ASHRAE Journal - September 2019 - 28

TECHNICAL FEATURE

could be analyzed. In the first case,
the primary return pressure was kept
constant at 57 psig (393 kPag) while the
primary supply pressure was varied
from 45 to 70 psig (310 to 482 kPag).
In the second scenario, the primary
supply pressure was kept constant at
59 psig (406 kPag), while the primary
return pressure was varied from 50 to
70 psig (344 to 482 kPag). The simulation's primary pressure data and
ranges were based on trended yearly
data patterns.

FIGURE 4 Hydraulic loop simulation model.

Bldgs. with PSV
SUP 3
CUP
B

C

Building Pump and Primary Loop Pressure
The simulation results in Table 2 are
D
shown to compare building pump
A
capacity and its power consumption
for different scenarios (with and without PSV). Table 2 exhibits primary supTABLE 2 Primary supply pressure vs. top coil pressure and pump data.
ply versus top coil pressure, pumping
METHOD
PRI. SUPPLY
COIL INLET
COIL OUTLET
PUMP
PUMP
PUMP
PRESSURE, PSIG
PRESSURE, PSIG
PRESSURE, PSIG POWER, HP
HEAD, FT SPEED (%)
power, and pump speed for Building
W/O PSV
A. Without the PSV installed, the top
45
10.2
-27
20.8
117.6
99%
coil inlet pressure was 10.2 psig (70
50
10.2
-27
18.8
106.1
96%
kPag) and the top coil outlet pressure
55
10.2
-27
16.7
94.6
92%
was -27.0 psig (-186 kPag). With the PSV
60
10.2
-27
14.7
83.0
88%
the top coil inlet pressure decreases
65
10.2
-27
12.7
71.5
84%
from 10.2 psig to 5.2 psig (70.3 to 35.8
70
10.2
-27
10.6
60.0
79%
kPag), and the top coil outlet presPSV
45
5.2
3.1
18.8
106.1
96%
sure becomes 3.1 psig (21.3 kPag). As
50
5.2
3.1
16.7
94.6
92%
primary supply pressure increases
55
5.2
3.1
14.7
83.0
88%
from 45 psig to 70 psig (310 kPag to 482
60
5.2
3.1
12.7
71.5
84%
kPag), pumping speed decreased from
65
5.2
3.1
10.6
60.0
79%
99% to 79% without the PSV, and 96%
70
5.2
3.1
8.6
48.44
74%
to 74% with the PSV. Pump head with
PSV dropped on average 14%, around
11.5 ft (3.5 m), compared to the pre-PSV option. With
both pump power and head differences (with PSV or
the PSV the power consumption is about 2 hp (1.5 kW)
not) are independent of primary return pressure.
lower than without the PSV, which declined about 13%.
Return Pressure Blockage Identification
The PSV method is able to reduce CHW pump power
One of the concerns that needed to be addressed was
at $2,380/year and has an estimated payback period of
how the installation of PSVs on each of the tallest build3.5 years.
ings on campus would affect the return loop pressures
Field observations display that each existing pump
of nearby buildings. A hydraulic simulation for Building
was oversized and ran at full capacity before PSVs were
A (with PSV) and its surrounding Buildings E, F, and
installed, so the actual pump power savings from the
G (without PSVs), was performed for this hydronic
PSV installation is more than the simulation estimation
return pressure blockage issue. Figure 5 shows the return
at Table 2. The second scenario simulation shows that
28

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ASHRAE Journal - September 2019

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

Contents
ASHRAE Journal - September 2019 - Intro
ASHRAE Journal - September 2019 - Cover1
ASHRAE Journal - September 2019 - Cover2
ASHRAE Journal - September 2019 - 1
ASHRAE Journal - September 2019 - Contents
ASHRAE Journal - September 2019 - 3
ASHRAE Journal - September 2019 - 4
ASHRAE Journal - September 2019 - 5
ASHRAE Journal - September 2019 - 6
ASHRAE Journal - September 2019 - 7
ASHRAE Journal - September 2019 - 8
ASHRAE Journal - September 2019 - 9
ASHRAE Journal - September 2019 - 10
ASHRAE Journal - September 2019 - 11
ASHRAE Journal - September 2019 - 12
ASHRAE Journal - September 2019 - 13
ASHRAE Journal - September 2019 - 14
ASHRAE Journal - September 2019 - 15
ASHRAE Journal - September 2019 - 16
ASHRAE Journal - September 2019 - 17
ASHRAE Journal - September 2019 - 18
ASHRAE Journal - September 2019 - 19
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