This standard provides guidelines and mathematical methods for estimating the thermal performance of building envelopes. It details the calculation procedures for overall thermal transmittance (U-value), thermal time lag, decrement factor, and solar heat gain to aid in energy-efficient architectural design and accurate HVAC load estimation.
Provides methods for calculating the thermal performance of buildings, aiding in energy efficiency design.
Quick Reference Values
Internal surface resistance (Rsi) for horizontal heat flow0.12 m²K/W (typical)
External surface resistance (Rso) for normal exposure0.05 m²K/W (typical)
Calculation of thermal resistance (R)Thickness / Thermal Conductivity (L/k)
Key Formulas
U = 1 / (Rsi + R1 + R2 + ... + Rso) — Overall thermal transmittance (U-value)
R = L / k — Thermal resistance of a single homogenous layer
q = U * A * (To - Ti) — Steady state heat transmission
Practical Notes
While this standard establishes foundational thermal physics calculations, modern projects should always cross-reference baseline requirements with the Energy Conservation Building Code (ECBC).
When referencing Table 1 for thermal conductivity (k-values), keep in mind that modern manufactured insulation and aerated concrete blocks may perform significantly better than the conservative 1978 baseline values.
Calculations for time lag and decrement factor are crucial for designing passively cooled buildings in tropical climates to utilize thermal mass effectively.