[BLDG-SIM] DOE2.1E Chiller performance

Jon McHugh mchugh at h-m-g.com
Thu May 15 13:52:39 PDT 2003


Varkie,

The percentage higher energy consumption at different leaving water temperatures is more useful than, " was higher, but not significantly higher (relative to potential savings in the pump operating, heat transfer equipment and piping costs)".  How much higher was the energy consumption in percentage?

When you are talking about "heat transfer equipment" above are you talking about coils or something else?  If you are talking about coils - the next sentence says you haven't investigated this.

How much did the coil loads change (%) from reducing the leaving water temperature?
How much did chiller efficiency change (%) from reducing the leaving water temperature?
How much did pumping energy change (%) from reducing leaving water temperature?
Was piping diameter resized?

Thanks,

Jon McHugh

-----Original Message-----
From: Varkie Thomas [mailto:Varkie.Thomas at som.com]
Sent: Thursday, May 15, 2003 12:58 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] DOE2.1E Chiller performance


This is in response to comments and questions that I received.

This was a preliminary attempt using DOE2.1E to find out large tonnage chiller energy usage at decreasing LWTs and a fixed EWT to reduce the CHW-flow.  I may not have used the DOE2.1E correctly because results showed the chiller LWT was always the default value of 44F.  The test building was a single zone per floor, 70% single glass, with multiple floors to produce over 6000 tons.  The DOE2 program was run with SOM office building template defaults.  The TRACE program was run twice, with all TRACE defaults for an office building, VAV system and water-cooled centrifugal chillers, first with CHW temp range of 38 to 56 and next with 42 to 56.  In the first case the program gave warning messages for LWT < 40 and CHW-DT > 15.  

The energy usage of a chiller operating from 38 to 56 was higher, but not significantly higher (relative to potential savings in the pump operating, heat transfer equipment and piping costs) than 42 to 56.  This might be because of limitations in the energy program algorithms, and actual physical tests with chillers might produce different results. 	Cooling coil sizes in terms of fins, rows, etc are going to be affected.  I did not check this out using cooling coil selection programs.  I did not check or compare the results of the air-side system equipment performance.

What would be the results from other energy programs such EnergyPlus, HAP and eQUEST?  I would be particularly interested in the results from HAP.  We do not have this program in this office.  I would also be interested in comments from Trane regarding the results from TRACE. Was the program used incorrectly?

Varkie
-------------------------------------------

-----Original Message-----
From: Varkie Thomas 
Sent: Thursday, May 15, 2003 8:48 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] DOE2.1E Chiller performance


To those who responded to this inquiry:

We tested the two conditions with TRACE-700.  There is little difference in the energy consumed by the chillers for CHW temp range of 38F to 56F and 44F to 56F particularly in the large tonnage range.  This is also indicated in chiller performance data catalogs.  There is a big difference in pumping and piping costs.

Varkie Thomas
---------------------------------------

We are trying to compare the performance of a 2000 ton chiller operating at (1) 42 F LWT and (2) 38 F LWT.  The chiller EWT is 56 in both cases.  The tower temp range is 85 F to 100 F.  We want to know how the chiller COP varies under these conditions.  

The hourly output for the design day from DOE2.1E shows chiller LWT of 44 F (DOE2 default) no matter what the input.  Here is the input and output for the option with 38 F Chiller LWT.  Can the Chiller LWT be changed from the default value of 44 F ?  How do I check that the CHW EWT & LWT temps are being maintained? Is the input below correct to model the conditions described?

----------------------------------------------------------------

PLANT-PARAMETERS

CHILL-WTR-T = 37                     $ Def = 44. LWT at bottom of Thrott Range $
CHILL-WTR-THROTT = 2.0         $ Def = 2.5. Thrott Range = 37 to 39.  LWT = 38 $

TWR-SETPT-T = 85                      
TWR-DESIGN-RANGE = 15.0        $ Def = 10. Tower temp range :85 to 100 $ 

CCIRC-DESIGN-T-DROP = 18       $ Def = 10. Chiller EWT = 56 $

----------------------------------------------------------------


MMDDHH    OPEN-CEN       OPEN-CEN    OPEN-CEN   OPEN-CEN   OPEN-CEN   OPEN-CEN
	T-CHLR         T-CHLR      T-CHLR     T-CHLR     T-CHLR     T-CHLR  
	LOAD           ELECTRIC    OPER PT    FRAC HR    ENTERING   LEAVING 
	USE         LD RATIO   OPERATED   COND TEM   COLD TEM
	BTU/HR         KW          FRAC.OR    FRAC.OR    F          F  	 
	MULT.      MULT.                    	 
	----( 1)       ----( 3)    ----(10)   ----(11)   ----(12)   ----(13)
	7 1 1             0.         0.000      0.000      0.000        0.0     	0.0
	7 1 2             0.         0.000      0.000      0.000        0.0     	0.0
	7 1 3             0.         0.000      0.000      0.000        0.0     	0.0
	7 1 4             0.         0.000      0.000      0.000        0.0     	0.0
	7 1 5             0.         0.000      0.000      0.000        0.0     	0.0
	7 1 6       8887730.       528.301      0.328      1.000       84.6     	44.0
	7 1 7      20704076.      1019.228      0.760      1.000       83.7     	44.0
	7 1 8      25529894.      1301.530      0.940      1.000       84.3     	44.0
	7 1 9      25563408.      1312.150      0.944      1.000       84.7     	44.0
	7 110      22676038.      1142.870      0.838      1.000       84.9     	44.0
	7 111      23148816.      1167.610      0.855      1.000       84.7     	44.0
	7 112      22012680.      1103.797      0.813      1.000       84.7     	44.0
	7 113      22536236.      1132.213      0.832      1.000       84.7     	44.0
	7 114      22738694.      1144.069      0.840      1.000       84.7     	44.0
	7 115      22827700.      1149.287      0.843      1.000       84.7     	44.0
	7 116      22768860.      1146.011      0.841      1.000       84.7     	44.0
	7 117      21899154.      1097.228      0.809      1.000       84.7     	44.0
	7 118      20232738.      1007.025      0.747      1.000       84.7     	44.0
	7 119             0.         0.000      0.000      0.000        0.0     	0.0
	7 120             0.         0.000      0.000      0.000        0.0     	0.0
	7 121             0.         0.000      0.000      0.000        0.0     	0.0
	7 122             0.         0.000      0.000      0.000        0.0     	0.0
	7 123             0.         0.000      0.000      0.000        0.0     	0.0
	7 124             0.         0.000      0.000      0.000        0.0     	0.0

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