Dell-Point
From Cornburning
Contents |
Normal Operation
General
Background & Description
The Dell-point operates differently than most other corn or pellet stoves. It uses a patented burner and control system, which is billed as a "Biomass Gasification Combustor". If operated correctly, the Dell-point pyrolyzes the fuel, producing carbon and combustible gases, which are then burned with a limited amount of air. The small amount of excess air passing through the stove contributes to its efficiency since excess air does nothing but transport heat up the flue.
The Dell-Point incorporates an electronic control system which regulates the fuel supply rate, the ash removal rate, the combustion air blower, and the circulation blower. There are adjustments which can be made to all the settings except the circulation blower. The combustion blower and the circulation blower are driven by electronically commutated motors which are both very efficient and variable speed. The average electric power consumption of the stove is about 25 watts, with a maximum of about 55 watts. It can easily be set up to run from an off-the-grid 12-volt supply. It is supplied with an automatic gel-cell battery backup that the manufacturer claims will run the stove for 7 to 9 hours.
The control panel includes a Dwyer Minihelic differential pressure gauge, which has a full-scale reading of .5 inches of Water Column. The low-pressure tap of the gauge is connected to a port in the rear wall of the firebox.
Quotes from the patent:
(S)olid fuel fed to the grate at the bottom of the gasification/combustion chamber is pyrolyzed in the presence of a limited air supply to form combustion gases which are drawn upwardly through the gasification/combustion chamber while contacting heated combustion air entering through the spaced air inlets.
This is operated as an air-tight system with the only exterior connections being an inlet for combustion air and an exhaust gas outlet.
The pellets are fed into the gasification/combustion chamber either from a top feeder or a bottom feeder and rest on the grate at the bottom. In that location, the pellets receive a very limited combustion air supply sufficient only to raise the temperature in the pellets to about 480 to 590.degree. C., i.e. below melting temperatures of the minerals that may be present. At this temperature, gases are released and rise within the combustion zone where they are super-combusted with controlled flow of hot combustion air. The spiral array of combustion air inlet holes is located sufficiently far above the pellets being gasified on the grate so as to induce by negative pressure the gases and flames away from the grate area, thereby keeping the pellets on the grate below the temperature at which slag and clinkers are formed. The duel (sic) spiral array of air inlet holes arranged in the above manner cause the introduction of super heated combustion air into the chamber with a vertically swirling and turbulent motion which results in very complete burning of the gases emanating from the solid fuel below. This complete burning is achieved at temperatures in the order of 1200 to 1370.degree. C. without the need of a large excess of air and this means that the flow of exhaust gas is substantially reduced compared to conventional pellet stove appliances. The burner of this invention operates very efficiently at air:fuel ratios of less than 8:1 and an excess air level of no more than 100%.
Settings
Fuel Bed Level
The fuel bed level is not an adjustment. The adjustments effect the fuel bed level. The fuel bed level is a critical operating parameter. It should be about 5 inches below the top of the burn pot. Since it is not practical to stick a ruler into an operating burn pot, here is an illustration to help in judging your fuel bed level.
The correct fuel bed level is between Hole #4 and Hole #5. You may need to open the firebox door to be able to see that far down in the burn pot. If you can see Hole #5, then the fuel bed level is too low. If you can't see Hole #4, then the fuel bed level is too high.
Combustion Air
According to FPI, for maximum efficiency the combustion air control should be set so that the Minihelic gauge displays the following Water Column values. They also say; "These can vary with fuel type, quality and size.", but give no indication of how they might vary.
If you are using an outside air intake, then the high pressure port of the gauge should be connected to a tap in the intake line as close as possible to the burn pot. The pressure changes across the intake and exhaust plumbing can be considered immaterial to the combustion air setting, although they do affect it. The crucial operating parameter is the differential pressure across the burn pot, so that is what the Minihelic gauge should be measuring.
| Heat
Level | Inches
W.C. | Burn Rate
lb/Hr |
|---|---|---|
| 1 | .10 - .15 | 1 - 1½ |
| 2 | .12 - .17 | 1½ - 2 |
| 3 | .15 - .20 | 2 - 2½ |
| 4 | .20 - .26 | 3 |
| 5 | .24 - .30 | 4 |
This graph shows the Control Voltage fed to the combustion air blower speed control for all five Heat Level Settings, and all 20 Combustion Air settings. The speed of the blower is supposed to be linear with the control voltage, so this should be an accurate model of the blower speed. The blower motor speed is rated at 900-3600 RPM. Reading across the chart gives the Combustion Air setting for equal blower speed at different Heat Level settings. For example, 9 on Heat level 5 is the same speed as 13 on Heat Level 4, 15 on Heat Level 3, and 17 on Heat Levels 2 and 1. Heat Levels 2 and 1 are identical from 12 to 20.
Ash Auger
This adjustment controls the rate of ash removal. Most fuels seem to work well with a low setting. Set it at 1 to start, then adjust it upward if the fuel bed height increases above normal.
Heat Level
The Heat Level setting does exactly what it sounds like it would do. But it doesn't just increase the rate of fuel feed. It increases the Combustion Air and the rate of ash removal as well. If you change the Heat Level, you may not need to make any other adjustments. Then again, you might. The range of the Heat Level adjustment is 1 to 5. 1 is the lowest setting, 5 is the highest. The burn rates specified in the manual, and on the label inside the control door, are shown in the table above.
Fuel Type
Some newer GF75-1 models have the corn and wheat buttons disabled. They are configured for pellets only, the use of any other type of fuel will void all warranties.
Fuel Trim
This adjustment is not documented in the owner's manual. To access it, press and hold the Manual Feed button for about three seconds. The upper display will change to 0. Then press the Combustion Air + or - buttons to change the setting. The range is from -3 to +3. Since this adjustment is undocumented, its exact effect on the burn rate is unknown. Unlike the other adjustments, the Fuel Trim adjustment retains its setting through shutdown/restart cycles.
Corn
Add Corn-specific tips and info here.
Wood Pellets
Add Wood pellet-specific tips and info here.
Problems & Fixes
Low Fuel Bed
Probably you have one or more air leaks into the ash pit or too much draft. The Dell-Point requires the ash pit to be airtight for correct operation. Other symptoms of ash pit air leaks can include a band of bright coals along the rear of the burn pot, a persistent vertical flame at the rear of the burn pot, and dark brown or black ash in the pan.
Leak Locations
- Around the ash auger shaft where it passes through the rear ash pit wall.
- The teardrop-shaped tab on the right side, near the rear, behind the right access door and panel.
- Around the front ends of the door handle bushings.
- Where the ends of the door gasket meet.
Seal the leaks using high temperature RTV silicone gasket material available from any auto parts store. Seal the ash auger shaft immediately before operating the stove, so that the sealer doesn't cure stuck to the shaft.
Reducing Excessive Draft
The Dell-Point requires little or no draft because the combustion air blower provides all the draft it needs. If you are seeing high readings on the Minihelic gauge even with the combustion air set low, then you have excessive draft. Install a restrictor plate. Start with the larger of the two.
