Bitcoin Mine Cooling Options - What are my choices?

When a Bitcoin miner is designing their mine including: what mining hardware to run, where to locate or colocate and how to keep everything cool.  This is the purpose of this article.   Bitcoin mining hardware takes electricity to power the hashing chips and converts it to process Bitcoin transactions.  Most of the power gets converted into heat which needs to be dealt with or you can slow down and ruin your mining hardware.  Thermal Management is crucial in getting the most out of your mining hardware.
When approaching cooling I find it helpful to recognize that if you are looking for optimal hashing performance, you need to understand the difference baseline cooling and supplemental cooling strategies.   Now I understand that is some overlap in a couple of these technologies but in my experience you need to focus on baseline cooling if you want to operate year round. 
Here is a basic outline of the different cooling technologies and how each one operates:
Direct Cooling / DX – This is the traditional method of cooling most people have experienced.  This is involves a HVAC unit that has two pieces.  One is the blower unit that is located inside the facility and it moves the air through you ducting and the unit contains a compressor and this does part of the cooling process.  Second is the condenser that is located outside either on the side of the building or on the roof.   These units take the heat exhausted from the mining units and uses it to warm the cooling fluid that is then sent outside to be cooled and then it is sent back to the blower unit.   This is a great approach and will give you year around cooling.  The biggest downside is that is isn’t as efficient as other options and the power draw for each unit is not trivial so you need to make sure you have power reserved to power this cooling.  Note that over 30 tons (12,000 BTU = 1 Ton) in a single unit, you will need to use a different baseline solution
Water Chiller / CRAC – This is another very popular option and is used in many datacenters.  This uses the same principle as DX cooling but instead of using a cooling refrigerant to extract the heat, Water Chillers use water at a lower temperature than the desired temperature inside the mine to deliver the cooling needed.   Chillers still have a blower / air handler but these take much less power to run because most of the power is used at the compressor and pumping gear.  This type of installation should only be done at a location you know you will be using for at least 5 years or you may find the installation and upgrades were not worth it compared to accepting less efficiency but having a lower build-out expense.  This is a involved process and you should consult with consultant that has a track record of designing and assisting in implementation of water chillers.  These units usually start at 30 tons and can go up to over 100 tons or more. 
Evaporative Cooling – This is a good option and the reason it is under supplemental cooling and not baseline is because humidity can hamper your cooling and because a miner can’t control that aspect, you can’t honest count it as “Baseline Cooling” because there are reasonable things that do happen over a year that will hamper your cooling efforts and will force a rolling blackout and possible hardware damage.  Used in conjunction with strategies outlined above works quite well and can lead to great efficiency.   Sorry I had to jump the horse, I know some people would gasp if I didn’t make that clear.  Evaporative cooling uses a know fact that when you have low humidity and you blow air over water, as it evaporates the water, the air on the other side of the water is cooler than before it came into contact with the water.  This is why low humidity is key because if the humidity is high, that means more water is already in the air so that mean there is less room for it to take on more heat.   How it is used is be sending the hot exhaust air through a cooling tower or something to that effect.  It basically has a medium that is used to drip the warm water over while large fans draw the outside air through it to produce cooler air.  Interesting little fact is that to a point, hotter temps outside actually increase the cooling effect.  This is a large subject and many ways to approach it so please do research to understand it thoroughly.
Direct Air Cooling / Free Cooling – This is pretty self explanatory, it is the process of using outside air that is at or lower than your desired temperature.   Airflow is the real challenge in this model to make sure you are moving enough air to get the hot air out and the colder air inside.  Outside temperature is the main determinate of the effectiveness of this option.  Some hosting startups use this exclusively and with that there has been many reports of damaged and underperforming mining hardware.  This should honestly be only supplemental to increase efficiency and it should be used in conjunction with other strategies.  It is also important to note that you need a good filtering solution or you will be particulates from outside and they will get into the mining hardware and you will see failures, slow-downs and visible build-up over time.
Immersion Cooling – This is the future of cooling in datacenters but it is still likely a decade out for full commercial use, this due to the fact that hardware manufactures need to be involved so they can design hardware that is made for immersion cooling.  The basic concept is that you take a special liquid that is non-conductive, non-corrosive and have excellent properties to remove heat.  The heated liquid is then cooled and re-circulated through the system for more cooling.  Allied Control is a company I have met with one of their co-founders in person and he discussed the technology.  They current have working installations that are proving this technology. 
Hope this helps shed a little light into this subject and it gives you ideas and items to do additional research.  In the end, cooling is critical for a well functioning mine and having the right amount of cold air year round is the best long-term approach for addressing this issue.
Lauren Miehe

Co-founder of   Washington State.


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