Abstract:
Substituting a solar concentrator for a conventional burner for heating is desirable. However, the sun&#39;s energy is diurnal and cannot be counted upon even during daylight hours. To ensure heating is available, a backup conventional combustor can be provided. According to the present disclosure, a heat exchanger element of the heater assembly is directly acted upon by solar rays via a solar concentrator and by combustion. The heat exchanger acts as the combustion holder. Fuel provided to the outside of the heat exchanger is adjusted based on the demanded for heating and the amount of insolation achieved via the solar concentrator. The heat exchanger can be part of a conventional heater or a heat pump for heating water.

Description:
FIELD 
       [0001]    The present disclosure relates to a heater that combines a solar concentrator and a burner. 
       BACKGROUND 
       [0002]    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 &#39;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. 
       SUMMARY 
       [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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&#39;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. 
         [0009]    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. 
         [0010]    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. 
         [0011]    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. 
         [0012]    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. 
         [0013]    The method may further include adjusting the flow rate of fuel and air based on the desired heating demand. 
         [0014]    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. 
         [0015]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is an illustration of a heater according to an embodiment of the present disclosure; 
           [0017]      FIG. 2  is a plan view of the heat exchanger of  FIG. 1 ; 
           [0018]      FIG. 3  is a plan view of the solar concentrator of  FIG. 1 ; 
           [0019]      FIG. 4  is an illustration of a heliostat configuration to reflect rays into a solar concentrator; 
           [0020]      FIG. 5  is an illustration of the burner and an electronic control unit to control the burner; 
           [0021]      FIG. 6  is an embodiment of a solar concentrator with the incident solar rays vertical; 
           [0022]      FIG. 7  is the solar concentrator of  FIG. 6  in which the incident solar rays are displaced by an angle with respect to vertical; 
           [0023]      FIG. 8  is an illustration of a Vuilleumier heat pump, an example of one device that can be combined with the heater disclosed herein; and 
           [0024]      FIG. 9  is a flowchart illustrating one embodiment of operation of the heater. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    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. 
         [0026]    A heater assembly  10  is shown in  FIG. 1 . Heater assembly  10  has a solar concentrator  12 . Solar concentrator  12  has a concave reflective parabolic bowl  14  portion that reflects the sun&#39;s parallel rays to a convex reflective parabolic disk  16  portion. Disk  16  reflects the sun&#39;s rays downwardly. Solar concentrator  12  also includes a convex reflective parabolic ring  18 . 
         [0027]    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 . 
         [0028]    In one embodiment, window  32  is a quartz crystal due to quartz&#39;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. 
         [0029]    The sun&#39;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&#39;s rays that hit parabolic ring  18  are directed onto window  32  and transmitted to heat exchanger  30 . The embodiment shown in  FIG. 1  is one non-limiting example configuration. 
         [0030]    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. 
         [0031]    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 . 
         [0032]    Heat exchanger  30 , shown in plan view in  FIG. 2 , has two tubes  50  and  52  that are entwined in a spiral. Inlets  60  and  62  and outlets  70  and  72  are provided to tubes  50  and  52 , respectively. The embodiment of heat exchanger  30  in  FIGS. 1 and 2  is one non-limiting example showing two outlets to provide two supplies of heated working fluid evenly distributed. Alternatively, only one tube could be used. Or, more tubes could be used to branch out the heated working fluid even more. 
         [0033]    In  FIG. 3 , a plan view of solar concentrator  12  is shown. Parabolic ring  18  surrounds parabolic bowl. Window  32  is at the center. Parabolic disk  16  is supported by arms  17 . Such a configuration provides a more compact solar concentrator than if parabolic ring were to extend further into the center of the device. The embodiment shown in  FIGS. 1 and 3  is one non-limiting example of a solar concentrator. Other configurations could be substituted. 
         [0034]    In  FIG. 1 , parallel rays are shown entering solar concentrator  12  in a vertical direction. However, the sun is directly overhead only momentarily in particular geographical locations during certain seasons. To collect the sun&#39;s rays throughout the daylight hours, either the position of heater  10  is moved to track the position of the sun or a heliostat is used to cause the sun&#39;s rays to be reflected vertically. A heliostat embodiment he is shown in  FIG. 4 . Parallel solar rays  78  are arriving at an angle displaced from vertical. A mirror  82  is provided which reflect the rays into a vertical column into solar concentrator  90 . Mirror  82  is attached to a frame  84  via a geared system. The angle of mirror  82  moves with respect to a pivot point  89  when a small gear motor  85  rotates. Teeth of small gear motor  85  engage with a gear  87  coupled to mirror  82 . A motor  88  also attached to frame  84  causes the heliostat to rotate with respect to the centerline of motor  88 . Heliostat  80  is one example of suitable arrangements for directing the sun&#39;s rays to a stationary heater. Frame  84  and motor  88  are shown just below solar concentrator  90 . However, depending on the embodiment, frame  84  and motor  88  are displaced from the bottom of solar concentrator  90  to provide space for components associated with heater  10 . 
         [0035]    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. 
         [0036]    In  FIG. 5 , an electronic control unit (ECU)  100  and associated controllers and sensors are shown. ECU  100  receives input from a thermostatic control  106  or other suitable device to provide a signal to ECU  100  indicative of desired energy input. Outlet  72  of heat exchanger  30  has a thermocouple, thermistor, or other suitable temperature measuring sensor  102  disposed therein to provide to ECU  100  a measure of output temperature. Based on the results of temperature sensor  102  and/or based on other sensors  110  providing signals of conditions within the heater and/or the environment. The amount of pressurized gaseous fuel  104  is supplied to inlet  36  via a venturi  108  which pulls in air  109  in proportion to the fuel quantity. Fuel quantity is metered via a valve  104  with valve  104  commanded by ECU  100 . The fuel/air metering arrangement in  FIG. 5  is but one example for metering the fuel and air. 
         [0037]    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. 
         [0038]    In  FIG. 1 , heater  10  has a nearly flat heat exchanger  30  and a nearly flat window  32  that are parallel to each other. In an alternative embodiment in  FIG. 6 , a solar concentrator  300  has parabolic mirror  302  and two parabolic mirrors  304  disposed above mirror  302 . A domed window  306  is provided above heat exchanger  308 . Parallel rays entering to mirror  302  nearly all cross the same point that is between and below parabolic mirrors  304 . Rays are transmitted through window  306  onto a heat exchanger  308 , which is dished. Working fluid is provided to heat exchanger  308  through inlets  310  and  312  and removed from heat exchanger  308  through outlets  320  and  322 . An advantage of the embodiment in  FIG. 6  is that only solar concentrator  300  is moved when tracking the sun. In  FIG. 7 , sun rays coming in at an angle are incident upon mirror  302  and directed onto one of mirrors  304  which direct the rays through window  306  onto heat exchanger  308 . 
         [0039]    In the embodiment in  FIG. 1 , either a heliostat is provided (such as the example shown in  FIG. 4 ) or the entire heater moves to obtain a favorable position with respect to the sun. If the entire heater is moved in relation to the sun, flexible tubing is provided at locations in which a fluid leaves the apparatus. The heater in  FIG. 1  is advantageous in using a flat window and a flat heat exchanger. The embodiment in  FIGS. 6 and 7  is advantageous in that only solar concentrator  300  is moved to track the sun. However, window  306  and heat exchanger  308  are of a more complicated shape. 
         [0040]    In  FIG. 8 , a Vuilleumier heat pump  120  is shown that has a burner  122  and a heat exchanger  124 . ( FIG. 8  is described in more detail in U.S. application Ser. No. 61/622,547 which is incorporated herein by reference in its entirety.) In place of burner  122  shown in  FIG. 8 , heater  10  of  FIG. 1  is provided. In another alternative, a Vuillemier heat pump in which the displacers are electromagnetically actuated, as disclosed in U.S. application Ser. No. 61/622,547, is coupled with the burner of  FIG. 1  of the present disclosure. 
         [0041]    In  FIG. 9 , a control system according to one embodiment of the disclosure starts at  200 . In block  202 , the amount of heating desired is determined. In block  204 , the heliostat is positioned so that maximum insolation is directed on the solar concentrator. In embodiments in which the entire heater is moved to collect the sun, instead of positioning the heliostat, the heater, in particular the solar concentrator, is positioned to provide the maximum insolation onto the heat exchanger. In block  206 , it is determined whether the available solar insolation is sufficient to provide the desired heating. If so, control returns to block  202 . If not, the burner is started beginning in block  208  in which the fuel valve is opened to provide fuel into the fuel-and-air delivery chamber. The fuel and air are drawn into the combustion chamber through the heat exchanger. The ignitor is commanded to ignite the fuel and air in the combustion chamber in block  210 . The desired heating rate is determined in block  212 . The fuel flow rate supplied is adjusted in block  214  to meet the present demand. Of course, the energy from combustion supplements the solar energy that is received. Control passes to block  214  in which it is determined whether the fuel is substantially zero. If not, control returns back to block  212  to determine the present demand level. If a positive result in block  216 , control passes to block  218  in which the fuel valve is closed to discontinue flow of fuel and air. Control returns to block  202 . 
         [0042]    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&#39;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. 
         [0043]    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.