Abstract
The overall U-factor values for an attic assembly are usually computed with the ANSI/ASHRAE/IES based R-value (thermal resistance) conversion. In the ANSI/ASHRAE/IES Standard 90.1 (2010), the effects of attic air resistance, roof pitch and attic width are not taken into account while calculating the U-Factor values. In addition, the R-value is estimated using a one dimensional thermal resistance model. In ventilated attics, where the insulation near the roof sheathing is tapered, it is difficult to find the correct R-value of the attic system as the heat transfer becomes two dimensional. In this paper, a 2-dimensional CFD model is developed for various insulation R-values and insulation taper angles near roof decks. COMSOL Multiphysics 4.4 is used to model and analyse the attic structure. Results show that a discrepancy in overall U-factor for entire attic assembly between the developed model and the existing standard estimation. These results are pronounced for lower slope roofs with high insulation thickness.
| Original language | English |
|---|---|
| Pages (from-to) | 3198-3203 |
| Number of pages | 6 |
| Journal | Energy Procedia |
| Volume | 78 |
| DOIs | |
| State | Published - Nov 1 2015 |
| Externally published | Yes |
| Event | 6th International Building Physics Conference, IBPC 2015 - Torino, Italy Duration: Jun 14 2015 → Jun 17 2015 |
Keywords
- Heat flux
- Insulation
- R value
- Taper angle
- U value
- Ventilation