Ken Carpenter · Follow
Published in · 5 min read · Jan 16, 2019
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Over the course of the past year and a half, Obelisk has developed and shipped two generations of miners for Siacoin and Decred. During that time, I have spoken with dozens of data centers and hundreds of miners. One area of interest that kept coming up over and over again was using liquid immersion and pumps to cool miners instead of air and fans.
The promises of liquid immersion include:
- Lower data center construction costs
- Lower cooling equipment costs
- Lower energy costs to operate (low PUE)
- Silent operation
- Increased hashing performance
There are two main types of liquid immersion: two-phase and single-phase. We’ll discuss both briefly below, and then talk about what Obelisk is doing in this area.
Two-phase immersion refers to a cooling technique that immerses electronic equipment in a dielectric (non-electrically conductive) fluid. When the fluid comes in contact with high enough heat such as that from a CPU or an ASIC, it changes phase from a fluid to a gas (hence the name, two-phase immersion) and rises up through the fluid as bubbles. Once past the surface, the gas then comes into contact with a cold water loop at the top of the tank, where it condenses back into a liquid and drips back into the tank again. The cold water loop warms up in the process and carries away the heat away to an external heat exchanger.
The primary vendor of two-phase immersion fluids is 3M with their line of Novec fluids. This fluid is currently extremely expensive though ($200+ per gallon). This cost, along with the requirement for a complex and costly recirculating water loop for cooling, makes this technology too expensive for cryptocurrency mining at this time. If the cost of the fluid drops it may be worth considering again.
The following is a good introductory video on two-phase immersion:
Single-phase immersion refers to another cooling technique for electronic equipment that also uses a dielectric fluid, but rather than a costly custom fluid, a blend of much less expensive mineral oils is typically used. These fluids have a heat capacity about 1,200 times that of air.
The physical setup for single-phase immersion cooling normally involves a large vat of mineral oil that is essentially a data center server rack, but laying down on its back like a bathtub. The equipment is fully immersed in the unit, often including power supplies. In the image to the left, you can see an example of an immersion rack from Green Revolution Cooling, and a 1U server being inserted into it.
These types of immersion tanks were originally intended for data center equipment like servers, however, recently, cryptocurrency miners have started to use them too. Companies like Green Revolution Cooling (GRC) are making products specifically for the mining market.
The following video is a good overview of the benefits of a single-phase immersion system.
It’s also interesting to note that these immersion cooling tanks are very often combined together and deployed in shipping containers, making them easy to relocate if, for example, cheaper power is found. This helps make these immersion tanks a good long-term investment.
Over the past several months, we’ve been working with some customers who are mining with these single-phase immersion tanks. Until now, they’ve been using an ad hoc metal chassis for each type of miner that they submerge. Since those miners were not designed for use in liquid immersion, the chassis designs have been far from optimal, and have not been able to reach the hashrate density that the immersion tanks are capable of supporting.
In other words, the heat handling capacity of the immersion tanks is far higher than what the miners have been able to generate. This means miners are paying for more cooling capacity than they need.
Obelisk believes that investing in liquid immersion infrastructure could give large miners a long-term advantage against their air-cooled competitors. For this reason, We are very pleased to announce today the Obelisk SC1 Gen 2 Immersion miner!
We’ve created a 1U rackmount chassis that is custom-designed to hold 4 Obelisk SC1 Gen 2 hashboards, and 2 x 1000W PSUs, all managed by a single controller board.
Here is a photo of the first prototype:
At the beginning of this post, I mentioned that increased hashing performance is one of the promised benefits of using immersion cooling. In our early experiments with immersion cooling, an air-cooled Obelisk SC1 Gen 1 was able to achieve 600GH/s, but it exceeded 750GH/s in immersion. That’s an increase in hashrate of 25% with the same hardware!
We have also seen a similar 25% increase in hashrate with the new Obelisk SC1 Gen 2 Obelisk Immersion miner, and we have some performance tweaks coming very soon that we believe will bring the hashrate even higher.
During the process of designing this chassis, we’ve come to better understand what makes a good immersion miner, and have planned optimizations for the:
- Chassis
- Power supply
- Hashboard size and shape
- Cable placement and routing
- Control board design and placement
We will be incorporating these improvements into our next generation designs, and expect to be able to provide even greater efficiency, better hashrate, and further increases to the hashing density. We will still, of course, ensure that we create products that continue to be as efficient as possible when operated with traditional air cooling.
If you have any questions about this new product or you are interested in purchasing the Obelisk SC1 Gen 2 Immersion Miner, please get in touch with me at ken@obelisk.tech.
