Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Measurement results

The measurements are taken every 10 seconds by a data collecting device (type: Schuehle, MAC 19). Normally, they are saved as 5-minute average values. Other saving intervals are possible. For most of the measurement values, the system also records the minima and maxima over a 30-minute interval. These provide further information of the system’s operation. Regular controls of the minima and maxima can detect measurement errors, which might be caused by faulty sensors. Incorrect average values can thus be singled out easily. Figure 5.1. and the Tables 5.1. and 5.2. provide an overview of the recorded data. The data logger records power (kW), volume flow (m³/h) and temperatures (°C) every 10 seconds, as well as the total operating hours every 2 seconds. All the values are saved every 5 minutes.

Intensive Measurement

In the course of the program Solarthemie-2000, an intensive measurement phase of two years is a requirement. Thereby, system values are intensively monitored and evaluated. The objective of this detailed monitoring is twofold: on the one hand, it serves to optimize the plant operation and increase the system’s efficiency, on the other, it helps to test the manufacturer’s specifications in relation to the energy yield.

The pdf documents below show the most important measurement results of the first two years of the solar thermal system HBK Singen. These include the useable solar energy, the solar fraction, the system’s overall efficiency and the collector efficiency.

Specific daily sums of the radiation and useable solar energy (averaged over weekly sums) and weekly averages of the system’s efficiency (1st year of intensive measurement)
Specific daily sums of the radiation and useable solar energy (averaged over weekly sums) and weekly averages of the system’s efficiency of Mindelheim County Hospital (2nd year of intensive measurement)

System’s Efficiency

In the first year of measurement, a total of 105 178 kWh was transferred via the heat exchanger of the collector circuit to the buffer storage (QSP) (secondary circuit). This corresponds to an irradiation on the surface of the collector field (EITK) of 316 226 kWh (3,3 kWh/(m²d)). The energy difference between EITK and QSP was either reflected at the collectors or emitted as thermal loss to the environment. In percentage terms, this amounts to a transfer of 32.6 % of the total irradiation to the loading of the solar storage (collector circuit efficiency). 

The useable solar energy from the solar thermal system (QSV), i.e. the energy transferred from the solar reservoir to the potable water via heat exchanger, amounted to 99 522 kWh.

In the second year of measurement, the irradiation on the surface of the collector field amounted to 308 217 kWh 3,2 kWh/(m²d). Out of these, 99 656 kWh were fed into the buffer storage (QSP). The system’s efficiency thus lay at 32%. 

The pictures on the right show the daily averages calculated by the weekly sums of irradiation and useable energy as well as the system’s efficiency for both years.

The yield is particularly low in winter, which is due to the unfavorable location of the buffer storage connections. Since irradiation is lower than in the summer, this does not affect the total yield of the system. On average, the system’s efficiency lay at 31,5 % in the first year of intensive measurement and 32,4 % in the second.

Weekly sums of the useable solar energy, energy for warm water heating and the weekly averages of solar fraction in relation to the energy of the water used (1st year of intensive measurement)
Weekly sums of the useable solar energy, energy for warm water heating and the weekly averages of solar fraction in relation to the energy of the water used(2nd year of intensive measurement)
Weekly sums of the useable solar energy, energy for warm water heating and the weekly averages of solar fraction in relation to the energy of the water used and circulation (1st year of intensive measurement)
Weekly sums of the useable solar energy, energy for warm water heating and the weekly averages of solar fraction in relation to the energy of the water used and circulation (2nd year of intensive measurement)

Heat consumption and solar fraction

The two diagrams on the sides (top) show the solar fraction as related to the energy requirement for hot water consumption only (required solar fraction); the diagrams underneath show the solar fraction as related to the energy requirement for the hot water consumption including the circulation loss.

The bars show the weekly sums of useable solar energy of the solar thermal system and the corresponding energy demand for warm water consumption only, inclusive of circulation loss. 

On average, the solar fraction was at 28 % in the 1st year of intensive measurement and 29 % in the second. 

This corresponds to the design criteria, which assumed a solar fraction of 30% as its optimum. The average proportion of solar fraction in relation to the energy needed for heating the amount of water used and for covering the circulation was 9 % in the first and 10 % in the second year of intensive measurement.

This value strongly deviates from the actual amount of energy needed for heating the amount of water used as circulation loss is fairly high at HBK Singen. The medial loss amounted to 1 822 kWh/ day when operated 24/7 (app. 8.2 m³/h) amounts 1.822 kWh/Tag. Compared to the energy required for warm water discharge (979 kWh/day), the circulation loss were almost double, which is to say that the main portion of the energy necessary for reheating the potable water heating is used for covering the circulation loss.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Further Information

The following Pdf documents show the flyer of the results and give more information of the energy’s warrantee in each measurement year.

 

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