Home mining is a great project not only to learn something new but to earn some dollars on the side. But for those of us living in a cold climate, there is an extra opportunity to “double-spend” our utility bills by making use of the heat that Bitcoin mining generates.
Don’t beat your utility bill, Eat your utility bill!
Most home miners calculate their profitability like this:
Profit = (Mining Revenue)-(Energy Cost)
Googling “Mining Calculator” will yield dozens of results, all of which take the cost of electricity as a core input. Many miners will sell their equipment as soon as the above formula dips negative.
But what if instead of mining with additional energy, you could repurpose your existing energy usage. What if Energy Cost was zero! or close to it.
Starting Small
I started with viewing an ASIC miner as a “garage heater”. This was simple and effective, warming up an otherwise cold space with a “space heater” that had a revenue stream. It definitely worked as planned, but ASIC miners are loud and unpleasant to spend time around, and especially annoying to bring into your home.
However, after enjoying a toasty garage through a full Canadian winter, I was determined to try and do just that, bring my mining operation inside.
After some research, I targeted Hot Water Heaters. The average Canadian household uses the equivalent of ~900 Watts 24/7 and year-round to keep a constant supply of Hot Water. Even in the height of summer, our utility bill is partially paying for this heating.
A standard ASIC miner uses about 1300 Watts around the clock, more than enough. I decided to try and repurpose this constant heating cost, with a constant revenue stream.
Immersion Cooled Mining meets Hot Water Heating
Using an immersion cooling design did two things:
1) Drastically reduced the noise involved in mining, by removing the noisy fans from the miner.
2) The heat created by the miners was captured in fluid, making it more workable than warm air.
I purchased an “indirect water tank” with a built-in heat exchanger, and installed it upstream of my existing natural gas water heater. This ensured my system would work “cold”, and even if the miners weren’t running I would never run out of hot water, I would just need to pay for heat, and only the heat :(
I passed the immersion fluid through the heat exchanger built into my tank. When I pushed the system to its limits, the water got above 60° C and my on-demand didn’t kick in at all. It was working!
But what about when I was sleeping, or if I went on vacation? Once the water was heated up, there was no more heat to be absorbed by the water, and nowhere else for the system to dump it. I needed a secondary loop.
An “Electric-Furnace” Loop
Following the theme of repurposing my utility bill, I decided to pipe the excess heat back into the HVAC system of my home. I combined an in-line fan with two in-line radiators. This pulled the heat from the immersion fluid into the air, which was then pushed into my existing ducting system. The hot air now trickles through the vents of my home, reducing how often the natural gas furnace runs.
I used two automated dampers, and a wye adapter, to enable the system to dump air into the ducting (for winter), or out the chimney (for summer). While this added to the complexity of the system, it also made it viable for year-round use.
Automation and System Logic
My design required a “brain” that could send the heat where it was needed, and more importantly, make sure the system would not overheat. I used a Rasberry Pi 3 as my controller.
The first decision the “brain” needs to make is if the system should be heating water or air. Luckily my tank came with an electric temperature probe, which I plugged into my Pi as an input.
I used two stainless steel valves to control which loop was active at a given time. Once the water has reached a sufficient temperature the “water loop” valve closes, and the “air loop” valve opens, dumping warm air into my ducts.
The last set of logic is to determine if the air should be piped into the ducting (when the house is calling for heat), or right out my chimney (when the house doesn’t need heat). This is done with a relay switch, which the Pi uses to control both the valves and the dampers.
The Final Result, and Current Economics
The project has been a great success.
Currently, the rig uses 1700 Watts continuously and generates $15 USD/day. This generates a “subsidy” to my utility bill of $450/month. Nice!
Now my on-demand hot water heater barely kicks in at all, and my furnace runs less frequently. The utility bill is successfully being double-spent, and I am on track to be paid to heat my home!
I encourage anyone living in a cold climate, and with a heating system in their home, to try and eat away at their heating bill too. If you use propane or natural gas for heating, a project like this can even be considered green, reducing hydrocarbon fuel sources for heating!
For any questions or comments, please contact me on Twitter
Lessons Learned…
While this was a great project, I would certainly do a few things differently next time. Here are a few lessons I learned along the way:
- Design all components around the immersion fluid. The fluid is corrosive to many materials. Most pumps won’t work because the fluid will dissolve the seals, and start leaking.
- Copper is nice for rigid piping, but a poor and expensive choice to build the structure with.
- Use stainless steel tub instead of an aquarium, unless you are aiming for aesthetic appeal. Glass can break, it can scratch, and it can build up static electricity as the fluid moves through it.
- DO NOT put the Power Supplies in the fluid. They fail at much lower temperatures than the miner hash boards.
- If you do an air loop, test your fan inside before you build your system. The fan can still be noisy, although nothing like an ASIC Fan.
