Thermostatic valve

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Radiator thermostatic valve approx. 1975, horizontally spaced temperature sensor head made of NiRo , wax-filled, graduation in degrees on the rotary knob only between “2” and “4”, hexagonal union nut
Thermostatic valve lower part, without regulator attachment. Spring pressure has pushed the actuating pin far out, so the valve is open. Fine thread M30 × 1.5 for union nut, the large protruding hexagon nut serves as an anti-twist device for the base of the thermostatic head
Disassembled thermostatic valve head with expansion element (2nd from right)
Information about the standardized setpoint temperature symbols on the thermostat head, standard logo EN 215, fluted union nut

A thermostatic valve is a temperature regulator that controls the flow rate depending on the measured temperature in order to keep the set temperature constant.

The measuring sensor and the control of the valve can be implemented by a single element (e.g. an expansion vessel) or by various components, or they can also be structurally directly connected to the valve, as is the case with simple heating thermostatic valves that use the Control the flow of room radiators.

Thermostatic valves are also used in cooling circuits and refrigeration machines (hot gas bypass), as self-regulating mixer taps on showers or bathtubs and as oven thermostats on gas stoves.

Radiator thermostatic valve

A radiator thermostatic valve (occasionally also written radiator thermostatic valve) according to DIN EN 215-1 is a throttle valve that is thermostatically controlled. It combines sensors , controllers , actuators and setpoint adjustment in one unit. It consists of the lower part (valve) and the upper part (thermostatic head), which contains the controller, sensor and setpoint adjustment. It is also known as a thermostatic valve as well as a radiator thermostat . Colloquially, it is also known as a thermostat for short .

The inside of the thermostatic head is filled with wax, liquid or gas. This so-called expansion element consists of a metal bellows similar to a corrugated pipe coupling or a corrugated pipe and expands according to the room air temperature. This change in length is transferred to a transmission pin (plunger) and via this to the valve (lower part, see illustration), which changes the flow cross-section of the heating flow and thus the flow rate. A return spring opens the valve when the stretched body contracts. The continuous regulation of the heating water flow results in a largely constant room air temperature.

Without the thermostatic head screwed on, as in the illustration, the heating valve is fully open. Alternatively , the valve can be partially or completely closed with a simple hand control cap that is screwed onto an existing fine thread instead of a thermostat head.

The room air temperature is selected by turning the adjustment head. If you turn the head to the right, the entire head with the expansion element and transmission pin is screwed closer to the valve housing. The opening of the valve is thereby reduced, the flow through the radiator is reduced and the heating output and thus the room air temperature is reduced. When turned to the left (analogous to simple valves) the valve opens more and the heat dissipation increases. A frost protection mark »*« on the setting ring indicates the frost protection setting as the lowest possible, so that the room cannot cool down below approx. 6 ° C in order to prevent frost bursting . The setting to the medium level (usually "3") means a room temperature of around 20 ° C. Every change of the manual setting by a numerical value 1 up or down causes a temperature change of about 4 K. A change in room temperature due to solar radiation, several people or other heat sources is perceived by the thermostat in the same way as the heat produced by the radiator. He regulates accordingly independently. When the room temperature drops, the valve is increasingly opened again.

Since thermostatic valves are proportional controllers , theoretically there is always a small deviation from the setpoint ; the actual value fluctuates approx. 2 K.

For efficient heating, the water flow must be pre-set (either on the valve in the inlet itself or in the lockshield). Furthermore, the adjustment range should be limited internally in order to be safe from incorrect operation. With decreasing heating power, e.g. B. by lowering the heating water temperature at night , the valve opens because the thermostat tries to maintain the setpoint.

Thermostatic valves must be surrounded unhindered by the room air. The prerequisite is horizontal installation so that the warm pipe does not run under the thermostat head. If the heads are covered by curtains or are located in niches , remote sensors or remote adjusters (see below) are helpful, which transmit the thermal expansion to the thermostatic valve via a capillary tube . A low thermal influence on the thermostatic valve by the warm radiator is unavoidable without a remote sensor, but decreases at low heating water temperatures.

In order to increase the service life of the valves, they should be turned to maximum flow outside the heating season so that the elements that generate the pressure on the valve body are relaxed as much as possible.

According to the Energy Saving Ordinance, individual room or group temperature control is currently prescribed (exception: individual stoves for operation with solid or liquid fuels), combined with central heating flow temperature control and shutdown depending on the outside temperature or other suitable reference variables.

A hydraulic balancing of the system for an equal on all radiators operating point (room temperature, setpoint temperature and flow rate) is further prerequisite for a good function.

For the control of floor heating, a return temperature limiter (preferably English Return temperature limiter , RTL) is used. This thermostatic valve does not measure the room temperature, but the water temperature in the return of the underfloor heating. In comparison to conventional heating valves, it is only used at the end of a heating cycle. In the case of underfloor heating, RTL can avoid damage caused by a flow temperature that is too high or prevent water that is too warm from flowing back to the heat generator and thus reducing its efficiency.

The operation of the mechanical heating thermostatic valve appears to be very simple, nevertheless it comes to operating errors because many users mistakenly believe, due to the optical similarity to a tap, that the heating warms up faster if you turn it up more. "In fact, when the thermostat is fully turned up, you don't heat faster, just longer, because the heat supply is regulated by a temperature sensor in the thermostat head."

The life of the mechanical heating thermostatic valve is not unlimited - most copies should be replaced every 15 years.


Remote adjuster

In the case of a mechanical thermostatic valve with remote control, the thermostat and valve are designed as separate units. This is particularly advantageous for radiators that are not free in the room, but are more difficult to access and / or are built into a housing. Because on the one hand a conventional thermostat directly on the heater is awkward to operate (ergonomically unfavorable), on the other hand the thermostat does not measure the temperature in the room itself (but the usually much higher temperature in the housing), so that a good control of the room temperature is not possible is.

The functionality of the remote control is basically the same as that of the mechanical thermostatic valve described above: A change in temperature leads to an increase in the volume of an actuator . But instead of directly driving the transmission pin to the valve, this increase in volume displaces a hydraulic fluid. This acts through a capillary tube (the mostly gray “wire” between the thermostat and the valve unit) on a small hydraulic cylinder directly on the valve, which in turn opens or closes the valve. As described above, the user can set a desired room temperature by turning the remote control to reduce the volume available to the actuator (higher temperature desired) or increase it (lower temperature desired).

Electronic execution

Autonomous controllers

Electronic thermostatic valve Honeywell rondostat, bar display of heating and economy times (above), digital temperature display (center) and adjusting wheel for temperature and time (below)

With electronic thermostatic valves (also called energy-saving controllers ) it is possible to set different setpoints for the room temperature, which the valve then specifies in a time-controlled manner. This means that the compromise between energy savings and living comfort can be better adapted to personal preferences than with conventional mechanical thermostatic valves. The electronic valves are usually supplied with energy via batteries and, like conventional thermostatic valves, are attached directly to the radiator . The valve position is specified either via electronics directly on the valve or via a central control unit via radio transmission. The advantage of electronic controllers is that they work without a permanent control deviation and can therefore maintain the setpoint more precisely. Savings potentials result from the defined lowering over a programmed time. The manufacturer's data assume at least 13% (up to 20%) savings in residential use. The Stiftung Warentest reckons with around 10%. The savings are correspondingly higher in functional buildings , since the degree of utilization (time of room occupancy) is lower.

With radio communication

Special functions can be enabled for thermostatic valve actuators with radio communication:

  • Integration of window contacts to close the valves when the window is open
  • Central absence circuit, e.g. B. by a switch near the apartment door
  • Use of a further setpoint for shorter absences (stand-by), in addition to comfort, reduced operation and protective operation
  • Adaptation of the control parameters to the building / room
  • Automatic optimization of the control parameters
  • Automatic calculation of the start time for heating based on the current room temperature / outside temperature
  • Automatic calculation of the start time for the lowering phase based on the current room temperature / outside temperature
  • Central operation of the system at the central apartment unit, e.g. B. to enter absence times
  • Calculation of the flow temperature setpoint based on the heat demand in the connected rooms
  • Coordination of several radiators in one room
  • Coordination of underfloor heating with radiators
  • Limescale protection for the valves by briefly opening them weekly
  • Attachment of the control sensor at the optimal measurement location, regardless of the radiator, e.g. B. if this is behind a curtain
  • Remote control of the system via telephone / internet
  • If the temperature is too low / too high, alarm is given locally at the control center and / or via telephone / internet
  • Integration of further alarm devices such as smoke alarms, pipe burst sensors

Control by an intelligent central device will enable additional smartphone and internet communication from around 2015:

  • Learning about the thermal inertia of the apartment
  • Learning the influence of tanning in comparison with the weather report and thus heating adapted to the weather forecast
  • Learning user behavior (getting up, leaving the apartment, coming home)
  • Predictive heating when the approach is detected via GPS in the smartphone before coming home

Authority model

Thermostatic valve as an "authority model"

The authority model is the special version of a thermostat sensor (also called thermostat head), which regulates the water flow of a thermostatic valve for radiators .

It differs from a standard model in that the setting range can be limited (e.g. 17–21 ° C) or blocked (e.g. exactly 20 ° C). No other setting can be made without special tools or precise background knowledge of how or where the lock is to be released. The authority models are mounted on radiator thermostatic valves in authorities and other publicly accessible areas in order to prevent the desired room temperature from being adjusted by unauthorized persons.

Government models are also manufactured in a mechanically reinforced design to prevent damage in publicly accessible areas.

Web links

Commons : Thermostatic Valves  - Collection of pictures, videos and audio files

Individual evidence

  1. Wolfram Pistohl: Handbook of building control technology - heating | Ventilation | Lighting | Saving energy - planning principles and examples . 7th, revised and expanded edition. Werner, Cologne 2009, ISBN 978-3-8041-4685-3 , 5.3 Operating and safety devices, p. H197 .
  2. a b c Joachim Albers, Rainer Dommel, Henry Montaldo-Ventsam, Haral Nedo, Eugen Überlacker, Josef Wagner: Central heating and ventilation construction for system mechanics SHK technology . 5th revised edition. Handwerk und Technik, Hamburg 2005, ISBN 978-3-582-03123-5 , 14.1.2 Radiator control valves.
  3. a b Radiator thermostats: programmed to save. In: . Retrieved February 27, 2019 .
  4. Heinz Eckard Beele: Design of thermostatic valves . In: IHKS Industry Association for Heating, Air Conditioning and Sanitary Technology Bavaria, Saxony and Thuringia eV (Hrsg.): Fach Journal . Archive 2003/2004 ( digitized version [PDF; accessed on February 27, 2019]).
  5. a b "Using heating thermostats correctly" in: Mieterzeitung, 2017 edition 1, p. 26.
  6. Test thermostatic valves of the Stiftung Warentest test 5/2008.