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Indirect free cooling of DX cooling unit (Part 3)

Indirect free cooling of DX cooling unit (Part 3)

By Michael Young

Is the integration of the pumped refrigerant loop the future of a DX system, and will this become the new industrial norm?

Part 1: Indirect free cooling of DX cooling unit
Part 2: Indirect free cooling of a DX cooling unit (Part 2)

The easiest way to answer this question is to compare the performance of the system for different locations and operating conditions in the form of a case study. We will consider two different site locations. One site will be located in Durban, South Africa, while the other site will be located in Hamburg, Germany. Both sites are similar in elevation but differ greatly in season ambient temperatures.

The study will be conducted for the following requirements:

  • Number of cooling units: 6
  • Required cooling per unit: 96kW
  • Return air temperature to computer room air conditioning (CRAC): 35°C
  • Ambient temperature: 35°C

Let’s start with the energy consumption of the system at each of the different locations. For Durban, the system consumed 989 592kWh, while for Hamburg, the system consumed 696 060kWh. Comparing the electrical consumption, the unit consumed 293 532kWh less energy in Hamburg than in Durban. So, why is there such a large difference in performance?

The winters in Hamburg are much colder than those of South Africa. So, in Hamburg, the units will operate on pumped refrigerant mode for a longer period than in Durban; hence, a more energy-efficient solution for the use in Germany.


Higher energy-saving capabilities will come at a higher premium on the cooling equipment.


Higher energy-saving capabilities will come at a higher premium on the cooling equipment. So, the key to determining if a specific type of cooling technology is feasible for a specific project, is to determine the energy savings per year and then offset that against the premium spent for the energy-saving technology.

The result from this calculation will yield the payback period on the capital cost of the cooling unit. It is important to remember that the cost of energy will also vary from country to country, so this is another factor that will influence the payback period.

For our case study, the payback period for Durban was estimated to be approximately seven years. This value was estimated on the current price of energy and excluded any escalations on the price of energy.

So, you may be thinking, seven years is a long time to obtain a payback period on this type of cooling technology. But if you think about it, if the unit is well maintained and serviced, you may get up to 15 years’ service from this system. You can gain eight years of energy savings within your data centre and the operational cost savings will increase each year as the price of energy increases.

Will these energy-saving features become the new standard for all DX cooling system? I would like you to let me know your thoughts by emailing me at michael@myhvaccoach.com. I look forward to hearing your comments and your views into the future of the DX cooling system.

Wishing you a successful month ahead.
Mike signature 14 8 2017


Click below to read the February 2018 issue of RACA Journal

RACA FEB2018

06 Jun 2018
08:00AM -
FRIGAIR Expo 2018 - Day1
07 Jun 2018
08:00AM -
FRIGAIR Expo 2018 - Day2
08 Jun 2018
08:00AM -
FRIGAIR Expo 2018 - Day3
16 Oct 2018
08:00AM - 12:00AM
Chillventa 2018 - 16-18 October

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