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FREQUENTLY ASKED QUESTIONS
Q. how do I choose the system for my requirements?
A. Don’t worry RAC can do all that for you with a no hassle site survey we can tall you exactly what you need.
how easy are the systems to keep clean
A. They are very easy to keep clean with easy access filters and wipeable fascias.
you supply portable air conditioning units
A. Yes, RAC can supply a wide range of portable A/C units for sale or hire.
Q. Do you do air conditioning for cars?
A. We do not undergo work on cars, but can recommend various companies that do.
Q. Do we need to have extensive building work to accommodate a system?
A. No, due to the large choice available we can recommend the right one to fit your situation and so limit disruption to your existing surroundings, any necessary pipe work or electrical cables can be kept to a minimum.
Air conditioning includes both 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:
an expansion valve or metering device
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.
Perfect comfort all year round - How air-conditioning works Air-conditioning is an ingenious way of controlling not only the temperature but also the movement and cleanliness of air inside the building. Although the process is relatively complex, the operation itself is quite simple. In most systems each indoor unit is connected by inconspicuous pipe work to an outdoor unit attached to a wall, rooftop or balcony, or located in a plant room.
Not just cooling but heating - Lower heating bills
Good for business - Better productivity Only a few years ago air-conditioning was considered as a luxury in the UK. Today many businesses regard it a necessity. In air-conditioned offices, staff work more productively and managers make better decisions.
|The demand for air conditioning continues
to grow. We all demand higher levels of comfort in our work places, hotels,
restaurants and other public places. Air conditioning in cars has become
a standard feature - no longer restricted to luxury models. Despite our
unpredictable climate the UK enjoys Europe's 4th largest market for air
conditioning and yet only some 15% of commercial buildings are air conditioned
and the residential market is only just beginning to develop.
WHY DO WE NEED AIR CONDITIONING: To offset unwanted energy (heat) in an occupied space (due to lighting, computers, people, heat gains from outside etc). To offset cold conditions (due to winter climate) i.e. to add heat. To provide clean, healthy conditions. To improve productivity by providing comfortable conditions. To improve living conditions (comfort). To increase the value of property.
WHERE DO WE NEED AIR CONDITIONING: Air conditioning is used in virtually all walks of life, as it is no longer considered a luxury, especially with the lifestyle we have today and the amount of pollution that exists. Also, with the advancement of electronics and manufacturing processes, manufacturers are capable of producing highly flexible, simple, energy efficient and low cost equipment compared to our present standards of living.
There are many types of air conditioning systems available and therefore there are factors to take into consideration when choosing a suitable system:
Capital Cost: Includes not only the cost of equipment and its installation, but also all ancillary requirements such as build work, plant location and size, electrical work, progress time, administration, etc. Whole life costs also consist of maintenance, energy efficiency and life expectancy.
Energy Efficiency (Running Cost): Energy efficiency of air conditioning systems is becoming increasingly important as it can account for the largest single element of the energy requirement of a building. Also, in the near future, energy tax might be introduced. It may be more cost effective to install a system with higher initial cost but which provides greater energy efficiency.
Maintenance Cost: Maintenance cost is often over looked in any calculation and can be very costly dependent on the complexity of the system and the availability of professional service companies.
Flexibility: Flexibility of the system should be assessed in terms of installation, operation, future expansion and changes, operation, maintenance and controls.
User friendliness: This needs to be assessed in relation to the occupier or user, the operator and/or the maintenance personnel. Many systems have standard controls, which are simple in concept yet sophisticated in nature and can combine user friendliness with full technical diagnostics.
Environmental Issues: These need to be checked, such as equipment compliance with current and future legislation in terms of CO2 emissions, Ozone Depletion & Health & Safety.
ABSOLUTE ZERO: Absolute zero is that temperature at which molecular motion stops. It is the lowest temperature possible. There is no more heat in the substance at this point.
AIR CONDITIONER: Device used to control temperature, humidity, cleanliness, and movement of air in conditioned space.
BOILING TEMPERATURE: Temperature at which a fluid changes from a liquid to a gas/vapour. At atmospheric pressure water boils at 100°C, refrigerant (R22) at -40.8° C.
BRINE: Water saturated with chemical such as salt.
CAPACITOR: Type of electrical storage device used in starting and/or running circuits on many electric motors.
CARBON FILTER: Air filter using activated carbon as air cleansing agent.
CHLOROFLUOROCARBON (CFC): A compound containing chlorine, with high risk of damaging the ozone layer.
COEFFICIENT OF PERFORMANCE (COP): The ratio of work or energy applied as compared to the energy used.
COMPRESSOR: The pump of a refrigerating mechanism which draws a vacuum or low pressure on cooling side of refrigerant cycle and squeezes or compresses the gas into the high pressure or condensing side of the cycle.
COMPRESSOR, HERMETIC: Compressor in which driving motor is sealed in the same dome or housing that contains the compressor.
COMPRESSOR, OPEN-TYPE: Compressor in which the crankshaft extends through the crankcase and is driven by an outside motor.
COMPRESSOR, RECIPROCATING Compressor, which uses a piston and cylinder mechanism to provide pumping action.
COMPRESSOR, ROTARY: A compressor, which uses vanes, eccentric mechanisms, or other, rotating devices to provide pumping action.
COMPRESSOR, SCROLL: A compressor which uses two scrolls, one is fixed while the other revolves in orbit to provide pumping action.
COMPRESSOR, SCREW: A compressor which consist of rotors having male and female gears and compresses by engaging one screw rotor and two gate rotors to provide pumping action. COMPRESSOR, CENTRIFUGAL: A compressor, which consists of impeller and volute. The impeller rotates at aprox. 10,000 rpm. Such force changes the gaseous refrigerant into speed energy, which is converted into pressure energy for compression.
CONDENSING TEMPERATURE: Temperature at which a gas changes from a gas to a liquid.
CONDENSER: The part of refrigeration mechanism which receives hot, high pressure refrigerant gas from compressor and cools gaseous refrigerant until it returns to liquid state.
CONDENSING UNIT: That part of refrigerating mechanism which pumps vaporised refrigerant from evaporator, compresses it, liquefies it in the condenser and returns the liquid refrigerant to refrigerant control.
COOLING TOWER: Device, which cools water by water evaporation in air. Water is cooled to wet bulb temperature of air.
CRYOGENICS: Refrigeration which deals with producing temperatures of 250°F below zero (- 157°C) and lower.
D-BACS (Daikin Building Air Conditioning Control System): Computer operated control/management system utilising information generated by Daikin and other equipment.
DEFROST CYCLE: Refrigerating cycle in which evaporator frost and ice accumulation is melted.
DEHUMIDIFIER: Device used to remove moisture from air in enclosed space.
DRY BULB: An instrument with sensitive element, which measures ambient (moving) air temperature.
DRY BULB TEMPERATURE: Air temperature as indicated by ordinary thermometer.
ELECTROSTATIC FILTER: Type of filter, which gives particles of dust electric charge. This causes particles to be attracted to a plate so they can be removed from air stream or atmosphere.
ENERGY: Energy is the capacity or ability to do work.
EVAPORATION: A term applied to the changing of a liquid to a gas. Heat is absorbed in this process.
FREEZING POINT: The temperatures at which a liquid will solidify upon removal of heat. The freezing temperature for water is 32°F (0°C). at atmospheric pressure.
GRAIN: A unit of weight and equal to one 7000th of a pound (0.064 grams). It is used to indicate the amount of moisture in the air.
HEAT RECLAIM VENTILATION (HRV): Ventilation system operates on the principle of reclaiming energy from exhaust air.
HEAT: Heat is a form of energy. It is related to the molecular motion or vibration. HEAT EXCHANGER: Device used to transfer heat from a warm or hot surface to a cold or cooler surface. Evaporators and condensers are heat exchangers.
HEAT LOAD: Amount of heat, measured in Btu, which is removed during a period of 24 hours.
HEAT PUMP: A compression cycle system used to supply heat to a temperature controlled space, which can also remove heat from the same space.
HEAT TRANSFER: Movement of heat from one body or substance to another. Heat may be transferred by radiation, conduction, convection or a combination of these three methods.
HORSEPOWER: A unit of power equal to 33,000 foot pounds of work per minute. One electrical horsepower equals 746 watts.
HUMIDIFIERS: Device used to add to and control the humidity in a confined space.
HYDROCHLOROFLUOROCARBON (HCFC): A compound containing chlorine but since hydrogen is present, the risk of damaging the ozone layer is low.
HYDROFLUOROCARBON (HFC): A compound which does not contain chlorine and does not damage the ozone layer.
HUMIDITY: Moisture; dampness. Relative humidity is ratio of quantity of vapour present in air to greatest amount possible at given temperature.
LATENT HEAT: Heat energy absorbed in process of changing form of substance (melting, vaporisation, fusion) without change in temperature or pressure.
POWER: Power is the time rate of doing work.
PSYCHROMETER OR WET BULB HYGROMETER: An instrument for measuring the relative humidity of atmospheric air.
PSYCHROMETRIC CHART: A chart that shows the relationship between the temperature, pressure and moisture content of the air.
REFRIGERANT: Substance used in refrigerating mechanism to absorb heat in evaporator coil by change of state from a liquid to a gas, and to release its heat in a condenser as the substance returns from the gaseous state back to a liquid state.
RELATIVE HUMIDITY: Ratio of amount of water vapour present in air to greatest amount possible at same temperature.
REVERSING VALVE: Device used to reverse direction of the refrigerant flow depending upon whether heating or cooling is desired.
SENSIBLE HEAT: Heat, which causes a change in temperature of a substance.
SHELL_AND_TUBE FLOODED EVAPORATOR: Device, which flows water through tubes, built into cylindrical evaporator or vice-versa.
SKYAIR: Skyair is a trade name of Daikin middle range split systems. SOLAR HEAT: Heat from visible and invisible energy waves from the sun.
SPECIFIC GRAVITY: Weight of a liquid compared to water, which is assigned value of 1.0.
SPECIFIC HEAT: Ratio of quantity of heat required to raise temperature of a body one-degree to that required to raise temperature of equal mass of water one degree.
SPECIFIC VOLUME: Volume per unit mass of a substance.
SPLIT SYSTEM: Refrigeration or air conditioning installation, which places condensing unit outside or remote from evaporator. Also applicable to heat pump installations.
SUBCOOLING: Cooling of liquid refrigerant below its condensing temperature. SUCTION LINE: Tube or pipe use to carry refrigerant gas from evaporator to compressor.
SUPERHEAT: Temperature of vapour above boiling temperature of its liquid at that pressure.
TEMPERATURE: Degree of hotness or coldness as measured by a thermometer; measurement of speed of motion of molecules.
THERM: Quantity of heat equivalent to 100,000Btu (105,500 kJ).
THERMOSTAT: Device responsive to ambient temperature conditions.
VACUUM PUMP: Special high efficiency compressor used for creating high vacuums for testing or drying purposes. VAV (Variable Air Volume): A central air conditioning system which works on the principle of supplying constant temperature air volume to a space, and by varying the volume, controls room temperature.
VRF (Variable Refrigerant Flow): A direct expansion, modular central air conditioning system providing heating and cooling. Operates on the principle of varying the flow of refrigerant to a room terminal unit to achieve desired temperature.
VRV (Variable Refrigerant Volume): Trade mark for Daikin VRF systems:
VVT (Variable Volume Variable Temperature): Same principle as VAV, except two ducts are required, one for heating, one for cooling, with variable control dampers.
VWT (Variable Water Temperature): Same as VWV but changing both the volume and the temperature of the water to achieve room temperature.
VWV (Variable Water Volume): A central water based system operating on the principle of supplying constant temperature of chilled/hot water to room terminals and varying the flow to achieve room temperature.
WET BULB: Device used in measurement of relative humidity. Evaporation of moisture lowers temperature of wet bulb compared to dry bulb temperature in same area.
WORK: Work is force multiplied by the distance through which it travels.
Refrigeration and Air Conditioning Kettering was founded in 1970's and has now become one of the most respected names in the UK air conditioning industry, distributing air conditioner products.
Philosophy : To sell the best and widest range of available products. To offer the best engineering solutions.To provide a complete service from training to delivery, seminars to design assistance and a complete range of complementary accessories. RACe's long term strategy has always been to develop the UK market from a position of strength via technical knowledge, experience and sound financial management supported by technical expertise and long term vision. RAC has high service standards and is committed to customer satisfaction, ensuring the customer receives the right system to suit their requirements and budget, perfectly, right from the very beginning.
Air conditioning in a motor vehicle is a combination of the car heater and a refrigerant circuit. This allows the desired climatic conditions to be maintained regardless of the outdoor conditions. This makes air conditioning a significant factor for safety and driving comfort. The refrigerant circuit. The individual components in the refrigerant circuit are connected with one another by hoses forming a closed system. The refrigerant circulates in the system driven by the compressor. The circuit is divided up into two sections: The section between the compressor and expansion valve is called the high-pressure side (yellow/red). Between the expansion valve and compressor we speak of the low-pressure side (blue). In the compressor the gaseous refrigerant is compressed and thereby heated highly. Under high pressure it is pressed through the condenser. Here heat is removed from the highly heated refrigerant causing to condense and thereby changing its state from gaseous to liquid. The drier, the next station, separates impurities and air inclusions from the now liquid refrigerant. This ensures the effectivity of the system and protects the components from damage resulting from contamination. Then it passes from the drier to the expansion valve. This valve is similar to a dam. In front of the dam it maintains a uniform pressure, and in back of the dam this pressure is relieved due to the increase in volume. Since the expansion valve is located directly in front of the evaporator, the refrigerant expands into the evaporator. During evaporation, a change in the state from liquid to gaseous, heat is absorbed from the surroundings. The evaporator is a heat exchanger similar to the condenser. It has an enormously large surface, over which it can absorb heat from the surroundings for evaporation. This cold air is then blown into the vehicle passenger compartment by the ventilation system where it ensures the comfort of the passengers. On the low pressure side the refrigerant is again gaseous flows to the compressor where the circuit starts over again.
a computer room air conditioner
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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