9 April 2009
Author: Giorgos LazaridisPC Cooling Methods
The first computers that was ever made, could only operate under a very steady temperature, about the room temperature. Therefore, special cooling systems needed to be used in order to achieve the appropriate temperature and humidity conditions so that the computer would run flawlessly. From then on, things changed dramatically. Modern computers can operate in higher ambient temperatures performing millions of calculations per second more than the Z3 and the ENIAC. The cooling methods for modern computers have been significantly minimized.
Over the years, various cooling methods have been introduced. Each one with it's advantages and disadvantages. We will try to cover the most of those cooling methods in a way that you can choose the one that fits your needs.
Active air cooling:
This method is by far the cheapest and commonly used method for cooling a PC. A fan is blowing fresh air on a cooling plate placed over the components that needs to be cooled. The cooling plate has usually a flat surface that touches on the part to be cooled, and on the other side there are several fins attached. Those fins will increase the surface of the plate and therefore the heat exchange capability of the plate. The fan is blowing air between those fins making the exchange quickly and more efficient, as it rapidly removes the heat surface of air that is produced between the fins.
Active air cooing is an efficient way of cooling in terms of power saving with one main drawback: It can only reduce the working temperature of a part to temperatures that are always higher than the ambient temperature. This could be a problem when a PC is working in harsh environments or if near the PC there are other components that could produce high temperatures when in operation.
The reliability of those systems is very high, because even if the fan stop working, the system may work for a few minutes as a passive air cooling (see bellow). Moreover, when a fan is about to die, it usually makes a strange sound many days before, giving the operator enough time to replace it. The serving costs of this system is in really low prices and affordable from anyone.
Passive air cooling:
Same as the Active air cooling method, in passive air cooling there is a same plate that will simulate a larger cooling surface of a part. But in passive air cooling, this plate is multiple times bigger than the ones in active air cooling, and this is because there is no fan to blow within the fins. The fins must be large enough and must also have enough space between them, so that a natural flow of air can be achieved.
The cooling plates can be very heavy and sometimes require special parts to be fixed over the part to be cooled, to that they will not mechanically damaged the part or the PCB itself.
Passive air cooling is the most efficient way of cooling in terms of power saving, as it needs actually no power at all to operate. This method carries a major drawback: Weight! Heavy and large plates must be fixed over small parts, increasing the total weight of a computer and reducing the usable area inside the box. Also, the ambient temperature could not be very high as this would make the passive air cooling inefficient. In many cases, the computer housing has 1-2 fans to circulate the air inside the computer.
The reliability of this system is top high. There is actually no reason that this system would for any reason sop cooling the parts. If the cooling demands of the parts to be cooled meets the cooling capacity of this system, then it is the number one choice. The serving costs are as low as 0.
This is a rather new trend on PC cabinet cooling systems. The basic system is composed from the cooling plates, hoses that the coolant flows within, a small coolant tank, a circulation pump and a radiator. Each component to be cooled has a cooling plate attached on it. This plate, usually made of copper or aluminum, is a hollowed plate with an input and an output for the coolant. The circulating pump will circulate the coolant from the radiator, to the cooling plates, then to the tank and back to the radiator. In the radiator the coolant will reduce it's temperature. According to the radiator, the water cooling could be distinguished into two categories: The active and the passive water coolant.
Passive water cooling: With this method, the radiator is made of a long thin copper or aluminum hose, that it has fins made of the same material in various ways attached to it's perimeter. When the hot coolant goes through the pipe, the water exchange temperature with the environment and it cools into ambient temperatures.
Active water cooling: With this method, the water is not cooled naturally, but using other means of cooling, like small freon heat exchangers of Peltie thermo elements.
In some cases, the coolant can circulate naturally. For this to be achieved, the tank and radiator needs to be placed higher than the highest cooling plate of the system, the hoses needs to be larger in diameter and the radiator must be specially designed, in order to allow the coolant to flow freely.
In general, the water cooling can be quite messy when a failure in pipe connections occurs. It also needs a lot of power to operate the pump decreasing it's efficiency, but this can be overtaken if natural flow is chosen. On the other hand, it can rapidly reduce the working temperature into ambient or even lower temperatures when active water cooling applied. A major drawback is the reliability of the system, as a failure on the pump would mean an almost instantly temperature increment on the CPU, therefore special security measures needs to be taken in order to increase reliability. Also, water cooling has technical problems when tried to applied on all parts that would need cooling, such as hard disc drives, memory banks, north/south bridge chips etc. Not all parts can be equipped with water cooling plates making for them water cooling impossible. Therefore, fans to circulate the air inside the cabinet are almost always present on these systems. The serving costs are sometimes higher than the previous referred systems, as a regular pump maintenance is required
This is a rather unusual cooling device, a hybrid of water cooling and air cooling. The parts that needs to be cooled carries cooling plates similar to those used for air cooling. Only now, inside the cabinet, fresh air is blown from a device called 'bong'. This device, will use water to cool the air. The bong is usually a large cylinder about 15 cm diameter and more than 1 meter long. This cylinder is placed vertical. The bottom side is closed and on the top side, there is a water vaporizer. The water is circulated with a pump from the bottom of the cylinder to the top, and then it falls in small drops back to the bottom of the cylinder. About 20 cm from the bottom and 20cm from the top, there are two holes. A fan is attached to the bottom hole blowing air inside the cylinder. The air is taken out cooled from the top hole, driven directly in the PC box.
This method is not so widely used because of the obvious drawbacks it carries. It is messy, it has a low efficiency and it needs a lot of space to place the device itself. But the basically disadvantage is that the cooled air carries a lot of humidity that will finally arrive in the PC box.
Bong cooler can achieve ambient temperatures or even sub ambient temperatures if the water is cooled with active components such as Peltier TE. It also carries a unique advantage against the others, that it can operate as a filter for heavy dust. The dust will be connected with the water making it heavier and will fall down to the bong tank. A regular water change on the bong is required to keep the water clean.
The reliability of this system is higher than the water cooling method, and this is because even if the pump fails, the whole system will operate as a fully featured active air cooling system. The serving cost is higher than an air cooling method as the pump needs usually regular maintenance and the water circuit needs regular cleaning from the air dust.
Peltier Thermo Elements:
Finally, the Peltier thermo elements. Those devices are thin plates, 3-8mm thick with different sizes, usually rectangular shape 3x3 cm or more. Peltier is an active component. When power is applied to it's leads, the temperature from one of it's surfaces will carried to the other surface. That's why they are also known as Heat Pumps. The cold surface is applied on the element to be cooled.
Peltier can achieve really low temperature, sometimes bellow zero! But this is almost the only advantage od these systems. A lot of disadvantages comes along with them. First of all, the power consumption. They can draw up to 180 Watts in full operation making them completely inefficient. They have to be direcly attached on a surface on the part to be cooled, making them sometimes inappropriate and impossible to be used, especially with parts like memory banks hard discs drives etc. This means that extra air circulation using fans must be used.
Another major drawback is the condense of humidity. This phenomenon occurs when low temperatures are found somewhere. The humidity that exists in the air is condensed on the cool plate of the peltier and becomes ice. This ice will melt and become water when the cooling system is turned off.
The reliability of this system is lower than the others. A power fail on the Peltier would mean instant temperature climb. The service cost is not very high as Peltier nowadays are cheap enough to buy.
The following table carries the rates of the above systems in respect to some parameters such as efficiency, reliability etc.
Choosing the most appropriate cooling method has to do with the requirements. The power consumption, the ambient temperature, the humidity, the operating temperature and the housing of the parts are the most important parameters that needs to be taken in account when choosing water cooling method. But some times, especially when someone is moding a computer, extreme systems can be used. When this happens, the only parameters taken into account is 'Style' and 'Creativity'.