Advanced electrode boilers are being installed to replace outdated, inefficient fuel-burning equipment in district heating applications as part of broader effort to meet ambitious International Energy Agency decarbonization goals.

District heating—the generation of heat in a central location and distribution of it to local residences, businesses, and industry at greater economies of scale than individual heating systems—plays an important role in helping the transition to clean energy in the fight against climate change. The challenge, however, is that district heating, used to provide hot water and heat within buildings through an insulated pipe system, must soon pivot from burning fossil fuels to cleaner forms of energy.

Electrode boilers can match the heating output of fuel burning boilers while converting almost all the energy to heat.

“District heating networks offer great potential for efficient, cost-effective, and flexible large-scale use of low-carbon energy for heating. However, the decarbonization potential of district heating is largely untapped, as 90% of the heat supplied in district networks is produced from fossil fuels …,” according to the International Energy Agency (IEA), a Paris-based autonomous intergovernmental organization that provides policy recommendations, analysis, and data on the global energy sector. The 31 member countries and 13 association countries of the IEA represent 75% of global energy demand.

Aligning with the IEA’s Net Zero Emissions by 2050 Scenario requires significant effort to rapidly improve the energy efficiency of existing networks, switch to renewable heat, integrate secondary heat sources, and develop new high-efficiency infrastructure.

Fortunately, innovation in the form of the latest, high voltage immersed electrode or jet type electrode boilers makes district heating much greener, particularly when the electricity comes from renewable sources like solar, wind, and hydro power.

The most advanced types of electrode boilers, such as Acme’s CEJS or CEJW, also offer greater safety than traditional fuel burning models.

Municipalities and businesses relying on district heating are already pivoting away from often inefficient, outdated equipment that produces excess carbon emissions in favor of economical electrode boilers that can quickly, flexibly rival the output of large gas or oil-fired boilers in a much smaller footprint, The advanced electrode boilers do not have a high minimum operating level to make them immediately available and offer much faster start-up and shut down time while being safely and easily maintained.

The Renewable Promise of District Heating with Electrode Boiler Technology

District heating systems offer substantial potential for improving energy efficiency, reducing greenhouse gas emissions, and integrating renewable and waste heat sources, particularly within urban centers.

In this effort, an increasing number of district heating plants are turning to high voltage, electrode boilers to absorb excess power production, quickly provide grid service, and cost-effectively balance out fluctuations. A growing number of municipalities are also installing new or retrofit high voltage electrode boilers that are compact, economical, and produce no emissions. The upgrades often entail retrofitting or replacing boilers (the heat source) with cleaner, more efficient electric alternatives, along with the heat distribution network (pipes/ heat exchanger stations).

Electrode boilers utilize the conductive and resistive properties of water to carry electric current and generate steam with great responsiveness and efficiency.

“An A.C. current flows from an electrode of one phase to ground using the water as a conductor. Since chemicals in the water provide conductivity, the current flow generates heat directly in the water itself. The more current (amps) that flows, the more heat (BTUs) is generated, and the more steam produced for use in district heating,” explains Robert Presser, Vice President of Acme Engineering, a manufacturer of industrial and commercial boilers with operations in the U.S., Canada, and Europe.

When supplying district heating, electrode boilers are much more responsive and flexible than fossil fuel burning units.

“With electrode boilers, the energy input and adjustment are very precise and virtually immediate. In contrast, increasing or decreasing the temperature in a gas fired boiler is a slower process because it takes time for the heat in the boiler to rise or dissipate before reaching the targeted output,” says Presser.

The energy efficiency of electrode boilers is one of their most remarkable characteristics; they are much more responsive and flexible than fossil fuel burning units.

Advanced high voltage electrode steam boilers like Acme’s CEJS also have a 100% turndown ratio, the ratio between a boiler’s maximum and minimum output. Most gas boilers have a ratio of 10:1 or 5:1, which means the units take a significant time to reach full capacity.  The CEJW and CEJS immersed electrode hot water and steam boilers have a minimum output level of 7-8% of rated capacity, still far better than a modern gas-fired boiler.

“With a 100% turndown ratio, you can leave the boiler in standby at low pressure and bring it to full capacity in about 90 seconds as needed, which no other boiler type can achieve today,” says Presser.

“Communities and businesses utilizing district heating also appreciate the eco-friendly nature of electrode boilers. Without combustion, these boilers are clean and emission free. The design also eliminates many environmental issues associated with fuel burning boilers such as fuel fumes, fly ash, and large obtrusive exhaust stacks,” says Presser.

The energy efficiency of electrode boiler technology, however, is one of its most remarkable characteristics.

“For district heating, the extraordinarily efficient power-to-heat generation capability of electrode boilers, in which almost 100% of the electrical energy is converted into heat with no stack or heat transfer losses, combined with an ability to use and balance intermittent renewable energy, makes the technology crucial today,” says Presser.

As an example of energy and design efficiency, Acme’s CEJS electrode steam boiler produces maximum amounts of steam in minimal floor space, with boiler capacity from 6MW to 68MW. The electrode boiler operates at existing distribution voltages, 4.16 to 25 KV and is up to 99.9% efficient at converting energy into heat. The boiler can produce steam in capacities up to 270,000 pounds per hour, with pressure ratings from 75 PSIG to 500 PSIG. All CEJS boilers are designed to ASME Code or EU Pressure Vessels Directive and are certified, registered pressure vessels. Electrical standards meet CSA, UL, or CE requirements.

According to Presser, there are additional reasons for municipalities and businesses to use high voltage, jet type electrode boilers for district heating. “Electrode boilers can match the heating output of fuel burning boilers while converting almost all the energy to heat. Electrode boilers also are much smaller than fossil fuel burning boilers so are easier to use in smaller structures,” he says.

For residential or commercial property owners, electrode boilers also lower costs for installation, operation, and maintenance. Gas-fired boilers require fuel lines, storage and handling equipment, economizers, and emission control equipment. Advanced jet type electrode boilers have a minimal number of components and electrical controls, with fewer parts. Under normal operation, the absence of excessive temperatures and electrode burnout also assures long operating life.

In addition, the units further lower operating costs with automatic controls that reduce the need for operating personnel.

The most advanced types of these boilers, such as Acme’s CEJS or CEJW, also offer greater safety than traditional fuel burning models. “With the electrode boilers, there are no combustion hazards because there are no flames, fumes, fuel lines or storage tanks. There are no problems with heat buildup or electrode burnout even if scaling should occur, and thermal shock is eliminated. Also, there is no low water danger since the current cannot flow without water,” Presser explains.

Unlike fossil fuel burning boilers, electric boilers require minimal maintenance since there is no burner, no material burned, no soot created, no chimney, and no wearing mechanical parts, says Presser. With fewer parts than more complex fossil fuel burning units, electrical boilers are also more compact and simpler to install than conventional systems.

Finally, the electric units are exceptionally quiet compared to fuel fired boilers. Unlike gas-powered burners that throttle like turbine engines almost continually, electric boilers keep operational noise levels down.

With all the advantages of high output jet type electrode boilers, in addition to their value in balancing out the use of intermittent renewable energy in the power grid, it is evident why a growing number of communities and businesses are selecting them for district heating.

As the effects of climate change become more severe, the urgency of switching to clean energy and decarbonizing the energy sector will only increase across the globe. In this effort, district heating paired with electrode boilers will be a vital part of the solution, as member countries strive to meet the IEA decarbonization goals.

By Del Williams, a technical writer based in Torrance, California.

At the Taco Comfort Solutions booth at this year’s AHR Expo, the company had a new twist—a virtual reality (VR) demo and a glimpse into the future of training. Mechanical Hub caught up with Dave Holdorf, Product & Application Instructor – East for Taco. Here is what Dave had to say:

With the success of the Taco training department in the residential and commercial realms, as well as our webinar series of Taco Tuesday and Taco After Dark, what could be next? We have asked customers over the years what can we do to make the training experience better? The number one answer has always been more hands on. I would then ask, “how do we do that, you mean like installing a circulator and zone valves, joining pipe and flanges and tightening bolts … you mean like work on a jobsite you were at earlier in the week?” VR gives us that ability now—building a system, repairing the seals and bearing in a split case commercial pump, things like that.

Imagine maintenance on that split case pump is coming up and you have never, ever taken one apart much less seen one in the wild, but it‘s now your responsibility to do the repair in an effective and allowable timeframe. What are the proper steps … is there a YouTube video you can watch the night before … so much pressure to get the job done right.

Now imagine a call to us and we can meet you in the “mechanical room” with that very pump in front of us. We’re standing right next to each other virtually, but you’re in Walla Walla, Washington and we‘re in Cranston, R.I. rebuilding it with you—greatly improving your confidence level, and ready for the next day. With this capability, you know the sequence, you know the names of the parts, what to look for and what not to do.

In the end, attendees of the show were surprised, but not too much. I mean, the training department has been up to  so much over the last decade bringing content online and in person that it wasn’t surprising that Taco would try to increase out reach even further.

Of course, we’re just scratching the surface of where we can go with this!

Anyone with a military background will recall the U.S. Government’s penchant for acronyms. MREs, BDUs, MRAPs, the list goes on. Unfortunately, this dynamic is also present when discussing the efficiency enhancing feature known as outdoor reset. ODT, SWT, LWT, etc. It’s enough to cause a BM in your BVDs! Well, U.S. Boiler Company has once again developed a solution to make all this NBD.

First a few simple facts.

1. Flue gas will condense when temps are at or around 130° or less.

2. When vapor contained in flue gas condenses it releases a significant amount of heat.

3. Without question, optimal efficiency is achieved by heating a home using the lowest possible water temperature that will maintain the desired indoor target temperature, usually the thermostat set-point.

4. Using a Mod-Con, or high efficiency, gas boiler like the ALTA can take full advantage of the condensing action allowed by low water/flue temps.

Outdoor reset sensors do a wonderful thing. They enhance efficiency by matching water temperature to varying conditions.  For example, one would want to maintain indoor design temp, normally 70°, during outdoor design temps (in CT normally 7-10 degrees.) Assume a 7° ODDT, and required SWT of 180. This means the boiler must deliver 180° supply water consistently at a 7° outdoor design temperature to maintain the desired indoor temp (IDT). This all simply means we need the hottest water when it’s coldest outside. Good so far?

As Paul Harvey used to say, “And now-The rest of the Story!” We now all understand (hopefully) what happens in our heating systems on the coldest day of the year. What about the rest of the time? Sure, that 180° water will heat the house just fine on a 50 degree day. But what about all the energy used to unnecessarily heat the water way past what would be required to keep the home comfortable? This is a net negative on many fronts, but most significant is the increased wear and tear on the heating unit.

So, your now asking “Tom, how low can my water temp be?” The answer will likely surprise you. Standard fin tube radiation works ok down to 130° water temps in most applications. Same with cast iron radiators. For the fin tube baseboard system in my house the minimum boiler water temp on my ALTAC-136 is 125 degrees.  Hydro-air (hydronic coils added to or contained within hot air furnaces or air handlers) can often be run around 130° as well, depending on the occupant’s expectations. Remember, these SWT’s are typically targeted when the ODT is ~70°. We don’t need to transfer much heat to maintain indoor setpoints at these conditions. How does all this magic happen? Outdoor reset. Using a thermistor mounted outside, typically out of the sun on the north facing wall we monitor ODT and adjust SWT temp accordingly. So my personal curve used to be 180° SWT @ 7° ODT, and 125°SWT@70° ODT, but no more.  My ALTA figures this out automatically without an outdoor reset sensor.

While outdoor reset simply monitors outdoor temperatures, rate-based reset works by looking at boiler run time, firing rate, and other parameters and adjusting accordingly. Here’s a few examples. Say it’s a beautiful spring day. Nice and sunny with a gentle breeze and 50° outdoor temperatures. The boiler run times are likely short, and the firing rate is likely low. The boiler knows from these conditions the heat loss from the house is minimal, and adjusts, incrementally dropping the boiler water temp until the minimum setpoint is reached, or our algorithm (the “secret sauce”) calculates that based on run time and firing rate the water temp will deliver enough heat to match the rate of heat loss and maintain indoor temp setpoints at the lowest possible SWT. As night rolls in and the temperature drops, average run times and firing rates increase, and once again, rate-based reset will adjust (increase) SWT’s to maintain indoor comfort and optimal efficiency. “Brilliant!” you say. I agree. But wait-there’s more!

Conventional ODR has limitations. Say the calculated water temp for a 45 degree day is 142°. It’s a moderately windy day. Consider two different houses, both 2,500 ft. The first has a well-sealed envelope, double pane windows, and effective insulation. The second has old single pane windows, minimal (or no) insulation, and is as drafty as old fence. The boiler doesn’t know what the indoor conditions are, just that it must target 142 degrees. That 142° SWT might be fine for the first, but far too low for the second. Now to be fair, all U.S. Boiler products with outdoor reset offer a “boost” feature that will automatically bump the temperature up every “X” (boost time value) minutes, default being 20. This means every 20 minutes with an uninterrupted call, the SWT will rise 10 degrees until the max setpoint is reached. The benefit of rate-based reset is we are always looking at indoor conditions and adjusting accordingly. Rate-based reset always uses the lowest possible water temp that will maintain the desired indoor temp, and then has the boost feature if an increase above the calculated target temp is required. Like a samurai sword: simple, elegant, and effective!

There are other benefits as well. Remember the test I mentioned? Here it is. What factors showcase the benefits of rate-based reset? See the answers below. Correct your test answers accordingly…

1. No sensor to install. Rate-based wins!

A) No sensor for landscape professionals to damage.

B) No sensor for contractor to install (or throw away!)

C) No wire required from boiler to sensor.

D) No worries about where the contractor will mount the sensor, if it will be impacted by the sun, or heat migration from the interior affecting the sensor calibration.

E) Enabled from the factory. No worries for homeowner regarding whether the contractor enabled ODR. The Alta boiler is set up for maximum comfort and efficiency right out of the box!

2. No Lemon Faces! Rate-based wins!

A) Always monitoring indoor temp. Onboard algorithms are constantly at work to meet heating demands while maintaining maximum efficiency. Tens of thousands of units installed with zero complaints about indoor temperature. When not writing informative and engaging articles such as this, I am a member of the renowned U.S. Boiler tech support team. I’ve honestly never received one complaint regarding rate-based reset. If you have, please contact me.

B) Not reliant on a technician with advanced, comprehensive knowledge of ODR curves. Works fine out of the box with no programming in most applications, and, where required, only minimal adjustments for almost all applications, including low temp radiant.

C) If the homeowner is made aware that during mild temperatures the radiators will not be the same temperature as the skin of the space shuttle during re-entry, and that these cooler temperatures mean more money in their pocket for candy/wine/shuffleboard, they will instead have smiles every time they touch the radiator. Or better yet, they will abandon the practice entirely…

3. Takes full advantage of condensing aspect of mod con boilers. Again, rate-based wins!

Regardless of ODT, rate-based reset always targets the lowest possible temp, thereby maximizing the potential for the boiler to run cool enough to operate in a range where flue gas condensation occurs.

I can almost feel grizzled old contractors firing up HP 386’s and waiting for the comforting squawk of their dial up modems connecting. I imagine most of the responses will begin with:

“Dear factory stooge/shill. Your article may fool the unwashed masses, but not me. My mom’s uncle’s grandmother has a hunting cabin with 1 radiator and 600 feet of ¾” pipe to connect the boiler to the house (it’s in the barn where we milk the squirrels). How does your new-fangled boiler work in my application? Hah!!! Gotcha!!!”

It will be this, or something substantially similar. There’s always at least one. For the rest of the world (and fortunately, most of the squirrels) these anomalies are rare. There is no magic solution for a poorly designed or installed system. But when a competent, capable, and progressive contractor is installing a new or replacement system, the advantage of rate-based reset over conventional sensor-based reset is clear. Reduced (or no!) programming required, no wires to pull, and no exposed exterior sensor susceptible to damage. Save time, money and aggravation.  Go ahead and skip a step with ALTA.

For more information on the Alta boiler, visit our Alta Product Page.

GUEST BLOGGER: Tom Secondino is a Technical Sales Support Specialist for U.S. Boiler Company, a manufacturer of residential and commercial heating products, including condensing, non-condensing and electric boilers.

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