[Equest-users] Chiller Curves (oh boy!)

[Nick Caton]

Hi everyone!

 

I think I have finally wrapped my mind completely around custom chiller
performance curves for a centrifugal VSD chiller.  I've got a few
specific questions now that I'm on the other side of the fence:

 

1.       Is it necessary for the data points of a part load efficiency
curve (EIR-FPLR&dT in my case) to originate from data with a 1.0 (100%)
PLR ratio corresponding to a maximum vs. a design load capacity?  From
what I gather in the EDR reference
<http://www.energydesignresources.com/Portals/0/documents/DesignGuidelin
es/EDR_DesignGuidelines_%20HVAC_Simulation.pdf>  (re: "Method 2" on PDF
page 32/65), this curve can be generated using part-load readings
assuming a design capacity at the 100% loading mark... but the DOE2 help
entry for "EIR-FPLR" seems to suggest otherwise (copied below - see
highlighted line).

2.       If the above part load efficiency curve is created based on
data where the 100% loading point corresponds to the maximum (not
design) capacity, should "DESIGN-PLR" (the ratio of design to maximum
capacity) be set to 1.00 and the capacity of the chiller be specified at
its maximum (not design) for the design/rated conditions?  As I write
this question it sounds like I'm chasing my tail - someone straighten me
out =)!

3.       When you veterans finish a project with sets of custom
performance curves, do you have any suggestions for a naming scheme for
future reference/re-use?  I'm currently thinking to keep the curves
grouped in an .inp snippet I for importing along with an equipment
cutsheet... but I'm certain I'll forget the all the details as quickly
as humanly possible when this project is behind me...

 

 ~Nick

 

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

EIR-FPLR

Takes the U-name of a curve that adjusts the electric input ratio as a
function of

* The part load ratio (PLR) -  The PLR is defined as the ratio of the
hourly load to the hourly capacity;  Load / Caphour

* The evaporator/condenser dT -  The temperature differential between
the condenser and leaving chilled-water. The  meaning of the condenser
temperature varies according to condenser type. 

For most chillers, the dT has a relatively small effect on part-load
performance. However, for variable-speed centrifugal chillers, the
effect of dT is as important as the PLR.  This is because the pressure
rise across the impeller is proportional to the square of the impeller's
speed. Unless some form on condenser temperature relief is employed to
reduce the temperature (and pressure) differential across the chiller at
part load, the performance of a variable-speed chiller may not be
significantly different than that of a constant-speed chiller.

To model power consumption as a function of the PLR only, use a
CURVE-FIT of TYPE = QUADRATIC or CUBIC.  To model as a function of both
PLR and dT, use a BI-QUADRATIC-RATIO&DT curve. The curve must be
normalized to 1.0 at full load and the rated temperature differential. 

Note that, for centrifugal chillers, 'full load' is defined as the
'maximum capacity', not the 'design capacity'. Refer to the DESIGN-PLR
keyword for more information.

 

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