Since its modern reinvention, free-cooling has become increasingly popular in a wide range of cooling and ventilation applications. From shelter cooling and office ventilation through to large scale data centre cooling, the benefits of free-cooling are being used to save more and more energy and decrease CO2 emissions.
Whilst the deployment of free-cooling is gathering considerable pace, there is still a huge amount of opportunity that can be capitalised upon. With the opportunity to save up to 95% spend on environmental cooling in telecommunication networks, a closer look needs to be taken on how this reduction in energy usage can be achieved. With ASHRAE TC9.9 guidelines increasing the operational window for data centres and ETSI class 3.1 allowing dry bulb conditions up to 40°C (35°C maximum for 90% of the year), there is an ever expanding range of locations that can be considered for free air conversion.
Higher temperature limitations may be one aspect enhancing the suitability of free-cooling, but an often overlooked factor is the advances in fan technology. As well as the substantial advancements and roll outs of speed controlled DC and EC motors, higher airflows and static pressure capabilities mean that otherwise unsuitable locations can be readily economised. Typical design calculations for free-air roll outs have typically relied on there being an 8-10°C temperature difference between the internal and external spaces, but with higher airflow products this can be reduced as low as 1-2°C without any loss of credibility. Through positive displacement ventilation, the volume of air required to maintain cooling with such a low temperature delta ensures sufficient air change rates to provide consistent and suitable conditions for optimum equipment operation.
Climates that have been previously overlooked for free-cooling are now being revisited to explore the energy saving potential. Southern hemisphere countries such as South Africa and Australia are surprisingly well suited for near complete year-round free-cooling, whereas previously unexplored ‘constant temperature’ locations such as Singapore, are now suitable for modern free-cooling technologies. Taking a common telecommunications arrangement with 4kW of total heat load and a modern air conditioning system installed, an example of the potential savings 4energy’s COOLflow4E FORCE free-cooling system can deliver, can be seen in the figure below:
As can be seen, the potential benefits of adopting a free-air cooling strategy are considerable even in the toughest of conditions. Whilst remaining within ETSI class 3.1 limits, up to 90% savings are possible in Singapore whilst this level of savings are possible in South Africa with a set point as low as 30°C. Whilst battery life is an obvious consideration at these operating temperatures, the addition of a low energy battery cooler takes little away from the potential savings.
Note: Two units have been used in the Singapore study to maximise the available potential temperature delta between the internal space requirement and the ambient conditions. The split air conditioning system EER has been assumed to be 3.5 against standard EN14511 conditions (35°C db outdoor, 27°C/19°C db/wb indoor).