This is the first part of the guide to building a cooling system for your miner.
We’ll cover the following points:

• Basic principles of heat
• Difficulty in transferring heat
• Important things to consider when designing a cooling system
• Calculating the heat to be disposed of

Basic principles of heat

In the mining world, we’ve become accustomed to dealing with various metrics such as hash rate, power consumption and temperature.
Usually we measure the temperature of the video card core because this point is subject to temperature increases during the calculations required to find blocks and because it’s very important to monitor this value to avoid the following phenomena:

• Electromigration – progressive damage leading to the death of the GPU caused by the migration of atoms due to heat
• Thermal runaway – The chip exceeds the permitted temperature, resulting in an increase in current consumption. The increased current consumption leads to further heat production, which will lead to the melting of solder bumps (especially in BGA packages) or die detachment.
• Solder joint failure – due to the increase in temperature, the micro solder joints inside the GPU break or degrade, leading to malfunctions, instability or failure to boot (an example are video artifacts when connecting a monitor to the output of the damaged video card)

A lesser-known unit of measurement is the joule (J), which indicates the heat of a body (in our case mainly GPU and video memory).
The difference between temperature and heat is important because it will help us better design our cooling system.
Temperature – Temperature measures the energetic motion of a body’s particles. It is a property of a body and is measured in °C (degrees Celsius), °F (degrees Fahrenheit), or K (kelvin).
Temperature indicates “how hot” a body is, not how much energy it contains.
Heat – Heat is energy in motion that passes from a hotter body to a colder one. It is measured in J (joules) and only exists when there is heat exchange!

What is important to understand is that the temperature drops if there is heat exchange.

Difficulty in transferring heat

Now that we have highlighted the importance of transferring heat to lower the temperature, we need to understand what elements oppose this movement of energy.

Conductivity of materials.
One of the best materials used when cooling electronic components is copper due to its excellent performance; it is found in mid- to high-end products for heat sinks and heat pipes. Other materials used include aluminum and steel for construction of supports or closed enclosures (such as cases).
When building our cooling system, we must take into account the low conductivity of materials such as wood or plastic (materials that are prone to flammability).

Temperature difference.
It may seem strange, but it’s easier to cool from 90°C to 60°C than from 60°C to 40°C. This happens because heat transfer slows as the temperature difference decreases.

Thermal Resistance
Every transition from one surface to another or from one material to another creates a bottleneck. Too many transitions in the cooling chain should be avoided wherever possible.

Heat Capacity
The more mass an object has, the more energy it stores. Therefore, large heat sinks or structures accumulate a lot of heat, which is more difficult to transfer or dissipate.

To summarize, we can say that the temperature drops “easily” only if the system can transfer heat efficiently.

The real problem is not the temperature, but the ability to move energy out of the system!

Important things to consider when designing a cooling system

Before purchasing the materials needed to build our miner cooling system, it’s a good idea to first evaluate the operating parameters.

Amount of heat to be dissipated.
This is the main value to start with: “How much heat does my miner generate that I will need to dissipate?”
It seems like a difficult question, but I’ll help you figure it out in the next chapter.

Temperature difference.
A miner’s operating temperature is a fairly easy value to find, as mining software often displays the GPU temperature.
The ambient temperature is equally easy to measure with a simple thermometer, but there are some challenges. This value is affected by several factors, such as:

• Seasonality – obviously winter will be a better situation than summer
• The presence of other heat sources – other electronic devices, a heating system, direct sunlight
• Ambient humidity—drier air will facilitate heat transport by the air, while the presence of humidity in the air will hinder heat dissipation. It should be noted that high ambient humidity will cause deterioration of our mining system due to oxidation of the metals, a phenomenon that will increase thermal resistance.

Total thermal resistance.
All the components we’ll use have their own thermal resistance to heat transfer. When designing a cooling system, individual thermal resistances resulting from imperfect contacts, poorly conductive materials, or excessively small surfaces must be taken into account.

Conductivity of Materials
When choosing materials, their conductivity must be considered.
Copper is one of the best materials, followed by aluminum. Steel has low conductivity, and plastics are even worse. If an object you’ll be using in the system will contribute to heat dissipation (for example, air ducts), consider its material.

Heatsink Surface
Obviously, the larger the surface area of ​​an object, the more heat it can transfer. Choosing GPUs with large heatsinks is definitely preferable, and even better if the heatsink fins are arranged along the length of the card (I’ll explain why later).

Noise and Power Management
Another environmental parameter we’re accustomed to in the mining world is noise (measurable in decibels).
In designing, we must take into account the noise generated by cooling fans, as well as the noise of the air passing through the various stages of the cooling system. This includes the air passing through the heat sinks, the air flowing through the pipes, and the turbulence created by surfaces that aren’t perfectly smooth or have curves. Power consumption must also be kept under control to make mining economically productive. The more the system exploits the laws of nature or uses passive solutions, the lower the power consumption will be.

Reliability and Safety
A cooling system must ensure temperature management, but it must also continue to do so without interruption and ensure safety. A stopped fan degrades the cooling performance but could also trigger fires (due to overheating of electrical components), with disastrous consequences. A single fan forcing cold air into a room and then stopping (or tripping a safety switch) could cause temperatures to rise, halting mining (safety features on motherboards and graphics cards) or, in the worst-case scenario, overheating of the materials, potentially creating a fire hazard.

Calculating the heat to be disposed of

Our miner generates heat, and we need to calculate how much energy we’ll need to dispose of.
To get a reference value, we can start with the electrical power consumption.
Let’s imagine we have a miner with six graphics cards (about 120 watts each) for a total of 850 watts (including the motherboard, CPU, RAM, and three 120mm fans). Round up to 1000 watts to simplify the calculation and make the explanation easier.

1000 watt = 1000 J/s

To calculate how much heat energy you produce in a given time, use the formula:

E=(P/1000)⋅t

E (energy in kilowatt-hours)
P (power in kilowatts)
T (time in hours)
In our case, EkWh = (1000/1000)*24
We will have 24kWh to dispose of each day, equal to 86400000 joules (86.4 Mjoules).
To calculate the air flow rate you need to exchange, there is the formula:

Q=m˙⋅cp⋅ΔT

Q (thermal power to be dissipated expressed in watts)
m (mass flow rate of air in kg/s)
Cp (specific heat capacity of a substance at constant pressure, the amount of joules required to raise one kg of a given substance by one degree)
ΔT = increase in air temperature (°C or K)
To simplify matters, I’ve provided the following indicative table for 1kWh of electricity consumption, an ambient temperature of 20°C, a target miner temperature of 60°C, and air exhaust to the outside.

• 10°C difference from the ambient air temperature → ~300 m³/h
  Air exits at 30°C
• 15°C difference from the ambient air temperature → ~200 m³/h
  Air exits at 35°C
• 15°C difference from the ambient air temperature → ~150 m³/h
  Air exits at 40°C

The higher the acceptable air temperature exiting the miner, the lower the air volume required.
In this example, I used three 120mm fans, which typically each move between 50 m³/h (at low speed) and 100 m³/h (at maximum speed).

All together, they’re in the 150-300 m³/h range, which is perfect for our case!