Equest:Variation in pumping energy for Baseline system 8

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Dear friends,

I am working on two projects of core and shell where the baseline system is
system 8 i.e VAV with fan powered boxes.

There are two different building which are very similar in nature (not same)
and situated at same location.

However there are differences in the way the two models are behaving.

I have shown the breakdown of different end uses as a percentage of overall
baseline energy consumption

Project 1

Plug loads: 25.5 %

Interior Lighting: 16%

Cooling energy: 28.7%

Fan energy: 21%

Pumps: 6.3 %

Space heating: 0.1%

Domestic hot water + Exterior Lighting: 1.3 %

Project 2

Plug loads: 24 %

Interior lighting: 15%

Cooling energy: 18%

Fan energy: 25%

Pumps: 15 %

Space heating: 0.3%

Domestic hot water + Exterior Lighting: 1.3%

It can be seen that the energy consumed due to plug loads and interior
lighting as a percentage of baseline are all most equal in both the cases.

Can anyone suggest possible explanation or give hints as to why the pumping
energy as a percentage of baseline has more than doubled in the

second case given that the characteristics of chiller, condenser and pump
remain same ,given it is the baseline case.

One difference is that the first project uses two chillers as it has
conditioned area more than 1, 20,000 sq ft while the second project has only

one chiller ,its conditioned area being less than 1, 20,000

Vishnuraj Nair

Vishnuraj Nair's picture
Joined: 2011-10-02
Reputation: 0


I am guessing you let eQuest size the pumps. I will also bet you have the pumps set on STANDBY vs. DEMAND, Therefore, CHW pumps run all the time for the two chiller scenario, regardless if two chillers are needed.

See if that helps.

John R. Aulbach, PE, CEM

John Aulbach's picture
Joined: 2011-09-30
Reputation: 1

Your pumps are probably constant volume on the condenser (cooling tower)
loop. Doubling your chillers will double the amount of power required for
pushing the same volume of water to both chillers.


Shariq Ali EIT, LEED AP BD+C

Shariq_Ali at URSCorp.com's picture
Joined: 2011-10-01
Reputation: 200


If I get your question correct, then you are wondering why is your project 1 with 2 chillers showing less pump energy than Project 2 which has 1 chiller, the other parameters being the same with a slight difference in areas of both the project. Is this correct?

If I got your question correct, which I think I do, as I was able to duplicate the same behavior in a test project. I changed only the number of chillers and simulated in two locations.....( I know you might think I have got a lot of time on my hand..... but believe it or not this is a break from EnergyPro....anyway....)

Here are the results:

Project with 2 chillers: Less Pump Energy

Project with 1 chiller: More Pump Energy

However, I can offer only a partial answer. May be somebody reading this may have the complete answer.

The answer to your question is in the CW loop pump. The project with 2 chillers, shows that the CW loop pump runs in lower part load ranges than the project with 1 chiller (see the PS-H Report). A Pump sized for peak load conditions would use less energy when running at part load. Therefore, the project with 2 chillers uses less pump energy than the project with 1 chiller.

Hope this helps.

Best regards,

Gaurav Mehta

Gaurav Mehta2's picture
Joined: 2011-09-30
Reputation: 0