HVAC Psychrometric Chart Practice Questions Sprinkler System Design: Spacing & Pipe Sizing

Sprinkler System Design

Spacing, Arrangement, Location, and Pipe Sizing

Based on BS EN 12845:2004 Standards

High-Rise Office Building Case Study

This analysis covers sprinkler spacing, arrangement, location, and pipe sizing according to BS EN 12845:2004 standards for Block 6.
Sprinkler Spacing Requirements

Sprinkler spacing was determined according to design criteria with maximum coverage area per sprinkler of 12m².

Maximum coverage area per sprinkler: 12m²
Total floor area: 757.47m²
Minimum sprinklers required: 757.47m² ÷ 12m² = 63.1 → 64 sprinklers

Actual number of sprinklers installed: 100 (>64 minimum required)

Placement Considerations

Sprinkler placement considered multiple factors:

  • Sprinkler spacing requirements
  • Constructional features (walls, columns)
  • Architectural features (ceiling layout)
  • Beam layout and depths
Both pendant and upright sprinklers were used based on ceiling conditions

Deflector Positioning Relative to Beams

Upright sprinkler deflector positions were determined based on beam height and slab thickness:

Beam Height (mm) Slab Thickness (mm) Min. Horizontal Distance (X) (mm) Vertical Distance (Y) (mm)
750 200 1450 +100
750 150 1650 +150
700 200 1100 +50
700 150 1450 +100
650 200 200 0
650 150 1100 +50
500 200/150 Can install below beam underside (no effect)
Engineering Standard: Deflector positioning follows beam geometry to ensure proper water distribution

Pipe Sizing Methodology

Riser, Arm & Drop Pipes

Pipes connecting to single sprinklers sized at 25mm diameter:

25mm × 15mm reducers used to connect to sprinklers
Standard Reference: BS EN 12845:2004, Table 36 (20mm allowed for ordinary hazard with k factor ≤80)
Range Pipe Sizing

Pre-calculated tables from BS EN 12845:2004 used for range pipes:

Pipe Type Diameter (mm) Max Sprinklers
Last range pipe 25 2
Last range pipe 32 3
Last range pipe 40 4
Last range pipe 50 9
Other range pipes 25 3
Other range pipes 32 4
Other range pipes 40 6
Other range pipes 50 9

Design Points & Distribution Pipes

Design Points

Design points located where maximum number of sprinklers fed by a distribution pipe becomes 18 (per Table 26 of BS EN 12845:2004)

Floor Number of Design Points
LL3 21
LL2, LL1 19 each
GF, 3F, 5F 13 each
1F, 2F, 4F 12 each
6F 10
Distribution Pipe Sizing

Different approaches for downstream and upstream of design points:

Downstream of Design Points

Sized using pre-calculated tables:

  • 32mm → 3 sprinklers
  • 40mm → 6 sprinklers
  • 50mm → 9 sprinklers
  • 65mm → 18 sprinklers
Upstream of Design Points

Sized using hydraulic calculations:

  • Max friction loss: 0.5 bar at 1000 L/min
  • Static head gain considered for lower elevations
  • Pipe Frictional Loss ≤ 0.5 bar + Static Head Gain
Objective: Achieve equal pressure loss (static head + pipe friction) to each design point
Standard Reference: BS EN 12845:2004, Sub-clauses 4.4.3.2 and 13.3.4.3

Engineering Design Strategy

Hydraulic Balance Approach
  • Upper floors: Larger pipe diameters (DN150, 100mm) to reduce friction losses
  • Lower floors: Smaller pipe diameters (DN65, 80mm) as static heads are smaller
  • Compensates for different static pressures at various elevations
Design Methodology
  • Pre-calculated tables used where possible
  • Hydraulic calculations for upstream distribution pipes
  • Most remote design point considered first in sizing
  • Sub-distribution pipes sized to achieve required pressure drop
This approach ensures adequate water flow and pressure to all sprinklers while optimizing pipe sizes throughout the system.
Design Documentation

Critical documentation for sprinkler system design:

Sprinkler Layout Diagrams Pipe Sizing Calculations Hydraulic Calculations Design Point Analysis Beam Clearance Documentation Pressure Loss Calculations