111005 domestic water sizing

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WATER SYSTEM DESIGN

WATER SYSTEM DESIGN

Water Supply System Design Objectives

Six Important Reasons for Proper Water System Design

Health – Improper sizing can cause decrease in pressure which can cause backflow or siphonage.Pressure – Maintain proper pressure so fixtures will operate.Flow – Adequate flow at fixturesWater Supply – corrosion or scalePipe Failure – Due to high velocitiesNoise – High velocities can cause noise and hydraulic shock

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WATER SYSTEM DESIGN

Flow Pressure

Flow Pressure is that pressure that exists at any point in the system when water is flowing at that point.

Flow Pressure is not static pressure which is typically one of the pressures that we receive from the water company or fire department. The other is residual pressure which is another discussion for another day.

When a manufacturer lists the minimum pressure requirement for a fixture (such as 25 psi for a water closet) it it the flow pressure requirement which is being noted.

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WATER SYSTEM DESIGN

Flow at a Outlet

If you need to determine what flow (gallons per minute) is being delivered at an outlet and you know the flow pressure just prior to the outlet and you know the inside diameter of the outlet the following formula can be used.

q = 20 x d^2 x p^0.5

Where q = flow rate at outlet in gpm d = inside diameter of outlet in inches p = flow pressure in psi

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WATER SYSTEM DESIGN

Material Selection

Typically we use copper pipingType “K” copper with brazed joints undergroundType “L” copper with soldered joints aboveground

Based upon size (usually 4” and larger) we’ll use ductile iron piping.

Starting to use CPVC and PEX piping on some projects. Different type of design with these systems.

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WATER SYSTEM DESIGN

Inadequate Pressure

Municipalities usually maintain water pressure in the 50 to 65 psi range due to sprinkler system requirements.

If pressure in the public mains is inadequate for building operation, other means must be utilized to increase the pressure. Three typical means are:

Gravity tank systemHydropneumatic tank systemBooster pump system

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WATER SYSTEM DESIGN

Flow Definitions

Maximum flow or maximum possible flow – flow that will occur at the outlets on all fixtures if they are opened simultaneously.

Average flow – flow likely to occur in the piping system under normal conditions.

Maximum probable flow – the maximum flow in the piping system that will occur under peak conditions. Also known as peak demand or peak flow.

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WATER SYSTEM DESIGN

Demand Types

Continuous Demand – Water flow over an extended period of time.

Intermittent Demand – Water flow over a relatively short period of time.

Water Demand - Ultimately related to the number of fixtures, type of fixtures, and probable simultaneous use.

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WATER SYSTEM DESIGN

Design Loads

Maximum and Average flow really are not of any help in designing the piping system in buildings. These are of more interest in determining the ultimate water usage of the building.

We need to know the Maximum Probable Demand on the system.

Two methods have evolvedEmpirical methodMethod of probability

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WATER SYSTEM DESIGN

Fixture Flow Rates

The Federal Energy Policy Act (EPACT92) established the following water use criteria:

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WATER SYSTEM DESIGN

Water Supply Fixture Units

National Bureau of Standards published the work of Dr. Roy B. Hunter, entitled “Methods of Estimating Loads in Plumbing Systems.”

Fixture Unit Weights and the Hunter Curves

At TES we call the fixture unit weights the water fixture units (WFU).

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WATER SYSTEM DESIGN

Water Fixture Units

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WATER SYSTEM DESIGN

Converting Fixture Units to Equivalent GPM - Hunter Curves

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WATER SYSTEM DESIGN

Example

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WATER SYSTEM DESIGN

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WATER SYSTEM DESIGNQUESTIONS? DISCUSSION?

THANK YOU.