Design of an Automatic Control Circuit for Ventilation and Humidification in a Small Orchid Room

With the advancement of management techniques andcultivationorchidsthe improvement in grade, more and more people are adopting transparent, enclosed, heat-retaining orchid rooms. There are many forms such as fully enclosed, semi-enclosed, automatic and semi-automatic, all of which have achieved good results. Especially in large and medium-sized cities with severe air pollutiongrowing orchids, the role of this kind of orchid room is particularly notable. The author lives in the city center of Guangzhou, growing orchids on a seventh-floorbalconygrowing orchids, and in the past relied only on ordinary shading equipment; despite great effort, the orchids still inevitably "lost their shoots" year after year, and countless fine varieties were lost. Since October 1989, the south balcony was converted into a humidity-retaining orchid room enclosed with fiberglass windows, equipped with an electric fan, an ultra-fine humidifier (sprayer) and an inverter (emergency) power supply, and a set of automatic control circuits was designed and installed by the author, implementing semi-automatic management, and the situation improved greatly. Not only were the fine varieties preserved, but most orchid plants produced shoots, some sprouting twice a year, and diseases such as black spots, scorched edges and burnt tips were markedly reduced. This self-designed ventilation and humidification automatic control circuit, installed with domestic components and suitable for small orchid rooms, has been tested for many years with good results. A brief introduction is now given for the study and reference of interested orchid enthusiasts, and suggestions for improvement are welcome. I. Working Principle of the Circuit 1. When the relative humidity of the orchid room drops to a certain limit (set at 70%), the pointer A of the hair hygrometer touches contact B (made of silver-plated copper wire), the 12V DC power supply is sent through the normally closed contact of relay J2 to the magnetic coil of relay J1, causing it to actuate (pull in), and the 220V AC power supply passes through J1-6,5 to switch K4; if the switch is closed at this time, the power enters the sprayer, making the sprayer work (spray). When the pointer gradually leaves contact B, the 12V DC power supply maintaining the actuation of J1 is instead supplied by J1-2. 2. When the sprayer is working, the humidity of the orchid room gradually increases; when it reaches the preset humidity (set at 85%), the pointer A of the hair hygrometer touches contact C, the 12V DC power supply is sent through J1-9,10 to the magnetic coil of J2, causing J2 to actuate, cutting off the 12V DC power supply to the magnetic coil of J1, J1 returns to its normal state, and the sprayer stops working. 3. The exhaust fan and the leaf-blowing fan are under dual control: ① Temperature control - the contact thermometer is preset to a control point (for example 25 degrees); when the room temperature reaches or exceeds this control point, the mercury column connects with the contact, the 12V DC power supply reaches the magnetic coil of relay J3 through the contact thermometer, causing J3 to actuate (pull in), and the 220V AC power supply passes through J3-6,7 to switches K2, K3; if the switches are closed at this time, the power is sent respectively to the exhaust fan and the leaf-blowing fan, putting them into working state; when the room temperature drops below the control point, the mercury column separates from the contact, the 12V DC power supply is cut off, J3 returns to its normal state, the 220V AC power supply is open-circuited, and the exhaust fan and leaf-blowing fan stop working, reducing unnecessary consumption. ② Spray control - the 12V DC power supply supplied by the contact thermometer to the magnetic coil of J3 is taken from the normally closed contact J1-4; when J1 and the sprayer are not working, the 12V DC power supply is controlled only by the contact thermometer; when J1 and the sprayer are working, J1-4 is open-circuited, the 12V DC power supply is cut off, J3 stops working, making the 220V AC power supply passing through J3-6,7 open-circuited, and the exhaust fan and leaf-blowing fan temporarily stop working, avoiding discharging large amounts of mist outdoors and blowing the leaf surfaces wet; when J1 and the sprayer stop working, the exhaust fan and leaf-blowing fan immediately resume working. 4. The floor-blowing fan has two functions: ① To blow up the moisture from the floor (provided with water-absorbing sponge) to increase the humidity of the orchid room. ② To introduce fresh outdoor air and keep the indoor air circulating. The floor-blowing fan needs to work for relatively long periods and is not controlled by temperature or spraying, so only a manual switch is provided. In order to strengthen indoor air circulation so that orchid plants in every position are often in a good ventilation state, the power supply of some leaf-blowing fans can be connected in parallel with the floor-blowing fan or provided with separate switches, free from the control of temperature and spraying. 5. In places where power outages are frequent, in order to ensure the normal operation of the orchid room, a large storage battery and inverter (emergency power supply) should be equipped, so that the ventilation and humidification system can operate as usual during power outages. If these conditions are not available, the doors and windows of the orchid room should be opened immediately during a power outage, and water sprinkled on the surrounding floor to keep the orchid room ventilated and moist. II. Some Understanding of the Heat-Retaining Orchid Room Some people call this kind of orchid room a "greenhouse", which is a misunderstanding. It has no special heating or cooling equipment, and the main function of enclosing it is heat retention. Therefore, the author believes that calling this kind of orchid room a "humidity-retaining orchid room" is more appropriate. In fact, the so-called enclosure is not long-term enclosure either. In seasons when temperature and humidity are relatively suitable fororchidgrowth and on most evenings, the doors and windows can all be opened to allow natural ventilation; only in hot, dry weather, or when nearby chimneys are emitting large amounts of smoke and the wind direction is directly toward the orchid room, must it be closed and the ventilation and humidification equipment started. The sprayer usually adopts an automatic control switch (which can be purchased together with the machine), starting automatically when humidity is insufficient and stopping automatically when humidity reaches the preset control point. Adopting this ventilation and humidification system can not only constantly maintain the humidity of the orchid room, but also play a certain role in cooling (in the high-temperature season generally 3 to 5 degrees lower than outdoors) and purifying the air, achieving three benefits at once, making it suitable fororchidgrowth and propagation needs. Therefore, orchidscultivatedin this kind of orchid room are not, as some people say, pampered "greenhouse orchids" that cannot grow when moved elsewhere. Practice has proved that they are in no way inferior to orchidscultivatedin natural orchid sheds with the same environment, and because light, temperature, humidity, wind and other management are appropriate, the orchid plants will be healthier and the marketable rate will also be higher. Therefore, it is suggested that orchid enthusiasts growing medium- and high-gradeorchidsmight as well consider giving it a try; this investment is well worth it. Tan Futai