Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Solar Heating of Potable Water at the Bath and Wellness Center Waldbronn

The circuit diagram below shows a simplified version of the solar thermal system with the corresponding components. The whole system is subdivided into three different circuits: the collector circuit, the shower circuit and the pool circuit. There is no buffer storage circuit in this system.

During times of irradiation when the liquid in the collectors is heated, the circulation pump (P1)switches on. In operation, the potable water for the showers can thus be heated by the heat exchanger for potable water (WT1) or the freshwater can be heated by the heat exchanger for the pool water (WT2). Both heat exchangers are connected in series, which is to say that the water flows through WT1 first and afterwards through WT2. In principle, it would also be possible to connect them parallel so that both were simultaneously supplied with hot water. This is just a matter of valve adjustment.

If the temperature difference of the collector circuit is slightly higher than that of the potable water reservoir, the charging pump (P2) switches on and the water from the potable water tank (with a capacity of 2500 ltrs) is heated. If the temperature of the solar heated potable water exceeds a set maximum temperature, a mixing valve makes sure to guide the remaining volume flow past the heat exchanger, which reduces the the transmission at the heat exchanger.

When potable water is used, the solar heated water flows from the potable water tank to the consecutive preheating tanks of each shower area. If the water is not hot enough, it can be re-heated to the required temperature by the conventional gas boiler. The cold freshwater initially reaches two small buffer storage tanks with a capacity of 500 ltrs each. It is preheated by the remaining heat of the waste water of the showers.

If the temperature of the collector liquid is higher than the freshwater temperature for the pools after it flew through the heat exchanger for potable water, it is heated by the heat exchanger for the pool water. Again, a mixing valve limits the temperature of the freshwater.

After having passed through one or both heat exchangers, the cooled-down collector circuit liquid returns to the collectors, where it is heated again by the sun.

There are two effects because of the serial connection of heating the shower water first and the pool water afterwards: For one, the temperature of the liquid of the collector circuit is still sufficient to heat the thermal water of the pools (at 17° C) after passing WT1. Second, the temperature of the collector circuit is cooled further after passing WT2, which in turn increases the collector efficiency. 

These effects could only be used after adapting the thermal water feed. Therefore we have developed and implemented a new concept for feeding freshwater to the pools. Initially, the freshwater flows through the heat exchanger of the pools and then into surge water containers. Level measurements ensure the regulation of the freshwater flow. The freshwater pools provide the water for circulating the pool water, for compensating the loss of water and for filtering. If the temperature of the surge container is too low, it is re-heated to the required temperature via the heat exchanger with the help of the conventional boilers. 

The water collected by the overflow channels is returned to the surge water containers. If the level of water in the surge container falls below a certain minimum level, freshwater will be added. Water losses are caused by general evaporation or by bathers taking water out when leaving the pools. However, the biggest losses result from filtering, which must be done every 3-4 days for health and safety reasons.

Simplified hydraulic diagram of the solar thermal system at the Bath and Wellness center Waldbronn

Specifications

This table shows the most important specifications of the solar thermal system at the bath and wellness center Waldbronn.

Project data
Surface234 m²
Collectors typeflat plate collectors
Buffer storage2500 l
Project costs177 851 € (760 €/m²)
Heat exchanger2 plate heat exchanger
Azimuth/ InclinationSouth +15° / 30
Lowest energy cost0.12 €/kWh
Highest solar yield128 657 kWh/a (569 kWh/m²a)

Click on the pdf-file to receive detailed information on the specifications of the solar thermal system at the Bath and Wellness Center Waldbronn. The file also includes details of the collectors, the pipes, the carrier medium in the collector circuit and the heat exchanger between the different circuits.

Measurement Technique

The following diagram shows the system’s measurement and monitoring sensors. The monitoring sensors are essential for the functioning of the whole system; the measurement sensors are used for the extended functionality control of the solar thermal system.

The first diagram shows the collector circuit focusing on the shower water or potable water circuit. The diagram below shows the systems monitoring points focusing on the pools.

Diagram of the measurement and monitoring points at the bath and wellness center Waldbronn (potable water – shower)
Diagram of the measurement and monitoring points at the bath and wellness center Waldbronn (swimming pool)

DATAPOOL provides access to our 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 bath and wellness center Waldbronn 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 above.

For a list of the measurement points, click here.

 

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