[Equest-users] Chiller curve ball

Pasha Korber-Gonzalez pasha.pkconsulting at gmail.com
Thu Mar 10 12:04:18 PST 2011


Well, maybe I am finally "aging" myself (I didn't think I was getting so
old-school so quickly.)

My past experience with scroll chillers versus screw chillers is that there
'used' to be more of an efficiency difference at the part load values
because of the limitation (or lack thereof) of unloading capability with
scrolls.   Screws were the answer that filled in the blanks between recips &
centrifugals originally, and then scrolls filled in at the small tonnages.

So there isn't as much of a difference in the ARI performance values as
maybe I had recalled or conceived in my head, but how do the points look for
the unloading in the scrolls vs. the screws, and for the 140 ton unit you
were looking at how many scrolls were on that unit to make up the tonnage
vs. one/two screws.   Do they have 70 ton scroll compressors now?

---which then brings us back to the discussion of how to properly represent
the curve data with multiple compressors----as long as the manufacturer
provides the correct performance data and info for the inputs, then it
should be that easy....

My thoughts were more towards the expected increase in energy use with the
difference in design performance of the compressors themselves.     However
the unloading is presented for the *equipment*  as a whole unit not for the
individual compressors, and the performance curves are for the whole unit
performance.

...I'm with you on this--just a bit off on my peformance spread with the two
compressors I guess.   Maybe I just picked up on a tanget point that was
"mute" to begin with!  :)

I welcome any thoughts back.

Pasha

On Thu, Mar 10, 2011 at 10:43 AM, Paul Diglio <paul.diglio at sbcglobal.net>wrote:

>  Pasha:
>
> I question you comment that scroll compressors are way less efficient than
> screw compressors.  Can you explain what constitutes way less?
>
> I looked up two air cooled Carrier chillers, both sized 140 tons.
>
> The screw machine (30XA) has a full load EER of 10.6.  The scroll (30RB)
> has a full load EER of 9.7.
>
> The screw machine has an IPLV EER of 14.3 and a COP of 4.2.  The scroll has
> a IPLV EER of 13.6 and a COP of 4.0.
>
> Yes, the screw is slightly more efficient, but I can't see a 10-15%
> increase in energy usage especially since the IPLV EERs are so close.
>
> Can you give an example of the EERs you have used for screws v. scrolls?
>
> Paul Diglio
>
>
>  ------------------------------
> *From:* Pasha Korber-Gonzalez <pasha.pkconsulting at gmail.com>
> *To:* Paul Diglio <paul.diglio at sbcglobal.net>
> *Cc:* "Sami, Vikram" <Vikram.Sami at perkinswill.com>; "
> equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>
> *Sent:* Thu, March 10, 2011 12:10:09 PM
> *Subject:* Re: [Equest-users] Chiller curve ball
>
> Aside from the curve input data--wouldn't you expect to see at least a
> noticeable increase in chiller energy as Scroll chillers are WAY LESS
> Efficient than Screw chillers anwyay?
>
> Vik--if you are staring with a screw chiller profile and then are adjusting
> to represent scroll compressor systems I think you would expect to see some
> increase in chiller energy for your scroll compressors---and you probably
> have multiple scroll compressors where typically the screw chiller profiles
> are representing a single compressor unloading performance versus multiple
> compressors unloading on one machine...
>
> I agree that maybe 30% increase is out of whack, but my experience tells me
> that a 10-15% increase in compressor energy would not be out of line for
> scroll compressors and chillers versus screw chiller performance
> capabilities.
>
> I'm sorry I can't offer any help with the input of the curve data, my
> experience with custom curves is less than ideal (or successful).  I have
> found that my attempts at using custom chiller curves yields too much
> questionability (& confusion on my end) and less than confident energy
> results with each manipulation of the eQuest equipment performance curves
> and variables.
>
> Pasha
>
> On Wed, Mar 9, 2011 at 6:19 PM, Paul Diglio <paul.diglio at sbcglobal.net>wrote:
>
>>  Vikram:
>>
>> When defining a screw compressor in eQuest, I see three curves required.
>>
>> 1. EIR f(CHWT & ECT) which is the energy input ratio as a function of the
>> evaporator leaving water temperature and the condenser water entering
>> temperature.  This is called lift.  eQuest calls this DT.
>>
>> 2.Cap f(CHWT & ECT) which is the capacity as a function of lift.
>>
>> 3.EIR f(PLR & DT) which is the energy input ratio as a function of the
>> part load ratio and the DT or chiller lift.
>>
>> Creating a  performance curve using the temperature difference between the
>> condenser water entering and leaving temperature is incorrect.  I think you
>> realize this because your chiller energy went up 30%.
>>
>> If you are modeling a constant chilled water supply temperature you can
>> plug that in as Independent 1 and use the condenser entering water
>> temperature as Independent 2.  If your chilled water temperature will be
>> reset based on terminal load or outside air temperature, then you would need
>> to get the chiller modeled by the manufacturer.
>>
>> Paul Diglio
>>
>>
>>  ------------------------------
>> *From:* "Sami, Vikram" <Vikram.Sami at perkinswill.com>
>> *To:* "equest-users at lists.onebuilding.org" <
>> equest-users at lists.onebuilding.org>
>> *Sent:* Wed, March 9, 2011 6:54:13 PM
>>
>> *Subject:* [Equest-users] Chiller curve ball
>>
>>  Ok – so I’m probably doing this all wrong.
>>
>>
>>
>> I am trying to model a York scroll chiller in EQUEST. The table below
>> illustrates the Part Load rating Data
>>
>>
>>
>> *Load % ** ***
>>
>> * **Capacity (Tons) ** *
>>
>> * **Cond. EWT (°F) ** *
>>
>> * **Cond. LWT (°F) ** *
>>
>> * **Compressor kW ** *
>>
>> *EER*
>>
>> *COP*
>>
>> *EIR*
>>
>> 100
>>
>> 135.8
>>
>> 85
>>
>> 95
>>
>> 104.1
>>
>> 15.6
>>
>> 4.6
>>
>> 0.217391
>>
>> 83.3
>>
>> 116.8
>>
>> 79.4
>>
>> 87.9
>>
>> 81
>>
>> 17.3
>>
>> 5.1
>>
>> 0.196078
>>
>> 66.7
>>
>> 96.9
>>
>> 73.5
>>
>> 80.4
>>
>> 60.1
>>
>> 19.3
>>
>> 5.7
>>
>> 0.175439
>>
>> 50
>>
>> 73.5
>>
>> 66.7
>>
>> 71.8
>>
>> 41.7
>>
>> 21.2
>>
>> 6.2
>>
>> 0.16129
>>
>> 33.3
>>
>> 48.2
>>
>> 65
>>
>> 68.4
>>
>> 26.6
>>
>> 21.7
>>
>> 6.4
>>
>> 0.15625
>>
>> 16.7
>>
>> 23.6
>>
>> 65
>>
>> 66.6
>>
>> 13.1
>>
>> 21.7
>>
>> 6.4
>>
>> 0.15625
>>
>>
>>
>> eQUEST doesn’t seem to have a scroll chiller option – I assume screw is
>> the closest thing to it.
>>
>>
>>
>> As far as I can tell – you need to define 3 performance curves:
>>
>> 1.       A curve that defines the EIR based on the condenser water temp
>>
>> "York - Temp vs EIR" = CURVE-FIT
>>
>>    TYPE             = BI-QUADRATIC-T
>>
>>    INPUT-TYPE       = DATA
>>
>>    INDEPENDENT-1    = ( 85, 79.4, 73.5, 66.7, 65, 65 )
>>
>>    INDEPENDENT-2    = ( 95, 87.9, 80.4, 71.8, 68.4, 66 )
>>
>>    DEPENDENT        = ( 0.217391, 0.196, 0.175, 0.161, 0.156, 0.156 )
>>
>>    ..
>>
>> 2.       A curve that defines the part load based on the condenser water
>> temp
>>
>> "York Temp vs Part Load" = CURVE-FIT
>>
>>    TYPE             = BI-QUADRATIC-T
>>
>>    INPUT-TYPE       = DATA
>>
>>    INDEPENDENT-1    = ( 85, 79.4, 73.5, 66.7, 65, 65 )
>>
>>    INDEPENDENT-2    = ( 95, 87.9, 80.4, 71.8, 68.4, 66 )
>>
>>    DEPENDENT        = ( 1, 0.833, 0.667, 0.5, 0.333, 0.167 )
>>
>>    ..
>>
>> 3.       A curve that  defines the EIR based on the part load.
>>
>> "York Part Load vs EIR" = CURVE-FIT
>>
>>    TYPE             = QUADRATIC
>>
>>    INPUT-TYPE       = DATA
>>
>>    INDEPENDENT      = ( 1, 0.833, 0.667, 0.5, 0.333, 0.167 )
>>
>>    DEPENDENT        = ( 0.217, 0.196, 0.175, 0.161, 0.156, 0.156 )
>>
>>    ..
>>
>>
>>
>>
>>
>> When I apply these curves to my chiller, my cooling energy goes up by 30%.
>> Seems like a lot.      Is this reasonable or am I doing something wrong with
>> my curve selection?
>>
>>
>>
>> Muchas Gracias in advance
>>
>> *We've moved!  Please note our new address. ***
>>
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>>
>> Sustainable Design Analyst
>>
>> 1315 Peachtree St. NE, Atlanta, GA 30309
>>
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>> www.perkinswill.com
>>
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