Product category:
Building management systems
News Release from: Seeley International (Europe) | Subject: EAC
Edited by the Processingtalk Editorial
Team on 09 November 2004
Evaporative cooling saves energy costs
Evaporative air-cooling can provide excellent cooling and ventilation with minimal energy consumption using water as a working fluid and avoiding the use of ozone-destroying CFCs in compressor systems
Evaporative air-cooling (EAC) can provide excellent cooling and ventilation with minimal energy consumption using water as a working fluid and avoiding the use of ozone-destroying chlorofluorocarbons (CFCs) as used by compressor type systems Compressor systems also remove essential moisture whereas evaporative systems add health-giving moisture inside a building
This article was originally published on Processingtalk on 3 Jul 2008 at 8.00am (UK)
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EAC technology is simple, functional, can be used in both industrial and commercial applications and consumes less than a quarter of the energy of refrigerative air-conditioning systems.
Heat exists in two forms, Sensible heat, and Latent heat.
Sensible heat is the heat you can feel, or "sense".
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It is a property in Nature that can be detected with a thermometer.
A pavement heated by the sun, a stove burner, or a hair dryer, are examples of sensible heat.
Latent heat is hidden heat that cannot be detected with a thermometer.
The heat used to evaporate water into water vapour is called "Latent Heat Evaporation".
For example, it is the heat from the hot pavement that is given up to evaporate the water after a summer rainstorm.
As the liquid water changes its state into vapour, it absorbs heat from is surroundings; the temperature does not change but the amount of heat or energy it absorbs is contained in the molecular structure of the vapour.
Evaporative air conditioning is only possible because of this natural phenomenon of latent heat.
Total heat is the sum of latent heat and sensible heat.
It is the total amount of heat in a room, made up of heat you can feel and heat you can't feel.
Total heat is measured in kilojoules (kJ).
1000kJ is approximately 1000 BTU.
The complete evaporation of one litre of water absorbs about 2000kJ of heat energy and that occurs within the process without any external energy input.
This is way evaporative air conditioners use a very small amount of electrical power to operate.
Until recently, companies have discounted the use of EAC through lack of knowledge.
Instead, they have either had to put up with no cooling at all or have installed extremely expensive refrigerative air conditioning systems.
This is unfortunate both for the user and the global environment.
The reason evaporative systems use less energy is that unlike refrigerative systems, they do not have to an energy-consuming compressor to compress vapour and condense it back into liquid to repeat the cooling cycle.
Instead, evaporative coolers just use fresh water to achieve high efficiency cooling.
According to the World Bank report, 4 million EAC units in operation in the United States provide an estimated annual energy savings equivalent to 12 million barrels of oil in addition to an annual reduction of 5.4 billion pounds of CO2 emissions.
In industrial applications, EAC may be used to moderate the effects of an additional internal heat source that does not depend on the climate or the time of the year.
For example, temperatures may rise inside warehouses or buildings because of the operations of ovens, machines or the presence of livestock.
These heat sources exacerbate already high ambient temperatures and may need cooling year-round.
In many of these cases EAC is the only practical solution as air conditioning cannot function or compete effectively because of high operating costs.
Historically in applications such as hotels, restaurants and offices air conditioning has been the first choice, now due to cost savings, the added advantages of "air washing" (to avoid sick building syndrome) and ventilation many commercial establishments are finding EAC the most cost conscious and effective solution.
Advantages of evaporative systems versus air conditioning.
Evaporation is a highly efficient natural heat exchange process because there is no third element in the exchanger.
As the air is in direct contact with the refrigerant, in this case water, the heat is transferred extremely efficiently.
In compressor systems, the exchangers involve a third element - the metal coil, which interferes with the efficiency of the heat transfer.
With compressor systems there are two heat exchangers, the evaporator and the condenser, so there is a double negative effect.
The only power-consuming components of a direct evaporative cooler are the fan and small water pump.
The energy savings of EAC units vary with humidity levels and temperatures, however, typically in the UK; EAC systems will yield 50 to 70 percent energy savings compared to conventional air conditioning.
For example in a typical hourly cycle a three and a half ton refrigeration unit consumes 8,698-kilowatt hours of electricity compared to an equivalent evaporative cooler, which consumes 1,800-kilowatt hours of electricity.
Benefits of Evaporative Air-Cooling Versus Air-Conditioning Item.
Power consumption of EAC is 25 to 70% lower than AC.
Maintenance on EAC takes the form of an annual pad change.
EAC has no pollution emissions, no CFC emissions.
Conventional air-conditioning impacts significantly on a building's operating costs as it uses in excess of 25% of its electricity consumption.
It therefore makes sense to create a pleasant environment for workers to maximise productivity whilst at the same time minimising energy costs.
Evaporative cooling enhances the well being of individuals in areas where ambient temperatures are high, providing comfort cooling in buildings such as schools, libraries and offices.
It is also the best, and often the only solution for commercial and industrial applications such as greenhouses, laundries, warehouses, factories and commercial kitchens.
Article by Nigel Egginton, BEng (Hons) CEng MIEE, General Manager, Seeley International (Europe) Ltd.
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