[Equest-users] Waterside Economizer (WSE)

[Carol Gardner]

WATER-ECONO-EFF

<type63.htm>  <returnductthermallosses.htm>
 Varkie,Here's some of the inputs you need. The info is in the DOE2.2 Volume
2r which includes the refrigeration equipment definitions. Sorry about the
font difficulties - this comes from cutting and pasting.


WATER-ECONO-EFF

for a WATER-ECONOMIZER, specifies the effectiveness of the heat-exchanger.
The simple heat-exchanger model in this component assumes a constant
effectiveness for all chilled-water and condenser-water flows. It is used in
the following equation for load:

Qecono = Mchw * Cpchw * Eff * (Treturn - Tcw)

where

Qecono        maximum load the economizer can handle
Mchw          chilled-water mass flow rate
Cpchw         chilled-water specific heat
Eff            heat-exchanger effectiveness
Treturn         chilled-water return temperature
Tcw              condenser-water supply temperature

The default effectiveness is 0.8. To model direct-injection (strainer cycles),
specify an effectiveness of 1.0.

 Chiller Water-Economizer


 Chiller Water-Economizer

A water-side economizer provides “free cooling” by allowing cooling tower
water to bypass the chiller(s) and directly cool a chilled-water loop. The
cooling is not actually “free”, as energy must still be expended in the
cooling tower fans and pumps. Water-side economizers may be divided into
three principal configurations:

Direct injection – The condenser water is filtered and directly injected
into the chilled-water loop. While this method maximizes the effectiveness
of the economizer, it introduces oxygen and other contaminants into the
piping. These contaminants may ultimately corrode and/or foul the piping and
coils; thereby degrading the performance of the system and shortening its
life.

Indirect heat-exchanger – A plate-and-frame heat-exchanger to indirectly
cools the chilled-water loop. The heat-exchanger prevents the relatively
dirty condenser water from fouling the chilled-water components. Since the
effectiveness of a heat-exchanger is always less than 1.0, this method
cannot achieve the same performance as direct injection.

Thermocycle – A chiller can be configured so that its heat-exchangers and
refrigerant act as a passive heat transfer mechanism. Like the indirect
method, this method prevents cross-contamination of the chilled and
condenser loops. However, it does not usually achieve the same
coolingcapacity for a given temperature differential.

The capability to simulate a water-side economizer was omitted from earlier
versions of DOE-2 because of the lack of funding necessary to implement this
component properly. Nevertheless, many high-rise buildings utilize
water-side economizers, and many users have expressed the need to simulate
these components.

The program now partially remedies this problem by introducing a new type of
chiller that is a simple plate-and-frame heat-exchanger. This is not a
complete implementation, and the following rules must be understood:

The program assumes a water-side economizer is used in an “all or nothing”
mode. If the water-side economizer can handle the entire cooling load, then
it will be used. Otherwise, the loop will use its other chillers. A
water-side economizer cannot precool the return flow prior to entering the
chillers.

The “all or nothing” mode precludes the use of an EQUIP-CTRL sequence to
coordinate the operation of an economizer chiller with other chillers. If
you list a water-side economizer chiller in an EQUIP-CTRL sequence, it will
be ignored.

There must be a one-to-one correspondence between a CHW loop, a water-side
economizer, and a CW loop. A CHW loop may be supplied by only one water-side
economizer, and a CW loop may supply only one water-side economizer. In
other words, a plant may have any number of chilled water loops having
water-side economizers, but those economizers cannot draw from the same CW
loop. The program will generate an error if this condition is not met.

If a CW loop supplies a water-side economizer, it may also supply chillers
serving the same CHW loop as the economizer. However, it cannot supply
chillers serving other CHW loops. The program will generate an error if this
condition is not met.

A CW loop supplying a water-side economizer should have only one
coolingtower. More than one
cooling tower is allowed, however only the first tower defined will be
checked to see if sufficient free cooling capacity is available. Once free
cooling is allocated to a CW loop, the program may use any combination of
towers to satisfy it. *The program may underpredict the water-side
economizer savings if more than one cooling tower serves a given CW loop. To
minimize the underprediction, define the largest tower first.*

If there is any water-cooled packaged equipment in the SYSTEM command, this
equipment will be ignored when determining whether the tower has sufficient
free cooling capacity. *This may cause the program to overpredict water-side
economizer savings.*

For maximum effectiveness, the CHW loop should have COOL-SETPT-CTRL =
LOAD-RESET. This allows the CHW temperature setpoint to rise during periods
of low loads, maximizing the effectiveness of the water-cooled economizer.
------------------------------

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On Mon, Jul 5, 2010 at 10:01 AM, Varkie C Thomas <thomasv at iit.edu> wrote:

> I have not been able to model WSE in eQUEST (DOE22).  I have
> received advice and instructions on this subject. * I need an example
> project or the Plant section of the DOE22 inp file.*  I have done this in
> DOE2.1E (sample Plant inp attached).  The attachment includes the results of
> my efforts to understand how WSE works and attempts at modeling it with eQ.
>
>
>
> I cannot find the equivalent DOE2.1E keywords in the DOE22 manuals:
>
>
>
> DIRECT-COOL-MODE:            STRAINER-CYCLE - THERMO-CYCLE
>
> DC-MAX-OAT                          DC-MAX-CHILL-WTR-T
> DC-TWR-WTR-SETPT
>
> DIRECT-COOL-SCH                  DIRECT-COOL-KW
>
> *The best way to teach (learn) building energy modeling & simulation is
> with case studies.*
>
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>


-- 
Carol Gardner PE
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