Modern Building Services
Ground-source energy serves school buildings in Sheffield
Published:  02 April, 2008
Ground source, Heat pump, Eco heat pumps

60% of the energy needed for heating, cooling and domestic hot water for new buildings at a school in Sheffield is provided by a ground-source heat-pump installation. Sharrow School is little more than a mile from the city centre.

21 boreholes drilled into the coal measures and mudstone beneath a grassy knoll serve a system designed by Eco Heat Pumps which can provide 220 kW of heat. Before installation began, Eco Heat Pumps carried out a week-long thermal-conductivity test programme using a special rig, complete with mobile LPG boiler plant and computer equipment to monitor the energy drawn from a trial borehole.

A water-glycol mixture is pumped through pipework in the boreholes to extract energy from the ground, which is at a temperature of 4 to 9C according to the season. The temperature of this heat is upgraded by the heat pumps.

An ample supply of hot water is held at 60C in two 1000 l storage tanks.

Cooling is provided by passing water at 14 to 15C from the 1800 l buffer tank through plastic pipes embedded in the floor. If this approach to cooling is insufficient, it can be supported by the heat pumps. It is expected that passive cooling will be adequate for virtually all occasions. Integral dew-point protection is provided via a controller linked to the BMS.

Five Thermia Robust heat pumps serve the 2888 m2 of buildings. COP for DHW is 2.8, with a seasonal COP for heating of up to 4.1. The cooling requirement is provided using very little energy a COP of around 100).