ASHRAE Journal - February 2015 - 66

TECHNICAL FEATURE

connects back to the chilled supply. This pump is variable
speed to match the pressure of the CHW supply main
when the main chillers are on, and to feed any campus
winter cooling requirements when the main chillers are
off. There is a recirculation valve from the evaporator
outlet back to the inlet, serving two purposes: to ensure
minimum flow through the evaporator; and to ensure
that chilled supply temperatures are appropriate. CHW
supply can go either to the Science Center or to the campus. The HRC operates for all campus winter cooling
when the main water-cooled chillers are drained. The
HRC may be operated for load in summer using its condenser when the campus loop is at capacity.

new HW return line. This reuse saved considerable dollars and time.

First Cost

Comparing the synergistic approach to the standalone approach was almost a break-even proposition.
* The heat recovery machine with condenser and
glycol loop was estimated to be $25,000 more than a
split-system air cooled chiller of equal capacity;
* 4 in. (100 mm) supply and return mains from Science Center to Academic Center (850 ft [259 m] total)
were estimated to cost $53,600; and
* Second boiler eliminated if installed at the Academic Center (redundancy available from the Science
Connecting to Cordier Auditorium
Center) was estimated to save $62,500.
The existing air handlers at Cordier Auditorium are
The above equals a $16,100 increase in cost versus the
hot-deck/cold-deck constant volume.
stand-alone approach, less than 1% of
Academic center atrium.
The hot deck is a hot water coil, fed
the total Academic Center mechanifrom a steam-to-water heat exchanger
cal renovation budget. However, the
and sized for 180°F (82°C). Because
project also eliminated the need for
there was a significant need for reheat
boilers at Cordier, estimated to save
for humidity control, the connection
$100,000 per the Utility Master Plan.
to the HRC was important, and HW
This resulted in a net savings of
was piped to the existing hot deck
$83,900 to Manchester using the
coil. However, because the new heat
synergistic approach. Plus, without a
source was only 130°F (54°C) in winboiler room at the Academic Center,
ter, it would not be adequate to prothe required mechanical space is
vide heat using the old hot deck coil.
now 300 ft2 (28 m2) smaller than it
The cold deck piping was modified to
would have been in the stand-alone
allow it to be used for heating when
approach. That additional space has a
the hot deck would no longer meet the
value (±$45,000) to the university.
space needs. AHU controls were modified as necessary
to reverse the thermostat operation from summer to
Energy Impact
winter.
Prior to this project, all of the gas used at the Science
The availability of HW for summer reheat was a signifi- Center was used in the Science Center for space heatcant indoor air quality improvement.
ing and domestic hot water. Steam usage at Cordier and
One other interesting part of the Cordier switch to HW H-K was metered separately, as was the line loss. Table
was the reuse of the old steam pipe for HW, suggested
1 shows a dramatic decrease in gas use at the Science
by the university maintenance staff. The steam main
Center, in spite of almost twice the space being heated.
had been installed 36 years prior, but it was in excellent
If the steam use and steam line losses were included,
shape. It was insulated and on roller hangers, and larger the three buildings now are being heated with 41% of the
than what would have been required for a new HW line. gas previously used. This is a savings of $35,945 per year
The old steam return line from Cordier was too small to
using 2010 gas rates.
reuse, and in slightly worse shape than the steam line.
There has been an increase in electric usage at the
The steam main that was to be abandoned south of the
Science Center due to operation of the heat recovery
Academic Center tunnel junction (see map, Figure 1) was chiller and due to the location of the heating pumps for
winched down the tunnel to Cordier and became the
Cordier and the Academic Center in the Science Center.
66

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