[Equest-users] Chiller Curves (oh boy!)
Paul Diglio
paul.diglio at sbcglobal.net
Wed Nov 3 11:39:27 PDT 2010
Michael:
Thank you very much for the offer. Next time I am auditing a site with a York,
I will be sure to contact you.
Paul Diglio
________________________________
From: "Michael.Hupel at jci.com" <Michael.Hupel at jci.com>
To: Carol Gardner <cmg750 at gmail.com>
Cc: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>;
equest-users-bounces at lists.onebuilding.org
Sent: Wed, November 3, 2010 2:07:37 PM
Subject: Re: [Equest-users] Chiller Curves (oh boy!)
As the OEM rep for YORK chillers I am more than willing to provide NPLV/IPLV and
other part loading efficiency data. Can even provide a comparison to other
chiller manufacturers or some of the options such as VSDs or hot gas by-pass
options.
Chillers are normally specified to supply cooling for the hottest day of the
year and yes add a factor for potential future load such as increased occupancy,
equipment etc.
Michael Hupel, B.Tech., LEED AP
Account Executive
Project & Business Development
Johnson Controls L. P.
3070 Mainway Drive
Burlington, ON L7N 3X1
(905) 335-3325 ext. 237
(905) 730-9642 cell
From: Carol Gardner <cmg750 at gmail.com>
To: "John T. Forester" <JohnTF at bvhis.com>
Cc: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>
Date: 11/03/2010 01:54 PM
Subject: Re: [Equest-users] Chiller Curves (oh boy!)
________________________________
I agree with you, John, but have a couple of other thoughts to add. The first is
I have not met a mechanical engineer that does not select a chiller that is
capable of supplying all loads. In fact, they generally oversize a bit to
accommodate possible future loads. The only piece of equipment I have ever seen
selected at over 100% was a VRV system and that is because they actually work
better at 120% loading. The second is that you can generally get a catalog from
a manufacturer to have on your shelf that has technical information like how the
chiller unloads based on temperatures and what the efficiency is at part load so
you can look up the chiller you need info for and not need to bother the ME or
the vendor. If you can't get/don't want a hard copy, most of this info is on
line, just look for technical specifications.
Best,
Carol
On Wed, Nov 3, 2010 at 9:48 AM, John T. Forester <JohnTF at bvhis.com> wrote:
Nick,
I think you’re on the right track. Below are some of my thoughts on your
conclusions. I hope the modeling community will set me straight if I’m wrong
here.
1. Getting multiple performance runs from vendors that show part-load
performance independent of the CW and CHW temps can often be challenging.
Adding the “maximum capability” task to that for each of the conditions requires
a pretty detailed understanding of the selection software. I’d say if you can
get PLR data for 3-4 different CHW temps while holding the CW temps constant at
85, 75, 65 (and sometimes lower) – you’re ahead of most modelers. Working with
the Mechanical Design Engineer and the vendor together has been successful for
me in the past.
2. Defining the chiller capabilities at the “maximum” may only come into
play if you expect your model to overload the chiller above the specified design
capacity (I’m thinking building additions or process loads). At this point, this
data (or knowing what the default eQuest curves do in that range) would be
useful. Depending on your project, the time spent on developing curves for PLR
>1.0 may not be justified.
3. If you don’t have “max” data and don’t want eQuest to assume
performance at a part-load ratio >1.0, you can set the DESIGN-PLR to 1.0.
4. Either way, you want your curves to be normalized at whatever
condition you specify (Design or Rated) and you want to enter those values on
the Basic Specifications tab.
John
John T. Forester, P.E., LEED AP, Mechanical Design Engineer I BVH Integrated
Services I617.658.9008 tel I617.244.3753 fax IOne Gateway Center Suite 506,
Newton MA 02458 I www.bvhis.com I Hartford ● New Haven ● Boston
size=2 width="100%" align=center tabindex=-1>
From: Nick Caton [mailto:ncaton at smithboucher.com]
Sent: Wednesday, November 03, 2010 12:06 PM
To: John T. Forester; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Chiller Curves (oh boy!)
John,
The design/max ratio is exactly what I’m discussing below when I say “DESIGN-PLR
ratio,” so we’re definitely in the same ballpark =).
I’d like to apply/paraphrase your advice to a few conditions to be sure I’m
getting it correctly:
- If we create all 3 custom curves, and normalize each to a point at
maximum (not design) capacity, then the design-to-max ratio (DESIGN-PLR) should
be set to 1.00.
- If we create only the part load efficiency curve (EIR-FPLR or
EIR-FPLR&dT), and wish to use the library defaults for EIR-FT and CAP-FT, then
we should normalize this curve’s data points to ARI conditions (as that’s what
the library curves are normalized to, per James’s email – I think I’ve read this
somewhere also), specify an ARI capacity, EIR and conditions on the basic
specifications tab, and enter a DESIGN-PLR of [ARI capacity/maximum capacity
(for the same conditions)].
- If we create all 3 custom curves, and try to normalize each to either
ARI or design conditions, then we should specify capacity, EIR, CHWT, CWT and
condenser GPM corresponding to either the ARI or design conditions of that
normalizing point. In that case, we also specify a DESIGN-PLR using either the
ARI or design capacity divided by the maximum capacity for the same conditions.
Profound (to me) Conclusion: In No instance should we Ever attempt creating
custom curves and NOT have at least one run from our manufacturer telling us
what the maximum (not design) capacity is for the normalizing point. This
conclusion would only apply to centrifugal chillers only.
Does this all sound right?
~Nick
James,
Yeah, if all the part load data you received held the same CHWT and CWT equal,
you might be able to make your part-load curve if it could have been a quadratic
EIR-FPLR curve (like a reciprocating chiller), but not a bi-quadratic
EIR-FPLR&dT (as with my centrifugal VSD chiller). You definitely could not
approach generating custom EIR-FT or CAP-FT curves without varying condenser and
chilled water temps. That exact issue happened to me the first few times I
tried to reign my chiller reps in =).
This time, I convinced my rep to give me multiple part load runs holding the
CHWT constant and varying the CWT incrementally. This let me build the
bi-quadratic EIR-FPLR&dT curve as I had at least three different dT’s
represented in my part load data points. I plotted the 3D curve in excel to
check my work and darned if the generated coefficients seem to be really
accurate =)! It’s currently looking like a bittersweet revelation however –
the library curve for a water-cooled centrifugal VSD chiller (see attached
visualization) seems a LOT more generous (more efficient) at low part loads than
the one I’ve generated which matches my rep’s data… I might share a visual of
my custom curve for comparison once I’m dead-sure it’s accurate – I’m trying to
clarify a few things with my rep right now.
~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
From: John T. Forester [mailto:JohnTF at BVHis.com]
Sent: Wednesday, November 03, 2010 10:29 AM
To: Nick Caton; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Chiller Curves (oh boy!)
Nick,
When defining a centrifugal chiller in eQuest, one of the items on the Basic
Specifications tab under the Design vs. Rated Conditions is a Design/Max Cap
ratio. By default, this is 92% for a water cooled unit. I believe this gets at
the discussion in the help pages that talks about maximum capacity versus design
capacity and how the chiller vendor will spec a piece of equipment. Typically,
vendors don’t often get asked (or provide) what the “Maximum” capacity of a
spec’d unit is. Therefore the performance data that they provide are at “design
conditions.”
If you change the chiller type to a reciprocating chiller, this “Design/Max Cap”
ratio is disabled and the default specified condition changes from “Design
Conditions” to “Rated Conditions.” This suggests that there is little “extra”
capacity when a selection is done for that type of chiller.
If you do get “maximum capacity” data and create curves from that data, you will
want to change the Design/Max Cap ratio to 1.0 so eQuest knows that there isn’t
any spare capacity at the chiller. Also if the data points you are using to
normalize your curves are different than the design conditions for your energy
model, you will want to change the “Chiller Specified at” value to “Rated
Conditions” and enter the rated conditions for CHW temp, CW temp and CW gpm/ton
to match your normalized curves.
Hope this helps,
John
John T. Forester, P.E., LEED AP, Mechanical Design Engineer I BVH Integrated
Services I617.658.9008 tel I617.244.3753 fax IOne Gateway Center Suite 506,
Newton MA 02458 I www.bvhis.com I Hartford ● New Haven ● Boston
<hr size=2 width="100%" align=center tabindex=-1>
From:
equest-users-bounces at lists.onebuilding.org[mailto:equest-users-bounces at lists.onebuilding.org]
On Behalf Of Nick Caton
Sent: Wednesday, November 03, 2010 11:03 AM
To: Carol Gardner; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Chiller Curves (oh boy!)
Thanks for the response Carol!
That 120% load case is what I’m getting at – let me try to explain a little
further:
In the DOE2 help files, the vocabulary for centrifugal chillers is “design
capacity” and “maximum capacity,” where “design” means the capacity at the rated
or designed conditions (at which you define / specify your chiller), and
“maximum” means the capacity the chiller is really capable of under the same
conditions if it runs balls-out (maximum power to the refrigerant drive).
The help file excerpt I copied below with the red line is pretty explicitly
telling us to normalize the part load values to the maximum capacity for
centrifugal chillers. I’ve highlighted a second line for clarity. The EDR
guidelines I linked below are saying you can instead normalize to the design
capacity for the EIR-PLR curve if that’s all your field measurements or
manufacturer rep can provide.
I’m asking – are both approaches right?
My first and second questions are kinda tied together… How would choosing to
normalize to either the maximum or design conditions affect how we should handle
the DESIGN-PLR ratio, if at all?
~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
From: Carol Gardner [mailto:cmg750 at gmail.com]
Sent: Tuesday, November 02, 2010 10:04 PM
To: Nick Caton
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Chiller Curves (oh boy!)
Let me take a crack at this. If by design capacity you mean the chiller running
at 100% load, you would create the curve(s) by normalizing around your ARI
design conditions i.e. the PLR curve would be 1.0 at this point, call it ARI Cap
and the other points would be 90% Cap/ARI Cap, 80% Cap/ARI Cap, etc. The same
would go for your temp curves. If, however, your chiller is operating at 120%,
or some such other level, I would normalize the curve around the ARI design
conditions of the chiller at 120%. I had to do this for a VRV hp that was
selected at the 120% design condition.
I find this from the DOE2 manual the most helpful:
Volume 2: Dictionary> HVAC Components> CURVE-FIT> INPUT-TYPE = DATA
INDEPENDENT-2
Used for all curveshaving two independent variables. A list of up to twenty
values of the second independent variable. The number of values should be the
same as for DEPENDENT.
Example 1: defining a curveby inputting a set of data points.
A packaged system (PZS) has cooling performance significantly different from
that used in the default model. The manufacturer lists the data shown in Table
46, for cooling capacity, at 2000 cfm design air flow rate, as a function of
outside dry-bulb temperature and entering wet-bulb temperature.
Table 46 Cooling capacity (kBtu/hr) vs. temperature
Outside
Dry-bulb Entering Wet-bulb
72F 67F 62F
85F 69 65 60
95F 68 63 (ARI) 57
105F 65 60 53
115F 62 55 49
In this example the independent variables are the entering wet-bulb temperature
and the outside dry-bulb temperature. Because there are two independent
variables and they have units of temperature, we input a curveof TYPE
BI-QUADRATIC-T using the given data points. The dependent variable is not the
cooling capacity listed in the table but rather the cooling capacity divided by
the cooling capacity at the ARI rating point (95 F outside dry-bulb and 67 F
entering wet-bulb). In other words, the capacities should be normalized to the
ARI rating point., as shown in Table 47
Table 47 Normalized capacity vs. temperature
Outside
Dry-bulb Entering Wet-bulb
72F 67F 62F
85F 1.095 1.032 0.952
95F 1.079 1.0 (ARI) 0.905
105F 1.032 0.952 0.841
115F 0.984 0.873 0.778
The CURVE-FITinput will look like the following:
CAP-CURVE-1 = CURVE-FIT
TYPE = BI-QUADRATIC-T
INPUT-TYPE = DATA
DEPENDENT = (1.000,1.079,0.905,1.032,0.952,0.841,
0.984,0.873,0.778,1.095,1.032,0.952) ..
IN-TEMP1 = ( 67, 72, 62, 72, 67, 62,
72, 67, 62, 72, 67, 62) ..
IN-TEMP2 = ( 95, 95, 95, 105, 105, 105,
115, 115, 115, 85 85, 85) ..
Example 2:Defining a curveby inputting coefficients
We want a furnace to have a constant efficiency as a function of part load. To
do this we must replace the default FURNACE-HIR-FPLR with a curvethat will give
a constant efficiency. The curveTYPE is QUADRATIC in the part load ratio (PLR).
PLR correction curvesare always multiplied by the unit capacity, not the load,
to obtain the energy (fuel or electricity) use. Thus the curvewe want is: 0.0 +
1.0*PLR + 0.0*PLR*PLR. The input will look like:
New-Furnace-HIR-fPLR = CURVE-FIT
TYPE = QUADRATIC
INPUT-TYPE = COEFFICIENTS
COEFFICIENTS = (0.0,1.0,0.0) ..
Then in the SYSTEM command we include:
FURNACE-HIR-FPLR = New-Furnace-HIR-fPLR
On Tue, Nov 2, 2010 at 3:21 PM, Nick Caton <ncaton at smithboucher.com> wrote:
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(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
olatheks 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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