Active ΔT Control vs. 0–10V Modulating Actuators in Hydronic Underfloor Heating Systems

The Logic Gap in Modulation

Most modulating actuators used in hydronic underfloor heating systems operate based on external commands. They receive a 0–10V or PWM signal from a central controller and adjust to a corresponding valve position, without any direct feedback from the actual water temperature within the loop.

This approach assumes that a specific valve position will consistently deliver a predictable thermal result. In real-world underfloor heating manifolds—where loop lengths, heat loads, and pump pressures vary—this assumption often breaks down.

Understanding this logic gap is critical when comparing traditional modulating actuators with newer control approaches based on active thermal feedback.

Passive 0–10V Modulation: Position Without Verification

The traditional 0–10V modulation model relies on the central controller’s estimation of the required flow rate. Valve position becomes a proxy for thermal performance.

The limitation:

The controller has no real-time visibility into the actual temperature drop (ΔT) across individual loops. As a result, it cannot verify whether a 40% valve opening truly achieves the intended heat transfer—or whether excess flow is simply bypassing the thermal demand.

In underfloor heating systems with high thermal inertia, this lack of verification can lead to unstable comfort, inefficient energy use, and reduced heat pump performance.

Active ΔT Control: Modulating Toward a Thermal Result

Active ΔT control represents a fundamentally different philosophy. Instead of assuming that valve position equals outcome, the actuator continuously evaluates the actual temperature differential between supply and return water.

By using ΔT as the control variable, the actuator modulates its position until the desired thermal result is achieved—regardless of pressure fluctuations or upstream hydraulic changes.

This result-oriented approach aligns more closely with how underfloor heating systems behave in practice, especially in low-temperature, heat-pump-driven applications.

Decentralized Intelligence: Reducing System Complexity

For brand owners and system integrators, system complexity directly translates into cost, commissioning time, and long-term risk.

Traditional modulating solutions depend heavily on centralized logic, additional sensors, and extensive wiring. In contrast, active ΔT control shifts hydraulic decision-making to the circuit level.

By decentralizing the balancing logic, each loop becomes self-regulating. This reduces the processing burden on the central controller, simplifies system architecture, and improves overall robustness—particularly in multi-zone residential or light commercial projects.

Implementation Example: Closed-Loop Precision with SA905-T

The Saswell SA905-T applies active ΔT control through an integrated stepper motor actuator designed specifically for underfloor heating manifolds.

Unlike open-loop modulating actuators, the SA905-T continuously monitors the actual temperature differential across its assigned loop and adjusts valve position accordingly. This closed-loop behavior allows the actuator to actively correct for conditions such as excessive flow, narrowing ΔT, or pressure imbalance.

By maintaining an optimal ΔT at the loop level, the SA905-T helps stabilize heat pump COP, reduces unnecessary circulation losses, and ensures consistent thermal performance across the entire manifold.

Conclusion: Choosing Control Logic, Not Just an Actuator

The difference between passive modulation and active ΔT control is not about signal type—it is about control philosophy.

While 0–10V modulating actuators respond to commands, active ΔT solutions respond to results. For HVAC professionals focused on system stability, energy efficiency, and predictable real-world performance, this distinction becomes increasingly important.

Rather than functioning as a conventional valve, the SA905-T serves as an active hydraulic control element—reducing commissioning effort, improving operational efficiency, and enabling more resilient underfloor heating designs.

👉 Ready to upgrade your project with a high-performance integrated UFH control solution? Explore the full technical specifications of the SA905-T.