HVAC control system

A heating controller is a device for control of heating systems with the aim to maintain a preselected room temperature in all rooms supplied constant.

Properly used and set the heating controller provide an energy-saving heating.

Modern controllers are capable of system temperatures for hot water heating ( flow temperature, return temperature) to change depending on the need. This oversupply is avoided distribution losses are minimized and the energy efficiency of modern heat source increased ( condensing boilers, heat pumps, solar systems ).

In addition, they offer time-dependent intervention options, such as the absence of operation, night shut-off or night, they ensure the achievement of the heating limit for switching off the heating system

  • 2.1 night setback
  • 2.2 execution
  • 2.3 Checking the heating controller

Types of control

Room temperature compensated control

Technically, a service associated with a heater heating controller a control loop structure hold the product room temperature corresponds to the control variable, which is to be influenced. The difference between the value of the controlled variable and its nominal value, ie, the desired room temperature, is the error signal. From the deviation of the heating controller calculates the control value, with which the room temperature is affected.

Controller types differ based on the manipulated variable and how it is moved.

Controller types:

  • Thermostat: The manipulated variable can assume only two states: on or off. That The heater runs on either full load or is switched off. Such simple bimetallic find hardly use today.

A more precise control of the room temperature can be achieved by a cascade control. Rather than regulate the heat output from the heating controller directly, the controlled system is divided into easier to regulatory sections:

From the difference between the desired room temperature and the actual value ( deviation ) of the heating controller calculates the manipulated variable flow temperature ( management control). This serves as the setpoint of the downstream secondary controller in the heater, which in turn controls the flow temperature of the heating water.

  • Manual control: is need for an external controller, the flow temperature can be adjusted by a knob on the device itself. In this case, the regulator needs to be adapted to the current heat demand and personal well-being manually.
  • 2-point - controller: The flow temperature can take only two values ​​: either the set on the devices knob maximum value or the minimum value ( heater off).
  • Continuous controller: can assume the flow temperature continuous values ​​between the minimum and maximum value as a continuous variable. A continuous control is generally only useful when the performance of the heater can be approximately matched to the current heat demand of the building. Otherwise, there are strong overshoots the supply temperature, which can not be compensated solely by modulating the heat output. As a result, there are frequent burner starts ( " clocks " ), which ensures no optimal economic operation. In this case the two-point control is recommended in order to achieve a longer torch lead times. Many heating controller can be switched between two -point and continuous operation.

When using today's room-temperature heating controller, the activity of the heater is only on the temperature conditions of a space - the so-called guiding or Leitraum - a centrally supplied space group made ​​dependent. Is the set temperature of this room is reached, the central heating is switched off and thus all other radiators. Ensuring there all the rooms are supplied with sufficient heating capacity, a room is selected as the lead room in need of the greatest heat output - and even after taking into account any external heat influences such as TV, computer, people, animals etc.. ( This means that the heating is effectively must longest running there until the room has its desired temperature. )

Usually radiator dimensions are chosen to match the heated room, so that all rooms centrally heated space group usually heat up just as fast (at least provided that no serious external heat influences are present). Therefore exists in a centrally supplied space group rarely a room maintained at any power setting to its radiators - including the highest - always takes longer to heat up, as all the other rooms even at their highest power settings on their radiators. Therefore, this strict performance gap must normally be produced artificially. This is achieved by reducing the power of the radiator in the lead room " slowed down " so that the radiator the room while still able to heat is just as strong, but requires significantly more time. Two typical methods are available for:

  • On radiators with thermostatic valves in the reference room, they must be fully open. Then, the water flow is throttled by an adjustable lockshield and this set as short as possible.
  • At radiators in the lead room with pre-set hand valves allow flow is choked with the manual valves and adjusted here as brief as possible.

In the other rooms in the desired temperature can then be adjusted with conventional thermostatic valves. If, in this scenario, the guide space should need much too long to be heated satisfactorily, the flow rate of the radiators can be simply controlled somewhat.

One advantage of the artificial production of the guide space is that this usually have several rooms as candidates. Here, then, can be considered in the selection also irrelevant aspects, such as a favorable location for mounting the control unit.

Advantages:

  • At constant external heat influences on the guide space, fast response to external heat influences in the other rooms
  • Heater and Heat Pump theoretically run only if at least one room really needs and consumes heat.

Cons:

  • Temperature regulation of residential premises is carried out depending on the guide space
  • In poor coordination of the guide space or fluctuating foreign heat sources to the same, insufficiency in the other rooms
  • In case of insufficient thermal insulation ( especially in the non- management areas ) or at different orientations of the rooms no need-based heat supply
  • Guide space must be constantly heated, otherwise no continuous control is possible.
  • Is the guiding chamber have cooled substantially (about to leave), it takes a long time to heat up
  • Nutzungs-/Lageabhängig frequent user intervention may be necessary if, for example, Be sunshine warmed the guide space, thus undersupplied other rooms
  • Unsuitable for larger buildings and multi-family houses

Outside temperature compensated control

The currently measured outside temperature is also suitable as a reference variable for the heating control. With weather- compensated control is determined from the measured value for the outside temperature with the help of a so-called heating curve matching the flow temperature. This in turn is used as the setpoint for the boiler temperature control in the heater. The heating curve is defined by slope and parallel shift and must be manually adjusted to the respective building. When weather-compensated control the use of thermostatic valves on the radiators in addition is useful to ensure a constant room temperature. Careful adjustment of the heating curve is necessary to use the energy-saving potential.

Advantages:

  • No dependence on reference spaces, so standard with larger objects
  • User-friendly

Cons:

  • Without external temperature compensation for rapid adjustment of the flow temperature at an outside temperature fluctuations.
  • Internal heat gains influences may be disregarded.

Outdoor temperature compensation

With this measure, the disadvantage of rapid adjustment to the flow temperature should be improved. Especially in well-insulated buildings or tall building masses as is reasonable.

Of room temperature

You may make sense for individual properties. In this case, the heating controller is calculated from the measured values ​​for the outdoor and indoor temperature setpoint for the flow temperature, external heat influences are recorded here. Radiant panel heating this is unnecessary, since they have a so-called self -regulating effect.

Control over the heater difference Vorlauf-/Rücklauftemperatur

This type of system makes use of the fact that the return temperature at a constant flow temperature decreases with increased heat demand. The controller responds by increasing the flow temperature.

Advantages:

  • No determination of the heating curve more needed, no user intervention required. Indoor and outdoor temperature sensor omitted. External heat influences are captured. For boilers with sliding temperatures unnecessary burner starts can be avoided.

Cons:

  • The heating system requires a careful hydraulic balance, otherwise the controller is not correctly processed by the temperature difference between flow and return.
  • Assign individual rooms, for example, by constant ventilation increased heat consumption, the return control responds by increasing the flow temperature. Here, all rooms with increased flow temperature can be heated. This can lead to a repeal of the central night-time reduction and consequently to an increase in energy consumption.

Other features of a heating controller

Night setback

The heat losses of a heated system ( home or space ) dependent (see Basics ) on the difference between indoor and outdoor temperature and its isolation.

Because at night the lack of solar radiation does not heat the environment, reduces the external temperature, and the heat loss increases. Through the so-called night-time reduction can be counteracted.

Assuming the usage habits ( absence, ventilate, sweat, sit ... ) of the "inhabitants" let it, it may be economical to change the setpoint of the room temperature depending on the time.

For example, at night to sleep a lower room temperature ( lower temperature) than during the day is sufficient. On the other hand can also weekday absence of the occupants offer a meaningful time frame.

The savings can only be estimated, since the heat difference in the course of 24 hours varies daily.

In addition, the so-called night-time reduction can be conventionally used only once in 24 h.

Modern heating controller therefore have a daily or weekly program that switches to independently programmable times between day and lowering temperature.

Note:

A spatial individual thermostat setting, eg by radiator thermostats, is a useful addition that should not be forgotten when planning. Unplanbares, such as ventilation or excursions, should not become the " energy guzzlers ".

Basics:

Since the heat loss from a building is proportional to the temperature difference between indoor and outdoor space (→ Fourier 's law), energy can be saved by such a night setback. However ( eg solid walls ) the effect is small in highly insulated buildings or for buildings with very high heat capacity. The widely held view that the reheating would cost more energy than would be saved by lowering, in contrast, can not be justified physically.

Structurally the inhabited space is a constantly changing complex, temperature, oxygen content and humidity change frequently. The occurrence of condensation (low temperatures for condensing water ) in or on the walls contributes to the conduction of heat and mold growth. The minimization of condensation is useful, as energy, building materials and occupant health are valuable.

Execution

Heating controls are usually associated with a 2 -wire ( the thermostat) or a 3 -wire cable to the heater. In the event that such a line is not present or a more flexible installation of the controller is desired, connect controller with radio transmission on the market.

Review of the heating controller

With a temperature-humidity data logger, it is very easy for extended periods to check the control behavior of heating systems. The data logger records the temperature of the living space. If the data logger is placed directly on the radiator, it records the progress of the flow temperature. The data is transferred via USB interface to the PC and displayed by the accompanying software.

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