New cooling technologies that use evaporative mechanisms play a significant part in helping data centres reduce their energy consumption. However, does this simply shift the environmental burden from energy to water use? Yan Evans, global director for FläktGroup’s data centre business argues why this isn’t the case, and how adiabatic systems can be designed to minimise both energy and water consumption.
The energy used for climate control and UPS systems can be around 40% of a data centre's total energy consumption, and efficient cooling systems can significantly cut carbon footprints and energy costs. That’s why, in recent years, technologies have been introduced to the data centre market that take advantage of local climates for energy efficient operation.
This includes adiabatic cooling, which is based on the simple principle that evaporating water removes heat from its surroundings. Units that use this method spray water to cool the warm outdoor air via evaporation – this now cold outdoor air draws heat through the heat exchanger from the data centre air which then is cooled as well, instead of using compression refrigeration systems which consume more electricity.
In doing so, some argue that evaporative cooling needs vast quantities of water – an increasingly scarce and costly resource in parts of the world. But a number of technologies have been developed for data centres which rely on adiabatic solutions, that reduce their water consumption without compromising on energy efficiency.
Reducing water consumption
Water needs to be treated before it can be used for evaporative cooling to prevent limescale. Softened water is the norm for many of the adiabatic solutions on the market. However, at FläktGroup we recommend the use of reverse osmosis (RO) water for our Adia-DENCO AHU system, which can achieve in excess of 10 cycles of concentration before it is discharged to drain.
Instead of treating water with biocides to maximise hygiene, RO removes over 99% of water contaminants and 100% legionella by passing water through membranes with microscopic pores. These are between 0.0001-0.0005 µm in diameter, which is only slightly larger than individual water molecules. Many contaminants, including legionella bacteria that are 0.3-0.9µm in diameter, are too large to pass through these pores and are left behind.
RO also removes more of the magnesium or calcium ions which cause limescale. This demineralisation leads to a lower concentration of dissolved solids in the water after some of it is evaporated in the AHU heat exchanger. That’s why it can be recirculated and dramatically reduces flush cycles from every hour to typically once a day. With softened water, these ions are not removed; the treatment process simply replaces the limescale-causing compounds with sodium ions. As the water evaporates, their levels become more concentrated, reaching a conductivity limit where the water becomes too saturated with these solids and cannot be reused.
Not only does the right water chemistry help to reduce its consumption, the mechanics of how it is sprayed onto a heat exchanger also plays a role. By coating the plate heat exchangers in our Adia–DENCO units with a hydrophilic coating, the angle at which the water droplets hit the plates changes from 80 to 20 degrees – often referred to as the “contact angle”. This creates greater cohesion between the water and the surface of the plate heat exchanger, increasing the energy transfer efficiency of the heat exchange process, and further minimises the amount of water needed.
Although additional expenditure would be required to provide RO water, the reduction in water consumption would lead to a payback period on the capital investment of within four to five years out of the AHU’s 15-year lifespan. Further benefits can also be gained; the use of reverse osmosis water considerably reduces the amount of cleaning, maintenance and sampling required.
Improving energy efficiency
In addition to water-saving technologies and design, it is important to remember that adiabatic cooling and the water supplied for the process is not used constantly. At ambient conditions below approximately 21°C (at 25°C supply air, which only accounts for a low number of hours per year), colder outdoor air can be employed to provide precision cooling with minimal energy requirements – otherwise known as “free cooling”. This further negates the need to rely on refrigeration technology and direct expansion systems, thereby reducing energy usage.
Water chemistry can contribute to energy savings too. By specifying RO water for our adiabatic system, less water is needed, which means operators can use less power-hungry pumps in their plant.
More than ever, there is a need to employ smarter technologies that deliver close climate control in a more energy efficient way. But this should not, and need not, be done in a way that compromises the availability of other natural resources.
The latest adiabatic systems show that energy consumption can be significantly curbed, especially when combined with “free cooling”, without putting a strain on water supply. If other water-saving measures such as rainwater harvesting are installed, data centres that operate in wetter climates can save even more water.
As the industry continues to be heavily scrutinised for its impact on the environment, solutions that are efficient in both energy and water usage can have a big impact on the bottom line, whilst meeting increasingly important environmental objectives.