ASHRAE 90.2: Complete Guide to Energy-Efficient Design of Low-Rise Residential Buildings
Guide to ASHRAE 90.2 residential energy efficiency: building envelope U-factors, HVAC equipment efficiency, service water heating, lighting, and compliance methods.
ASHRAE 90.2: Complete Guide to Energy-Efficient Design of Low-Rise Residential Buildings
ASHRAE Standard 90.2 establishes minimum energy efficiency requirements for the design and construction of new low-rise residential buildings. This standard addresses the unique characteristics of residential construction, including diverse building types, owner-occupied operation, and varied climate conditions. Understanding ASHRAE 90.2 is essential for residential designers, builders, and code officials.
The standard addresses building envelope, HVAC systems, service water heating, and lighting. It provides prescriptive requirements and performance-based compliance options. This comprehensive guide covers all major sections, calculation methods, and practical applications.
Introduction to ASHRAE 90.2
Purpose and Scope
ASHRAE Standard 90.2 serves multiple functions:
Energy Efficiency:
- Minimum efficiency for residential buildings
- Energy cost reduction
- Environmental protection
- Resource conservation
Code Compliance:
- Residential energy code basis
- Building permit requirements
- Certification programs
- Utility programs
Design Guidance:
- System efficiency requirements
- Building envelope standards
- Equipment selection
- Design optimization
Scope
Applies to:
- Single-family detached
- Townhouses
- Low-rise multi-family (≤ 3 stories)
- Manufactured homes
- Modular homes
Building Envelope
Thermal Requirements
U-Factor Requirements by Climate Zone:
Zone | Ceiling | Wall | Floor | Fenestration |
|---|---|---|---|---|
1 | 0.044 | 0.082 | 0.064 | 1.20 |
2 | 0.044 | 0.082 | 0.064 | 1.20 |
3 | 0.030 | 0.057 | 0.051 | 0.75 |
4 | 0.030 | 0.057 | 0.051 | 0.65 |
5 | 0.026 | 0.051 | 0.038 | 0.50 |
6 | 0.026 | 0.051 | 0.038 | 0.50 |
7 | 0.026 | 0.043 | 0.033 | 0.40 |
8 | 0.026 | 0.043 | 0.033 | 0.40 |
Solar Heat Gain Coefficient:
- Climate Zones 1-3: Maximum 0.30
- Climate Zones 4-8: No maximum
Air Leakage
Building Air Leakage:
- Maximum: 0.30 cfm/ft² at 0.2 in. w.g.
- Blower door testing
- Documentation required
HVAC Systems
Equipment Efficiency
Air Conditioner Efficiency:
Minimum SEER by capacity:
Capacity | Minimum SEER | Notes |
|---|---|---|
< 45,000 Btu/h | 14.0 | Split systems |
≥ 45,000 Btu/h | 13.0 | Split systems |
Package units | 13.0 | All capacities |
Heat Pump Efficiency:
Minimum SEER/HSPF:
Type | SEER | HSPF | Notes |
|---|---|---|---|
Air-source | 14.0 | 8.2 | Split systems |
Package | 13.0 | 8.0 | Package units |
Furnace Efficiency:
Minimum AFUE:
Type | Minimum AFUE (%) | Notes |
|---|---|---|
Gas furnace | 80 | Standard |
Oil furnace | 82 | Standard |
Duct Systems
Duct Insulation:
- R-6 minimum (unconditioned spaces)
- R-8 (attics)
- Sealed ducts required
Duct Leakage:
- Maximum: 4 cfm per 100 ft²
- Testing required
- Sealing required
Service Water Heating
Equipment Efficiency
Water Heater Efficiency:
Minimum energy factor (EF):
Type | Capacity | Minimum EF | Notes |
|---|---|---|---|
Gas storage | < 20 gal | 0.59 | |
Gas storage | ≥ 20 gal | 0.62 | |
Electric storage | All | 0.90 | |
Heat pump | All | 2.0 |
Distribution Systems:
- Insulated pipes
- Recirculation controls
- Timer controls
Lighting
Lighting Power
Interior Lighting:
- Maximum: 1.2 W/ft² (13 W/m²)
- High-efficacy lamps required
- Controls required
Exterior Lighting:
- Maximum by application
- Automatic controls
- High-efficacy sources
Compliance Methods
Prescriptive Method
Meet all prescriptive requirements:
- Building envelope
- HVAC systems
- Service water heating
- Lighting
Performance Method
Energy cost budget or performance rating:
- Baseline building
- Proposed building
- Comparison and compliance
Best Practices
Design:
- Exceed minimums
- Optimize envelope
- High-efficiency systems
- Integrated design
Construction:
- Quality installation
- Proper sealing
- Testing and verification
- Documentation
Conclusion
ASHRAE Standard 90.2 provides comprehensive energy efficiency requirements for residential buildings. Key aspects include building envelope, HVAC systems, service water heating, and lighting requirements. By understanding and applying ASHRAE 90.2, designers and builders can create energy-efficient residential buildings.