[Equest-users] Chiller curve ball

[Paul Diglio]

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
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