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What are differences between Modulating and on-off control valve?

What are differences between Modulating and on-off control valve?

Heating and cooling systems in modern buildings use like fan coils units, chilled beams, heat pump, gas boiler and so on to create comfort room temperature.

The valve’s control type directly influences the precision of temperature control, global flow and the pump head. The choice of valve control mode include 2 way or 3 way with on/off or modulating control, influence directly the return temperature for the heat sources, such as boilers, chillers, heat pumps etc.

But what is modulating control and what is on/off control? What are features of these two types? Today I will clarify as following.


Modulating Control Valve

Modulating control signals are mostly in the range of voltage 0-10v or current 4-20mA. Which requires a proportional control signal from room temperature control or BMS, with a proportional actuator valve.

The control system produces a control signal from 0% up to 100% to deliver the necessary output power to keep temperature constant. Then the proportional actuator will completely closed the valve at 0 VDC, and completely open it at 10 VDC or above.

Features of modulating control valve

- Stable temperature

- Optimal return temperature.

- High energy efficiency of heat sources.

- Higher cost but with long span life


On-Off Control valve

On-Off control is the simplest form of feedback control. In on-off control mode, the control valve with an on-off actuator delivers fully opened or fully closed. On-off control is widely used in domestic system’s temperature control.

On-off control will affect the temperature fluctuations. The swing can be reduced by reducing the temperature difference, but it will increase the number of switching points and reduce the life of the control element due to excessive use.


Features of on-off control valve

- Temperature fluctuations

- Negatively affected return temperature.

- Lower energy efficiency of heat sources.

- Lower cost but with short span life


Hotowell, as a professional manufacturer of HVAC products with more than 10 years. Our valves include on/off and modulating types, and our thermostats also can control on/off or modulating valves. The following is our main products, any interest welcome to contact me at anytime.

Welcome to contact me as following methods if there is any interest of our products or any questions.

Email: delta@hotowell.com

Tel.: +86 153 5987 4486

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