Boiler controls are the devices used to turn on and to control the burner operation. It is important to consider the impact of boiler performance when selecting which controls to use on your boiler. This article will cover the types of controls used and the benefits of each, focusing on steam & hot water applications with modulating firing.
What are boiler controls?
Boiler controls consist of a system of devices used to sense the operating condition within the boiler, provide safety interlocks and increase or decrease the burner output to maintain a desired temperature or pressure.
The most basic systems consist of a Flame Safeguard and Temperature/Pressure sensing device. The temperature/Pressure device can either directly control the burner actuators, or for better control, a microcontroller or PLC-based computer may be used to manage the firing rate more accurately.
What are my options for boiler controls?
Basic: Linkage-based controls with direct acting modulating motor.
These controls are reliable and simple. The downside is they rely on linkage and cams which decrease the accuracy of Fuel/Air mixing and increased the cost of fuel.
- Temperature/Pressure controller
- Flame safeguard and appropriate interlocks/limits
- Modulating motor to move the burner control linkage.
Better: Parallel Positioning with independent actuators and smart controller.
These controls provide greater precision in metering the FUEL/AIR ratio, built-in thermal shock protection and PID-based control schemes for better load following.
The downside is the fuel/air is set at the time of commission and does not follow changes in operating conditions. This control is a great improvement and can typically result in 3% savings in fuel cost compared to a basic linkage system. The Honeywell FARC was a popular boiler control choice in this category. It has since been obsolete. If your boiler currently functions on this control, you might consider updating it. The uncertainty of readily available replacement parts could put you in a bind. An example of this is the Siemens LMV Boiler Control.
- Same basic controls with the addition of Independent actuators for each fuel and air damper.
Best: PLC Controls Parallel Positioning, O2 Trim and VFD
These controls provide the same benefits as the parallel positioning system, but it is controlled by a much more powerful industrial PLC. PLC-based controls include a color touchscreen HMI. This system provides precision actuators and adapts to the excess O2 utilizing an O2 sensor to optimize combustion. VFD (variable frequency drive) control is available to optimize airflow and reduce electricity. The PLC-based control system offers the best performance with an excellent graphical interface for ease of use. Also, it offers the same 3% savings in fuel cost compared to a basic linkage system plus 1-2% O2 Trim savings. An example of this is the Cleaver-Brooks’ Hawk Boiler Control.
- PLC controller and (including a Flame Safeguard & sensors)
- Color Touchscreen (HMI)
- O2 Trim (Oxygen trim)
- VFD (Variable Frequency Drive)
For assistance on the best boiler control for your application, contact us.