Professionals who care
MICHAEL YOUNG
Michael Young is a trainer, coach and contracts engineer in the HVAC industry. He graduated from the
University of the Witwatersrand in the field of Mechanical Engineering (B.Sc Mech Eng) in 2008 and
qualified as a Professional Engineer (Pr.Eng) in 2013. Michael is passionate about promoting knowledge
and helping other young engineers grow within the industry through his training workshops and
coaching sessions.
PERFORMANCE,
FLEXIBILITY, RELIABILITY
PART 6
By Michael Young
All our articles have spoken about performance and costs. So, where
do flexibility and reliability come into the picture? Can they really influence
the final design of our cooling system?
T
he other day I was working with a client where they
were comparing the performance of cooling equipment
from different suppliers. So, being an application engineer,
I submitted our proposal as well as our calculated value of
Power Usage Effectiveness (PUE).
Two days later, the client came back to me and asked
how my calculated PUE value was so much lower than
our competitors. The first question I asked was, “Are you
comparing PUE or partial PUE for cooling?”. It was later
discovered that the client was comparing my partial PUE to
overall PUE of his data centre.
The most accurate illustration of
partial PUE is to sum the overall
absorbed power of the cooling unit
over the entire year and then apply
the partial PUE calculation.
We then got our client to compare the partial PUE for cooling
and the figures were substantially different. Partial PUE is
defined as cooling requirements plus the IT load divided by
the IT load. So, just like ordinary PUE, the closer the quotient
is to a value of 1, the better the performance of the cooling
equipment.
After confirming that we were both looking at partial PUE,
we requested more information and later discovered that our
www.hvacronline.co.za
competitor offered standard cooling units while we offered
units with modulating capacity.
This changed the entire analysis as the partial PUE for the
modulating cooling unit would be much lower than the unit
with standard cooling capabilities.
Ambient temperatures fluctuate hourly, which affects
the energy consumption of the cooling unit. As ambient
temperatures decrease, the absorbed power from the cooling
units also decreases. So, the most accurate illustration of
partial PUE is to sum the overall absorbed power of the cooling
unit over the entire year and then apply the partial PUE
calculation.
It is important to specify if you are dealing with
instantaneous partial PUE or annual partial PUE when
performing the analysis, as each of the results will be different.
So, that brings an end to the “Cooling the cloud” series. I
hope you enjoyed this series as much as I enjoyed sharing my
knowledge with you.
We would love to hear your experiences with data centre
cooling, so drop me an email and tell me your story at
[email protected]. The best story will receive a
special complimentary gift.
Wishing you a successful month ahead. RACA
RACA Journal I June 2019
65