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TDS 7 : Interpreting the FHC report

 

TDS 7 : Interpreting the FHC report


 

This technical data sheet provides information on how to interpret the FHC hydraulic calculation report and each item of information.  The report is divided into three sections:

1.The first page provides an overall summary of the project (project data and design parameters)

2.Operating sprinkler heads, nozzles and hydrant

3.Hydraulically significant pipes

The hydraulic calculation report should provide a permanent record for the calculation and is suitable for submitting to the authority having jurisdiction (AHJ).

Project data and design parameters

The project data and design parameters is the first page of the report provides a summary of the calculation. Most of this information is for reference and does not influence the calculation such as the project name, drawing numbers and designers reference to take a few examples

Some other information which we have numbered will influence the hydraulic calculation and should be selected carefully.

Key

Description

1.

FHC will consider any design authority requirements so careful selection is important.

2.

The discharge density sometimes known as design density is the minimum amount of water required the design area.

3.

Assumed maximum area of operation

4.

The number sprinklers which have been selected to operate in this calculation.

5.

The pressure loss formula which has been used.

6.

The pipe data table which has been used for the calculation

Depending on the type of system which has calculated to which fields are important.  For instance, for water mist systems or fire hydrant design the design density may not be applicable. 

 

Operating sprinkler heads, nozzles and hydrant

This section details each sprinkler head nozzle or hydrant which is operated in the calculation as below:

For simplicity, we will only talk about a nozzle but this can be a fire sprinkler, water mist or other output device where we have a known K-factor (metric value).

Key

Description

1.

The K-factor (metric – (L/min)/Bar0.5) for the nozzle or other output device.

2.

The actual flow from the operating nozzle in L/min

3.

The area operating nozzle is covering in m2

4.

The minimum required design density and the actual design density from the nozzle. This is calculated from the area (3) and the flow (2) for the nozzle. In some systems such as water mist these columns may be empty as they are not required.

5.

The minimum nozzle pressure and the actual pressure for the nozzle under consideration.  You must always specify a minimum nozzle pressure.

6.

The height source node for the nozzle

Hydrants or hose stream allowance is will also be shown as a output device on this report and will only specify a flow rate.  Dependent on the type of system to which columns will have data entered but as a minimum you must have a K-factor and a minimum nozzle pressure.

 

Hydraulically significant pipes

In this section, each pipe which is hydraulically significant is represented that is pipe in the hydraulic model which has water flowing. 

Each pipe in the system is represented with a start and end node.

The following lists, the significant information which is provided for each pipe in the system.

Key

Description

1.

Is the internal diameter of the pipe

2.

The C-factor for the pipe represents the pipe roughness coefficient which is used in the Hayes and Williams pressure loss formula

3.

The flow within the pipe in litres per minute

4.

The water velocity in the pipe in metres per second

5.

The length of the pipe in metres

6.

The total hydraulic length of the pipe this is the actual length of pipe (5) plus the equivalent length of any fittings and valves (6)

7.

The pressure loss in millibars per metre

8.

Pressure at the start node in Bar

9.

Pressure at the end node in Bar

10.

The total pressure loss in the pipe in Bar, this is the start pressure (9) less the end pressure (10). 

11.

The pressure loss or gain due to change in elevation in Bar

12.

The pressure loss in the pipe due friction.  Calculated using the pressure loss formula specified on the header page.

If we now consider the first pipe in the system which is represented by node number 100 – 210

This pipe is a vertical rise 1.5 m in length, it has a gate valve and the internal diameter is 105.14mm.  The pressure at node 100 is 1.951 Bar and the pressure at node 110 is 1.802 Bar.  As the pipe is vertical we have the static gain of 1.5m x 0.098 = 0.147 Bar and the pressure loss in the pipe is 0.002 Bar.  Therefore, the total loss in this pipe is the pressure loss due to friction plus the pressure required to overcome the difference in height this is equal to 0.147 + 0.002 = 0.149 Bar.

We can also determine this by subtracting the start pressure from end pressure in this case 1.951 – 1.802 = 0.149 Bar.

 

 


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