Heating control

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The heating control is a system with which the output of a heating system can be individually adapted to your own needs. It is a sub-category of control technology and aims to reduce energy consumption. In addition, the heating control ensures greater comfort and lower pollutant emissions. A widespread example is weather-compensated heating control, in which the heat output of the heating system depends directly on the outside temperature.

history

When chimneys and kitchen stoves were standard in heating technology, heating control only worked manually. In this way, consumers could regulate the heating output solely through the amount of wood supplied or the position of the combustion air flaps.

Technology made a leap with the development of the first steam central heating in Germany. This came from the engineer Johannes Haag, who had the heater installed in Sigmaringen Castle in Baden-Württemberg in 1843 . It was not until the beginning of the 20th century that central heating systems for oil and gas also moved into German residential buildings. The systems worked on the principle of gravity ( gravity heating ) and could already be controlled to a limited extent. This was made possible with bimetal thermostats, which let the boiler start and stop depending on the boiler water temperature.

Up until now, radiators could only be switched on or off. That was not very efficient, time-consuming and associated with high costs. Danish inventor Mads Clausen changed that with one of the first radiator thermostats that his company (now known as Danfoss) launched in 1940. Radiator thermostats automatically control the heating water throughput through the radiator depending on the room temperature.

After the Second World War , oil and gas heating became more and more popular. At that time the systems could be controlled with valves, the position of which depended on the heating water temperature. In the 1960s, room temperature sensors came onto the market and heating control became more convenient. It was thus possible to switch the heating technology on and off automatically depending on the temperature in a control room. In connection with this, simple time programs such as night setback were also possible. Even if it relied on a little trick: For example, a heat source simulated a higher temperature to the thermostat at preset times, so that the output of the heating was reduced.

In the 1970s, oil prices rose sharply. Heating increased very quickly and the demand for efficient and cost-effective technology grew. In order to do justice to this, boiler manufacturers developed the weather-compensated heating control. It regulated the output of the heating depending on the outside temperature and thus adapted consumption to demand. Even today, the weather-compensated heating control is standard and used in most central heating systems.

Components of the control of a heating system

Control systems consist of at least three components. These are the sensor, the control unit and the actuator. The sensor is the measuring organ. It monitors the input variable, generates an electrical signal and forwards it to the control unit. The control unit is the head of the system. It evaluates the received signals and acts according to its programming. The control unit then forwards the instruction (control signal) to the actuator. The actor is the executive organ. It receives the control signal and actively influences the system to be controlled. The control unit does not find out whether the output variable corresponds to the target variable. For this reason, experts speak of an open mode of action when it comes to heating control.

Example: weather-compensated heating control

A typical example of the function of the heating control is the weather-compensated control of heating systems. Its aim is to select the flow temperature in the heating system so high or low that the amount of heat transported can compensate for the losses through the building envelope in order to ensure the desired room temperature. The following applies:

  • If the outside temperature rises, the heat losses through the building envelope decrease and the heating has to do less. The flow temperature can be reduced.
  • If the outside temperature drops, the heat losses through the building envelope increase and the heating has to do more. The flow temperature must therefore increase.

The connection between the outside temperature and the heating flow temperature is stored in the form of a heating curve for a weather-compensated heating control . The mathematical function assigns a certain flow temperature to each outside temperature and must be set individually for each building.

The function of the weather-compensated heating control relies on the components already described: the sensor, the control unit and the actuator.

In this case, the sensor is an outside temperature sensor. It sits on the facade and continuously transmits the current measured values ​​to the control unit. The control unit receives the data and processes it. This is possible with the heating curve already described. The control then generates an instruction which it sends to the actuator. This is, for example, a motorized three-way valve. The motor brings the valve to the appropriate position, which sets the desired flow temperature.

However, it cannot be said with certainty whether the planned room temperature will actually be reached. Because the heating control only reacts to the outside temperature. Other disturbances such as solar radiation, internal heat gains or open windows are not taken into account.

Difference between control and regulation

While a control influences technical processes depending on known disturbance variables, a control ensures that the desired setpoint is also maintained. This is possible through a closed action path - the so-called control loop. The sensor detects the output variable of the control and feeds it back to the control device. The latter continuously compares target and actual values ​​so that an approximately constant output value can be guaranteed.

One example is room temperature-based control. Here a sensor, in this case a room temperature sensor, continuously measures the temperature in a control or reference room. The control unit compares target and actual values ​​and, in the event of deviations, determines an instruction. The latter transfers it to the actuator, which here can also consist of a motorized valve. While the heating control does not continue to work at this point, the control system continuously records the room temperature. It can therefore also take into account unknown disturbance variables (solar radiation, people or devices in the room) and ensure that the heating never delivers more energy than is actually necessary.

In practice, the functions described in the examples can also be combined. Experts then speak of a weather-compensated heating control with room temperature connection.

Central and decentralized heating control

When it comes to heating control, central and decentralized systems can be distinguished from one another. With the central heating control it is usually a matter of adapting the flow temperature of the heating system to the heat demand in the house. One example of this is the weather-compensated heating control described above, which affects the boiler. The decentralized control, however, affects the individual rooms or heating surfaces. It can be implemented with radiator thermostats , the so-called thermostatic valves .

Thermostats for heating control in rental apartments

Thermostatic valves are small components that sit directly on the radiator. They consist of a valve and a thermostatic head. The latter contains a waxy medium that expands or contracts depending on the temperature in its surroundings. As this happens, it affects the valve position. Rising room temperatures ensure that the valve closes and less heating water can flow through the radiator. The heating surface cools down and brings less heat into the room. If the room temperature drops, the medium in the thermostat head shrinks. The valve opens, more heating water flows through and the room is supplied with heat. When the thermostatic valve opens or closes depends on the setting on the thermostatic head.

Decentralized heating control is particularly beneficial in rental apartments. Tenants rarely have access to the heating system (with the exception of floor heating) and can therefore only influence their heat consumption with the thermostats.

The future of heating control is digital

Regardless of whether it is a central or a decentralized heating control: In both cases, homeowners can usually change target values ​​and certain parameters such as the heating curve themselves. However, this is complicated and only possible directly on the heater or radiator. This fact changes with digitization. This is because the heating can now be controlled remotely using a smartphone, tablet or PC. For example, consumers can start the heating when they are out and about if they come home earlier than planned on a cold day. With geofencing (geographic positioning of digital devices) the heating can even react automatically to where a person is. If it moves away from the house, the heating control reduces the flow temperature to save energy. When homeowners approach their home, the heating system registers that too. It increases its output and heats the building to comfortable temperatures. In addition, it is possible to take the weather report into account when controlling the heating and to switch off the boiler early if there are many hours of sunshine ahead.

Individual evidence

  1. ^ Danfoss - The Journey to "Engineering Tomorrow" | Danfoss. Retrieved October 16, 2019 .
  2. ↑ a b [PDF] Terms of DIN regulation and control - Free Download PDF. Retrieved October 16, 2019 .
  3. ↑ a b Albers, Karl-Josef, Vulkan-Verlag GmbH: Recknagel - Pocket book for heating and air conditioning 79th edition 2019/2020 - basic version PDF-eBook on CD-ROM . 79th edition. Essen 2018, ISBN 978-3-8356-7414-1 .
  4. ↑ Control heating: increase comfort and save energy. Retrieved October 16, 2019 .
  5. ↑ Thermostats - save energy with the right turn. Retrieved October 16, 2019 .
  6. ↑ When gadgets know where their users are. Retrieved October 16, 2019 .