We did not want to waste a calorie
Visit to the Baden 'Haslenhof' and its heating-hydraulic feature
An authorised signatory says goodbye to his well-paid job, does what many dream of, namely becomes a farmer, but does not ignore his technical knowledge and therefore allows himself to be convinced by a connection of his wood boiler and collector system that is still considered unusual today. He invited people to visit.
Fig. 1: The Haslenhof in Dauchingen
Fig. 2: "With the three-chamber distributor, we have made considerable progress in energy utilisation" Plant engineer Steffen Knöbel
The farmstead nestles against a gently sloping foothill of the Black Forest. As a recognisable neighbour, only the church spire of Dauchingen, two kilometres away, stretches across the fields. The afternoon late summer sun bathes the property in mild warmth. A few guests sit at a rustic wooden table under the pergola in the front courtyard. With bees and all kinds of other flying creatures, they share thick slices of the yeast plait freshly baked in the early morning.
The taste of origin
Fig. 3: 24sqm collector area for hot water supply
And listen to what Hans Schlenker tells us: "The Haslenhof offers our visitors 'contact with food'. We grow everything ourselves and produce milk, eggs, cheese, meat and sausage. Whoever eats with us tastes the taste of origin. "Do you like the Zopf?" Yes, it tastes good.
Everything is available "to feed not only us, but also many private customers within a radius of maybe 20 or 25 km. Our main business is slaughtering, processing and selling. That is our mainstay, which we built up a few years ago, namely catering. But we don't deliver, or only very rarely. We feed our guests on our farm."
For parties, weddings, birthdays, company events, meetings... "You see, and that is why you are here now, because we have a great need for hot water for cleaning work, for the milking system, for cleaning the sausage kitchen or the cheese area. We don't want to have to fire up the log boiler in the summer for this hot water. Our new solar system has to manage that." It does - the boiler was not in operation from May until the date of the visit on 5 October 2009.
In nature and function
Well, to set the record straight, Hans Schlenker's guests had not signed up because of the collectors; they brought expertise in solar energy themselves. As well as in lump wood boilers, whose switched-off representative on the Haslenhof sends its water into a classic radiator high-temperature heating system during the heating season. Nothing exciting, then. They, the plumbers, were only interested in the wiring of the heating technology according to the rendeMIX principle. They had already read a lot about it, but had not yet seen it in reality and in operation.
Fig. 4: Training event in the "Event Room" of the Haslenhof: Hans-Georg Baunach explains theory and practice on the "living" object
Engineer Hans Schlenker, who had quit his job as an authorised signatory years ago to manage the farm inherited from his parents-in-law, had come into contact with this unusual mixing method during conversion and renovation work through his plumber Steffen Knöbel. The intelligent fitting based on a multi-way mixer is capable of both operating and exploiting different temperature levels. This impressed and convinced the ex-manager and led to the corresponding installation order. As a result, Steffen Knöbel's colleagues are now also looking into the matter. Just like on that late summer day.
The circuit diagram
The diagram is divided into three sections: left the rendeMIX station as a fixed value controller for loading the wood boiler. The emphasis is on loading, because this heat generator requires a return temperature above the dew point, i.e. at least 60° C, so that no acidic condensate can settle in its "organs". In one of the chambers of the multi-way fitting, a partial flow of the 85-grd boiler flow (yellow line) is first mixed with a partial flow of the 50-grd return (violet line) for this task. As a result, the "hot" buffer gets hotter faster, while the "cold" buffer stays cold longer. In this way, the wood boiler and the solar system do not get in each other's way.
MiddleThe solar gain flows to the two buffers via three feed points. On cloudy days, with collector temperatures of 30 or 40 oC, the sun's rays only benefit the annual fuel costs if the tanks are also able to absorb the heat. The corresponding exchanger must therefore only be surrounded by 20- or 30-gram water, otherwise the heat transfer will not work. Consequently, the control system controls the high (70-90 °C), medium (45-70 °C) or low (below 45 °C) temperature zones according to the collector temperature. The first two zones are located in the hot buffer tank, the third zone in the cold buffer tank.
The collector medium first acts on the exchanger in the hot area of the first tank, continues to circulate through its lower spiral and tempers the environment there, in order to then discharge the majority of its residual heat in the second buffer. The wood boiler either enters the hot zone of the hot buffer or the water heater.
Right: the discharge group in the form of the three mixer stations for the two floor and radiator circuits as well as a stationary box without mixing function with pumps and fittings for supplying the hot water tank. Most of the radiator circuit makes do with the 60-gram return flow from the hot water installation. It is designed for a 70/50 °C spread. Only when the outside temperature is low does it have to draw "hot" 85-grade water from the flow buffer tank to increase the temperature. In milder weather, 50-gram water from the "cold" buffer is mixed with the 60-gram return flow of the water heater to achieve the exact setpoint temperature control.
For the correct setting of the feeds of the two floor heating circuits, the control system also has different variants available, depending on the weather and the set and actual temperatures in the circuits. Depending on supply and demand, the "rendeMIX" modules pick up the most cost-effective combination of distributor "yellow", "violet" or "blue". Example of underfloor heating on the left: Depending on the situation, the flow of 40 °C is supplied by the "violet" and "yellow" busbars in combination with an admixture from the 30-grid "blue" return.
Three temperature levels
Fig. 5: The lump wood boiler from the company has an output of 50 kW. Rennergy, Kempten/Allgäu
The 550 square metres of the Haslenhof to be heated extend over an old building with underfloor heating on the ground floor, radiators on the first floor, the event or catering room - with panel heating - for about 100 guests, and a new extension, also with low-temperature heating. The old wood boiler had to make way for a modern log boiler as part of the construction work. It is supported by 24 square metres of solar panels.
On the consumer side, the 400-litre domestic hot water storage tank with integrated heat exchanger for the 80/60 °C spread makes the highest temperature demands. Meanwhile, two additional buffers of 1,830 litres each form the actual centre of the heating and hot water network. They store the different temperatures. In tank 1 (in the circuit diagram "buffer storage tank hot"), water of about 45 - 85 °C is normally stratified, in tank 2 ("buffer storage tank cold") water of 25 - 45 °C. Normal case means, unless there is an oversupply of solar heat that buffer 1 alone cannot absorb.
Fig. 6: The "hot" and "cold" buffer tanks each hold approx. 1,830 litres. Steffen Knöbel: "Rennergy supported us optimally in the design of the hydraulics and the buffer management. The individual components have to be coordinated very sensitively with each other. For example, the buffer storage size with the wood boiler control. Sensors monitor the temperatures in the buffer and register if they rise quickly or slowly. They switch the boiler to partial load when they notice that the storage tank will soon be full, thus prolonging the heat output. Rennergy has integrated this buffer management into the wood boiler control system. The systems are specially made for this supplier according to his ideas." (www.rennergy.de)
This structuring of the energy levels with assigned inlet and outlet points at the boilers creates, among other things, the prerequisite for the highest solar gains: the control system always controls the zone of the storage tanks with the greatest temperature difference to the collector, so that even when the sky is overcast or the light is diffuse, the flow of this circuit, which may only be 40 degrees, can feed a considerable part of the absorbed solar energy into the buffers. This is possible via the lower solar exchanger in the "cold" storage tank, because a return flow of 30 °C or less, the return flow from the various heat consumers in the homestead, flows around it (see circuit diagram in the adjacent box).
Probably the most modern state of the art
Fig. 7: The "rendeMIX" three-chamber mixers from HG Bauchnach guarantee optimum use of solar heat and wood combustion.
"We assume that the investments in the collectors and in the convenient Baunach control system will pay off because our heating system should now work much more efficiently. We were promised that it would not waste a single calorie. The back-to-back connection of the heating circuits is the latest state of the art. We are saving the wood for the winter. And we also hope to have to chop less, because the sun also contributes to the demand in winter.
The 50 kW boiler pushes its 80 °C directly to the 400 l water heater and the surplus into buffer tank 1, whose uppermost hot zone also serves the water heater. All other consumers are connected to its and other returns. They are supplied from the higher-temperature pipe sections. This sounds simple, but it requires a very complex fitting, the "rendeMIX". On the other hand, this fitting can be used with any commercially available mixer control to adjust the hydraulics in the mixers to the exact litre and degree and to supply each consumer exactly as required.
Fig. 8: The high demand for hot water is primarily used to clean the various food production areas of the farm. In the picture, the cheese dairy and with his back to the photographer Hans Schlenker.
In the early days, this technology was limited to connecting a high and a low temperature circuit in series. At the Haslenhof in Dauchingen near Villingen-Schwenningen, the invited craftsmen saw the further development, namely the three-chamber distributor for three temperature ranges, for maximum temperature (hot water), high temperature (radiators), low temperature (underfloor heating), with which optimum use of the buffer and the heat stored in it is guaranteed.
No new ground
Steffen Knöbel admits: "When we received the request from the Haslenhof, we faxed our hydraulic plan to the Baunach company for review and received the reply 'We can improve this considerably, for example, increase the solar utilisation and optimise the loading cycles of the wood boiler'". Although the new solution cost around 3,000 euros more, it met with an open ear from owner Hans Schlenker.
Fig. 9: rendeMIX group for return flow boosting of the wood boiler and optimum stratification of the buffer tank
The corresponding additional costs will pay off, the first evaluation suggests. Hans Schlenker has confidence in the technology because it sounds plausible to him and "because I haven't heated since May. Everything we need in terms of temperature, especially for hot water, is generated by the solar collector. It used to be replaced by an electrically heated drinking water boiler. That cost a lot of money.
"I recognised the effectiveness of the solar system by the fact that I had to add noticeably less wood even in winter with the slightest ray of sunshine," adds Lisbeth Schlenker, who is responsible for the fire on the farm. On days like this, she likes to save herself the fifteen minutes of work involved. "And if we do have to heat the fire in the evening, the hot water is ready in just 20 minutes!" says Sascha Ohnmacht, the son-in-law of the house, happily. "That feels good after working in the cold all day!"
With the company Knöbel Sanitär Heizung Blechnerei, Königsfeld, the farmer also thought he was on the safe side in terms of execution. The plant manufacturer celebrated a kind of small anniversary in 2009: seven or eight years ago, he realised the first rendeMIX installation. "With this one at the Schlenkers', it must now be 30. He admits that he has not counted them exactly, "but in this order of magnitude.
Fig. 10: The drinking water is stored in a 400-litre storage tank because of the high short-term demand for the dairy operation and cleaning. It has a lower and an upper storage point and can be supplied in parallel to the heating circuits. The upper hot zone is charged by the wood boiler or the buffer, the lower heat exchanger is directly supplied by the solar system. The minimum withdrawal temperature is 60 °C.
The new technology heats a total of 550 square metres. A tiled stove in the form of a classic ground stove still provides cosiness in the residential building. In addition, Hans Schlenker had an attractive stove with 18 kW installed in the catering area, so that the heating there is not dependent on the operation of the entire system. By "catering area", the farm owner primarily means his large function room, which offers space for 100 guests at the laid table. With a buffet and standing reception, it can also be more.
With public funding
What did the total investment cost? Hans Schlenker adds it up: "Just under 40,000 euros, namely for the solar system, for the wood boiler, for the distribution, for the additions and for the connection to the existing heating circuits. For the solar system, we received an innovation bonus from the BafA of 210 euros per square metre. This is available for collector areas above 20 square metres. Ours has 24 square metres. The public sector contributed 1,125 euros for the wood boiler; it also subsidised the installation of the new circulation pumps.
The farmer does not want to say anything about the concrete monetary benefit, "because we burn wood from our own forest. Here at Haslenhof, we live with and from nature, so it is only logical to use wood and sun for heating purposes. And if you decide to do so, it is also logical to strive for the optimum yield within the financial scope."
Half-heartedness will be more expensive. Hence the efficient "rendeMIX" control technology, "which of course cost money." But it is obviously money well spent, "because the fact that we haven't had to chop and burn wood for either heating or hot water for five months until today, 5 October, is something we didn't expect from the sun and the technology."
Fig. 11: A glass of fresh milk straight from the cow.
The Haslenhof
The farm in Dauchingen at the foot of the Black Forest has about 40 ha of land, 12 dairy cows plus calves, about 20 fattening pigs, 200 laying hens, and on average 30 to 50 broilers. The 40 hectares are divided into half arable land, i.e. grain, and half grassland (hay, fodder). The Schlenker family grows organic vegetables on half a hectare. The area also includes about 0.5 ha of forest.
But the trees do not grow to the sky, Hans Schlenker admits. "I left an authorised signatory's chair in 1994 and this gigantism, always more, even bigger, even higher turnover. It was not that easy to retrain from procurator to farmer, but we inherited the farm of our parents-in-law and live here with our family. We don't need employees. Our work output is enough to feed us. We don't need more than that."
In the meantime, some of Germany's top chefs appreciate this work performance. Those for whom only the best is good enough have joined forces in the "Eurotoques", an association of European culinary artists who buy exclusively from suppliers who have committed themselves to glass-based and natural production. For example, the Haslenhof in Dauchingen.
"This means, however, that we often work in five to six professions every day. First of all, there is the farmer for the classic livestock breeding in the barn and the arable farming, then the butcher for the meat processing and the sausage production, the milk processor and cheese producer, the baker, the cook, the marketer of the catering."
However, Hans Schlenker rejects the construction of the heating system: "The former heating system that we found was probably self-made. You could see that in the consumption, so to speak. I could also weld pipes, but more expertise is needed to minimise the costs.
The Haslenhof does not only cater for wedding parties, birthday parties and other guests. It also offers itself for further education and training events. If you would like to take advantage of the healthy, educational Black Forest air for these purposes, please write or call: Family Hans Schlenker, Vor Haslen 1, 78083 Dauchingen, Tel. 07720/ 5311, Fax 07720/ 957318.
Bernd Genath
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