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Orchids Cultivation



Design of a Phalaenopsis greenhouse in the United States
Chiachung Chen, Biosystems Engineering Laboratory
National ChungHsing University

The adequate climate for growth of Phalaenopsis is high temperature, high range of humidity and low light intensity. The adequate climate for flowering is low temperature and high light intensity than that at growth stage. No natural climate fits for the Phalaenopsis culture in the United States. Therefore, a greenhouse with environmental control equipments is essential for Phalaenopsis industry in this country.

The major production area for orchids is California, Florida and the northeastern region. Each region has special climate characteristics. The weather conditions for the four regions are as follows:

1. Southern California:

This subtropical zone is dry in summer, with little rain. Summers are very hot and winter is mild.

2. Northern California:

This temperate region has an oceanic pattern. The temperature of the coldest month is > 0.

3. Northeastern region:

This temperate region has hot summers and temperature of the coldest in winter is < 0℃.

4.  Florida:

The climate is subtropical humid, usually on the east side of the continents. The summer rainfall is high, with rainfall throughout the year. There is no drought in summer.

No universal greenhouse design can be applied to all orchid production regions. The greenhouse design and its devices for the four regions are as follows:

The possible layout for a Phalaenopsis nursery includes hot and cold sections. The hot section is used for growing and the cold section for spiking and flowering. The setting temperatures of the hot and cold section are affected by the variety. The setting values of environmental control system are very important for a Phalaenopsis nursery.

I. Southern California

A. Weather conditions

The typical weather for Riverside, Los Angeles is in Figures 1 and 2. Light intensity and period are stable in this region. The light environment is good for Phalaenopsis.

The average and maximal temperature distribution is sin Figure1. In summer, the average day temperature is about 35℃ and the average night temperature is 18℃. In winter, the day and night average temperatures are 20℃ and 5℃. The night temperature is < 20℃ throughout the year. Inducing and flowering of Phalaenopsis is easy in this region. However, the high day temperature could affect the flower quality in summer.

The absolute temperatures are in Figure1. The highest temperature is > 40℃ from March to October. The evaporative cooling equipment is the basic equipment for the Phalaenopsis greenhouse. The absolute low temperature pattern indicates the lowest temperature was < 0℃. To maintain the flower quality, heating devices need to be installed in the greenhouse. The heating capacity needs to be increased 20℃ in the greenhouse.

The advantage of this region is the low humidity. The day temperature is high in the summer. However, the low air humidity helps the cooling ability of the evaporative cooling technique. The evaporative efficiency is nearly to 80%; the cooling temperature in the greenhouse is shown in Figure 2. The air temperature during the day for greenhouse is < 22℃. Thus, inducing spiking for Phalaenopsis is very easy.

B. Greenhouse structure and equipment

The specifications of Phalaenopsis greenhouse are as follows,

1. Exhaust fans with the ventilation rate is 1.25-1.5 Vol/min. If the volume of the greenhouse in 7200, the required ventilation rate is 9000-10800m3/min (CMM). The ventilation capacity for the exhaust fan is 550 CMM. The required number of fans is 17-20.

2. Pad thickness

The traditional thickness of pad materials in this region is 5 cm, but too narrow for cooling. The adequate thickness of pad is from 10 to 15 cm.

3. Roof covering

Because of sand accumulation, the light transmittance of the cover materials is low. The roof materials need to be cleaned regularly.

4. External shading nets

The external shading net is basic equipment to reduce the light intensity into the greenhouse.

5. Wall materials

Double-layered plastic is the best for Phalaenopsis. It can reduce the heat transfer between the inside and outside environment.

6. Internal circulation fans

This ventilation device is important to keep the air circulating in the greenhouse.

7. Humidifying devices

Because air humidity is low, a humidifying device is necessary to increase the humidity level in the greenhouse. However, air circulation is necessary with the humidifying operation.

Ⅱ. Northern California

A. Weather conditions

The weather conditions of the Salinas, San Francisco are presented in Figures 3-4. The solar hours (Figure 3) is > 10 hours all over the entire year. In the rainy season (Oct.-Dec.), the number of solar hours may be too low. However, average light hours are 13.5 in other months. The solar energy helps the accumulation of dry materials of Phalaenopsis.

The high /low temperature distribution (Figure 4) indicated the highest temperature is 22℃ in September. The low night temperature is 10℃ from November to the next May.

The natural air temperature is San Francisco is good for inducing and flowering of Phalaenopsis.

The absolute high and low temperature is shown in Figure 4. The lowest absolute temperature is below 0℃ and the highest is 40℃. Control equipment is needed to install with these extreme temperatures.

B. Greenhouse structure and equipment

1. External shading nets: to be prepared to reduce the entering solar energy in summer. Internal shading nets or energy-saving curtains are recommended.

2. Double-layered wall: could isolate the heat transfer capacity between the inside and outside environment.

3. Ventilation rate: from 1.2-1.3 Vol/min.

4. Pad material > 10cm thick.

5. Typical humidifying: misting in the air or spraying on the ground. Humidification and internal air circulation needs to be coordinated.

6. Heating systems: recommended the hot-air heater and hot-water pipe.

 Ⅲ. Northeastern region

A. Weather conditions

The temperature and relative humidity distribution of Brewster, NY and Ringoes, NJ, are in Figures 5 and 6.

There are four environmental control stages of temperature:

1. April and May: ventilation during the day and heating at night.

2. May to September 15: cooling during the day and ventilation at night. Air is exchanged between outside air and internal air circulation.

3. September 15 to October: ventilation during the day and heating at night.

4. October to the next April: heating during the day and night.

 The environmental control of relative humidify has two stages:

1. September to the next May: humidifying during the day.

2. May to September: cooling with pad and fans to increase the humidity.

The air humidity in summer is > 50%, and the cooling capacity of the internal air temperature is > 23℃. The inside temperature is not low enough to enhance spiking. If the spiking function is necessary in this region, a mechanical cooling room needs to be installed inside the greenhouse with cooling ability controlled by mechanical equipment.

A. Greenhouse structure and equipments

Wind load and snow accumulation weight are the main factors for the roof strength in this area. Other required equipments is as follows:

1. External shading net

The local wind pressured is strong, so the net structure needs to be enhanced.

2. Positive pressure fan

Fans installed at both sides to exit the accumulated heat between the roof and internal shading nets.

3. Internal shading nets or energy saving curtains.

4. Artificial light: minimum light supply is 6,000 lux.

5. Internal circulating fans to provide air movement in the greenhouse.

6. Pad thickness: 10cm or 15cm.

7. Exhaust fan: ventilation rate 1.25 Vol /min.

8.  Two stage curtains at outsider pad structures: In winter, intermittent air movement is necessary to exchange the inside and outside air. However, cool air could be cooling stress for plants. A special device is used to change the cool air direction to react with plants directly.

9. Misting equipment: to humidify the inside air.

10.  Hot-water heater and hot-air heaters.

11.  Light curtains: at both sides of the greenhouse. The curtains are open in winter and closed in summer.

Ⅳ. Florida

A. Weather conditions

The typical weather of Homestead, FL, is in Figures 7 and 8. The average maximum day temperature in summer is > 32℃ and the average maximum night temperature nearly 25℃. However, the record for the minimum temperature in winter is < 1℃.

The relative humidity of the air (Figure 8) indicates that humidity is nearly saturated at night and > 60% during the day. The higher humidity limits the evaporative efficiency of the pad and fan system.

The cooling temperature in the greenhouse by the pad and fan system is > 25℃. It is difficult to induce spiking of Phalaenopsis. Only in winter can the inside temperature be cooled to < 25℃. This region is good for growth and inadequate for spiking.

The design of the cooling room for spiking is similar as in Southern Taiwan and so could be applied in Florida.

B. Greenhouse structure and equipments

The subtropical greenhouse used in Taiwan could be applied in this region. The basic requirements of such greenhouses are as follows:

1. Resist the high wind speed and heavy rain.

2.  Maintain high ventilation rate.

3. Shading with external and internal nets.

4. Pest control: more difficult than in other regions.

The required equipments included the following:

1. Exhaust fan with 1.5-1.8 Vol/min ventilation rate.

2. Hot-air heater to increase the inside air temperature in time.

3. Mechanical refrigeration for inducting of spikes.

4. Internal and external nets.

The details of these novel technologies are as follows:

(1)   Algae prevention technology

The exterior of pad surfaces is covered by shading nets to reduce light intensity. Before the pumps stop, all the water in the pad is sucked out to reduce the risk of algae development.

(2)   Internal circulation fan

The industrial ventilation fan is adopted to circulate the internal air without inspiring outside air. With special criteria of the number and installation angle of these fans, the temperature and relative humidity of inside air could be uniform to reduce the risk of disease development.

(3)   Internal energy-saving curtains

Moveable systems include plastic curtains, insulating curtains, a driven mechanism and control devices. Curtains could help decrease the required internal space for heating or cooling. The required energy cost could be reduced.

(4)   Uniform distribution of hot-air heater or hot water heater

The hot air exited from heaters is distributed by the perforated-tube air circulation system. To ensure the uniform distribution of hot air, the size and distance of holes in the perforated-tube was studied by the fluid theory. A software program was developed to calculate the required open area and to determine the position of holes. The air distribution with the hot water heater is assisted by internal fans to ensure uniform temperature distribution.

(5)   Silver shading nets

The silver shading nets are used to replace the black shading nets. The quality of solar irradiance could be modified by this shading net.

(6)   Insects screens

The installment of the insect screen is to keep out the insects entering the greenhouse. However, the air-resistant characteristics could reduce the ventilation capacity. A special design for the screen installment can avoid air circulation problems.

(7)   Cooling house for flower induction.

The cooling ability of the pad and fan system was limited by the wet bulb temperature of the outside air. Because of higher humidity environment, the internal temperature is 7-8 lower than the outside air temperature. The air temperature of the greenhouse is usually 27-28 in summer. The required flower-inducing temperature is lower than this range. To ensure that the inside temperature meets the requirement for spike induction temperature, a special cooling house is designed and installed in the greenhouse.

Figure 1. The typical weather information in Riverside, Los Angeles


Figure 2. The cooling ability of greenhouse in Riverside, Los Angeles


Figure 3. The sun hour conditions of the Salinas, San Francisco


Figure 4. The temperature distribution of the Salinas, San Francisco


Figure 5. The temperature distribution of the Brewster, NY and Ringoes, NJ.



Figure 6. The relative humidity distribution of the Brewster, NY and Ringoes, NJ.










Figure 7. The temperature distribution of Homestead, FL










Figure 8. The relative humidity distribution of Homestead, FL