Hydraulics made visible

Without coordination, it’s like an orchestra without a conductor – a seminar in Arnsberg

There is a great need for information in the SHK industry. However, further training does not have to be packaged in a lavishly designed social evening. If the topic is the standard problem area – hydraulics – and a non-sales-oriented institution invites you, such as a chamber of crafts or the new energy communities, the training room fills up. If an experiment in the heating laboratory then confirms the theory, the audience asks the host almost expectantly at the end: “What is your next topic?” Hydraulics is a problem area. It is growing more and more with networked digitalisation and the Internet of Things. Those who want to be in the wholesale trade in the future will need to be able to handle individual components for a system. “What is your next topic?”*

Hydraulics is a problem area. It is becoming increasingly important with the advent of networked digitalisation and the Internet of Things. In future, anyone buying individual components for a plumbing, heating or air conditioning system from a wholesaler will be buying pieces of a puzzle. As we know, these only fit together to form a complete picture when they are in the right place. The right place, in terms of hydraulics, means the right adjustment. The individual components only perform efficiently when they are optimally coordinated with each other. No one is able to build an efficient system with inefficient components. On the other hand, combining efficient components to create an inefficient system is not the rule, but it is also not the exception. “Although every musician is a virtuoso, “Although every musician is a virtuoso, an orchestra concert without a conductor would not be a treat for the ears,” said the speaker at the hydraulics seminar at the vocational training centre of the South Westphalia Chamber of Crafts in Arnsberg at the beginning of February, emphasising the need for professional coordination.

Charging and discharging buffer storage systems

Buffer storage systems and their most efficient charging and discharging, for example, will in future have to take on responsibility not only for supplying buildings, but also for the energy transition. This is not an exaggeration. Currently, heat storage also serves as a pressure relief valve because wind farms and solar farms are growing faster than the infrastructure. Faster than road construction. Experts estimate a transition period of a good ten years for the expansion. This means that in order to prevent the grid from overheating, renewable energies would have to be taken off the grid in the next decade. This is not in the interests of the energy transition. “That is why,” said Stefan Kapferer, Chairman of the Executive Board of the Federal Association of Energy and Water Management, recently. decade. That is not in the spirit of the energy transition. “That is why,” said Stefan Kapferer, Chairman of the Executive Board of the German Association of Energy and Water Industries, recently, “we must take advantage of every small measure that alleviates the current situation. These options include using the surplus in , namely converting it into heat.” The energy transition is one thing, making the infrastructure adaptable is another. And that includes power-to-heat, among other things. The German energy and heating sector is becoming more electric with wind and PV power. The natural decoupling of supply and demand that comes with this must be systematically offset. Comfortable and efficient heating with what is essentially fluctuating energy is made possible by power-to-heat, i.e. sector coupling with heat pumps, among other things. Power-to-heat enables comfortable and efficient heating with what is actually fluctuating energy, including sector coupling with heat pumps, thermal solar systems and buffer storage to temporarily store the heat until the evening hours or another time slot. The more efficiently the control system utilises the capacity of such a storage tank, the more the overall efficiency of the system increases. The more efficiently the control system utilises the capacity of such a storage tank, the more the overall efficiency of the system increases.

Incidentally, this applies to any integration of a buffer into a heating circuit, regardless of who supplies the heat: a condensing boiler, wood or pellets, the collector, CHP or the heat pump. But how do you approach the optimum? That was precisely the topic in Arnsberg.

How do you approach the optimum?

Let’s start with a question: How great are the buoyancy forces that stratify warm and hot water? The excursion into hydraulics, given by Hans-Georg Baunach from HG Baunach GmbH & Co. KG, presented some little-known figures. The buoyancy is caused by differences in density. Water at 0 °C weighs 1,000 g per litre, while water at 100 °C, directly at boiling point, weighs only 950 g. The difference of 50 grams means that in a storage tank with a diameter of 50 cm cm in diameter – and thus with an area of around 2,000 cm² – a 1 cm thick layer of water with a volume of two litres will, roughly speaking, exert an upward pressure of 100 grams – the buoyancy of boiling water in ice-cold water. That’s not much. Even the slightest disturbance to this low level of dynamics can cause the contents to lose their tendency to stratify. A modest counterbalance: the lightness of water in the upper temperature band, from around 50 °C upwards, means that the buoyancy force is only about 100 grams. Even the smallest disturbances to this low dynamic can deprive the contents of their tendency to stratify. Modest compensation: the lightness of the water increases disproportionately in the upper temperature range, i.e. from around 50 °C. In the cold range, on the other hand, between 0 °C and 20 °C, relatively little happens in terms of density difference. In other words, the hotter the water, the more stable the stratification: and thus the usable heat content of a buffer or its usable storage capacity. In other words, the hotter the water, the more stable the stratification and thus the usable heat content of a buffer or its usable storage capacity. Let’s consider the load. When completely mixed at 50 °C, the heat flows backwards, so to speak, counteracting the system concept. Namely, from the buffer into the 45-degree brine of the connected solar system, if it does not exceed 45 °C. Namely, from the buffer tank into the 45-degree brine of the connected solar system, if it does not offer more than 45 °C. If, on the other hand, the contents stratify from 30 to 70 °C, which means the same amount of heat as in the previous case, the collector can transfer its solar gain to the cold zone of the water heater.

Destructive turbulence

Admittedly, none of this is unknown. However, the majority of listeners admitted that they do not consider the consequences of incorrect charging and discharging of storage tanks so drastically. Or rather, they do not draw the conclusion that the return temperature from a heating system should be as cold as possible. It has a decisive influence on the usable heat content. Firstly, it should be very low, secondly, the return should flow into the buffer very far down and thirdly, at low speed. This is to avoid creating turbulence. Ideally, no more than ten centimetres per second. However, this value is not a rule of thumb. Of course, any turbulence destroys the stratification. We have already mentioned the buoyancy forces. However, this value is not a control variable. This is because any turbulence naturally destroys the stratification. We have already mentioned buoyancy forces. Turbulence really exacerbates the malfunction of the tank because the heat output of the flow depends on the throughput and the temperature. If the flow is 60 °C and only 70-degree storage water is available, more mixed water must circulate compared to an 80-degree fluid. A higher volume means a necessary increase in the circulation speed. A higher circulation speed means an increase in the momentum of the water flowing into the tank – and thus an increase in turbulence. The Hydraulics expert Baunach calculated the effect: the kinetic energy increases quadratically with the flow velocity, so the turbulence climbs by 77 per cent with a throughput increase of 33 per cent. This acts like a large whisk. It mixes all the heat zones to a low delta T between the top and bottom. The practical consequence:

“If the mixing temperature in the boiler does not exceed 50 °C, for example, the boiler will start up after a few minutes of showering, despite the solar system. With a spread of 90/30, on the other hand, the boiler remains off during showering and the collector can even continue to charge,”

explains Hans-Georg Baunach.

The more condensate, the more efficient

He has a corresponding slide ready for almost every statement. He does not expect everything to be understood immediately live.

“At many such training courses, we see wide eyes, furrowed brows and astonishment at the beginning. That’s why we have our practical section. What sounds very complicated to some people is clarified by the laboratory experiment. It makes the theory understandable.”

Hans-Stefan Albers later summarised the feedback from the audience.

Albers heads the Sanitary and Heating Technology Department at the South Westphalia Chamber of Crafts. Hydraulics seminars are a regular feature of his programme. The installations are dismantled from time to time to make way for other demonstrations, but they are refined and made available again for the next course. Refined means, for example, that the thermographic camera, which currently makes the layering transparent, will soon be supplemented with a data logger with ten measuring points above the container height. Refined means that, for example, the thermographic camera, which currently makes the stratification transparent, will soon be supplemented with a data logger with ten measuring points above the container height.

“Then we can present the exact temperatures to the participants,”

said Albers.

Advantage of two-zone loading and unloading

If the temperature of the purple layer is above the set target value of this sensor, it signals to the boiler that ‘it is enough’. So the burner switches off. Consequently, only the lift is available in practice for the single-zone principle in the heating system. The two graphs on the left for the single-zone principle and on the right for the two-zone principle show the temperature conditions during filling and consumption. The two dotted squares – with the water temperatures on the abscissa and plotted above the height of the water column in the tank on the ordinate – represent the theoretical storage capacity. The partial areas marked represent the actual usable heat volume.

We will refrain from explaining their geometry and the individual measuring points T of the long-term experiment in Biberach at this point. The decisive factor is the different surface area: the charging and discharging strategies with the two multi-path mixers in the right-hand graph are designed to achieve a high spread in the storage tank. For example, in a building with radiator and underfloor heating, only the 30-degree return flow from the low-temperature heating system flows into the bottom of the tank, while the 50 °C radiator return flow is directed into the mixing zone. The temperatures in the upper third remain similarly well stratified. The pre-mixer may not even use the highest temperature, as the temperature of the middle zone is sufficient. The heat-controlled CHP unit therefore remains switched off. The flow mixer may not even use the highest temperature, as the temperature in the middle zone is sufficient. The heat-controlled CHP unit therefore remains switched off. If the “Rendemix” draws heating water from the middle zone, this zone shrinks and makes room for hot water from the “Dachs”. In the standard case of a three-way mixer, however, the mixed return flow from the radiators and surface heating already has a temperature of over 40°C, depending on the output of the two heating circuits. This means that the mixed flow from the radiators and surface heating is directed into the mixing zone, while the return flow from the radiators is directed into the bottom of the tank. In the standard case of the three-way mixer, on the other hand, the mixed return flow from the radiators and the surface heating already has a temperature of over 40 °C, depending on the output of the two heating circuits. Firstly, this is at the expense of the spread. Nothing can be taken directly from the purple warm zone. Secondly, this restricts the storage space for the hot water. Thirdly, for each flow temperature, the mixer must access the valuable And thirdly, for each flow temperature, the mixer has to draw on the valuable hot water supply, which the machine then has to replenish in the experiment.

The result: with two-zone charging and discharging using a multi-path mixer in a system configuration as described in the thesis, the usable storage volume is exactly 2.4 times that of the single-zone design. Instead of the “roof” that was available in Biberach, a boiler could also have been used. The conditions are exactly the same for a boiler-storage combination. Instead of the “roof” that was available in Biberach, a boiler could also have been used. The conditions are exactly the same for a boiler-storage combination. Incidentally, the start-stop cycles of the “roof” were also reduced by a factor of 2.4.

It is very impressive,

“to see the amount of condensate and to be able to calculate how low return temperatures increase the efficiency of a condensing boiler system and, in combination with a two-zone charging and discharging strategy instead of single-zone systems, increase the storage capacity of a hot water buffer”

admits the head of department.

His charges at the vocational training centre are primarily master craftsman students. To provide practical proof of the efficiency of the special hydraulics according to the Baunach method – “It’s almost enough to put your hands on the pipes.

Then you can feel what’s happening” – he had also invited the South Westphalia Energy Community, which is affiliated with the Chamber of Crafts. The plant managers and owners, although in the midst of their professional lives, Then you can feel what’s happening” – he also invited the South Westphalia Energy Community, which is affiliated with the Chamber of Crafts. The plant managers and owners, although in the middle of their careers and therefore largely familiar with hydraulics, were just as impressed by the results as the master craftsman students.

Too cumbersome by hand

The installation effort is minimal. As mentioned, the Baunach development handles the three tasks of hydraulic optimisation, firstly system efficiency in heat utilisation, secondly system efficiency in heat distribution and, thirdly, system efficiency in heat storage, with a single fitting. Assembling this architecture manually from individual components requires a great deal of effort and expertise. With “rendeMIX”, all you need to do is screw on the supply and return pipes. The mixer block originated from the idea of converting the prevailing complex and energy-wasting dual-circuit systems, which send the high-temperature return flow from the radiators to the boiler instead of to the underfloor heating coils, into a fuel-saving single-circuit system. This requires the different water volumes in the fitting to be balanced. The application then expanded the company’s expertise to include the optimal loading and unloading of dual-zone buffer storage tanks. This requires the different water volumes in the fitting to be balanced. The company then expanded the application to the optimal charging and discharging of dual-zone buffer storage tanks and the connection of solar systems. As part of a diploma thesis, Biberach University of Applied Sciences determined the optimal gain with a buffer and combined heat and power plant connection: dual-zone loading and unloading with one mixer each increases the usable heat content of a storage tank by 240% compared to the single-zone principle (see box). The short laboratory test in Arnsberg was naturally unable to produce this astonishing value. Neither the equipment nor the time available was sufficient for this. However, the measured temperatures and thermal outputs tended to confirm the results from Biberach.

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