LOAD TESTING
Reducing
xxxxxxx the Cost of Cooling
Heat Load Testing
By Dave Wolfenden, Director, Mafi Mushkila
Introduction
It doesn’t matter whether it’s a new
data centre or a refurbishment,
getting the cooling balance wrong
means throwing money away. The
problem for many data centre builders
is that irrespective of new build or
refurbishment, they often have no idea
what the real heat load will be. As a
result they do limited testing, which is
often poorly designed, and their clients
eventually end up paying the price.
What can be done to
make heat load testing
more effective?
Heat Source
One of the biggest problems with
testing is making it representative of
the end use of the product. It doesn’t
matter if it’s a car, a washing machine,
a laptop computer or a data centre.
If the tests have no basis in reality,
then not only is the time and money
spent on them a waste, but the false
impression that they give of efficiency
means that future waste is completely
undetected.
In the data centre, one of the most
common ways of testing the heat load
is to introduce a heat source. There
is nothing inherently wrong with this
provided that it is done in a real-world
way. For example, introducing a heat
source of 20kW, 40kW, 60kW or higher
might seem like a good way to discover
what the cooling system can handle.
However, if there is no equipment other
than the heat source in the room, all
that is being tested is the ability of the
cooling systems to deal with hot spots
rather than normal computer load.
One of the hardest things to get from
the end-user client is expected loading
inside the data centre. While customers
put down numbers in their specification,
they are often ‘guestimates’ rather than
realistic numbers. With long lead times
for data centre construction, it is also
possible that the hardware originally
destined for the data centre may have
changed.
The solution is to get a customer to
provide a range of value for each data
centre hall giving the expected lower
end, the maximum expected load and
some idea of the type of systems to
be installed. With the latter, it is then
possible to place variable heat sources
around the data centre in order to best
match how heat will be generated when
systems are running.
Effective Testing
There are a range of actions that can
be taken to make testing more effective
and it doesn’t matter if this is a new
build or a refurbishment. The key is to
get infrastructure and load emulators
into the hall and configure them to be
as representative of reality as possible.
Ten things that can be done to make
testing more effective include:
Racks and cable trays are the
minimum type of equipment
required. To make the cable
trays more effective, tape off some of
the ducts to represent different densities
of cable load.
1
Make sure that the racks are
all properly blanked off to
prevent air mixing and
arrange them in a similar configuration
to the end user requirement.
2
Not all infrastructures will be
rack mounted, so add in
additional components to
represent the type of equipment often
found in the data centre.
3
Make sure that the expected
means of input and exhaust
air are accounted for along
with the common types of air flow
interference and arrange the room
accordingly.
4
Place multiple sensors in each
rack and row to get a granular
view of air from the ground to
the ceiling.
5
Use multiple heat emulators
per rack and place them
where the load will occur. For
example, if the rack will have multiple
switches mounted at the top, place a
heat emulator there. Similarly, if there
are going to be blade servers that
generate large amounts of heat at the
bottom, place a larger heat emulator at
the bottom.
6
Don’t test with a single heat
load. Vary the loads from the
emulators across the racks and
throughout the day to make this
representative of normal workloads.
7
Testing vendors will be able to advise on how best to create realistic baselines for the types of workload to be run.
22 NETCOMMS europe Volume V Issue 4 2015
www.netcommseurope.com