ASHRAE Journal - August 2019 - 22

TECHNICAL FEATURE

only upgrades to their controls,
drives, and related moving parts
as well as normal maintenance.
Their industrial-grade evaporator, condenser and surface
condenser shells often require
only replacement of their tubes,
while the shells remain in excellent condition. From an overall
energy perspective, maintaining existing equipment-and
improving its efficiency close to
the performance of new equipment-retains the embedded
energy and reduces energy
needed to build new units.

Energy and CO2 Savings

TABLE 1 Steam turbine upgrades summary.
ENERGY
BUILDING
(LOAD TONS)

A
(3,200)
B
(4,600)
C*
(3,000)
D*
(2,250)
E
(1,475)
F
(3,000)
G
(3,200)
H*
(1,200)

SCOPE

FLOOR AREA
(FT 2)

ACTUAL AND ESTIMATED SAVINGS
OVERALL CO 2 REDUCTION
(T CO 2E)
(MMBTU)

STEAM USE
(MLBS)

ELECTRIC
(KWH)

928,000

8,411

0

10,043

377,927

2,690,000

1,180

465,198

2,996

53,144

1,270,000

44,177

0

52,747

1,985,084

1,321,000

3,718

232,759

5,233

167,128

866,000

1,872

410,808

2,235

84,118

Two Turbine/Chiller Controls

1,899,000

12,420

0

14,829

558,090

Two Turbine/Chiller Controls

1,272,119

5,237

0

6,253

235,323

Turbine/Chiller Controls
Side-Mounted Electric Driveline

535,720

16,029

-319,345

18,049

720,177

COST EFFECTIVENESS
INSTALL
INCENTIVE
COST
AWARDED

COST
SAVINGS

Turbine/Chiller Controls
Single-Stage Compressor
Turbine/Chiller Controls
Pump Control Upgrades
Turbine/Chiller Controls
Single-Stage Compressor
Turbine/Chiller Controls
Pump Control Upgrades
Turbine/Chiller
Pump Control Upgrades

BUILDING

PROJECT

SIMPLE PAYBACK (YEARS)

Table 1 shows some steam turTurbine/Chiller Controls
A
$430,200
$150,000
$152,000
1.8
bine retrofit energy savings and
Single-Stage Compressor
Turbine/Chiller Controls
CO2 reductions in several existB
$900,000
$425,000
$109,000
4.4
Pump Control Upgrades
ing installations. Some are based
Turbine/Chiller Controls
C
$164,160
$815,000
0.2
Single-Stage Compressor $350,200
on annual savings according to
Turbine/Chiller Controls
bills, while others are estimates
D
$897,200
$419,500
$111,000
4.3
Pump Control Upgrades
of declines in steam consumpTurbine/Chiller Controls
E
$765,100
$382,500
$110,600
3.5
Pump Control Upgrades
tion. Understandably, many of
F
Two Turbine/Chiller Controls $1,312,600
$656,300
$273,000
2.4
these plants have not had sigG
Two Turbine/Chiller Controls $845,600
$591,900
$78,000
3.3
nificant upgrades over the years,
Turbine/Chiller Controls $651,300
H Side-Mounted
$261,000
$200,000
2
only replacement of worn-out
Electric Driveline
Conversion Factors: 2.1625 MMBtu/metric ton of delivered steam, 95.0535 kgCO2e/metric ton, 981 Kbtu/Mlbs, 260.0656 kg CO2e/
or failed components. In some
MWH3; Typical Utility Costs: $0.18/kWh, $20/Mlb steam
cases, tenants installed separate
*Actual savings per utility and interval analysis
plants, and, along with new
code requirements on tenant retrofits, cooling loads
FIGURE 1 Typical steam turbine flow diagram.
were reduced still further, making optimization control
panels more beneficial. Costs in some cases have been
significantly incentivized by the local utility.

Steam Turbine Chiller Operation
For commercial applications, steam turbine-driven
chillers use high pressure steam to drive turbines, which
in turn power centrifugal compressor chillers. There are
two typical types: condensing and non-condensing systems. This article will address only condensing turbine
steam chillers, which extract most of the kinetic energy
from the steam (Figure 1). Residual condensate is typically returned to most steam generation systems; however, in the case of Manhattan's district steam system,
22

ASHRAE JOURNAL

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A U G U S T 2 0 19

there is no formal condensate pipe return system. Good
practice is to recapture the waste heat remaining in the
condensate at the building for domestic water heating,
etc., and to use the resultant cooled condensate as grey
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ASHRAE Journal - August 2019

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