Hydraulic balancing

from Wikipedia, the free encyclopedia
Without hydraulic balancing, there will be a temporary undersupply of the remote radiators, especially when heating up (in the morning). An unfavorable control behavior of the thermostatic valves can increase the effect. If the heating or pump output is inadequate or if the radiators are incorrectly dimensioned, the supply will be permanently uneven.
Hydraulic balancing should enable the entire system to be supplied evenly in all operating states.

A hydraulic balance is necessary in order to achieve that set in a branched hydraulic system certain volume flows. If the volume flow in certain branches or circuits of the system is too low, the flow of other branches or circuits is deliberately throttled in order to achieve compensation.

In the following, hydraulic balancing in hot water heating systems and in the circulation of hot water pipe networks is dealt with.

Hot water heating systems usually have individual room controls that reduce the flow rate when the desired room temperature is reached. As a result, the flow rates in the heating circuit fluctuate considerably and, in certain operating states, there may be an undersupply of certain lines. Modern circulation pumps adapt the pump pressure to the flow rate, which makes hydraulic balancing easier.

Ideally, the flow rate and flow temperature as the operating point of the heating system are regulated in such a way that each room is supplied with the correct amount of heat in order to achieve the desired room temperature.

Since the operating behavior of a hydraulically not optimized system causes a certain additional consumption of electrical energy and fuel, the Federal Environment Ministry is promoting a campaign for hydraulic balancing. Hydraulic balancing is also often a prerequisite for funding from the Reconstruction Loan Corporation and the BAFA's Market Incentive Program for the Use of Renewable Energies (MAP) . There are different implementation procedures, depending on the funding program.

Insufficient hydraulic balancing

If there is no hydraulic balance, radiators that are closer to the heat source are better supplied. Radiators that are further away may not get warm enough or the control behavior is poor.

In the case of unfavorable hydraulic conditions and moderate pump or heating output, rooms further away are only supplied with heat when the rooms near the heat source have already reached the temperature set on the thermostatic valve. In this case the thermostatic valves there close, which means that a sufficient amount of the heat transfer medium is available for the rooms further away.

The flow resistance in the heating circuit increases with the length of the pipeline. If no throttling was carried out as part of the hydraulic equalization, the heat transfer medium therefore initially flows to the radiators that are closest to a heat source ( boiler , buffer storage , heat exchanger ) (this results in a "hydraulic short circuit"). Due to the lower flow resistance, more water flows through these radiators than required and leaves the radiators at a comparatively high temperature. The return to the heat generator consists largely of the return from the first radiator. As a result, the return temperature is higher than if it were evenly distributed to all radiators.

The thermostatic valves usually contained in the heating circuit throttle the flow of heat to the nearby rooms only when the room temperature has risen to the setpoint set on the thermostatic valve. When the setpoint is approached, the valve closes and slows down the flow.

Due to the increased temperature of the heating return

  • the efficiency of low-temperature and condensing boilers is reduced
  • there are increased thermal losses in the pipe network and boiler
  • the heating control may reduce the heat supply early or switch the heat generator on and off frequently ("Cycle", see also Boiler # Cycle ).

In the past, in order to avoid uneven heat distribution, the heating water circulation pumps were dimensioned larger and / or the flow temperature was set higher than actually necessary. Both are associated with energy losses, which one would like to avoid today. Excessive volume flow and increased flow temperature often result in the same disadvantageous effects that are described above for an increased return temperature.

Technical consequences of a heating distribution without hydraulic balancing in systems with a boiler :

  • The higher return temperature results in higher flue gas temperatures, which in particular reduces the efficiency of condensing and pellet boilers.
  • The delayed heat release requires more frequent burner stops. The period from one burner start to the next is called the "cycle". By frequent cycling of the gas or oil burner
    • the wear increases
    • heat losses occur during the cooling phases of the burner when the burner chamber is flushed with cold supply air (the heat energy is lost with the exhaust gas) and
    • the efficiency is reduced due to the incomplete combustion in the first minutes of the burner start-up phase and carbon monoxide (with residual calorific value) is formed.

Savings potential

In the OPTIMUS program funded by the Deutsche Bundesstiftung Umwelt (DBU) , savings potentials were determined in practice in 92 single and multi-family houses in northern Germany, and the heat losses were then minimized with a restricted catalog of services. Among other things, the objects examined had heating circulation pumps that were three times oversized on average, based on the actually sufficient electrical output.

The countermeasures were (2003) comparatively inexpensive with costs of € 2 to € 7 per square meter living space. The success of the individual heating systems improved in the OPTIMUS project, extrapolated to the entire Federal Republic of Germany, resulted in savings potential of between 20,000 and 28,000 GWh per year.

Only:

  • Presetting of the flow limitation of the radiator thermostatic valves (= hydraulic balancing)
  • Settings of the heating circulation pumps (lower output) or their differential pressure regulators
  • Setting the heating controls

A meta study by the ITG Dresden in 2019 came to the result that the savings through hydraulic balancing are in the range of 7-11%. The largest study cited in the study was a project by the Evangelical Church in Baden , in which 555 church buildings were compared. The current evaluation of the project showed average savings of almost 7%.

Signs of a lack of hydraulic balancing

  • Individual radiators do not get warm while other parts of the system are oversupplied.
  • The boiler burner switches off too often and switches on again soon after (it clocks).
  • If the pump output is increased to compensate for an uneven distribution of heat, noises can arise from the increased flow velocity in the radiator valves and pipes. An increased pump pressure can have a negative influence on the control behavior of thermostatic valves.
  • The increased flow in preferred rooms can also influence the control behavior of thermostatic valves. Rather, there is an overshoot (alternating room temperature that is too high and too low).
  • The required flow temperature is higher than calculated.
  • The required pump output is higher than calculated.
  • The return temperatures are higher than planned.

Matching methods

The basis of the hydraulic balancing is a corresponding calculation model. It must

  • the heat output of the individual radiators
  • the size of the room
  • the exchange of air through doors and ventilation
  • the heat loss through walls and windows

be known. The less known, the worse the calculation model is supplied. A better distribution of the heating water is achieved with hydraulic balancing.

Another metrological approach uses a temperature measurement on the return of the individual radiator. With hydraulic balancing, approximately the same temperature is achieved at all return throttles.

In the case of a new building or heating system, hydraulic balancing is achieved through good planning, checking and settings when the system is commissioned.

If the fittings required to reduce the flow rate are available for individual radiators, subsequent hydraulic balancing is also possible through

  • pressure-controlled feed pumps
  • adjustable return flow throttle valves
  • Installation of presettable thermostatic valves or
  • Installation of pressure-independent, presettable thermostatic valves
  • Installation of line differential pressure regulators.

Hydraulic balancing is a task for heating contractors, specialist planning offices, energy consultants and chimney sweeps. They can advise and carry out the calculations or measurements.

Hydraulic balancing in theory

DIN EN 12831 (June 2003) has been in force in Germany since April 1, 2004. After that, a professional planning with heating load , pipe network and heating area calculation by a planner is required. The planning results in the heat requirement and volume flows .

In Germany, tradespeople who want to complete their work in the interests of the associations are obliged, according to the procurement and contract regulations for construction services ( VOB ) Part C, to hydraulically balance heating pipe networks. This is particularly necessary for heating systems without flow control.

A stationary (quasi-static) hydraulic balance is achieved when all parallel systems (e.g. radiators on a line or apartments in a building) each have the same hydraulic resistance . In principle, however, this is only possible for one operating point (desired room temperature) and with constant system conditions, i.e. a certain flow rate. For example, the pump delivery rate must not fluctuate or individual radiators must not be closed. For this reason, the stationary hydraulic balancing is carried out for a particularly critical condition: the maximum heating load at which all heating surfaces are flowed through.

In modern heating systems with regulated pump pressure (results in a variable total flow rate), with thermostatic valves on the individual radiator (results in a variable individual flow rate) and with variable heat consumption, the stationary hydraulic balancing is of less importance. Instead, the maximum possible flow rate for the individual radiators must be limited there. A dynamic comparison is thus achieved.

Hydraulic balancing in practice

Hydraulic balancing of the heating system for an operating point that is the same on all radiators (current room temperature, target temperature and flow rate) is a prerequisite for good function, especially for condensing boilers.

In order to preset the flow rate for each radiator, either thermostatic valves with a flow rate parameter (adapted kV cone) are used, on which the calculated value is set, or the flow resistances are regulated by the lockshields . It is generally possible to set an operating point in accordance with a model calculation. A thermostat-controlled limitation of the return is better. This is always recommended for rooms with several heat sources that shift the operating point.

Carrying out the presettings is made easier by special lockshields with two setting options (coarse open-close and fine 0-100%), which support a fine adjustment and are not only used to shut off.

Radiator valves with an integrated volume flow adjuster can also be used. With these valves, the maximum volume flow required for the radiator is set once. Then the thermostat is mounted on the valve. The thermostat now only regulates in the range from zero to the preset volume flow. A system equipped in this way works stably at all times, as the influences of other system parts have no repercussions on the radiator. It only has to be ensured that there is a sufficient differential pressure on the radiator.

The heating pump must be electronically regulated to an adjustable differential pressure, because it is a prerequisite for an optimal flow rate of water corresponding to the maximum delivery head. This must also be set after the calculation made for the operating point.

Systems without individual room temperature control

The German Energy Saving Ordinance prescribes the installation of individual room temperature controllers (and self-regulating circulating pumps) for systems to be built or renovated. The use of thermostatic valves for individual room control has been common since the energy crisis in the 1970s .

This is only deviated from in special cases.

Highly insulated buildings often have such a low demand for thermal energy that, especially when using ventilation convectors and surface heating in combination with heat pumps and solar heating support, the flow temperature of the heating circuit is only slightly above room temperature. Since the heat output drops sharply when the temperature of the heating surfaces approaches room temperature, there is a certain self-regulating effect, which makes it possible to do without thermostatic individual room control without too great a loss in comfort and energy consumption. The condition for this is usually that there are no disruptive influences from solar radiation or other heat sources or that specific room temperatures are not required.

Since there is no need to regulate the volume flows through the individual room temperature control, hydraulic balancing must be carried out in any case in order to enable even distribution of the thermal energy.

Hydraulic balancing in hot water circulation networks

A circulation system is often installed for heated drinking water , which maintains the temperature up to the last consumer via a return line. In large systems it makes sense to hydraulically balance this pipe network similar to that of the heating system. The circulation pump in the return line can often run up to 50% more efficiently and thus save electricity. In addition, the risk of legionella occurring is reduced, since the better flow ensures a sufficiently high temperature even at consumers that are far away.

The DVGW worksheet W 553 provides information on the correct dimensioning of the corresponding pipe dimensions. The term "large system" is also specified here for the area of ​​hot water preparation: As a small system in the sense of the worksheet, only systems in buildings with 1 residential unit (WE) or 2 WE if the owner lives in the house are to be considered. The contents of the water heater (WWB) and the pipe contents of the installation also play a role. If the nominal volume of the WWB is 400 liters or more, it is a large system. In addition, an installation defined as a small system must not have more than 3 liters of pipe content in the hot water network.

The most important difference between small and large systems is the required operating temperature for hot water preparation and distribution. A hot water network in large systems must always be operated with at least 60 ° C, the cooling down until the circulation re-enters the water heater (WWB) must not be more than 5 K. In small systems, the water heater can be operated at 50 ° C, but here too, due to the legionella problem, a permanent 60 ° C or weekly heating to 70 ° C is recommended.

literature

Web links

Individual evidence

  1. ↑ Forms for confirmation of hydraulic balancing (for tradespeople and experts) from VdZ
  2. ↑ Hydraulic balancing - do you need it? accessed on November 15, 2018
  3. ↑ Jagnow, Wolff: OPTIMUS short report, page 3 ( Memento of the original from November 27, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 198 kB) @1@ 2Template: Webachiv / IABot / www.optimus-online.de
  4. ↑ The OPTIMUS project ( memento of the original from October 2, 2013 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.optimus-online.de
  5. ↑ Jagnow, Wolff: OPTIMUS short report, page 7 ( Memento of the original from November 27, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 198 kB) @1@ 2Template: Webachiv / IABot / www.optimus-online.de
  6. ↑ Jagnow, Wolff: OPTIMUS short report, page 5 ( Memento of the original from November 27, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 198 kB) @1@ 2Template: Webachiv / IABot / www.optimus-online.de
  7. ↑ ITG Dresden: Energy saving potential and economic evaluation of hydraulic balancing for systems of building energy technology . Ed .: Bettina Mailach, Florian Emmrich, B. Oschatz, L. Schinke, Dr. J. Seifert. ( hydraulischer-abgleich.de [PDF]).
  8. ^ Felix Schweikhardt: Hydraulic balancing and pump replacement in the Evangelical Regional Church 2013 to 2019 . Karlsruhe May 28, 2019 ( ekiba.de ).
  9. ↑ The heating circulation pump
  10. ↑ The return screw connection
  11. ↑ http://www.haustechnik-hart.de/foerderungen/hydraulischer-Abgleich.html Structural requirements for hydraulic balancing
  12. ↑ See § 14