ASHRAE Journal - December 2019 - 41

SOLVING PROBLEMS

Redundancy improves resilience as long as systems are
designed to appropriately react in a loss of main power
event, he said.
Another basic resilience question is how long an
event duration should the CHP system or microgrid be
designed to serve, said Sweetser, adding requirements
can range from hours to days to weeks depending on the
facility's critical needs.
"This clearly impacts the site or microgrid design,
as hurricanes can blot out the sun for many days and
cause windfarms to shut down for extended periods
of time due to high wind speeds. We are now learning
that California electric utilities are systematically shutting down large parts of their electric grid for days to
reduce the risk of wild ﬁres during the dry windy season. Since today's battery storage systems are not cost
effective to provide power for days, other technologies
such as CHP can ﬁll in to efﬁciently provide power," he
said.
Keeping the grid stable is becoming more complex and
time-sensitive as variable generation resources play a
larger role in meeting the usual ﬂuctuations in demand,
Sweetser said.
"As intermittent energy sources like wind and solar
become more prevalent, the need for grid services
becomes even greater," he said.
In the past, grid operator service requests usually
required a 10-to-30 minutes response. Today, a ﬁveminute response is required sometimes. "In emerging
frequency regulation markets, a response is now needed
in mere seconds," he said.
The additional revenue from providing the grid with
ancillary services such as voltage or frequency support could increase a CHP system's beneﬁts by making
it a revenue generator for the manufacturing facility,
according to Sweetser.
"Small and medium-sized industrial facilities with
signiﬁcant thermal and electric loads are often good
candidates for CHP systems. Traditionally such CHP
systems have been sized to match the facility's own
energy needs," he said. "However, for a relatively modest investment, industrial customer-sited CHP systems
could be designed with adequate additional generating
capacity to support the electric grid. Because customersited CHP units typically operate continuously, they can
respond rapidly whenever grid services or added power
are needed."

Powering Patient Care in Grid
Isolation Mode

Mississippi Baptist Medical Center: Jackson, Miss.ÑIn 1991, A 4.6 MW
CHP system was installed to meet a large portion of
the medical center's energy needs. During normal
operation, the CHP plant works parallel to the electric grid to provide about 80% of the facility's power.
When the grid is unavailable, the plant was designed
to provide electric power and heat. The system supplies steam to provide building heat, generate domestic water heating and provide chiller water using
absorption chillers.
Event: Hurricane Katrina: Aug. 29, 2005
Hour One. Within an hour of Hurricane Katrina hitting Jackson, Miss., the main power grid failed, and
restoration efforts created an unstable power source.
Hour Three. The medical center had shed 1.2 MW of
non-essential load.
Hour Five. After hours of unstable operation, the
facility was put on the CHP plant and disconnected
from the grid. Elevators were connected to emergency
generators, and the use of MRI was restricted.
Hour 52. The power grid was restored, and the medical center was reconnected and continued normal
operation.
Mississippi Baptist was the only hospital in the
Jackson, Miss., metro area to remain about 100%
operational and could receive patients from other
medical facilities. The medical center also served as
an operations center for emergency responders.

Integrating CHP and Renewable Energy

Renewable energy sources can often be integrated with
CHP, according to Foley. There are two paths: renewable
energy can fuel the CHP systems, or renewable energy
resources can be combined with CHP plants to provide a
hybrid system.
Coupling CHP systems with intermittent renewable
energy resources such as PV or wind is relatively new
while the use of renewably fueled CHP systems is well
understood with system installations going back to the
1940s, said Sweetser.

Solar PV and Batteries

Integrating solar PV with CHP is more widely used
than other hybrid CHP system options.
D E C E M B E R 2 0 19

ashrae.org

ASHRAE JOURNAL

http://www.ashrae.org

ASHRAE Journal - December 2019

Table of Contents for the Digital Edition of ASHRAE Journal - December 2019