Greenhouse heating automation control and others

Greenhouse automation

1. APPLICATIONS OF GREENHOUSES Green house heating and alternate use as dryers

2. Heat losses can occur in three different modes of heat transfer, namely conduction, convection, and radiation

3. About 10% of total heat loss from a structurally tight glass greenhouse occurs through infiltration loss. Table 2.  Natural Air Exchanges for Greenhouses Construction System Air Exchanges per Hour 1 New Construction, glass or fiberglass 0.75 to 1 New Construction, double layer plastic film 0.5 to 1.0 Old Construction glass, good maintenance 1 to 2 Old Construction glass, poor condition 2 to 4 Air leakage is less in double layered plastic film convered GH When compared to New Glass house or FRP house. Compared to new Glass house, Old and poor condition glass house leaks more

4. Material Overall R-Value Roof and Wall Coverings Glass, single layer 0.91* Glass, double layer, ¼” space 2.00* Polyethylene or other film, single layer 0.83* Polyethylene or other film, double layer separated 1.43* Polyethylene film, double layer, separated, over glass 2.00* Fiberglass reinforced pane 0.83* Double acrylic or polycarbonate 2.00* Which is the high insulating covering material?

5. Radiation heat loss A third mode of heat loss from a greenhouse is that of radiation. Warm objects emit radiant energy, which passes through air to colder objects without warming the air significantly. The colder objects become warmer. Glass, vinyl plastic, FRP, and water are relatively opaque to radiant energy, whereas polyethylene is not. Polyethylene, greenhouses can lose considerable amounts of heat through radiation to colder objects outside, unless a film of moisture forms on the polyethylene to provide a barrier.

6. What Is the Cheapest Way to Heat a Greenhouse in Winter? the most cost-effective method to heat a greenhouse in winter is  insulation . Bubble wrap, specifically designed for greenhouses, is an inexpensive yet efficient way. A dead air space between two coverings appears to be the best system. A saving of 40% of the heat requirement can be achieved when a second covering is applied.

7. Most heat is lost by conduction through the covering materials of the greenhouse. A dead air space between two coverings appears to be the best system. A saving of 40% of the heat requirement can be achieved when a second covering is applied. For example greenhouse covered with one layer of polyethylene loses, 6.8 W of heat through each square meter of covering every hour when the outside temperature is 1 º C lower than the inside. When second layer of polyethylene is added, only 3.97 W/m 2 is lost (40% reduction).

8. HEATING SYSTEMS UNIT HEATER SYSTEM

9. HEAT DISTRIBUTION SYSTEMS In the convection tube method, warm air from unit heaters are distributed through a transparent polyethylene tube running through the length of the greenhouse. The second method of heat distribution is horizontal airflow. In this system, the greenhouse may be visualized as a large box containing air, and it uses small horizontal fans for moving the air mass. The fans are located above plant height and are spaced about 15 m (50 ft) apart in two rows.

10. Convection Tube (with punches or holes

11. Convective Tube Cooling

12. Horizontal air flow system

13. CENTRAL HEATING SYSTEM A second type of system is central heating system, which consists of a central boiler than produces steam or hot water, plus a radiating mechanism in the greenhouse to dissipate the heat. The heat is exchanged from the hot water in a pipe coil located across the greenhouse or an in-bed pipe coil located in the plant zone

14. Central heating system with boilers located outside the greenhouse.

15. RADIATION HEATING SYSTEM The third type of system is radiation heating system. In this system, gas is burned within pipes suspended overhead in the greenhouse. The warm pipes supply heat to the plants. Low intensity infrared radiant heaters can save 30% or more, of fuel compared to conventional heaters.

16. INFRARED SPACE HEATER

17. SOLAR HEATING SYSTEM The fourth possible type of system is the solar heating system. Solar heating is often used as a partial or total alternative to fossil fuel heating systems. Main components collector, heat storage facility, and exchange to transfer the solar derived heat to the greenhouse air.

18. Water vs Rock as heat storage Heat Capacity: Water: Stores more heat per kilogram (4.23 kJ/°C) than rocks (0.83 kJ/°C). This means you'd need a much smaller water tank compared to a rock bed to store the same amount of heat.

19. How to pick the right greenhouse heater? What size is your greenhouse? How cold does it get in your location? What resource is the cheapest/most affordable option in your area? How well is your greenhouse insulated? How many plants do you want to grow? What type of plants are you going to grow?

20. Gas greenhouse heaters Pros Effortless to use A thermostat easily controls the temperature of the greenhouse High temperatures are easily accessed No power connection needed The traditional way of heating Cons Condensation problems are expected The fumes emitted may be toxic Needs a spare cylinder on hand at all times Needs refills of gas bottle

21. Electric greenhouse heaters Pros: Effortless to use Electricity is readily available (for most people) Doesn’t need to be refilled Thermostat for easy control over temperature (no overheating or freezing) Provide a tightly controlled temperature to a specific area No toxic fumes Cons: Heat may not be distributed evenly in some cases (some plants may get too much heat and others may freeze) Setting up electrical wires (if not there yet)

22. Which type of greenhouse heater should you pick? The most common heater types are  electric and gas . Most gardeners prefer gas heaters because they are affordable, especially in their local area. It uses natural or bottled gas. Gas heaters have the same effects as electric heaters. You simply need to install sufficient ventilation in your greenhouse because it may emit a significant amount of fumes. Confined fumes can be bad for you and your plants’ health. The  electric  heater is so popular because of its efficiency in keeping warmth at a consistent level. It does not release any dangerous fumes. This is best for those greenhouses with insufficient ventilation. It might be best, but it is also the most expensive of the three.

23. Utilize passive solar heat Passive solar heating is a straightforward and eco-friendly approach to warming your greenhouse. By placing black water containers against the north wall, they absorb solar heat during the day and release it at night, helping to maintain a consistent temperature with minimal cost.

24. Thermal mass heaters The concept of thermal mass heaters is simple: they absorb heat when it’s available and release it when the temperature drops. You can create your own by filling containers with water and painting them black to absorb maximum heat during daylight hours. Place these containers throughout your greenhouse to act as heat sinks, slowly radiating warmth overnight.

25. Solar-powered greenhouse heaters Greenhouse heating can cost a lot of energy consumption with the use of pumps and devices as well as maintaining the right temperature. While any type of solar panels can be used for your greenhouse, the more efficient ones are the monocrystalline solar cells and the polycrystalline solar cells.

26. This consists of a flat black plate (rigid plastic, film plastic, sheet metal, or board) for absorbing solar energy. The plate is covered on the sun side by two or more transparent glass or plastic layers and on the backside by insulation. The enclosing layers serve to hold the collected heat within the collector. Water or air is passed through the copper tubes placed over the black plate and absorb the entrapped heat and carry it to the storage facility. Flat black plate solar collector

27. Monocrystalline solar cells Pros: High-efficiency rate of 15-20% that requires less space The usual warranty is for 25 years because manufacturers believe in the long lifespan of the solar cells Works efficiently even on cloudy days because they have always shown peak performance even on low sunlight levels Cons: Very expensive, in fact, the most costly solar cell available on the market A rise in temperature can sometimes affect the levels of their performance Manufacturing them leads to a lot of silicon waste

28. Polycrystalline solar cells Pros: Silicon waste is avoided Effects on efficiency are not negatively affected by hotter temperatures More affordable option than the monocrystalline cells Cons: The low purity levels of silicon do not make them an efficient solar panel option They are less space-efficient because of their lower output rates. Installing them means more roof space

29. Natural Convection Greenhouse Dryer : Utilizes a greenhouse structure to capture solar heat and dry products. Components: Drying platforms made of wire mesh on wooden frames. Inclined glass roof for capturing sunlight. Black painted internal walls for better solar radiation absorption. Ridge cap with an opening for air ventilation. Shutters on the sides to regulate air inlet. Working Principle: Sunlight passes through the glass roof and heats the air inside the greenhouse. Black walls further absorb heat and warm the air. The warm air naturally circulates within the greenhouse, drying the products on the platforms. Airflow can be adjusted through the ventilation openings.

30. Open Drying of Agricultural Products The use of the greenhouse as a dryer is the latest development. The drying capabilities of the greenhouse can be utilized for curing tobacco leaves, while guarding the harvest from rain damage.

31. GREENHOUSE DRYER The thought of a greenhouse dryer is to combine the function of the solar collector with a greenhouse system. A natural convection greenhouse dryer consisted of two parallel rows of drying platforms (along the long side) of galvanized iron wire mesh surface laid over wooden beams.

32. Sun drying of chillies

33. Tobacco curing

34. Types of Solar Dryers Tent dryer Box dryer

35. Solar cabinet dryer

36. Solar Dryers have many advantages over open traditional drying. Safe & hygienic Free from insect and bird contamination Clean & dust free products More uniform quality products Uniform in colour , texture, appearance of the product Evenness in drying Moisture control to optimum levels Nutrient retention especially beta carotene Yields high quality, Export products Products qualify for quality & sensory tests Long shelf life to the products Processed to International Standards

37. SOLAR DRYER SALIENT FEATURES Zero energy cost. Cabinet temp : 40 – 65C. Temp. diff. T : 15 – 30 C Temperature indicator Moisture & Humidity control. Stainless Steel Trays Standby Electrical back up U.V. Reduction blue filter glass. Rain & Dust proof Dryer. Dust, insect & rodent proof