6 Sustainable Benefits of Steam Boilers

Improved technologies help transition equipment for environmentally friendly applications.

What do a condensing boiler in an institutional and commercial facility and a Formula 1 race car have in common? At first glance, most people probably would say nothing.  

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But a closer look by a maintenance and engineering manager would unearth at least one similarity: The hot water-generating vessel and the high-speed vehicle are engineered to recover and reuse heat from exhaust gases. This capability makes them more efficient and helps reduce emissions while maintaining performance.  

The condensing boiler also converts a higher percentage of fuel into usable heat, which further reduces emissions and energy waste and lowers fuel consumption, says Gary Williams, senior director of sustainability and energy solutions for ESFM, an integrated facilities management firm.  

“Modern boilers, especially condensing boilers, can achieve efficiency levels of up to 95 percent,” he says. 

Myths and misconceptions 

Although boilers are not typically regarded as green technology, the levels of efficiency are among reasons hot water and steam boilers used for heating systems are considered environmentally friendly, a trait that often overlooked and one that may dispel some myths. 

“One myth that stands out is the claim that steam boilers operated on fuels such as natural gas are unfriendly to the environment,” says Mike Valentino, technical consultant with the American Boiler Manufacturer Association. “In fact, steam boilers are operated under strict environmental constraints when it comes to potentially hazardous pollutants, such as carbon monoxide (CO) and oxides of nitrogen. Many boilers today are fitted with the latest in emissions reduction and control technology.” 

Another myth is that steam boilers are outdated and inefficient, says Chris Hacker, global engineering director with JLL. 

“While steam boilers have been around for a long time, they can still provide efficient heating solutions in many buildings,” he says. “Modern steam boilers incorporate advanced technology to optimize efficiency and reduce energy consumption.” 

The idea that boilers are expensive to maintain is not necessarily accurate, Hacker says.  

“Like any equipment, steam boilers require regular maintenance to ensure efficient and safe operation,” he says. “However, with proper maintenance, the longevity of a steam boiler can be extended, and repair costs can be minimized. Additionally, advancements in technology have made steam boilers more reliable, reducing the frequency of repairs.” 

Sustainability benefits 

Condensing boilers, which produce hot water, are one type of boiler used for heating systems in commercial and institutional facilities. They are among the kinds of boilers Williams says are categorized as green boilers. Others include:  

• Electric boilers use electricity instead of burning fossil fuels and can be greener if the electricity comes from renewable sources. 
• Biomass boilers burn organic materials such as wood pellets, which can be carbon-neutral if sourced sustainably. 
• Hydrogen boilers use hydrogen as a fuel and produce only water vapor as a byproduct. 

When determining the characteristics that contribute to boilers’ sustainability advantage over other forms of heating methods, Hacker says it depends on the definition of sustainability. 

“In the general sense, sustainability refers to the ability to maintain or support a process continuously over time,” he says. “If you look at steam boilers that way, the ones used in the s were sustainable back then.” 

The United Nations Brundtland Commission in defined sustainability as “meeting the needs of the present without compromising the ability of future generations to meet their own needs.” The commission breaks those categories down to six items: 

Efficiency. Steam boilers offer high energy efficiency, particularly when used in large-scale heating applications. The thermal energy produced can be distributed efficiently throughout a building, reducing overall energy consumption and recovering heat from condensate. 

Fuel flexibility. Steam boilers can run on a variety of fuels, including natural gas, oil, biomass, electricity and waste materials or biofuels. This fuel flexibility allows for renewable and low-carbon options, reducing reliance on fossil fuels and promoting sustainability. 

Longevity. Steam boilers are known for their durability and long operational life. With proper maintenance and care, steam boilers can last for several decades, minimizing the need for frequent replacements and reducing waste. 

Heat distribution. Steam can distribute heat evenly throughout a building, resulting in more consistent and comfortable temperatures compared to electric heating methods and can lead to reduced energy consumption and improved occupant comfort. 

Thermal storage. Steam boilers can be used in combination with thermal storage systems, allowing excess heat to be stored for later use. This can help optimize energy use by using off-peak electricity or low-demand periods to generate steam, reducing reliance on grid energy during peak hours. 

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Retrofits. Steam boilers can often be retrofitted or upgraded with modern control systems and efficient burners, improving their overall performance and energy efficiency. This enables existing steam systems to be made more sustainable without the need for full replacement. 

Most commercial-industrial boilers use gaseous fuels, such as natural gas and liquid propane. While natural gas is not considered a sustainable energy source, it offers several benefits over other heating sources. 

“Natural gas is plentiful, clean and relatively inexpensive compared to electric boilers and serves to provide a sensible migration toward more renewable energy sources and sustainable sources of energy,” Valentino says. “Natural gas is the best solution to meeting our energy requirements today and in the foreseeable future. In contrast, electric boilers typically rely on power supplied by the public and private utility grid system.” 

Looking to the future 

Like the boiler comparison to Formula 1, which has set a goal of being net zero carbon by , the future of hot water and steam boiler technology is expected to become even more environmentally friendly. 

“Technological advances will continue in the hot water and steam boiler marketplace,” Valentino says. “These advances center around efficiency improvement, advanced controls and emissions reduction. Additionally, alternative fuel sources such as pure hydrogen and hydrogen-enriched natural gas firing, which produces lower to no carbon dioxide levels, will continue to be explored and developed, much of which is driven by the U.S. Department of Energy.” 

Other technologies being explored include solar-powered boilers and heat pump boilers. 

The integration of smart technologies and the Internet of Things are “revolutionizing boiler operations,” Williams says. “These advancements allow for real-time monitoring, predictive maintenance and improved efficiency through data analytics and innovations in materials and design are enhancing the performance, durability and energy performance of boilers.” 

New regulations are also influencing boiler designs, particularly with a focus on increasing efficiency standards and promoting the use of condensing technology. 

“Federal standards proposed last year would call for these products to use only condensing technology,” Williams says. “Washington state now requires the installation of heat pump water heaters and electric boilers in most new commercial buildings to eliminate the use of fossil fuels, and in Washington, D.C., gas boilers will be phased out by the end of in new buildings, tightening restrictions on the city’s greenhouse gas emissions.” 

“As the industry continues to prioritize sustainability and carbon reduction, the ability of steam boilers to integrate with low-carbon and renewable fuel sources positions them as an attractive option” for heating systems, Hacker says. “As environmental regulations and energy efficiency standards are becoming increasingly stringent, pushing businesses and institutions to seek more sustainable heating options, steam boilers’ versatility is a sustainable option.”  

Frank Rigas is a freelance writer based in Sheboygan, Wisconsin. 

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When a fuel, in this case gas, is burned, flue gases are produced in addition to the measurable heating energy. These consist largely of hot water vapour, the components of which can be acidic. To protect the boiler itself and the flue system from this acidic water vapour, older boilers discharge the flue gases directly into the open air. Depending on the heating technology, the flue gas temperature can be up to 200 degrees Celsius. Condensation of the water vapour in the flue gases is thus intentionally prevented.

The fact that hot water vapour still contains energy can be proven with a simple trick: if you hold your hand over a pan of boiling water, you will soon notice this energy on your palm. This is because the steam condenses on the surface of the hand and at that moment releases the latent heat, also called the heat of condensation. Gas condensing technology involves recovering this heat of condensation and adding it to the heating water. For this, the hot flue gases are passed through a heat exchanger before they are released into the open air.

The heat exchanger is made of moisture and acid resistant stainless steel and is very compact due to its special design. As the hot flue gases flow through its coil, they are cooled down by the heating water that is flowing back to the boiler from the radiators (return water). The flue gases gradually condense. The heat from the resulting water vapour is then transferred to the heating system. To ensure that condensation occurs, the temperature of the return water must not exceed the limit of 57 degrees Celsius. Otherwise, the hot flue gases cannot condense. Area heating systems such as underfloor heating are suitable for cooling this return water.

The heat exchanger is therefore an important component of a gas condensing boiler and indispensable to this technology. It is able to transfer the heat of condensation obtained to the heating system with virtually no losses. In this way, it converts up to 98 percent of the energy contained in the hot gas into heat. An indestructible component for which system owners have a guarantee of up to ten years.

The deliberate condensation of the water vapour contained in the flue gases produces condensate. This can normally be discharged into the waste water (not small sewage treatment plants), provided the pH value is not too high. In addition, the drainage system must be acid-resistant. Code of Practice "DWA-A 251" of the German Association for Water, Wastewater and Waste (DWA) is used as the basis for the calculation. The size of the gas condensing boiler is also an important factor. If the rated heating output is less than 25 kilowatts (kW), the condensate does not need to be neutralised. If it is between 25 kW and 200 kW, direct discharge into waste water is only permitted in some circumstances by diluting with waste water. For gas condensing heating systems with an output of more than 200 kW, neutralisation is generally mandatory.

In addition to condensate drainage, the flue system must also be designed for condensing technology. Here it's important that the amount of acid contained in the condensate does not damage the system. The positive pressure generated by the use of a fan (e.g. a burner fan) must also not affect the new pipe system. Flue pipes made of stainless steel or special plastic are tried and tested. If a chimney is already in place, the new pipe can usually be inserted into the existing chimney. Routing to the outside without using the existing chimney is also possible. However, it is essential that the advice of a flue gas inspector is sought in this case.

You can also find more information on how gas condensing technology works in the Guide to gas heating at heizung.de.

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