Fig. 1 shows the meteorological conditions during the test period. On fair days from September 3 — 6, the amount of solar radiation exceeded 800W/m2 and the daytime highest temperature passed 30°C. On September 3, a 5mm rainfall was recorded between 16:00 and 17:00. Using the actual measured data of September 3 (the highest temp: 34.5°C) and September 4 after a rainfall, we examined the cooling effect for each Case.

Fig. 2(a) shows the change in the rooftop surface temperature Ti in Case 1~5. Although a cooling effect on the surface temperature of several degrees was observed immediately after sprinkling in Case 2~5, the effect was temporary. Fig. 3 shows the time change in the surface temperature immediately before and after sprinkling. The change was proportional to the solar radiation at the time of sprinkling in the order of Morning (sprinkling) < Evening < Noon. On the other hand, the duration of the continuous effect was longer in the order of Noon (sprinkling) < Evening < Morning. The duration is normally two hours or less with this kind of sprinkling. Thus, to expect a continuous effect during daytime, one needs to use water-permeable materials.

The decrease in the upper test piece temperature (Tii) can contribute to a reduction in the convective sensible heat on the atmosphere. Thus, by comparing the upper test piece temperature (Tii) to the rooftop surface temperature, we regarded the surface temperature difference as the cooling effect on the atmosphere. Fig.2(b) shows the change in the surface temperature and the upper test piece temperature in Case 6~9. First, the temperature difference ДТ was compared

Spnnkimg Spunking

Outdoor air temperature

Horizontal global solar radiation ”

Outdoor air temperature

Horizontal global solarradiation “

Precipitation

Precipitation

Date, Time- fa) Surface temperature of the Rooftop (T^i

Spunking Sprinkling

Date, Time

Case 10

Case6

Outdoor air temperature ‘Precipitation

Horizontal global solarradration ~

(b) Top temperature of exeprimentalbodies (Tn)

Date, Time

(c) Bottom temperature of experimental bodies (Тш)

Fig.2 Temperature change of outdoor air, surface temperature of rooftop, top&bottom temperature of the test pieces

Fig.3 Lapse time of cooling effect after sprinkling.

between T| in Case 1 and Tn in other Cases. Case 6, 8 showed a low surface temperature in the afternoon in comparison to Case 1. Meanwhile, Case 7, 9 showed a large decrease in the surface temperature towards the middle of the day. AT reached its maximum before and after 14:00 when the highest daytime temperature occurred, recording -5.3°C in Case 6, -12.9°C in Case 7, -5.2°C in Case 8 and — 9.1°C in Case 9. After sunset, the differences between Case 6~9 were very small. By 5:00 when the lowest daytime temperature occurred, AT were somewhere around -2.5°C in all Cases. Next, from the temperature difference AT in TII

between Case 6,7 and Case 8,9, the effects of water content and white-paint coating were examined. In the comparison of surface temperature between the cases of water-permeable tiles with and without water content, a maximum temperature difference of 8.9°C was recorded. Comparing the cases with or without a white-paint coating, the maximum temperature difference was 7.4°C. On September 4, there was no major difference in the surface temperature during daytime in Case 6,7. This was presumably because the amount of water content had been recovered to a great extent in both Cases because of the rainfall on the evening of September 3. Thus, it became clear that, when using water-permeable materials, the cooling effect for the next day and later could be expected not only from human-induced sprinkling but also from natural precipitation in a temperate climate region.

20

□ 2Т, Д зт о 4Т, 0 5Т, ♦ 6ТП • 7Т„ ■ 8ТП ▲ ОТ о 6ТШ О 7Тп. □ 8ТШ д етш X ютш

^G4 : Decrease of temperature on indoor is expected from the cooling effect of 3°C or more on the rooftop surface, mainly during the daytime

G3: Decrease of temperature on atmosphere is expected from the cooling effect of 8°С or more during the daytime, 4°С during the nighttime on the roof­top surface

.G2: Decrease of temperature on f ♦atmosphere is expected from vJJL* the cooling effect of 3-4°C throughout the day on the rooftop surface _G1: Decrease of temperature on atmosphere and indoor is not ex­pected

16 —

□ $

12

S 8 — f, <

CX /

The lower test piece temperature (TIM) in each Case is believed to contribute to the overall heat transfer into the room while, as a boundary condition for the rooftop slab, having a time delay due to the heat transmission of the rooftop slab. Therefore, by comparing the lower test piece temperature (Tm) to the rooftop surface temperature in Case1, we regarded the surface temperature difference as an index for the cooling effect on the indoor side. Fig. 2(c) shows the change in the surface temperature and the lower test piece temperature in Case 1 and Case 6~9. As a general trend, the daily change in Tm in each Case was observed to be 1~3 hours late in comparison to the change in the amount of solar radiation. Looking at Ti in Case 1 and AT, the temperature difference in Tiii in other Cases, the difference was almost none at night. Yet, a relatively large cooling effect was obtained towards the middle of the day in Case 6~10. AT reached its maximum around 14:00 when the daytime temperature became maximum, recording (a) -20.3°C in Case 7, (b) -13.8~-

15.1 °C in Case 6, 8 and 9 and (c) -9.5°C in Case 10. (a) In the Case 7 in which the greatest effect was observed, TIII was controlled in correspondence to the air temperature, blocking off most of the radiation heat. As with the change in TII in Fig.2(b), such effect lasted until September 4 because of natural precipitation. (b) The effects in Case 6, 8 and 9 are believed to stem mainly from the heat capacity and heat resistance of the test piece. In the case of the lower test piece temperature, the difference with or without a white-paint coating was about 1.3°C maximum, not a very large number. The reason was that the test was conducted under weak wind conditions that day; thus, the effect of removing heat from the radiation by the ventilation of perforated bricks turned out to be small. (c) In the case of artificial turf, though the cooling effect on the atmosphere could not obtained, that on the indoor side was expected.

12 ,[°C]

16

20

A T

ghttir

A : Temperature difference during the daytime A T lljim: Temperature difference during the nigthtime daytime: 2003/09/03 10:00-15:00 nighttime: 2003/09/04 22:00-2003/09/05 3:00

Fig.4 Cooing effects during the daytime and the nighttime.

In Fig.4, based on the discussion results in above, we obtained the difference between TI in Case 1 and TII, TIII in other Cases and then grouped the decreases in surface temperature by day and night. In G1 (Case 2~5), the decrease in the surface temperature was 1 °C or lower all day long; a cooling effect on the atmosphere and the indoor side cannot be expected much. In G2 (Case 6, 8) and G3 (Case 7, 9), the decrease in the surface temperature of 3

~4°C was observed all day; a reduction in the heat load in the atmosphere can be expected. Especially in G3, the surface temperature dropped by more than 8°C during daytime. In G4 (Case 6~10), a decrease of 8°C or higher in the daytime surface temperature was observed; a cooling effect on the indoor side can be expected.

One can deduce from those analysis results: Case 6~10 are effective in reducing the air­conditioning load during daytime; Case 7, 9 are effective in inhibiting the heat island phenomenon during daytime; and Case 6~9 are effective in preventing tropical nights.