Exploring the mechanics of individual room temperature control for radiant heating and cooling systems

The role of individual room temperature control

The European Union's Energy Performance of Buildings Directive (EPBD), revised in 2018, mandates the installation of self-regulating devices for room-by-room temperature control, such as room or radiator thermostats, in buildings where this is technically and economically feasible. This requirement applies to all EU member states, who are free to implement these requirements according to their national context.¹ In Germany, for example, this is regulated, among other things, in the Building Energy Act (GEG). Individual room control has been mandatory there in new systems since 1995. What many people don't know is that a retrofitting obligation for existing systems has been in force as well since 1997. This means that individual room control has been mandatory for all old and new systems in Germany for almost 30 years now.

Individual room control allows occupants to set their preferred temperature for the various rooms in a building with sufficient accuracy to ensure each room is sufficiently heated, but not overheated. By only heating occupied spaces to the desired temperature and adjusting the heating times to their daily routines, they can combine significant energy savings with enhanced indoor climate comfort. Schedules can, for example, be configured so that bedrooms are heated during the night when needed, while living areas are fully heated during the day.

This doesn’t mean that some rooms are heated and others aren’t. A distinction is simply made between full heating (comfort temperature) and reduced operation (reduced temperature, eco-mode, night setback, etc.). Even a prolonged room temperature setback of 1°C can save up to 6% energy for that room. Depending on the heat transfer system (radiators, panel heating, etc.), the room temperature is usually reduced by 2 to 5°C. Completely switching off the heating in individual rooms should only be considered in exceptional cases as it increases the control times of a single-room control as well as the power requirements for heat transfer and heat generation.

Individual room control systems can also easily be integrated into Building Management Systems (BMS) to enable centralised control and remote monitoring. Furthermore, you can opt for smart thermostats, which can be linked to an IoT platform. This allows for the room temperature and time programmes to be adjusted in real time via a mobile app or voice assistant.

Components of individual room temperature control systems

An individual room temperature control system for radiant heating and cooling typically consists for 4 components:

1. Temperature controllers/thermostats

Different types of thermostats can be selected depending on the project requirements. Wired thermostats, for example, provide a fixed connection with a cable between the thermostat and the actuator, and are ideal for new buildings. Wireless, battery-powered thermostats, on the other hand, offer maximum flexibility as they communicate wirelessly with the actuators. This means no cables need to be laid between the thermostat and the actuator, which is especially practical in renovation projects.

Moreover, each type of thermostat is available in different models to meet individual user requirements. Ranging from simple models that only control the temperature to more advanced thermostats with time control and combined heating and cooling operation, there is a suitable solution for everyone.

As mentioned above, another option is to use smart thermostats which can be integrated into home automation systems and/or controlled via an app and/or voice assistant. Most modern time-controlled thermostats are also equipped with an adaptive self-optimisation function to optimise heating cycles based on user behaviour and the control speed of the heat transfer.

2. Actuators

To open or close a valve on a radiator or radiant heating manifold, an actuator is required which receives and processes the signals from the thermostat. For radiant heating and cooling systems, electrothermal actuators are generally used and mounted on the heating circuit manifold. In this case, the actuator is opened or closed when de-energised via a heated expansion element, depending on whether or not power is applied.

For radiators, so-called stepper motors are usually installed, in which a motor transmits the thermostat signals to the valve via a gear mechanism. Due to their low power consumption, these actuators can also be operated with batteries, thus eliminating the need for a power connection at the radiator.

3. Wiring centres

The wiring centre in a radiant heating and cooling system serves as its communication hub, linking the thermostats to the actuators on the heating circuit distributor. The connection between a thermostat and the wiring centre is made via an electric or bus cable in wired systems and by radio in wireless systems. Furthermore, additional functions such as pump and boiler control, valve protection or the switchover from heating to cooling mode are often integrated into the wiring centres.

4. Sensors

In some systems, additional sensors are used alongside the thermostats. These provide the control system with additional information and can further increase the control performance of the system. For example, there are floor sensors that limit the floor temperature or maintain it at a certain minimum value. There are also control systems that allow presence control via motion sensors or adaptive adjustment to the outdoor temperature, for example, via outside temperature sensors.

How individual room temperature control works in practice

The room thermostat is used to set the desired room temperature. It records the actual room temperature and compares it with the set desired temperature. If the actual temperature is below the set temperature, the actuator opens the valve on the manifold, allowing warm water to flow to the designated zone and the room to be heated. If the actual temperature reaches or exceeds the set temperature, the actuator closes again and the circuit cools down. In case of cooling, it’s exactly the other way around.

Each thermostat functions according to a certain control algorithm. In addition to simple continuous thermostats (P-controller) or 2-point controllers, there are also more complex thermostats with PI or PID algorithms that follow a control curve. The type of thermostat that is used depends on the user and system requirements.

Installation considerations for HVAC professionals

The question is not whether to install individual room control in new or existing buildings, as this is a legal requirement. Rather, it’s a matter of deciding which control is best for the specific application. When retrofitting individual room control to existing systems, for example, a wireless solution facilitates installation as it avoids the need for retrofitting wiring between the thermostat and actuators.

In new installations, on the other hand, wired systems are generally used because the layout planning and laying of the cables can be integrated directly into the construction process. In terms of operation, control quality, etc., both systems are comparable.

However, it’s also important to remember that individual room control is only a small part of the entire heating and cooling system and thus of the resulting control quality. Therefore, the following points are also important for a well-functioning system:

• correct dimensioning of heat and cold generators, radiators, surface heating, etc.;
• the correct heating curve and thus a suitable flow temperature depending on the outdoor temperature;
• correct dimensioning of the pipe network, the circulation pump and the setting of the correct pump curve;
• hydronic balancing of the system;
• correct selection and setting of the control parameters for single-room control;
• advising users on the correct operation of the single-room control.

Read more about the role of manifolds and flow meters in achieving a balanced system

Conclusion

Appropriate planning and installation of an individual single-room control system significantly enhances the performance and efficiency of a heating and cooling system. Precise temperature management improves occupant comfort and reduces the system’s energy consumption. HVAC professionals equipped with a technical understanding of control strategies and component integration are able to deliver and install optimal heating solutions for their customers that are tailored to legal requirements and modern energy standards.

Should you have any questions about implementing individual zone temperature control or need advice for a specific project or application, please feel free to contact our experts. We are happy to help.

Get in touch

Sources:
1. https://build-up.ec.europa.eu/sites/default/files/content/eu.bac_guidelines_on_revised_epbd_june_2019.pdf