Install Instructions
IM-PR 566442 1114 (Design Manual)
114
5.7 Selecting the circulator
Pump curves help you to select a circulator based
on the feet of head expected at the design flow
rate. The selected pump must have a capacity
greater than or equal to the system flow rate and
a head greater than or equal to the total system
pressure drop. Derive the system flow rate from
Section 5.6.1 and the pressure drop from Section
5.6.2. Once these two system characteristics are
known, a pump curve can be used to identify the
best match for the system. Follow the procedure
below to select a pump sourced from Viega:
1. Locate the pressure drop on the left vertical
axis.
2. Locate the total system flow rate on the
bottom horizontal axis.
3. Follow to the intersection of both variables.
4. Select a pump with a curve just higher than
this intersection. If there are multiple pumps
with curves higher than this point, then
consider selecting the pump with the lowest
watts for the best energy performance. Large
commercial and industrial applications may
require larger pumps.
Figure 5-3a Pump curves
Stock Code Speed Amps Watts HP
12126
HI 0.75 87 1/25
MED 0.66 80 1/25
LOW 0.55 80 1/25
Figure 5-3b Pump curves
Stock Code Speed Amps Watts HP
12127
HI 1.8 197 1/6
MED 1.5 179 1/6
LOW 1.3 150 1/6
5.8 Approximating the operating cost
Use this equation to calculate the cost to use a
snow melting system for 1 year:
where
O = Operating cost ($/yr)
A = Area (ft²)
qa = Annual heat flux requirement (Btu/ft²), refer to
Table 5-1 or 5-2
F = Fuel cost ($/Btu); useful conversions: 100,000 Btu/
therm; 3,412 Btu/kWh; 91,500 Btu/gal propane; 138,700
Btu/gal fuel oil
B = Back and edge loss (% multiplier), refer to Table 5-3
nb = combustion efficiency of boiler, dimensionless
ne = energy distribution efficiency, dimensionless
NOTE: This calculation is sensitive to the proper
construction and control of the snow melt system.
Example:
A = 2,000 ft²
qa = 7,694 Btu/ft² (in Boston)
F - assume $0.80/therm; 100,000 Btu/therm
F = $0.000008/Btu
B = 10%, assuming insulation below but no edge
nb = 0.85
ne = 0.90
A x q
a
x F
[1 - (B/100)] x (n
b
x n
e
)
O =
(2,000 x 7,694 x 0.000008)
[1 - (10÷100)] x 0.85 x 0.90
Operating cost =
= $179/yr
Without Check Valve
HI
MED
LOW
20
18
16
14
12
10
8
6
4
2
0
0 24681012141618
Head (ft)
Flow (GPM)
Without Check Valve
HI
MED
LOW
Head (ft)
Flow (GPM)
30
25
20
15
10
5
0
0510 15 20 25 30 35