Water Source Heat Pumps

A water source heat pump (WSHP) uses the heat energy from water to provide heating and hot water for your home. A WSHP receives water through pipes that absorb heat from contact with water. The water may be from a river, open water or even the sea in the case of a marine source heat pump.

There are two main Water Source Heat Pump designs; a closed loop system or an open loop system. In a closed loop system, sealed pipes filled with an anti-freeze fluid (refrigerant) are submerged under the water. The anti-freeze fluid is pumped through the pipes to gather heat energy in the water.

Heat from the water is absorbed into the fluid, which then passes through a heat exchanger into the heat pump. The compressor unit raises the temperature of this fluid through compression, and a heat exchanger transfers the warmth to the water that circulates round the central heating system. The heat is then transferred to the property via radiators or under floor heating. Once the water is cooled it is pumped back out to the submerged loop system and the cycle begins again.

In an open loop system, water is taken from a borehole and lifted to the surface. Heat energy is extracted from the water and then returning the cooled water to a separate borehole. Open loop systems move larger volumes of water through the heat exchanger than the closed loop system. As a result, open loop WSHPs are more efficient than equivalent ground or air source heat pumps. 

Castle Park Water Source Heat Pump Project

The Castle Park Heat Project is one of the schemes launched by Bristol City Council in response to climate emergency. Water is pumped from the nearby floating harbour via the pipework which is submerged below the waterline. The water is filtered to prevent debris from entering the system. The filtered water is pumped through a second filter which removes smaller particles like mussel eggs which can hatch and grow in the pipework.

Once the water is filtered it passes through the water source heat pump where the ambient heat reacts with ammonia and creates low pressure vapour which can be compressed to a high-pressure vapour of around 110°C. Heat from the water source heat pump is directed into a thermal store which then feeds into the Bristol Heat Network where it contributes to heating 1,000 homes and businesses.