More about Air Conditioning Systems
Traditionally energy consumption was higher in commercial buildings during the winter months with a need to heat occupied spaces. In recent years we have seen a shift to a high summer demand for energy as there is a need to ‘comfort cool' occupied spaces through the use of air conditioning. The energy efficient performance of an air conditioning system is reliant upon good design, comprehensive commissioning and effective operation and maintenance.
A chiller is a machine that removes heat from a liquid via a refrigeration cycle. Chillers can be of varying sizes and types to best suit a distribution system and building design. The majority of chillers installed are either water cooled or air cooled.
A chilled beam is a building cooling device that circulates air using the principles of natural heat convection. The major advantage of a chilled beam over more common forced air systems is that it circulates building air without the noise and expense of ductwork and air handlers. Typically mounted overhead near or within a ceiling, the beam is a type of radiator, chilled by an external source such as Recirculated water. It cools the space below it by acting as a heat sink for the naturally rising warm air of the space. Once cooled, the air naturally drops back to the floor where the cycle begins again.
A condenser is a heat exchanger in which the refrigerant, compressed to a hot gas, is condensed to liquid by rejecting heat to achieve a cooled space. The condenser in an air conditioning unit is very similar to that used in a common refrigerator.
Constant Air Volume (CAV)
Constant Air Volume (CAV) is a type of heating, ventilating, and air-conditioning (HVAC) system. In a simple CAV system, the supply air flow rate is constant, but the supply air temperature is varied to meet the thermal loads of a space. Most CAV systems are small, and serve a single thermal zone. However, variations such as CAV with reheat, CAV Multizone, and CAV primary-secondary systems can serve multiple zones and larger buildings.
A system of distribution channels used to transmit heated or cooled air from a central system (HVAC) throughout a building.
Fan Coil System
A Fan coil system is an air conditioning system used in buildings. A fan unit is placed at each place which needs to be heated or cooled. A central plant delivers hot or cold water to fan units. The fan draws air from the room, blows it over the water coil and returns it to the room. Dehumidified air from a central plant or fresh air from outside may also be used by a fan coil system.
In the context of mechanical building services the internal environment refers to the strategy employed to heat, cool and distribute air around a building. The Internal environment can be heated and/or cooled, whilst air distribution could be through natural or mechanical methods, or a mixture of the both for a mixed-made strategy. If comfort cooling is provided throughout the internal environment would be fully air conditioned.
A mixed mode system combines the best aspects of both natural ventilation and mechanical ventilation/air conditioning. The simplest example being the opening of windows to enable natural ventilation with air conditioning available when windows can not be opened.
Seasonal Energy Efficiency Ratio (SEER)
Seasonal Energy Efficiency Ratio applies to air conditioners and heat pumps and describes the relationship between the Btuh, or cooling capacity of a unit, and the amount of electricity required to run the unit. This ratio is based on normal annual usage. Units with higher SEER ratings require less electricity to cool a building and are therefore more efficient.
A Terminal unit is the final device in an air conditioning system located in the space being heated or cooled. The terminal unit can be utilised to determine the flow and direction of air whilst re-heating/re-cooling to achieve the desired local temperature.
Variable Air Volume (VAV)
Variable air volume (VAV) is a technique for controlling the capacity of a heating, ventilating, and/or air-conditioning (HVAC) system. The simplest VAV system incorporates one supply duct that, when in cooling mode, distributes approximately 55 degree F supply air. Because the supply air temperature, in this simplest of VAV systems, is constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the thermal zone served.
- CIBSE Guide B 'Heating Ventilation Air Conditioning and Refrigeration'
- CIBSE Guide H 'Building Control Systems'
- CIBSE TM44 'Inspection of air conditioning systems'
- CTG005 'Air Conditioning Technology Guide' available from www.thecarbontrust.co.uk