# [BLDG-SIM] Steam-Turbine Drive Centrigugal LiquidChillers

stvgates at pacbell.net stvgates at pacbell.net
Fri Oct 1 12:35:31 PDT 2004

```specific energie in office buildingsVarkie and Konstantine,

I am not sure this example goes far enough, for a couple of reasons.  Note, however, that I am not an expert on steam turbines, and that last time I looked at this issue was over 10 years ago.  Hopefully, other people can contribute better information:

1)  It is my understanding that the efficiency of a steam turbine degrades markedly when you throttle the steam to unload the turbine.  If so, then the part-load performance of a steam-turbine centrifugal will degrade significantly during most hours of operation, and custom temperature and PLR curves must be used to model this effect.  Default DOE-2 curves would not suffice.

2)  What pressure steam is available?  If 150 psig, then the maximum thermodynamic efficiency of the turbine is less than 10% (I don't recall the exact figure anymore), and the mechanical efficiency is only about half of that.  And at 50% part load, the efficiency is considerably less than at full load.

3)  On an annual basis, a 150 psig steam turbine would be less than 5% efficient.  Coupled with a chiller COP = 5, the annual COP of the combination would be less than 0.25.  In comparison, a single-stage absorption chiller has a COP of about 0.7, and a two-stage absorption chiller has a COP of about 1.2.  So, unless there is a use for the waste heat, this type of chiller will consume quite a bit of energy, and I don't see how it could be cost effective.

Before analyzing this problem any further using an energy simulation program, I suggest researching the performance of a steam turbine at the available steam pressure, and then doing some back-of-the-envelope calculations to determine whether the effort of a detailed analysis is worth it.  If the detailed analysis is justified, DOE-2 does have a steam turbine electric generator algorithm.  You might start with the performance curves contained in that algorithm.

----- Original Message -----
From: Konstantine Babets
To: BLDG-SIM at GARD.COM
Sent: Friday, October 01, 2004 8:51 AM
Subject: [BLDG-SIM] Steam-Turbine Drive Centrigugal LiquidChillers

Varkie,

From my experience in modeling similar plant combinations in NYC and using Con-Ed steam and electric rates you mentioned, for a typical office building you will see a benefit in using steam-turbine chillers (either option 2 and 3, depending on your electrical load factor and refrigeration full load hours). Of course, assuming that in all the cases you use reasonably efficient refrigeration machines.

Here is how you do it in Doe2.1:

INPUT PLANT..

ELEC-DRIVE=PLANT-EQUIPMENT

TYPE=HERM-CENT-CHLR

SIZE=24

INSTALLED-NUMBER=1

MAX-NUMBER-AVAIL=1 ..

STEAM-CHILLER = PLANT-EQUIPMENT

TYPE = ABSOR2-CHLR

SIZE = 24

MAX-NUMBER-AVAIL=1 ..

..

ABSOR2-CAP-FT=CCAPT3

ABSOR2-HIR-FT=EIRT3

ABSOR2-HIR-FPLR=EIRPLR3

..

.

.

.

Then in PLANT PARAMETRS you specify

ABSOR2-HIR = ?

Hope this helps.

Please let me know if you have further questions

Konstantin Babets
Jaros Baum and Bolles
(212) 530 9455
----- Original Message -----
From: Varkie Thomas
To: BLDG-SIM at GARD.COM
Sent: Friday, October 01, 2004 10:40 AM
Subject: [BLDG-SIM] Steam-Turbine Drive Centrigugal LiquidChillers

Steve:

I received other responses suggesting the same thing:

1. Use 2 stage absorption chiller with HIR of the turbine

2. Assign PLR curves of centrifugal chiller to corresponding curves of absorption machine.

I assume this will produce reasonably accurate steam consumption of the steam-turbine.  I need a sample DOE2 Plant "inp" or "bdl" statements showing how to do this.  The chillers in question are York model YST.  York will provide the performance data.  The location is NYC and the utility rates are ConEd Steam Service Classification 2 (lower rates in summer) and ConEd Electric Service Classification 9 Rate II - General Large Time of Use

http://q050-www5.coned.com/es/tariffs/ps.asp?URL=tariffs.htm&s=tariffs

Since there are several buildings in NYC that use a hybrid plant of steam-turbine and electric-motor drive chillers, I assume studies have already been done justifying this combination.  So far I have found the ASHRAE Sept 2003 article: Advances in Steam Cooling by Ian Spanswick

I would like to compare the following alternative options: (1) two 2000-ton electric-drive chillers, (2) two 2000-ton steam-drive chillers and (3) one 2000-ton electric-drive chiller and one 2000-ton steam-drive chiller sequenced to "start first" based on ConEd year-round steam and electric rates.  This would be for (A) a building that operates 24 hours per day such as a hospital, and (B) an office building that operates 7 AM - 6 PM, Mon-Fri.  I would also like to see a life cycle cost analysis of the alternative options.  Have such studies been done for buildings located in cities with district steam (NYC, Boston, Philadelphia, Minneapolis)?

The Trane TRACE700 program (which we also use in this office along with Carrier's HAP program) models steam-turbine chillers.  However the building in question has already been modeled in detail with DOE2.1E using electric chillers.  I prefer to use DOE2.1E directly (we also have eQUEST and EnergyPro in the office) for LEED certification and to show Code compliance.  The building description language (bdl) provides flexibility and it can be read like a specification for others to review.  Does this program have a future?  How many A-E design firms are using EnergyPlus on large commercial building projects?

Varkie Thomas

-----Original Message-----
From: postman at gard.com [mailto:postman at gard.com] On Behalf Of stvgates at pacbell.net
Sent: Thursday, September 30, 2004 5:13 PM
To: BLDG-SIM at GARD.COM
Subject: [BLDG-SIM] Steam-Turbine Drive Centrigugal Liquid Chillers

You would need to model it as an absorption chiller.  The chiller's heat input ratio and performance curves would need to reflect the combination of the steam turbine and the chiller compressor.

----- Original Message -----

From: Varkie Thomas

To: BLDG-SIM at GARD.COM

Sent: Thursday, September 30, 2004 12:58 PM

Subject: [BLDG-SIM] Steam-Turbine Drive Centrigugal Liquid Chillers

Has anyone modeled steam turbine drive centrifugal chillers with DOE2.1E?  Is it possible to add this equipment to DOE2, given the part load performance data?

Varkie Thomas

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