Agricultural planting and flower greenhouses require high temperature in winter, so heating measures should be taken. Common heating methods include boiler, electric fan and heat pump heating which has emerged in recent two years. This paper introduces the investment cost, operation cost and relative advantages and disadvantages of these common heating methods for your reference when you choose to use them.
1, boiler
Boilers are divided into oil-fired boilers, gas-fired boilers, coal-fired boilers, biomass boilers and electric boilers according to the types of fuels used. Because of the low cost and moderate operation cost of boiler equipment, it occupies a large share in greenhouse heating equipment.
Coal boiler
Advantages: low cost and low operation cost.
Disadvantages: the operation efficiency is low, because small and medium-sized boilers are generally used for greenhouse heating, and the efficiency is between 50-70% according to the advantages and disadvantages of coal burning; The equipment occupies a large area and needs a special equipment site; Coal-fired boilers also need special personnel to look after them, which has high labor cost and potential safety hazards such as fire and explosion during use. The biggest disadvantage of coal-fired boilers is serious environmental pollution. Dust (including fly ash and carbon black), sulfur and nitrogen oxides contained in the flue gas of coal-fired boilers are all substances that pollute the atmosphere, including nitrogen oxides, sulfur dioxide, soot, mercury and carbon monoxide. When they are not purified, their emission indicators can reach several times to dozens of times of the environmental protection regulations. These pollutants have caused serious air quality deterioration and environmental pollution, and notorious smog, acid rain and room temperature effect are all related to them. The country has strengthened environmental protection and issued a series of national and local policy documents. All parts of the country are vigorously promoting the cancellation of coal-fired boilers. In the near future, small and medium-sized distributed heating coal-fired boilers will quit the heating stage.
gas fired boiler
Advantages: moderate cost.
Disadvantages: the operation efficiency is not high, and the efficiency of small and medium-sized gas boilers is between 80-90%; The equipment occupies a large area and needs a special gas station equipment site; There are potential safety hazards such as fire and explosion during use; Gas-fired boilers also have environmental pollution problems, and are not environmentally friendly heat sources. The operating cost of gas-fired boilers is generally 2-3 times that of coal, and the operating cost is high.
Biomass fuel boiler
Advantages: moderate cost and low operating cost.
Disadvantages: the equipment occupies a large area and needs a special equipment site; Need special care, labor costs are high, and there are safety hazards such as fire and explosion during use; Biomass fuel boilers also have environmental pollution problems, so they are not environmentally friendly heat sources. At the same time, there are few fuel sources and few use occasions.
Electric boiler
Advantages: low cost and convenient use.
Disadvantages: the operation efficiency is not high, and the efficiency of electric boiler is between 80-90%; Large power consumption and high operating cost.
2. Electric wind
Electric heating hot air blower takes air as heat carrier and adopts electric heating device to provide high-temperature and clean hot air for various drying equipment and HVAC industry.
Advantages: low cost, convenient installation and use, and high temperature control accuracy.
Disadvantages: the operation efficiency is not high, and the thermal efficiency of the electric fan is between 80-90%; Large power consumption and high operating cost.
3. Heat pump
Heat pump technology is a new energy technology that has attracted worldwide attention in recent years. The familiar "pump" is a kind of mechanical equipment that can improve potential energy. For example, a water pump mainly pumps water from a low position to a high position. "Heat pump" is a device that can obtain low-level heat energy from air, water or soil in nature and provide high-level heat energy for people to use after doing work with electric energy. Heat pumps can be divided into water source heat pumps, air source heat pumps and multi-source heat pumps according to different sources.
Water Source Heat Pump
Water source heat pump is an air conditioning technology that uses solar energy stored in the earth's water as a cold and heat source for conversion.
Advantages: high efficiency, energy saving and low operating cost.
Disadvantages:
① High cost. Because all the energy obtained by water source heat pump comes from groundwater, there is a great demand for drilling wells, and professional geological exploration is needed in the early stage. Water quality testing is very expensive.
② Unstable use, the water source heat pump takes heat from the ground in winter and stores heat in the ground in summer, and the groundwater temperature is unbalanced due to the unbalanced cold and heat load in winter and summer; Because the heat supply in winter is much greater than the cooling capacity in summer, the heat imbalance problem of water source heat pump in north China is particularly obvious. Many water source heat pump projects have just started for a year or two without considering this problem. After a few years, the temperature of groundwater is getting lower and lower, which leads to the worse effect of heat pump and even unusable.
(3) The maintenance is complicated, the water quality in China is hard, and the water pumped from underground is easy to scale after passing through the heat exchanger. The water source heat pump needs to clean and maintain the water source heat exchanger 1-2 times a year at least, and it is difficult to pump it back into the well and maintain it.
(4) Pollution destroys groundwater, so water source heat pump needs to pump groundwater. The pumping capacity of large-scale projects can reach 500T/H, and the water will be polluted after passing through the main engine. The most serious problem is that the quality of water source heat pump projects is uneven, and many projects are not recharged in place (less than the same pumping layer) or even directly discharged into sewage pipes or the surface, resulting in urban groundwater level and land subsidence, which has geological risks and is easily investigated by water conservancy and environmental protection departments. Therefore, many local governments began to strictly control water source heat pump projects and groundwater exploitation;
air source heat pump
Air energy (source) heat pump is driven by motor. Based on the working principle of vapor compression refrigeration cycle, it uses ambient air as cold (hot) source to produce cold (hot) wind or cold (hot) water. The main components include hot side heat exchanger, heat source side heat exchanger and compressor. The air energy (source) heat pump uses the heat in the air as a low-temperature heat source, exchanges heat through the condenser or evaporator in the traditional air conditioner, and then extracts or releases heat energy through the circulation system, and transfers energy to the building through the unit circulation system, so as to meet the needs of users for domestic hot water, floor heating or air conditioning.
Advantages: convenient installation and use, energy saving, safety and durability.
Disadvantages:
① The effect is unstable. Due to the low air energy density and heat exchange efficiency, air source heat pump has poor heating effect, low energy efficiency and huge power consumption in extreme weather.
(2) Defrost is needed. When the air source heat pump heats in winter, the ambient temperature is lower than 10℃, and it is easy to frost. Defrosting after frosting will affect the heating effect and increase power consumption.
(3) Due to geographical limitations, air source heat pumps are only suitable for use in the south. Although various types of cryogenic technologies have been developed in the north, the use effect is still unsatisfactory and the power consumption is high.
Multisource heat pump
Multi-source heat pump is a device that relies on advanced control system and couples low-level energy such as solar energy, geothermal energy and air energy to provide heating and cooling and domestic hot water.
Advantages:
① It is convenient to install and use, and the units are all of modular design, so it can be used only by connecting waterways as specified.
② Energy conservation and environmental protection. The unit adopts American low-noise and high-efficiency scroll compressor, and the heat exchanger adopts high-efficiency hydrophilic copper tube heat exchanger with internal thread. Combined with the comprehensive utilization of various energy sources, the operating efficiency of the unit is 20%-30% higher than that of the conventional air source heat pump unit, and the comprehensive energy efficiency ratio can reach 7.0 in summer, which greatly saves the operating cost. In line with national policies on energy conservation, emission reduction, environmental protection and low-carbon economy.
③ Safe and durable. All accessories of the unit are made of well-known brands at home and abroad, with high reliability, safety and durability.
(4) Stable and comfortable. Because of multi-source reuse, there is no need to defrost in winter, which ensures the heating effect, and high-temperature refrigeration can also ensure efficient operation in summer.
⑤ Wide application range, multi-source heat pump coupled with multiple energy sources, suitable for heating and cooling in low temperature environment in the north and high temperature environment in the south.
Disadvantages:
(1) has high system integration and high engineering requirements;