sequencing chillers using Equipment Controls

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Hi All,

I'm using eQuest version 3.65 and am having trouble with sequencing my
chillers - I've combed through the archives but haven't found anything that
has helped.

I have 3 chillers in my model, a water-side economizing chiller and two
air-cooled scroll chillers. I would like to control them such that my WS
economizing chiller runs up to a certain capacity only (175 Tons = 2.1
MBtu/h). Without any controls, eQuest is ignoring the capacity I have
entered, and is meeting my building's entire cooling load. Beyond the 2.1
MBtu/h, I would like my 2 other chillers to run to meet the remaining load.

I've created an Equipment Control (and selected it on my CHW loop) that has
my WS Econo Chiller as sequence no. 1 with a max load of 2.1 (I believe
units of MBtu/h). Then I have my other chillers as sequence 2/3 and left
max loads as "999". I've played around with the "Max Load" values and also
the "Loads Through" value and nothing I do changes the outcome. Is anyone
able to help me figure out why eQuest is not capping my WS Econo Chiller at
the 2.1 MBtu/h and why it continues to meet the entire cooling load (with a
peak approaching 4 MBtu/h)?

Thank you in advance.

Chris Hadlock, M.A.Sc ., P.Eng, LEED AP BD+C
Founder & Senior Energy Consultant

201 Candlewood Cr
Waterloo, ON N2L5T3
tel: (519) 804-1223
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Chris Hadlock's picture
Joined: 2012-01-23
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The issue is not with Equipment Controls but with the Water Side economizer ?chiller?.

I thought the water side economizer was an all or nothing element, so your mention of Equipment Controls gave me hope that someone had found a way around this limitation. But I?m afraid it wouldn?t appear that?s true.

Per the Help files ? Volume 2: Dictionary > HVAC Components > CHILLER? and ?Chiller Water-Economizer? :
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.

So, Sad day. Super creative ? which is awesome and exciting. But can?t do it. bummer

Mechanical Engineer, Energy Analyst

Henderson Engineers
Tel (913) 742-5530
daric.adair at

Licensed in KS

Daric Adair's picture
Joined: 2017-10-21
Reputation: 0

Hey guys,

I?ve run into this exact scenario before ? answer was to develop the calibrated eQuest model to quantify savings for all other ECM?s, then export the hourly loop loads, temperatures, and weather data (needed to model OA-resets & tower interactions), into an 8760 spreadsheet model to wrap up the interactions with the WSE chiller.

Once built to a sufficient level of detail (At minimum: capture any TOU rate structures in play. Ideally if time allows, I would typically want to regress some custom performance curves, at least as detailed as what would be done in eQuest/doe2 if not more so? those regressions are relatively easy through Excel?s built in statistical analysis toolset), you can iteratively determine from your suggested starting point the logic resulting in a sweet spot for an optimal sequence of operations to minimize energy and/or dollars spent.

Sorry, that was a terrible sentence grammatically. Hope it was interpretable!


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Nick Caton, P.E., BEMP
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Schneider Electric

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