The efficiency of bitcoin mining has increased by 9% in 2022. Partly due to more efficient machines, but also partly due to immersion cooling.
Immersion cooling
Immersion cooling consists of immersing mining machines (let’s call them antminers) in a heat transfer liquid. This type of liquid has the particularity of absorbing heat and not conducting electricity.
The goal is to cool the components by transferring the heat to the liquid rather than to the air as has always been done using fans.
The following graph by Braiins shows that the watts consumed by an S19j Pro antminer increases as the system temperature rises. The experiment is performed from a constant hashrate:
Clearly, the rise in temperature causes an increase in energy consumption, which reduces the margins of the miner. Or a drop in hashrate if ever the antminer is restricted by a maximum wattage.
According to tests carried out by Braiins, the power required is 2,500 W around 20 degrees Celsius, but 3,550 W around 75 degrees. Assuming the standard hashrate of 104 TH/s for an S19j Pro, this represents a change in efficiency from 24 W/TH at 20°C to 34 W/TH at 75°C.
That’s a difference of 29% on the electricity bill! Ensuring that its ASICs remain at the right temperature is therefore crucial.
And the fact is that immersion cooling is more efficient due to its increased density compared to air cooling systems. Among other advantages.
In concrete terms, cold mining
Easier said than done. The first step is to unscrew the fans from the machines and connect ” fan spoofer ». This is a small device that simulates the presence of fans. Otherwise the machines do not run, for safety.
A tank is obviously necessary to accommodate the machines and the heat transfer liquid. To this tank must be added a pump circulating the liquid towards a heat exchanger. That is to say cold water which absorbs energy (heat) by simple thermal transfer.
Unless you have plenty of fresh water, you need an outdoor cooling system to transfer the heat energy from the water to the outside air.
It is then “just” to manage the temperature by increasing the speed of the pumps and/or by making the fans of the outdoor coolers run more.
Immersion cooling offers much more stability and makes sense for miners operating in hot climates. Not to mention the drastic noise reduction.
Many miners such as riot and Argo are now building infrastructure that works exclusively with immersion cooling:
So much so that the oil company Shell offers them its solutions. The energy giant claims to be able to reduce up to 48 % the costs and carbon emissions associated with bitcoin. And this thanks to “high cooling efficiency, optimized flow and excellent thermodynamic properties”.
This figure is in line with Riot’s observations. The Texas miner said in late 2021 that its immersion cooling tests left to hope “A 25% increase in hashrate, with overall ASIC efficiency potentially increasing by 50%.”
Overclocking antminers
To briefly summarize, immersion cooling offers the following advantages:
- More efficient heat dissipation. The fluids used in immersion, called dielectric heat transfer fluids, are much more thermally conductive than air. They are therefore more efficient in dissipating heat.
- Increase in the life of the material. Small fan vibrations and rapid temperature fluctuations accelerate hardware deterioration. Immersion cooling considerably reduces these two phenomena.
- Less maintenance. Immersion fluid prevents dust and debris from entering the hardware.
- Less noise. However, there will still be some noise outside due to the air cooler water cooling system which uses fans.
- Improved efficiency (W/TH).
And, above all, overclocking becomes much safer (more TH/s). The more efficient and stable heat dissipation of overclocking antminers.
This last point is very important. It is indeed possible to “unleash” your antminer by installing the software Brainin OS+. Overclocking means pumping more power into the ASICs to chop at higher frequencies. This therefore makes it possible to produce more hash than with the original settings.
For example, “an Antminer S9 that typically produces 13.5 TH/s with 1200W power consumption could be overclocked to produce 16 TH/s with 1600W power consumption”, declared Brains.
Mining and Autotuning
It is obviously dangerous to push the machines to their limits. The risk is to grill the components if the cooling does not follow. Overclocking has become less risky, however, thanks to immersion cooling.
Also, potential improvements to the software running antiminers don’t stop at overclocking. A lesser known ASIC performance enhancement, similar to overclocking, is autotuning.
Both overclocking and autotuning involve adjusting the hash frequencies of ASICs. The difference between overclocking and autotuning lies in the intelligence and sophistication of the latter’s frequency adjustments.
Overclocking is a brutal adjustment that increases the hash frequency of all of the hundreds of chips in each antminer. Autotuning, on the other hand, will manage the frequency on a case-by-case basis.
In other words, the autotuning software will send higher frequencies to chips in better condition and lower frequencies otherwise. The reason being that chip-to-chip performance can vary greatly due to inherent flaws in the complexity of semiconductor manufacturing.
The result of autotuning is better W/TH efficiency. Brains argues that “the same Antminer S9 typically producing 13.5 TH/s at 1150W with standard software could produce 15.5 TH/s at 1150W with autotuning software”.
All of these efficiency gains are not negligible. It miners can no longer ignore the benefits of immersion cooling. Especially in these lean times.
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