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.

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.

The pdf documents below show the most important measurement results of the first two years of the solar thermal system at the Thermal Baths and Wellness Center Waldbronn. 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 (2nd 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 (3rd year of intensive measurement)

System’s Efficiency

In the first year of intensive measurement (05.11.2003 – 04.11.2004), a total of 127016  kWh was transferred via the heat exchangers WT1 and WT2 to the shower water and pool water circuits. This corresponds to an irradiation on the surface of the collector field (EITK) of 306614 kWh or 1356 kWh/m² respectively.

Out of the total amount of 127 016 kWh, 115 553 kWh (91 %) were used for heating the shower water and 11 463 kWh for heating the pool water.

The energy difference between EITK and QSOL was either reflected at the collectors or emitted as thermal loss to the environment. In percentage terms, this amounts to a transfer of 41.4 % (system’s efficiency) of the total irradiation to the shower and pool water circuits.

In the second year of intensive measurement (05.11.2004 – 04.11.2005), the irradiation on the surface of the collector field amounted to 305251 kWh respectively 1349 kWh/(m²a). Out of these, 43 405 kWh were used for heating the pool and shower water. 40790 kWh were used for heating the shower water and 2614 kWh for heating the pool water. The system’s efficiency thus lay at 14.2 %. This is very low compared to the first year and largely due to disruptions that inhibited a smooth operation of the system.

In sum, 36.7 % (111 483 kWh) of the total solar irradiation of 303.477 kWh (1342 kWh/m²) could be turned into useable heat in the 3rd year of intensive measurement (15.11.2008 - 14.11.2009). 68 508 kWh were used for heating the shower water and 42 975 kWh for heating the pool water. After the disruptions were resolved (see report), the solar yield of the 3rd year reached a satisfactory level. 

The pictures 6.14 to 6.16 indicate the specific daily sums of the radiation and useable energy as well as the system’s efficiency (averaged over the weekly sums and weekly averages).

 

 

 

 

 

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)
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 (3rd year of intensive measurement)

Heat Consumption and Solar Fraction

The usable energy provided by the solar thermal system covered 22.1% of the energy needed for the water usage of the showers in the first year, 8.9% in the second and 28.7% in the third year of intensive measurement. This percentage refers to a total of 115 553 kWh (1st year) and 40 790 kWh (2nd year).

Since there are not enough measurement points to determine the solar fraction required for heating the freshwater for the pools, the energy demand needs to be estimated on the basis of average values. Loss at the boilers or the distributors, or any other kind of energy loss cannot be accounted for in detail; only the energy of the warmed freshwater that is fed into the pools can be calculated in detail. When assuming a steady heating from 17°C to 40°C, we arrive at a total of 208 540 kWh (1st year), 161 600 kWh (2nd) and 158 646 kWh (3rd year) being the annual sum of the energy required for warming the freshwater for the pools. The usable solar energy of 11 463 kWh in the first year, 2 614 kWh in the second and 42 975 kWh in the 3rd indicate a solar fraction of 5.5%, 1.6% and 27.1% respectively. Because of the said leakage of the heat exchanger for pool heating, the device could only be used occasionally, which accounts for the low figures in the initial two years of the system’s operation. 

The usable energy provided by the solar thermal system amounts to a total of 127 016 kWh (1st year of intensive measurement), 43 405 kWh (2nd year of intensive measurement) und 111 483 kWh. This corresponds to a solar fraction of 17.4 %, 7.0 % and 26.6 % of the entire potable water and freshwater supply of the Thermal Baths and Wellness Center Waldbronn.

The images 6.17 to 6.25 show the course of the solar fraction in relation to the energy requirement for the showers and freshwater supply as well as the total amount of water used (freshwater and shower water). The bars show the weekly sums of usable solar energy of the solar thermal system and the corresponding energy demand for warm water consumption only, i.e. without taking circulation or any other kind of losses (boilers, storage) into account.

 

Further Information

Click on the pdf documents below for an overview of the results as well as more information on the energy guaranteed for the individual years.

toTopto top