A solved problem

Whether the Christian imperative to “preserve creation” was the deciding factor in his commitment to energy-efficient building services was not discussed during the SHT’s visit to the pastor Christof Bärhausen in Maibach, Franconia. About 30 years ago, the Ecumenical Council of Churches had, in a manner of speaking, written the imperative into its programmes, thus proclaiming ethics as About 30 years ago, the Ecumenical Council of Churches wrote the imperative into its programmes, so to speak, thus apostrophising ethics as the powerful cornerstone of a sustainable environmental policy. However, when talking to the South German theologian, it seems that it was more physics than metaphysics that drove him not only to preach efficiency but also to demonstrate it competently to his congregation: he simply has a strong penchant for technology. A penchant that does not stop at the level of a gifted layman. that drove him not only to preach efficiency but also to demonstrate it competently to his congregation: he simply has a strong penchant for technology. A penchant that is not satisfied with the level of a talented layman. Christof Bärhausen delved deeper into the subject matter. He finally received his high ordination from the Chamber of Crafts for Lower Franconia, where he passed the “exam with all the trimmings and all that goes with it” (Bärhausen) to become an energy consultant (HWK). Seen in this light, physics and metaphysics are intertwined in his life: today, the churchman makes his practical contribution to the preservation of creation in his own home and through “domestic” parish work.

Image 1: A total of nine heating circuits supply the house, five on the ground floor and four on the upper floors. Each heating circuit has its own return temperature limiter (on the lower return manifold). RTB valves are also installed in the risers on the left to the radiators on the top floor. Furthermore, it is intended to connect the radiators, which are now oversized due to the energy-efficient renovation of the attic, directly to the flow and return of the floor circuit as low-temperature heat exchangers. The dynamically regulating RTBs balance the installation hydraulically. The three servomotors on the right respond to the impulses from the electric room thermostats.

Guided by mistrust

First, a look back at the past: the unsatisfactory integration of the solar system via a buffer into the oil boiler system of his residential building at the time confronted him for the first time with the laws of hydraulics and with the realisation that hydraulics must be the very first starting point for optimisation measures. How should temperature stratification, loading and unloading be structured to waste as little solar gain as possible?

The Roman Catholic pastoral advisor studied the flow paths in the multi-path mixer “rendeMIX”, which came onto the market about 15 years ago and which a friend who was an engineer had brought to his attention.

He installed it. The Baunach development with its internal bypasses balances out different water volumes, thus allowing, for example, the return flow of a He installed it. The Baunach development with its internal bypasses balances out different water volumes, allowing, for example, the return flow of a high-temperature circuit (radiator) to be used as the flow for underfloor heating. Or it first draws unmixed water from a two-zone or multi-zone boiler, thereby retaining valuable high-temperature exergy – before mixing hot with cold. As it strives to stabilise the spread in a stratified storage tank, it also increases the solar yield because the tank itself absorbs collector heat a few degrees above cold due to its cold zone.

The current problem

Image 2: Typical of southern German architecture: underfloor heating downstairs, radiator heating on the upper floors.

The heat meter at the Bärhausen plant demonstrated the success of the mixer retrofit at the time. It ran more slowly. The positive experiences confirmed to the energy consultant the importance of correct and sensitive hydraulics. However, it also made him sceptical about the savings effects of other measures that had been undertaken, such as a curtain wall timber façade with 21 cm of insulation between the cladding and the stone, roof renovation, insulated glazing and thermal bridge removal, which were intended to raise the single-family house from the period before the first thermal insulation regulations to the KfW 55 standard.

Image 3: Return temperature setting on the RTBs between approx. 17 and 22 °C, depending on the room and heat exchanger size, usage and desired temperature. Fine adjustment is the responsibility of the user.

How do you regulate the water flow in an old building with a large number of circuits for living rooms, bedrooms, children’s rooms and studies, for the kitchen and bathroom, for rooms under the roof with now oversized radiators, for underfloor heating in the living area to meet reduced demand?

With older thermostatic valves without the option of presetting the flow rate? But even those with presetting would react relatively statically “on” and “off” and not efficiently and dynamically, in terms of water volume, to regulate changing influences and conditions. The KfW subsidy regulations now stipulate hydraulic balancing – and, as described, for Christof Bärhausen it was a must anyway.

Dynamic instead of static

As chance would have it, Hans-Georg Baunach, valve tinkerer and managing director of HG Baunach GmbH & Co. KG in Hückelhoven near Aachen, had been preoccupied with similar thoughts. His tests and successes with the “rendeMIX” had taught him that manual hydraulic balancing remains a mixture of trial and error – if it is even attempted at all. The classic method also has to live with the weakness that limiting the flow to one litre per minute on a rigid flow rate wastes some of the profit potential. However, Baunach’s “rendeMIX” multi-way valve does not serve this purpose. It is designed to mix water of different temperatures, not to regulate water flow. The engineer therefore sought another solution to the regulation problem. It had to be both optimal and simple.

“Simple” in two respects: it must be accepted by tradespeople and the price, let’s put it this way, must increase its acceptance. The calculation should not be based on the working time saved, compared to the effort required for the usual adjustment. Hardly any company would use such a calculation. It could only be a product costing a few pounds. The idea of return temperature limitation as a thermal-hydraulic balancing method was a success. Various pilot projects have been running for about a year, including the Bärhausen plant. It is nothing more than a return temperature limiter, as the name suggests: an RTB valve for installation in the return flow of a heating circuit behind the heat exchanger.

Figure 4: The potential thermal bridges at windows and balcony doors are minimised with insulating fill to such an extent that they do not compromise KfW 55.

Image 5: The heated living space totals 160 m², of which 120 m² has underfloor heating and the attic has radiators. Next to the windows are the ventilation valves for the decentralised ventilation units. Pictured: Christof Bärhausen.

Ideal, because no calculations are required

How does it work? As with thermostatic valves, room-related empirical values must also be used for the basic setting on the RTB. An example: The bedroom should be 18 °C. The thermostatic valve is assumed to be set to level 3. On the throughput side, level 5 or 23 °C on the RTB scale may be sufficient for this 18 °C. As mentioned, the setting depends on the thermal properties of the building. Towards evening, the outside and room temperatures drop. The radiator valve opens. Without RTB, the full nominal output would be reached almost spontaneously. As mentioned, the setting depends on the thermal properties of the building. Towards evening, the outside and room temperatures drop. The radiator valve opens. Without RTB, the full nominal throughput would almost spontaneously rush through the heating surface, affecting other circuits. The RTB, on the other hand, waits.

Technical data for valves

Return temperature limiters for underfloor heating circuits (RTB-Fbh) and a version for the thermal-hydraulic balancing of heat exchangers in domestic hot water storage tanks, air heaters, swimming pool heat exchangers and ventilation and air conditioning systems (RTB balancing set). Fittings exclusively for radiator heating systems are currently being tested. The The underfloor heating variant, as in the Bärhausen property, consists of a brass base and a thermostatic head with an integrated temperature sensor. As is usual with thermostatic valves, the setpoint value for the return flow, which is adjusted to the room air temperature, is set using the rotatable cap on the upper part.

The RTB supports and accelerates the self-regulating effect of the underfloor heating. Its return temperature increases when the room temperature rises, i.e. when the excess temperature of the heating surface increases. The RTB supports and accelerates the self-regulating effect of the underfloor heating. Its return temperature increases when the room temperature rises, i.e. when the excess temperature of the heating surface decreases relative to the room temperature. The usual two-point single-room controller, which can only switch the circuit on and off, blocks the flow in this case.

When the controller opens, it allows the full water volume to flow through the circuit, i.e. it does not interfere with the volume flow. For this reason, all underfloor heating circuits must be set to a non-trivial value. When the controller opens, it allows the full volume of water to flow through the circuit, i.e. it does not interfere with the volume flow. For this reason, all underfloor heating circuits must be calculated in a rather complicated manner and the calculated water volumes must then be regulated via an actuator. This is a very time-consuming method. And, of course, all settings influence each other: if the last three loops are introduced, the flow that should flow through the first loop is reduced. This is a very time-consuming method. And, of course, all settings influence each other: if the last three loops are activated, the flow that should flow through the first circuit is guaranteed to change. The process is similar to an equation with many unknowns. The optimal point is random.

With the return temperature limitation in the form of a proportional RTB valve, on the other hand, the partial areas always circulate exactly the amount of power that the partial area is supposed to deliver. The return temperature as a control variable dynamically regulates the flow rate. For practical application, Baunach recommends installing the RTBs directly on the return manifold of the distributors. Nominal diameter of the valve DN 15, pressure loss 100 mbar at a throughput of 0.40 m³/h, Kvs value 1.3 m³/h, setting range for return flow setpoint 0 to 40 °C, permissible operating overpressure 10 bar. The second model, the RTB balancing set for automatic thermal-hydraulic adjustment of the flow rates of heat exchangers in drinking water storage tanks, air heaters, swimming pool heat exchangers and ventilation and air conditioning systems, is available in three sizes: DN 20, 25, 32, Kvs 2.5, 5.7 and 6.7, output at 20 K Delta T 18, 42 and 49 kW. Return temperature range 20 to 70 °C.

In contrast to the RTB-Fbh, a remote sensor with a capillary tube is attached to the thermostatic head so that the sensor can be placed anywhere in the return flow of a heat exchanger. Both variants, which are designed for underfloor heating systems as well as for various heat exchangers and air heaters, operate exclusively on a thermal-hydraulic basis without external energy. They do not close completely. A minimum flow rate of 1% of the nominal value is guaranteed so that the sensor is always immersed in the return water. A minimum flow rate of 1% of the nominal value is guaranteed, so that the sensor is always immersed in the return water.

It opens slightly when the return temperature tends to fall due to the falling outside temperature, and it reduces the throughput when the room thermostat has opened completely and the measured value at the RTB sensor now wants to rise above the setpoint value. The other heating circuits are not deprived of heating water as a result. Their RTBs naturally also react by opening the measured value at the RTB sensor now wants to rise above the setpoint. This does not deprive the other heating circuits of heating water. Their RTBs naturally also react by opening the cross-sections. The entire system stabilises itself automatically. The principle of power control of the highly efficient, self-regulating circulation pumps remains unchanged. They automatically adjust their wattage to the differential pressure. Christof Bärhausen enthuses:

Audible success

Image 7: Return temperature limiter test in a chemical factory in Limburg, Belgium, with an RTB behind each of the 30 fans supplied with hot water. The thermocouple prevents the return temperature from climbing above 45 °C due to low heat absorption by the heat exchanger by adjusting the delivery capacity of the circulation pump in response to the increased differential pressure. This makes the return water suitable for condensing boilers.

For the other planned renovation measures on and in the house, the energy consultant has therefore decided against presettable radiator valves, “because they only allow a constant amount to pass through. They don’t work dynamically. For the presetting, I would have to carry out a heating load calculation for each room. I don’t have to do that with the RTB. Now, classic radiator thermostats.” The homeowner is certain that the thermal-hydraulic balancing alone will significantly reduce the vegetable oil bill for his CHP unit. This was originally intended to supply some neighbours in the local heating network. However, they later withdrew, but for certain reasons, the oil boiler was still replaced with the combined heat and power unit. The The system was already running noticeably less efficiently in the first phase of the energy-efficient refurbishment, during the six months when only the radiator thermostats had been installed.

“At least something had audibly changed. I can’t provide a degree day correction, but the situation is such that, according to general experience, better heat distribution saves 10 to 15% in heating energy on average. This will also apply to us, because immediately after adjusting the RTBs, the CHP started up much less frequently. Incidentally, we are registering this effect for a second time. We had also noticed this at the time of the oil boiler, back then, after installing the “rendeMIX” fitting in the solar circuit. The volume of the combi buffer tank was better. We had also noticed this at the time of the oil boiler, back then, after installing the “rendeMIX” fitting in the solar circuit. The volume of the combi buffer tank was better utilised, it gave off heat for much longer, and the boiler recharged less frequently.”

Fine adjustment by the residents

Fine-tuning by the residents

The Franconian by choice rolled up his sleeves. He has work to do. The insulation of the pipes in the boiler room is next on the agenda.

At the distributor on the first floor, he explains the settings:

Just a little patience

Mr Bärhausen, in your experience, what do you need to tell a planner or plant engineer with regard to return temperature limitation?

Figure 8: Two decentralised single-room ventilation systems with ceramic heat recovery units are installed per room. They act alternately as supply and exhaust air units by switching from exhaust air to supply air mode every 70 seconds. For the Vento-Expert type, manufacturer Blauberg specifies a delivery rate of up to 50 m³/h and a heat recovery rate of 97%. www.blaubergventilatoren.de

“Nothing really. As I said, the system regulates itself. There is no preset setting as such. You have to approach it with a little sensitivity and look at the room, its use, its north/south orientation, its heat exchangers/radiators and pre-adjust it to a value. Every user or homeowner can then readjust it themselves. Be a little more careful with underfloor heating. This is a slow system, so it takes a little longer. If you adjust the RTB by perhaps two degrees, you should wait a day or two and only then look at the effect. But you don’t need to make any calculations. To my knowledge, this is the only system that works like this. With all other methods of hydraulic balancing, I have to take the radiator size and other factors into account and combine them to achieve the desired effect. knowledge, it is the only system that works this way. With all other methods of hydraulic balancing, I have to take the radiator size and other factors into account and coordinate them in order to adjust the presettable valves or zone valves accordingly. And then they are almost set. Whether it will work is not guaranteed. Here, the operator makes the readjustment, but sets it to a temperature setpoint, not to a cross-section and thus to a throughput. There is no guarantee that it will work. Here, the operator carries out the readjustment, but sets it to a target temperature value, not to a cross-section and thus to a target throughput value. The RTB finds this itself.”

Sample confirmation for KfW

KfW has agreed with the VDZ, the umbrella organisation for building services engineering, on a procedure for hydraulic balancing, which must be documented in a corresponding form. However, KfW is not opposed to innovation. It states that deviations from the specified procedure are permitted if the alternative can be assigned to point 5.25 “Opening clause for innovative technologies” in the information sheet on heating efficiency measures (KfW publication 600 000 3140). For heating engineers whose customers wish to take advantage of KfW/Bafa subsidies and who request confirmation of hydraulic balancing, Baunach has prepared a corresponding template.