Water side economizers
This technique extracts heat using an
economizer from the returning water (coolant) before it reaches the
chiller unit. This reduces the heat load on the chiller. The chiller
unit consumes a lot of power to remove heat from the water before
pumping it to the air handling units in a data centre.
This type of economizer works best if
the ambient air temperature outside of the building is cool. It might
take the shape of a free air heat exchanger where the "hot
water" is cooled without any compression except some form of
pump to circulate the water. Air convection removes some of the
excess heat. It might be some type of evaporative cooler (example1, example2) where a
water mist spray removes heat. In some case this may be a geothermal buried pipe
loop system or borehole where excess heat is transferred to the soil.
This type of installation can generally
be retro-fitted without too much disruption of the existing air
condition system.
Air side economizers
These work by taking cold air from the
outside of the building and feeding it directly into the air
conditioning ducts. Hot air generated by the equipment is vented to
the outside air. Simple in concept but it is not always easy to
retro-fit. The technique can make substantial savings in the energy
bill. It was known to our grandfathers as "opening a window"
when the room gets too hot.
The incoming air has to be humidity
controlled (de-humidified/re-humidified) and filtered to remove dust.
The building also has to have sufficient air conditioning plant to
handle the situation when the free cooling air side economizers
cannot be used. It may be too hot, too smoky or too dusty at certain
times of the year to use the air from outside of the building. There's a useful discussion here.
Retro-fitting such a system might
involve substantial changes to the air duct system and can be
difficult in data centres where hot air removal is not in place.
Other ideas
Other techniques such as hot/cold aisle, hot air containment, equipment cabinet blanking panels, pumpable ice, increased ambient data centre temperature, can be used to reduce the energy bill.Here's a free cooling system by Stulz.
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