During the early 1980s, America was enjoying video-cassette recorders and cable television and marveling at the invention of cellular telephones and personal computers. Meanwhile, the average hydronic heating-boiler was only slightly more sophisticated than a bucket of water and campfire.
At the time, the controls on many mid-range (400,000- to 2.5 million-Btuh input) boilers consisted of a basic single-pole/single-throw thermostat that turned gas valves on and off. Overheat protection consisted of manual reset high limits, and pilots were started with a match.
Evolution of Boiler Technology
During the mid-1980s, fan-assisted combustion became the first significant new boiler technology introduced since the invention of natural gas. Sealing a boiler's combustion chamber and blowing in only the air needed for combustion eliminated efficiency-robbing excess air. Fan-assisted combustion was the breakthrough needed to increase thermal efficiency from the high-70-percent to the high-80-percent range.
A new combustion process meant new controls. Over-the-counter ignition controls managed the ignition process, but did not have blower connections, so a special ignition module had to be commissioned to control the ignition process and power blowers. Previously, most boilers had been operated with over-the-counter controls that were mechanically operated and basically designed. Special electronic boards were needed to control increasingly more complex boiler designs.
As the industry was toying with fan-assisted combustion, it simultaneously was developing stage control. Instead of firing an entire burner tray fully on and off, the boiler was divided into smaller sections, each of which was fired separately. Over-the-counter stage controllers originally were established to stage the firing of boilers separately. Multiboiler step controllers with a minor modification or two now could be applied directly to boilers. Banks of burners could be fed by smaller, more cost-efficient redundant gas valves and controlled with a built-in stage control.
Still major players in the product offerings of every boiler manufacturer, fan-assisted combustion and stage firing were historical changes that laid the groundwork for dramatic new products that now are starting to take over the mid-range commercial-boiler market. These new products have two design features that could not have been achieved without newer and smarter controls. The first design feature is a new heat-transfer process: Boilers have moved from non-condensing to condensing. The European market led the development of stainless-steel and cast-aluminum heat exchangers that could extract heat from not only a flame, but the warm, moist flue products produced by combustion. This technology was the push the industry needed to propel thermal efficiency from the high-80-percent range to 98 to 99 percent, which is possible when boilers are fired in optimal condensing conditions.
There also have been developments in burner modulation. Modulation has been around since atmospheric boilers were invented, but its latest advancements have required greater component improvements. On an atmospheric rigid-tube burner, modulation could reduce only so much before the flame touched the burner's metal. This inadequacy spurred the development of ceramic and micro-metal-fiber burners, which can burn infrared cleanly across a greater modulation range.
Modulation also required changes to the gas train. Today, a new and more precise method — negative regulation (neg-reg) — is used. Neg-reg is a design that combines blower and gas-valve operations. Negative pressure created at the blower's intake pulls gas through the gas valve. As the blower speeds and slows, intake pressure rises and falls, pulling more or less gas from the valve. With this configuration, the air-to-gas ratio remains constant across a wider band of input.
Boilers received new electronics for neg-reg combustion, as well as smarter blowers and gas valves. Now, blowers and gas valves have their own circuitry to perform their balancing act. For example, blowers have electronics that employ power inverters and pulse-width modulation to regulate revolutions per minute without damaging or overheating a motor.
Advances in combustion and heat-transfer technology would not have been possible without corresponding control changes.
Recent Control Developments
Three developments have occurred in on-board control strategies of condensing modulating boilers, including control of a boiler's internal operations and control of and communication with its external systems.
The way in which electronics control a boiler's internal operations is considerably more complex than simply turning on a boiler to meet heating demand. Condensing-boiler controls strive for low inlet-water temperatures, which effect the best burn and highest efficiencies. Specially commissioned electronics monitor inlet-water, outlet-water, flue, system, and, in most cases, outdoor-air temperature. After operational parameters (most of which are field-adjustable) are set, control boards can begin balancing boiler functions. Boiler controls also can read burn cycles; recognize bad firing patterns, such as short cycling; and adjust heating requirements.
Condensing-boiler electronics have switched from somewhat blind and mechanical control systems to systems that read more, understand consequences, and operate with sensitivity. Controls now look outward to provide better internal management by controlling a boiler's external systems.
Intermittent pump operation, an early example of external boiler control, prompted pumps to shut off during boiler shutdown. This saved energy by reducing electricity consumption and heat loss caused by water flowing through the boiler. As boilers were connected directly to remote controls, the need to control system pumps became apparent.
The most important boiler-control advancement has been the development of built-in multiple-boiler control. Previously, unified multiple-boiler control required a remote-control board or building-management system. With onboard programming, multiple boilers now can be wired together to cascade.
Onboard programming was developed for two reasons: cost and control. A boiler system's overall cost is reduced by eliminating the expense of a separate multiple-boiler control. Three boilers with built-in cascade are cheaper than three boilers and a separate control system. Onboard programming also improves multiple-boiler control. Three similar boilers with built-in cascade provide better control than a remote control that may not be perfectly tuned to the firing characteristics of the boilers, especially modulating boilers.
The next electronic update will improve a boiler's ability to communicate with building-management systems, which now are common in commercial installations. Recent technologies include the direct connection of a boiler to a computer. Some of the best control programs have onboard three- or four-character liquid-crystal displays that relay information in display codes. With a boiler's direct connection to a laptop computer, readout information appears in full, clearly understandable words. Instead of scrolling through a boiler's simple display to read several data points, the laptop shows all of the main data points on one page.
Built-in dial-up or Internet capabilities are not far behind. These capabilities assist boiler-supplied computer programming, which shows boiler operation in real time. Although a cable can be run directly from a computer to a boiler if both are in the same room or building, more computer-savvy engineers, designers, and building managers want to look at their boilers from somewhere off site. Further, more installers and plumbing contractors offer maintenance services that would be improved vastly if a boiler could be seen all day, every day.
The boiler industry has made some real advances in design and electronics. New boilers have a great deal of new technology. Make sure to use it. Go shopping to see what control features can be used. Find out about your boiler's control features. It is easy to find features that can be beneficial on your next job.
The next time you design a system, look past what input and output the system needs. A controls professional should be involved early in the project. Questions, such as whether a third-party control is needed or onboard cascade is available, should be answered. If a third-party control system is planned, boiler inputs and outputs should be considered.
A product manager for Lochinvar Corp., David A. George is a 20-year veteran of the boiler industry. He can be reached via e-mail at [email protected].