Water Side Economizers

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Hi All,

What is the difference between a "water side economizer chiller" and a
"water side ecomizer," which you find under the air-side HVAC cooling
subtab? What does each do for their respective systems?

I am trying to model a water-side economizer that runs in series with the
other chiller, so I am pretty sure that I want the "water-side economizer
chiller." I just want to be sure because there is a substantial difference
between the two in energy savings (water-side ecomizer chiller is more



Patrick J Keeney

Patrick Keeney's picture
Joined: 2011-09-30
Reputation: 0

My understanding (feel free to correct, those who know):

- the water side economizer chiller is the newer, more correct way of
modelling the system you describe -- where a plate frame heat exchanger
is in parallel with the chiller with chilled water on 1 side and
condenser water on the other. This is what I use.

- the air-side, water-side economizer tab adds a new cooling coil
connected to the condenser loop to precool your incoming air as well as
pre-cooling the condenser water before it goes to the chiller. Similar
but this adds fan energy (static across the new chiller) and pumping
energy and isn't really how a water-side economizer system that I am
familiar with is implemented (at least around here).

- in DOE-2.1e, you used to be able to set your cooling tower control to
"strainer cycle" which would also give you a water-side economizer but I
believe this was lost in going to DOE-2.2, with real loops etc. Adding
the water-side economizer chiller, restored this function.

One more note -- I understand that you do not need a load management or
equipment control to operate a water-side economizer chiller ... and
further if you add them, they will be ignored anyway. If there is
sufficient cooling based on the outdoor air temperature for the
water-side economizer chiller to carry the full cooling load, then it
will operate (for that 1 hour timestep). Otherwise, it will not operate
and the chillers will carry the full cooling load. There is no partial
operating mode.



bfountain's picture
Joined: 2011-09-30
Reputation: 201