Thermo-Fluids Design and Analysis
Work Example
2017
Design Problem:
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A chiller and three air handling units are to be installed in a cold-water cooling system (shown to the right) in the air conditioning network. Size the chiller, the three air handling units, the pump and all the pipe in the network. Finally, specify the valve settings to achieve the required flow rate.
Chiller Requirements:
The chiller must be designed to cool water from 55 °F to 40 °F. Design a 15-tonc chiller that makes 2 passes of R134a at 35 °F, and the inside convection coefficient is known to be 1250 BTU/(hr*ft2*°R). Start with a tube design of 1‑in. OD tubes and 13 BWG laid out on a 1¼-in. square pitch. Limit the water pressure drop to 10psi.
AHU Requirements:
The AHU will extract 4-tonc from an airstream that enters at 75 °F and must leave at 62 °F. Assume water enters the tubes of the air handling unit at 42 °F and leaves no higher than 54 °F. Design an AHU (tube‑and-fin heat exchanger). Start with tubes constructed from standard ¼â€‘Type K copper tubing placed on a 1-in hexagonally close-packed array (SD = 1in.). Limit the overall pressure drop on the air side to 5 in.-of-H2O and the velocity to 20 ft/s.
Pipe, Pump and Valve Requirements
Size all pipe based on the economic velocity of water. Size the pump based on the calculated head loss. Construct a pump curve and head loss functions. Specify valve settings to achieve the required flow rate.