Design and research of solar hot water system for residential buildings?

As an important material basis for economic and social development, with the development of China's economy, the demand for energy has shown a trend of sustained growth, especially in recent years, with the rapid development of China's construction industry, it has also brought about rapid growth of building energy. At present, China's building energy consumption is close to 30% of the total energy consumption, and will continue to increase. With the improvement of people's living standards and the construction of a well-off society, people's demand for domestic hot water is increasing. The energy consumption of domestic hot water in developed areas of China has accounted for 15-20% of the total energy consumption of buildings. China is not only a big consumer of conventional energy such as coal, oil and natural gas, but also a country with a shortage of conventional energy resources. The energy structure dominated by conventional energy has produced a lot of pollutants, which has caused great pollution to the overall environment of our country. The contradiction between the way of energy development and utilization, which is dominated by disposable energy, and the ecological environment is becoming increasingly serious, which poses a severe challenge to the sustainable development of human society. Therefore, vigorously developing and utilizing clean and renewable energy-solar energy is one of the strategies to optimize the energy structure, improve the environment and promote sustainable economic and social development.

1 system selection

Most of the urban houses in China are multi-storey, small high-rise and high-rise houses. The technology of solar hot water system in developed countries is not applicable in China. Although China is the largest producer of solar water heaters and the country with the fastest development and largest scale of civil buildings, the per capita heat collection area is only 1/20 of that of Japan and Israel. Moreover, at present, most of them are distributed supply of hot water for one household, and they are installed afterwards, which is chaotic. The design, production and construction of solar water heaters are seriously out of line, and the utilization rate of solar energy resources is extremely low. Considering the regional resource conditions, residential types, residents' economic ability, plane layout, building appearance, hot water consumption and working conditions, the form and performance of heat collectors, system configuration, operation mode, installation mode, interface form and size, safety, maintenance and economy and technology, it is urgent to give priority to the principle of making full use of solar energy. And the use principle of providing stable hot water supply. Through technical and economic comparison, a reasonable residential solar hot water supply system and corresponding supporting products are designed to make the residential solar hot water system safe, reliable and stable in performance, and in harmony with the building and surrounding environment.

First, the current situation of solar energy

In the field of solar energy utilization, including photoelectricity and photothermal technology, photothermal technology is one of the most mature, widely used and promising fields, and its reliable technical performance and obvious economic performance are increasingly accepted by everyone. China is the largest producer of solar water heaters in the world, but compared with developed countries, the per capita heat collection area is less than 0.06㎡, so it is urgent to seek a breakthrough in the integrated development of solar water heaters and buildings.

Second, the status of solar water heaters in residential buildings

With the increasing popularity of solar water heaters in cities, a series of problems and contradictions caused by post-use installation and disorderly installation are gradually emerging. For example, it affects the appearance of buildings and urban landscape, destroys the use function of houses, and disorderly and irregular installation also causes some security risks. The biggest constraint is that the plot ratio of most residential quarters is high and the space between houses is too small. According to the data obtained from sunshine analysis, the distributed solar water heating system can only meet the demand of solar water heaters for 4 hours in winter solstice. At present, only the top floor residents are installing and using solar water heaters, and the per capita solar energy utilization rate is extremely low. It is a big problem for every household to enjoy and make full use of solar energy resources.

Thirdly, the position of solar water heaters in residential buildings.

From the point of view of the integration of residential buildings and solar energy, solar collectors can be arranged on roofs, walls, south balcony fences of every household, air conditioning panels and so on. Theoretically, setting solar collectors at the above positions is a good choice for low-density detached houses or row-by-row ground-floor houses, while the arrangement of decentralized solar collectors. According to the current residential standards, residential orientation, sunshine standards, residential spacing, etc. For the actual situation in Shanghai and even the whole country, developers want to achieve their maximum economic benefits. The floor area ratio of general houses is relatively high, with the spacing between multi-storey houses only 1.2 times the height of houses, and the spacing between small and high-rise buildings is about 40 meters. Solar collectors are installed on balconies, outdoor units of air conditioners, external walls, etc. And residents in middle and low areas of multi-storey and high-rise residential buildings can not meet the standard requirement of "Technical Specification for Application of Solar Water Heating System in Civil Buildings" that the average sunshine hours per household should not be less than 4 hours per day. Even residents in high-rise residential areas can meet the 4-hour illumination. However, due to the limitation of the installation angle of the collector, it is necessary to compensate a certain heat collection area when it is installed in external walls, cornices, balconies, building awnings, sun visors, etc. , resulting in an increase in one-time investment and a decrease in heat utilization. In addition, how to ensure the safety protection of collectors and the safety of residents is also a big problem.

Decentralized solar collectors can meet the above requirements, except for the upper part of the house, the lower part of multi-storey houses and the middle and lower parts of high-rise houses are mostly difficult to meet the requirements, and the utilization rate of solar energy resources is extremely low. Although concentrating on the roof can meet the requirements of sunshine hours, in actual operation, two pipes per household of decentralized solar hot water system need to increase the position of pipe wells, especially the pipe from the lower part of the house to the roof is too long, which will emit a lot of heat and discharge a lot of cold water in the pipe during use, which is not conducive to water saving and energy saving. How to make full use of solar energy resources so that every household can enjoy green, clean and renewable energy? The only practical position is to arrange solar collectors.

Four, the principle of setting the solar centralized heat collection system

(1) The design of solar hot water system is carried out at the same time as the architectural design. As an integral part of the building, the heat collector should be organically combined with the building to achieve beautiful appearance, durable components and convenient installation and maintenance.

(2) Make full use of solar energy resources, provide domestic hot water for every household in the house for 24 hours, adopt mature solar water heating technology, control costs and avoid complicated later operation and maintenance management.

(3) Carry out economic and technical analysis to meet the requirements of land saving, water saving, energy saving, safety, sanitation and environmental protection.

(4) The heat collector and its components are standardized and modularized, which is convenient for maintenance and update.

2 Calculation of heat collection area of solar centralized hot water system

I. Water consumption

(1) hot water consumption standard: 50l/person/day (60℃).

Residential area less than 90㎡ is considered as 2.5 people per household.

Residential area greater than 90㎡ is considered as 3.0 persons per household.

qmax day 1 = 50-2.5 = 125 l/d

Qmaxday2=50-3.0= 150L/d

Each household with less than 90m2 is equipped with 120L water tank.

Each household larger than 90m2 shall be equipped with 150L water tank.

Second, the determination of the area of solar heat collection system

(1) per household120l/day

Among them:

AC-daylighting area of direct system collector, ㎡;

Qw—— average daily water consumption,120kg; ;

Tend—— The final temperature of water in the water storage tank is 60℃;

CW-specific heat capacity of water at constant pressure, 4.187 kJ/(㎏-℃);

ρ-density of hot water, (㎏/L);

ti？ -The initial temperature of water is 65438 00℃;

JT—— the daily total radiation of the heating surface of the collector on a sunny day in the autumn equinox in Shanghai:12220kJ/㎡; /㎡;

F-solar energy guarantee rate; 50%

—— All-day thermal efficiency of the collector, with a value of 50%.

—— The heat loss rate of pipelines and water storage tanks here is 20%.

Then there is the solar heat collection area.

(2) per household150l/d.

3 Principle Description of Solar Centralized Hot Water System

First, the shortcomings of the previous centralized solar water heating system

In the past, the centralized solar hot water system mostly adopted the mode of centralized heat collection and household metering, and used the hot water meter to measure, which involved two problems: water quantity and water temperature. Because the water temperature of solar hot water system is unstable, it is necessary to configure auxiliary heat sources to meet the water temperature requirements, and conventional electric heating is adopted, which involves the allocation of electricity bills. Many metering and accurate allocation often lead to user rejection.

Second, the characteristics of this system

Design ideas: First, make full use of solar energy resources, so that every household can fully enjoy clean and renewable energy for the benefit of residents. Second, the system should be simple and reasonable, especially not to add trouble to users. The third is to ensure the safety of water quality. Only in this way, the energy-saving and environment-friendly solar water heating system is worth popularizing and applying.

Thirdly, the design of system collector.

(1) Orientation and inclination of the collector: due south, so that the collector can obtain more solar radiation energy; The inclination of solar collectors used throughout the year should be consistent with the local latitude.

(2) Connection of current collectors: There are many current collectors, so parallel connection is adopted to reduce resistance.

The number of collectors is small, and they are in series.

(3) Foundation: concrete foundation.

The bracket is made of hot-dip galvanized No.4 angle steel, with wind-resistant design, firm connection with the base and strong typhoon resistance.

(4) Calculation of the distance between the front and rear row collectors: There should be a certain distance between the front and rear row collectors to prevent the front row collectors from affecting the lighting of the rear row collectors. When used all year round, as long as the back row is not blocked from winter to the day before, it will not be blocked at other times. L=H-Ctga= 1.4H

L= the distance between the front row and the back row H= the height of the collector a= the local solar altitude angle at noon from winter to Sunday.

The layout of single row before and after will not affect the overall appearance of the building.

Four. System introduction

The system adopts centralized heat collection, and each household is equipped with exchange water tanks with different volumes according to the number of households. The hot water generated by the solar collector is supplied to the exchange water tank for heat exchange, and then returned to the solar heat storage tank. The outlet temperature of the exchange water tank is set to 60 degrees. In case of cloudy day, when the outlet temperature is lower than 60 degrees, residents will automatically (manually or automatically) start the electric heating device of the exchange water tank or connect the gas water heater after the outlet of the exchange water tank. The biggest feature of this system is that it does not involve the measurement of water, point and coal. The system

The following picture shows the plan and schematic diagram of the centralized solar hot water system for multi-storey and small high-rise buildings in a residential district.

Four. System control and operation instructions

T 1 collector outlet temperature

T2 outlet water temperature at the bottom of hot water tank

Temperature of hot water in T3 exchange water tank

(1) temperature difference heat collection cycle

When T 1-T2 > 5℃, the circulating pump 1 is started, and the water in the heat collection tank continuously exchanges heat with the heat collector. When their temperature is lower than 5℃, the circulating pump stops working.

(2) heat exchange cycle

When T2-T3 > 5℃ and T3 ~ 60℃, the solenoid valve in front of the exchange water tank is in the open state, and the circulating pump 2 is started at this time, and the circulating pump 2 generates constant-pressure variable-frequency water to exchange heat with each exchange water tank. When T2-T3 < 5℃ or T3≥60℃, the solenoid valve in front of the exchange water tank is closed. When all families in T2-T3.

(3) antifreeze cycle

When T 1≤3℃, start the circulating pump 1, and pump the water in the heat collection water tank into the heat collector for antifreeze circulation until T 1≥3℃, and the circulating pump 1 stops working.

(4) Overheating protection

When the heat collection water tank T2 is more than or equal to 80℃, the circulating pump 1 is turned off to stop heat collection.

(5) Water leakage control and explosion alarm of vacuum collector tube.

The working state of the system is monitored by the water level sensor. When the vacuum tube of the collector explodes, the water level in the pipe drops rapidly. When the water level sensor obtains abnormal water level, turn off the circulating pump 1. At the same time, the remote monitoring system is controlled to send an alarm signal to inform the property owner to replace the vacuum tube in time.

(6) Water level control of heat collection tank

The water inlet solenoid valve is controlled by the water level sensor. When the water level of the heat collection tank is lower than the set water level, the water inlet solenoid valve is opened, and when the water level is higher than the set water level, the water inlet solenoid valve is closed.

(7) anticorrosion

The air contains chloride ions, which will cause serious corrosion to metal structures. The metal materials used in the system have taken anti-corrosion measures.

(8) Lightning protection

In order to prevent lightning damage, the steel structure support in the system is reliably connected with the building grounding system.

(9) windproof

The installation of the collector and bracket shall conform to the specifications of the atlas. In order to ensure safety and prevent slippage, the heat collection tank should be fixed and reliable with the base.

(10) grounding

All electrical equipment and metal parts connected with electrical equipment shall be grounded.

(1 1) insulation

All exposed pipes and heat collection tanks are insulated.

4 Economic and energy-saving benefit analysis

A, solar energy, electricity, gas water heater heating energy consumption per shower:

The daily hot water quota for each person is 50L (60℃), and the tap water temperature is calculated as 10℃.

Heat consumption per person per day: 10.5MJ

If you take a bath once a day, each person will consume about 3820.6MJ of calories every year.

Solar energy (per capita 1㎡ collector)

The average solar thermal efficiency is 50%.

Take the annual solar radiation in Shanghai as an example.

The annual average calculated minimum heat preservation capacity of solar water heating system is 2100J/㎡.

The annual energy saving rate of solar water heating system (excluding 20% heat loss of the system) is about 44%.

Second, the shower cost comparison of various water heaters

Heat consumption of shower

Set the bath water temperature at 40℃, the cold water temperature 10℃, and a shower needs 50L, which consumes heat.

=50-(40- 10) -4 187- 1

= 6.28 MJ

= 1.74KWh

1. Heating cost of each shower using solar water heater:

(1) 150L solar water heater is equipped with a 3.0m2 collector. Taking Shanghai as an example, the annual total radiation dose of latitude inclined plane in Shanghai area is 4200 MJ/㎡ a. If the heat collection efficiency is 50%, the annual heat gain of each 1㎡ collector is 21100mJ, which is about 582KWh, so the annual heat gain of this water heater is:

582-3.0= 1745Kwh

The number of times you can take a shower in a year is:

1745kwh/1.74kwh =1003 times.

It is estimated that there are 1003 showers a year. According to 50L water per shower, this product can provide 6.43 showers per person per week for a family of three. Therefore, taking 1003 showers per household as the design condition, the shower cost of electric water heater and gas water heater is calculated and compared.

(2) The average service life of a solar water heater is 15 years, * * You can take a shower1003-15 =15045 times during use.

(3) If a centralized solar hot water system is set up, and the investment allocated to each household is 7,000 yuan, then the heating cost of each shower is the depreciation cost of the equipment.

7000/ 15045 = 0.47 yuan

2, the use of gas water heaters every shower heating costs

(1) Air consumption per shower:

The thermal efficiency of gas water heater is 80%.

The calorific value of natural gas is 35MJ/ m3.

The air consumption of each shower is:

6.28/35-80% = 0.22 cubic meters

(2) Fuel cost for each shower

The cost of natural gas in Shanghai is 2.50 yuan/㎡.

Fuel cost per shower

0.22-2.50=0.55 yuan

(3) The investment for setting up a gas positive displacement water heater is 3,000 yuan.

During the service life, according to the test life of 10 year, the number of showers of households is 10030.

Depreciation cost of equipment for each shower.

3000 \ 10030 = 0.30 yuan

The heating fee for each shower

0.55 0.30=0.85 yuan

3. Heating cost of using electric heater in each shower.

(1) The thermal efficiency of electric water heater is 90% of the power consumption per shower.

The power consumption of each shower is

1.74÷90% = 1.93 kwh

(2) The electricity charge for each shower is 0.6 1 yuan/kwh.

The electricity bill for each shower

0.61-1.93 =1.18 yuan.

(3) Depreciation cost of equipment for each shower.

The investment of installing a set of water storage electric heater is 2000 yuan, and the family will shower 10030 times in the service life of ten years.

Depreciation cost of equipment for each shower.

200010030 = 0.20 yuan

The heating fee for each shower

1.180.20 =1.38 yuan

Calculation of payback period of solar water heater investment

1, solar water heaters save energy every year.

(1) A family of three is equipped with a 3㎡ collector. In Shanghai, the annual heat gain of the collector is 6300MJ, which is equivalent to 1745KWH. When residents make full use of solar energy, this value is the annual energy saving of solar water heaters.

(2) The thermal efficiency of the electric water heater is 90%, providing 6300MJ heat for residents to shower.

Power consumption: 1745÷90% = 1939 kwh.

(3) The thermal efficiency of the gas water heater is 80%, providing 6300MJ heat for residents' showers.

Heat consumption: 6300÷80%=7875MJ

The low calorific value of natural gas is 35MJ/ m3.

Gas consumption: 7875÷35=225 cubic meters.

2. Solar water heaters save operating costs.

The cost of natural gas in Shanghai is 2. 1 yuan /m3, and the electricity fee is 0.6 1 yuan /Kwh.

(1) Compared with electric water heaters, solar water heaters save operating costs every year:

1939-0.61=1183 yuan.

(2) Compared with gas-fired water heaters, solar water heaters save annual operating costs:

225-2.50=563 yuan

3. Increase the payback period of investment.

(1) The investment of solar water heater is 3,500 yuan more than that of electric water heater, and the payback period is:

35001183 = 3 years.

(2) The investment of solar water heater is 4000 yuan more than that of gas water heater, and the payback period is:

4000÷563=7. 1 year

Four. Environmental benefit evaluation of solar water heating system

The environmental benefits of solar water heating system are mainly reflected in the reduction of CO2 emission due to the saving of conventional energy.

According to a household installation of 2.9㎡ heat collection area calculation:

/kloc-in 0/5, the carbon dioxide emission reduction per household is about 8.33 tons,

Each household saves about 4872MJ of energy every year.

5 concluding remarks

In today's world, many problems, including energy, climate change and environment, have become increasingly prominent and become common challenges faced by all countries. In the 2 1 century, China must ensure sustained and stable economic growth, eliminate environmental damage and excessive greenhouse gas emissions caused by unreasonable energy consumption structure, and reduce the actual cost of economic development. As the key work of the Tenth Five-Year Plan of the Central Committee, resource conservation has clearly put forward two related goals: First, it is determined that the energy consumption per unit of GDP will decrease by 20% by 20 10; The second is to determine the decrease of emissions of major pollutants (including carbon dioxide) 10%, and put forward the goal of building a resource-saving and environment-friendly society. China's first renewable energy law was officially implemented on June 5438+1 October12006. In the increasingly tense energy market, new residential quarters will fully and reasonably develop and utilize solar energy resources and reduce the consumption of conventional energy.

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