A data centre cannot go a second without power and not a minute without cooling.
If cooling stops, air heated by the ICT equipment cannot be cooled and supplied again. The uncooled air is heated again and this dangerous cycle continues until the ICT equipment overheats.
A data centre with 100kW of ICT capacity and a malfunctioning air-conditioning installation is within one minute heated to 34ºC, within 10 minutes it's 46ºC and within 15 minutes the data centre tops 50ºC.
Conventional cooling for data centres is usually based on compressor cooling systems, which work with a certain refrigerant.
The liquid refrigerant is expanded through an expanse valve in an air cooler or evaporator, the expanded liquid refrigerant withdraws heat from the hot air of the ventilated air in the evaporator. The air becomes gaseous. The compressor then compresses the gaseous air to high pressure.
After this the heat in the refrigerant spreads until the gaseous refrigerant becomes liquid in the condenser. The refrigerant is liquid again and the process repeats itself. This is called the direct expansion method. A lot of variations of this method are possible.
Sometimes the data centre air is not cooled directly but first water is cooled which cools the air with an extra heat exchanger and pump. This way the overheated refrigerant is cooled by water. This type of cooling requires a lot of mechanical components such as pumps, compressors and fans.
All necessary components have a high energy consumption, maintenance costs and malfunction risk. Then there is the phasing down of high Global Warming Potential (GWP) refrigerants, another reason why adiabatic cooling is a good alternative. It is an energy saving natural alternative that uses evapotative cooling with water as a refrigerant.
To determine if it is energy friendly or unfriendly, check the Energy Efficiency Ratio (EER) or the Power Usage Effectiveness (PUE). The definition of PUE is the total energy consumption divided by the ICT energy consumption.
Originally this formula was designed to measure the efficiency of the complete data centre. This formula is also used for measuring the efficiency of the cooling: PUEcooling.
The EER is the ratio between the cooling capacity or cooling power (in kW) and the quantity of electrical energy that needs to be supplied. This is everything that is necessary to supply the wanted cooling power – compressors, fans, pumps etc
Indirect cooling
How does indirect adiabatic cooling work? Indirect adiabatic cooling is a cooling process where the temperature of a data centre is decreased by evaporating water in another air stream with a plate heat exchanger.
The data cente air is completely separated from the humidified air stream, which goes outside the data centre so it does not have an impact on the humidity level.
The cooling of the hot air by evaporating water in the air stops when the air is 100 per cent saturated. This is called the wet bulb globe temperature. Water as refrigerant is a natural, energy friendly and durable alternative for traditional cooling processes, without the use of chemical refrigerants.
With minimal components, two fans and a water valve is the most reliable and maintenance-free cooling system possible. The basis of indirect adiabatic data centre cooling is the StatiqCooler synthetic heat exchanger.
The StatiqCooler heat exchanger is a component that transfers hot air from one air stream, the outside air - through a thin separating plate to the different air stream - the datacentre air. At a low outside temperature, the outside air indirectly cools the data centre air without water.
When it becomes warmer outside, the plate heat exchanger is humidified. The water evaporates on the plate in the heat exchanger and withdraws the heat from the data centre air. Because of the thin synthetic plates and the hygroscopic layer the heat exchanger has a high heat coefficient.
The ASHRAE TC 9.9 2011 standard provides an Allowable (red) and Recommended (blue) guidelines for cooling the data centre. (See diagram)
For compressorless cooling, the system must meet the temperature values in the allowable frame. At Air@Work we go a step further. Because of the efficient indirect adiabatic StatiqCooler our systems always meet the temperature in the recommendable frame (in the Dutch climate).
Based on the most extreme situation in the Netherlands, where the maximum temperature is not important but the combination of temperature and humidity are - compressorless cooling is always possible.
In the example (green line) the air of 32ºC / 50 per cent RH is humidified to 100 per cent relative humidity. With a wet bulb globe temperature of 23.5ºC a data centre can be cooled!
Maximum load
The cooling capacity or cooling power of a data centre is designed for the worst case scenario. It must be able cope if it is hot outside or ICT capacity needs to be ramped up over a short period of time.
Most installations cool at partial load. The energy efficiency of indirect adiabatic cooling works better at partial load than maximum.
Moreover, as long as the outside temperature is low enough the exchanger works as a normal counter-flow heat exchanger.
The outside air cools the data centre air. The two air streams affect each other but they do not mix.
Finally, the starting point for our system is the usage of an approved bacteriological and legionella safe system.
By applying indirect adiabatic cooling, data centre cooling becomes very efficient. The energy usage of the system is only the necessary consumption of propelling the fans.
A saving of 90 per cent on energy costs can be realised in comparison to conventional systems. It also reduces e-infrastructure and there are less moving parts, low maintenance and high availability.
To find out more, visit www.uapcooling.com.au.