- Technical Area
- University of comfort
A set-point system is the most simple way to control temperature. It guarantees the system a constant fluid flow temperature.
The value is set manually via a thermostatic valve. The compact size of this type of control unit means it can be housed in a box connected directly to the manifold - a feature that facilitated its widespread use in the past.
The major limitation is that the user has to adjust the system every time the external conditions change. To reduce the need to do this, the practice has become to calibrate the thermostatic valve to the design temperature (equal to the maximum temperature necessary on the coldest day of winter) and to install thermostatically-controlled electrothermic actuators on the system.
The thermostat compares the temperature set by the user with the temperature of the room. If the temperature in the room exceeds the temperature set by the user it disconnects the power to the actuator which closes the circuit(s). All actuators are equipped with an auxiliary microswitch which allows the circulation pump to be turned off when all circuits are closed, without the need to add link modules.
In the case of a single temperature-controlled room, the room thermostat can be connected to the pump supply. When the set temperature is reached, the fluid flow in all of the manifold circuits is stopped. In these types of systems, the characteristics of the thermostat are of particular importance.
If the room thermostat detects a temperature above the set temperature, it means the screed and fluid are at a higher temperature than necessary. If this happens, the excess heat of the screed will have to be dumped while continuing to provide heat to the room. However, this will not prevent the room temperature from continuing to rise and hours may pass before the screed cools down sufficiently to reduce the temperature of the room.
When the temperature of the room has dropped to below the set temperature, the thermostat will reopen the circuits to allow the screed and fluid to heat up until the room is again at the ideal temperature.
In a set-point control system, the water circulates at a temperature that corresponds
to the value required for the coldest day of winter.
In summary, the room‘s temperature will continually oscillate. The greater the difference between the required water flow temperature and the temperature of the water actually circulating in the system, the more noticeable the phenomenon. This means that the temperature set on the thermostatic valve must not be too high. To minimise the oscillation effect, it is important to select a thermostat with a small differential, although the best solution would be to use a proportional thermostat, such as the built-in Evo thermostat.
This particular thermostat is a modulating thermostat rather than an on/off thermostat. Within a differential of 1.5°C, the thermostat opens the valve for a period of time proportional to the difference in temperature between the value set and the value recorded. This means that as the desired temperature is reached, the amount of heat supplied is progressively reduced, with the effect of reducing temperature oscillation in the room.