Belimo HVAC Solutions: Room Operating Units, Sensors, and Controllers

HVAC control devices are designed to optimize indoor comfort and energy efficiency by regulating temperature, airflow, and air quality in various settings. This article covers key products from Belimo including VAV controllers, room temperature sensors, positioners for wall mounting, and room operating units, detailing their functionalities, features, and selection criteria.

Table of contents

• VAV controllers
• Room temperature sensors
• Positioners for wall mounting
• Room operating unit
• Selection criteria

VAV controllers

A VAV (variable air volume) controller is a device used in HVAC (heating, ventilation, and air conditioning) systems to regulate the flow of air to different areas or zones within a building to optimize comfort and energy efficiency. One VAV controller is designed to control a single zone. It can switch between cooling and heating modes, monitor room temperature, and even handle specific conditions like kitchen and bathroom humidity.

The Belimo VAV controllers come in different models, such as the CRA24-B3, which offers advanced control with multiple inputs and outputs, and the simpler CRA24-B1P, which is easier to use but has fewer features. The controllers have various features, such as:

• Variable voltage outputs:
  • Supply air control: Both models can control the damper actuator for the supply air, allowing the controller to adjust the amount of air entering the zone based on current needs, whether for cooling or heating.
  • Exhaust air control: The Belimo CRA24-B3 model includes an additional variable voltage output for controlling the damper actuator for the exhaust air, maintaining the desired air quality and pressure balance within the zone. The CRA24-B1P does not support this feature.
  • Heating output: The Belimo CRA24-B3 model has a versatile heating output that can be configured for either 2-point (on/off) or 3-point (modulating) control, allowing the system to adjust heating levels based on the room's temperature requirements. The CRA24-B1P does not support heating valve control.
• Override functions:
  • Kitchen override: The Belimo CRA24-B3 model can increase the exhaust airflow to manage pressure changes and humidity levels caused by kitchen activities.
  • Bathroom override: Similar to the kitchen override, this function in the CRA24-B3 model increases the exhaust airflow to quickly remove humid air from the bathroom, preventing moisture buildup. The CRA24-B1P does not support these override functions.
• Energy hold off (EHO): This output function, available in the Belimo CRA24-B3 model, reduces energy consumption during periods of inactivity by adjusting air volumes and heating settings, helping to conserve energy when the zone is not in use. The CRA24-B1P has basic energy efficiency features but does not include EHO.

Read our Belimo VAV controller article for more details on the controller features, operating modes, and installation.

Room temperature sensors

A room temperature sensor (Figure 1) measures the temperature of a specific area or room and provides this data to a building's HVAC system. It is a simple device focused solely on temperature monitoring. This ensures optimal comfort and energy efficiency in residential, commercial, and industrial settings. Temperature sensors provide crucial data that is used by controllers, such as VAV controllers, to regulate heating, cooling, and airflow to maintain desired environmental conditions.

Typically, room temperature sensors are installed on walls or ceilings and are often integrated with other units such as thermostats, controllers, and building management systems.

Positioners for wall mounting

Positioners for wall mounting are devices designed to control the position of modulating damper actuators, such as those used in HVAC systems. These positioners receive a control signal and adjust the actuator's position accordingly to regulate airflow or other parameters. The Belimo positioner for wall mounting, for example, can operate independently or in conjunction with temperature controllers to fine-tune setpoints.

Typically installed on walls, these positioners are connected to modulating damper actuators and receive input signals from control systems or temperature controllers. The output is a modulated signal that adjusts the actuator's position, thereby controlling the airflow.

Room operating unit

A room operating unit in an HVAC system is a device designed to measure and control the temperature within a specific room. It typically includes a temperature sensor and an interface for setting the desired temperature (setpoint). It offers flexible cable entry options with wire openings at the backside for in-wall wiring and the top/bottom side for on-wall wiring. It can be easily integrated with third-party controllers to enhance room climate control.

Differences from a VAV controller and temperature sensor

• A room operating unit measures temperature and allows for setpoint adjustments. It provides an interface for users to control the room's climate.
• A temperature sensor only measures the temperature and sends this data to other devices like controllers. It does not have an interface for user interaction.
• A VAV controller manages the airflow to different zones or rooms based on input from temperature sensors and other data. It adjusts the volume of air to maintain the desired temperature and is more about controlling the HVAC system's operation.

Selection criteria

When choosing HVAC control devices, it's essential to consider various factors to ensure they meet the specific needs and integrate seamlessly with the existing system.

1. Measured values: Ensure the device accurately measures the specific environmental parameters needed, such as temperature, humidity, air quality (e.g., CO2 levels), and pressure, to maintain optimal conditions.
2. Sensor type:Choose a sensor type that offers the precision and reliability required for the application. Examples include:
   1. NTC (Negative Temperature Coefficient): Cost-effective and widely used for temperature measurement.
   2. Pt1000 (Platinum Resistance Thermometer): Offers high accuracy and stability over a wide temperature range.
   3. NDIR (Non-dispersive Infrared): Used for measuring gas concentrations like CO2 with high precision.
   4. Ni (Nickel): Provides stable, linear responses for temperature measurement.
3. Application:
   1. Intended environment: Ensure the device is suitable for residential, commercial, or industrial settings.
   2. Environmental conditions: Consider factors like humidity, dust, and exposure to chemicals. For example, sensors in kitchens or bathrooms should handle high humidity.
   3. Specific use cases: Verify the device meets specific application needs, such as airflow control in VAV systems or CO2 monitoring in rooms.
   4. Integration with existing systems: Ensure seamless integration with existing HVAC systems and third-party controllers.
4. Measuring range: Select a device with a measuring range that covers the expected temperature variations in the environment for comprehensive monitoring.
5. Output signal compatibility: Verify that the output signal type and amplitude are compatible with the HVAC system requirements.
6. Degree of protection (IP rating): Ensure the device has an adequate IP rating to protect against dust and moisture, suitable for the installation environment.
7. Voltage compatibility: Ensure the device operates at the required voltage level for the system to avoid compatibility issues and ensure proper functioning.
8. Mounting method: Verify that the device supports various mounting methods, such as surface mounting or in-wall mounting, to accommodate different installation setups and ensure ease of installation and stability.
9. Material and quality: Choose a housing material that will not corrode from the media or environment and can withstand the application's temperature and pressure. For example, thermoplastic provides excellent insulation, durability, and resistance to environmental factors such as moisture and temperature fluctuations.
10. Display and indication: Determine if a display or LED indication is necessary for the application to provide real-time monitoring and ease of use.
11. Override functions (for VAV controllers): Consider if the VAV controller needs advanced features like kitchen/bathroom overrides, Energy Hold Off (EHO), or room protection to manage specific conditions and enhance energy efficiency.