Due to the low COP value, large unit power consumption, difficult defrost control in winter and large temperature fluctuation, the unit has no real energy adjustment and the rated refrigeration (heating capacity) of the single-phase motor unit is too small , Causing inconvenience to the users and exacerbating the contradiction between supply and demand of urban power grids. The solution of the ground-source heat pump household type ice-storage central air conditioner was put forward. The dual-thermal expansion valve, double-evaporator and ice melting outside the coil Unit structure form. Also on the improvement of living standards of urban and rural people, expansion and diversification of residential area, urban construction landscape and environmental constraints, the electric power sector will implement the "family" peak electricity price "and other aspects of ground source heat pump type of ice storage central air conditioning broad market expectation.
1 type of central air-conditioning development
Huxing central air conditioning that residential air-conditioning, since entering the Chinese market in the 1990s, has been rapid development. For its part, first of all, our country has always taken urban and rural residential housing as the top priority.
In recent years, per capita housing area has been greatly improved, and the housing also has to large-sized apartment, multi-bedroom villas, multi-storey and high-level development trend; Second, improve people's living standards, rich urban and rural residents up to the interior of the apartment "Well-off" level, room air conditioning has been unable to meet their requirements, more people are spending on the type of central air-conditioning; Third, the mature production technology and fierce market competition, making the type of central air conditioning costs gradually accepted by working-class Fourth, restrictions on the landscape and environment of urban buildings have also led some small-scale commercial users in cities to switch to small centralized air-conditioners. The above points can be seen, concern and discussion apartment central air conditioning is not ahead, apartment central air conditioning will be the 21st century new consumer hot spots.
2 type of central air conditioning problems and solutions
2.1 Unit central air conditioning current problems
After the investigation and understanding of the current type of central air conditioning, we found that there are the following problems:
1) Most of domestic-produced units are mainly heat pump units with air as heat source. Although they are convenient to use and install, in the hot area in summer, the condensing temperature is higher, the COP value is lower, and the unit consumption Electricity is large. In the areas with low temperature and high humidity in winter, the unit needs to defrost again, which causes large temperature fluctuation and the power consumption of the unit also increases.
2) Heat pump with air as heat source is greatly influenced by outdoor air. With the outdoor air temperature changes, heat pump unit cooling (heating) and building the amount of cooling (heat) changes in the opposite direction, it is difficult to match.
3) At present, there is no real energy adjustment in the domestic central air conditioner. Due to the large outdoor air temperature changes, the heat pump unit is at a low COP value under partial load most of the time in the entire cooling or heating season. Therefore, there is currently a "residential central air conditioning affordable, can not afford to use" argument. It is understood that in Chongqing Municipality, the construction area of ​​about 250m2 apartment central air conditioning, electricity bills in more than 1,000 yuan.
4) More than 6kW cooling unit central air conditioning and more require the use of three-phase power, and many users do not have the conditions of the use of three-phase power, when the user needs a larger capacity, often with two single-camera group in parallel, which Not only increased investment but also caused inconvenience to the installation.
5) Household air conditioners, especially the development of household type central air conditioners with large power consumption, have led to the rapid growth of city peak load and aggravated the contradiction between supply and demand of urban power grids. For example, the economically developed Shanghai Municipality, with a power supply of 9,600 MW and residential air-conditioning electricity accounts for about 30%. In August 1998, the continuous high temperature and residential air-conditioning were all turned on, causing Shanghai air-conditioning load to soar to about 3000MW. On the 13th of the same month, Shanghai's highest electricity load reached 9018MW, a net increase of 1000MW over the same period of 1997, resulting in a power shortage of about 700MW and peak power , Trough load difference of 3700MW.
2.2 Ground source heat pump type ice storage central air conditioning
For air-source heat pump type central air-conditioning problems, the author proposed ground source heat pump type ice storage central air-conditioning, its advantages are:
1) Taking soil as a heat source, soil temperature changes are relatively stable with the increase of soil depth due to small fluctuations of soil temperature throughout the year. Winter soil temperature is higher than the air temperature, summer and lower than the air temperature, so the heat pump heating and cooling COP values ​​are high. According to the determination made by Professor Liu Xiangying of Chongqing University, the COP value of ground source heat pump is about 30% higher than that of air source heat pump [4], which can greatly reduce the power consumption of residential central air conditioning and save the operation cost for users .
2) When the outdoor temperature is in an extreme state, the user's demand for cold (heat) amount is at its peak. Due to the delay of the soil temperature, the temperature of the user is not in an extreme state. It can provide a smaller condensation temperature and Higher evaporation temperature, improve the unit's cooling (heating) ability, as much as possible to meet user requirements.
3) Ground-source heat pump buried coil does not require defrosting, reducing the frost and defrosting losses and complex defrost control, thereby reducing the unit central air conditioning unit cost.
4) Ground source heat pump does not require fans, can reduce noise and hot air pollution, and operating conditions better than air source heat pump, with higher reliability. For the user's use of a great convenience.
5) The ground source heat pump host, can be installed in the storeroom or garage, does not affect the appearance of the building.
6) It is also due to the delayed role of soil temperature, which can increase the unit central air conditioning single cooling capacity. Coupled with the ice storage at night, can reduce daytime unit cooling capacity, reducing the unit compressor capacity, reduce unit cost, but also can adapt to the needs of more single-phase electricity users.
7) In summer, condensing temperature of ground-source heat pump is lower than that of air-source heat pump even at night, so the compression ratio during cooling system operation can be reduced. This creates an extremely favorable condition for residential central air conditioning using low-trough electricity storage ice .
3 ground source heat pump unit ice storage central air conditioning application prospects
Ground source heat pump unit type ice storage central air conditioning needs buried coil, to its application to bring some restrictions, but I still think it has a larger market prospects:
1) Small villas are increasing year by year, ground source heat pump house ice storage central air conditioning is rich first choice for urban and rural households air conditioning. This part of the inhabitants accounts for a small proportion of our population, but it is definitely not small.
2) The expansion of urban greening area also provides some low-level households and small-scale commercial and office users with the conditions of using ground-source heat pump type ice storage central air conditioners.
3) Industrial and mining enterprises office, measurement, testing, testing and other ancillary buildings also have the use of ground source heat pump unit ice storage central air conditioning conditions.
4) According to foreign data, under the condition of constant load operation, energy-saving rate of regenerative air-conditioners is 13% over non-regenerative air conditioners. Therefore, the storage and air conditioning will receive national attention and promotion, and may obtain state subsidies to reduce the user's investment.
5) In order to solve the problem of uneven power load, China will further widen the peak-to-valley electricity price ratio and move closer to the internationally prevailing peak-valley electricity price to encourage the utilization of low-valley electricity. At the same time, "peak valley price" is about to enter the family.
Shanghai has taken the lead in implementing "peak-valley tariffs" for residential households and has now been piloted in some households. In order to encourage the rational use of electricity by urban and rural residents, Sichuan Electric Power Company issued a series of preferential policies for peak and valley electricity prices. Installed a table of time-sharing degree of residential users, in the 6-11 mid-seasons wet period late at night, each kilowatt-hour electricity only pay 0.1 yuan. The rest of the season, late at night, low electricity consumption per kilowatt hour was 0.1875 yuan, while the conventional electricity per kilowatt-hour electricity was 0.3878 yuan. With the full implementation of the "peak valley electricity price" policy, ground source heat pump type of central ice storage will have a broader market prospects.
6) In recent years, foreign small-sized ice-storage air conditioners have been developed rapidly. Five Japanese BAC companies jointly developed several small ice-storage air conditioners of less than 10 horsepower to provide several types of ice melting, frequency conversion and frequency fixing Model, can be cold storage 5h. Japan's Mitsubishi Corporation has developed a power of 0.75kW cold storage air conditioning unit. After foreign products enter the Chinese market, consumers will inevitably attract the attention and selection, but also will promote the development of domestic units ice storage central air conditioning.
Discussion on Structure Types of Ground Source Heat Pump Unit Centralized Air Conditioning Unit
For ground-source heat pump unit type ice storage central air-conditioning, due to the domestic achievements in researching ground source heat pumps in recent years, the technology is also mature, so the development of such products should mainly be focused on small ice storage. The author believes that the ground source heat pump unit ice storage central air conditioning should consider the following questions:
1) Double thermal expansion valve
Thermal expansion valve is the most commonly used throttling element, which relies on the evaporator outlet refrigerant degree of superheat to adjust the valve opening, to automatically adjust the cooling capacity of the unit to meet the needs of changes in the external heat load.
Thermal expansion valve capacity and refrigerant mass flow, the valve before and after the differential pressure and other cooling conditions. Due to the differences between the air conditioning conditions and the refrigerant flow in the ice storage condition, the differential pressure before and after the valve, and the operating characteristics, it is obviously unreasonable to adopt the same expansion valve in the two conditions. In particular, due to the thermal expansion valve itself is limited by the construction, the applicable temperature and the adjustment range are small; In addition, the liquid-filled thermal expansion valve running in the ice storage conditions, the evaporator outlet overheating than air-conditioning conditions More. If the capacity of the expansion valve is too small, the heat transfer area of ​​the evaporator will not be fully utilized and the cooling capacity will drop. If the capacity of the expansion valve is too large, it will affect its regulating performance, increase the temperature fluctuation and superheat of the evaporator, Refrigeration system efficiency decline, there will be serious liquid hammer phenomenon.
As the main engine in the air conditioning operating conditions or in ice storage conditions, are generally rated load work, so its operating conditions are relatively stable, more suitable for the use of dual expansion valve, that is, according to air conditioning and storage conditions Respectively select the thermal expansion valve, the unit running in the air conditioning conditions, the use of air conditioning expansion valve; in the ice storage conditions, the use of ice storage expansion valve.
In order to meet the requirements of modern control level, the use of electronic expansion valve is better, the refrigerant flow adjustment range, allowing system load fluctuations. According to introduction and engineering practice, under low load, chillers with electronic expansion valves operate at 28% higher efficiency than those with thermal expansion valves, and the chilled water temperature can be controlled within ± 0.1 ° C.
2) double evaporator
Air conditioning conditions and storage conditions of the evaporation temperature difference is large, the same refrigeration compressor, cooling capacity is also quite different. In order to improve the heat transfer efficiency of the evaporator and ensure a good oil return of the refrigeration compressor, the unit should be equipped with two evaporators, one for ice storage in the low electricity section and one for the peak discharge in the power section. Take chilled water for air conditioning use.
Dual evaporator, such as matching reasonable, a little improvement can also be ice and frozen water system to meet the low-section air-conditioning cooling capacity required.
3) Melting ice outside the coil
As a household ice storage central air conditioning system, the process should be as simple as possible, the unit size can not be too large. Adopting the method of coiling and melting ice to cool the coil, the coil becomes the evaporator of the direct evaporative cooling system. The water in the cold storage tank forms a certain thickness of ice on the outer surface of the coil, which not only can reduce the volume of cold storage tank and reduce the volume of ethylene glycol The complicated process of the aqueous solution and the cold loss can also increase the evaporation temperature of the refrigeration system, increase the cooling capacity of the unit and reduce the unit cost.
External melting ice way allows air conditioning backwater and cold storage tank directly exchange heat, ice melting speed, release temperature can be greater than or equal to 1 ~ 2 ℃, and air conditioning backwater mixed directly available 7 ℃ chilled water .
5 conclusions and recommendations
In summary, the current production and use of air-source heat pump unit type central air conditioning there are some urgent problems to be solved, research and development of ground source heat pump unit type ice storage central air conditioning, energy saving, lower user operating costs and peak regulation is very important The significance and development prospects. In order to expedite the development and application of ground source heat pump type central ice storage central air conditioner, it is suggested that the electric power department establish and improve the preferential policies of encouraging low valley electricity as soon as possible, such as widening the peak / valley electricity price ratio as much as possible and giving the ice storage air conditioner equipment development and subsidies. At the same time, it is also suggested that the relevant manufacturers should strengthen the research and development of ground source heat pump type of central ice storage central air conditioning, reduce the cost and improve the overall efficiency, open up a broader market for the central storage air conditioners.
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