ASHRAE Journal - August 2019 - 28

TECHNICAL FEATURE

discharge and vacuum pump water supply.

Replacing Original Compressors
Replacing the original compressors with modern
single-stage units, which most of the latest steam turbines employ, can bring the performance of these chillers up to current steam turbine chiller performance.
They allow the efficient compressor unloading from
full to part. Typically, they can be powered by the existing steam turbine motor with a fully accessible housing
and an operating assembly that is removable from the
compressor and scroll housing. Capacity control is also
accomplished through pre-rotation vanes and varying
turbine speeds to provide modulating control from minimum to maximum load and an improved turn-down
ratio. Other features of a modern compressor installation of this type are included, such as a force-fed lubrication system. In some cases, the original compressors
have been downsized to replicate the latest cooling loads
consistent with reduced interior cooling loads for lighting and equipment.

Electric Drivelines
Another efficient way to improve the operation of
steam turbine chillers is to add electric drives to operate
the system when electricity is economical, such as offpeak or in the shoulder seasons. The electric driveline is
placed near the existing steam turbine (Figure 5, Page 26).
Suction and discharge lines are inter-connected, and
all other controls are integrated, such as common oil
returns, hot gas bypass and level controls. New isolation valves and related safety and other controls are all
integrated with the existing system and control panel.
Typically, the electric driveline has a smaller capacity
than the steam drive, in which case the oversized condenser and evaporator surfaces further improve the system's performance, especially during light cooling loads.

Summary
Many existing high-pressure steam turbine chillers are
in operation in the US in cities like New York and large
campuses. They are generally robust units that perform
an important role in using steam efficiently, sometimes
as a by-product of electrical generation to stabilize the
overall efficiency of steam plants. These chillers can be
improved to meet the performance of modern steam
chillers with modern controls, single-stage compressors
and added electric drivelines, thereby using electricity at
off-peak rates and, most importantly, further reducing
our carbon footprint.

Acknowledgements
The author appreciates the assistance of Tristan
Schwartzman, P.E., principal and director of Energy
Services at Goldman Copeland Associates, as well as
Russell Thompson, vice president of Fresh Meadow
Chiller Services, who helped develop the steam turbine
technology.

References
1. Wikipedia. 2019. "New York City Steam System." https://
en.wikipedia.org/wiki/New_York_City_steam_system. Accessed June
2019.
2. EIA. 2019. "Monthly Energy Review." April 2019. "Power Plant
Operations Report." Tables 7.1, 7.2a, 7.3a, 7.6, and A6; and EIA, Form
EIA-923. https://www.eia.gov/totalenergy/data/monthly/pdf/flow/
electricity.pdf.
3. MacWhinney, R., O. Klagsbald. 2017. "Inventory of New York
City Greenhouse Gas Emissions in 2016." The City of New York,
New York City Mayor's Office of Sustainability. https://www1.nyc.
gov/assets/sustainability/downloads/pdf/publications/GHG%20
Inventory%20Report%20Emission%20Year%202016.pdf.
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https://en.wikipedia.org/wiki/New_York_City_steam_system https://en.wikipedia.org/wiki/New_York_City_steam_system https://www.eia.gov/totalenergy/data/monthly/pdf/flow/c https://www.eia.gov/totalenergy/data/monthly/pdf/flow/c https://www1.nyc.gov/assets/sustainability/downloads/pdf/publications/GHG%20Inventory%20Report%20Emission%20Year%202016.pdf http://www.shortridge.com/ https://www1.nyc.gov/assets/sustainability/downloads/pdf/publications/GHG%20Inventory%20Report%20Emission%20Year%202016.pdf https://www.ashrae.org/

ASHRAE Journal - August 2019

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