A Harry Potter Box

With the help of the Hydrock engineers, we’re working through options for energy sources for hot water and heating.  The fabric first approach of going large on insulation and preventing leaky air flows in the building (no period house draughts) means that we shouldn’t need much in the way of space heating.  We will though be wanting a hot shower and so will also need an energy-efficient way of heating the water.

Instead of a gas boiler, our favoured option is an air source heat pump (ASHP). It lives in a box outside, ideally on a wall of the house. Bizarrely it doesn’t create heat but just moves the heat from place to place.

It’s a bit like a backwards fridge, with the reverse refrigeration cycle warming stuff up instead of cooling it down. Instead of the magic pixies turning the light on when you open the fridge door, the ASHP pixies magic up heat from the outside air.  It’s pretty incomprehensible that heat might be available on a cold winter’s day and the clever bit is what happens to heat flow when you crank up the pressure. Thermodynamics is one of the dark arts with the magic box moving the heat from the outside air into the liquid refrigerant. Then, using electricity, the pump compresses the liquid refrigerant to increase its temperature, making it boil and turn into a gas.  When the refrigerant condenses back to a liquid it releases its stored heat and that heat gets transferred to our hot water system. Magic, although best not to think about it too hard.

The ASHP needs electricity to run, but it will use less electrical energy than the heat it produces. We’ve yet to firm up where the electricity comes from – either the grid, or a solar panel, or the grid for now and the option of adding a solar panel in the future.

The strange thing is why ASHPs aren’t everywhere.  Perhaps we’re on the cusp of this, like electric cars?


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