[Regenerative electric heater]Characteristics of regenerative electric heater

strong>

The application and promotion of electric heating systems should be based on the premise that electricity is relatively abundant. In fact, the most prominent problem in electricity is the continuous widening of the peak-to-valley difference. If the electric heating system only operates during the low power period, the peak-to-valley difference of the power load will be reduced, which is conducive to the safe and stable operation of the power grid. From an economic point of view, cheap valley-price electricity can be used, which greatly reduces the operating cost of the electric heating system. In order to realize the low power operation of the electric heating system, it is necessary to use regenerative electric heating equipment.

Regenerative electric heating equipment is a clean, safe, comfortable and reliable heating method, which is currently very popular in North America and Europe for winter heating. In contrast, there are few applications of thermal storage in my country, mainly focusing on waste heat or waste heat utilization. The role of the heat storage device is to balance the relationship between heat supply and heat load, reduce equipment capacity and improve system efficiency. Therefore, in the case of a certain heating load, change the amount of heat supplied by the electric heating system at different times, use more electricity for heating during the power trough period, and use less or no electricity for heating during the peak power period. The balance between the loads can be achieved through the heat storage device, so as to achieve the purpose of reducing the difference between the peak and valley of the power.

According to the different storage medium, there are two types of thermal storage: direct storage and indirect storage. Indirect storage uses an intermediate medium as a storage medium to store heat. The heat storage temperature of this heat storage method is relatively high. For example, the heat storage temperature of the storage medium composed of salt and oil can reach 340 °C, and the heat storage temperature of a molten nitrate as the heat storage medium can reach 566 °C. However, the investment of indirect storage method is large, and the heat temperature used by heating and air conditioning is relatively low, so it is not suitable to adopt this heat storage method. Direct thermal storage can directly store the hot water or steam to be stored in the thermal storage container. Direct thermal storage can be divided into pressureless thermal storage and pressure thermal storage. The maximum heat storage temperature of the pressureless heat storage method can reach 95 ℃, and the investment is low. The pressure heat storage method is to store steam or high-temperature hot water directly in a spherical or cylindrical pressure vessel, and the heat storage temperature can reach up to 200 °C. However, the pressured heat storage method has a large investment, which is equivalent to 2 to 5 times that of the pressureless method.

2. Comparison of several thermal storage electric heating systems

(1) Hot water thermal storage device

Due to the use of heat storage, from an overall point of view, the electric heating system has played a role in shaving peaks and filling valleys for the power grid. Locally speaking, due to the consumption of low-cost electricity, the operating cost of the heating system will be greatly reduced. . However, the investment in heating equipment will also increase accordingly, because the heat source capacity is increased compared to when there is no heat storage, and energy storage equipment is added at the same time. In terms of energy consumption, the energy consumption of the system increases compared to without thermal storage due to energy storage losses. For the heat pump system, the coefficient of performance of the heat pump is significantly reduced due to the increase of the temperature at which the heat is produced, and the energy consumption of the system is increased at the same time.

For the electric heat pump heating device, since the performance coefficient COP of the heat pump decreases significantly with the increase of the temperature of the heat produced, the maximum temperature of the hot water produced by the heat pump is selected as 70 ℃ in this paper, and the corresponding The COP is taken as 2.0, and the heat accumulator can only be in the form of no pressure. The electric furnace heating system can use both pressure and non-pressure heat storage devices, and because the heat storage device is water, the electric furnace should be applied in the form of an electric boiler. Assume that the thermal storage efficiency of hot water is 85%, and the peak and valley of electricity each account for 12 hours in a day. Therefore, Table 1 gives the relevant indicators of the heating system after adopting the thermal storage device. It can be seen that the electric furnace heating system after adding the heat accumulator plays the most significant role in terms of power peak shaving and valley filling. Judging from the volume of the heat accumulator, the volume of the pressurized hot water heat storage is obviously less than that of the unpressurized hot water heat storage, but the pressurized hot water heat accumulator is a pressure vessel, and there is a safety problem.

After adding heat storage device, the initial investment of heating system will increase, including investment in heat storage device and investment in heating system itself due to heat storage. The size of this part of the additional investment is related to the type, volume, location and system operation mode of the heat storage device. For the electric heat pump, only when the additional investment of the unit heating system is <1 500 yuan/kW (heat), the economy of the heating system will be better than that without heat storage. In general, the system additional investment is less than this value. However, if the space occupation of the heat accumulator is expensive, for example, if it is set in a prime area of the urban area, the additional investment of heat storage in the system may increase sharply, resulting in that heat storage cannot improve the economy of the overall system. For electric boilers, as long as the additional investment in heat storage per unit of heat supply is less than 4 900 yuan/kW (heat), the economy of the heating system will be better than when there is no heat storage. Usually, the additional investment in system heat storage will not be greater than this value. Therefore, for electric heat pump heating, whether to add a heat storage device should be determined after analyzing and demonstrating according to the specific situation. The effect of adding a heat storage device for electric boiler heating is obvious.

(2) Thermal Storage Electric Heater

In electric heating, the peak-shaving and valley-filling of electricity can be realized through thermal storage of hot water. However, due to the large volume of the heat accumulator, it can only be used in a centralized electric heating system. If it is combined with a household electric heating system, it will occupy a large space in the room, which is unrealistic. Therefore, a heating device combining electric heater and phase-change heat storage—phase-change heat storage electric heater is proposed. The phase-change heat storage electric heater comprises a temperature-controlled and time-controlled dual control switch, an electric heating device, a heat exchange container, a phase-change material sealed therein, and a thermal insulation jacket. It is characterized in that the time-controlled program is solidified in the time-controlled switch, so that the electric heater can only be turned on within a certain period of time (the grid load valley section). When the electric heating device is powered on, the phase change material begins to heat up and melt. When the phase change material is completely melted, the temperature control switch stops the heating device from working. At this time, the heat is mainly stored by the phase change material in the form of latent heat. When the room needs to be heated, open the damper or turn on the electric fan, the electric heater starts to emit heat to the outside, and the liquid phase change material gradually solidifies, and at the same time, the solidification heat is released. Since the phase transition process is an approximately isothermal process, the latent heat of the phase transition is relatively large, so it can be approximately isothermally exothermic for a long time even in the absence of electricity. In practical applications, an insulating jacket is provided on the outside of the electric heater, which can achieve a good thermal insulation effect. The heat insulation cover ensures that the stored heat exists in the electric heater. When it is necessary to take the heat, the heat insulation cover is partially or completely opened, and the heat exchange container emits heat to the outside. The shape of the heat insulation sleeve can be made into an integral box structure with an inlet and outlet valve, and an exhaust fan can be installed at the air outlet, or no fan can be installed, and the heat exchange with the indoor air is completely relied on by natural convection. Due to the large heat capacity and high heat storage efficiency of the phase change material, and the low cost of the electric heater as a heat source, it can overcome the above shortcomings of hot water heat storage.

It can be seen from Table 1 that the heat storage volume of this heating device is only about 1/8 of that of the unpressurized hot water accumulator, which is a About 1/3 of the heater. In addition, the phase change thermal storage electric heater can be adjusted flexibly and is installed in the heating room, which can be used immediately. The economy of this heating device is better than that of electric furnace and gas boiler heating. At the same time, this kind of electric heater can reduce the peak-to-valley difference, which has positive significance for the safe and efficient operation of the power grid. Therefore, the phase change thermal storage electric heater is a new type of heating system with good development prospects. However, due to the high power consumption of the phase-change thermal storage heater, when the room heating load is large, there is a problem of user circuit reconstruction.

3. Advantages of regenerative electric heating system

The regenerative electric heating equipment embodies a brand-new humanized design concept, which is in line with the user’s changing ” “Passive heating” is “active heating”, and it is gradually favored by more and more people to independently improve the quality of life and the consumption requirements of the quality of life.

Compared with other traditional heating systems, regenerative electric heating systems have the following advantages:

(1) Simple installation, no need to consider piping

Central heating involves multiple business links such as power plants, heat plants, and users, and is prone to disputes over payment. At the same time, central heating consumes a lot of coal, and also adds investment and management such as pipeline laying and maintenance, land occupation, etc. Cost, trouble and waste, while the regenerative electric heating system only needs a flat wall for fixing and a wire connected to the power supply, so it does not bring inconvenience to the room layout. Without any heavy equipment and pipes, the installation cost can be saved by at least 50%.

(2) Small heat loss

The traditional heating system will lose 10% to 30% of the heat through the heating pipeline, while the regenerative electric heating All electrical energy in the system can be directly and completely converted into heat energy, with an efficiency of nearly 100%.

(3) Sub-room heating, temperature control at will

In winter, users can get warmth at any time as needed without being limited by heating time. Works independently, so it can provide heat energy according to the different needs of each room. Individual thermostats and thermostats can set the desired temperature for each room, making the room more comfortable and reducing power consumption.

(4) No pollution, protect the environment

Electricity is a clean energy, easy to use, and without any pollution.

(5)Small size and space saving

And with various design styles, it can match any decoration.

(6) Safe and reliable

Because the electric heater itself has low temperature and long service life, there is no need for regular maintenance. Safer and more reliable, and data shows that coal-fired heating systems are detrimental to health, and gas is a safety hazard.

4. Conclusion

In summary, the thermal storage electric heating system is a kind of heating form with very good economic and social benefits. It can effectively reduce the environmental pollution caused by heating in winter; because it has the function of “shifting peaks and filling valleys”, it can also improve the operation efficiency of the power grid. However, the large investment cost is also a bottleneck hindering the promotion of electric thermal energy storage heating systems. Therefore, government departments should introduce corresponding preferential policies to encourage heating systems to add thermal storage devices. In today’s widening gap between power peaks and valleys, the application of thermal storage in electric heating should be further paid attention to.

With the continuous growth of the economy, China has begun to attach importance to the protection of the ecological environment to ensure sustainable development. In order to reduce urban pollution, the Chinese government has also begun to take measures to promote the use of electric energy and other clean energy sources superior to coal, and to encourage people to use electric heaters in their homes to replace traditional coal or gas heating. It is regenerative electric heating equipment. In the future when the energy crisis is becoming more and more serious, this heating method should be popularized as one of the main heating methods.