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​Solar water heater efficiency calculation

Views:14     Author:Site Editor     Publish Time: 2019-03-28      Origin:Site

The calculation and analysis method of annual solar water heater efficiency is based on the sub-project "Solar air-source coupled hot water system", a housing renovation project engineered by Environmental Protection Agency of Guangxi, China. In this project, the annual  solar energy saving rate is analyzed and calculated in detail. In view of the calculation process and basis, this kind of calculation method is scientific and reliable, which provides important reference for the analysis and calculation of energy saving.


Guangxi, China, belongs to the south subtropical monsoon climate. It has a mild climate, with average sunshine duration of 1600 hours per year. Its solar irradiation is about 4578 MJ/㎡annually. It is rich in solar energy resources and has great potential to utilize solar energy. At present, the centralized solar air-source coupled hot water system is being popularized in society. However, the calculation and analysis of energy saving still has no scientific, reliable and convincing method. Therefore, we take the project of "Solar air source coupled hot water system" as an example, devote to find a new way to analyze and calculate solar energy saving rate.

Working process of hot water system

“Solar air-source coupled hot water system” is controlled by automatic control module to achieve full automation control. When there is enough solar radiation, solar energy is preferred to produce domestic hot water in the hot water system. If the weather is rainy or solar radiation is insufficient, air-source heat pump, as an auxiliary heat source, starts to produce domestic hot water.

Definition of annual energy saving rate

The annual energy-saving rate of solar water heating system refers to the proportion of the energy saved by solar water heating system (excluding the energy saved by other auxiliary heat sources) to that consumed by conventional hot water heating system in annual operation.

Thermal efficiency of solar collector system

Take centralized solar energy collecting system which equipped with circulating water pump as an example to calculate the thermal efficiency of solar energy collecting system. Under solar irradiation, The water of solar energy collecting system is heated from initial temperature to set temperature. Only circulating water pump consumes a small amount of electric energy in solar energy collecting system, and no other equipment consumes electricity. Take the circulating water pump equipped with this system as an example. The input power is 0.265 kw, time required to circulate 1000kg water which has been heated up to 35℃ is 0.128 h, and the consumed power is 0.034 degrees. Therefore, we can get the real calorific value: 35000/0.034 = 1029411.76 kcal/degree; the comprehensive thermal efficiency is 1029411.76/860=119699%.

Thermal efficiency of electric water heater

The conventionally residential heating equipment in this area is the electric water heater installed independently. The working principle of the electric water heater is resistance heating. The thermal efficiency of the electric water heater is 95%, that is, the energy efficiency ratio is 0.95.

Setting of unified conditions for calorific value calculation

Nanning, China is located in the south of the Tropic of Cancer. Its geographic coordinate is 108 22', 22 48', North latitude. It has abundant sunshine and rainfall, little frost and no snow, the climate is warm, and the annual average temperature is 21.6℃. The coldest month in winter is 12.8℃ on average, and the hottest month in summer is 28.2℃. There average annual rainfall is 1304.2 mm and the average relative humidity is 79%. According to the climate characteristics of Nanning, China, the demand for domestic hot water is divided into summer, winter and transitional seasons. Summer is from May to September, a total of 153 days, hot water demand coefficient is 0.6; winter is from January to December, a total of 90 days, hot water demand coefficient is 1; transition season is from March to April, plus October and November, a total of 122 days, hot water demand coefficient is 0.8.

Calculation of annual energy consumption and demand

The total heat of each ¢58 x 1800 solar vacuum collector is 91.313 kw/h. The number of solar vacuum collector installed in this project is 2600, and the whole heat collected is 2374.138 million kw/h. To collect these heat, the energy consumed by the solar collector system is: 2374 138÷1196 99%=198.34 (kw/h). That is to say, the annual energy saving of the solar collector system in this project is: 2374138-198.34 = 237215.46 (kw/h). The annual energy saving rate of solar collector system in this project is as follows: 237215.46÷563980.5×100%=42.1%.

Error analysis

From the analysis of calculation process and basis, the calculation method of annual energy saving rate of solar collector system in this project can be called "daily calculation method". There are errors in the calculation and analysis of the day-to-day calculation method. The magnitude of the errors is mainly related to several parameters.

Solar irradiation data are obtained by referring to China Meteorological Radiation Data Yearbook (2001). The climate varies every year compared with 2001, but usually little.

The collector efficiency of solar vacuum collector is 92%. This is the experimental data provided by the manufacturer of solar vacuum collector. The parameters can also be measured by experiments.

The heat loss rate of pipes and tanks can be directly reduced if the insulation measures are well done in practical projects.

The total amount of actual heat used by users every year is related to season and climate, so the coefficient of heat used in each season is different.


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