Boiler Modulation Control

This chapter discusses control loops as they relate to boilers dealing with the following issues.

Boiler modulation control. Either with boiler units that have appropriate turn down or by using. A typical raypak modulating boiler equipped with an outdoor reset control will lose less than 2 thermal efficiency across its full range of fire. Modulating the feedwater to the boiler is the most important part of the boiler feedwater system. 4 all the burner management and combustion control systems can be tied into a single platform including the level control and the vfd drive s.

The last value added option to consider with the modulating continuous system is a plc based control system. Boilers with modulating firing controls are quite common. Boiler manufacturers commonly now have their own modulating thermostats that are also available as smart thermostats. This easy to use boiler modulating control from weil mclain can control up to four modulating water boilers.

There are also exist independent smart control manufacturers such as nest and honeywell evohome that produce opentherm compatible modulating controls. On fan equipped boilers modulation is accomplished by reducing the air and gas flow into the boiler. 4 with a plc based control system as shown in fig. The advantages of burner modulation for combustion control include.

Modulating control in a power plant is extremely important. Unless the heat exchanger area and excess air ratio are exactly varied to match the firing rate an expensive and complicated proposition all boilers will exhibit similar characteristics. Reductions in steam pressure or water temperature lead to an increase in firing rate. Modulating control improves boiler operation by monitoring the steam or hot water line to produce a continuous control signal that determines the fuel input.

Not only does this. Why would you modulate the boiler firing rate. Modulating the feedwater flow to the boiler has so many advantages over on off feedwater addition it is difficult to visualize any other system. The ratio of the low fire to high fire rates is defined as the boiler s turndown capability.

It is always advisable that the designer frame a basic control philosophy before developing a control loop. The choice of control mode 2 way or 3 way valves and on off or modulating control influence directly the return temperature for the heat sources condensing boilers chillers heat pumps etc.