Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Measurement Data Evaluation

The measurements described below are taken every 10 seconds by a data collecting device (type: Schuehle, MAC 19). Normally, they are saved as 30-minute average values. Shorter saving intervals (< 30 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 the following parameters: power given in kW, volume flow given in m³/h and temperatures given in °C every 10 seconds, as well as the total operating hours every 2 seconds. All the values are saved every 30 minutes. 

In addition to the electronic data acquisition, the various measurement instruments that are equipped with counters are checked once a week. In addition, pressure readings are taken in the collector and buffer storage circuits.

By analyzing the measurement data with a fairly high temporal resolution (average values over 5 and 30 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.

Carpet-Plots for the visualization of large spaces of information

For the graphical representation of long time periods, the data are represented in carpet plots. Here, the days are represented side by side along the X axis in a diagram. The measuring points of each day are represented one upon the other along the Y axis. The reading level is shown by color coding. Below, the measuring values from some important measuring points are represented as carpet plot and thus illustrated how these can be used for the analysis of data and errors’ search. The diagram illustrated here presents the measuring values from the year 2004.

Solar Radiation (EI1) in W/m² 2004

Solar Radiation

 The diagram below shows the solar radiation on the collector surface (EI1) over the course of one year. It is easy to distinguish the times without solar radiation and days of bad weather by the blue gaps. It is also easy to see the change of radiation in relation to the change of seasons and the duration of radiation. The maximum radiation of 1100 W/m² was measured in June.

Power of collector circuit (PKT) in kW, 2004


Power Delivered from the Collector Circuit to Heat Exchanger 1

The power delivered from the collector circuit to the buffer storage clearly related to the solar radiation. Days with bad weather are clearly recognizable as the system operated at lowest level or not at all. The maximal power is just below 156 kW and was measured in June. 


Power of potable water circuit (PSV) in kW, 2004

Power Delivered to the Potable Water in Heat Exchanger 2

The power transferred to the potable water at the discharge heat exchanger relates to that of the amount of water used. By buffering the heat in the tanks, the potable water can be heated even at times with little or no solar radiation. The maximum power of 109 kW was measured in June.

Amount of water used (VVV) in m³/h 2004


Amount of Water Used

The data acquisition clock remains tuned to winter time, so that there is a detectably shift of one hour at the end March and October. Between 5 A.M. and 8 P.M. warm water ist used with a decreasing flowrate On weekends, less water is required since the hospital service is reduced to basic medical care.

The maximum amount of water used was 2.7 m³/h, a peak that usually occurred in the mornings.

Top buffer storage temperature in °C (TPS3), 2004

Top Buffer Storage Temperature

 In summer, the top buffer storage temperature stays at a high level almost throughout the entire day. (higher than 60°C) and stays until the following morning. Due to the large consumption around 6 a.m., the tank temperature drops until it is heated again by the heat from the collector circuit. As it would be expected, the temperature is significantly lower in winter.

Bottom buffer storage temperature in °C (TPS1), 2004


Bottom Buffer Storage Temperature

In relation to the top buffer storage temperature, the bottom buffer storage temperature does not reveal temperature layers that are as clearly distinguished. The control of the feeding of the storage tanks seems not to be working at its best in 2004. In particular in the period between mid-July to mid-September, the tank temperature was constantly higher than 60°C.

Intensive measurement

In the course of the program Solarthermie-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.

Access our Data Sever via DATAPOOL


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.

HBK Singen can also be found on the Datapool pages under Solar Thermal Systems.

The individual measurement points of the data pool can be found in the diagram on the side or  here.

For a list of the measurement points, click here

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