won an RPA System Showcase award with this project. The system is simple, reliable and affordable. This is all done without additional mixing controls. The manually set mixing valves in the manifold loops allow proportional reset of the supply temperature to the floor circuits. Piotr used a boiler reset control to reduce the supply temperature. The largest pipe used outside the mechanical room is 1-inch PEX-AL-PEX. He designed a system that carried hot water through a parallel primary loop to "satellite" manifold loops in each apartment as shown in Figure 5. When faced with designing a hydronic floor heating system for an apartment building in Harvard, Ill., Piotr remembered the "magic" that's possible with a high-temperature drop system. It's well suited to slab heating because the high thermal mass dampens out the pulses of heat input to produce a relatively stable floor surface temperature.įigure 5 Hydronics In Harvard Still another twist on the minitube concept comes from Piotr Zelasko of Park Supply in Chicago. The injection pump cycles on and off to maintain a calculated "average" supply temperature to the distribution system. (We discussed this concept in the June 2001 Hydronics Workshop column.) His variation on the original concept was to use on/off injection pumping rather than variable speed injection pumping. What a great place to try out an unproven heating concept, don't you think?Īnyway, Roy went over all the numbers and was confidently ready to serve as the official guinea pig for the minitube system. In case you've never been there it's about a 10-hour drive north of Calgary, and has a winter design temperature of - 41 degrees F. Oh and by the way, the building was in Fort McMurray, Alberta. industrial building to make it into a minitube system. I expected Roy, a real diehard pipes-and-pumps type of guy, to show me what I was overlooking.Ī few days later Roy calls to say he's going to change the current design for the floor heating system in a 70,000-sq./ft. At the time I wasn't totally convinced it would work. Roy was the first person I bounced the minitube concept off after sketching it back in 1996. Who says you can't teach an old dog new tricks? (No, not you John I'm talking about that old heating system.)įigure 3 Way Up North Another adaptation of the minitube concept comes from Roy Collver of Mechanical Systems 2000 in Calgary, Alberta. Imagine what the original installers would think of the modern technology that's keeping the tubing they laid down more than 50 years ago delivering comfort to the home's current occupants. That 90-degree temperature difference lets every gpm of injection flow carry about 44,000 Btu/hr. The right gauge shows the return temperature at 95 degrees F. The left gauge is on the supply minitube, and reads 185 degrees F. Rather than do the mixing near the boiler, and run 1.25-inch rigid copper tubing all the way to the manifold, John decided to use 5/8-inch PEX-AL-PEX minitubes and do the mixing at the manifold.įigure 3 is a photo John sent me showing supply and return temperatures with the system in action. After learning how a minitube system works, he used it to supply a remote portion of an older copper-tube floor heating system.įigure 2 shows the new piping connected to an old manifold that's located quite a distance from the new boiler. John Pughe of Utica, N.Y., recognized this. The low loss manifold detail is also simpler and less expensive than constructing a parallel primary loop to achieve the same hydraulic separation between circulators.Figure 2 Old Pipes/New Brains Although most minitube systems are installed in new construction, the concept certainly holds potential for retrofit jobs. This, in turn, minimizes interaction between the injection circulators as they operate at various speeds. The relatively low flow rate (for two-inch pipe) and short manifold length reduce head loss along the manifold to almost zero. At design load, these pumps have a combined flow rate of approximately nine gallons per minute. The low loss manifold supplies three independently controlled injection pumps, each equipped with internal spring-loaded check valves. Heated water is delivered to a low loss manifold via a pair of closely spaced tees. ![]() ![]() The latter purges residual heat from the boiler heat exchanger. ![]() The former uses heat from the system water to warm the boiler's heat exchanger prior to firing, and thus minimize flue gas condensation. Each boiler circulator operates independently, turning on three minutes before the burner fires and remaining on three minutes after the burner turns off. The dual boiler system supplies 360,000 Btu/hr at design load. Running the Numbers Figure 3 shows the piping schematic for a three-zone minitube distribution system recently installed in a 9,000-square-foot garage building.
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