This question is incomplete, the complete question is;
The chilled water system for a 27-story building has a pump located at ground level. The lost head in a vertical riser from the pump to an equipment room on the twenty-seventh floor is 40ft of water, and the pump produces 270ft of head. What is the pressure on the suction side of the pump for a pressure of 8 psig to exist in the riser on the twenty-fifth floor
Assume 12ft of elevation per floor
Answer: 48.68 psig
Explanation:
First we calculate the elevation of the building
hb = 27 story * 12ft per floor/story
hb = 324 ft
given that the head lost in the vertical riser hL = 40 ft
now the delivery head required in the riser on he 27th floor;
hd = 8 psig * (2.31 ft / 1 psig)
hd = 18.46 ft
Now calculate the suction head required by balancing the energy per unit weight of water, considering pump as the control volume
hp = (hb + hL + hd) - hs
hs = hb + hL + hd - hp
where hp is the head developed by the pump (270 ft)
hb is the elevation of the 27th floor of the building ( 324 ft)
hL is the head lost in the vertical riser ( 40 ft)
hd is the head required to exist in the riser on the 27th floor (18.46 ft)
so we substitute
hs = 324 ft + 40 ft + 18.46 ft - 270 ft
hs = 112.46
so 112.46ft * (1 psig / 2.31 ft)
= 48.68 psig
