2. LITERATURE REVIEW
3.3 Results
3.3.3 Stratification of internal microclimate conditions
Figure 3.8 shows the hourly mean temperatures and relative humidity at different positions inside the tunnels. The positions were selected to represent the vertical and horizontal profiles of temperature and relative humidity along the centre of the greenhouses and allowed the investigation of the stratification and microclimate distribution inside the tunnels
Figure 3.8 shows that there was more variation in temperature and relative humidity throughout the observation period during the daytime than at night, in both the NVT and the FPVT. The daytime and night-time temperatures and relative humidity at the different positions were significantly different (P<0.001) in both tunnels. The highest temperature and relative humidity differences were observed at midday, when solar radiation was at its highest. However, in October and November, there were no significant differences (P>0.05) in the night-time temperature between the lower and upper levels in the NVT.
Inside the FPVT, the air temperature was significantly (P<0.001) lower at the pad section and highest at the fan section, on both the lower and the upper levels, as shown in Figures 3.8b, 3.8d, 3.8f and 3.8h. The horizontal difference was significantly (P<0.001) higher at the upper than at the lower level. The highest temperature differences were observed in October (Figure 3.8b). The highest horizontal temperature difference between the pad and fan sections was 7.97°C and 4.25°C at the upper and lower levels, respectively. At the upper level, the highest temperature difference between the pad and the fan was in October. The highest vertical temperature difference between the upper and lower levels was 7.43°C.
The daytime relative humidity in the FPVT was significantly higher (P<0.01) at the pad section than at the middle and fan sections. The air humidity level was also significantly higher at the lower level than at the upper level. The highest relative humidity level was at the lower pad section and was lowest at the upper fan section. As in the NVT, the air humidity was significantly higher at the lower level than the upper level. There were smaller differences in the relative humidity between the recording points at the lower level in the NVT. At the upper level, the relative humidity was significantly higher (P<0.01) at the east- end than the middle and west-end of the NVT.
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Inside the NVT, the temperature differences were significantly higher (P<0.001) at the upper level than at the lower level in all months, except in December. The highest temperature difference between the upper and the lower levels was 5.78°C in November. There were also significant (P<0.01) differences between Positions 1, 2 and 3. At the upper level, the air temperature was highest at the west end (Position 1) and lowest at the east-end (Position 3) of the tunnel. At the lower level, the air temperature was lowest at the east end of the tunnel in all months except October. During the months of November, December and January, the temperature in the middle of the tunnel was at the same level as the west-end of the tunnel.
Similarly, there were significant differences (P<0.01) in the night-time air temperatures and air humidity levels at the various positions inside both tunnels. The air temperatures were significantly lower (P<0.001) at the upper levels (2.3 m from the floor) than at lower levels (1.15 m above the floor) inside the FPVT. Similarly, the air temperature was significantly (P<0.001) higher at the middle section than the pad and fan sections. Similarly, the upper level in the NVT was significantly (P<0.001) cooler than the lower level, except in November and December. The lowest temperatures were at the upper east-end and the highest temperatures were at the lower middle section.
The night-time relative humidity levels were significantly (P<0.01) higher at the upper than the lower level in the FPVT. The middle section air moisture content was significantly (P<0.01) higher than the pad and the fan sections. Conversely, in the NVT, the air humidity levels were significantly higher at the lower levels than at the upper levels, as shown in Figures 3.8c, 3.8e and 3.8g. At the upper levels, the relative humidity was significantly (P<0.01) lower at the middle section than the east and west ends of the NVT. At the lower level, the relative humidity was significantly (P<0.01) lower at the west of the tunnel than the middle and the east end.
53 40 60 80 100
12 16 20 24 28 32
06:00 12:00 18:00 00:00 06:00
RH (%)
Temperature (°C)
October
NVLT1 NVLT2
NVLT3 NVUT1
NVUT2 NVUT3
NVLR1 NVLR2
NVLR3 NVUR1
NVUR2 NVUR3
40 60 80 100
12 16 20 24 28 32 36
06:00 12:00 18:00 00:00 06:00
RH (%)
Temperature (°C)
October
FPLT1 FPLT2
FPLT3 FPUT1
FPUT2 FPUT3
FPLR1 FPLR2
FPLR3 FPUR1
FPUR2 FPUR3
40 60 80 100
14 17 20 23 26 29 32
06:00 12:00 18:00 00:00 06:00
RH (%)
Temperature (°C)
Time of day (hours)
November
NVLT1 NVLT2
NVLT3 NVUT1
NVUT2 NVUT3
NVLR1 NVLR2
NVLR3 NVUR1
NVUR2 NVUR3
40 60 80 100
13 17 21 25 29 33
06:00 12:00 18:00 00:00 06:00
RH (%)
Temperature (°C)
Time of day (hours)
November
FPLT1 FPLT2
FPLT3 FPUT1
FPUT2 FPUT3
FPLR1 FPLR2
FPLR3 FPUR1
FPUR2 FPUR3
a b
c d
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Figure 3.8 Twenty four hour mean hourly temperatures (T) and relative humidity (R) at Positions 1(fan section), 2 (middle section), and 3 (pad section) on the lower (L) and the upper (U) levels in the naturally-ventilated (NV) and fan-pad evaporative cooled(FP) tunnels.
40 60 80 100
15 18 21 24 27 30 33 36
06:00 12:00 18:00 00:00 06:00
RH (%)
Temperature (°C)
December
NVLT1 NVLT2
NVLT3 NVUT1
NVUT2 NVUT3
NVLR1 NVLR2
NVLR3 NVUR1
NVUR2 NVUR3
40 60 80 100
14 17 20 23 26 29 32
06:00 12:00 18:00 00:00 06:00
RH (%)
Temperature (°C)
December
FPLT1 FPLT2
FPLT3 FPUT1
FPUT2 FPUT3
FPLR1 FPLR2
FPLR3 FPUR1
FPUR2 FPUR3
40 60 80 100
17 23 29 35
06:00 12:00 18:00 00:00 06:00
RH (%)
Temperature (°C)
Time of day (hours) January
NVLT1 NVLT2
NVLT3 NVUT1
NVUT2 NVUT3
NVLR1 NVLR2
NVLR3 NVUR1
NVUR2 NVUR3
60 80 100
17 22 27 32
06:00 12:00 18:00 00:00 06:00
RH (%)
Temperature (°C)
Time of day (hours) January
FPLT1 FPLT2
FPLT3 FPUT1
FPUT2 FPUT3
FPLR1 FPLR2
FPLR3 FPUR1
FPUR2 FPUR3
e f
g h
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