"A whole new shine" by Sonne Wind und Wärme www.sunwindenergy.com

Released April 16th, 2010

Solar heat
Process heat
A Whole New Shine

Solar process heat for commerce and industry is still in its infancy. Has the breakthrough come with automobile painting?

Painting Center CEO Herbert Schulte (links) inspects the newly installed solar system with S-Power Managing Director Günter Schaffron.

Photos (5): Jens-Peter Meyer

At 70 °C, it is pleasantly warm in the cabin - at least for those who love a sauna. But nobody starts sweating here, as this is a dry cabin in which freshly painted metal parts dry under definite conditions. The painting center Schulte in Meppen gives automobile body parts a new appearance. The most frequent work involves repair paintwork needed after accidents. However, entire ambulances are also given the design of their rescue organization here.

"We've got enormous energy costs", states Managing Director Herbert Schulte. On average the company used to use 30,000 liters of heating oil a year. In order to be less dependent on the price of oil, Schulte consequently decided to install a solar energy system last year. "I'm a green pioneer in this regard. We were the first paint shop to use water-based paint", replies Schulte when questioned about his motivation behind using solar heat. It was certainly helpful that the company S-Power Entwicklungs- und Vertriebs GmbH is located just around the corner in the same industrial area. This enterprise has been selling vacuum tube collectors fitted with Narva tubes since the beginning of 2008. Personal contacts helped to boost confidence in solar energy - because, of course, the "paint shop company did not want to be adversely affected", as Herbert Schulte at first feared. When Bolin Heatex Technology GmbH, which services the painting cabins, gave the green light to build the installation, S-Power got down to developing the system concept in collaboration with Berliner Solarpraxis AG.

Since December 137 m2 collectors have been crowning the hall roof of the painting center. The KfW-funded installation is to reduce oil consumption by 30% according to the simulation. Schulte estimates an amortization time of seven to nine years, depending on the trend taken by oil prices. No question about it, the installation is a long-term investment. But the calculation is simple: What the company saves in oils costs is enough to cover the financing. Once the credit is paid back, the investment will be even more worthwhile year after year. "I can't wait to find out whether the system will live up to its saving potential as expected", says Schulte.

Painting needs a constant temperature

Freshly painted car parts dry in the drying chamber at 70 °C.

Yet the 70 °C hot drying chamber mentioned at the start is not the greatest consumer of heat in the company. This is namely the painting chamber. During painting, the painting chamber must always have a constant temperature of 24 °C. A fresh air flow rate of 22,000 m3/h flows through it for this purpose. While 100 % fresh air is required in the painting chamber, this sum is only 10 % in the drying cabin. A fresh air flow rate of 1200 m3/h is therefore adequate. Owing to the high volume flow rate, the painting itself needs about half the thermal energy in summer. This is because the ambient air does not always reach 24 °C even during a Meppen summer - and, if so, only during noon hours.

In winter, the painting chamber requires the lion's share of heat, while the drying cabin has an almost constant requirement when observed over the year. The total annual heat consumption of the painting center amounts to more than 180 MWh. Roughly 70 % of this goes to painting and 30 % to drying. As the hall only has to be heated to 17 °C in winter, this thermal energy is less than 3 % of the total requirements.

The first step towards increasing efficiency was therefore a heat recovery system for the painting cabins, installed by the company Bolin. Only then could solar heat come into play. The old boiler which directly heated the supply air flow had outlived its usefulness. Instead, S-Power installed two buffer stores each with a capacity of 5000 liters - two stores so as to be able to serve the different temperature levels for painting and drying. The buffers are now supplied with solar energy as well as additionally by an existing oil boiler, which was mainly used for heating the hall in the past. An air-water heat exchanger brings the supply air flow from the upper zone of the hotter buffer to the required temperature, in order to attain the 70 °C in the drying cabin. In just the same way, the supply air to the painting cabin from the colder store is heated with an air-water heat exchanger. As the required inlet temperatures depend on the outside temperature, the regulation is external temperature dependent. The hall heating is also connected to the buffer.

The solar installation is divided into four subfields each with their sown solar station. The solar heat is transferred from the collector field via a solar circuit to a plate heat exchanger, where it is then transferred to the charging circuit of the buffer. If the temperature in the charging circuit is not sufficient to supply useful heat to the buffer, the heat is kept in the circuit until the required temperature for feeding has been reached. Three-way valves ensure that the solar heat is stored evenly in the two buffers, depending on the strength of the sunlight.

A unique feature of the collectors: The rear of the absorber plates is also provided with a selective blue Tinox coating. The hall is covered with a metallic trapezoidal roof and reflects part of the solar radiation that is incident between the tubes on the roof. The rear of the absorber then captures this radiation. Measurements by the German Technical Inspection Association Rhineland have revealed that the peak performance of the collector is increased by 20 % in this way. The vacuum tubes not only have the advantage of greater efficiency than flat collectors at the high temperatures needed for the drying - they are also more lightweight. "The load bearing capacity of the hall roof just wouldn't have been adequate for flat collectors", says S-Power technician Daniel Feuerborn.

S-Power staff first mount the assembly rail on the hall roof. They then insert the vacuum tubes individually.

Less excess in summer

The concept developers have also thought of a protection against stagnation: the system is designed so that both cabins receive almost the entire solar heat in summer. To attain the required solar coverage of 30 %, however, the planners had to accept a minimum summer excess in the solar heat gained of around 1.3 %. As a result, a situation may occur - for example at the weekend - where the buffers are charged to full capacity with 95 °C. In this case, the control then switches on the paint cabin for a short time, thereby releasing the excess heat to the outside air.

Not only Herbert Schulte is doing something about his oil expenses - a bill that rises from year to year. His colleagues in the several thousand paint shops making up some of Germany's small and medium-sized businesses have to deal with the costs. If the pilot system in Meppen works as anticipated, Bolin intends to market the solar-assisted painting technology. The first step would then be taken towards a market for solar process heat systems.

Jens-Peter Meyer

Further information:

• Painting Center Schulte
• S-Power Entwicklungs- und Vertriebs GmbH