ASHRAE vs GB vs SHASE: Heating Load Standards Comparison
A side-by-side comparison of heating load calculation parameters from ASHRAE 90.1 (USA), GB 50736 (China), and SHASE-S 101 (Japan). Understand how U-values, infiltration rates, orientation factors, and radiator outputs vary across the three major HVAC standards.
Overview
Heating load calculation is the foundation of any HVAC system design. Three dominant standards govern heating load calculations globally: ASHRAE 90.1 used in North America, GB 50736 used in China, and SHASE-S 101 used in Japan. While all three follow the same fundamental heat balance principles, they differ significantly in specific parameter values based on regional climate conditions, construction practices, and energy policy goals.
ASHRAE standards are developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers and are widely adopted internationally. GB 50736 is the Chinese national standard for heating, ventilation and air conditioning design. SHASE-S 101 is published by the Society of Heating, Air-Conditioning and Sanitary Engineers of Japan and aligns with Japan's ZEH (Zero Energy House) and HEAT20 G2 energy targets.
Parameter Comparison
| Parameter | ASHRAE | GB 50736 | SHASE-S 101 |
|---|---|---|---|
| Wall U-value — poor insulation | 1.80 W/(m²·K) | 1.50 W/(m²·K) | 1.80 W/(m²·K) |
| Wall U-value — average insulation | 0.60 W/(m²·K) | 0.80 W/(m²·K) | 0.55 W/(m²·K) |
| Wall U-value — good insulation | 0.38 W/(m²·K) | 0.45 W/(m²·K) | 0.35 W/(m²·K) |
| Wall U-value — excellent insulation | 0.22 W/(m²·K) | 0.25 W/(m²·K) | 0.20 W/(m²·K) |
| Infiltration — residential | 0.35 ACH | 0.5 ACH | 0.35 ACH |
| Infiltration — commercial | 0.6 ACH | 0.8 ACH | 0.6 ACH |
| Orientation factor — south | 0.80 | 0.80 | 0.80 |
| Radiator output (standard section) | 150 W/section | 140 W/section | 150 W/section |
| Building energy target | ASHRAE 90.1 | 65-75% saving | ZEH / HEAT20 G2 |
Formula Differences
All three standards use the basic heat loss formula Q = U × A × ΔT for envelope transmission losses and Qinf = 0.5 × ACH × V × ρ × cp × ΔT for infiltration losses. However, the reference outdoor design temperatures differ significantly: ASHRAE uses the 99.6% design temperature, GB 50736 uses the average temperature of the coldest five days, and SHASE-S 101 uses region-specific design temperatures based on Japanese climate zones.
ASHRAE applies separate heating and cooling load calculation procedures (Heat Balance method or Radiant Time Series method), while GB 50736 uses a simplified steady-state method for heating with a single heat transfer coefficient that accounts for both transmission and infiltration. SHASE-S 101 follows a detailed hourly calculation method with dynamic thermal behavior for high-performance buildings.
Design Impact Analysis
The differences in U-value assumptions directly affect insulation thickness requirements. For average insulation, designing to ASHRAE (0.60 W/m²K) or SHASE (0.55 W/m²K) requires approximately 25-30% more insulation than GB 50736 (0.80 W/m²K). This translates to higher material costs but lower operational energy consumption.
Infiltration assumptions have a major impact on heating load. GB 50736's higher infiltration rates (0.5 ACH residential) result in approximately 40% higher infiltration loads compared to ASHRAE and SHASE. This can lead to oversized equipment if not carefully accounted for. Designers working across multiple standards should adjust airtightness specifications and ventilation heat recovery strategies accordingly.
Regional Applicability
ASHRAE is the standard of choice in North America and many countries following US-based building codes. It is well-suited for cold climates (Zone 5-7) with robust insulation practices. GB 50736 applies primarily in China across five climate zones from severe cold to hot summer/warm winter. It is legally mandated for all building HVAC design in China. SHASE-S 101 is used in Japan and aligns with Japanese building energy codes that target net-zero energy performance by 2030. It is especially relevant for high-performance residential and commercial buildings in temperate and subtropical climates.
Frequently Asked Questions
Which standard has the strictest wall U-value requirement?
SHASE-S 101 specifies the lowest wall U-value at 0.20 W/(m²·K) for excellent insulation, followed closely by ASHRAE at 0.22 W/(m²·K) and GB 50736 at 0.25 W/(m²·K). For average insulation, ASHRAE is the strictest at 0.60 W/(m²·K).
How do infiltration ACH values differ between standards?
ASHRAE and SHASE-S 101 both recommend 0.35 ACH for residential buildings and 0.6 ACH for commercial buildings, while GB 50736 uses higher values of 0.5 ACH residential and 0.8 ACH commercial, reflecting different climate assumptions and construction practices.
What radiator output does each standard specify?
ASHRAE and SHASE-S 101 both specify 150 W per section for standard column radiators, while GB 50736 specifies 140 W per section under the GB/T 13754 reference conditions at ΔT = 64.5 K.
What are the building energy targets for each standard?
ASHRAE references ASHRAE 90.1 as the minimum energy standard. GB 50736 targets 65-75% energy savings compared to baseline. SHASE-S 101 aligns with ZEH (Zero Energy House) and HEAT20 G2 levels for high-performance buildings.
Do orientation factors differ between ASHRAE, GB, and SHASE?
All three standards use an identical south orientation factor of 0.80 for heating load calculations. Minor differences may appear for other orientations, but the south-facing reduction is universally accepted.