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Optimizing your HVAC systems control : the SSR solution

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Optimizing your HVAC systems control: the SSR solution

HVAC (heating, ventilation and air conditioning) systems are used in many households but also industrial spaces to maintain a specific temperature. A reliable and precise control of the temperature for HVAC systems can be really important. One of the best examples would be data centres in which HVAC systems are installed to avoid a complete meltdown of servers and other devices to make sure a precise humidity level is maintained. Non-reliable or approximative control of the temperature would have catastrophic repercussions.

This is where Solid State Relays have a big role in HVAC systems in terms of temperature control and in terms of motor control. SSRs have many advantages, including high life expectancy, no wear and tear of the switching systems (as there is no movement), fast switching, and control of all types of loads.

This article will inform you about the different temperature and motor control solutions that are used in HVAC systems, and is what celduc’s offer.

Temperature control solutions

The most common technologies integrated in HVAC systems are :

  • On-off control
  • Pulse Width Modulation (PWM)  control
  • Proportional – Integral – Derivative (PID) control

On-off control

One of the easiest ways to control temperature is with an on/off switch. This method of control is based on giving the system complete power until the desired setpoint is attained. The power to the heater is totally cut off once the pressure feedback approaches and exceeds the setpoint.

Power will switch back on when the pressure falls below a setpoint, until it is once more attained. Continuously repeating this cycle of on/off switching keeps the pressure within the specified bandwidth over time.

On-off control graph

Pulse width modulation (PWM) control

PWM is a closed-loop control algorithm that combines individual pulses of different widths to create a time-averaged signal. The greater the difference between the setpoint and the feedback from the device, the longer the duration of each pulse. By adding pulses, an average amount of current is supplied to the heater to achieve a constant temperature level without completely shutting down the system.

Pulse width modulation (PWM) control graph

Proportional, integral, derivative (PID) control

PID control is a closed-loop mathematical function used to regulate process variables allowing the system to react to changes that cause deviations from a setpoint. This type of control can highly improve the efficiency of HVAC systems. A PID controller compensates for changes in the environment by automatically adjusting the device based on sensor data.

  • Proportional control relies on the error between the setpoint and the feedback from the system. The larger the error, the greater the increase in output.
  • Integral control integrates or sums the error over time. Since the error can be positive or negative, even small error terms will slowly add up over time, increasing or decreasing the output to the system until there is no steady-state error.
  • Derivative control is proportional to the derivative of the error or its rate of change. Increasing the derivative gain will make the system more responsive to error changes.

Solid State Relays: the solution for precise temperature control

Solid State Relays allow very precise control of heating elements. They have a high life expectancy, are provided with a very high performance, do not cause any electric arc disturbances and are resistant to shocks, vibrations and dust.

Heating elements with temperature regulation need high-frequency ON/OFF, PWM, or PID control.

celduc® relais offers a lot of solid state relays and solutions corresponding to HVAC systems control such as :

Solid State Relays and motor control in HVAC systems

Air Handling Unit (AHU) compressors

Air Handling Units main function is to manage proper ventilation of interior air with outside air thanks to their key component: the compressor. Solid state relays are integrated in the AHU compressors to effectively control their motors.


The main role of fans in HVAC systems is to make sure the air circulates correctly in the system. Solid-state relays are integrated to control the speed of the fans in HVAC systems to ensure safe and reliable operations.

celduc® relais offers solid state relays that are 100% compatible with HVAC systems to replace electromechanical relays and contactors by providing highly reliable, silent and fast switching solutions.

Main sectors of industrial HVAC applications

Industrial HVAC systems are required in many sectors to ensure air conditioning and heating systems are large enough for a company or hospital and/or to help keep a good temperature to maintain the quality of goods in the food or pharmaceutical industry for instance.

Food and beverage sector

HVAC systems in the food and beverage industry aim to:

  • Avoid dust spreading and move in the food/beverage processing area in order to respect sanitary regulations and avoid cross-contamination.
  • Regulate humidity levels and prevent unwanted condensation.
  • Diffuse unwanted and strong smells during food processing

Pharmaceutical sector

To avoid any sanitary risks, it is mandatory to provide precise and reliable temperature and ventilation regulation during the making of drugs and vaccines. High-quality HVAC systems are then required in the pharmaceutical industry to comply with every type of process regulation.

Health sector

High-quality HVAC is highly important in the health sector such as public hospitals and clinics to avoid any complications or difficulties during the recovery of the patients as well as the spreading of viruses or any kind of high-risk micro-organisms.

Offices and buildings

At work or in vast buildings such as shopping centres, it is a real need to get quality HVAC for general comfort and good working conditions.

Ships and luxury yachts

Heating, ventilation and air conditioning systems are crucial to provide safety and comfort to crew members and passengers. Indeed, ships have precise requirements in terms of energy consumption, durability and space optimization.

Railway industry

HVAC systems are used to control the temperature inside cabins.

Solid state relays are then ideal to control HVAC systems components and ensure high reliability and precise control of the systems. For more information, about celduc solid state relays, feel free to visit our website.

With nearly 200 full-time employees in 4 countries on 3 continents, celduc® relais is a leading player in the global market for industrial automation and magnetic proximity sensors. Founded and located in Sorbiers, France, celduc® relais, is known as the expert in solid state relays and magnetic sensors. Every year, we are proud to manufacture more than 1 million relays sold worldwide, helping to promote French industrial expertise and “100% made in France” quality.