Balancing of a Water and Air System (PDF
Balancing of a Water and Air System (PDF
Balancing of a Water and Air System (PDF
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57<br />
Venturi<br />
The venturi is a device permanently installed in the pipe that has been calibrated by<br />
measuring the pressure drop against a known flow. Venturis must be located according<br />
to the manufacturer's recommendations to maintain accuracy <strong>of</strong> 2% (Figure 11.2).<br />
Hydronic Pitot Tube Traverse<br />
The Pitot rod is a pair <strong>of</strong> tubes in a casing. One tube measures a static head pressure,<br />
<strong>and</strong> the other tube which faces in the direction <strong>of</strong> flow, measures the total head pressure.<br />
The Pitot rod is a manually inserted device used to take a series <strong>of</strong> velocity<br />
measurements, which are averaged <strong>and</strong> used to determine flow. (Figures 11.3 <strong>and</strong> 11.4).<br />
A manometer is attached to measure flow.<br />
GPM = FPM X Gallons per foot<br />
FPM = 1040 X √ VP<br />
Example 7A<br />
Find the Gpm <strong>of</strong> a system that has a Cfm <strong>of</strong> 10,000 with a entering air <strong>of</strong> 80°F Dry bulb,<br />
67°F wet bulb <strong>and</strong> a leaving air <strong>of</strong> 62°F dry bulb , 57.5°F wet bulb. The water entering is<br />
45°F <strong>and</strong> leaving is 55°F.<br />
80°F dry with a 67°F wet is a 31.51 enthalpy <strong>and</strong> 62°F dry 57.5°F wet is a enthalpy <strong>of</strong><br />
24.77 with a air density <strong>of</strong> 0.0757<br />
Solution<br />
Gpm = <strong>Air</strong> Density X CFM X ∆ Enthalpy / 8.337 X ∆ temperature <strong>of</strong> the water<br />
0.0757 X 10,000 X 6.74 / 8.337 X 10 = 5102.18 / 83.37 = 61.2 GPM<br />
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