Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Measurement Results

The measurements described below are taken every 1-2 seconds by a data collecting device (type: HWH DL32). Normally, they are saved as 5-minute average values. Shorter saving intervals (< 5 mins) are possible; they are usually carried out to monitor the dynamic behavior of the system, e.g. during trial runs. 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 a faulty sensor. Incorrect average values can thus be singled out easily.

The data logger records power (kW), volume flow (m³/h), temperature (C°), pressure (bar), energy (kWh) as well as the total operating hours every 1 to 2 seconds. All the values are saved every 5 minutes.

By analyzing the measurement data with a fairly high temporal resolution (average values over 5 minute intervals), it is possible to assess the system’s performance and identify problems. On the basis of the malfunctions identified through these analyses, the solar thermal system was modified substantially after start-up.

Intensive Measurement

In the course of the program Solarthermie2000plus, 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 three years of the solar thermal cooling system at Festo AG & Co KG Esslingen. These include the useable 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 (2nd year of intensive measurement)

System’s Efficiency

In the first year of measurement, a total of 542 146 kWh was transferred from collector circuit to the buffer storage (QKT). This corresponds to an irradiation on the surface of the collector field (EITK) of 1563613 kWh (1284 kWh/m²). The energy difference between EITK and QKT was either reflected at the collectors or emitted as thermal loss to the environment. In percentage terms, this amounts to a transfer of 34.7 % of the total irradiation (collector efficiency) from the charging circuit to the storage tanks. 29.4% of these were used again (system’s efficiency).

In the second year of intensive measurement, a total of 575095 kWh was transferred from collector circuit to the buffer storage (QKT). This corresponds to an irradiation on the surface of the collector field (EITK) of 1586057kWh (1302 kWh/m²). In percentage terms, this amounts to a transfer of 36.3 % of the total irradiation (collector efficiency) from the charging circuit to the storage tanks. 33.4% of these were used again (system’s efficiency).

The diagrams on the right shows the specific daily averages calculated by the weekly sums of irradiation and usable energy as well as the system’s efficiency. 

 

 

 

 

Weekly sums of the useable solar energy, energy for freshwater consumption and the weekly averages of solar fraction in relation to the energy for freshwater consumption (1st year of intensive measurement)
Weekly sums of the useable solar energy, energy for freshwater consumption and the weekly averages of solar fraction in relation to the energy for freshwater consumption (2nd year of intensive measurement)

Heat Consumption and Solar Fraction

In the first year of intensive measurement (01.08.2008 - 31.07.2009), the average heat consumption lay at 20871 kWh per day. The total amount lay was measured at 7617870 kWh. The adsorption chillers consumed 3634748 kWh. The effective consumption was thus 27 % higher than the consumption measured before the solar thermal system was installed (2864121 kWh). 459465 kWh of solar heat were fed in the heating network, which corresponds to a solar fraction of 6%.

In the second year of intensive measurement (01.08.2009 - 31.07.2010), the average heat consumption lay at 16773 kWh per day. The total amount lay was measured at 6122952 kWh, hence about 20% less than the first year. The heat consumption of the adsorption chillers cannot be given as the cold sensor did not work properly over that period. 529134 kWh of solar heat were fed in the heating network, which corresponds to a solar fraction of 8.6%.

The diagrams on the side show the course of the total heat consumption of the network as related to the solar heat fed into the network. The solar fraction is rather slim. The amount of roof space was the limiting factor for the size of the collector field. 

In comparison to 2008, the solar fraction could be increased in 2009 and 2010 from an average of 8,6% to peaks of 25% in some weeks. The reasons for such peaks lie on the different manner of operation of the adsorption chillers.

Monthly Values

The diagram on the side shows the monthly sums and averages of the most important parameters measured since the setup of the system in 2008. 

The values of the graphs indicate that the increase of the system’s efficiency is mainly due to the optimization of process monitoring and control. 

Small discharge capacity between 06 – 15.08.2008 due to a faulty valve. Assumed loss of storage at about 9% (based on average values of the week before and after) between 15.09 and 06.10.2008 due to sensor failure. Repeated use of adsorption chillers (also with heat generated by gas boilers) due to high demand on July and August 2009.

DATAPOOL provides access to our measurement data server

Via DATAPOOL you can access selected data of this solar thermal system. You can choose from various illustrations like line charts, carpet plots, or scatter plots.

The solar thermal system at Festo AG & Co KG, Esslingen can be found on the Datapool pages under Solar Thermal Systems as far as measurement data are available for this system. 

The individual measurement points of the data pool can be found in the diagram above or here

For a list of the measurement points, click here