A heat pump achieves a COP (coefficient of performance) of approx. 3-4 (e.g. by investing 1 kWh of electricity, a heat pump generates 3-4 kWh of heat by extracting from the surroundings, air or sole, 2-3 kWh). In this example, by pre-heating the air, you supply the heat pump with ~0.9 kWh of thermal energy (the miner will convert 900 watt directly to heat I would assume). So instead of 1 kWh of electricity consumption from the heatpump, you have 1 kWh of electricity for the heat pump, plus 0.9 kWh for the mining, and you end up with a bit more than 3-4 kWh (since the COP of a heat pump increases if the source temperature is higher).
So in a nuthsell:
before: in 1 kWh, out 3-4 kWh
after: in 1.9 kWh, out 3.5 - 4.5 kWh
A heat pump achieves a COP (coefficient of performance) of approx. 3-4 (e.g. by investing 1 kWh of electricity, a heat pump generates 3-4 kWh of heat by extracting from the surroundings, air or sole, 2-3 kWh). In this example, by pre-heating the air, you supply the heat pump with ~0.9 kWh of thermal energy (the miner will convert 900 watt directly to heat I would assume). So instead of 1 kWh of electricity consumption from the heatpump, you have 1 kWh of electricity for the heat pump, plus 0.9 kWh for the mining, and you end up with a bit more than 3-4 kWh (since the COP of a heat pump increases if the source temperature is higher).
So in a nuthsell: before: in 1 kWh, out 3-4 kWh after: in 1.9 kWh, out 3.5 - 4.5 kWh
so you lose 0.4 kWh?