A Thermostatic Radiator Valve (TRV) is a self-regulating valve fitted to hot water heating system radiators. The TRV controls the temperature of a room by regulating the flow of hot water to the radiator. Thermostatic radiator valves (air vent valves) also exist for steam radiators.
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Many years ago the first ideas for heating controls saw the light of day, but it was not until 1943 when Mads Clausen, founder of Danfoss, invented the first radiator thermostat that the development of TRVs became serious. However, from the first invention to mass production to the European market it took almost 15 years, and it was not until 1973 when the first oil crisis hit the world that the installation of TRVs really took speed.
Today TRVs have a wide market distribution and acceptance worldwide as an energy efficient and competitive technology. In spite of this there is still a huge potential for further implementation of TRVs as replacement of old manual valves to benefit the environment and reduce the energy costs for people around the world.
A TRV consists of two parts: a valve that opens or closes to control the hot water flow and a sensor that controls the opening of the valve. The sensor contains an actuator with a sensing substance, which adjusts the valve opening based on the temperature in the room and via a physical connection between the actuator-spindle and the valve-spindle/cone.
The sensors are for the most part made of plastic in many different designs and shapes. The actuator usually contains a sensing substance, such as wax, liquid or gas.
The valves are mainly made by brass or bronze and have different sizes, shapes and connections to the radiator. The majority of valves are mounted on the piping connected to the radiator; however, the valves may also be mounted as an integrated part of the radiator.
TRVs are not self-regulating devices, which control the temperature in the room based on an individually set temperature and heat load. TRVs can work together with outdoor temperature controls, supply flow temperature controls, pressure controls and time set-back devices.
The overall principle can be described in this way:
The process is completely self-contained and without complex electronic controls. The TRV keeps the room temperature at a desired level even through fairly wide swings in indoor temperature due to external conditions such as sudden temperature drops, solar radiation, wind velocity or wind direction.
Note that a TRV cannot manage room temperature without a thermostat somewhere in the system to signal the heating source to kick in and produce hot water or steam. For example, in a three bedroom apartment with a living and dining area, there has to be a thermostat in the apartment to signal the boiler to produce hot water. If the thermostat for the apartment is located in say, the living area, then any TRV's installed on radiators in the bedrooms can manage temperatures in those rooms, provided the thermostat in the living room is calling for heat. So if we wish to turn down the thermostat in the living room when we go to bed then the bedroom radiators will only get heat if the living room temperature is above the temperature in the living room.
One way to get around this problem is to use a second, or third or fourth, thermostat in other rooms, each with a separate connection to the boiler or heating source.
After installing TRVs, owners have to get used to the self-regulating principle which means that they do not have to turn the thermostat up and down. When room temperatures vary, the valve automatically opens or closes to regulate the flow of hot water until the desired temperature is achieved. Only if the desired room temperature has to be changed or if windows are opened or closed for ventilation does the sensor setting need to be adjusted.
A TRV should not be fitted on a radiator where it is in the same room as the main house/rooms thermostat, as this can lead to inaccurate overall house temperature control. Refer to BS5449 or equivalent.
TRVs are suitable for all kind of radiator systems, radiators, convectors and towel dryers. Designs of the sensors can be tailored to suit the specific applications. TRVs are cheap and easy solutions with a significant potential for energy savings and CO2 reductions from heating installations. In fact the replacement of a manual heating control with a TRV can save at least 280 kg CO2 per year.[1]
When dimensioning a heating system in a building, it is necessary to perform a precise calculation of the total system. As part of this calculation it is important to secure proper hydraulic balancing of the complete heating system. For this balancing, the presetting feature in the valve or a special hydraulic balancing valve can be used.