09/18/03
FINAL
Evaluating Rooftop and Vertical Gardens as an Adaptation Strategy for Urban Areas
Fall and Winter Performance Since the indoor temperature was kept higher than the outdoor temperature in the winter, the building usually lost heat through the roof as well as through the other parts of the building envelope. Snow cover had an insulating effect and reduced the heat loss through the roofing system during the winter months. The three curves in Figure 4.15 represent the heat flux recorded by the three HFT embedded in each roof section on December 3, 2000, a typical winter day when no snow was accumulated on the roof. Reference Roof
Rooftop Garden 40
40 R1 R2 R3
20 10 0
20 10 0 -10
-10
-20 0:00
-20 0:00
G1 G2 G3
30 Heat Flux (W/m2)
Heat Flux (W/m2)
30
3:00
6:00
9:00
12:00 15:00 18:00 21:00
0:00
3:00
6:00
9:00
12:00 15:00 18:00 21:00
0:00
Time
Time
Figure 4.15: The heat flow through the roofing systems on a cold fall day without snow coverage (December 3, 2000). The Reference Roof lost heat at a rate of 10W/m2 during early morning and late evening. However, the rate of heat loss decreased during the afternoon as the roof membrane absorbed the solar radiation. During the warmest part of the day, heat entered the building and resulted in positive heat flow for about 2h around noon. On the other hand, the Green Roof lost heat at a steady rate of about 7W/m2 throughout the day. This rate was steady and was not affected by solar radiation due to the insulation effect from the growing medium, which acted as an effective thermal mass to moderate the thermal performance of the roofing system. On January 18, 2001, a typical winter day with the roof covered under a heavy blanket of snow the building lost heat through both roof sections at essentially the same rate of 8W/m2 (Figure 4.16). The heavy snow coverage provided extra insulation to the roofing systems and reduced the heat flow through the roofs. This observation was consistent with the stable temperature profiles observed within the roofing systems during heavy snow coverage.
CCAF Report B1046
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