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an economic benefit and no complications with regards to resilience for data centre owners .
Does it therefore follow that the source of waste energy ( the data centre ) has to be located adjacent to the facility or process that requires heating ?
Low grade energy
The simplest way to redistribute what is traditionally still seen as low grade energy , ( server air exhaust air temperature 28oC – 40oC , with cooling water return temperatures rising to 32oC ) despite the shift in data centre operating parameters ( ASHRAE TC9.9 – 4th Edition 2015 ), is to redirect the warm air to a building which requires heating . However , in accordance with the ERE metric requirements , this space shall not form part of the data centre operating facility , such as a battery room , as this would form part of the PUE metric assessment .
The centralised ‘ indirect ’ air cooling systems , which have seen a recent uptake in the UK , use outside cool ambient air to cool the data centre air through an economiser or plate heat exchanger . These could also be utilised to provide a warm fresh air source to a building requiring heating . Clearly the adjacency of the data centre and heated building would need to be close to make this both economically viable and practical as it involves the transportation of air , which as we know is not a particularly efficient energy transfer medium .
Moving beyond the immediate vicinity of the data centre , and in considering the recipient of this energy , its operational profile and the data centre location relative to these facilities .
Most facilities , whether it be residential or commercial in the UK , need heating for large parts of the year , and some can utilise
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‘ The simplest way to redistribute low grade energy is to redirect the warm air to a building which requires heating .’ |
heat energy all year round , such as swimming pools and a domestic hot water requirement in hospitals and hotels . Like other waste energy systems such as Combined Heat and Power ( CHP ) and Energy from Waste ( EfW ) it follows that there must be a potential heat sink , creating a thermal mass which can absorb and redistribute this energy in a controlled manner to where it is needed and at a grade at which it can be used . The latter two points are particularly relevant to data centre facilities , which operate 24 / 7 / 365 and traditionally produce low grade heat energy .
District heating systems
An obvious application and one that has seen some exploitation in the UK but a higher exploitation in the Nordic countries are district heating systems . Due to a long term decentralised energy approach in the UK , there is unfortunately limited scope in these systems in terms of load , number of recipients and geographical coverage on a town or city wide basis . In 2009 however , Telehouse , as part of its West Data Centre development , did make provision within the design of the facility to export waste heat to serve a number of homes in the Docklands area .
In recent years the UK government , through Carbon Targets for residential developments , has encouraged the use of waste energy such as CHP and EfW . As a consequence there has been increased uptake in the use of common centralised heating systems employed to comply with planning and energy target requirements , with traditional gas boilers replaced by a high efficiency heat exchanger . The adjacencies of the ‘ use ’ and ‘ source ’ have therefore been driven by this demand , are
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relatively close geographically and consistent with dense population areas .
The DoEE , in its promotion of CHP schemes , dedicate a webpage section to this . Various maps covering the whole of the UK are provided to highlight district heating schemes and thermal power stations , and show energy to waste and the potential heat load density – the latter being primarily driven by a residential need .
These types of systems provide high grade heat energy as a primary or by-product of their process and generate higher value waste energy , as a derivative of a low fuel cost ( Gas at 2-3p / kWhr ). They also have high system efficiency , in which the waste heat output can be transported relatively easily either in a gaseous state such as steam , or pumped hot water . The waste heat is however derived from burning a carbon based fuel or waste both of which have an impact on air quality .
The waste heat from a data centre , is being generated at a better grade ( higher than ground source applications ), which to serve most district heating applications still has to undergo an elevation in grade , which is traditionally achieved through heat pumps . The energy required to elevate can be obtained from a source which is becoming more carbon neutral , due to its ever increasing renewable content .
The location of the data centre adjacent to and within a practical pumping distance of a thermal heat sink , in the form of district heating systems serving large residential or commercial facilities , will ensure a practical reuse of this true waste heat source . Unlike CHP and EfW it has a clean waste heat potential , which could become a significant contributor to the heating demands of the UK building stock , located in urban areas .
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18 | May 2017 |