Large scale equipment (500L +)

[klangers]

It is theoretically possible to build an electrical boiler with a COP greater than 1, eg a heat pump. As I understand it, the large "lift" involved means that the COP won't be anywhere near that available from a normal heat pump so the extra capital expense isn't worth it.

Yeah. The issue is that there is no known refrigerant with high enough efficiency and with the right p/t phase transitions. To boil water you need a heat source significantly greater than 100 degrees, unless you have a massive and expensive heat exchange surface. Then if you want to raise a useful pressure of steam (no offense to noted success of flash boilers in previous posts above - but industrial steam needs greater pressures) you need temperatures several hundreds of degrees. The most efficient boilers currently known - in power stations - raise supercritical steam to in excess of 500 deg C. You'd need a refrigerant which can be compressed to a pressure where it will condense and release latent heat at >100 degC, but also expanded evaporate below ambient temperature so that the "cool" can be released, without requiring more work input to achieve those pressures than available thermal output.

That said there are off the shelf hot water "boilers" aka domestic hot water units that use heat pumps and achieve great COP. But they aren't trying to heat anything beyond 70 degrees.

EDIT: My beery idea for the evening: A heat pump mash heater? With in-mash condenser coil? Now we're talking efficiency!