If water freezes in winter its volume increases, maybe damaging closed pipework in a heat pump. The solution to this problem is to lower the freezing point temperature of the heat pump fluid to less than 0°Celsius, a temperature less likely to be reached in a Cornish winter. Adding a liquid with a low freezing point such as proylene glycol will do this. The more is added, the lower the temperature can go before the mixture freezes. How much antifreeze is needed to beat a Cornish winter? To give down to -10°C before freezing happens, a 20% by volume solution is introduced into the system using a power flusher. How do we know when the mix is 20%? A simple optical device called a refractometer is used to check the concentration. Anticipated lowest temperatures in Cornwall are given as – 2/3°C. The hourly dry bulb temperature ( average low mean temperature) figure used in our heat loss calculations based on the MCS guide is – 0.2°C for Cornwall and the South West, so the 20% propylene glycol mix is more than sufficient for the heat pump to work safely through the winter.
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