ASHRAE Journal - September 2019 - 32

TECHNICAL FEATURE

Pri. Supply and Return, Bldg. Supply and
PSV Upstream Pressure (psig)

FIGURE 7 Primary pressure and building pressure profile.

95
85
75
65
55
45
11:45p

8:00a

10:45a

1:30p

4:15p

7:00p

9:45p

Bldg. Supply Pressure
PSV Upstream Pressure

5:15a

PSV Position

8:00a 10:45a

Pump Speed

1:30p

4:15p

Top Coil Inlet Pressure

7:00p

9:45p

10
9
8
7
6
5
4
3
2
1
0

Top Coil Supply and Return
Pressure (psig)

100
90
80
70
60
50
40
30
20
10
0
11:45p 2:30a

Top Coil Outlet Pressure

TABLE 3 PSV operation and performance.

This follow-up study confirmed that the PSV method
is an energy-saving as well as practical solution. The
operation study revealed the installation of PSVs
reduces pumping power by 13% and pump head
by 14%. These improvements resulted in one existing CHW pump to save an estimated $2,380/year at
Building A with an associated payback period of 3.5
years. The PSV solution not only saves money, but also
eliminates the problem of insufficient PSP on the large
campus loop and improves the hydronic loop performance. The PSV method does not cause any blockage on the return flow from surrounding buildings,
and the high PSV operation performance indicates
the building pump capacity for PSV method is much
smaller than pre-PSV's requirement. This study will
help engineers fully understand hydronic loops, building pressure distribution, and building pump requirements. It offers a cost-effective solution and can be
used as a resource for PSV design and operation for
design engineers and facility personnel.
ASHRAE JOURNAL

5:15a

FIGURE 8 Daily PSV and pump operation.

Conclusion

2:30a

Pri. Supply Pressure
Pri. Return Pressure

PSV Position and Pump Speed (%)

clearly exhibit that both pump speed and
PSV modulation converged at the PSV set
point, and pump power consumption
and pump head were reduced, compared
to the existing pump without the PSV, a
high operation performance as designed.
The PSVs are in full operation at all four
buildings which previously experienced
negative pressures in their top coils, and
all PSVs have been tuned, balanced and
commissioned.
Table 3 shows an inspection of PSV's operation as of May 15, 2018. The top coil outlet
pressure stays around 5 psig (34 kPag) for
all buildings, which provides some safety
during operation should anything not act
according to design. The building PSV position varies from 11.6% to 45.3%, which is
related to the PSV's distance from the plant
and its modulation to keep its set point. In
same way, pump speed is also related to
each buildings demand flow, PSV set point,
and distance from the plants. The inspection indicates these PSVs performed as
designed.

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S E P T E M B E R 2 0 19

BUILDING
NAME

HYDRONIC
TYPE

TOP COIL OUTLET
PRESSURE PSIG

DT °F

PSV
POSITION (%)

PUMP
SPEED (%)

CHW

4.1

24.2

LTHW

4.5

23.5

CHW

4.8

25.4

LTHW

5.1

30.7

CHW

5.0

11.6

LTHW

4.3

22.8

CHW

5.5

35.6

LTHW

4.5

45.3

References
1. Hui Chen, et al. 2017. "Dealing with insufficient plant static
pressure: improving thermal loop performance." ASHRAE Journal
59(4).
2. 2017 ASHRAE Handbook-Fundamentals, Chapter 3, Fluid Flow,
pp. 3.2.
3. 2017 ASHRAE Handbook-Fundamentals, Chapter 22, Pipe Design,
pp. 22.5.
4. 2016 ASHRAE Handbook-HVAC Systems and Equipment, Chapter
44, Centrifugal Pumps, pp. 44.9.

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ASHRAE Journal - September 2019

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