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C.H. Mohammud, A.R. Rohazrin, A. Mohd Yusoff and Z. Abd. JamilJ. Trop. Agric. and Fd. Sc. 39(2)(2011): 267– 277

Performance of ventilation and cooling system on in-house environment in controlled environment structure(Prestasi sistem pengudaraan dan penyejukan terhadap persekitaran dalaman di dalam struktur pesekitaran terkawal)

C.H. Mohammud*, A.R. Rohazrin*, A. Mohd Yusoff** and Z. Abd. Jamil**

Keywords: controlled environment structure, ventilation, cooling system, temperature

AbstractCrops grown under tropical conditions are often faced with problems of high temperature and relative humidity. A controlled environment (CE) structure was deployed to create a favourable environment for cultivation of vegetable crops. Devices such as thermal screens, circulation fans and foggers were used for improving the capability and the functionality of the structure to maintain the proper ambient temperature and humidity inside the structure. The performance of the thermal screen, circulation fan and fogger cooling system for a controlled environment structure was investigated under Malaysian tropical conditions. The results revealed that ventilation and cooling system with circulation fans, thermal screens and foggers had successfully lowered the in-house temperature and increased the humidity which was favourable for chilli cultivation. Circulation fans alleviated the wind movement within the CE structure. Temperature of the growing media with cooling treatment was also lower in comparison to those without cooling.

*Mechanization and Automation Research Centre, MARDI Headquarters, Serdang, P.O. Box 12301, 50774 Kuala Lumpur, Malaysia**Strategic Resources Research Centre, MARDI Headquarters, Serdang, P.O. Box 12301, 50774 Kuala Lumpur, MalaysiaAuthors’ full names: Mohammud Che Husain, Rohazrin Abd Rani, Mohd Yusoff Abdullah and Abd. Jamil Zakaria©Malaysian Agricultural Research and Development Institute 2011

IntroductionControlled Environment (CE) structures such as greenhouses commonly found in Malaysia are usually characterized with increased in-house ambient temperatures and decreased air humidity during the day, especially when both solar radiation and external temperatures are high (Bailey 2004). The in-house air temperature can reach more than 40 °C and humidity less than 60% in the afternoon (Mohammud and Rezuwan 1995). These conditions exceed the hyper-limit for natural ventilation to provide sufficient cooling and subsequently will cause unfavourable plant’s physiological

condition such as high transpiration and respiration that may affect the plant growth. Practically, natural ventilation is induced by the stack or wind effects or a combination of both (Rezuwan and Faisal Mohammed 2007). Thus, it is necessary to modify the natural internal climate to avoid high temperature and low humidity which affect plant growth and reduced worker productivity. Generally, lowland temperate vegetable crops require comfort zone with average in-house temperature in the range of 25 – 30 °C and relative humidity between 60–70% (Mat Sharif 2003, Baudoion and

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Zabeltiz, 2002, Grange and Hand 1987). According to Bailey (2004), when the average maximum outside temperature exceeds 28 °C, then artificial cooling may be necessary. Currently, the available commercial scale of CE structure is adapted to natural ventilation system and is not designed to cater and accommodate mechanical ventilation system using circulation fans and foggers. Temperature is the most important variable of the micro-climate that can be controlled (Bailey 2004). Air movement under CE structure may be limited or unevenly distributed causing air temperatures inside the system to escalate. Effect of air movement is significant for crop pollination in the CE structure. The recommended wind speed in the CE structure is 2 m/s (Bailey 2004). Wind speed is usually dependent on air movement outside the CE structures and supports devices such as the circulation fans. Handarto et al. (2007) in his study demonstrated that fogging was effective for lowering air temperatures as much as 6 °C and increasing relative humidity inside the greenhouse. The use of mechanical environmental control system in the CE structures, particularly for vegetable cultivation is relatively new in Malaysia. There is little information on the interactive effects of mechanical ventilation and cooling systems on the in-house environment. The effect of mechanical environment control systems such as circulation fans and foggers to lower the air temperature, humidity, air movement and environment spatial homogeneity has created great interest to Malaysian researchers. This paper presents results generated from research works in development of climate control system in a commercial scale CE structure that can provide conducive micro-environment for vegetable production in the tropics. The information could be used to determine the appropriate ventilation and cooling system required for crops grown in CE structures.

Materials and methodsThe structureThe study was conducted during January 2007 in a semi-mechanically CE structure located at MARDI Headquarters, Serdang Selangor, Malaysia with latitude 2°59’N and longitude 101°42’E. The CE structure is a saw tooth type with a gable span width of 6.4 m by 40 m long and consists of 3 bays (Plate 1). The structures are constructed using galvanized steels and C-column bar framing. The roof and sidewalls are respectively covered with 200 microns transparent polyethylene film and 50 mesh insect proved netting. The floor is covered with woven polyethylene sheet. The height of the CE structure is 5.6 m, 1.15 m higher than conventional design. To increase thermal buoyancy or thermal inertness and uniformity, three units of circulation fans per house were used (Plate 2). These circulation fans were used to circulate the greenhouse air horizontally in the space above the plants. The aim is to create large volume, slow moving current of air which is able to penetrate into the crop. The laminar airflow rate of the fan at 5,000 m3/h, helped to reduce the rate of heat build-up in the structure. A total of 80 units of high pressure-low volume fogging nozzles that operate at 4 bars with flow rate of 30 l/h were installed in rows 3.2 m apart and spacing of 3 m within rows below the roof so that sufficient moisture could be sprayed into the internal air volume of the CE structure. The fine moisture absorbed the heat and evaporated. Thus, the system would reduce air temperature and regulate the air humidity in the structure. The top and side vents with 1.6 m and 4.5 m height respectively, were installed and managed according to ambient wind speed and direction by a computerized control system. The top and side vents were operated separately using electric motors and they will be fully opened when the wind speed within the CE structure is less than 3 m/s.

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Plate 1. Semi-mechanically controlled environmental structures at MARDI Headquarters, Serdang. The structures are covered with 200 micron transparent polyethylene and 50 mesh insect proof netting. Top and side vents are part of natural ventilation system

Top vent

Side vent

Plate 2. Circulation fans, fogging nozzles and thermal screen installed in the structure to control the in-house environment. The floor is covered with woven polyethylene sheet

Thermal screen

Circulation fan

Side vent

Fogger

Motorized retractable thermal screens made of aluminized fiber netting were installed to provide 30–40% shading and to reflect light during bright day that reduced thermal load and to increase the effectiveness of the cooling system. The thermal screen operation was done through the control system in response to preset temperature. A computerized control system was employed to automatically control the

operation of the devices such as top and side vents, circulation fans, thermal screens and foggers based on temperature and humidity inside and outside the CE structure. One set of temperature and humidity sensors were placed at the middle and outside the CE structure to monitor air temperature and humidity status and linked to a computerized control panel.

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The cropChilli (Hungnong hybrid) was planted in the CE structure in flexible polypropylene containers (300 mm width and 200 mm height) filled with coco-peat (Plate 3). Each container was planted with 74 chilli plants in single rows, and grown until 6 months old. Drip fertigation system was used to apply nutrients and water uniformly to each plant four times a day. Nutrient solution was prepared by dissolving a straight, highly soluble hydroponic grade fertilizer in the irrigation water.

The treatmentsTo analyse the system, several experiments were conducted when the crop was 12 weeks old by comparing between system with cooling (side and roof vent opened, thermal screens, circulation fans and foggers operating) and system without cooling (side vent and roof vent remained open) as control treatment. These experiments were aimed to analyze the capability of circulation fan and fogger system which could be used to mobilize the air and to increase air humidity respectively.

Sensor installation based on grid lineIntegrated sensors known as ‘Watchdog’ manufactured by Bowthorpe Thermometrics (2010) were used to measure air temperature and relative humidity. ‘Watchdog’ adapted thermal resistor type (ceramic semiconductors) as temperature sensor that consist of an electronic component that exhibits a large change in resistance with a change in its body temperature. The humidity sensor is made of non-refresh type waterproof polymer. These integrated sensors were placed on the grid line at a spacing of 8 m by 6.4 m with a total of fifteen locations as shown in Figure 1.

Air temperature and humidity contour mappingThe air temperature and humidity data were collected using the ‘Watchdog’ sensors (mentioned above) and data logger, placed 2 m above the ground, in the CE structure (Figure 1). Each sensor was shaded from direct solar radiation by placing it in a measuring box with a reflective outer surface. Temperature and humidity data were taken within 24 hours from 12 a.m. to 12 a.m. the next day at hourly intervals. One

Plate 3. Chilli plant in the growing container filled with coco-peat and burnt rice husk

Growing container made of flexible polypropylene filled with coco-peat

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sensor was placed outside the CE structure for measuring the outside temperature and humidity. These data were used as reference for comparison purpose. The maximum temperature and minimum humidity on that day were taken and analysed. Normally, the maximum temperature and minimum humidity were recorded at mid day, between 12.00 a.m. and 02.00 p.m. The temperature and humidity differences between inside and outside the CE structure were taken and contours were made. These contours mapped the horizontal temperature and humidity at 2 m height above the ground inside the CE structure. The 2 m height was used as reference point as it was above the plant canopy.

Air temperature and humidity profilingTo obtain data of air temperature and humidity profiling at each elevation, one set of ‘Watchdog’ sensors and data logger

were placed at seven different heights (50, 100, 150, 200, 300, 400 and 500 cm from the ground). The sensors were placed at 15 locations as in the above experiment for 10 min and the data were logged on at 1 min intervals during mid-day. Similar to the previous experiment, one sensor had to be placed outside the CE structure to record the outside temperature as control. Temperature differences from the data were plotted versus elevation. The plotted graph will show different temperature at each elevation and temperature build-up could be clearly seen.

Air movementAn experiment was carried out to determine whether the circulation fan adapted in the CE structure was strong enough to facilitate air movement. The comparison was made during mid-day with and without the circulation fan operating. Six ‘Hot Wire

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Figure 1. Temperature and humidity sensors placement on the grid line system

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Thermo-Anemometer’ wind speed sensors were placed at six locations, 2 m above ground inside the CE structure and two sensors were placed outside the structure to get the average wind speed. In order to see the mapping or distribution of wind speed in the CE structure, wind speed contour was made. The contour depends on actual wind speed in the CE structure. The actual speed was derived from the average wind speed at the designated location.

Temperature of growing mediaCrops growth in CE structure is influenced by temperature of growing media. Low growing media temperature is better for certain crop growth. The ideal growth media temperature for temperate crop is in the range of 25 to 28 °C (Mat Sharif 2003). The effects of cooling system on the temperature of the growth media were evaluated. Growth media temperatures were recorded by thermocouples which were connected to the data logger (DELTA-T). The sensors were placed at 15 cm depth in the growing media, replicated three times, and one sensor was placed outside the media (placed between growing containers) to measure in-house temperature. The temperature measurements were taken within 24 hours from 12 a.m. to 12 a.m. on

the next day. The temperatures were logged on at hourly intervals. This experiment was implemented in two conditions: with and without cooling system. Graph of temperature versus time was plotted and the comparison between the two graphs was made.

Results and discussionAir temperature and humidity contourThe air temperature differences between inside and outside CE structure with and without cooling system during mid-day are presented in Table 1. The average air temperature in CE structure was slightly lower than outside when the cooling system was operated. The maximum temperature difference was only 4.9 °C but when the cooling system was not operating, the maximum temperature difference distributed in many places in the CE structure was 5.9 °C and higher. This can also be seen clearly in the temperature contour shown in Figure 2. There are many low temperature spots (blue color) in the contour. The cooling system that consisted of circulation fan, fogger and thermal screen affected the temperature in the CE structure. The most affected areas with lower temperatures were the points where

Table 1. The average air temperature differences between inside and outside CE structure with and without cooling systems during mid-day (12:00 noon)

Day The air temperature difference between inside and outside CE structure With cooling system (included vents, Without cooling system (only thermal screens, circulation fans vents) (°C) and foggers) (°C)1 2.79 3.472 2.08 3.543 2.30 3.004 1.24 3.725 4.90 5.906 3.90 5.207 1.90 3.90Average 2.73 4.10Max 4.90 5.90Min 1.24 3.00Positive value indicate temperature inside CE structure is warmer than outside

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Figure 2. Temperature (°C) contour in the controlled environment structure

Temp. (°C)Temp. °C

Width (m) Width (m)

8 8

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Table 2. Differences (outside-inside) in air humidity between inside and outside CE structure with and without cooling systems during mid-day (12:00 noon)

Day Differences (outside-inside) in air humidity between inside and outside CE With cooling system (included vents, Without cooling system thermal screens, circulation fans (only vents)(%) and foggers) (%)1 –15.8 –20.02 –10.7 –14.83 –20.1 –24.74 –16.5 –19.45 –9.9 –10.66 –9.2 –15.77 –21.7 –30.1Average –14.8 –19.3Max –9.2 –10.6Min –21.7 –30.1The negative value indicated that relative humidity in the CE structure is lower than the outside

the circulation fans were located (Figure 1). It was shown that the non-uniform temperature profile occurred within the structure especially near the sidewalls due to additional surface area for heat gain from outside. Table 2 presents the air relative humidity differences between inside and outside the CE structure with and without cooling systems during mid-day. The negative value indicated that relative

humidity inside the CE structure was lower than outside, but when cooling system was operating, the differences were much less. This means that the temperature inside could become lower than the outside. High temperature will create low humidity. Contour mapping of humidity differences is shown in Figure 3. The red area in the contour indicated the driest area (low humidity) in the CE structure while the minus sign indicated that the relative

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humidity was lower inside compared to outside. The patterns of the contour showed the differences between situations with and without cooling system. The pattern was influenced by the circulation fan which changed the contour in accordance with air movement. The spot with low air humidity and high temperature was identified at the centre of the CE structure. Generally the relative humidity was within the range of 60–90% and this had little effect on the plants. Values below 60% did occur sometimes during mid-day but no indication of crop water stress was observed.

Air temperature and humidity in respect to elevationThe differences in air temperature between inside and outside increased from the ground to the top of the CE structure as shown in Table 3. There were some differences in temperature when cooling system was operating as compared to when cooling system was not operating. The temperature difference was nearer to zero with the cooling system on indicating that the temperature inside and outside was almost the same. The results revealed that the use of cooling system has a cooling effect on in-house temperature even though generally, the temperature inside the CE structure was warmer than outside. At higher

R.H. (%)

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Figure 3. Relative humidity (%) contour in the controlled environment structure

Figure 4. Vertical temperature (°C) difference profiling in the controlled environment structure

500 cm

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200 cm

150 cm

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100 cm

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Table 3. Differences between inside and outside air temperature with elevation from the ground to the top of the CE structure during mid-day (12:00 noon)

Elevation Difference in air temperature with elevation from the ground recorded for 7 consecutive daysabove the

ground (cm) With cooling system (included vent, thermal Without cooling system (only vent) screen, circulation fan and fogger) (°C) (°C) 1 2 3 4 5 6 7 Ave 1 2 3 4 5 6 7 Ave50 1.3 1.0 0.9 0.7 –0.1 –0.5 0.2 0.7 2.1 2.0 2.4 3.2 2.9 2.9 2.4 2.6100 0.8 0.5 0.6 0.2 –0.1 0.1 1.1 0.5 2.8 2.7 3.4 4.4 4.2 3.9 3.1 3.5150 0.8 0.5 0.9 0.5 0.1 0.5 2.1 0.8 3.0 2.9 3.4 3.9 3.6 3.4 2.8 3.3200 0.4 0.1 0.0 –0.2 –0.8 –0.6 1.4 0.5 2.4 3.0 3.4 4.1 3.7 3.1 2.5 3.2300 0.4 0.5 0.4 0.2 0.0 0.6 2.6 0.7 2.2 2.6 3.7 4.6 4.2 4.2 3.9 3.6400 4.3 4.0 4.3 4.1 4.0 4.6 6.6 4.6 6.0 6.3 6.9 7.2 6.8 7.1 7.2 6.8500 4.7 4.4 4.3 4.1 4.2 4.8 6.5 4.7 7.1 7.4 8.5 8.8 7.9 7.7 7.5 7.8Average 1.8 1.6 1.6 1.4 1.0 1.3 2.9 1.7 3.7 3.8 4.5 5.2 4.8 4.6 4.2 4.4max 4.7 4.4 4.3 4.1 4.2 4.8 6.6 4.7 7.1 7.4 8.5 8.8 7.9 7.7 7.5 7.8min 0.4 0.1 0.0 –0.2 –0.8 –0.6 0.2 0.3 2.1 2.0 2.4 3.2 2.9 2.9 2.4 2.6

Figure 5. Wind speed (m/s) contour in the controlled environment structure

Wind speed (m/s)

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elevation nearer to the roof, the difference in temperature for both conditions (with and without cooling) was also quite large (Figure 4) even though the cooling system (fogger and circulation fan) was located close to the roof at 3.5 m above ground surface.

Air movement within CE structureWithout circulation fan, air movement in the CE structure was slow. The netting

size was the main factor for less wind penetration into the CE structure. The wind speed contour in Figure 5 showed that the air movement or wind speed in the CE structure could be improved by using circulation fans. The speed could be increased up to 3 m/s, but only at the areas where the fans were located. The function of the fans was to disperse the heat and at the same time to circulate the air. The arrangement and number of fans have to be

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considered in the design of the CE structure for better air movement. This is one aspect of researchable area for future work.

Root zone temperatureFigure 6 shows that temperature of coco-peat was not affected by the environment in the CE structure and it was quite constant throughout the day with just 2 °C variation. The mean temperature for cooling treatment was lower compared to without cooling situation. The maximum media temperature was 28 °C for both conditions (with and without cooling). The increase in media temperature was slow compared with the increase in in-house temperature. There was some buffering or damping effects which occurred in the coco-peat even though there was temperature build-up under the CE structure. The irrigation water in coco-peat may have caused the buffer effect in temperature variation that stabilized the temperature in the root zone. The graphs demonstrated that it takes time for the coco-peat to reach the daily maximum temperature. The heat transferred to a deeper coco-peat layer was slower, especially when the top layer was shaded by the plant canopy.

ConclusionControlled environment structures which are naturally ventilated when fitted with a cooling system that comprises of vents, circulation fans, thermal screen and foggers successfully overcome overheating in the in-house environment. Results indicated that opening the top and side vents alone was not capable to reduce the in-house temperature lower or at par with ambient. However, lower temperature was obtained with the application of circulation fans and foggers. It was found that the cooling effect can be increased further by introducing thermal screen which increased the effectiveness of the cooling process. The spatial uniformity of the temperature and humidity was generally good. The environment non-uniformity had been overcome by using circulation fans that circulate the air horizontally in the space above the plants. The circulation fans had created large, slow moving current of air which was able to penetrate into the crop canopy. In order to improve the air movement up to 3 m/s, the number of circulation fans need to be increased by two folds, two units per bay. The air temperature was lowered by 2.7 °C and humidity increased by 14.8% when cooling system was employed. This suggests that cooling

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system can reduce air temperature and increase humidity which is favourable for chilli cultivation.

ReferencesBailey, B. (2004). Natural and mechanical

greenhouse climate control. Acta Hort. 710: 135–142.

Baudoion, W. O. and Zabeltiz, C.H.R. (2002). Greenhouse construction for scale farmer in tropica regions. Acta Hort. 578: 171–179

Bowthorpe Thermometrics (2010). WATCHDOG temperature and relative humidity sensor and data logger. Specification and user manual. Sommerset, UK

Grange, R.I. and Hand, D. (1987). A review of the effects of atmospheric humidity on the growth of greenhouse crops. Journal of Horticultural Science 52: 123–134

Handarto, H.M., Goto, E. and Kozai, T. (2007). Experimental verification of control logic for operation of a fog cooling system for a naturally ventilated greenhouse. Environ. Control Biol. 45: 47–58

AbstrakTanaman di bawah persekitaran tropikal sering berhadapan dengan masalah suhu dan kelembapan udara yang tinggi. Struktur persekitaran terkawal (CE) digunakan untuk mewujudkan persekitaran yang sesuai untuk penanaman sayur-sayuran. Peranti seperti skrin haba, kipas peredaran dan pengabus telah digunakan untuk meningkatkan keupayaan dan fungsi struktur untuk mengekalkan suhu ambien dan kelembapan di dalam struktur. Prestasi skrin haba, kipas peredaran dan sistem penyejukan pengabus untuk persekitaran terkawal telah dikaji dalam keadaan tropika Malaysia. Hasilnya menunjukkan bahawa sistem pengudaraan dan penyejukan yang terdiri daripada kipas peredaran, skrin haba dan pengabus telah berjaya mengurangkan suhu dan meningkatkan kelembapan dalaman bagi menggalakkan pertumbuhan cili. Kipas peredaran telah meningkatkan pergerakan angin didalam struktur CE. Suhu media tanaman yang menerima rawatan penyejukan juga lebih rendah dibandingkan dengan tanpa penyejukan.

Mat Sharif, I. (2003). Controlled environment system for the production of selected temperate crops in lowland tropics. Project Report MTEN 2003, UP/1.08.01.06 MARDI

Mohammud, C.H. dan Rezuwan, K. (1995). Prestasi system pengairan mikro untuk tanaman sayur-sayuran di bawah struktur pelindung hujan di tanah bris. Tekno. Kejuruteraan Pertanian 6: 27–32 (Abstract in Handarto, E., Kosai, T. and Hayashi, M. (2007). Air and leaf temperatures and relative humidity in a naturally ventilated single-span greenhouse with a fogging system for cooling. Proc. of the international symposium on greenhouses, environmental control and in-house mechanization for crop production in the tropics and sub-tropics. Published by ISHS and Acta Horticulture.

Rezuwan, K. and Faisal Mohammed, S.A. (2007). Natural ventilation by attack effect in multi-span tropical greenhouse structure. J. Trop. Agric and Food Sc 32 (2): 221–230

Accepted for publication on 21 July 2011

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