Hydronic Balancing in Comparison: Static vs. Dynamic vs. Adaptive vs. Thermal

In today’s article, I’ll try to explain the differences between static, dynamic, adaptive (automatic) and thermal hydronic balancing. I’ll also explore the following question:

Is automatic hydronic balancing possible with smart radiator thermostats?

As these terms for hydronic balancing are thrown around wildly, this article should help you to differentiate between the terms and then decide for yourself which balancing you would like to carry out and which components you need for this. I will also look at the question of whether automatic hydronic balancing is possible with smart radiator thermostats.

First of all, thanks to Mingiam10, who asked me the following question on X (formerly Twitter). It’s not that easy to answer, so I’ll try to go into a little more detail. You will find a conclusion and my recommendation at the end of the article.

@MartinSchlobach Hello Martin, I’m currently reading your HP on the subject of hydronic balancing with great enthusiasm. I’m an engineer myself and also deal with heating technology in my private life…

read from your website that, in your opinion, there is currently no system…

– 15.3 kWh / 100 km (@Mingiam10) January 3, 2024

Is Hydronic Balancing worthwhile?

The purpose of hydronic balancing is to distribute the heat in your home optimally. In a hot water heating system, the medium water is the carrier for energy in the form of heat. Hydronics describes the technology for using fluids, which also includes energy transfer. This is why experts refer to the improvement of heat distribution in a heating system as “hydronic balancing”. You can find more information in my article “What is hydronic balancing?“.

Due to rising energy prices and increasing awareness of energy efficiency, hydronic balancing is an important measure for optimizing the heating system, heat distribution and reducing heating costs. Depending on the building and the technology installed, the savings are between 5 – 15 %. Balancing your system is therefore worthwhile in any case!

Note: In 2009, I carried out a static balancing in an older existing building (built approx. 1890, approx. 1,950 m² heated net floor area) as part of a pilot project. As there were no as-built documents for the heating system, the hydronic balancing was carried out using the simplified calculation method and calculated with approximate values and assumptions. For this purpose, pre-settable radiator valves and new thermostatic heads were installed on 125 radiators. In addition, 19 differential pressure regulators and three electronically controlled circulation pumps were installed for the individual heating circuits. The energy savings amounted to 13.1% of thermal energy in the first year. The payback period for the measure was 5.54 years and was therefore short to medium term.

You can find out how you can carry out balancing yourself using the simplified procedure in my series “Hydronic Balancing DIY“.

Differences between Hydronic Balancing – Static, Dynamic, Adaptive and Thermal

Whether static, dynamic, adaptive or thermal, the components for hydronic balancing have evolved over time, simplifying and improving them. It is therefore difficult to distinguish between the individual terms. The individual terms are therefore explained and described below. As hydronic balancing must also be carried out in cooling systems, I will only refer to heating systems below.

Note: Hydronic balancing in single-pipe heating systems is carried out differently than in two-pipe heating systems. The following descriptions apply to two-pipe systems.

The information is based on the german DIN 94679 “Hydronic systems in heating, cooling and ventilation systems”, which is currently still in draft form, but will be the standard for hydronic balancing in the future.

Static Hydronic Balancing

With static hydronic balancing, the water flow rates at the radiator are set manually using a presettable radiator valve and cannot be changed during operation. Figure 1 shows an example of a presettable radiator valve with six presetting stages. The water flow rate is preset via the setting gate using a special key.

The amount of water per radiator and the resulting preset values are based on the calculation with the maximum load requirements (heating load design case, when it is coldest outside according to the standard) and aims to supply each room with sufficient heat via the existing heating surfaces. In the partial load case and with changing conditions, however, the hydronic conditions are not adjusted.

Note: Some instructions for static hydronic balancing provide for presetting via the return screw connection of a radiator. This procedure is not recommended, as the presetting is difficult to understand and very imprecise, can hardly be documented and the actual task of the return screw fitting is to quickly shut off the radiator.

Summary

• Constant limitation: Uses only constant presettings of valves for flow limitation, based on a setpoint determined once.
• Pressure-dependent: Control of the actual flow rate is pressure-dependent and aims to ensure that the setpoint is not exceeded only under the operating state originally considered. Deviations may occur in other operating states.
• Electronical Pumps: Electronic circulation pumps are a component in hydronic balancing, but cannot replace it on their own. You can use electronically controlled circulation pumps to store the calculated pump head (delivery pressure) and the calculated total volume flow and thus ensure energy-efficient water distribution.

The most important questions and answers are summarized below.

Manual Thermostatic Heads

Presettable Radiator Valves

Electronically Controlled Circulation Pump

Oventrop*

Oventrop*

Grundfoss*

Heimeier*

Heimeier*

Wilo*

Danfoss*

Danfoss*

Biral*

Manual Thermostatic Heads

Oventrop*

Heimeier*

Danfoss*

Presettable Radiator Valves

Oventrop*

Heimeier*

Danfoss*

Electronically Controlled Circulation Pump

Grundfoss*

Wilo*

Biral*

* Affiliate Link - Last updated prices on 2024-10-10 / Picture source: Amazon affiliate program

Note: In larger buildings with many heating lines, manual line regulating valves are also used, which are used to preset the water volume in the heating line. Figure 2 shows a balancing valve (1) with a presetting gate valve and the presetting 4.9 (3) in the return and a shut-off valve (2) in the flow.

Dynamic hydronic balancing

With dynamic hydronic balancing, “pressure independent control valves (PICV)” are used so that hydronic balancing is possible at full and partial load. Pressure independent control valves are also used to preset the water volume at the valve. As the valves also have an internal differential pressure regulator, pressure losses in the heating network and fluctuating volume flows can be compensated for at any time. Figure 3 shows an example of two cut-open, pressure independent control valves.

The preset volume flow and the differential pressure specified by the valve (e.g. 100 mBar) thus remain constant in every load case. The following video of a Danfoss Dynamic Valve explains this as an example.

Summary

• One-off setting: Here too, the flow rate is set once to a fixed setpoint value based on a specific operating state (heating load design case).
• Pressure-independent: The control of the actual flow rate is pressure-independent and can maintain the setpoint in any operating state.
• Electronical Pumps: Electronic circulation pumps are also used for dynamic hydronic balancing. Here you can set the calculated pump head (delivery pressure) and the calculated total volume flow.

The most important questions and answers are summarized below.

Smart Radiator Thermostats

Pressure Independent Control Valves (PICV)

Electronically Controlled Circulation Pump

Homematic IP*

Oventrop*

Grundfoss*

Tado*

Heimeier*

Wilo*

Danfoss*

Danfoss*

Biral*

Smart Radiator Thermostats

Homematic IP*

Tado*

Danfoss*

Pressure Independent Control Valves (PICV)

Oventrop*

Heimeier*

Danfoss*

Electronically Controlled Circulation Pump

Grundfoss*

Wilo*

Biral*

* Affiliate Link - Last updated prices on 2024-10-10 / Picture source: Amazon affiliate program

Note: In larger buildings (from a pump head of around 1.5 mWs), automatic line regulating valves (also known as differential pressure regulators – see Figure 4) are also used, which usually consist of a setting valve (1) with a diaphragm plate (3) in the return line and a partner valve (2) in the flow line. The adjustment valve and partner valve are connected with a pulse line (4). This ensures that the flow rate is already limited in the individual heating lines and that a constant differential pressure prevails.

Adaptive (automatic) Hydronic Balancing

In the brochures of many thermostat manufacturers, they advertise their smart radiator thermostats with “adaptive” or “automatic” hydronic balancing. According to this, you should simply fit these thermostatic heads to existing radiator valves (without presetting) and then the hydronic balancing would be carried out automatically based on a control algorithm – without any calculation.

If you follow the draft of DIN 94679 Part 1, adaptive hydronic balancing on a radiator is not usual and also not possible, as “adaptive control valves” are required for this. These are able to influence the control adaptively, i.e. self-learning or automatically. However, it is clearly defined here that adaptive control valves must have an integrated electronic flow sensor , which measures and adjusts the actual water flow (volume flow) using ultrasound, for example:

I am not yet aware of any smart thermostat (including those I have tested) that has this feature.

IMPORTANT: According to this definition, adaptive or automatic hydronic balancing is not possible with smart thermostats!

Note: In the draft of DIN 94679 Part 1, Table 2 – Overview of procedures for balancing system areas, it is also emphasized that hydronic balancing using “smart valves” on “radiators, radiators, convectors (two-pipe)” is not common.

I tried to address this in my article “Automatic hydronic balancing – all nonsense?“. But why do so many companies advertise adaptive or automatic hydronic balancing? The answer may be found in the next section on “thermal balancing”.

Summary

• Adaptability: These systems adapt continuously and independently to the current demand by limiting flow rates according to the current operating status.
• Procedure: Permanent automatic detection of the target flow rate and pressure-independent control to adjust the actual flow rate accordingly.
• Installation: The necessary measuring and evaluation equipment must be permanently integrated. Currently almost impossible to implement for radiator systems.
• Components: I am not currently aware of any smart thermostats that can fulfill these tasks.

Possible solution: In my opinion, one system that could meet the requirements for adaptive hydronic balancing would be the decentralized pump system “Geniax” from Empur, which was originally developed by the pump manufacturer Wilo. Instead of thermostatic heads, small circulation pumps with their own power connection and connection to the control technology are installed on each radiator. However, this system is very expensive and does not usually pay for itself.

Thermal Balancing

There is an extra section for “thermal balancing” in the draft of DIN 94679: “Part 4 – Temperature-based alternatives to hydronic balancing“. Thermal balancing or the temperature-based alternative is described in the document as “simultaneity-based optimization without individual balancing“. This means the optimization without volume flow limitation at the heat transfer point such as radiators or underfloor heating.

The basic principle of this method is to avoid situations in which all transfer devices request maximum output at the same time. The simultaneity of such demands should be reduced by suitable components (such as smart thermostats) and reduce areas that are undersupplied with energy without directly limiting the flow rates at each point.

Area of application

As I understand the draft of DIN 94679 Part 4, this form of optimization is particularly suitable for integrated heating systems such as underfloor , wall and ceiling heating systems. On the one hand, explicit reference is made to DIN EN 1264 (standard for underfloor heating systems), and on the other hand, it is emphasized that it is particularly suitable for systems with high thermal inertia and temperature spreads ≤ 9 K.

For a better understanding, the following figure (Figure 5) shows a heating circuit manifold for underfloor heating with control valves and suitable control.

Thermal balancing for radiators?

Although the process is primarily described for integrated heating systems, it can theoretically be applied to other types of delivery systems, including radiators, provided the control technology is capable of optimizing the performance requirements accordingly. However, for typical radiators, which have low thermal inertia, the implementation could be more complex and may not offer the same efficiency benefits.

Note: In the draft DIN 94679 Part 1, Table 2 – “Overview of methods for balancing system areas”, it is emphasized that adaptive thermal balancing on “radiators, radiators, convectors (two-pipe)” is not common.

TÜV certificates and confirmation from Fraunhofer

I have tried to understand the confirmation from Fraunhofer for Homematic IP (german) and the TÜV certificates for Danfoss (german) for “automatic hydronic balancing”. As a result, I can only imagine that these are temperature-based alternatives to hydronic balancing.

The optimization is then carried out with smart radiator thermostats, which use the room temperature as a measured variable and are controlled in such a way that not all radiator valves are open at the same time. Instead, the thermostats are controlled so that the radiators call up heat alternately. The thermostats then receive the control information from additionally installed room thermostats, for example. Danfoss states that thermal balancing can be carried out with its thermostats (Ally and Eco) with a maximum of 20 radiators, and with underfloor heating systems (Icon 2) with a maximum of 20 heating circuits.

Note: Danfoss points out on its website that well-functioning hydronic balancing (they call it “efficiency-optimized hydronic balancing”) can only be achieved in combination with calculation and automation (see here – further down in the article – only in german). This would then be equivalent to dynamic hydronic balancing with electronic thermostats.

What irritates me somewhat about the TÜV certificate for Danfoss is the following statement. It seems that the TÜV did not carry out the test itself, but only reviewed the results of a Danfoss report. If anyone here has any other information, please post it in the comments.

When I asked Homematic IP how their thermostats perform hydronic balancing, I was told that this is proprietary information that cannot be shared with third parties.

Summary

• Thermal inertia: The key to the effectiveness of this method lies in the thermal inertia of the system. Surface-integrated heating systems such as underfloor heating store heat over longer periods of time and respond more slowly to changes, making it more practical to optimize simultaneity requirements.
• Limits of use: For systems with fast responsiveness, such as traditional radiators, the application of the simultaneity-based optimization method without individual balancing may be less effective, as the needs for rapid adjustment to room temperature are different and individual flow control is not available.

The most important questions and answers are summarized below.

Conclusion

The draft of the third part of DIN 94679 “Procedure for existing heating systems in residential buildings“ has not yet been published. I am curious to see whether smart radiator thermostats will be included as a temperature-based alternative for hydronic balancing on radiators.

It is also difficult to say at present whether hydronic optimization with smart radiator thermostats is worthwhile. As I understand it, the confirmations for “automatic hydronic balancing” have only been tested on a few radiators, in small heating circuits and under laboratory conditions. There is therefore a lack of valid empirical values from practice for these systems.

To come back to @Mingiam10 ‘s question, I can answer it as follows after this article:

In my opinion, there is currently no system that can implement automatic hydronic balancing with smart radiator thermostats alone.

Therefore, my recommendation is that dynamic hydronic balancing should be carried out for two-pipe heating systems, supported by smart radiator thermostats. There is a lot of useful information on this in my series “Hydronic Balancing DIY“. Here are the components for dynamic hydronic balancing: smart radiator thermostats, pressure independent control valves (PICV) and electronically controlled pumps.

Smart Radiator Thermostats

Pressure Independent Control Valves (PICV)

Electronically Controlled Circulation Pump

Homematic IP*

Oventrop*

Grundfoss*

Tado*

Heimeier*

Wilo*

Danfoss*

Danfoss*

Biral*

Smart Radiator Thermostats

Homematic IP*

Tado*

Danfoss*

Pressure Independent Control Valves (PICV)

Oventrop*

Heimeier*

Danfoss*

Electronically Controlled Circulation Pump

Grundfoss*

Wilo*

Biral*

* Affiliate Link - Last updated prices on 2024-10-10 / Picture source: Amazon affiliate program

If you see my assessment differently and you understand the draft DIN 94679 differently or have other information, I look forward to your comments. I like to learn and maybe I have overlooked something. I have to admit that the draft of DIN 94679 is not easy to read and understand.

Nevertheless, I hope I was able to give you an overview of the different variants of hydronic balancing. If you have any questions, suggestions or criticism, please use the comments function.

Best regards! Martin

Further links and sources:
TÜV certificates Danfoss
Fraunhofer confirmation Homematic IP

Cover picture: I created the cover picture with DALL-E from OpenAI.