Proper boiler operation involves many professions, including the facility operator, design engineer (DE), manufacturer’s representative (MR), installing mechanical contractor (MC), controls contractor (CC), and commissioning authority provider. Issues one can experience may include the selection of improper equipment and installation, whether it’s mechanical or controls, improper maintenance, or total lack of maintenance. The technology is always evolving, so whether an engineer has any of the aforementioned specialties, he or she needs to continue learning and be open to training. What may have worked at a school in North Dakota could be excessive and not necessary for a school in Texas.
The process of the application of hydronics dates back to the 1700s. Obviously, the technology has improved greatly over the years, with the newest systems utilizing hydrogen to create a cleaner burning fuel. Going forward, the industry will need to utilize all the resources available to us, employing solar, wind, and fossil fuels, to provide clean energy for the future. As experienced during the Texas power outage in February 2021, if one zone fails, the results can be catastrophic. Investments are necessary in all the sectors, and engineers need to be as resourceful as possible.
Hybrid Boiler Plants
Some designers prefer to utilize hybrid boiler plants, composed of condensing and noncondensing boilers. Depending on the location and load, most boiler plants are equipped to handle condensing boilers only, which allow for efficiency during the winter and the ability to provide terminal box reheat water during the summer.
While performing commissioning services for a K-12 school system in the Houston area, the DE insisted on installing a hybrid boiler plant. He planned to use the hybrid boilers in not only existing schools, which were equipped with dual-duct equipment, but any new schools as well. I told him I felt the hybrid systems were unnecessary. Hybrid boiler systems certainly have their places, but in areas south of St. Louis, a fully condensing system is more than sufficient to handle most loads.
We had many respectful conversations on the topic. And, while many of his coworkers agreed a full condensing boiler plant was sufficient, he was unwavering in his decision. It’s possible he previously experienced a failure of a full condensing boiler plant, and maybe he preferred this type of redundancy.
Hybrid boiler plants showcase the industry’s advancing skill set. They require advanced education from the school system through the MR and beyond, though they shouldn’t be installed without justification.
Installing a hybrid boiler system is not overly complicated, but programming the boilers is essential. During a July site visit to a new school in the Houston area, I inspected the boiler plant and found the noncondensing boiler functioning with a return water temp to the plant of 95°F.
Operating a noncondensing boiler with a return water temperature less than 140° will cause the exchanger to experience condensation; corrosion; and, eventually, failure. The noncondensing boiler mechanical pad was stained brown with rust, indicating it has been operating since startup last month, which I was not contracted to attend. I contacted the MC and explained to him the system is set up incorrectly, but he was defiant, stating this was his 18th boiler plant for the district. He had set up the 17 others in the same manner. I then contacted the manufacturers’ representative (MR) that provided the boilers and scheduled a meeting that included the CC, due to another error.
At the meeting, the MR determined the plant was set up incorrectly and that the condensing boiler should always be the lead boiler. As he was updating the programming and explaining the intent and purpose of each boiler to the MC, I asked if the setup was completed together with the CC because the supply water temperature was 10° above the supply water set point. Most building automation systems (BASs) will be utilized to send a reset schedule for the hot water supply set point to the boilers. Most boiler manufacturers can do this as a stand-alone operation, but it’s easier for the operator to utilize one system to change set points.
The hot water design temperature range was 120°-160°, controlled by a 0- to 10-V direct current (DC) signal sent to the boiler’s main controller, which navigated the necessary firing rate to provide the proper temperature for the heating water. To ensure proper operation, this needs to be completed with the control contractor and the installing contractor for the boiler. This is a critical step to ensure proper operation of a boiler system. Unfortunately, neither party contacted the other when they were on-site to complete their portion of the contract, only telling the commissioning team the boiler plant was ready to be commissioned. The BAS was sending a signal for the set point of 120°, but the supply water to the building was over 140°. The reason was the 0- to 10-V DC signal being sent by the BAS was not set up properly to match the voltage signal range on the boiler control. Thus, the water temperature exceeded the desired set point.
The purpose of condensing is to save energy by maximizing the amount of heat energy transfer to the water during the combustion process. The byproduct of this process is wastewater or condensate.
With condensing boilers, the condensate neutralizer station tank is often overlooked. Condensate from the boiler combustion process is acidic and has the potential to cause damage to the plumbing drain piping, sewers, or local water treatment facilities. To prevent damage to the drain piping, a neutralization kit is required. Often, the neutralization tank material is not added, or a minimal amount is added at installation. If operators aren’t informed this container needs to be filled periodically to reduce the acid going down the drain during the owner’s training, problems may ensue.
Condensate media is a powder or gravel-like substance to raise the pH level of the acidic condensate. The media’s life cycle depends on different factors — the larger the equipment the more condensate released. It’s suggested to check the media initially during the daily inspection of the equipment and weekly thereafter. Adding to the media is a simply process — some incorporate a loose material, or it can be purchased in a disposable bag for easier replacement.
Proper Water/Glycol Conditions
When replacing equipment, ensure the coils within the new equipment are equipped with the proper amount of water. Once the control valves are open and the system is bled of air water and or glycol, if necessary, ensure fluid is added to bring the system back to the proper operation pressure. Again, this is often overlooked, and the contractor is typically obligated to return the system back to the original conditions. During this process, ensure the proper percentage of glycol is present. Failing to return the system to the proper operating pressure can cause a number of problems from proper heating to pump cavitation due to low operating water pressure.
Proper water treatment is essential to ensure the operation and efficiency is achieved. When a new boiler is installed, the boiler tubing needs to be cleaned before the boiler is placed into service. This is called the boil-out procedure and ensures the oils left behind during construction are fully removed. This is accomplished by adding chemicals. It may include properly circulating the water and chemicals through the boiler in low-fire mode.
On one high-pressure steam boiler plant I commissioned, the installing contractor used hydronic fittings for domestic water instead of fittings for high-pressure steam. At the rear of the boiler was the downcomer with a water test heat exchanger to provide a sample to test the boiler’s water. The installed unions were a ½ inch in diameter size. The MC used 24-inch pipe wrenches to snug them up to ensure the unit was leak-free. The brand-new union looked 10 years old, because it was not built for the heat of the water it was enduring. After a brief discussion, he agreed to replace the unions. I also suggested installing isolation valves, so the system could be taken out of service if necessary. This plant had three boilers, and the center boiler was especially problematic. Black water was visible within the sight glass, and fluorescent green water was discharged from the test water sampling station in the back of the boiler.
A discussion with the startup technician revealed boiler No. 2 was the first one started and put online to allow the temporary rental boiler to be returned without incurring additional rental charges. Due to the condition of the water, I demanded the boiler be taken out of service. When the startup technician objected, I had him speak with the owner and insist he was accepting responsibility for the boiler by signing the signup report. The very next day, during functional testing, the 1/2-inch union blew out, causing 350° water at 100 pounds of pressure to spew out of the pipe. Again we were fortunate no one was injured. Unfortunately, I cannot say the same for my backpack — while waterproof, it was not equipped to handle high-temperature water.
After numerous boiler blowdowns, the water quality did improve. Again, not all representatives were present during the startup, from the commissioning provider or the water treatment contractor. If we were present and observed the water quality present, we would have objected to the rushed attempt to put this boiler in service due to the potential of damage to the product. Whether it’s a propulsion steam plant or a small, low-pressure boiler plant, water treatment is critical to control the boiler water’s pH level. The pH should remain between a pH of 10.5-11 to prevent acidic corrosion. Other tests include alkalinity, phosphates, hardness, sulfite, and dissolved solids. An inexpensive way to measure the quality of the water treatment process is a corrosion coupon rack, which is used in hydronic systems to monitor corrosion rates in the water system. Metal coupon weights are recorded prior to insertion and removed after roughly 90 days. The difference in coupon weight is then calculated and is expressed in mils per year metal loss.
At a school in the south Chicago suburbs, I was performing an energy audit for the district. The construction director was also responsible for the facilities and their operation, which he lacked the skills to execute. He asked if I could go over a few items with him in hopes of better understanding the facilities. We toured a couple of mechanical rooms and then the boiler room, which consisted of two low-pressure, noncondensing boilers supplying 160° water to the facility. As we were speaking, I had my back turned to boiler No. 1. As I heard the boiler start, his face showed an expression, questioning the noise. As I turned to look over my shoulder, I saw nothing out of the ordinary. I asked him what he observed, and he said the sides of the boiler popped out when the unit started. This attracted my interest, and I stood alongside him to watch the operation of the boiler more intently. Boiler No. 1 cycled off, and the sides of the boiler popped in. Once it restarted, I saw the sides of the boiler expand as the director had noted. At this point, I shut the boiler down and began accessing the situation.
The normal operating pressure of these boilers was 15 pounds, and the pressure on the boilers was 55 pounds. Their safeties were set to relieve at 60 pounds of pressure. There was too much water in this system, but why? The first thing we checked was the pressure fill station, which, for some reason, was valved off. It was explained later that the pressure fill regulator was defective and needed to be replaced. I gathered the boiler maintenance mechanic, school facility engineer, and janitor and asked them to present the daily boiler log. Inside, it showed no abnormalities.
I then asked who completed the logs for the day, and the boiler mechanic said he did. I was informed the boiler was having operational issues and needed to be reset almost daily to operate. At this point, the janitor stated that, before leaving last evening, the boiler was off in alarm. He thought it needed water in order to operate. I asked if he opened the bypass at the pressure fill regulator and he said no, he used the bypass at the back of the boiler. Upon going around the rear of the boiler, there was a piping configuration that was utilized to add water directly into the boiler. When the janitor observed the boiler off, it was at 5 pounds of pressure. He then added enough water to increase the pressure to 25 pounds. He neglected to observe what the temperature was. I asked why 25 pounds of pressure, and he responded that more is better. At this point, the boiler mechanic said the boiler was off on alarm when he arrived in the morning, and he had to reset the alarm to get it to operate. This is the same individual completing the logbook. He was doing so without looking at or understanding how or why the system was malfunctioning.
Falsifying a daily log is dangerous enough though not investigating why the system is failing is another. Operation of a boiler plant with equipment that is over-rode or failed is a hazard and needs to be avoided at all costs. Operating in an emergency condition is one thing, making it the normal operation mode is another. Once we knew the problem, we addressed the situation by removing water from the boiler, returning it to the proper pressure. We ordered the replacement pressure fill regulator and removed the bypass configuration at the back of the boiler.
Hydronic piping, whether it be low- or high-pressure systems, requires proper insulation throughout the design. Fiberglass insulation may be adequate for hot water, low-pressure systems, but for steam and high-temperature piping, I prefer calcium silicate and mineral fibers insulation. Insulation saves energy, reduces loss of heat transfer, and prevents injuries from hot surfaces. For the correct insulation and thickness, follow ASHRAE 90.1 and the International Energy Conservation Code (IECC), which will provide the basic requirements based on the fluid operating temperature. It’s important to note that piping up to 6 feet above the floor or exterior piping will require additional protection. This generally includes aluminum, plastic, or sheet metal coverings to protect the piping from sunlight, wind, and weather.
Poor installation by an MC needs to be identified by the commissioning provider or facility operator. Some projects may not receive commissioning because the owner believes it’s not necessary. Because a DE was hired for the job, he or she believes a commissioning agent is unnecessary. This mindset needs to be corrected. It’s likely the DE did not conduct a site visit during the final punch list walkthrough following the equipment installation. And, during that walkthrough, the DE may have been more interested in determining if the equipment was installed per the design intent rather than if it operated correctly.
If commissioning is not utilized, the facility operator needs to take ownership of his facility and request access to the project documents. Once he understands the project intent and is empowered with this knowledge, he needs to conduct the site visit and document any issues observed, similar to the tasks a commissioning agent provides. Unfortunately, if it’s an existing facility, staffing may be tight, and the operator may not have the leisure to attend every meeting, review every document, or identify every installation error. Each professional has a responsibility and needs to be involved with the project.
The proper, efficient, and safe operation of a boiler is a team effort. With the correct suggestions from the manufacturers’ representatives and DE buy-in, a proper review of the submittal of the commissioning provider, and an adequate installation by the contractors, and a final commissioning once the plant is ready, everything’s sure to function as intended. The right training for the maintenance and operation of the boiler and components, including the water treatment, will ensure safe and efficient operation for years to come.
Editor's Note: Peter Turek will be presenting at 2023 CxEnergy, May 2-5 in Dallas/Fort Worth. For more information, visit www.cxenergy.com.