Power plants using low-temperature energy sources. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

 Comments on the article

Ground heat exchangers in vertical wells have been widely used in the last 10-15 years as a low-temperature heat source for heating and hot water supply systems using heat pumps. This environmentally friendly heat source is used quite often, for example, in Switzerland, where about four thousand such installations are currently in operation.

The Altai Regional Center for Non-traditional Energy and Energy Saving conducted research on the mutual influence of a vertical ground heat exchanger and a heat pump. The automated heat pump unit ATNU-10 (working fluid - R22) was taken as the basis, developed by AK "INSOLAR" within the framework of the State Scientific and Technical Program of Russia "Environmentally Clean Energy" and manufactured by the "ECOMASH" enterprise (Saratov). The system also includes a vertical ground heat exchanger in a well with a depth of no more than 100 m (as hydrogeological studies have shown, 67% of the population of the Altai Territory lives in the territory where the depth of the first aquifer is less than 30 m). The base soil temperature is assumed to be 280 K, which corresponds to the average temperature estimate at a depth of more than 5 m for the conditions of the Altai Territory.

The automated control system of the ATNU type heat pump is designed in such a way that it works under optimal conditions with a constant value of the heat flux determined by the heat flux from the primary heat source, the inlet temperature of the high-temperature circuit and the mass velocity of the heat carrier of the high-temperature circuit. If the required heat load decreases, the heat pump must be switched off until the set temperature is restored. If the power of the ground heat exchanger is insufficient to cover the heat losses in the high-temperature circuit, a peak closer must be switched on.

The results showed that the thermal energy extracted from the soil linearly depends on the logarithm of the working length of the heat exchanger. Under these conditions (filtration rate 10 m/day), to obtain 5-6 kW of thermal power from the soil, the required depth of the heat exchanger will be 50-60 m. The minimum flow rate in the heating circuit must be 0,3 kg/s (1 m*/h). At smaller volumes, heat accumulation will begin in the system and, as tests on a full-scale installation have shown, this will lead to an increase in the temperature and pressure of freon, a deterioration in the operation of the evaporator and a decrease in heat removal in the ground heat exchanger. And although at the same time the temperature of the coolant of the high-temperature circuit increases, the efficiency of the entire circuit, determined by the heating coefficient, decreases.

Great interest in the use of soil as a source of heat is shown in Europe. The design of the evaporator is proposed in the form of a serpentine of tubes with a diameter of about 25 mm, laid at a constant depth over an area of ​​several hundred square meters. In order to reduce capital costs, the tubes are located as close to the surface as possible.

The study of soil as a heat source conducted in Europe showed that the heat flow to the evaporator from the soil is 20-25 W/m, the minimum value for Europe is 10 W/m, the maximum is 50-60 W/m.

The optimal depth and spacing of the tubes are 1,5 and 2 m, respectively. In some cases, due to mutual influence, the limit of 2 m is extended. The pipes can be placed at a shallower depth, but the heat pump performance can be reduced by 5% for every degree of evaporator temperature drop.

In addition to the option of evaporating the refrigerant directly, it is possible to use an intermediate heat carrier - brine circulating through pipes in the ground and giving off heat to the refrigerant in a special heat exchanger. The average brine temperature in winter is -3°C.

If the water content of the soil is high, the performance increases due to the increase in thermal conductivity and good contact with the tubes. A large concentration of gravel in the soil causes deterioration in performance.

In Denmark, the possibility of using not horizontal, but vertical tubes, which can be used in the mode of not only heating, but also cooling the building in summer, when a reversible heat pump is used, has been considered.

An interesting detail was also discovered. The minimum ground temperature is always higher than the air temperature and is reached two months later when the required heating output decreases.

Vertical tubes take up less space and allow some use of the heat stored during the summer months, which gives them an economic advantage. Studies of vertical U-tubes have shown the possibility of significant heat recovery. A horizontal evaporator from an area of ​​150-200 m allows you to get 12 kW of heat. U-tubes placed in wells with a diameter of 127 mm and a depth of 8 m made it possible to obtain 12 kW from only two wells. It can be seen from this that U-shaped tubes reduce the required soil surface by 10-20 times compared to horizontal ones.

Despite the relative cheapness of domestic heat pumps compared to foreign ones, given the current weak financial situation of enterprises, the introduction of heat pumps encounters certain difficulties. Not the last role is played by the great novelty and unusualness of this technique for our consumers. These problems were overcome abroad by granting privileges for several years to enterprises implementing heat pump installations. In most Western European countries, the income generated from the use of heat pumps was taxed less, and in some countries direct financial subsidies were made. For example, in Austria, firms using heat pumps were given a financial subsidy of up to 100 shillings, while in the early 90s, such firms were entitled to a tax rebate of up to 7,5% of capital costs in Germany (subject to their capitalization), which is equivalent to a financial subsidy of up to 20% of the cost of heat pump installations. As a result, 105 HPPs are currently operating in Austria, saving 116 tons of fuel oil annually.

In addition to the use of ground heat, the most attractive for use in home heat pump applications is the "free" source of heat for creating comfortable conditions inside the house - air. It is publicly available and has attracted the most attention in mass production. Where water is available, it has several advantages over air. The use of waste heat or solar collectors is being actively explored, in which there is interest in both Europe and America.

The most widely used heat pumps with air as a heat source from the very beginning of their use in the home. Basically, air is also a heat sink. As a heat source, air has a number of disadvantages, so careful optimization of the design is required depending on the installation location, where the air temperature can vary significantly.

The performance of the heat pump, and especially the COP, decreases as the temperature difference between the evaporator and condenser increases. This has a particularly unfavorable effect on air source heat pumps. As the ambient temperature drops, the amount of heat required for heating increases, but the ability of the heat pump to maintain even a constant heat output is significantly reduced. To overcome this shortcoming, additional heating is often applied.

For the conditions of England and most European countries, the cost of a heat pump with any heat source is noticeably higher than that of a conventional central boiler. The larger the share of the heat pump in the domestic heat load, the higher the difference in investment, so heat pumps are usually calculated for only a part of the annual heat load, and the rest is provided by an additional heater, most often electric (in the USA) and fossil fuel (in Europe). The choice between them is determined by the ratio of capital and operating costs. If a heat pump also provides air conditioning in the summer, its size and power may be dictated by this particular application.

Additional heating is required when the ambient temperature drops below zero, and the heat loss of the building exceeds the heat output of the pump. In order to increase the economic efficiency of the system, the inclusion of an additional heater, in this case electric, is recommended only when the heat pump cannot cover the full load.

All heat sources for heat pumps are more or less affected by solar energy, but it can also be used directly with the help of solar collectors with heat carrier circulation, heating the air entering the evaporator with the help of solar concentrators. Although solar concentrators seem to be more suitable for absorption heat pumps. They are still little used at home, but are the subject of significant research work. To heat up a generator in an absorption cycle, higher temperatures are required than are achievable with conventional flat-plate collectors. However, the use of an absorption cycle for air conditioning allows heating from flat-plate collectors, since the temperature here must be lower and therefore air cooling is carried out in the summer, just when solar radiation is intense and the temperature of the collector is increased.

Together with other sources of heat for heat pumps, flat-plate collectors placed on roofs are widely used. In general, solar collectors are intensively studied for use not only with heat pumps, but also independently, as well as in circuits with heat accumulators. The latter are also of interest to heat pumps as a source of heat on cloudy days or at night.

By supplying heat to the evaporator at a temperature higher than the ambient air, ground or water, solar collectors increase the COP of the heat pump.

Usually the intermediate coolant - water transfers heat from the collector to the evaporator. But there may be a complete combination of the collector with the evaporator, where the refrigerant evaporates directly inside the tubes of the solar collector.

Often the heat from the solar collector is fed into a liquid heat storage where the evaporator tubes are immersed. The heat storage plays an essential role in any solar heat pump system. In a Phillips house, for example, a solar collector (20m2) collects 36-44 GJ of heat per year (with an average efficiency of 50%) stored in a 40m3 tank at temperatures up to 95°C.

A minimal energy house scheme was proposed using three heat pumps: one to transfer heat with increasing temperature from the solar collector to the battery, the second from the battery to the heating system, and the third from the battery to the hot water system.

Solar collectors are also considered in combination with ground collectors. It has been established that the dimensions of the solar collector should be more than 3 m2 per 1 kW of heat loss from the dwelling. With a solar collector with an area of ​​30 m3 with a ground evaporator occupying only 100 m, COP = 3,4 is achieved. If only a ground evaporator is used, then a surface of 300 m is required, and this results in a COP = 2,7.

However, it may be that despite the increase in COP, the fuel savings may not justify the cost of the installation, especially the solar collector. Other works in this area show that with a thermal power of HPI of 6 kW, a surface of 20m2 is required.

In addition, HPP can use heat discharges from the housing itself, for example, exhaust gases from kitchen stoves or from the kitchen in general, waste water. In Holland, TN was applied to a domestic dish dryer. The heat of the ejected moist air is used to heat the dry air supplied to the dryer. The warm moist air from the dryer passes into the HP evaporator and is cooled down. When cooled, moisture falls out of it, and the air becomes suitable for recirculation. The evaporator uses both the sensible and latent heat of the outgoing air. The recirculating air passes through the condenser and is heated by the heat of condensation. Energy savings reach about 48%. The following are some characteristics of HPPs that are widely used abroad.

Tab. 2.1.2. Characteristics of the HP-installation "Carrier" (USA) - a simple reversible air-to-air heat pump

Tab. 2.1.3. Characteristics of Lennox HP, combined with a fired heating system, which eliminates the additional heating system

See other articles Section Alternative energy sources.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Alcohol content of warm beer 07.05.2024

Beer, as one of the most common alcoholic drinks, has its own unique taste, which can change depending on the temperature of consumption. A new study by an international team of scientists has found that beer temperature has a significant impact on the perception of alcoholic taste. The study, led by materials scientist Lei Jiang, found that at different temperatures, ethanol and water molecules form different types of clusters, which affects the perception of alcoholic taste. At low temperatures, more pyramid-like clusters form, which reduces the pungency of the "ethanol" taste and makes the drink taste less alcoholic. On the contrary, as the temperature increases, the clusters become more chain-like, resulting in a more pronounced alcoholic taste. This explains why the taste of some alcoholic drinks, such as baijiu, can change depending on temperature. The data obtained opens up new prospects for beverage manufacturers, ... >>

Major risk factor for gambling addiction 07.05.2024

Computer games are becoming an increasingly popular form of entertainment among teenagers, but the associated risk of gaming addiction remains a significant problem. American scientists conducted a study to determine the main factors contributing to this addiction and offer recommendations for its prevention. Over the course of six years, 385 teenagers were followed to find out what factors may predispose them to gambling addiction. The results showed that 90% of study participants were not at risk of addiction, while 10% became gambling addicts. It turned out that the key factor in the onset of gambling addiction is a low level of prosocial behavior. Teenagers with a low level of prosocial behavior do not show interest in the help and support of others, which can lead to a loss of contact with the real world and a deepening dependence on virtual reality offered by computer games. Based on these results, scientists ... >>

Traffic noise delays the growth of chicks 06.05.2024

The sounds that surround us in modern cities are becoming increasingly piercing. However, few people think about how this noise affects the animal world, especially such delicate creatures as chicks that have not yet hatched from their eggs. Recent research is shedding light on this issue, indicating serious consequences for their development and survival. Scientists have found that exposure of zebra diamondback chicks to traffic noise can cause serious disruption to their development. Experiments have shown that noise pollution can significantly delay their hatching, and those chicks that do emerge face a number of health-promoting problems. The researchers also found that the negative effects of noise pollution extend into the adult birds. Reduced chances of reproduction and decreased fertility indicate the long-term effects that traffic noise has on wildlife. The study results highlight the need ... >>

Random news from the Archive Genes against gravity 31.03.2015 The device of living organisms depends on where they live, and a huge number of very different factors determine the structure of the body, and physiology, and behavior - even in bacteria, even in people. Among these factors, the most universal ones can be distinguished, which are easy to enumerate: for example, the temperature of the environment, or humidity, or the concentration of oxygen in air or water. But there is something that is rarely mentioned. We are talking about the force of gravity, which acts on everyone and always. Could she play a role in shaping the appearance of living beings? Biologists have been asking this question for quite a long time: for example, 100 years ago, D'Arcy Thompson suggested that in animals the shape of the body is largely determined by the force of gravity, and if it were twice as large on Earth, primates would not have developed any upright posture, and in general all tetrapods would be short-legged and move like lizards. Apparently, evolution had to somehow respond to the gravitational factor, but what kind of molecular-cellular mechanisms helped us adapt to gravity, we can only now find out. Makoto Furutani-Seiki (Makoto Furutani-Seiki), together with his colleagues from the University of Bath and with the participation of researchers from Japan, Austria and the United States, were able to find a gene that is responsible for the formation of a "three-dimensional" body in animals. When it was turned off in fish, the development of tissues was disturbed, they were located incorrectly relative to each other, and the whole body was strongly flattened in the direction of the gravitational force. If it did not work in cultured human cells, they ceased to combine into volumetric clusters. In an article in Nature, the authors write that this gene, called YAP, serves as a regulator of the molecular machine that controls the mechanical forces in and between cells - the correct distribution of such forces is necessary to create most organs and body parts. Roughly speaking, thanks to YAP, we can resist gravity and generally have a more or less voluminous, rather than flat, body. How exactly the anti-gravity gene works, how and when it turns on, and what other genes are under its control, we have yet to find out. Further experimentation here will not only reveal why we have come to look the way we do now, but will also help develop reliable methods for creating artificial organs. By controlling the genetic system responsible for the "bulkness" of an organ, we can, for example, grow a liver or kidney of the right size in the laboratory, which will not differ from the real ones - in order to transplant them later to replace the spoiled ones.

Other interesting news:

▪ Smart cocktail stand

▪ The bird flies out and helps catch the robber

▪ Brewing coffee with a laser

▪ Dove visual memory

▪ 3D graphene

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Voltage stabilizers. Article selection

▪ article Release press. Drawing, description

▪ article What could the machine gun of 1912, considered the world's first computer game, do? Detailed answer

▪ article Common blueberry. Legends, cultivation, methods of application

▪ article Quartz chaotic oscillator. Encyclopedia of radio electronics and electrical engineering

▪ article Metal pattern by galvanoplastic method. Chemical experience

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024