Module 2 Activity 2

INSTRUCTIONS:

Complete the following set of technical instructions. Please make notes to reflect any issues you may encounter.

Basic Sprinkler calculations

When designing a sprinkler system only a certain amount of sprinklers are required to be readily available in the event of a fire. For example in a 10’ by 8’ room only a water supply for 6 sprinklers may be necessary. This is called the demand area.

How to calculate and draw the demand area on a sprinkler grid

In order to find the demand area for a light hazard office space one can follow the following procedure.

Important terms:

hydraulic demand area:

k factor:

branch line:

Using the given instructions find the demand area of the following example. The system has a given hydraulic demand area of 1500 ft2, a K factor of 5.6, and a layout shown in figure 1.

Figure 1. Basic Sprinkler Layout

1) Find coverage area per sprinkler. This is the distance between sprinkler heads (vertical distance between the circles in figure 1) times the distance between the sprinkler branch lines (horizontal distance between the lines in figure 1).

coverage area = distance between heads distance between branch lines

2) Find the number of sprinklers by dividing demand area by sprinkler coverage.

#sprinklers = hydraulic demand areasprinkler coverage

a) Always round up when calculating the number of sprinklers to have conservative final calculations.

3) Find the number of sprinklers per branch line. This is given by the length of the demand area (vertical distance in figure 1) divided by the distance between sprinkler heads.

Note: Given a hydraulic demand area, one can take the square root to represent the length of the demand area (given the area is square in shape).

# of sprinklers per branch line =demand lengthdistance between heads

a) Again, round conservatively,

4) The total number of sprinklers and the number of sprinklers per branch line have now been calculated. To outline the demand area in the given sprinkler follow the following procedure:

i) Identify the sprinkler farthest from the water supply (shown by an x inside a circle) and branch line.

ii) Starting at the farthest sprinkler, count towards the main sprinkler line. Once the number of sprinklers per line is reached, stop.

iii) The first branch line sprinklers has been sectioned off, now move to the next branch line closer to the water supply. Start at the farthest sprinkler from the branch line and redo step ii. Continue this process until the number of sprinklers left is smaller than the number of sprinklers per branch line.

iv) When the number of sprinklers left is less than the number of sprinklers per branch line, start at the sprinkler closest to the branch line and count away from the branch line until there are no sprinklers left.

v) The sprinklers that were sectioned off will be the demand area.

Answer

If the total number of sprinklers allocated is 9, the final demand area will look something like this:

For more information reference NFPA 13 (2013 edition)