ASHRAE Journal - February 2015 - 63

TECHNICAL FEATURE

use space and excess boiler capacity in the Science Center. A chiller would be added, but it would be capable of
heat recovery to eliminate summer boiler operation at
the Science Center. This approach would also provide
boiler capacity for the Cordier Auditorium. The university opted for the synergistic approach.

FIGURE 1 Synergistic approach connected three buildings.

Before the Project
H-K, Science Center and Cordier Auditorium were
already built, and H-K was being renovated into the
new Academic Center (Figure 1). H-K and Cordier had
steam heat to be converted to low temp HW per campus master plan. Cordier is an unscheduled future
project. Space would need to be carved out of H-K
and Cordier for boiler rooms. The Science Center's
mechanical room has 150% excess boiler capacity
and lots of open floor space. The Science Center and
Cordier need summer reheat for humidity control,
but it was not available at Cordier because the campus
steam system was shut down from mid-April to midOctober. Campus chilled water was connected to all
three, but the loop was short of capacity.

After the Project, Benefits
Of Synergistic Approach
Chiller capacity was added for Academic Center,
installed in the Science Center and connected to the
campus loop. A heat recovery chiller (HRC) was chosen
and designed with air-cooled condensers so it could
operate either as a heat recovery machine or as a conventional chiller. The HRC eliminated summer boiler
use at the Science Center, and it provided a source of
summer reheat at Cordier and the Academic Center. The
project eliminated steam to the Academic Center and
Cordier, and decommissioned 870 ft (265 m) of steam
lines. No boiler room was required in the Academic
Center or Cordier, equaling more assignable space. The
project was nearly cost neutral vs. boilers and chiller at
the Academic Center; it saved +$80,000 versus the utility
master plan for Cordier conversion; and it accelerated
the conversion of Cordier from steam.

The System
To connect the Academic Center and Cordier to the
Science Center, new hot water mains had to be run in

the existing tunnel. Chilled water lines already connected all buildings.
There are now three heat sources available for these
buildings: first, the heat recovery chiller (HRC); second,
a new high efficiency condensing boiler; and last the
existing conventional boiler plant. They are arranged in
sequence based on efficiency and operating cost.*
* Stage 1: The HRC will have a COP of about 6.5 to 7.0
when there is a concurrent cooling need, equal to a heating cost of $0.19/therm;
* Stage 2: The condensing boiler will operate at 90% seasonal efficiency, equal to a heating cost of $1.25/therm; and
* Stage 3: The conventional boilers that will operate
at about 80% efficiency if there is sufficient load to keep
them from short cycling. Estimated seasonal efficiency
places the existing boilers at a heating cost of $1.88/therm.
To get maximum use of the heat recovery chiller
(HRC), the HW supply reset schedule for the Science
Center was adjusted lower, such that it would run
temperatures only hot enough to condition the space
(Figure 2). A three-way diverting valve was installed in
the Science Center HW return line, and if the Science
Center HW return temperature was below 130°F (54°C)
(HRC high limit), it would be combined with return
from Cordier and the Academic Center and route
through the HRC.
Downstream of the HRC, heating water can go either
past or through the new high-efficiency condensing
boiler. There are many times of the year, including
all of the summer, when the HRC supplies all of the

*Costs are based on 2010 utility prices: gas at $1.13/therm and electricity at $0.067/kWh. Since 2010, utility costs have shifted dramatically: gas is now at $0.40/therm and electricity is at $0.083/kWh.
The benefit of heat recovery is still there, but not as great a difference as when designed.
FEBRUARY 2015

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