ON/OFF vs 0–10V: How to Choose the Right FCU Actuator?

In fan coil unit (FCU) systems, actuators are often underestimated components. However, they play a critical role in determining thermal comfort, system stability, and overall energy performance.

One of the most common questions raised by designers and system integrators is:

Should an FCU system use an ON/OFF actuator or a 0–10V modulating actuator?

Although this may seem like a simple signal-level decision, it is in fact a system-level choice that affects comfort control, operating efficiency, and project cost structure. This article provides a structured comparison from an HVAC engineering perspective.

1. What Is an ON/OFF FCU Actuator?

An ON/OFF actuator is the most traditional and widely used actuator type in FCU applications. Its operating logic is straightforward:

● Power on → valve opens

● Power off → valve closes

The actuator does not regulate intermediate positions; it simply executes open or close commands.

Key Characteristics of ON/OFF Actuators

● Simple control logic with broad system compatibility

● Cost-effective and easy to deploy at scale

● Compatible with most room thermostats

● Low commissioning and maintenance requirements

Limitations of ON/OFF Actuators

● Frequent valve cycling, resulting in pulsating water flow

● Larger room temperature fluctuations

● Energy efficiency relies heavily on overall system design rather than terminal modulation

For applications such as residential buildings, hotel guestrooms, and standard office spaces, ON/OFF actuators remain a mature and reliable solution.

2. What Is a 0–10V Modulating FCU Actuator?

A 0–10V actuator uses an analog control signal to regulate valve position proportionally:

● 0 V → valve closed

● 10 V → valve fully open

● Intermediate voltage → corresponding valve position

This enables continuous flow modulation instead of binary open/close control.

Core Advantages of 0–10V Actuators

● Smoother water flow and more stable room temperature

● Greater potential for energy optimization

● Seamless integration with BMS and DDC systems

● Suitable for dynamic load conditions and precise control strategies

System Requirements for 0–10V Actuators

● Controllers or BMS with analog output capability

● Clearly defined modulation logic during system design

● Higher requirements for commissioning and technical expertise

A 0–10V actuator should therefore be viewed not as an “upgrade” to ON/OFF, but as an extension of an advanced control strategy.

ON/OFF vs 0–10V: Key Differences Compared

The key difference is not which option is “better,” but which one aligns with the system objectives.

4. Why Not Use 0–10V Actuators in Every Project?

A common misconception in HVAC projects is:

If 0–10V control is more precise, why not apply it everywhere?

In practice, there are several reasons:

1.System-level mismatch: If the controller only provides ON/OFF outputs, a modulating actuator cannot deliver its benefits.

2.Lack of control strategy: Without a defined modulation logic, proportional control adds complexity without value.

3.Return on investment: In low-load-variation applications, ON/OFF control is often sufficient.

This explains why ON/OFF actuators continue to be a rational and widely adopted choice.

5. Fail-Safe ON/OFF Actuators: An Engineering Decision

Fail-safe actuators are designed to move the valve to a predefined safe position during power loss, typically closing the valve to prevent leakage or system damage.

In these applications:

● Predictable behavior is critical

● Safety takes priority over modulation accuracy

As a result, fail-safe FCU actuators are typically designed with ON/OFF control logic. This is not a technical limitation, but a deliberate engineering decision focused on risk management.

6. Practical Selection Guidelines

Recommended Applications for ON/OFF Actuators

● Residential and hotel projects

● Independent room-level control

● Cost-sensitive systems

● Applications without centralized BMS

Recommended Applications for 0–10V Actuators

● Commercial office buildings

● Hospitals and data centers

● Energy-optimized HVAC systems

● Deep BMS integration scenarios

7. Conclusion: Matching Matters More Than Complexity

There is no universally superior choice between ON/OFF and 0–10V FCU actuators.

What truly matters is whether the actuator matches the system architecture, control strategy, and project objectives.

In HVAC terminal control, rational selection almost always delivers greater long-term value than choosing the most complex option.

Right FCU Actuator > Advanced One

Match System Architecture On Demand, Stable Control & Energy Save