Batch Processing

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eQuest Users,

I was wondering if anyone has information or know any learning resources
on "Batch Processing"

Thanks in advice

Andres

Andres G. Fergadiotti, PE, LEED AP

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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 CATON, E.I.T.

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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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 curves having 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 curve by 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-FIT input 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 curve by 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 curve that
will give a constant efficiency. The curve TYPE is QUADRATIC in the part
load ratio (PLR). PLR correction curves are always multiplied by the unit
capacity, not the load, to obtain the energy (fuel or electricity) use. Thus
the curve we 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

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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 CATON, E.I.T.

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Nick,

I am also working away at the unsolved mystery of creating a chiller curve. I have come to the conclusion that if you are only inputting an EIR-PLR curve, you must do this at ARI rated conditions because the other two curves, (CAP and EIR) are equest defaults at ARI conditions. I failed at making all three curves as my results ended up cutting the energy use to about an 1/8. I think in order to make the (CAP and EIR) curves you must have a full range of chiller supply temps and condenser supply temps. The information I was provided was with the same supply and condenser temps with the variables being load and kw/ton. I'm going to try to construct a new curve with conforming everything to ARI conditions and see what the results come back as.

James M. Newman, EIT, LEED AP

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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 T. Forester, P.E., LEED AP

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My gut is telling me that unless you are selecting your chiller to function
at 120%, or in effect making that the "design" condition, you should use the
100% capacity for your curve.

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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 CATON, E.I.T.

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Hey Carol =),

My guts are all over the place on this issue (well that sounds
morbid...), but it would appear by the existence of the DESIGN-PLR
variable (for centrifugal chillers only), eQuest/DOE2 wants to scale
these normalized curves to that 120% mark. There's a pretty good
example explaining why under the DOE2 help entry for "DESIGN-PLR."

NICK CATON, E.I.T.

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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 T. Forester, P.E., LEED AP

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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

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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

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Oh boy! - It seems that there is some confusion with my thoughts on Nick?s chiller curve posts from earlier.

My experience has been that catalog and online data for water chilling packages provides typical ARI Standard 550/590 data. This data is NOT sufficient to create custom curves in eQuest unless each hour?s operating points never stray off of these curves (not likely). This is why I suggest working with the Mechanical Engineer and the Vendor. As a design/support community, I don?t believe this approach is a ?bother? to either one of these team members. The approach of an integrated design process has its merits and the participation of the energy modeler is welcome throughout the design process. I also recognize the time it takes vendors to provide this data. Therefore, suggesting that, unless it is expected that the chiller will be operating above its design point, this added data is not necessary for accurate custom curves.

Also, I am not suggesting that equipment is selected without sufficient capacity to serve the calculated loads of a building/process. I was simply stating possible cases where performance information for a chiller between design and maximum capacities may be needed.

John T. Forester, P.E., LEED AP

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Yikes? looks like a slew of responses got out before I finished this one, but I have a lot to say =)? For context you might want to check which email I?m responding to first, everyone ;).

John, thanks very much for the encouragement. I think I can help further your thoughts:

1. Getting a manufacturer vendor to cooperate is indeed tricky for all parties, and I?m not convinced their selection software really affords them the capability to find maximum loading points for varying condenser/evaporater temps in a time-efficient fashion? time will tell but I?ve got a very smart rep right now promising to see what he can do.

2. I?d rest easier knowing it?s perfectly fine to normalize all three curves to the design conditions and have a PLR of 1.0 equal the design conditions? except for the DOE2 help entries explicitly telling us that for centrifugal chillers, ?full load? means ?maximum? (see the highlighted copy-paste job way down below and the entry for EIR-FPLR as well).

That said, your call to better understand the default curves sounds a lot like a request, so perhaps I can scratch your back in return ;). Here are the three curves eQuest pulls from its library when you specify a water cooled centrifugal chiller? visualized!

Note that each curve is indeed normalized to (Z=1.0 at) ARI conditions. I?ve followed each with my (novice) observations/commentary.

The EIR-FPLR&dT curve seems, well, kinda wacky to me! I?ve conferred with a few other mechanical designers, and we seem to agree that an efficiency ?sweet spot? for a centrifugal variable speed chiller should lie somewhere between zero and full loading conditions ? this curve?s shape seems to demonstrate continually improving efficiencies as you approach zero loading. Truthfully, there?s a very slight apex that?s hard to see (you can tell by the curving bands) just off the charted values shown between the 10% and 20% loading marks, but what chiller has an optimum efficiency at 15% loading? I?d of this as a ?normal? shape if the z-axis were on some scale of straight power (kW)? I?d expect that to continually drop off with the PLR in this fashion, but that z-axis is normalized EIR (kW/ton conceptually, if not in magnitude)? shouldn?t the default curve have a ?sweet-spot? efficiency somewhere in the vicinity of 40-60% loading?

This EIR-FT curve is again normalized (1.0) at ARI conditions, and tells us that the chiller will be pretty much linearly more efficient as you increase the CHWT target temperature, and will exponentially increase in efficiency as the condenser water temperature drops. Raising either has less of an inverse effect. Nothing seems odd to me.

This curve is also normalized (1.0) at ARI conditions, and is telling us the chiller loses capacity when the condenser water either rises or falls from ARI conditions (20-30% drop from ARI, when CWT is at 100F or 50F, for example). I?m too new at this to know whether that makes total sense, but my initial guess would be that colder condenser water would always be help improve capacity? I?d infer from this curve that centrifugal chillers are designed and optimized around a specific condenser water temperature, and that hotter or colder condenser water temperatures, for the same CHWT, hurts your equipment?s potential capacity. I suppose it might well be a function of the refrigerant?s thermodynamic properties? The CHWT selected has a linear, but a relative to the CWT minor effect on the capacity of the chiller.

3. You?ve nailed my current approach on the head! I?m just concerned that going against the explicit instructions in the DOE2 help entries (mentioned above) may have some significant impact on what I?m modeling?

4. Fully agreeing. And kudos for condensing paragraphs of fretting into a single line answer =).

Thanks again so much for everyone?s input so far. I?d be curious to hear any other thoughts or second-opinions we as a group may have regarding:

A. Why does the default part load curve above seems such an odd shape (at least to my eyes) for a centrifugal VSD chiller? Are my chiller fundamentals off?

B. To what end/purpose do the DOE2 help docs and the EDR guidelines emphasis normalizing the EIR-FPLR curve to maximum vs. design capacities at the rated conditions, when you can normalize and specify to ARI conditions and set DESIGN-PLR=1.0 as John and I are discussing? I mean, I understand that you could get a ?comprehensive? set of curves allowing you to apply the same chiller to other projects where you have a higher design capacity (or expect higher capacities will be required), but is there any inherent loss of accuracy if you build everything around data points encompassing all extremes present in the simulated model?

NICK CATON, E.I.T.

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I?m also on board that engaging the vendor reps and mechanical engineers responsible for specification ?shouldn?t? be a bother, and that we energy modelers ?should? be welcomed as part of the design process. That said?

My experience includes mechanical designers and vendor reps who are? perturbed? when you start asking questions about variables they aren?t used to thinking around. Some will get unnecessarily defensive, and I think I have an idea why.

The most important quality in a great energy modeler is not the ability to use his/her tools and crunch the numbers (that?s more like a pre-req), but being an effective communicator/teacher of inputs and results to a wide range of audiences.

It?s deceptively easy to get bogged down when working with others for something like custom performance curves, and inquiries / suggestions of the best intentions can come across as challenging another?s thought process. To put it nicely, some will take that very personally, so it?s a delicate line to walk when having these conversations. Those of us who aren?t as advanced in experience (old) in this industry have the extra hurdle of not seeming pretentious/ignorant while trying to do our jobs!

Thanks again to everyone contributing? I?m learning a heck of a lot at a fast pace with you all!

NICK CATON, E.I.T.

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Nick,

Thanks for adding your thoughts. I believe you and I are on the same page here.

On item 2 below, the help files state that the EIR-FPLR&dT curve must be normalized to ?full-load? or ?maximum capacity? and not the design capacity. Intuitively (maybe), if you normalize these curves to the design capacity and then set the DESIGN-PLR to 1.0, it seems that this is locking in your design values as maximum values. Physically, the machine may have more capacity, but your energy model will be limited to these hard-coded design values.

One way to check the model curve accuracy is to use hourly report blocks/reports to track the CHW supply temp, entering CW temp, chiller PLR, chiller EIR. Use your normalized curves to calculate the EIR for each hour with the CHW and CW temps and PLR. Then compare your calculated EIR with the EIR from eQuest. I believe you can also track the chiller capacity to see if it is holding the max capacity based on the DESIGN-PLR value and chiller capacity value you enter.

John T. Forester, P.E., LEED AP

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Thanks to some extra guidance from John Forester and David Eldrige, I can tie up some loose ends Ieft on the list this week.

Analyzing the isolated default curves plotted out, I failed to keep one thing in perspective: while each demonstrates how the variables (CHWT, CWT, dT, PLR) independently affect a chiller?s performance, the three curves ultimately work in concert to produce a net effect each hour.

The EIR-FPLR&dT curve appeared wonky to me because I didn?t remember the normalized EIR is simulataneously affected by the CHWT and CWT values, independent of the dT.

I expect many eyes are glazing over =). This is really hard to convey in text alone, so I brought along some show-and-tell pictures for the group:

The following is the two default EIR curves: EIR-f(t1, t2) and EIR-f(PLR, dT) I showed earlier, multiplied together for a single CHWT and various CWT?s.

In a nutshell, this illustrates how efficiency changes independent of the effects of the water temperatures on the chiller?s hourly capacity.

The combined effects of the 2 curves moves their ?sweet spots? into the range I was expecting:

?And the following is the same thing, but adding the effects of the CAP-FT curve to the mix: all 3 default curves applied together in concert.

This is what you?re modeling for a centrifugal VSD chiller every time you rely on the library default curves.

Condenser water temps straying far from the rated conditions (85) get an efficiency penalty between these curves, just as the isolated CAP-FT curve indicated.

These curves pass my personal gut check: they look very much like some chiller curves I?m used to seeing.

Of note: This visual can serve as a great reference for judging whether developing custom curves is a worthwhile venture for a given chiller.

In conclusion, the default curves for centrifugal VSD chillers aren?t that crazy after all, but be cautioned they can definitely be very different from your actually equipment.

I tried briefly to figure out who the author(s) of that EDR guideline were 5 years ago, but came up empty handed?

Does anyone else agree or disagree with me & John regarding whether it should be fundamentally sound to define curves from design capacities on downward (setting DESIGN-PLR=1.0), as long as those capacities aren?t exceeded in the model at-hand? I?d feel comfier if it felt like a consensus =).

Thanks everyone,

NICK CATON, E.I.T.

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