Earth Sciences Building benefits from ground-source technology
Renewable energy meets much of the heating and cooling requirement of the Earth Sciences Building at the University of Oxford — overcoming a number of challenges on the way. Chris Davidson of GI Energy takes up the story.
Oxford University had the highest aspirations for environmentally friendliness when it briefed developers about the design of its new flagship Earth Sciences Building. As befits such an august institution, simply attaining a BREEAM ‘Excellent’ rating was not enough; it decreed that the carbon footprint for heating and cooling had to be as small as possible.
After careful consideration of the site, a ground-source energy system provided by GI Energy was selected as the mainstay of the heating and cooling system, backed up with conventional gas central heating boilers and electric chillers.
The results were spectacular; from April 2012 to March 2013 CO2 emissions were 128.6 t a year lower than for conventional systems — despite the completed building behaving quite differently from the way it was expected to when plans were on the drawing board.
In practice more heating and cooling were required than originally anticipated. Nevertheless the heating and cooling system coped admirably, delivering 11% more heating and 57% more cooling over a year of operation, from April 2012 to March 2013.
At the heart of this success lies GI Energy’s computerised control system, which is responsible for how the entire system operates. Programmed to maximise carbon savings, it continuously monitors the system and makes intelligent decisions based on monitored data.
Not only can the control system switch each of the three ground-source heat pumps individually from heating to cooling mode, it also decides to when to switch the gas boilers and electric chillers on and off and instructs the building-management system accordingly.
The key to the optimised carbon savings at Oxford Earth Sciences is the computerised control system that we have developed, drawing on our years of experience in the field.
The attraction of this control system is that it is not specific to ground-source energy systems — it is suitable for all conditioning systems, be they ground source, air source, boilers, chillers or combined heat and power.
Oxford Earth Sciences building has a floor space of 7100 m2 and comprises a 5-storey office and teaching wing and 4-storey specialist laboratory wing, linked by an atrium entrance. In some of the laboratories environmental control is of critical importance. The building also houses a server room and a number of hub rooms where 24-hour cooling is required.
The site of Oxford Earth Sciences presented several challenges, not least the risk of flooding parts of Oxford if the GSHP system was not properly installed!
There was the danger that underground pipework for the GSHP could hit a high-pressure underground aquifer directly beneath the building. The exact depth of the aquifer was not precisely known and had to be measured.
|Extracting heat from the ground and returning it to the ground is delivering efficient heating and cooling for the Earth Sciences Building at the University of Oxford.|
GI Energy worked closely with the Environment Agency to establish how deep it could safely drill down without hitting the aquifer. It was agreed that 63 boreholes could be sunk to a depth of 64 m.
The second issue was the size of the site. Even sinking the boreholes vertically rather than horizontally it was still not large enough to support a GSHP system that could meet peak heating and cooling. The maximum possible was 398 kW.
GI Energy took part in all the initial energy assessments with Oxford University, contractor Laing O’Rourke and consultants Hoare Lea, after which it was decided to install a hybrid system, with back up from gas boilers and conventional cooling. Crown House Technologies was appointed as mechanical and electrical contractor.
GI Energy’s brief was to provide as much heating and cooling as possible with a GSHP system, given the constraints of the site, providing conditioned water at 45°C for heating and at 6°C for cooling. All this was to be achieved while minimising carbon emissions across the whole heating and cooling system, including the gas boilers and electric chillers.
The design peak heating load was 977 kW, and the design peak cooling load was 727 kW. Performance data collected over the year showed that the total heating load was 1921 MWh and the cooling load was 1105 MWh.
The building required on average 160 MWh of heat a month, compared to the original estimate of 118 MWh. The cooling load averaged 92 MWh a month, compared to the initial estimate of 50 MWh.
Ground-source energy systems are most efficient when both heating and cooling are required, which is one of the many advantages of this renewable form of energy.
Ground-source energy systems extract heat from, and return it to, the ground – essentially recycling solar energy that is stored in the ground. They are many times more efficient than conventional heating or cooling.
At Oxford Earth Sciences performance data over a year showed that, for every kilowatt of power used to run the system, either 3.6 kW of heating or 4.7 kW of cooling was produced.
Ground-source energy systems have tremendous potential to both reduce heating and cooling bills and to cut carbon footprints.
Chris Davidson is director of development for GI Energy.