Greenhouse Heating Solution

Depending on the type of heat medium used as a heat transfer means in a heat source device, it can be divided into a case of using water and a case of using brine. Water has a low boiling point of 100°C and freezing point of 0°C. The cost of facilities increases and it is necessary to prepare for freezing when using low temperatures in winter.

For this reason, ethylene glycol, propylene glycol, etc. are sometimes used among brine with a high boiling point and a low freezing point. extremely limited.

A method of heating using a heating medium supplied to the farm through a pipe, that is, a method of raising the temperature of a greenhouse can be divided into underground heating, that is, root zone heating and space heating. As a method to do this, a 16mm Excel pipe is usually buried near the root of the plant at 500mm intervals and the underground temperature is controlled by circulating 40℃ hot water. In order to minimize it, the return pipe is designed in a reverse return method and designed according to the advice of experienced experts such as pipe diameter, pump capacity, hot water temperature, boiler capacity, etc. Space heating is a method of heating the air inside a greenhouse, and although it loses more heat than root zone heating, most of these methods are used because the installation cost is low and maintenance is easy. efficient in use. As a method of heating air, it is divided into a natural circulation method using the specific gravity difference of air and a forced circulation method using a fan and a heat exchanger.

The natural circulation method is a method of heating by installing a radiator heat sink, etc. on a pillar bench, etc. inside the outside of the greenhouse to circulate hot water inside the tube and heat exchange between the heated pipes and heat sink fins and air. The insufficient part is installed on the bottom of the inner middle column to circulate hot water inside the coil, and the fan attached to the front operates and exchanges heat with air. Due to this additional occurrence, a method of installing a pipe cone vector wound around a corrugated pipe aluminum iron pin at the bottom of a bench outside the greenhouse is mainly used.

Since the firebox corrodes after long-term use and the exhaust gas emitted after combustion is diluted with the indoor air and flows into the greenhouse, it can be checked by visual inspection and odor. do. As such, a hot air fan using fossil fuel loses about 30% of heat through exhaust gas discharged after heat exchange with air, so a heat exchanger is installed in the exhaust tube to recover it. Air, which is insufficient due to negative pressure, flows in through gaps in the greenhouse, such as the door, and increases the heating load. An exhaust heat recovery device for solving this problem and recovering the heat of the exhaust gas is important.

A small gas heat source hot air heater is mounted and installed on the upper structure of the greenhouse, and usually exhaust gas after combustion is discharged into the greenhouse, which serves to promote carbon assimilation of plants by supplying carbon dioxide.
However, ethylene gas in the exhaust gas can cause leaves to fall and fruits to ripen quickly, and excessive humidity and condensation problems can occur when the moisture content in the air increases.

Water flows from a high place to a low place, and a pump is used to move it from a low place to a high place. In this way, heat moves from a high place to a low place to achieve thermal equilibrium, and the outside temperature in winter is low and the greenhouse temperature is high. In such a situation, there are many difficulties in heat transfer using an air-heated heat pump. As the temperature difference between the outside and the room increases, the high and low pressure difference of the heat pump increases, so the power required increases and the movement energy is not large. As such, as the amount of refrigerant circulation is influenced by the outside temperature, the efficiency of the air-heated heat pump decreases as the outside temperature decreases. Also, in such an air heat pump, frost occurs in the heat exchanger of the outdoor unit. This is because the phase change temperature of the refrigerant inside the heat exchanger, that is, the evaporator, is mostly operated below 0℃. When is -10℃, the evaporation temperature of the refrigerant is about -17℃, and it maintains a deviation of about 7℃ from the normal outside temperature. This means that heat can be absorbed from the outside air only when the evaporation temperature of the refrigerant is lower than the outside air temperature. For this reason, frost occurs on the heat exchange surface of the evaporator, and it must be melted periodically. In winter, there are cases where it snows in general weather. In this case, the snow flows into the heat exchange pin coil of the evaporator and quickly blocks the passage of wind. The sensor detects this and circulates the heat pump in reverse to melt the evaporator. At this time, the necessary heat is taken from the inside of the greenhouse.

For this reason, the air heat pump discharges a certain amount of heat at room temperature, but the efficiency decreases as the temperature goes down and the defrost time becomes longer. As a way to solve this problem, geothermal water heat is used to operate the chiller. The use of water heat is a method of using groundwater in the ground. It is a method of absorbing energy from groundwater by exchanging the heat of evaporation of the evaporator with groundwater. Since there is much more than air, the heat pump can be operated stably. Efficiency COP part is also improved by 50% compared to air heat, so it is as high as 3.5~4. This is the amount of heat dissipated from the condenser compared to the equivalent of the working heat of the compressor, and it means that 4kw of heat is discharged from the radiator with the power of 1kw of the refrigerator, and the heating efficiency is higher than the cooling efficiency. The use of water heat causes the problem of returning the used groundwater back to the basement, but caution must be taken as the groundwater may become contaminated during this process.

The method of using geothermal heat is a system capable of heating and supplying hot water from a heat pump boiler by using thermal energy underground. A geothermal heat exchanger is installed at a depth of 150 m underground, and the cooling water of the geothermal heat pump chiller is transferred to the underground heat and heat exchange cooling water through the geothermal heat exchanger. It is a system that continuously supplies heat to the heat pump by maintaining a constant temperature. The heat transfer process of the system is a shell-and-tube water-cooled condenser, where the condensed heat of the refrigerant exchanges heat with the cooling water circulating inside the shell, that is, the heating water, and the refrigerant is condensed into a liquid phase change to absorb the heat exchange energy with the cooling water of the chiller chiller, the refrigerant evaporates and is sucked into the chiller. At this time, the water cooled by heat exchange with the refrigerant in the chiller is heated by geothermal heat while circulating underground through the pipe to maintain a constant temperature. This method uses the same principle as the heat circulation method of a water-cooled chiller chiller and uses stable geothermal heat to provide constant heating and cooling in four seasons, but the initial facility investment is high and maintenance costs are high.