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ME 390 Fall 2013 – Take Home Mid Term

The building shown below has three occupied floors and a mechanical basement, each are 15
feet high. Each  floor  is  air  conditioned  with  it’s own air handler. The 1st floor air handler unit
(AHU) has a chilled water cooling coil with a 50 Ton cooling capacity, the 2nd floor AHU has a
65 Ton cooling coil, and the 3rd floor AHU has an 85 Ton cooling coil. Each coil has a 9 ft.
pressure drop at full design flow. Each AHU coil chilled water control valve is designed to
have a 12 ft pressure drop at full design flow.

The 200 Ton chiller in the basement has a 7 ft pressure drop across the evaporator when at
full design flow. The chiller and all of the AHU coils are designed for a 12⁰F delta T across the
evaporator / coils when at full design capacity. The chiller is a semi-hermetic closed drive
centrifugal operating at 70% efficiency, the frictional and motor efficiency losses are rejected
thermally through the condenser water system. The condenser on the chiller at full capacity
has a 15 ft pressure drop.

The cooling tower on the roof has a condenser water inlet at the top in an open (air) hot
basin. The top of the cooling tower is 15 ft above the roof. The cold basin that has the
condenser water return piping connection at the bottom of the tower is 4 ft above the roof.
The tower is designed to achieve a 12⁰F condenser water temperature drop at full capacity.

http://www.prlog.org/11791291-hvac-schematic-drawings

ASSIGNMENT:

1 Chilled water system:

Draw a chilled water piping schematic showing adequate elbows, tees, control valves, coils,
chiller (evaporator), chilled water pump. Show all pipe lengths.

Determine the required flow rate.

Size the chilled water supply and return piping such that when operating at 4% of full flow
capacity the smallest standard pipe size possible will produce laminar or transitional flow (i.e.
next standard size smaller would result in turbulent flow), use .000017 ft2/s for kinematic
viscosity.

Determine the maximum pressure drop of the system. Plot the system curve.

Determine the chilled water pump performance requirements. Select a properly sized chilled
water pump from an online pump manufacturer, and plot the pump curve with the system
curve.

2 Condenser water / Cooling tower system:

Draw a condenser water piping schematic showing adequate elbows, pipe lengths, chiller (condenser),
condenser water pump, and the cooling tower. Show all pipe lengths.

Determine the required flow rate.

Determine the condenser water return pipe size (flow back to the tower) assuming it has 10% friction
loss (hL).

With this total return (pump discharge) flow and head capacities, and using the same size piping on
the condenser water supply line (from roof to chiller), determine the condenser water pumps total
head and GPM requirements, as well as the NPSHA. Select a properly sized condenser water pump
from an online pump manufacturer to meet these conditions.

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Show all work, including formulas used, assumptions made, schematics, equipment selection
submittals, charts and graphs, etc..

1 Ton of air conditioning = 12,000 BTU/hr

For water flow BTU/hr = GPM x 500 x ΔT (⁰F)