Free Cooling Chillers
Posted on 31st May 2011.
“Free” cooling can be provided to a mechanically cooled building using a packaged free cooling chiller in place of a conventional chiller. The free cooling chiller uses standard vapour compression technology with an additional free cooling coil which bypasses the compressor and circulates primary water around the outside of the chiller when the ambient temperature is lower than the return liquid temperature to provide cooling without the need to run the chiller compressors. Although pump and fan energy input is required, because the compressors represent the main source of energy input, this is termed “free cooling”.
Why use a free cooling chiller?
Free cooling chillers can form part of a more sustainable approach to meeting the cooling requirements of a building, by reducing primary energy consumption and carbon emissions. In the UK, the annual average temperature is 5.6°C minimum and 13.1°C maximum (1), therefore free cooling chiller plant could meet all or part of a building load without the need for bringing on compressors for a significant portion of the year.
Application of free cooling chillers
To optimise the benefits from a free cooling chiller installation, a cooling base load is required, ideally throughout the year – for example ICT equipment cooling or a process cooling load. In addition, elevating the chilled water flow and return temperatures can increase the amount and duration of free cooling available, although all cooling coils within secondary equipment would need to be selected to match these elevated temperatures. It may be advantageous to install plate heat exchangers to separate the primary and secondary water circuits as a glycol mix is usually required to the primary circuit to reduce the risk of freezing as water circulates around the free cooling coil. In order to accurately assess the viability of a free cooling chiller application, annual cooling loads (historic or design) should be compared with an annual local weather data set. Then by comparing free cooling available, based on ambient temperature, against building cooling demand on an hourly basis, it is possible to calcula
te potential primary energy savings and carbon reductions from a free cooling chiller installation.
For more information about free cooling chiller applications contact JPA.
(1) http://www.metoffice.gov.uk/climate/uk/averages/19712000/areal/england.html
(2) Image: Danilo Rizzuti / FreeDigitalPhotos.net
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