[Equest-users] Chiller curve ball
Carol Gardner
cmg750 at gmail.com
Wed Mar 9 20:12:56 PST 2011
Vikram,
One of the most common mistakes made when creating chiller curves is not
normalizing them around the ARI rating points. This is required for all
curves except for the new compressor curves.
This is the most helpful section of the documentation that I have found:
Volume 2: Dictionary <volume2dictionary.htm> > HVAC
Components<hvaccomponents.htm>>
CURVE-FIT <curvefit.htm> > INPUT-TYPE = DATA <inputtypedata.htm>
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
Try normalizing your dependent in the same way shown here and you should get
very different output.
Carol
*
*
On Wed, Mar 9, 2011 at 5:19 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
>
> *Perkins+Will.* Ideas + buildings that honor the broader goals of society
>
>
>
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--
Carol Gardner PE
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