I know there was a recent discussion about chiller curves, but I can't

seem to access www.gard.com right now, so I thought would send out this

email since I don't remember it being discussed.

I have two different curves for a standard water-cooled 200-ton screw

chiller:

1) EIR based on PLR, but with AHRI condenser relief

2) EIR based on PLR, with NO condenser relief, and varying return

chilled water temperature (from design at 100% to only about a 2 degree

delta between supply and return at the 20% load range)

Which curves should I modify with custom curves? I am so confused.

The f(PLR) curve says it should be the EIR vs PLR with no condenser

water reset. That one's the easy one. I already set that one up, and

it's about $1000 cheaper a year than the default curve, so I know it's

at least in the right range.

But the f(t evap leaving, t cond entering) says it's a quadratic curve,

but since there are two variables, shouldn't it be bi-quadratic like the

Cooling Capacity curve as a function of entering CW and leaving CHW?

When you all get chiller PLR curves with condenser relief, which

curve(s) do you modify and to what extent?

Thanks!

James Hansen, PE, LEED AP

Jim:

What do you mean by condenser relief?

Paul Diglio

Sorry, meant that my condenser water entering temperature to the chiller follows the AHRI guidelines for condenser water reset (83 degrees at full load, going down to 65 degrees at 50% in a linear fashion, and then staying at 65 degrees down to 10%).

Sounds like the same 2 curve names I received from Trane when I asked for them recently ? I did a Google search and found something James Hirsch Associates prepared for California at:

http://www.energy.ca.gov/title24/2005standards/archive/documents/measures/20/20_2002-03_CONDENSER.PDF

The text that made me assume that ?condenser relief? was synonymous with ?condenser reset? was contained on the first page within the ?Description? section.

Jeremy R. Poling, PE, LEED AP+BDC

Jim:

To avoid confusion, I look up the default curves and use the same type of curve.

For example, the EIR f(CHWT & ECT) default curve is a bi-quadratic in T curve as

you indicated below.

For the PLR curves, the default is a bi-quadratic in ratio and DT. eQuest

defines this curve as an EIR f(PLR & DT). Someone sent a cut & paste from the

DOE manual which stated this should be a quadratic curve, which I do not agree

with. Was that a DOE typo or can someone else explain why?

So normalize the PLR to AHRI standards. The DT is the difference between the

chilled water leaving temperature and the condenser water entering temperature.

Paul Diglio

Jim:

To avoid confusion, I look up the default curves and use the same type of curve.

For example, the EIR f(CHWT & ECT) default curve is a bi-quadratic in T curve as

you indicated below.

For the PLR curves, the default is a bi-quadratic in ratio and DT. eQuest

defines this curve as an EIR f(PLR & DT). Someone sent a cut & paste from the

DOE manual which stated this should be a quadratic curve, which I do not agree

with. Was that a DOE typo or can someone else explain why?

So normalize the PLR to AHRI standards. The DT is the difference between the

chilled water leaving temperature and the condenser water entering temperature.

Paul Diglio