Clarifying Condensing Boiler Applications One Master HVACR technician s journey through the world of condensing boilers. B y N. R o b e r t B u r g e s s, J r., R P A, C E M, C E A, L E E D A P Images courtesy of author uless otherwise noted. [Editor s Note: This feature has been left in first person to maintain the author s personal experience.] About eight years ago I started to get more involved with condensing boilers, from both an applications and a troubleshooting perspective. I found myself getting frustrated because it was difficult to determine when it was best to use a condensing boiler, for both new installations as well as replacements of non-condensing boilers. There was so much contradictory information out there that I decided to roll up my sleeves, do some research and get all of the facts myself. I spent the next few years traveling around the country attending various factory classes (there are a number of classes offered free of charge. Check with your local wholesaler to see about availability) and asking questions. In many cases these questions led me to ask other questions, which eventually got me the answers that I needed. In this article I want to explain these questions and bring in some real-life situations that I experienced. I will try and answer questions like: g When should you purchase a condensing boiler? g What about venting of the boiler? g Does water treatment need to be a concern? g What type of fuel do they use? g Are they different than other boilers that I am currently troubleshooting? Before answering these questions, I will start from the very beginning by discussing some boiler basics, related to hot-water boilers and hot-water heating systems. The basics What is a boiler? In simplest terms, fuel, air and an ignition are used to create a flame (heat) that heats up some form of heat exchanger (such as tubes) while on the other side, water 10 RSES Journal OCTOBER 2013 All boilers condense (which can be seen when a boiler fires up and the water is cold inside), but they condense at different points. A condensing boiler (shown here) was designed to handle all of these points. is heated. This water from the boiler is circulated through the home or office building in order to provide heat. Both non-condensing and condensing boilers serve this function. So what is a condensing boiler? One factory instructor stated that all boilers condense (which can be seen when a boiler fires up and the water is cold inside) at different points, but the condensing boiler was designed to handle all of these points.
Combustion deals with the fuel and air mixture, and thermal is the ratio of the heat absorbed by the water. Various codes, regulations, global warming, standards (such as ASHRAE 90.1), NOx emissions and energy costs have increased the need for higher-performing equipment, and for good reason. Looking at a non-condensing boiler, a lot of wasted heat goes up the stack (in the range of 200 F to 500 F depending on the application). Why not try and capture some of that with some sort of heat exchanger? In a condensing boiler, manufacturers are able to get this heat from the water vapor that is going up the stack through a latent-heat process that condenses this vapor into a liquid, thus, getting much higher efficiencies some manufacturers stating an almost 100% efficiency rate. It should be noted that for these efficiencies to get this high, the return-water temperature needs to be as low as possible, and typically no higher than 130 F. There are two types of efficiencies: combustion and thermal. Combustion deals with the fuel and air mixture, and thermal is the ratio of the heat absorbed by the water. Efficiency comparison ranges are typically 80% 84% for standard, 84% 88% for high efficiency and 88% and above for This Heating Season, Save BIG On The Industry s Leading Combustion Analyzers For complete product details and rebate form, go to: www.mybacharach.com/cash Visit us at the 76th RSES Expo - October 24, 2013 - in Pittsburgh, PA Get Cash Back On The Purchase Of These Products PCA 3 Industrial/Commercial Combustion Analyzer PCA 3 265 with Reporting Kit (with CO, NO, NO 2, O 2 sensors)...$250 BACK PCA 3 225 with Reporting Kit (with CO, O 2 sensors)...$200 BACK INSIGHT Plus Commercial/Residential Combustion Analyzer INSIGHT Plus Reporting Kit (with CO, Long-Life O 2 sensors)...$200 BACK INSIGHT Plus Reporting Kit (with CO, O 2 sensors)...$200 BACK INSIGHT Plus Basic (with CO, Long-Life O 2 sensors)...$150 BACK INSIGHT Plus Basic (with CO, O 2 sensors)...$150 BACK Fyrite InTech Residential Combustion Analyzer Circle Reader Service No. 35 Fyrite InTech Reporting Kit (with CO, O2 sensors)...$25 BACK All Reporting Kit packages include: protective rubber boot, detachable probe, 8 AA batteries, hard-carry case, printer, user software OCTOBER 2013 RSES Journal 11
Figure 1 Additional energy savings can be achieved by using a reset schedule, which can be applied to any type of boiler. Proper setup with a condensing boiler will provide savings customers will see in their energy bills. Image courtesy of Viessman Manufacturing. condensing boilers. Most condensing boilers use heat exchangers with cast iron, aluminum and stainless steel, each of which has its pros and cons. They are smaller than many of the older boilers, which helps getting into small spaces. Frequently asked questions Now that the basic information has been addressed, I want to answer those questions listed earlier. When should you purchase a condensing boiler? As with any type of boiler purchase, the entire system should be considered. A load calculation might need to be done because in many cases the current boiler was oversized. Overall, the condensing boiler will cost more but can be justified by energy savings. One area that needs to be looked at is what supply and return temperatures are currently being used. In many cases I find buildings running at a 180 F supply with a 160 F return. As you can see, 160 F is well above the 130 F needed to make the condensing boiler work, so take the time to understand the entire system before committing to an owner that they will achieve those savings. A condensing boiler used in buildings with water-source heat pumps may be the perfect application, however, in some cases, a hybrid system (the use of both a non-condensing and condensing boiler) will work best. Savings can be further achieved by using a reset schedule, 12 RSES Journal OCTOBER 2013 From a troubleshooting standpoint, working with condensing boilers is about the same as a non-condensing system. UV scanners and flame rods are used to detect flames, and electrodes are used to ignite the flame. which can be applied to any type of boiler. Proper setup with a condensing boiler will provide the savings the owner is looking for. Figure 1 illustrates an outdoor reset schedule. As the ambient increases within the heating season, less heat is
driven from the building and thus less heat is needed from the heating units in the space. A simple way to provide the reduced heat load through the heating unit is to reduce the heating water temperature proportionally with increasing outdoor temperature. This control strategy saves energy by allowing the boiler to condense on warmer days and reduce heat loss throughout the system. For example, on a typical schedule that provides 180 F water on a 14 F day with a 20 F Delta T, the same boiler will condense any time the outdoor temperature is above 35 F. Depending on the climate, this may be the majority of the heating season. What about venting of the boiler? This is an area that always seems to be an issue. Always follow codes and the manufacturer s installation instructions. This is easier said than done. Most venting falls into four categories: 1, 2, 3 and 4. Categories 1 and 3 are used above the dew point and 2 and 4 are used below the dew point. Frequently, the service person will follow category 2 and 4 for condensing boilers, and they should never use B vent. In many cases you will find stainless steel or a form of plastic (CPVC) that has been approved for condensing design. One area I have seen a lot of issues is when condensing boilers are being installed to replace 40-year-old boilers and running the venting to a large chimney. Gases will condense in the chimney causing the chimneys to collapse. In this case, a liner should be used. Another issue that applies to both condensing and noncondensing boilers is venting non-positive and positive draft boilers into the same vent. Severe backdraft can occur, corroding the vent pipe and triggering the boilers to go off on flame failure and not work correctly. I worked on a job where two of the eight boilers exploded as a result of this. Always refer to the manufacturer s instructions which usually follow ANSI and NFPA 54 guidelines. Does water treatment need to be a concern? In some cases aluminum heat exchangers are being used, which are great if used and maintained properly. I have walked into some boiler rooms with large signs from the manufacturer stating that the ph needed to be maintained between 6.0 and 8.5. The installer did a great job putting these up. The problem was no one was checking it, or if they did it was only once a month. I have taken tests and found ph levels between 4 and 14. When deciding on the type of boiler to install, something like this is important to consider. The in-house maintenance staff needs to be diligent and take daily readings. mtwfsusa.com Overachieving undercounter Presenting NEO, the everywhere you need ice machine. By providing increased levels in performance, intelligence and convenience, Manitowoc s new ice machine offers an all-in-one solution to your undercounter ice cube needs. 2013 Manitowoc Ice All Rights Reserved Thirsty for more? Talk with Manitowoc Ice. 1-920-682-0161 ManitowocIce.com/NEO Circle Reader Service No. 36 OCTOBER 2013 RSES Journal 13
Some companies sell corrosion and scale inhibitor for aluminum boilers and should be contacted if an issue is detected. What type of fuel do they use? Every condensing boiler I have worked on was either gas or propane. Some customers had been using both gas and oil and would switch between the two in order to save on energy costs with their current non-condensing boilers. It seems when I asked this question at the factories one key response was given: the sulfur content needs to be just right and many customers do not want any additional headaches from preventive maintenance work with oil. Are they different than other boilers that I am currently troubleshooting? From a troubleshooting standpoint, everything is about the same. UV scanners and flame rods are used to detect flames. Electrodes are used to ignite the flame. If possible, check to see if the building staff has a copy of the original start-up paper work. Sometimes, I have found that the system did not work correctly from the start. The combustion settings were usually in the 5% range for O 2, 9% for CO 2 for gas, and a little higher CO 2 for propane. As always, refer to the manufacturer s specifications, but I have found that these numbers as great ballpark settings. With the advance of direct digital controls, many boiler systems are tied into an energy-management system. I have worked on units that had two control systems along with the boiler controls, so it can get confusing at times. You do need to be careful about condensate pumps and how the condensate from the boiler and vent is disposed. Since it is acidic, most jurisdictions have codes preventing this from being directly put down the floor drain. As a solution, many manufactures can sell you a condensateneutralization box. By providing you with a few realworld examples, I hope that this information might save you a step or two when working with condensing boilers. I welcome any reader to please e-mail me with any comments and would enjoy carrying on a more detailed discussion. I would like to thank the many instructors at the various factories who have helped answer my questions. N. Robert Burgess, Jr., CEM, CEA, LEED AP, is a Master HVACR Technician and currently works as a consultant for the real-estate industry. Burgess, who currently holds 14 certifications and licenses within the engineering and propertymanagement field, has served as Vice President of Property Management for various companies, has authored three textbooks for BOMI and has been the lead instructor for the National Association of Power Engineers for more than 28 years. Currently, he serves on the Board of Directors for the Property Management Association. For more information, e-mail robertburgess@ burgessgreenfacilitiesservice.com. 14 RSES Journal OCTOBER 2013 Circle Reader Service No. 37
Purity, Proof, Payment: Airgas Airgas is a publicly traded, $5-billion dollar company, with a 30-year reputation of ethical, professional service. Our highly trained workforce gives you the quality and care you deserve. And when it comes to reclaiming your used refrigerants like R-22, we pay you for every ounce. We prove it with the industry s most accurate testing equipment GC mass spectrometers so our analysis is accurate every time. We pass the test when we ask for your trust. Do other reclaimers? Reclaim your used refrigerants with Airgas. Call Airgas today at 1-800-406-2292. www.airgasrefrigerants.com Circle Reader Service No. 38