ASHRAE Journal - February 2015 - 64

TECHNICAL FEATURE

heating requirements. Because the
Academic Center and Cordier are
designed to be heated with 130°F
(54°C) maximum HW supply, and
since the HRC is capable of making 130°F (54°C) water, if there is a
campus need for chilled water even
in winter, the HRC will be operating,
and it may generate enough heat to
keep boilers off.
There are two sets of heating
pumps. The original Science Center
pumps are downstream of the existing boilers. Those pumps and boilers continue to operate as designed
but with a lower HW supply temperature reset schedule. Boiler isolation
valves were installed, and there is
a now a bypass around the existing
boilers if they are not required.
There are new variable speed HW
pumps (two at 100% each) to serve
both the Academic Center and
Cordier. Because this plan installed
only one boiler on the Academic
Center/Cordier loop, and because
the university has a redundancy policy on heating systems, an HW injection line is installed from the discharge of the Science Center pumps
to the suction of the new pumps. This
provides heating in the event of an
outage at the new condensing boiler.
The HRC has pumps on both condenser and evaporator sides. The
constant speed condenser pump
is connected from and back to the
HW return lines. The air-cooled
condenser comes off the HW return
branch to make sure that any building uses for HW are met before heat
is rejected to the condenser. While
not shown in Figure 3, there is a heat
exchanger and glycol loop for winterizing the air-cooled condenser.
The HRC evaporator pump comes
off the chilled water return line and
64

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FIGURE 2 Synergistic three building heating system.

7 M

M 5

BLR-4

BLR-1
1

BLR-2
4

BLR-3

HRC

HWS
Hot Water To/From
Science Center M
3

HWS

9 M

HWR
HWS

HWR

1.
2.
3.
4.
5.
6.
7.
8.
9.

Hot Water To/From Cordier
and Academic Center

Existing boilers (3) and variable speed hot water (HW) pumps (2) to serve the Science Center.
New variable speed HW pumps (2) to serve Cordier Auditorium and the Academic Center.
New diverting valve to direct Science Center HWR to HRC if temperature is cool enough (130F max).
New heat recovery chiller, see Figure 3. This is Stage 1 heating.
Diverting valve, open when Boiler 4 is off. Valve modulates to ensure flow does not exceed manufacturer's recommendations.
New condensing boiler. This is stage 2 heating.
New Boiler 1 to 3 bypass valve. Valve is open if Stage 1 and 2 heating are able to satisfy Science Center heat requirements.
New boiler isolation valves (3), one to be open anytime boiler bypass valve is closed, others to be staged on as load requires.
New supplemental heat valve, modulates to raise HWS temperature to Cordier and Academic Center if Stage 1 and 2 heat are
not adequate.

FIGURE 3 Synergistic three building cooling system.

To/From Air
Air-Cooled Condenser
1

4
3

HRC
5

HWR

2
Chilled Supply (CHS)

To/From Science Center

To/From Campus Loop
Chilled Return (CHR)

1.
2.
3.
4.

100 ton heat recovery chiller (HRC) operates year-round.
Variable speed evaporator pump, operates to match campus CHW loop pressure.
Constant speed condenser pump.
Constant speed heat rejection pump, operates when HRC is running to meet CHW demand, rather than to satisfy heat/reheat
requirement. Heat exchanger and glycol loop not shown.
5. Modulating valve serves two purposes: evaporator minimum flow, and HRC discharge temperature control.

FEBRUARY 2015

ASHRAE Journal - February 2015

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