Churchill Hospital
CIAT Ozonair Ground Source Heat Pumps and Dry Air Coolers form an essential part of Europe's largest ground source system that has been installed at the Churchill Hospital in Oxford.
Haden Young Midlands and Southern worked in a joint venture with Alfred McAlpine and Impreglio to build the complex which comprises a state-of-the art cancer centre, surgery and diagnostics building and private patients unit. The Oxford Radcliffe Hospitals NHG Trust decreed at the outset that these new facilities should be exemplars of energy efficient, low carbon hospital design.
The backbone of the solution provided by Haden Young is an ambitious ground source heat pumpt system, which uses water to collect and return heat from some metres below the surface. The heat is transformed through CIAT Ozonair's heat pumps to provide the energy needed to heat or cool the buildings.
The system uses some 240 bore holes, each 100 metres deep, through which water is pumped in a closed loop of around 35 miles of pipe. The eight CIAT Ozonair LWP 2150 heat pumps are installed in two plant rooms (five in one and three in the other) one heat pump in each plant room being in standby mode. They provide more than 2.5 megawatts of heating and cooling with scope for a ninth unit to bring the system capacity to over 3 megawatts.
Each heat pump has a heating capacity of 522kW and a cooling capacity of 373kW in heating mode, and 505kW cooling capacity and 613kW heating capacity when in cooling mode. The installation is completed by two CIAT sequence control panels, three CIAT Vextra dry coolers and 14 heat exchangers.
In heating mode, the heat pumps draw cold water from the sealed geothermal ground loop. In cooling mode, the hot condenser water is pumped into the ground loop, which provides condenser water cooling. The overall design concept is to balance both heating and cooling requirements to ensure the most economical operation of the plant in all modes.
The central BMS (Building Management Control System) constantly monitors the hospital environment and determines whether to control the plant in either heating dominant or cooling dominant mode. The BMS sends a signal to the sequence control which in turn, operates the heat pumps in the required mode. The BMS will also vary the system water temperature via 0 - 20 mA signal to the sequence control system.
The sequence control panels measure flow and return water temperatures and ensure the heat pumps are used in the most economical mode, switching heat pumps as required. In doing so, they open and close both chiller and heating water valves, the design flow rates being maintained by inverter-driven pumps. The sequence panels also provide fault monitoring as well as duty rotation and standby selection.
Controlled by the BMS, the dry coolers are used to maintain the well field by either injecting or rejecting heat at times of high load.
The heating and cooling water is distributed around the hospital in secondary systems via CIAT PWA plate heat exchangers.
Haden Young estimate that for every kilowatt used to power the ground source system, up to six kilowatts are generated for heating and cooling. In this way they expect to achieve an energy of use of 38 GJ/100m3, which is substantially less than the maximum target of 55 set by the NHS for its new hospital developments
For further information please contact:
Mr.Barry Hennessy
Crystal Air Ltd
Unit 3
Butterstream Business Park
Clane
Co. Kildare
Email: barry@crystalair.ie
www.crystalair.ie