Hydronic Balancing DIY – Step 3: Data Recording

The third step in the “Hydronic Balancing DIY” series involves data recording for further calculations. To do this, we will record the radiators in the building and then determine the system temperatures. These are necessary for the subsequent calculation of the radiator output. However, before we start data recording, it is necessary to know which radiator types are installed in our building. I recommend the following document from DeltaQ – Heating surface types (Recknagel Sprenger). The document is unfortunately only available in german.

Preparation for Data Recording – Know the Heating Surface Types

Hydronic balancing is an optimisation of the heat distribution in the building, which is why you need to record the heating surfaces. Firstly, a distinction is made between the following heating surface types, which you can find in the Recknagel Sprenger document on the corresponding pages:

• Flat radiators (panel radiators) – from page 4 onwards
• Sectional radiators (steel and cast iron radiators) – from page 6 onwards
• Tubular radiators (incl. towel radiators) – from page 8
• Tubular and finned radiators – from page 13
• Convectors – from page 14
• Special constructions – from page 18

Note : To determine the radiator types and their calculation, I recommend that you also work with the article from DeltaQ – Heating surface types (Recknagel Sprenger) in the next steps. It describes the common types of heating surfaces and contains the tables required to calculate the standard heat output for radiators in accordance with DIN EN 442. In a later part of this series, I will give you an example of how the output of the radiators is determined using these tables.

In our example building, mainly profiled panel radiators (see Figure 1 – Fig. 1) and a towel radiator in the bathroom (see Figure 1 – Fig. 2) were installed during the renovation. The panel radiators are valve radiators and the towel radiator is a compact radiator. Furthermore, there is a floor heating system in the kitchen with an Oventrop individual room control “Unibox vario*” with the thermostat “Uni RTLH*“.

Before we finally start data recording, we should realise what data we need in order to save potential extra work afterwards. For panel radiators, it is important to know how high, deep and long they are. The number of panels and convectors are also necessary when recording data.

As described in the DeltaQ report – Heating surface types (Recknagel Sprenger) – from page 4 onwards, profiled panel radiators are given a type designation depending on their construction. P stands for panel and K for convector. The first digit stands for the number of panels and the second digit for the number of convectors. Figure 2 shows an example radiator (view from above) with the type designation PKKP 22.

If you do not have panel radiators in your building, it is necessary to record the number of radiator elements, columns or pipes in addition to the depth and height. These are needed to determine the performance of the radiators.

Data Recording of the Heating Surfaces and Valves

In this step, we start with the data recording and record the radiators. You will need a folding rule, a pencil, a writing pad, a copy of the floor plans of the building and, if possible, a digital camera or smartphone. Firstly, I created a table with the following columns:

• Room
• Radiator number (Ra no.)
• Radiator type (Ra type)
• Pre-adjustable valve (PV?) -Yes/No –
  I recommend you read my article on the thermostatic valve
• Valve type (V TYPE), a distinction is made between straight-way valve [SW], angle valve [A] or valve radiators (VR)
• Valve manufacturer (VM), for example Oventrop [O], Danfoss [D], Heimeier [HM], Honeywell [HW], unknown [UK]
• Depth [mm]height [mm] , width, width [mm]

Tip: I recommend that you take a photo of each radiator and each thermostatic valve and then write the corresponding photo numbers behind each radiator. This way you can then quickly call up all the information about each radiator.

Note 1 – Nominal pipe diameter: If no presettable radiator valves (see article about thermostatic valves) are installed in the building, the column “Nominal pipe diameter” in inches should be added to the table. The nominal pipe diameter can be determined using the outer diameter of the pipe on the valve. Of course, this only applies to radiators with a straight-through valve or angle valve. If you then commission a specialist company to install new thermostatic valves, you can pass this information on and the specialist company will know which valve types and sizes to procure.

Note 2 – Sectional radiators and tubular radiators: If no panel radiators are installed, but sectional radiators or tubular radiators, for example, the columns “Number of sections” and “Number of tubes” should be added to the table.

Note 3 – Large buildings with several heating circuits and lines: For larger buildings with multiple heating circuits, it is still important to allocate the respective heating circuit and the respective heating train. These can also be added as a column in the table. However, this is not necessary in our example building.

While data recording, I entered the values in the following table (Table 2) and then drew the recorded radiators in a copy of the floor plans (Figures 3 and 4).

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As there is no documentation for the underfloor heating (UFH) floor heating (FBE) in the kitchen, I will use the room load to determine the output, as suggested by the Bundesverband Flächenheizung und Flächenkühlung e. V. (BVF).

Tip: Here is a calculation tool for the rough hydraulic balancing of existing underfloor heating systems.

Determining the system temperature

If we follow the steps from the article Fundamentals of hydronic balancing, the system temperature for the heating system is determined after the heating surfaces have been recorded.

In our example building, the heating control system has a flow temperature of
75 °C with a standard outside temperature (NEW: design outside temperature) of -14 °C is stored in the heating control system. The room temperature should be 22 °C (you can specify this yourself in advance). Since a gas condensing boiler heating system is installed in our example building, a spread of 20 K (Kelvin) between the flow and return should be achieved in the design case after hydraulic balancing. This would mean a return temperature of 55 °C. The target system temperature is therefore 75/55/22.

Note: A condensing boiler is installed in our example building. For hydronic balancing, high temperature spreads of 15 to 20 Kelvin are aimed for with low-temperature and condensing boilers to achieve a high heat flow rate. Heat pumps, on the other hand, run more efficiently at low flow temperatures, so that only a low spread of between 5 and 10 Kelvin is aimed for. Table 3 shows examples of system temperatures for various systems. It is therefore necessary to check in advance which system temperatures the existing heat generator is suitable for.

The aim is to achieve a sluggish heating system. A sluggish heating system circulates the heating water in the heating network very slowly so that it has the opportunity to transfer its heat to the rooms and thus increase the temperature difference between the flow and return. As a result, less pump power is consumed and no unnecessarily hot water circulates in the heating network, which saves energy.

Conclusion

With the data recording of the radiators and the system temperature determined, the next step is to calculate the radiator output. If you notice an improvement in your data recording and thus an even simpler data recording is possible, you are welcome to leave a comment.

Important: Before you start with the instructions for hydronic balancing, I would like to point out that the procedures described here are based on my personal experience and my personal train of thought. Trying out and implementing the procedures described is entirely at your own risk and responsibility. I do not accept any responsibility. Furthermore, I recommend that you always have the calculated values checked by a specialised company or engineering firm. Because even if the method described here seems simple, calculation errors can always creep in.

With the data we have now obtained, we are able to take the next step in hydraulic balancing and calculate the radiator output. If you have any questions, suggestions or criticism, please use the comments function.

Best regards, Martin.

Further links and sources:
DeltaQ – Heating surface types (Recknagel Sprenger)
Calculation tool for the approximate hydraulic balancing of existing underfloor heating systems

Title picture: I created the title picture with DALL-E from OpenAI.