Air Conditioning
Split Systems
VRF
GHP
Air Handling Units
Heat Recovery Units
Chillers
Chilled Beams
Air Conditioning
Air conditioning is the treatment of air within a localized environment, this treatment may be heating, cooling, humidifying, dehumidifying, cleaning etc. the objective of this treatment is generally to make ourselves more comfortable where we work, live or play.
The comfort of the human body generally depends on three factors: the temperature of the air, its relative humidity and the motion of the air. The temperature of the air is perhaps the most important factor to consider, most people feel comfortable when the environment temperature is 22oC.
The relative humidity also has a considerable effect on comfort as it affects the amount of heat a body can dissipate through evaporation. Relative humidity is a measure of air’s ability to absorb more moisture. Most people prefer a relative humidity of around 50%.
Air motion is another important factor that affects human comfort, it removes the warm moist air that builds up around the body and replaces it with fresh air. Air motion aids the heat rejection of a body by both convection and evaporation. It is important to strike a balance between having air motion strong enough to remove the heat and moisture from around a body but not strong enough to be felt as a breeze as this could cause discomfort. An airspeed of 0.25m/s is gentle enough to go unnoticed but strong enough to remove the heat and moisture.
Other factors that affect comfort are air cleanliness, odour and noise.
Therefore the goal of air conditioning is to maintain these factors at the desired levels. This is achieved using air conditioning units, in its simplest form, one that only heats or cools the air, a simple refrigeration cycle is used which utilises an evaporator, a condenser, an expansion valve, a compressor, some piping to connect them all, some refrigerant and some fans. In cooling mode the refrigerant in liquid form passes through the expansion valve and into the evaporator, a fan blows air over the evaporator allowing the refrigerant to absorb heat from the air, in order for it to become gaseous, thus cooling the air. The refrigerant then passes through a compressor into the condenser; here it rejects the heat to the atmosphere and returns to a liquid state. In heating mote the process is reversed, where the evaporator acts like a condenser and the condenser becomes the evaporator.
Split Systems
In more sophisticated systems the evaporator and expansion valve are contained in a standalone unit termed an indoor unit, this unit is placed in a room that needs air conditioning and is connected to an outdoor unit by copper piping. The outdoor unit contains the compressor and condenser and is generally located outdoors on a rooftop or on the side of the building. This arrangement is called a split system. The indoor unit usually has a filter that will clean the air that passes through it, a fan that can be controlled to adjust the speed of the air and a control that can adjust the amount of heating or cooling provided depending on the unit chosen.
Split systems are generally used in single room applications such as comms rooms.
Multi-split systems are an extension of normal split systems and feature a greater number of indoor units connected to a single outdoor unit. The number of indoor units is generally between two and four. In such an arrangement all indoor units must be in the same mode; either heating or cooling. Multi-split systems can be utilised in a duty/standby mode.
VRF
Variable Refrigerant Flow also known as Variable Refrigerant Volume.This is an extremely efficient, reliable, energy saving way to heat and cool all types of buildings with minimum installation time or disruption. The volume or flow rate of refrigerant is accurately matched to the required heating or cooling loads thereby saving energy and providing more accurate control. In short, it is probably the best systems currently available for mid to large applications.
The term VRF generally refers to an air conditioning system that connects multiple indoor units to single outdoor condensing unit.
The refrigerant flow is controlled by inverter controlled variable speed compressors to fulfil your cooling or heating requirements. VRF systems generally come in two varieties; 2-pipe and 3-pipe. 3-pipe systems allow for simultaneous heating and cooling of indoor units, whereby the excess heat from one room can be used to heat another room in a different part of the building. In this system the refrigerant is provided in all three phases by the outdoor unit. Using this method conserves energy as it is not wasted to the atmosphere.
In a two-pipe system all the indoor units must be in the same mode, either heating or cooling, simultaneous heating or cooling is not available. Two pipe systems are generally used in areas where all the indoor units are located in the one room, such as a shop floor for example, where only one mode of heating will be required. Two pipe systems are also used as a cooling only system where the heating is provided by a different system i.e. under-floor heating.
A sophisticated control system enables switching between the heating and cooling modes In more sophisticated versions, the indoor units may operate in heating or cooling mode independently of others This latter arrangement offers potential energy savings when heating and cooling are required simultaneously in different zones This type of system requires no internal plant room space and offers great flexibility through the many types of air handling units available Applications vary from office, retail, hotel, luxury apartments, industrial, new and retrofitted buildings.
GHP
Gas Heat Pump
Standard outdoor condensing units are powered by electricity, in a GHP system the outdoor unit is powered by a gas engine. This system uses clean burning natural gas for a highly effective operation with very limited use of electrical power. It has a number of advantages over the standard electric VRF:
- Reduced electrical consumption
- Only requires single phase power supply
- Lower running costs
- Lower start-up times
- Maintained heating performance down to an ambient temperature of -20oC
- No defrost cycle requirement
- Reduced CO2 and NOx emissions
Air Handling Units
An air handling unit or AHU is a device used to provide conditioned air as part of a heating, ventilation or air conditioning system. The basic function of an AHU is to remove stale air from the rooms of a building and replace it with conditioned air.
Air handling units are usually made up of:
- A fan
- Filter
- Heating and/or cooling coil
- Heat Exchanger
- Sound attenuators
- Dampers
The AHU is connected to ductwork that distributes the air around the building; it can also extract the air back to the AHU and exhaust it to the atmosphere. There are a wide range of features and configurations available to suit your air conditioning requirements so that Air can be supplied at the required temperature, humidity, volume etc.
Small air handlers, for local use, are called fan coil units, and may only include an air filter, coil, and fan.
Heat Recovery Units
A heat recovery unit is a device that removes stale air while keeping the heat in. it operates on a principle similar to an air-handling unit. Two fans are used, one to remove stale air from the room and the other supplies fresh air from outside. The two air streams pass through a heat exchanger, in which the heat from the stale air is transferred to the fresh air. Up to 95% efficiency can be demonstrated.
Chillers
A chiller is a machine that removes heat from a liquid via a vapour compression or absorption refrigeration cycle. Generally the liquid being chilled is water; which can then be used in the cooling of machines and other industrial equipment. A water chiller is a complete system filled with refrigeration equipment, including a condenser, refrigerant, pipes, coolant expansion reservoir, pumps, and so on. In air conditioning systems, chillers can be used to distribute chilled water to the cooling coils of fan-coil units, where it can be used to cool the air.
Chilled Beams
A chilled beam is an air conditioning device that circulates air using its own natural convection. As air heats up it rises, a chilled beam unit located in the ceiling can the take in this air and cool it using piped chilled water from an external source. The air now cooled, naturally drops to the floor where the cycle can begin again.
There are two types of chilled beam, active and passive. In an active chilled beam, the beam is supplied with ventilation air to mix with recycled air from the area being cooled. The ventilation air can be pre-cooled giving active chilled beams greater cooling capacities over passive chilled beams. In passive chilled beams ventilation air must be supplied by a separate air handling system.
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