The present invention is in the general field of thermodynamics and solar energy conversion.
Due to a variety of factors including, but not limited to, global warming issues, fossil fuel availability and environmental impacts, crude oil price and availability issues, alternative energy sources are becoming more popular today. One such source of alternative and/or renewable energy is solar energy. One such way to collect solar energy is to use a solar receiver to focus and convert solar energy into a desired form (e.g., thermal energy or electrical energy). Thermal energy harvested from the sun is known in the art to be utilized in absorption heat pumps, domestic hot water and industrial processes, power generating cycles through the heating of a secondary heat transfer fluid, power generating cycles through the direct heating of power generating working fluid such as steam, and for heating. Furthermore, it is recognized that a wide range of energy consumers can be supplied via electrical and/or thermal energy such as air conditioning, refrigeration, heating, industrial processes, and domestic hot water. Given this, solar collectors that function in efficient manners are desirable.
Traditional solar systems utilize a non-expandable working fluid under pressures less than 50 psia, or working fluids having expandability ratios between the cold and hot temperatures of less than 3. The traditional solar systems utilize a working fluid that is a heat transfer fluid and thus isn't directly compatible as a thermodynamic cycle working fluid. As noted, the density of the working fluid by being expandable changes by an order of magnitude as a function of operating pressure and temperature. Furthermore by definition solar energy is a function of solar intensity and thus at the minimum is absent during the nighttime, unless significant thermal storage is utilized that is currently very expensive, the system will experience substantial changes in density according to operating and ambient conditions.
The combined limitations of each individual component being the solar collector and heat exchangers, pump, heat pump, and fluid control valves presents significant challenges that are further exasperated when seeking to operate the solar collector in a dynamic manner as function of ambient conditions and solar flux.
The present disclosure and related inventions pertain to solar collectors having an expandable working fluid and an integrated mass management system. The disclosed embodiments utilize gravity to discharge a cooler and more dense fluid as displaced by a volumetrically equivalent warmer and less dense fluid.
In accordance with one aspect of the disclosure and related inventions, there is provided a solar energy conversion system which has a working fluid circuit for receiving and hold a working fluid capable of expansion within the working fluid circuit; at least one solar collector in the working fluid circuit; at least one fluid accumulator in the working fluid circuit; a pump for moving working fluid in the working fluid circuit to the solar collector and to the fluid accumulator; the working fluid circuit also extending between the solar collector and the fluid accumulator, and from the fluid accumulator to the pump.
In accordance with another aspect of the disclosure and related inventions, there is provided a method of converting solar energy acquired from a solar collector and transferred to a working fluid in a working fluid circuit of a solar energy conversion system having at least one solar collector in the working fluid circuit, at least one fluid accumulator in the working fluid circuit, a pump for moving working fluid in the working fluid circuit to the solar collector and to the fluid accumulator, the working fluid circuit also extending between the solar collector and the fluid accumulator, and from the fluid accumulator to the pump, the method including the steps of: controlling the pump to move working fluid through the working fluid circuit to the solar collector and to the fluid accumulator; thermally controlling the fluid accumulator to cool the working fluid in the fluid accumulator; removing working fluid from the fluid accumulator by controlling a valve between the solar collector and the fluid accumulator to an open position when the working fluid has reached a target set point temperature, and controlling a discharge valve between the fluid accumulator and the pump to an open position.
These and other aspects and concepts of the disclosure and related inventions are further described herein in detail with reference to the accompanying drawings.
As used herein, the following terms have the respective meanings. The term “in thermal continuity” or “thermal communication”, as used herein, includes the direct connection between the heat source and the heat sink whether or not a thermal interface material is used. The term “fluid inlet” or “fluid inlet header”, as used herein, includes the portion of a heat exchanger where the fluid flows into the heat exchanger. The term “fluid discharge”, as used herein, includes the portion of a heat exchanger where the fluid exits the heat exchanger.
The present invention generally relates to a solar collect system having an integral working fluid management system that enables the system to increase or decrease the mass of the working fluid within the circulation loop of the closed loop system.
Here, as well as elsewhere in the specification and claims, individual numerical values and/or individual range limits can be combined to form non-disclosed ranges.
The heat transfer fluid within the embodiments is preferably a supercritical fluid as a means to reduce the pressure drop within the heat exchanger. The supercritical fluid includes fluids selected from the group of organic refrigerants (R134, R245, pentane, butane), gases (CO2, H2O, He2). A preferred supercritical fluid is void of hydrogen as a means to virtually eliminate hydrogen reduction or hydrogen embrittlement on the heat exchanger coatings or substrate respectively. A preferred supercritical fluid has a disassociation rate less than 0.5% at the operating temperature in which the heat exchanger operates. The specifically preferred heat transfer fluid is the working fluid wherein the combined energy produced (i.e., both thermal, and electrical) displaces the maximum amount of dollar value associated with the displaced energy produced within all of the integrated components including thermodynamic cycle operable within a power generating cycle, vapor compression cycle, heat pump cycle, absorption heat pump cycle, or thermochemical heat pump cycle.
All of the embodiments can be further comprised of a control system operable to regulate the mass flow rate of the working fluid into the solar collector, with the ability to regulate the mass flow rate independently for each pass by incorporating a fluid tank having variable fluid levels optionally interspersed between at least one pass and the other. One method of control includes a working fluid inventory management system. The control system regulates the mass flow rate through methods known in the art including variable speed pump, variable volume valve, bypass valves, and fluid accumulators. The control system is further comprised of at least one temperature sensor for fluid discharge temperature and at least one temperature sensor for ambient air temperature or condenser discharge temperature.
Exemplary embodiments of the present invention will now be discussed with reference to the attached Figures which schematically illustrate the methods and processes disclosed herein, as may be embodied in a device or system for conversion of solar energy into another form of energy or work by use of a working fluid contained in a working fluid circuit made up of conduit for containment and transfer or passage or flow of a working fluid through the conduit and into or through components which are operatively and fluidly connected to the conduit of the working fluid circuit. There may be additional components to the system and the working fluid circuit, such as one or expansion devices, valves, pumps, heat exchangers, recuperators, condensers or other components which are not depicted in the Figures. Such embodiments are merely exemplary in nature. The depiction of solar collectors predominantly as flat panel non-tracking solar absorbers with integral microchannel heat exchangers is merely exemplary in nature and can be substituted by tracking collectors of 1 axis or 2 axis type, vacuum evacuated tubes or panels, switchable configuration between solar absorber or solar radiator mode, low concentration fixed collector, or high concentration tracking collectors. The depiction of pump as a vapor compressor device is merely exemplary and can be substituted with a positive displacement device, a gerotor, a ramjet, a screw, and a scroll. Furthermore, and importantly, the pump can be a turbopump, a positive displacement pump where the selection of the device to increase the working fluid pressure and operate as a mass flow regulator is determined by the density at the inlet pressure and discharge outlet when the incoming working fluid has a density greater than 50 kg per m3, or preferably greater than 100 kg per m3, or specifically greater greater than 300 kg per m3. The depiction of valves as standard mass flow regulators is merely exemplary in nature and can be substituted by variable flow devices, expansion valve, turboexpander, two way or three way valves. The depiction of methods to remove heat from the working fluid as a condenser is merely exemplary in nature as a thermal sink and can be substituted by any device having a temperature lower than the working fluid temperature including absorption heat pump desorber/generator, liquid desiccant dehumidifier, process boilers, process superheater, and domestic hot water. With regard to
The second method of discharge centers around the condenser 50 operating in reverse mode, thus as a thermal source instead of a thermal sink. Under the second method, the control system will begin the process of using a relatively higher temperature heat transfer fluid into the embedded heat exchanger of the fluid accumulator 20 at which point of reaching either or both the target set point temperature and/or target set point pressure the cold inlet valve 40 is opened (this assumes that the resulting pressure within the fluid accumulator is at least temporarily higher than the closed loop system pressure).
The right side of
It is anticipated that the removal of working fluid from the closed loop system into the fluid accumulator 20 can result from the solar collector operating in essentially a stagnation mode (thus being a safety precaution to limit the solar collector from exceeding it's maximum operating pressure specifications), the closing and/or evacuation of a parallel circuit within the closed loop system, capturing at least a portion of the working fluid “charge” within the closed loop system prior to maintenance of the entire system, enabling the solar collector to operate at relatively higher ambient temperatures, and/or enabling the solar collector to operate at relatively lower operating pressure. The counterpart is the addition of working fluid into the closed loop system from the fluid accumulator 20 as a result of relatively lower ambient temperatures, the opening and/or filling of a parallel circuit within the closed loop system, enabling the solar collector to operate at relatively lower ambient temperatures, and/or enabling the solar collector to operate at relatively higher operating pressure.
It is understood in this invention that a combination of scenarios can be assembled through the use of fluid valves and/or switches such that any of the alternate configurations can be in parallel enabling the solar collector to support a wide range of thermal sinks.
Although the invention has been described in detail with particular reference to certain embodiments detailed herein, other embodiments can achieve the same results.
Variations and modifications of the present invention will be obvious to those skilled in the art and the present invention is intended to cover in the appended claims all such modifications and equivalents.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US10/44681 | 8/6/2010 | WO | 00 | 6/18/2012 |
Number | Date | Country | |
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61231674 | Aug 2009 | US |