Air Conditioning

In our units a heat pump is used in which the device uses energy to transfer heat from a cooler to a hotter location. In a standard air conditioner an unidirectional heat pump which moves heat only form a cool interior into a hotter exterior. Air conditioning units can reverse the refrigeration cycle, from removing cool air from the exterior and moving into the interior, it will remove the heat from the cooler exterior and re-produce it in the warmer interior, therefore heating the room in a given area. Using an air conditioner is a far more efficient way of heating a space as opposed to using an electric heater which uses an element to cool the room. When the heat pump is enabled the indoor evaporator coil switches roles and becomes a condenser coil, producing the heat, and the outdoor becoming the evaporator coil, venting air colder than the ambient outdoor air.

Heat pumps work most efficiently in mild winter climates, between 4-13 degrees Centigrade, this is because heat pumps become inefficient in extreme cold temperatures as ice forms on the outdoor unit coil, blocking the air flow, to compensate for this the air conditioner must temporarily switch back into the regular cooling mode to switch the outdoor evaporator coil back into the condenser coil to de-ice the coil. An air conditioner used this was used electrical resistance therefore heating the indoor air path in this mode to compensate for the temporary air conditioning, which would drop in interior temperature without this option. The icing problem becomes worse the lower the outdoor temperature reaches.

Hose systems are vented to the outside via air ducts. The “Monoblock” version collects the water in a bucket or a tray, the pump will stop once full. The air to air version re-evaporates the water and discharges it through the duct hose, this can then run continuously.A single-duct unit draws air out of the room to cool its condenser; it will then vent it out of the room. This air is reimbursed by hot air from outside or alternate rooms. Thus reducing the efficiency of the air conditioning unit. Modern units typically run on a 1:3 ratio, for example to produce 3kW of cooling this will only use 1kW of electricity. A dual-duct unit draws air from outside to cool its condenser instead of from inside the room, This is more efficient than most single-duct units. Here we recommend 25m2 can be cooled by 12,000BTU/h, 40m2 can be cooled by 18,000BTU/h etc. This is not a set rule, other factors will affect the total heat load, for example a conservatory will need a higher powered system due to glass having a low insulation factor. 

Portable air conditioners are one complete unit, on wheels to ensure it can easily be moved around the home or office. The portable units available are vast, ranging from 6,000 to 60,000 BTU, some will even come with heaters built in. Portable A/C units are commonly found in 2 forms, split and hose. Evaporative coolers are also available in a portable form. Air Cooled portable air conditioners are compressor based, using compressed refrigerant to exchange heat, in the same way a car and typical air conditioners work. With this type of system the air is dehumidified whilst it’s being cooled. They collect the water that is condensed from the cooled air, and will produce hot air which is vented outside the cooled area( released from the outdoor air conditioning unit).

In 1990 Aimed to reduce consumer energy bills by approximately 25 billion pounds in 10 years. As of the millennium, the standards reduced the American carbon emissions from fossil fuel consumption by almost two percent. To keep the emissions down, prices have increased slightly; the Lawrence Berkeley National Laboratory research indicated the benefit energy savings are over three times the cost on a net-present value basis.

In 2000, the standards reduced the peak generating needs by approximately 21,000 megawatts (MW), which is over 70 300 MW power plants thus reducing the costs. As redundant applications are replaced by new ones the positive impact of the energy efficiency standards will continue to grow. From 1990 to 2030, it is estimated that consumers and businesses will save approximately 90 billion pounds just from the existing standards that have been adopted. Currently, the debate concerning appliance efficiency standards has revolved around the Bush Administration’s proposal to weaken the standard for air conditioners from the SEER 13 standard set by the Clinton Administration to a SEER 12.

Air Conditioning units are operated by electricity as standard. Any input of energy into the system that will be used to maintain a set temperature, will require the energy rate from the air conditioner to increase. This increase has the effect that for each energy input the air conditioner has to remove it. In order for the air conditioner to do that the air conditioner must increase its consumption by the reverse of its efficiency. As an example, presume a closed system had a 100 watt light bulb activates, and the air conditioner has an efficiency of 200%, the air conditioner’s energy consumption will increase by 50 watts to compensate for this, thus making the 100W light bulb consume a total of 150 watts of energy.

Air conditioners typically operate at efficiencies of significantly greater than 100%, see the next blog.

With air conditioning units there are little maintenance that needs to be done to the machine to ensure it is working at optimum temperature. To ensure your unit is clean and is producing filtered air you need to clean the filters (simply pull out and wash in warm water) and ensure the inside of the unit is clean. If your unit is not cleaned and maintained regularly bacteria builds up and promotes the growth of germs, in poor circumstances Legionella pneumophila, the bacteria responsible for legionnaire’s disease.

Air conditioning units have many functions built in to prevent the growth of bacteria, such as, air filtration, dehumidification, cooling, humidification etc. When air conditioning is used, it filtrates the air, providing you with a safe and clean environment. Air conditioning has also been proven to be advantageous to sufferers of allergies and asthma.

In the summer seasons, air conditioning provides a cool sanctuary for the elderly and saves lives of many. Some councils have even created cooling centers for the less fortunate who cannot afford air conditioning.

Poorly maintained units can make excessive noise and in some extremes can even contribute to loss of hearing if endured for long times. Properly operational and maintained units create little to no noise, not effecting hearing.

The Refrigeration Cycle

Refrigeration cycles are the model used in refrigerators and air conditioning units and heat pumps. The man differences between the two is, heat pumps change from cooling to heating and refrigerators will cool only. Technically in the heat pump cycle it incorporates the refrigerator cycle. To put it in another way, a heat pump chooses which side of the system rejects the heat that was accepted by the evaporator to give the user the required temperature.

A heat pump removes heat from a low-temperature source, and expels it to a high-temperature sink, with a bit of help from external mechanical works.

The opposite of the heat pump cycle is called the thermodynamic power cycle. In this cycle, heat is supplied from a high-temperature source, to the heat engine, also a part of the heat is used to produce mechanical work and the rest being rejected to a lower temperature sink. Having this here satisfies the second law of thermodynamics.

Air is passed over the condenser coil, re-warming the dehumidified air. The terms condenser coil and evaporator coil do not refer to the behaviour of water in the air as it passes through each coil, instead it refers to the phases in the refrigeration cycle. Having the condenser coil in the main air path rather than in a separate outdoor air path ( just like a regular air conditioner) tends to result in two different consequences; the output air is warm as opposed to cold, and the unit is then able to be placed anywhere in the environment that is to be conditioned, without a need to have the condenser outdoors.

Ironically, unlike an air conditioner, a dehumidifier will actually heat a room lust like an electric heater that draws the same amount of electricity as a dehumidifier. A regular air conditioner transfers energy from the room by means of the condenser coil, which is outdoors. This is a thermodynamic system where the room acts as a system and energy is transferred out of the system. Conversely with a dehumidifier, no energy is transferred out of the thermodynamic system because the air conditioning unit is entirely inside the room. Therefore all of the electricity that’s consumed by the dehumidifier is energy that is input to the thermodynamic system, and tends to remain in the room.

Dehumidifiers are used in the cold, whereas cold, more damp climates to prevent mould growth indoors, especially in basements. They also are sometimes used in hot, humid climates for comfort because they reduce the humidity which tends to cause discomfort. (Just as a regular air conditioner, but without cooling the room in which its contained.)  

Comfort air conditioning is specially designed to create a 40%-60% humidity rating in the given space. In food retailers large open chiller cabinets are used as highly effective air dehumidifying units.

A specific type of air conditioner that is only used to take humidity out of the air, this is called a dehumidifier. Dehumidifiers are different from regular air conditioning units, whereas both the condenser and evaporator coils are placed in the same air path, the entire units are placed in the air that wants to be conditioned (in this case dehumidified), rather than the condenser coil being outside. Having both the condenser coil and the evaporator coil in the same air path produces warm, dehumidified air. The evaporator coil is placed in the first air path, dehumidifying the air just like a regular air conditioner does.

Cleanrooms also use them for the production of integrated circuits, pharmaceuticals etc, in which very high levels of air cleanliness and humidity control is needed to successfully complete the process. There are many other areas that use process air conditioning, for example, Breeding laboratories, aircraft air conditioning, data processing centres, Textile factories, physical testing facilities, plant nurseries, nuclear facilities, laboratories, mines and food processing areas.

In all of the above mentioned circumstances the air around will not only need to be temperature controlled but also to control the humidity, the air quality, air motion and air movement.

Humidity Control

Air conditioning equipment reduces the humidity of the air controlled by the given system. The relatively cold evaporator coil condenses the water vapour from the processed air sending the water to a drain and removing water vapour from the cooled space thus lowering the humidity in the given room. Since humans perspire, to provide natural bodily cooling by the evaporation of perspiration from the skin, dry air provides a more comfortable surrounding.