Problems with pumping energy and delta T

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I am having two issues with variable speed pumping and delta T of
heating and cooling loops. The problem is occurring in multiple models.
Anybody have any suggestions?

Two issues:

1) We are modeling a chilled water system with a centrifugal
chiller. We specify the delta-T at the loop and zone. When we review
the hourly reports, the delta-T is never maintained at the specified
design conditions regardless of chiller load. The pumps continuously
run at lower speeds (~40% of design capacity) which drives up the delta
T at high loads. We've come across this problem in both heating and
cooling loops, and in all models that we've looked at. Is this a known
issue? Do you have any suggestions to solve this problem?

2) A related issue concerns the energy balance in heating and cooling
loops. Looking at an hourly report of our primary heating or cooling
loop, if we calculate the product of 500* primary supply flow (variable
3) *deltaT (loop return temperature, variable 22 - loop supply
temperature, variable 21) we do not get the primary loop load (variable
5). We are concerned that all energy is not being accounted for. How
does eQuest perform the calculations for loop load and gpm? Are there
known issues with regard to the energy balance of heating and cooling



Justin Stenkamp's picture
Joined: 2011-09-30
Reputation: 0