3.5 The owner of a small office building has decided to design and install a pip

Question

3.5 The owner of a small office building has decided to design and install a piping network that includes five tankless water heaters to heat and transport water. The owner currently requires 18 gpm of hot water service. Cold water (feedwater) from the city will be supplied to each heater, and the piping connections were previously installed by the building contractor. The hot water, at 160 F, from the heaters will be transported through a main header for distribution in the rest of the building. Each heater has been specified to provide a maximum of 4.6 gpm of water. The heater unit has a dedicated pump that serves only to circulate the cold water through its internal finned- coil system. Unfortunately, the city supplies the feedwater at a low pressure of 40 psia, and the owner needs hot water at 80 psia for complete distribution though the building. Based on the sketch provided below, complete the design of the hot water supply lines in this system. Bear in mind that the owner would like to maintain flexibility to expand the system in the future to its maximum capabilities. Further Information: In practice, the lengths of the hot water supply piping that connect directly to the heaters are small in comparison to that of the main supply header. 9 Cold feedwater Hot supply water

Explanation / Answer

input 4.6 gpm and output 18 gpm. In a day if we supply for 12 hrs we have to store for 12 hrs. The capacity should be (18-4.6)*12*60=13.4*720=9648 gallons.

Five heaters of capacity 1929.6 gallons.

P + 1/2 rho v ^2 + rho g h is constant.

275.8 + 1/2 v1^2+ 10* 10= 275.8*2 + 1/2 v2 ^2

v1^2-v2^2= 351.6

v1=20 m per s

v2= 7.2 m per s.

Thus diameter of first pipe is 7.2 cm

Diameter of exit pipe is 20 cm.

The intermediate pipes dont matter as long as the range is the same. Best to divide all into one fifth to keep flow rate same.

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