Wood Gasification Boilers: Circulation, Power Interruption & Pump Acceleration Abby Thompson On the Hydronic-Based Biomass Heating Systems Discussion Board… Why we don’t use the UPS to drive the main circulator to continue operations in case of power interruption? What determines when wood gasification boilers begin to circulate? Do variable speed pumps allow us to control the rate at which the pump accelerates? John Siegenthaler investigates… Student 1: If we use a UPS to drive the circulator to the heat dump, why don’t we use the UPS to drive the main circulator to continue the standard operation of the system in case of power interruption instead? We could drive the boiler and the main circulator with the same UPS and the system would not even notice the power interruption. Is there something I am missing? John Siegenthaler: Student 1, you could use a larger UPS to drive the main system circulator, and operate the boiler. It would likely have to be significantly larger. The company SUMPRO offers some larger UPS systems that are designed for operating sump pumps during power failures. They operate with two larger deep cycle batteries, and can deliver up to 1800 watts for about 2 hours. They are available for around $1400. Something this large could likely keep the system in operation for several hours – it’s just a matter of expense. The UPS driven heat dump circulator can be set up at about 35 watts, and only needs to run on a wood gasification boiler for about 30-45 minutes (because the blower in the boiler would be off and the fire would die down rather quickly). The aquastat in the heat dump system only activates the heat dump if the outlet of the boiler is 180 ºF or higher. This application could use a small relatively inexpensive ($200) UPS. Student 2: Upon start up of the boiler is it typical for the circulator to come on right away or after a delay? What determines when it begins to circulate? It seems that it would make sense not to circulate the water in the boiler initially to allow the flue and top end of the boiler to warm up rather than cycling the water right away, thereby slowing the warming of the top end of the boiler. John Siegenthaler: Most gasification and pellet boilers will start their boiler loop circulator as soon as there is a call for heat. However, both of these boiler types require a mixing device – such as a 3-way motorized mixing valve, or a “loading unit” between the boiler loop and the load or the thermal storage tank. This mixing device acts like a “thermal clutch” to disconnect the load or storage from the boiler loop until the boiler gets to a temperature where water vapor in the flue gases is not condensing. At that point the mixing device will smoothly allow some heat to move out of the boiler loop to either the load or storage. This type of boiler protection is essential with all biomass boilers. Several types of boiler protections are discussed in the course. Student 2: With the variable speed pumps discussed in the lecture, are we able to control the rate at which the pump accelerates? I.e. is it possible to set the temperature at which we achieve full speed which would then determine the acceleration rate? It was clear that we are able to specify the minimum temperature at which they begin to circulate… Do they just ramp up at one predetermined rate? John Siegenthaler: Most of the smaller variable speed circulators with built in variable speed drives don’t allow you to change the range over which the speed change takes place. My understanding is that this range is about 5 ºF. However, with larger circulators that are controlled by a variable frequency drive (VFD) responding to a building automation system, you should be able to program the range over which the speed change occurs, and “map” this to the 2-10 VDC or 4-20 ma control input to the VFD. Enroll in Hydronic-Based Biomass Heating Systems (Approved for: 23 AIA LU Credits, 11.5 Building Performance Institute (BPI) CEUs) with John Siegenthaler About Instructor John Siegenthaler – Principal, Appropriate Designs John Siegenthaler, P.E., is a mechanical engineer and graduate of Rensselaer Polytechnic Institute, a licensed professional engineer, and Professor Emeritus of Engineering Technology at Mohawk Valley Community College. “Siggy” has over 32 years of experience in designing modern hydronic heating systems. He is a hall-of-fame member of the Radiant Professionals Alliance and a presenter at national and international conference on hydronic and radiant heating. John is principal of Appropriate Designs – a consulting engineering firm in Holland Patent, NY. The 3rd edition of his textbook – Modern Hydronic Heating – was released in January 2011. John currently writes about hydronic heating and solar thermal system design for several trade publications. John is teaching: Free Lecture: Temperature Stacking in Thermal Storage for Biomass Heating Systems Free Lecture: Low Temperature Heat Emitter Options in Hydronic Systems Free Lecture: The Importance of Low-Temperature Distribution Systems Hydronic Based Biomass Heating Systems – Light Version Combo Package: Mastering Hydronic System Design + Integrated HVAC Engineering Hydronics for High Efficiency Biomass Boilers – Sponsored by NYSERDA Free Lecture: Achieving Hydraulic Separation in Hydronic Systems Free Course: High Performance Building and HVAC 101 Hydronic-Based Biomass Heating Systems Mastering Hydronic System Design Biomass Hydronic Heating Originally posted on December 9, 2015 Written by Abby Thompson Abby is HeatSpring's Product Marketing Manager located in Boston, Massachusetts. She is passionate about people and education, particularly in diversifying the burgeoning fields of science, technology, engineering, and mathematics. Abby works with instructors to build new courses and engages with our community of students and experts through HeatSpring Magazine and social media. More posts by Abby