HVAC Psychrometric Chart Practice Questions CIBSE Guide C - Key Points

CIBSE Guide C - Critical Reference Data

1. Design Weather Data (UK Focus)
Parameter Summer Winter
External Design Temp (°C) 28-30 (DB) -3 to -5 (DB)
Daily Range (K) 8-12 N/A
Solar Radiation (W/m²) 500-800 peak 100-200 peak
2. Internal Design Conditions
Space Type Winter (°C) Summer (°C) RH Range (%)
Offices 21 24 40-60
Retail 19 23 40-60
Hospitals 22 24 50-60
3. U-Values (Building Regulations)
Element Max U-Value (W/m²K)
Walls 0.28
Roofs 0.18
Floors 0.22
Windows 1.6
4. Ventilation Requirements
Space Air Changes (ACH) L/s per person
Offices 4-6 8-10
Classrooms 3-5 8-12
Toilets 6-10 N/A
5. Heat Gains - CIBSE Standard Values
Source W/m²
Occupants (sedentary) 60-70
Lighting (general office) 10-15
Equipment (PC workstation) 45-55
Small Power (office) 15-25
6. Pipe Sizing & Fluid Flow
Pressure drop (Pa/m) = 100 × (flow rate (l/s))1.85 / (pipe diameter (mm))4.87
Pipe Size (mm) Max Flow (l/s) Velocity (m/s)
15 0.25 1.0
22 0.50 1.2
28 1.00 1.5
7. Duct Sizing Principles
Duct Type Velocity (m/s) Pressure Drop (Pa/m)
Main ducts 5-7 0.8-1.5
Branch ducts 3-5 0.5-1.0
Terminal connections 2-3 0.3-0.6