A linkageless burner is a burner with individual stepper motors for each fuel and air function. The advantages of a linkageless system are numerous, while mechanical linkages can have serious limitations.
Linkage vs. Linkageless Systems
Regardless of linkage quality, there always is some hysteresis or "drift" as a result of play in each connection point of a linkage arrangement. Generally, hysteresis increases with the number of connection points.
Other potential problems associated with the hysteresis inherent to linkages include the compromise of efficiency. For example, if a burner is capable of operating at 3-percent oxygen (O2) at a given firing rate, but there are multiple connection points from the modulating motor to the fuel- or air-control devices, these control devices will not necessarily return to precisely the same position when driven up as they do when driven down. For this reason, an O2 level generally
has to be set higher to compensate for this effect. This reduces combustion efficiency and increases fuel costs. If a connection point on a linkage system fails in a way that a joint becomes disconnected, it is possible, if not probable, that fuel and/or air settings will change radically. At best, this could cause a loss of efficiency. At worst, a fuel-air mixture that causes high carbon-monoxide levels could accumulate to a level sufficient to cause an explosion. With a linkageless system, the positions of all fuel- and air-control devices are monitored constantly and verified by the main module. A positioning error of any kind causes the burner to shut down safely. An alarm displays "positioning error" as the reason for shutdown and specifies which stepper motor is out of position.
Dual-fuel burners benefit from the fact that each fuel has a dedicated "curve," which is the position of each of the stepper motors for air, fuel, and other settings as required. Each curve is completely independent of other fuel settings. Linkageless systems allow a great deal of flexibility in the design of a burner: There are no mechanical constraints, as there are with linkage controls.
Linkageless burner systems have the potential to reduce or eliminate the need for multiple components and their associated costs. Control functions, such as proportional/ integral/derivative (PID) control, temperature or pressure control, cold start, O2 trim, and valve proving, are incorporated into a control as a single entity. There is no mismatching or installation costs associated with using separate components from multiple manufacturers. These features provide a smooth integrated control package with multiple options.
Commissioning Burner Systems
A burner is only as efficient as the technician who commissions it. Linkaged burners can present a major challenge to a technician. When an adjustment is made in a typical linkage setup to improve operation for one fuel, another fuel's setting may be affected. It is not uncommon to have to readjust a burner when switching from gas to oil and back. This usually requires a technician on site to make the adjustments.
A linkageless burner is commissioned using a programming pad. The position of each stepper motor, (i.e., fuel, pressure-side air, suction-side air, etc.) is programmable and independent. The position of each stepper motor and its capacity percentage is displayed in real time on the programming pad. Because the repeatability of a stepper motor is less than 0.5 of an angular degree (even less on some systems), the position of each is checked constantly. The fuel/air ratio can be maximized for the best efficiency without the need to compromise. There are separate and individual programmable fuel curves for each fuel type, eliminating the need to readjust when switching fuels.
Data Storage and System Safety
Burner systems are password protected on three levels: original equipment manufacturer, service technician, and end user. This prevents any accidental or improper changing of critical parameters.
The system-commissioning information is stored as data, in case the main control module or programming pad is damaged and needs to be replaced. In this situation, the commissioning values simply can be loaded into a replacement component with no need to recommission the burner. Some systems store data in two places (i.e., the programming pad and the main module). In this case, there is no need for a laptop or any special tools, depending on the system.
Technicians and end users can benefit from the operational history displayed and permanently stored on programming pads. History information includes hours of operation, total hours, gas starts, hours operating on gas, oil starts, hours operating on oil, total number of starts, fault history, lockout history, current temperature or pressure, and capacity. This information can be invaluable as a service tool for technicians and as a source of meaningful information for end users.
A linkageless burner is much more than the absence of mechanical linkages. Linkageless systems can communicate via a bus system. This provides burners the ability to communicate with building-automation systems, with each other, or via an intranet or the Internet.
End users have the ability to monitor the operation of a heating or process system in real time from a remote location. This feature provides an opportunity to change the face of service companies. There are service companies that already utilize this technology to monitor heating or process systems 24/7 from their locations and react as soon as there is a problem. This approach to service can be somewhat proactive.
Typically, in a commercial heating application in which boilers are not monitored, an end user discovers that a problem exists only because a building is cold. This situation has the potential to be damaging in a cold climate and can occur at a time when a building is unoccupied, such as the weekend.
The term "linkageless" suggests that the absence of control linkages is the only virtue, but there is much more to these systems than their name suggests. Those who do not fully understand the concept or are not aware of the capabilities available perceive linkageless systems as expensive and complicated. This is not the case. Some burners equipped with linkageless control systems cost no more than earlier linkaged versions. Any burner can benefit from a linkageless system and achieve a higher combustion efficiency than with a linkaged version. Typically, depending on a burner's quality and design, the efficiency gains offset any additional costs associated with a linkageless system.
In addition to improved combustion efficiency, there are system-efficiency gains that can be realized through better control of the entire heating or process system. Linkageless burners provide the means required to maximize system efficiency.
There have been very few major advances in burner design over the last 50 years. The linkageless system represents a quantum leap in an industry in which changes traditionally are infrequent and small.
In a world in which fuel prices are at an unprecedented high, every burner should be linkageless.
About the Author
Engineering manager for Weishaupt Corp. in Mississauga, Ontario, Canada, Colin Bale has been in the burner/boiler industry for 38 years. He began his career in the industry working for British Gas and has held positions with various burner companies.