Building Energy Efficiency, Codes and Standards
Energy questions test whether you know which requirement is a mandatory provision (强制性条文) and which is a design option. GB 55015-2021 sets the performance floor for new buildings; GB 50189-2015 gives detailed public-building requirements; both are read against the climate zone of the project.
Envelope
- Climate zones (severe cold, cold, hot summer cold winter, hot summer warm winter, temperate) carry different maximum U-values and SHGC. A heavily insulated wall is the requirement in Harbin; in Guangzhou shading and solar factor dominate.
- Window-to-wall ratio limits are set per orientation; larger glazing forces a trade-off calculation or a higher-performance window.
- Airtightness and thermal bridging are checked at junctions, not only in the wall schedule.
Systems
- Boiler nominal and part-load efficiency; chiller IPLV; pump and fan efficiency at design and part load.
- Heat recovery is required for large exhaust volumes - typically above 5000 m³/h where the building is heated or cooled for long periods; sensible-only recovery often suffices where latent loads are moderate.
- Variable-speed control on pumps and fans above a size threshold; insulation thickness by pipe diameter and fluid temperature.
- Economizer or free cooling where outdoor air enthalpy permits.
Worked example
A 20 m² facade, ΔT = 15 K, wall U = 0.45, window U = 2.2. At WWR 0.6: window 12 × 2.2 × 15 = 396 W; wall 8 × 0.45 × 15 = 54 W; total 450 W. At WWR 0.4: window 264 W; wall 81 W; total 345 W. Reducing glazing saves 105 W, about 23%, before any solar effect - and west-glass solar savings would be larger still. This is the arithmetic behind WWR limits.
Traps
Checking U-values while ignoring the WWR on which the limit depends; quoting one national insulation thickness for every zone; treating recommended practice as mandatory; forgetting that free cooling and heat recovery compete for the same duct space; and confusing the design standard (GB 50189) with the construction acceptance standard (GB 50243).