The present disclosure relates to a heater that combines a solar concentrator and a burner.
It is desirable to supplant nonrenewable resources, such as natural gas, with renewable sources such as solar. Solar, however, is diurnal. Either a large storage system is provided or the solar is supplemented. It is known to use a burner to supplement solar, such as is described in U.S. Pat. No. 4,328,791. A gas burner provides heat only in the event that the solar heating is insufficient. In '791, a water tank is provided with supply and return connectors for circulating water from the tank to a solar collector and back to the tank. A gas heater is disposed within the upper half of the tank by solar energy. The two heating devices are displaced from each other. It is desirable to have a more simplified heating system.
To provide at least one desired feature, a heater assembly is disclosed that includes: a window having an outer surface and an inner surface, a solar concentrator having a collection area many times greater than an area of the window, a heat exchanger that is arranged closer to the inner surface of the window, and a fuel-and-air delivery chamber defined by the inner surface of the window, a first surface of the heat exchanger, and a side wall of the delivery chamber with an inlet for fuel and air defined in the side wall of the delivery chamber. Most of the sun rays that impact the solar concentrator are reflected onto the outer surface of the window.
The heat exchanger comprises at least one tube arranged in a spiral with a distance between adjacent tubes displaced less than equal to a quench distance of the fuel and air. The heat exchanger may be alternatively be configured in any suitable formation.
The heat assembly also includes a combustion chamber defined by a second surface of the heat exchanger, a side wall of the combustion chamber, and a bottom wall with an outlet for exhaust gases defined in one of the side wall and the bottom wall of the combustion chamber and an ignitor disposed in the combustion chamber. The assembly further includes: a fuel supply duct coupled to an inlet of the fuel-and-air delivery chamber, an air supply duct coupled to the inlet of the fuel-and-air delivery chamber, a fuel valve disposed in the fuel supply duct, and an electronic control unit electronically coupled to the fuel valve and the ignitor.
The heat exchanger has at least one tube adapted to carry a working fluid, the tube is arranged in a spiral, and the tube has an inlet and an outlet. A temperature-measuring device is disposed in the outlet of the tube. An electronic control unit (ECU) is electronically coupled to the temperature measuring device and the fuel valve. The ECU controls the fuel valve based on the temperature at the outlet of the tube.
The window and the heat exchanger are substantially flat and parallel to each other. In one embodiment, the solar concentrator has a concave reflective parabolic ring adapted to reflect incoming solar rays onto the window, a convex reflective parabolic disk disposed opposite the upper surface of the window, and a concave reflective parabolic bowl disposed inside the reflective parabolic ring. The parabolic bowl is adapted to reflect incoming solar rays onto the parabolic disk and the parabolic disk is adapted to reflect incoming solar rays from the parabolic bowl onto the window.
Also disclosed is a heat assembly that includes a solar concentrator, a heat exchanger comprising at least one tube arranged in a spiral, and a window arranged between the solar concentrator and the heat exchanger. The at least one tube is adapted to conduct a working fluid. The solar concentrator is arranged to direct the sun's rays onto the heat exchanger. The heat exchanger is adapted to stabilize combustion at an outer surface of the heat exchanger when provided a combustible mixture of air and fuel and after combustion has been initiated. The heat exchanger is disposed within a chamber that is defined by: a window arranged substantially parallel to the heat, a side wall, and a bottom wall and the chamber is separated by the heat exchanger into a fuel-and-air delivery chamber and a combustion chamber.
The fuel-and-air delivery chamber defines a fuel-and-air inlet. The combustion chamber defines an exhaust outlet. The combustion chamber has an ignitor disposed therein.
At least one tube includes a first tube arranged in a first spiral with an inlet at the center of the first spiral and an outlet at the periphery of the first spiral and a second tube arranged in a second spiral with an inlet at the center of the second spiral and an outlet at the periphery of the second spiral. The first and second spirals are entwined and the outlets of the first and second tubes are arranged substantially diametrically opposed from each other. Throughout the spiral, a distance between adjacent tubes in the spiral is less than a quench distance.
The solar concentrator is substantially parabolic. The assembly further includes: a positioning system to move one of: a mirror of a heliostat, the solar concentrator, and the heater assembly so that available rays from the sun are directed into the solar concentrator substantially parallel to a central axis of the solar concentrator, a fuel delivery system having a valve to meter an amount of fuel provided to the fuel-and-air delivery chamber, an air delivery system for metering air provided to the fuel-and-air delivery chamber, and an electronic control unit electronically coupled to the valve, the ignitor, and the positioning system.
Also disclosed is a method to operate a heater assembly having a solar concentrator and a heat exchanger adapted to stabilize combustion. One of: a heliostat proximate the solar concentrator, the solar concentrator, or the heater assembly is positioned to cause solar rays to impact the heat exchanger. The method further includes determining a present heating demand and supplying fuel and air to the heat exchanger when the solar energy is insufficient to provide the heating demand. The method further includes actuating the ignitor when a temperature of the heat exchanger is below the ignition temperature of the fuel and air proximate the heat exchanger.
The method may further include adjusting the flow rate of fuel and air based on the desired heating demand.
When the fuel flow is very low, it may be difficult to sustain combustion and it indicates that the insolation, i.e., the amount of solar radiation reaching the surface (the heat exchanger, in this case), is sufficient to meet the demand. The method further includes determining whether the fuel valve is nearly turned off. If so, the fuel valve is commanded to close. In an embodiment with a heliostat, the method includes positioning a mirror of the heliostat substantially parallel to the heat exchanger when it is determined that it is night time.
Prior systems have provided a fuel-fired burner as a backup to solar energy. The present disclosure improves on prior systems by having the burner and the solar concentrator acting upon the same element thereby avoiding additional components and sources for loss.
As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated.
A heater assembly 10 is shown in
Heater assembly 10 also includes a burner that is enclosed in a chamber 20. Chamber 20 has two portions: a fuel-and-air delivery chamber 22 and a combustion chamber 24 that is separated by a heat exchanger 30. Fuel-and-air delivery chamber 22 is defined by a window 32, heat exchanger 30, and a side wall 34. Defined in side wall 34 is a fuel-and-air inlet 36. Combustion chamber 24 is defined by heat exchanger 30, a side wall 38 and a bottom wall 40. Exhaust exits combustion chamber 24 via an outlet 42 defined in side wall 38. Alternatively, outlet 42 exits through bottom wall 40.
In one embodiment, window 32 is a quartz crystal due to quartz's desirable optical properties. Any suitable material that is highly transparent to visible and UV light, substantially opaque to infrared, and withstands higher temperatures due to the proximity to the burner can be an alternative.
The sun's rays that hit parabolic bowl 14 reflect toward parabolic disk 16 and are directed onto window 32 and transmitted to heat exchanger 30. The sun's rays that hit parabolic ring 18 are directed onto window 32 and transmitted to heat exchanger 30. The embodiment shown in
Fuel and air supplied through inlet 36 are drawn into air-and-fuel delivery chamber 22 through gaps in heat exchanger 30 into combustion chamber 24. An ignitor 44 can be used to start combustion. After combustion is established, combustion occurs at the heat exchanger 30. Gaps in heat exchanger 30 are carefully sized to be smaller than the quench distance. By ensuring the gaps are sufficiently small, flash back into fuel-and-air delivery chamber 22 is prevented.
Quench distance is commonly defined as a width or a diameter through which a flame will not propagate. The quench distance depends on the geometry, (e.g., whether a slot or a tube) and the stoichiometry of the fuel-air mixture, primarily, with other secondary effects such as fuel type, the material around the gap, and temperature. For the present situation, the quench distance is determined for the operating condition anticipated which yields the smallest quench distance and is on the order of 0.5 mm. The gaps between adjacent tubes are spaced such that they are smaller than the determined quench distance throughout heat exchanger 30.
Heat exchanger 30, shown in plan view in
In
In
In one embodiment, mirror 82 can be tilted horizontally to protect heater 10 during night time hours when no solar energy is available. Furthermore, mirror 82 reflects any radiated energy from or through window 32 back to window 32 to at least partially prevent losses to the night sky.
In
ECU 100 may also control motors 86 and 88 associated to heliostat 80 for embodiments including a heliostat. ECU 100 may also control other actuators 112 that might be associated with other aspects of the heat pump or heater. ECU 100 is shown as a single unit. However in an alternative embodiment, the functions of ECU 100 are distributed among multiple controllers.
In
In the embodiment in
In
In
As described above, the solar collection system is arranged so as to provide the maximum insolation. However, there could be situations in which the amount of energy provided through the sun's energy is greater than that needed for the heating or cooling demand, the heliostat or solar collector can be adjusted to provide less than the maximum insolation, i.e., when the demand is less than the available solar energy.
While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.
Filing Document | Filing Date | Country | Kind |
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PCT/US2013/065582 | 10/18/2013 | WO | 00 |
Number | Date | Country | |
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61715341 | Oct 2012 | US |