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Using lake water for cooling and heating
White Young Green has produced a report on the feasibility of using water from a lake to feed into a heat pump. Instead of boreholes, coils of pipework are formed into rafts with netting, and weighed down in lakes or ponds. The lake water needs to be a minimum of 2 m in depth all year round. A 4 m deep lake with a 1 acre surface will be able to produce around 1.5 MW of cooling and 1.1 MW of heating. White Young Green鈥檚 calculations below demonstrate the savings in running costs that can be achieved using a pond or lake loop.
Comparison between heat pump with pond loop and conventional heating/cooling system
听	Energy consumption (KWhr) Electricity	Energy consumption (KWhr) Gas	Running cost (拢)	Approx installation cost (拢)	CO₂ emissions (KgC/m²)
Chiller boiler	952,626	1,298,606	47,243	220,000	12
Heat pump	671,972	0	24,863	265,000	3.5
Assumptions:
Two air-cooled chillers (600 kW each), two gas-fired boilers (450 kW each)
Heat pump option based on 10 heat pumps and 12 rafts sunk in lake
Price of electricity at 3.7p/kWhr, price of gas at 1.1p/kWhr