[Equest-users] Chiller curve ball

[Paul Diglio]

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. 
>Vikram Sami, LEED AP BD+C
>Sustainable Design Analyst
>1315 Peachtree St. NE, Atlanta, GA 30309
>t: 404-443-7462    f: 404.892.5823       e: vikram.sami at perkinswill.com   
>www.perkinswill.com
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