A common complaint about air heat is that the temperature dips and rises in a repeating cycle. Heating professionals, as well as consumers, say that such systems blow warm air to raise the temperature to a comfortable level and, when the living space grows chilly again, blow warm air again.
But a furnace manufacturer and a controller maker say they have come up with a way around that cycle. It involves combining a furnace and a two-stage burner. The result is a unit that provides a consistent, even temperature for the living space. It also is expected to offer greater fuel efficiency over the long term, said executives and managers of the two companies that teamed up on the project, Boyertown Furnace Co. of Boyertown, Pa., and Carlin Combustion Technology of East Longmeadow, Mass.
Dave Thomas, general manager of Boyertown Furnace, said of the unit, “This will give the homeowner more comfort and also, we’re hoping in the long run, it will give him fuel savings.”
The fuel efficiency is expected to stem from the incorporation of the two-stage burner, designed to provide a 50-percent turndown. That is, the fuel input at the lower firing rate is half what it is at the high-firing rate. Fuel savings are anticipated because the unit will typically operate at the low-firing rate except during those relatively few days of very cold weather in any given heating season, the developers said.
“You really don’t need full input for probably 80 to 90 percent of the heating season,” Thomas said.
“We know from a common sense standpoint that it is much more efficient,” Rosemarie Bartchak, sales manager for Boyertown Furnace, said of the new design. Exactly how much more efficient will be determined as more and more units are put into service and they build an operating record that can be studied.
Boyertown’s line of Regal furnaces featuring the two-stage burner is to be available starting in January.
Carlin and Boyertown personnel who worked on the development project said it was initiated by the National Oilheat Research Alliance.
Regal furnaces range in net output from 70,000 Btus to 140,000 Btus. There are five different firing rates among the Regal units. Any Regal furnace that is set up with a two-stage electronically commutated motor (ECM) is compatible with the Carlin two-stage burner, Bartchak said.
“But we’ve done it a little differently in that we are not using a timer board at all,” Bartchak said. “We are using a fan and limit control. Our switches are actually in the vestibule of the furnace.”
Designing the unit so that the switchboard is housed in the vestibule of the furnace is a departure from other industry designs, which usually place the timer board in the blower compartment of the furnace. The advantage of placing the switchboard in the vestibule is that it makes the task of servicing it easier, Bartchak said.
Bartchak said Boyertown Furnace is emphasizing the comfort and quiet operation of the new unit, which she described as “whisper-quiet,” especially in the low-firing stage.
If an ECM were to fail and a technician didn’t have a replacement in his truck he could set up the system to run with a traditional PSC [direct drive] motor, ensuring that homeowners wouldn’t be without heat, even temporarily.
Thomas pointed out another advantage stemming from the ECM: “That motor, as it ramps down in speed, drastically reduces electrical consumption,” he said.
The system works with a two- or multi-stage thermostat designed to respond to fluctuating demands for heat. A number of manufacturers make two- and multi-stage thermostats. Honeywell thermostats were used in the development of the Regal furnace with a two-stage burner.
Gerry Dwire, a sales representative for Carlin, said that when there is a large demand for heat, the thermostat will kick on the burner at high fire and bring the living space up to within, say, two degrees of the thermostat setting. Then it scales back to low fire to bump the temperature up the last two degrees. Once that is accomplished, the thermostat would normally run the unit on low fire, sufficient to maintain the temperature within the set point.
Another feature of the system is that the ECM changes the speed of the air going over the heat exchanger.
When the burner is on a low firing rate, the ECM will run at lower RPM to blow a smaller amount of air. At a higher firing rate, the motor will run at higher RPM to blow more air. The coordination of the burner and the ECM “is going to add much comfort to a home,” Dwire said. He described a typical experience of a couch potato in a house with a warm air furnace, laying on the couch, feeling chilly and covering himself with a blanket. Ten to fifteen minutes later the person will throw off the blanket because the furnace kicked on and delivered a mass of warm air – “and then you just repeat that process until you go to bed,” Dwire said with a laugh. “This [new unit] is going to deliver an equal amount of warm air” throughout the living space, he said.
Dave Rousayne, Carlin’s technical services manager, said it was unusual to have these technologies on a furnace. In combining an ECM and two-stage thermostat, he said, the aim is to “match input with load demand to give the best possible comfort at a fuel savings.
“It takes much greater energy to build temperature than it does to maintain temperature and that’s the goal here – to maintain a temperature,” Rousayne said. “We’re not blasting a whole bunch of energy to get temperature and then waiting till it cools down and then blasting a whole bunch of energy again.”
Because installers size a furnace for the worst case scenario – “those few days a year when we get bitter, bitter, dramatic cold,” Rousayne said, “the rest of the year, it’s basically oversized. Full input isn’t needed.”
In a house heated with warm air, Rousayne said, “For the most part, when the heat comes on you feel a blast of warm air, and the thermostat’s satisfied” – until the temperature drops, the heat comes on and generates a blast of warm air again.
“Instead of short, quick blasts of hot air, the idea is to elongate the run cycles to maintain an even temperature throughout the living space,” Rousayne said. “We can do that by lowering the input when it’s not needed in the furnace which also lowers the stack temperatures. Instead of sending energy up the chimney we’re putting it into the appliance, and the blower’s putting it into the living space.
“In other words, the furnace has a chance to absorb much more of the Btus rather than send them up the chimney,” Rousayne said.
For oil dealer’s technicians installing the units, Rousayne said, “there will be a learning curve, but basically it’s not that much different from putting in a commercial unit.”