When it gets really cold, heat pumps can lose some of their efficiency, so in that case this might not be much worse than just relying on the heat-pump itself.
It's still not a net-gain environmentally speaking, I guess, but since he uses GPUs he already had lying around I'd say it's not very bad at all.
And it looks like the unit he has (assuming I've found the right one) uses a heat pump for producing hot water, but for heating the home it would often be paired with an external heat pump: https://www.nilanuk.com/domestic-solutions/compact-p/
> My house is heated (and cooled) with a central ventilation system powered by a heat pump.
He is definitely using a heat pump.
He lists the equipment that he has, and the manufacturer deacribes it as a heat pump [1].
He also includes a photo of a compressor, which is typical of a heat pump.
You can see these four pipes here, around component (1): https://pictshare.net/1024/sbmusz.jpg
T_cold comes from outside and T_hot comes from inside; T_verycold and T_veryhot go to the outside and to the inside.
However, the efficiency of the heat pump decreases as T_cold lowers (see https://en.wikipedia.org/wiki/Heat_pump_and_refrigeration_cy... ).
So by "preheating" T_cold with the bitcoin miner, the efficiency of the heat pump itself increases.
However, the efficiency of the whole system (heat pump + miner) decreases when you have the miner on. (Otherwise, heat pumps would just have a built-in heater to do it.)
So adding the bitcoin miner decreases the power efficiency of the whole system; but it may increase the monetary efficiency, if the revenue generated by the miner is high enough to compensate for the increased power usage.
> Compact P recovers the energy from the extracted air using a highly efficient counter flow heat exchanger. The remaining energy that is not utilised by the counter flow heat exchanger is used by the heat pump to produce hot water, and to further heat the supply air.
https://en.nilan.dk/en-gb/frontpage/solutions/domestic-solut...
HRVs take out stale air, bring in fresh air, and pass both streams through a heat exchanger to heat up the cold air coming in (or vice versa in the summer) with efficiencies of up to 95%. This is a purely mechanical system - the only moving parts are two fans.
HRVs need a preheater in cold weather, so you don't have condensation or ice form inside the unit, however if your climate isn't that cold (and most importantly your home is well enough insulated), that heat can be more than enough to maintain your home at a comfortable temperature without additional heat sources.
In OPs case the preheater is using an electric resistance heater, but as they said there are options to buy a heat pump preheater, using the ground as a heat source but it was too expensive (they are typically more than the heat exchanger itself, plus the cost of installing the ground pipes). Using the miners as a preheater just reduces the work of the electric resistant preheater. If you take into account the value of the crypto currency produced, then yes it is better than using the built in preheater, but using the ground source heat pump preheater would result in an overall lower electricity consumption.
The heat pump part is purely on the exhaust air. There is always some loss in the heat exchanger, so if the incoming air from outside is 5c, the exhaust air to the outside may be 10c. This unit runs the exhaust air through a heat exchanger to produce hot water for taps, and if that is already satisfied, to attempt to preheat the incoming air to reduce the work of the preheater. (There's probably also an electric resistance heater for the hot water, in case demand is greater than what the heat pump alone can provide).
(didn't downvote you, just pointing out that you missed the point of the article)