smaller than where it just was. This now high-pressure freon gas, that is now many times hotter than it was before it got squeezed, runs through a set of coils outside where a fan blows on it to cool the high temperature gas, so that a large portion of this concentrated heat is removed from it. The fan and coil arrangement outside are very similar to a radiator on a car.
As the Outside unit (or radiator) cools this hot vapor, it condenses into a liquid just like steam condenses into water when it loses its heat. This high pressure freon liquid which has now had a lot of its original heat forced out of it, is then pulled back into the house where it waits its turn to pass through a tiny opening that is the entrance to the indoor coil that sits within your home's air stream.
By using this tiny opening to "back-up" the pressure on the outdoor part of the system, it allows the compressor to maintain a low pressure side within the indoor coil that is in your home's air stream. When the cooled High pressure gas finally passes into this low pressure area, the difference in pressure causes part of it to immediately expand into a gas. In a sense, this is like the compressor working in reverse, because now the cool freon is occupying a bigger area, so the heat that was left in it now has to spread itself out over its bigger size.
This need to use its limited heat over a now bigger gas molecule, causes it to rapidly become quite cold, so that as it passes through the indoor coil, the air passing over this coil (the radiator effect again) is cooled and then spread through your home by your home's duct work. Meanwhile the heat that was taken out of your home's air, has entered the warming freon gas so that when it gets back to the compressor the whole process is repeated.
In cooling mode, a fan draws warm air from inside through a filtration system and over the evaporator coil. As the air passes over the coil, any moisture in the air condenses on the evaporator coil and then runs off into a drip tray where it is drained away. The refrigerant in the evaporator coil enters as a liquid and as the filtered air passes over the cold coil, it reduces the air temperature. The refrigerant then carries the warm air in a gaseous state to a compressor where the vapour is compressed and passed through to the condenser coil. A fan then moves air across the warm refrigerant and expels the warm air outside while reducing the temperature of the refrigerant. As the refrigerant cools down, it changes back to its liquid state and is pushed back to the evaporator coil to repeat the process.
Air Handler The air handler functions as the evaporator section of the air conditioning system. The air handler is typically located indoors and its primary purpose is to circulate the conditioned air.
BTU - British Thermal Units 1 BTU = amount of heat required to increase the temperature of 1 pound (0.45kg) of water by 1 degree Fahrenheit (0.56 degrees Celsius).
Compressor The compressor is the motor which drives the condensing unit.
Condensing Unit The condensing unit acts as a pump which compresses the vaporised refrigerant from the air handling unit, liquifies the gas and returns it to the air handler.
Evaporator Coil The evaporator is located inside the air handler unit and is where the refrigerant vaporises and absorbs heat.
The refrigerant is a substance which absorbs heat by changing states from liquid to gas (evaporating). It then releases the heat by changing back to its liquid state (condensing).
SEER - Seasonal Energy Efficiency Rating The SEER of an air conditioning unit tells you how efficiently the unit uses electricity. The higher the SEER rating, the greater the efficiency. This can be calculated by dividing its BTU rating by the unit's wattage. For example, an 11,500 BTU air conditioner that consumes 1,200 watts will have a SEER of approximately 9.5 (11,500 BTU / 1,200 watts).
Split System. A split system air conditioner allows the air handler to be installed away from the condenser. This allows more flexibility in confined spaces and also helps reduce indoor noise by having the condenser located outside.
Thermostat The thermostat is a temperature-sensitive switch that controls the heating and cooling system. If the temperature varies from a predefined setting, the thermostat turns the air conditioner on to restore the temperature to the desired level.
Air conditioning includes the cooling and heating of air. It also cleans the air and controls the moisture level. An air conditioner is able to cool a building because it removes heat from the indoor air and transfers it outdoors. A chemical refrigerant in the system absorbs the unwanted heat and pumps it through a system of piping to the outside coil. The fan, located in the outside unit, blows outside air over the hot coil, transferring heat from the refrigerant to the outdoor air. Most air conditioning systems have five mechanical components: A compressor, A condenser coil and fan A metering device or an expansion valve, An evaporator coil and blower. A chemical refrigerant
Most central air conditioning units operate by means of a split system. That is, they consist of a "hot" side, or the condensing unit—including the condensing coil, the compressor and the fan—which is situated outside your home, and a "cold" side that is located inside your home. The cold side consists of an expansion valve and a cold coil, and it is usually part of your furnace or some type of air handler. The furnace blows air through an evaporator coil, which cools the air. Then this cool air is routed throughout your home by means of a series of air ducts. A window unit operates on the same principal, the only difference being that both the hot side and the cold side are located within the same housing unit.
The compressor (which is controlled by the thermostat) is the "heart" of the system. The compressor acts as the pump, causing the refrigerant to flow through the system. Its job is to draw in a low-pressure, low-temperature, refrigerant in a gaseous state and by compressing this gas, raise the pressure and temperature of the refrigerant. This high-pressure, high-temperature gas then flows to the condenser coil.
The condenser coil is a series of piping with a fan that draws outside air across the coil. As the refrigerant passes through the condenser coil and the cooler outside air passes across the coil, the air absorbs heat from the refrigerant which causes the refrigerant to condense from a gas to a liquid state. The high-pressure, high-temperature liquid then reaches the expansion valve.
The expansion valve is the "brain" of the system. By sensing the temperature of the evaporator, or cooling coil, it allows liquid to pass through a very small orifice, which causes the refrigerant to expand to a low-pressure, low-temperature gas. This "cold" refrigerant flows to the evaporator.
The evaporator coil is a series of piping connected to a furnace or air handler
that blows indoor air across it, causing the coil to absorb heat from the air.
The cooled air is then delivered to the house through ducting. The refrigerant
then flows back to the compressor where the cycle starts over again.
Air Conditioning Systems Unrivalled standards of experience,
professionalism and customer care have combined to establish Icecape Ltd t/a RAC
Kettering as one of the UK's leading distributors of Daikin Air Conditioning
Products and Systems. RAC Kettering has chosen Daikin in 1977 as its first UK
supplier and has since grown steadily to become a major UK Distributor of Air
Conditioning Equipment with special expertise in VRV and Chiller Systems. In
addition to just supplying Daikin Air Conditioning Products, we also operate a
highly professional distribution service and demonstrate our ommitment to fully
back-up our clients by maintaining a well-stocked spare parts department.
Similarly high standards apply to the full pre and after sales support services
provided by RAC Kettering. Clients throughout the UK depend on the expertise of
RAC Kettering whose Sales Engineers operate nation-wide to give a
comprehensive design and support service. This is reinforced with a programme of
specialised product training for client's design and engineering personnel. An
experienced Technical Department assists with any engineering issue and can
provide on-site commissioning and troubleshooting.
What is air conditioning? Throughout the ages, we have sought to improve the
level of comfort offered by our surroundings. In colder regions, we have tried
to heat our dwellings and in warmer climes, to cool them down because if we are
not comfortable, we can neither work nor relax. But thermal comfort vital to our
well being, is subject to three basic influences:
Among these influences, the human factor is somewhat unpredictable. The others can be controlled in order to provide that much sought after feeling of well being. Changing patterns in construction, working practises and internal occupancy levels have created new parameters within which designers must operate. Modern buildings for instance, generate far more heat than their predecessors of say, 50 years ago and there are several reasons for this:
Solar Infiltration Developments in building technology have also given rise to an increased use of glass - even when solar protective glazing is fitted, solar gains can be considerable.
Occupants Increasing numbers of occupants, each generating some 120W/h of heat, are routinely crammed into office areas.
Electrical Appliances Computers, printers and photo copiers, all part of the modern offices scenario, also generate substantial heat loads.
Ventilation Introducing the outside air into a building also introduces its temperature something of a problem if it's 30ÂºC outside!
The principles of air conditioning are based around the transportation of
heat from one place to another and the medium generally used to effect
transportation is refrigerant. Refrigerant is used because it evaporates at very
low temperature. Physics shows that the evaporation of a substance (change of
phase) requires considerable energy.
The low boiling point inherent in refrigerant enables it to be used at relatively low temperature, such as room temperature. When a liquid refrigerant evaporates it absorbs heat from its surroundings which therefore, cool down. Evaporation causes the refrigerant to change from liquid to gas (phase change), at which point it contains considerably more energy (heat) than in its liquid state the maximum amount possible, in fact. If the refrigerant is to be reused, this heat must be released, preferably at a point where it is no longer required. Once again, physics shows that when a substance condenses, it releases much of the energy it carries thus the refrigerant must be condensed. This requires its pressure to be increased in order to raise the condensation temperature above that of the heat exhaust point. This operation is carried out by a compressor. Once returned to its fluid state, the refrigerant can absorb heat again. But its pressure is now too high, as is its condensation point and also its evaporation temperature. The problem is overcome by use of an expansion valve which allows the pressure to fall, thereby reducing the evaporation temperature to its original level. At this point the cycle can recommence. Manipulation of the refrigerant pressure enables heat to be absorbed from an area of lower temperature and released to an area of higher temperature with the corresponding result of cooling or heating.
Air conditioners are part of our lives and we enjoy their comfort everywhere.
In shops, restaurants, offices, hotels ¦it's hard to imagine life without them.
Air conditioning provides you with pure cool air when it's hot outside. But what
about winter, and those cooler periods during spring and autumn? This is when we
need heating. Not cooling. ...heating in the winter The
ideal solution to this problem is the Heat pump. It cools when it's hot, and
warms when it's cold. The choice is yours, at the push of a button. Comfort and
well being all year round. A simple principle developed to perfection
Air conditioning works like your refrigerator, which removes heat
continuously from the cabinet and discharges it into the kitchen. You can feel
this 'free' heat by touching the coil on the back of your refrigerator. In
summer, the heat pump extracts heat from the warm air in your home and pumps it
outside. Your home stays comfortable and cool. In winter, it's the reverse.
Natural heat in the outdoor air - even when it's freezing - is extracted and
moved indoors. Wonderful warmth when you need it. Comfort that costs
less Three kilowatts of heat for each kilowatt of electricity used.
Heat pumps are up to three times more economical than conventional gas fired or
electric heating systems. Installation costs are lower too. With just one system
for cooling in summer and heating in winter, you save on equipment
If we look for AIR CONDITIONING in Collins English Dictionary it states:
"A system or process for Controlling the Temperature and sometimes the Humidity and Purity of the air"
Controlling the Temperature is being able to Heat and Cool. Not only cool. The air that we breathe is made up of 3 major components all capable of carrying energy (heat):
1) The component molecular constituents of air: Oxygen (23%), Nitrogen (76%), Carbon Dioxide (< 1%) and Inert Gases (< 1%).
2) Moisture or Water Vapour: Water vapour is present in the air at all times, the quantity present being dependent upon the air temperature. The higher the air temperature the higher the water vapour (quantity).
3) Airborne Particulate: These are the suspended impurities within the air from either industrial or natural pollution such as Pollen, Dust, Smoke, Germs… etc.
As air is the only media that encompasses the whole of our body, we need to condition this air to provide comfort.
The action we need to take is:
1) Control Temperature (Heating & cooling) which entails adding energy (heating) or removing unwanted energy (cooling). General comfort conditions range between 20 - 25 °C in the UK.
2) Control Humidity (moisture content in the air), either Humidify (add moisture) when dry, which can result in dryness of skin, dry throat and encourages static built-up) or de-humidify (remove moisture) when the amount of moisture in the air is high, which can result in breathing discomfort. Comfort humidity is generally between 30-70 % RH (Relative Humidity) for the UK.
3) Provide Ventilation to provide the necessary Oxygen for breathing and dispelling carbon dioxide, Odour,dust, smoke etc. General Ventilation requirement ranges between 5 - 18 litres per second per person.
4) Provide Filtration to clean outside and inside air by removing dust, pollen, etc. Dust in dry air combined with dryness (lack of moisture in the air) is the main cause of static shocks. Lack of ventilation and filtration combined with the lack of maintenance is the main causes of Sick Building Syndrome (SBS). Therefore air conditioning encompasses HEATING, COOLING, HUMIDITY CONTROL, VENTILATION, FILTRATION.
There are many different methods of achieving comfort conditions (Heating, Cooling, Humidity Control, Ventilation & Filtration).
1) Heating and Cooling (which should be treated as one entity) are the most important parts of the Air conditioning system. Heating (adding energy): Is achieved through electrical energy input, Natural Gas Boilers, Oil Boilers and Reverse Cycle Refrigerant Heat Pump. Transfer of this energy from source to the air-conditioned space can be via air circulation (Air systems), via water circulation (Water systems) or via refrigerant (Extended Direct Expansion systems). Cooling (absorbing/removing heat): This is the reverse of heating i.e. transferring unwanted energy/heat (generated by lights, computers, people, solar heat gains through glass, structure heat gains, ventilation heat gains, etc.) from inside to outside. The transfer method is via the same media as heating transfer: Air systems, Water systems or Extended Direct expansion systems. Statement: 95% of cooling systems (air, water or Extended Direct Expansion (EDX)) use Refrigerant (vapour compression cycle or VCC) in the heat rejection process, as Refrigerant is the most efficient media and has the advantage of having a boiling temperature of -40°C (water =+100°C) and an energy carrying capacity 10 times more efficient than water and 50 times more efficient than air.
2) Ventilation which can be: A part of the whole air conditioning system, (in the case of Air Systems) where Air is also used to transfer energy. Or an independent system mainly to provide ventilation (in the case of Water Systems and EDX). However, outside air needs to be treated (heated and/or cooled and filtered) to meet indoor temperature conditions, especially in extreme winter conditions and not so extreme summer conditions. Statement: Utilising ventilation in mid season to control temperature can also provide an acceptable energy efficient solution. This is more the case in outer city areas and areas of low level, internal energy gain. Ventilation can represent a high percentage of building energy consumption, especially in centralised systems. Modular systems are more controllable, run only where needed and easily added to when requirements change.
3) Filtration is an integral part of any air movement device; the level of it depends on the type of equipment selected to provide the other parts of the air conditioning system. It can also be added to an existing system or stand-alone (e.g. electrostatic) Dependent on the application (Public Houses, etc) and special requirements (Hospitals, etc). Statement: There may be applications where due to capital cost implication, excessive ventilation (oversized) is applied to overcome the above special requirements at the expense of running cost. Localised filtration is more possible these days at low cost rather than over sizing the ventilation system
Air conditioning is to control the temperature in the main, control the humidity and clean the atmosphere that we live in. To control the temperature we have to add heat (energy) when cold and remove heat (energy) when warm. This energy has to be transported from outside to inside (Heating) and from inside to outside (Cooling). There are three main methods to transfer this energy: Air Systems, Water Systems and Refrigerant Systems. Air Systems: This where we use the air to carry the energy from inside to outside and vice versa. The use of Air Handling Units (AHU) or Roof Top Packages (RTP) to condition the air (Temperature, humidity sometimes), filter and refresh the air and send it through ductwork to the occupied space where the conditioned air will heat or cool the space as required and return via return air ducts back to the AHU or RTP. Air Handling Units contain a cooling coil (connected to a chiller or condensing unit) a heating coil (connected to boilers or electric heaters) filters and circulating fan(s). Roof Top Packages contain refrigerant cooling cycle, heating coils (connected to boilers or electric heaters), filters and circulating fan(s).
Water Systems: In these systems water is used to carry the energy from inside to outside and vice versa. The use of a chiller (on roofs or plant rooms) to cool the water which would be circulated via circulating pumps to the occupied space where it will be passed through fan coils (terminal units) which circulate room air over the coil, hence absorbing unwanted heat. The use of boilers (in plant rooms) to heat the water (separate circuit from cooling) which would be circulated via circulating pumps to and back from the occupied space where it will be passed through the same fan coil which circulate room air hence adding heat to the space. Water Systems only control the temperature. Filtering of the air is normally carried out through the indoor fan coils (terminal units). Ventilation is normally carried out through a separate system with a range of AHU and ductwork distribution system (smaller than air systems) which can be localised to the air-conditioned space.
Refrigerant Systems (Known as Extended Direct Expansion or DX Systems): In these systems refrigerant is used to carry the energy from inside to outside or vice versa. The use of outdoor condensing units (can be reverse cycle heat pump for heating) cool the refrigerant and sends it through refrigeration small bore pipe work to indoor fan coils (terminal units) where it will expand to lower the temperature of the refrigerant in the pipe, hence room air when circulated over the coil will lose its unwanted heat. Heating is achieved via the same outdoor unit by reversing the cycle or utilising a third pipe to carry hot refrigerant to the indoor unit to provide heating. Filtering of the air is normally carried out through the indoor fan coils (terminal units). Ventilation is normally carried out through a separate system with a range of AHU and ductwork distribution system (smaller than air systems) which can be localised to the air-conditioned space.
The basis of most (more than 95%) air conditioning systems is the ' vapour compression cycle". The media (vapour) is Refrigerant (hydrochlorofluorocarbons - HCFC or hydrofluorocarbons - HFC) which is non-toxic, non-explosive and non-corrosive. These Refrigerants have a boiling point of aprox. Minus 40°C which means that even if the air (outside or inside) temperature is as low as minus 39°C it still has heat to be absorbed by refrigerants.
The vapour compression cycle requires four components:
1) The compressor: To raise the pressure of low-pressure low temperature gas to high-pressure high temperature gas. There are many types of compressors; the most common are Reciprocating, Rotary, Scroll, Screw and Centrifugal.
2) The Condenser: To change the state of high-pressure, high temperature gas to high-pressure, high temperature LIQUID. This is achieved by passing ambient air (known as air-cooled) or water (known as water-cooled) over the condenser tubes.
3) The Expansion Device: The purpose of the device is to change the state of the refrigerant from high-pressure, high temperature liquid to low pressure low temperature saturated liquid. This is achieved by passing the liquid through an orifice.
4) The Evaporator: To absorb the heat from room air or water, which in
the case of a chiller is circulated around the evaporator coil. This will change
the state of low-pressure, low temperature saturated liquid to low pressure,
low/medium temperature gas. These components are common to the
vast majority of domestic refrigerators and appear in slightly different forms
in 95% of air conditioning and refrigeration systems, Domestic, commercial or
industrial. This vapour compression cycle if reversed (condenser
becomes evaporator and visa versa) can now absorb heat from outside and transfer
it to inside, hence saving energy. This is called Reverse Cycle Heat Pump. Energy
savings can be as high as 4 to 1 (for every kW input we get 4 kW output).
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