Thermal implications of radiant roof barriers:

A field study in a hot and humid climate

V. Müller, U. Pont, P.H. Tan & A. Mahdavi

Department of Building Physics & Building Ecology

Vienna University of Technology

Title - 1/15

Content:

• Introduction

• Overview || Climate || Research Questions || Literature

• Approach

• Test Cells||Radiant Roof Barriers ||Ventilation || Rounds ||Monitoring ||

• Results & Discussion• Results & Discussion

• Temperatures

• Data distribution || PMV & PPD

• Conclusion

ToC - 2/15

Introduction:

• radiant roof barriers impact on thermal performance of test buildings

Climate:

• Malaysia: hot-humid tropical climate

Introduction - 3/15

• Malaysia: hot-humid tropical climate

Buildings:

• Traditional: light weight wooden

structures (low thermal mass)

• Modern: more and more brick

buildings

• Natural ventilation during night

• Massive use of A/C s…

Literature:

Research Questions:

• Do minor changes in the roof design of test-buildings (roof tiles, layer construction

influence the heat flow to the room(s) below)

• Does the application of radiant roof barriers and counter batten air spaces change the

thermal behavior of the indoor climate?

• Miller et al. (2010): Solar Reflectance Index for different materials and combinations

• Suehrcke et al. (2008): Clay vs cement tiles (in Australia) – no significant differences

concerning heat gains.

• Michels et al. (2008): Radiant barriers as reduction method against solar heat up

• Vandewater (2007): CFD study of the effect of counter-batten systems

Literature /Research Questions- 4/15

Test-Cells:

• Three per-se identical, free-standing test cells („A“, „B“

& „C“)

• 3x3 m floor area, 3.6 m room height

• 110 mm brick/mortar, ceiling insulated with 50 mm EPS

Approach – Test-Cells - 5/15

Test-Cells:

Approach – Test-Cells - 6/15

Test-Cells („A“ and „B“):

Approach – Test-Cells - 7/15

Test-Cells set up:

• 4 rounds (7 days monitoring

each)

• Increasing ventilation (in roof

space)

• Constant ventilation regime in • Constant ventilation regime in

room below.

Approach – Test-Cells - 8/15

Test-Cells set up:

Approach – Test-Cells - 9/15

Results (exemplaric for Round 1 – no ventilation in the roof):

Results- 10/15

Results (exemplaric for Round 4 – max. ventilation in the roof):

Results- 11/15

Results PMV/PPD / Data - Distribution

Results- 12/15

Day Night

„Comfort Zone“ 22-27 °C

Results PMV/PPD / Data - Distribution

Results- 13/15

Percentage of time with a PMV

between +1 and -1

Conclusion:

• Attic spaces with very low ventilation: Radiant roof barriers

showed a slight positive effect

• With increased ventilation, this effect disappears (test cells

without radiant roof barriers performed better)

• Clay vs cement: Clay test cell performed slighly better• Clay vs cement: Clay test cell performed slighly better

• Application of radiant roof barrier systems should be evaluated

case by case.

• Radiant Roof barriers in very good ventilated roofs might be

counterproductive, as night-time radian cooling is diminished.

Conclusion- 14/15

Thank you for your attention!