# Flow Rate Calculator

## Probable Simultaneous Demand

When sizing pipes for water systems, engineers need to consider the likely consumption of water. But, it’s not required to provide a pipe system that supplies the maximum flow at any one time because all the taps won’t necessarily run at the same time.

So, instead, the plumbing system is designed to consider the probable simultaneous demand (PSD) pattern of the users. The probable simultaneous demand is determined by converting the loading units or full flow rate of all the fixtures that are downstream of the pipe into a flow rate.

## PSD is measured as a flow rate in L/s, m3/s, or GPM

The conversion from loading units or full flow rate to probable simultaneous demand is dependent on what conversion method the user chooses.

H2X offers several probable simultaneous demand conversion methods:

DIN 1988-300:2012-05

AS/NZS 3500.1

Institute of Plumbing Barrie’s Book

IPC 2018

UPC 2018

BS 8558

BS 806

CIPHE

## Flow Rate Dynamics

### Volume Flow Rate

To manually calculate flow rate and convert the loading units or full flow rate of all the fixtures using the DIN 1988-200:2012-05 equation, you would have to use the following formula:

## VR - the design flow rate

Where the flow rate is below 0.2l/sec, the full flow rate is used.

Where the full flow rate is higher than 500 l/sec, a flow rate result will not be provided

a, b, c - the constants (as per the table below)

## AS/NZS 3500.1:2018:

### Certifying a Cold Water Plumbing Installation

The equation below specifies the method of sizing a typical installation in accordance with AS/NZS 3500.1:2018 for dwellings:

The table below specifies the method of sizing a typical installation in accordance with AS/NZS 3500.1:2018 for loading units:

## Institute of Plumbing:

### IPC 2018

The following table specifies the sizing methods under the International Plumbing Code for flush tanks:

The table below specifies the method of sizing a typical installation in accordance with AS/NZS 3500.1:2018 for loading units:

### UPC 2018

The following table specifies the sizing methods under the Uniform Plumbing Code for flush tanks:

### Dwellings:

The following table specifies the sizing methods under the Uniform Plumbing Code for the flushometer:

### BS 8558/ Institute of Plumbing/ CIBSE Guide G

The BS8558 and the CIBSE Guide G are two of the principal flow rate methods employed in the United Kingdom. The loading units take the flow rate into account and the length of time that the outlet will be in use:

### BS 806

The BS 806 is one of the principal flow rate methods employed in the United Kingdom for pipe sizing:

 Highest LU/Total 0 2 3 4 5 6 7 8 9 10 15 20 30 40 50 60 70 80 90 100 150 300 400 500 800 1000 2000 3000 5000 2 0 0.2 0.24 0.27 0.29 0.32 0.36 0.38 0.4 0.46 0.52 0.52 0.62 0.7 0.78 0.83 0.9 0.95 1 1.05 1.25 1.7 2 2.3 3 3.4 5.25 6.75 9 3 0 0.3 0.34 0.36 0.39 0.41 0.43 0.45 0.48 0.54 0.6 0.7 0.77 0.85 0.92 0.97 1.05 1.09 1.12 1.3 1.7 2 2.3 3 3.4 5.25 6.75 9 4 0 0.4 0.43 0.46 0.48 0.5 0.52 0.54 0.6 0.68 0.78 0.85 0.93 0.99 1.03 1.1 1.15 1.2 1.35 1.7 2 2.3 3 3.4 5.25 6.75 9 5 0 0.5 0.53 0.55 0.57 0.59 0.6 0.7 0.75 0.85 0.94 1 1.05 1.1 1.15 1.2 1.26 1.43 1.7 2 2.3 3 3.4 5.25 6.75 9 8 0 0.8 0.83 0.85 0.9 0.97 1.05 1.12 1.2 1.22 1.28 1.3 1.32 1.36 1.45 1.7 2 2.3 3 3.4 5.25 6.75 9 15 0 1.5 1.52 1.54 1.56 1.58 1.6 1.6 1.61 1.61 1.62 1.65 1.7 2 2.3 3 3.4 5.25 6.75 9

## Institute of Plumbing:

### Things to Consider

In some cases, the flow rate of a single fixture will exceed the flow rate provided by the probable simultaneous demand calculation.

For example, a birthing pool may have a flow rate of 1 L/sec but that will get diversified to < 1 L/sec. This means you need to be aware of the pipe sizing, velocity, and pressure loss calculations in that pipe would need to be reviewed with potential modifications made.

## Continuous Flow

Continuous flow rates are added to the probable simultaneous demand flow rates to get the total flow rate on a system:

Flow Rate = Probable Simultaneous Demand + Continuous Flow Rates

## Cold Water Pipes Supplying a Heated Water Plant

Where a cold water pipe supplies the cold water to fixtures and also the heated water plant that supplies the heated water to the same fixtures, the flow rate will usually take the largest of the two flow rates.​ However, in some instances, especially in the UK and US, it can be common to combine the loading units together which will allow for a fixtures hot and cold water taps to be used simultaneously.

## Volume Flow Rate

The volumetric flow rate is the volume of the water flowing through a cross-sectional area per unit of time. You would need to know a pipe size for the average volumetric flow rate formula (or to use a volumetric flow rate calculator).

## Mass Flow Rate

Where a cold water pipe supplies the cold water to fixtures and also the heated water plant that supplies the heated water to the same fixtures, the flow rate will usually take the largest of the two flow rates.​ However, in some instances, especially in the UK and US, it can be common to combine the loading units together which will allow for a fixtures hot and cold water taps to be used simultaneously.

Systems

Choose from cold water, hot water, warm water, or create your own

Parameters

Choose the material, spare capacity, maximum velocity, and minimum pipe size

Peak flow calculation method

Choose from the Australian, British, German, or the U.S. calculation methods

Plant

Add hot water, storage tanks, booster pumps, or create your own

Results

Pipe sizes, peak flow rates, flow velocity, pressure loss, and hot water return

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