Chapter hvac engineering Fundamentals: Part 1 Introduction

174
Chapter Six
Figure 6.15
Reverse-return piping system.
Figure 6.16
Reverse-return system pressure profile.
Figure 6.17
Loop piping system.
Design Procedures: Part 4
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Design Procedures: Part 4
175
Figure 6.18
Pressure profile for loop piping system.
Figure 6.19
Closed expansion tank.
water first enters it, (4) the initial fill pressure (minimum operating
pressure) at the tank, and (5) the maximum allowable operating pres-
sure at the tank. The initial fill pressure is determined by the system
static head at the tank location plus an allowance to maintain a net
positive head at the pump suction under all operating conditions.
Thus, if the tank is on the pump suction (Fig. 6.21), a few feet of gauge
pressure is sufficient. If the tank is on the pump discharge (Fig. 6.22),
the minimum pressure must include the pump head plus a small mar-
gin. For an attic tank (Fig. 6.23), the extra static head (if the pump is
in the basement or ground floor) will usually be sufficient. The max-
imum pressure allowable is determined from the lowest-rated device
in the system, most often the boiler or its pressure relief valve. Be-
cause of this, it is preferable to pump away from the boiler.
Design Procedures: Part 4
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