Hydronic balancing is the bugbear for many craftsmen and it is often claimed that hydronic balancing in existing buildings is not worthwhile.
The main argument: all the data needed for the calculation is missing. However, there is good news: The simplified calculation method for hydronic balancing is based on assumptions, and convinces with excellent results.
In this series you will learn how the hydronic balancing procedure works, using the simplified calculation method to reduce your heating bill by up to 13 %.
In this first step of the series “Hydronic Balancing DIY “, we will take a look at some basics and calculation methods for the simplified hydraulic balancing procedure. If you don’t know exactly what hydronic balancing is, I recommend you read my article “What is hydronic balancing?“. There you will find a simple and understandable explanation of hydronic balancing.
Table of Contents
- 1 Hydronic balancing in existing buildings
- 2 Realization of hydronic balancing
- 2.1 Heating load calculation – determination of the specific heat demand
- 2.2 Data recording of the heating surfaces
- 2.3 Calculation of the radiators
- 2.4 Calculate volumetric flow rate
- 2.5 Determine presetting of radiator valves
- 2.6 Use of differential pressure regulators
- 2.7 Calculation of the delivery head and flow rate for the circulation pump
- 2.8 Documentation of hydronic balancing
- 3 Conclusion
Hydronic balancing in existing buildings
In new buildings in Germany, hydronic balancing is calculated in accordance with VOB/C DIN 18380 via the pipe network and on the basis of the required heat demand. The nominal pipe diameters and the presetting values for radiator and pipe fittings are determined precisely.
In existing buildings, however, this is somewhat more difficult because as-built documents and schematics are not always available. A detailed data collection would therefore exceed the cost framework for a hydronic balancing and make it uneconomical.
This is where the “simplified method” for hydronic balancing comes into play. By calculating with approximate values and assumptions, this method allows hydraulic balancing to be performed with sufficient accuracy. I applied the simplified method for hydronic balancing in a field test in 2009. The aim was to demonstrate the energy saving potential of a hydraulic balancing, considering the economic efficiency in an existing building.
Result: The payback period for the project was 5.54 years and is therefore short to medium-term. Pre-adjustable radiator valves, new thermostatic heads, differential pressure regulators for each line and electronically controlled circulation pumps of energy efficiency class A were installed. Energy savings were 13.1% in thermal energy in the first year. The implementation of a hydronic balancing with the simplified procedure is therefore recommended as a cost-effective energy-saving measure.
In the following I will show you the steps which are used in the simplified procedure.
Realization of hydronic balancing
At the beginning of the hydronic balancing it is important to record some data, make assumptions and perform calculations.
Heating load calculation – determination of the specific heat demand
The first step is to determine the heat demand for each heated room. If the heat demand is not known, it is possible to determine it roughly for each room. It should be noted that the heat demand in corner rooms or rooms with a large window area is greater than in rooms with small windows or only one external wall.
I have used the values of “DeltaQ – Energetic classes of buildings” for the determination of the specific heat demand . Accordingly, the following values can be assumed for the specific heat demand. The unit for the specific heat demand is watts per square meter [W/m²].
- 15 – 30 W/m² ultra – low energy house (three-liter house)
- 25 – 40 W/m² Low-energy house
- 30 – 50 W/m² Building according to EnEV 2002 (EnEV is the German Energy Saving Ordinance)
- 40 – 60 W/m² Building according to heat protection ordinance of 1995
- 60 – 100 W/m² Buildings in accordance with the 1982 Heat Insulation Ordinance
- 70 – 130 W/m² Buildings according to heat protection ordinance of 1977
- 130 – >200 W/m² Buildings without thermal insulation from before 1977
Then the specific heating load of the respective rooms is determined. If you are not familiar with the term heating load, I recommend my article on heating load calculation. The specific space heating load is composed of the heated area of the room and the specific heat demand :
Note: In the article “Hydronic Balancing DIY – Step 2: Heat Load Calculation” (coming soon), I go into detail about the determination of the heating load and show the various options using examples. In addition to the energy class of the building, this also includes determining the heating load using an app or data slider.
Data recording of the heating surfaces
Next, the heating surfaces in all rooms are recorded. The following data is required for recording the radiators:
- Radiator dimensions (depth, height, length [mm])
- Radiator type (DIN radiator, panel radiator, tubular radiator, bathroom radiator)
- Valve type (presettable yes/no, make)
After recording the heating surfaces, it is necessary to determine the system temperatures of the heating system. This can be done, for example, using the parameters of the heating curve, which are stored in the heating control system. Typical system temperatures for hot water heating systems are 80/60 °C, 70/50 °C or 55/45 °C. When performing a hydronic balancing, the aim is to achieve a temperature spread of 15 to 20 Kelvin. It is therefore reasonable to expect a temperature spread of 15 or 20 Kelvin.
Note: In the article “Hydronic Balancing DIY – Step 3: Data Collection” (coming soon) I show step by step how you can identify the types of your radiators and then enter the data in a table.
Calculation of the radiators
The power of the radiators is then calculated. This allows the installed capacity of the radiators to be compared with the estimated room heating load. If the estimated room heating load is higher or lower than the installed heating capacity, it is possible to adjust the flow temperature following hydronic balancing.
Note: In the article “Hydronic Balancing DIY – Step 4: Calculate the Radiator Power Output” (coming soon) I show you step by step how to calculate and determine the output of your radiators.
Calculate volumetric flow rate
In the next step, the required volumetric flow rate for each radiator is determined. For this purpose, the radiator capacity , the density of water , the specific heat capacity of water and the temperature spread are required. The formula for volume flow calculation is as follows:
For the selection of thermostatic valves (also thermostatic radiator valves or thermostatic heads) it is recommended to use a control difference of 1 K. You can find an interesting article on the selection of thermostatic valves under the following link: IKZ-Haustechnik – Selection of thermostatic valves. The design differential pressure of the radiator valve should be approx. 50-100 mbar.
Note: In the article “Hydronic Balancing DIY – Step 5: Calculate volumetric flow rate” (coming soon) I show you step by step how to calculate and determine the volume flow of your radiators.
Determine presetting of radiator valves
With the calculated volume flow and the previously determined differential pressure of 50-100 mbar, the presetting values of the radiator valves can be determined via dimensioning diagrams of the valve manufacturers. Furthermore, there are free dimensioning programs or free apps for smartphones from various valve manufacturers, which simplify the determination of the presetting values.
Note: In the article “Hydronic Balancing DIY – Step 6: Presetting the radiator valves” (coming soon), I show you step by step how to determine the presetting values of the radiator valves using an example.
Use of differential pressure regulators
If you want to carry out hydronic balancing in a larger building, it is advisable to use differential pressure regulators line by line. On the one hand, differential pressure regulators ensure a constant differential pressure at the thermostatic valve in the full and partial load range, and on the other hand, differential pressure regulators protect against noise in the heating network. Since a thermostatic valve can operate quietly up to a maximum pressure drop of 150 mbar, the maximum differential pressure of 150 mbar should not be exceeded across a line. From a pump delivery head of 1.5 mWS (equivalent to 150 mbar), it is therefore advisable to use differential pressure regulators on a line-by-line basis.
Calculation of the delivery head and flow rate for the circulation pump
The next step is to calculate the delivery head and the flow rate of the circulation pump. In my article on the design of a central heating pump, I used an example calculation to show how a heating pump can be designed with just a few data. We will use this simplified procedure to design the heating pump.
Note: In the article “Hydronic Balancing DIY – Step 7: Calculate heating pump“, I show you step by step, using an example, which data you need for the heating pump and how you can design a heating pump if necessary.
Documentation of hydronic balancing
In order to obtain a quick overview of the calculation later or to make changes if necessary, it is important to document the implementation of the hydronic balancing. For this purpose, the recorded, assumed and calculated values and data are stored in tables and drawings. This includes, among other things, the respective radiators with the corresponding number (consecutive numbers are assigned), room, line, room heating load, radiator output, volume flow and, of course, the presetting of the radiator valves.
With these basics we are prepared to calculate a hydronic balancing with the simplified method ourselves. The next step is to record the data in the example house presented. Here you can find the overview of the series “Hydronic Balancing DIY”:
Overview of the series:
- Hydronic Balancing DIY – Example for a detached house
- Hydronic Balancing DIY – Step 1: Fundamentals
- Hydronic Balancing DIY – Step 2: Heating Load Calculation
- Hydronic Balancing DIY – Step 3: Data Collection
- Hydronic Balancing DIY – Step 4: Calculate the Radiator Power Output
- Hydronic Balancing DIY – Correction: Floor heating or floor heating?
- Hydronic Balancing DIY – Step 5: Calculate volumetric flow rate
- Hydronic Balancing DIY – Step 6: Presetting the radiator valves
- Hydronic Balancing DIY – Step 7: Calculate heating pump
Related articles outside the series:
- What is hydronic balancing?
- How do Thermostatic Radiator Valves work?
- Calculation of old radiators in stock
- What does a hydraulic balance cost?
Important: Before you start with the instructions for hydronic balancing, I would like to point out that the working methods described here are based on my personal experience and my personal thought processes. Trying out and implementing the described procedures is entirely at your own responsibility and risk. I do not take any responsibility. Furthermore, I recommend that you always have the calculated values checked by a specialist company or an engineering office. Because even if the way described here seems simple, calculation errors can creep in again and again.
I hope that I could show you some important basics for the implementation of the hydraulic balancing with this article and wish you a lot of fun with your hydronic balancing. If you require any further assistance, suggestions or have criticism, please use the comment function.
Further links and sources:
VDMA 24199 (GER)
ZVSHK – Technical information on hydronic balancing (GER)
DeltaQ – Energy classes of buildings (GER)
IKZ Haustechnik – Hydronic balancing (GER)
IKZ Haustechnik – Selection of thermostatic valves (GER)
Wikipedia – hydronic balancing
Wikipedia – Heating curve (GER)
Hydronic balancing – Bruno Bosy (GER)
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