Bob Harris, technical director. Telehouse Europe (below) tells DCM how it has approached HVAC in its new data centre

Telehouse Europe is currently constructing a new state-of-the-art multi storey data centre in addition to its two existing buildings on its site in the London Docklands. The new £80 million facility will add a further 19,000 square metres net of data storage space for UK businesses.  The data storage space will be provided over 5 floors with 4 levels of plant and a generator building.

The challenges of data centres
Without impacting on the mission critical nature of their data centres, operators must reduce their ever-increasing energy consumption and mitigate the resulting environmental impact.

As energy consumers on a massive scale - by virtue of their 24/7 operation and concentration of equipment - the activities of data centres have come under increasing scrutiny.
Data centres are complex and highly energy intensive buildings and are difficult to classify in the context of conventional buildings.  They are by their nature large electrical energy consumers.  Approximately 50% of the power delivered to site is unavoidably used directly by the IT equipment. The balance is consumed by the plant and equipment associated with maintaining the required operating environment within the IT facility.

The cooling equipment is normally the second biggest user of power after the IT equipment and as such is one of the most significant factors when assessing the environmental impact.

Considerable research is ongoing to reduce the power take of the IT - this is outside the scope of this article.

The problems with traditional approaches
Until relatively recently, many Local Authorities have been prepared to regard Data Centre IT loads and their attendant cooling systems as process loads and therefore outside their sphere of influence.  The GLA is, however, leading the way in designating the total energy needs including the IT processing as subject to Planning and Building Control requirements.

This is a considerable challenge to data centre design teams as target percentage energy reduction and renewable energy sources cannot be met, using conventional methods at the levels applied to ‘normal’ buildings.  There is commonly pressure to adopt CHP or CCHP solutions but these give little or no carbon reduction and are generally unsuitable for data centre applications.

The Telehouse West solution
The cooling strategy for Telehouse West has been significantly influenced by site constraints and the proximity of planned residential buildings of up to 35 storeys within a few hundred metres of the new building.  This has precluded the use of evaporative heat rejection in favour of speed de-rated Dry Air Coolers (DACs). High efficiency centrifugal water-cooled chillers are to be located within an acoustically treated plantroom.

The condenser water operates at a variable temperature depending on ambient air temperature.  The objective of the control of dry air cooler performance is to minimise condenser water temperature entering the chillers’ condensers in order to maximise CoP. DAC fans run generally  at the maximum speed within the ambient noise constraints for the site.

The new Telehouse West facility will mitigate its carbon footprint by providing the facility to export waste heat from its cooling processes to nearby homes and businesses. The system will be able to export up to 9 MW of waste heat.  This is a development of a smaller scheme used on one of WSP’s recently completed data centres - where the entire heating demand of an integral office block was satisfied by reverse cycle heat pumps extracting heat from the chilled water return.

For this building the energy export heat exchangers are located in the condenser water circuit flow from the chiller condenser to the Dry Air Coolers as this provides higher, though more variable, water temperatures than the chilled water return for a greater part of the year.

Given a fully loaded system, the maximum condenser water temperature at entry to the heat exchanger would be around 10˚C above ambient.  At its lowest, when the free cooling heat exchanger is in circuit, the entering temperature may be as low as 12˚C, at which condition the energy export heat exchanger would be unlikely to be able to provide water at above 12˚C to a third party user.  These temperatures are similar to those which might be looked for in conjunction with ground source or borehole heat pumps.

Expected performance
It will be a basic condition of use that any third party accepts that the temperature of the water offered is not guaranteed and will vary, neither will it be uninterruptible  It is expected that use of this medium will be supplementary to his primary heating plant to be used as and when available.  On the basis that the user has a usable threshold temperature, he will be satisfied for a greater part of the year with the condenser water system than with chilled water unless his threshold is below 15˚C.

Other sustainable approaches used
In addition to the innovative energy export solution, WSP have also incorporated a large photovoltaic installation into the data centres façade.

The array of Monocrystalline PV cells will cover an area of circa 77 square meters on the south façade of the new building and will have an estimated annual output of over 6000 kWh per annum.

This energy will be used to power small electric cars for general use. It has been estimated that the available power will be sufficient to power electric vehicles over a total range of 30,000 miles per annum.

To ensure the PV energy is fully utilised the photovoltaic array will be directly connected to the electrical infrastructure, via an inverter and power conditioner. The near constant load profile of Telehouse West means that the energy will be fully utilised throughout the charging periods. Therefore, this negates the requirement for batteries to store the energy thus saving costs and space internally in the building.

Lessons learnt from the process
The biggest risk to the Project was perceived to be the granting of and the time required to obtain planning.

The application was reported to a Greater London Authority (GLA) committee on the afternoon of 14th January 2009 where the Mayor signed off the development proposal and determined that he would not direct refusal and that LTGDC can approve the planning application.  This process took in the order of 6 months and was considered to be very fast in comparison to other projects.  The Planning Consultants Dalton Warner Davis, (DWD), confirmed it to be one of the fastest projects of this type of complexity from submission to award.

The planning involved a substantial EIA – which the WSP environmental team put together, this resulted in a number of conditions – in relation to ‘Black redstart’, (a protected bread of bird), mitigation etc. - all of which have been expedited or put into action 

As a point of note the GLA case officer expressed her acknowledgement and thanks in respect of the Client and his Consultancy Team, (in Particular Arcadis-AYH, DWD, YRM and WSP) with regard to their ability to listen react and attempt to respond to the policy context. 

This - they said - is not often the case and was very well received.