Evaporative cooling versus air conditioning

This installation of evaporative cooling at a printer in Feltham has reduced temperatures in the print area from over 35°C to around 24°C. The project was supported by an interest-free loan from the Carbon Trust covering about 90% of total installation costs. The four units installed deliver 20 air changes an hour cooled to around 23°C.
Alan Beresford explores the energy-saving and environmental benefits of evaporative cooling for reducing temperatures in buildings.Many modern buildings require cooling — either for the comfort of the occupants or to protect the processes or equipment they contain. There are three typical methods that can be employed to cool buildings: ventilation; evaporative cooling or a refrigeration-based air-conditioning system. The choice of system can have a dramatic effect on the total carbon emissions of the building due to their different electrical demands. Ventilation systems can provide comfort cooling for most of the year, but during prolonged periods of high temperatures are unable to maintain internal temperatures below 25°C. Refrigeration-based systems are effective but can be expensive to operate. Evaporative cooling can produce air consistently below 22°C in the UK climate and provides an intermediate solution which consumes much less electricity than full air conditioning. An evaporative cooling installation typically consumes less than 15% of the electricity compared with an equivalent-rated refrigeration based cooling system. The example in the table shows how this electricity saving can result in 1.5 t of carbon savings during a year for a 30 kW cooling requirement. These savings are sufficient for most EcoCooler [EcoCooling’s evaporative cooling system] installations in small to medium enterprises (SMEs) to qualify for an interest-free Carbon Trust Loan. The latest Building Regulations result in buildings which require less heating. The unintended consequence, in many instances, is that activities within the building generate more heat than is required to maintain a comfortable temperature. We are now experiencing buildings which require the air conditioning systems to operate during the winter! When this is the case, the electricity usage and the associated carbon effect is increased dramatically. A balanced ventilation system utilising evaporative cooling can address this with a cost-effective and low- carbon solution.

Evaporative cooling considerably reduces the cost of cooling and carbon emissions. (See text for more information on the building being analysed.)

Comparing the costs and environmental impact of evaporative cooling and air conditioning by considering a building in London with a peak cooling load of 30kW peak load and a minimum cooling load of 20kW highlights the cost- and energy-saving benefits of evaporative cooling. Cooling is employed from April to October from 6 a.m. to 6 p.m. five days per week. Electricity costs are taken at 8p/kWh and water at £1.20/m3. The bottom line for the environment is that carbon emissions are reduced by over 1.5 t a year. Alan Beresford is a director of EcoCooling.
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