Natural refrigerants in data centre cooling

The Swedish refrigeration industry's foundation KYS (Kylbranschens samarbetsstiftelse) financed this research work to stimulate the use of natural refrigerants in cooling of electronics.

EKA performed this research together with two students from KTH; Sahlsten and Heinerud, who did their master thesis project on “Natural Refrigerants in Data Centre Cooling with Thermosiphon Application”. Further, Jörgen Rogstam presented the results at the conference Thermal Management of Electronics Systems in Stockholm, September 7th 2017 with the title ”Natural Refrigerants in Data Centre Cooling”.

The energy savings are up to 88% and the total annual cost savings are up to 69%. The Power Usage Effectiveness is reduced with up to 6% and up to 8% if only cooling is considered.

Background

Ever since the computer was invented, there has been a need of data storage and the demand has strictly grown since. This has resulted in a huge amount of data centres and the trend has shown no signs of changing. Data centres are powered by electricity and in 2010 the electricity consumption for data centres accounted for 1.3% of the world’s electricity usage. The most energy intensive part of a data centre is the servers themselves, but the second largest energy user is the cooling system, which normally stands for 40% of the energy usage. Besides the energy usage, the cooling systems are in most cases a unit using HFC or even HCFC refrigerants. These refrigerants have a very negative effect on the environment since they have high GWP values (global warming potential) and HCFCs even an Ozone depletion potential (ODP).

Scope of work

• Find a way to make the data centre cooling systems more efficient by;

  • using free cooling from the ambient air as an effective method of reducing the yearly electricity demand

  • to use two-phase thermosiphons to move heat from the servers to the ambient, which reduces/eliminates the need of pumping power

• Find solutions using natural refrigerants with zero GWP (and certainly no ODP)

• Evaluate the potential to recover waste heat from the data centres.

Method

This work contains two systems being simulated using the software Engineering Equation Solver: a direct R744 system and an indirect system running with R290 and R744. Both systems are using a thermosiphon application, connected to a condenser, to use free cooling up to a certain set point temperature and the rest is covered with a vapor compression cycle. These systems are then matched to temperature profiles for five cities, Stockholm, Paris, Phoenix, Tokyo and Madrid, to see how many hours of the year are covered by free cooling. The systems are then evaluated considering both energy consumption and cost. To be able to compare these systems to a present cooling system, a reference system is modelled which uses R22 as refrigerant, which has been the most commonly used refrigerant in the world for the data centre cooling applications.

Central and local cooling unit systems with the condenser in the same level as the server room using thermosiphon technique.

Results

• The results show that a direct R744 system or an indirect system with R290/R744 with a thermosiphon application have both energy and economical saving potential compared to the reference system.

• The energy savings are up to 88% and the total annual cost savings are up to 69%.

• The Power Usage Effectiveness is reduced with up to 6% and up to 8% if only cooling is considered.

Total annual cost for the different system solutions for evaporative cooling.

The indirect R290/R744 system is the best in all cities considering energy efficiency. Both systems are also well suited for use with heat recovery. The Seasonal Performance Factor for the heat recovery is between 8.3 and 15.2, which is a consequence of the high evaporation temperature and low supply temperature to the heating system.

The whole presentation and report are available below.

Slutrapport Nat köldm i datacenters 17JA.

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