🚿Plumbing and Water System Design
Residential Water Systems
Fixture Flow Rates
Kitchen Sink: 1.5-2.5 GPM (5.7-9.5 L/min)
Bathroom Faucet: 0.5-1.5 GPM (1.9-5.7 L/min)
Shower Head: 1.5-2.5 GPM (5.7-9.5 L/min)
Toilet Fill: 3-5 GPM (11-19 L/min)
Washing Machine: 4-6 GPM (15-23 L/min)
Total demand: 15-25 GPM typical home
Pipe Sizing Guidelines
1/2" pipe: Up to 4 GPM (15 L/min)
3/4" pipe: Up to 10 GPM (38 L/min)
1" pipe: Up to 18 GPM (68 L/min)
1-1/4" pipe: Up to 28 GPM (106 L/min)
1-1/2" pipe: Up to 40 GPM (151 L/min)
Velocity should be 5-8 ft/s (1.5-2.4 m/s)
Irrigation System Design
Sprinkler Zone Calculations
Zone area: 5,000 sq ft lawn
Precipitation rate: 1 inch/hour desired
Flow required: 5,000 ft² × 1"/hr × 0.623 = 3,115 GPH
In GPM: 3,115 ÷ 60 = 52 GPM
In L/min: 52 × 3.785 = 197 L/min
12 sprinklers @ 4.3 GPM each
Drip Irrigation
Emitter flow rate: 2 GPH (0.126 L/min)
Plant spacing: 2 feet
100-foot row: 50 emitters
Total flow: 50 × 2 = 100 GPH
In GPM: 100 ÷ 60 = 1.67 GPM
Very low flow, high efficiency
🏢HVAC System Applications
Air Handler Sizing
Office Building Example
Floor area: 10,000 sq ft
Cooling load: 3.5 tons/1000 sq ft
Total cooling: 35 tons
CFM required: 35 × 400 = 14,000 CFM
In m³/hr: 14,000 × 1.7 = 23,800 m³/hr
Air handler: 15,000 CFM capacity
Duct Sizing
Main supply: 14,000 CFM
Duct velocity: 1,500 ft/min (7.6 m/s)
Required area: 14,000 ÷ 1,500 = 9.3 sq ft
Round duct: 42" diameter
Rectangular: 36" × 48"
Use 42" round or 36×48 rectangular
Chiller Plant Design
Chilled Water Flow
Chiller capacity: 500 tons
Temperature rise: 10°F (5.6°C)
Flow rate: 500 × 24 ÷ 10 = 1,200 GPM
In L/min: 1,200 × 3.785 = 4,542 L/min
In m³/hr: 4,542 × 0.06 = 272.5 m³/hr
Primary pump: 1,200 GPM @ 60 ft head
Condenser Water System
Heat rejection: 500 × 15,000 = 7.5M BTU/hr
Cooling tower range: 10°F
Flow rate: 7.5M ÷ (500 × 10) = 1,500 GPM
In L/min: 1,500 × 3.785 = 5,678 L/min
Tower capacity: 625 tons (500 × 1.25)
Condenser pump: 1,500 GPM @ 80 ft head
🏭Industrial Flow Applications
Process Water Systems
Cooling Water Circuit
Heat exchanger duty: 10M BTU/hr
Temperature rise: 15°F
Required flow: 10M ÷ (500 × 15) = 1,333 GPM
In L/min: 1,333 × 3.785 = 5,047 L/min
Pipe size: 12" (velocity = 6.8 ft/s)
Pump: 1,400 GPM @ 120 ft head
Chemical Feed System
Main flow: 5,000 GPM
Chemical dose: 10 ppm
Solution strength: 1% (10,000 ppm)
Feed rate: 5,000 × 10 ÷ 10,000 = 5 GPM
In L/min: 5 × 3.785 = 18.9 L/min
Metering pump: 5 GPM @ 100 psi
Gas Flow Applications
Compressed Air System
Plant demand: 2,000 SCFM @ 100 psig
Compressor efficiency: 85%
Required capacity: 2,000 ÷ 0.85 = 2,353 SCFM
Power required: 2,353 ÷ 4 = 588 hp
In kW: 588 × 0.746 = 439 kW
Install 600 hp compressor
Natural Gas Burner
Boiler input: 50M BTU/hr
Gas heating value: 1,000 BTU/ft³
Required flow: 50M ÷ 1,000 = 50,000 ft³/hr
In SCFH: 50,000 SCFH
In L/hr: 50,000 × 28.32 = 1.42M L/hr
Gas train: 2" line @ 5 psig
📏Flow Measurement Methods
Primary Flow Elements
Orifice Plates
Accuracy: ±0.5-2%
Pressure loss: 40-90%
Beta ratio: 0.2-0.75
Applications: Clean fluids
Low cost, high pressure drop
Venturi Meters
Accuracy: ±0.25-1%
Pressure loss: 5-20%
Beta ratio: 0.3-0.75
Applications: High flow rates
High accuracy, low pressure drop
Ultrasonic Meters
Accuracy: ±0.5-2%
Pressure loss: None
Installation: Clamp-on available
Applications: Large pipes
No pressure drop, non-invasive
Flow Measurement Calculations
Orifice Flow Rate
8" pipe, 6" orifice, ΔP = 25" H₂O
Beta ratio: β = 6/8 = 0.75
Discharge coefficient: Cd = 0.61
Flow area: A = π(3")² = 28.3 in²
Q = 6.24 × Cd × A × √(ΔP) = 6.24 × 0.61 × 28.3 × 5 = 538 GPM
Measured flow: 538 GPM
Pitot Tube Velocity
Velocity pressure: 0.5" H₂O
Air density: 0.075 lb/ft³
Velocity: V = 4005 × √(VP/ρ)
V = 4005 × √(0.5/0.075) = 4005 × 2.58 = 10,333 ft/min
In ft/s: 10,333 ÷ 60 = 172 ft/s
Air velocity: 172 ft/s
💡Flow Rate Conversion Tips
Common Conversion Factors
Liquid Flow
1 GPM = 3.785 L/min = 0.227 m³/hr
1 L/min = 0.264 GPM = 0.06 m³/hr
1 m³/hr = 4.4 GPM = 16.67 L/min
Gas Flow
1 CFM = 1.7 m³/hr = 28.32 L/min
1 m³/hr = 0.588 CFM = 16.67 L/min
1 SCFH = 0.0283 Nm³/hr
Design Rules of Thumb
Pipe Velocities
Water (suction): 3-6 ft/s (0.9-1.8 m/s)
Water (discharge): 6-12 ft/s (1.8-3.7 m/s)
Air (low pressure): 1000-3000 ft/min
Air (high pressure): 3000-6000 ft/min
HVAC Guidelines
Cooling: 400 CFM/ton (3.3 m³/hr/kW)
Chilled water: 2.4 GPM/ton (0.043 L/s/kW)
Fresh air: 15-20 CFM/person office
Exhaust air: 0.5-1.0 CFM/ft² general