US20020062828A1

US20020062828A1 - Solar collector system

Info

Publication number: US20020062828A1
Application number: US09/726,920
Authority: US
Inventors: John Nydahl; Bradley Carlson
Original assignee: Individual
Current assignee: University of Wyoming
Priority date: 2000-05-26
Filing date: 2000-11-30
Publication date: 2002-05-30

Abstract

A solar collector system is provided. The solar collector system comprises a frame member and a top plate supported by the frame member with the top plate being transparent to solar energy. A membrane is supported within the frame beneath the top plate and a solar absorber plate supported within the frame beneath the membrane. A collector or plurality of collectors removes heat from the solar absorber plate. The collectors have a fluid selectively flowable through the heat collectors wherein upon the membrane achieving a first predetermined temperature, the membrane becomes substantially taut within the frame and spaced from the solar absorber plate and wherein upon the membrane achieving a second predetermined temperature, the membrane becomes substantially flaccid and contacts the solar absorber plate thereby maintaining the solar absorber plate below the second predetermined temperature.

Description

The present application is a continuation of pending provisional patent application Ser. No. 60/207,999, filed on May 26, 2000, entitled “Double Glazed Solar Collector System for Inhibiting Freezing During No-Flow Conditions”.[0001]

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a solar collector system having a transparent film with a high thermal expansion coefficient and, more particularly, it relates to a solar collector system, which inhibits excessive solar collector solar absorber plate temperatures during no-flow conditions.

2. Description of the Prior Art

In a conventional double-glazed solar collector system, when the flow of liquid ceases through the system, extreme component temperatures may be produced. High temperature materials are required for the absorber assembly and inner glazing of an efficient system to prevent physical harm to the structure thereby damaging the solar collector. Therefore, conventional solar collectors that utilize inexpensive but low temperature materials for the solar absorber plate (such as plastics) must be downgraded to limit their maximum operating temperature. This is often accomplished by using an ineffective single glazed system and/or a nonselective surface absorber.

A need therefore exists in the art for a solar collector system, which inhibits excessive solar collector solar absorber plate temperatures during no-flow conditions. It is desirable that this be achieved, moreover, without compromising the solar collector system performance and the effectiveness of the materials. The present invention solves these problems and offers other advantages over the prior art.

SUMMARY

The present invention is a solar collector system. The solar collector system comprises a frame member and a top plate supported by the frame member with the top plate being transparent to solar energy. A membrane is supported within the frame beneath the top plate and a solar absorber plate supported within the frame beneath the membrane. A collector or plurality of collectors removes heat from the solar absorber plate. The heat collectors have a fluid selectively flowable through the heat collectors wherein upon the membrane achieving a first predetermined temperature, the membrane becomes substantially taut within the frame and spaced from the solar absorber plate below the first predetermined temperature and wherein upon the membrane achieving a second predetermined temperature, the membrane becomes substantially flaccid and contacts the solar absorber plate thereby maintaining the solar absorber plate at the second predetermined temperature.

The present invention additionally includes a system for collecting solar energy. The system has a solar absorber plate for absorbing solar energy and heat collectors for collecting the solar energy from the solar absorber plate during flow conditions. The system comprises means spaced from the solar absorber plate during flow conditions and contactable with the solar absorber plate during no-flow conditions for reducing the temperature of the solar absorber plate.

The present invention further includes a solar collector having a double-glazed configuration. The solar collector comprises means for transforming from a double-glazed configuration into a single-glazed configuration upon occurrence of a predetermined event.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view illustrating a solar collector system, constructed in accordance with the present invention, with the inner glazing film being in a taut condition during a fluid flow event; and [0010]
FIG. 2 is a sectional side view illustrating the solar collector system, constructed in accordance with the present invention, with the inner glazing film being in a sagged, elevated temperature condition during a high ambient temperature and high solar radiation, fluid no-flow or stagnation event.[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in FIGS. 1 and 2, a solar collector system, indicated generally at [0012] 10, passively, reliably, and inexpensively transforms a double-glazed solar collector system into a single-glazed solar collector system when the absorber starts to overheat. This extends the range of possible absorber materials that can be used without decreasing performance. Actual construction and operation of the solar collector system 10 will be described in detail below.
To accomplish the desired result, the [0013] solar collector system 10 has a supporting frame 12 having a first frame member 14 and a second frame member 16. A top plate 18 is supported on the first frame member 14 and the second frame member 16 to inhibit damage of the internal mechanisms (as described below) of the solar collector system 10 from weather elements. The transparent top plate 18 can be constructed from any material, which is transparent to solar radiation. For instance, the top plate 18 is preferably constructed from a glass material although it is within the scope of the present invention to construct the top plate 18 from any solar transparent material including, but not limited to, Sunlite HP, Lucite acrylic, Tedlar PVF, etc.
The [0014] solar collector system 10 of the present invention further includes a solar absorber plate 20 supported between the first frame member 14 and the second frame member 16 of the supporting frame 12. The solar absorber plate 20 absorbs solar energy entering between the first frame member 14 and the second frame member 16 of the supporting frame 12 through the top plate 18.
Beneath the [0015] solar absorber plate 20 of the solar collector system 10 is a single or plurality of heat collectors 22 removing the heat of the solar absorber plate 20 caused by solar energy. The fluid travels through a pipe or channel collecting heat from the solar absorber plate 20 and cooling the solar absorber plate 20. An insulation material 24 can surround the heat collectors 22 to minimize heat loss of the fluid traveling therethrough.
Between the [0016] top plate 18 and the solar absorber plate 20, an inner glazing film 26 is supported between the first frame member 14 and the second frame member 16 of the supporting frame 12. The inner glazing film 26 is a mechanically resilient, transparent film, which can withstand many thermal cycles, have a large coefficient of thermal expansion and a high operating temperature. Additionally, the inner glazing film must not become affixed to the solar absorber plate 20.
Preferably, the [0017] inner glazing film 26 is a membrane 26 constructed from a Teflon CLP material although other types of membranes 26, including, but not limited to, a Teflon PFA material, are within the scope of the present invention. The actual composition of the membrane 26 is preferably a transparent fluorinated carbon, which tends to be receptive to expansion with an increase in temperature.
During normal operation of the [0018] solar collector system 10 of the present invention, the solar energy passes through the solar transparent top plate 18 and the inner glazing film 26. The solar energy strikes the solar absorber plate 20 causing the temperature of the solar absorber plate 20 to be increased. The energy from this temperature increase is then transferred to the fluid, typically an antifreeze substance, flowing through the heat collectors 22 and through the glazing to the ambient air. While most of the absorbed thermal energy is transferred from the hot absorber plate to the colder fluid, some of the thermal energy is also transferred to the colder ambient air. Both of these transfer rates are proportional to the temperature difference between the mean solar absorber plate temperature and the respective fluid temperature.
As illustrated in FIG. 1, under normal operating conditions, the inner glazing film or the [0019] membrane 26 is designed to remain taut between the first frame member 14 and the second frame member 16 of the supporting frame 12. As illustrated in FIG. 2, when the fluid flow within the heat collectors 22 has ceased (stagnate or no-flow while still exposed to intense solar irradiation), the temperature of the all the components will increase, especially the solar absorber plate 20 and the components in its immediate vicinity. When the solar absorber plate 20 starts to overheat, the corresponding temperature increase of the inner glazing film 26 causes it to become flaccid and sag upon the solar absorber plate 20. The sagging of the inner glazing film 26 causes the inner glazing film 26 to substantially contact the solar absorber plate 20 effectively eliminating the gap, i.e., the solar area 28 between the solar absorber plate 20 and the inner glazing film 26. The elimination of the solar collection area 28 inhibits the minimizes the temperature difference between the solar absorber plate 20 and the inner glazing film 26 during no-flow conditions through the heat collectors 22.
With the elimination of the [0020] solar collection area 28, the temperature of the membrane 26 is maintained substantially equivalent to the temperature of the absorber plate 20. While these two temperatures are essentially equivalent, the solar absorber plate 20 is still dictating all the temperatures. For instance, there are two parallel paths for the absorbed solar energy as illustrated in FIG. 1, namely a low resistive heat transfer path from the solar absorber plate 20 to the fluid and a high resistive path from the solar absorber plate 20 to the ambient air. For a given temperature difference between the solar absorber plate 20 and the two fluid temperatures (fluid and ambient air), most of the energy is transported through the low resistive path (solar absorber plate 20 to fluid). During stagnation, only the high resistance path is available and it requires a large temperature difference between the solar absorber plate 20 (stagnation temperature) and the ambient air to transfer the same amount of absorbed solar energy to the air. The sagging of the inner glazing film 26 causes the magnitude of the solar absorber plate 20 to the ambient air resistance to significantly decrease (double glazing resistance to single glazing resistance) which translates into a large decrease in the required stagnation temperature to dissipate the absorbed solar energy.
Basically, in the [0021] solar collector system 10 of the present invention, the membrane 26 inhibits damage to the solar absorber plate 20 by transforming the solar collector system 10 from a double-glazed collector system to a single-glazed collector system during no-flow conditions. For example, when the fluid flowing through the heat collectors 22 beneath the solar absorber plate 20 ceases, the temperature begins to build in the solar collection area 28 between the membrane and the solar absorber plate 20. As the solar collection area 28 temperature increases, the temperature of the membrane 26 also increases in a corresponding manner. The molecules of the membrane 26 become more excited with the increased temperature and begin to increase the distance between the centers of the molecules causing the membrane 26 to become flaccid and drape closer to and upon the surface of the solar absorber plate 20 until substantially the entire membrane 26 is contacting the solar absorber plate 20.
Therefore, the solar energy entering the [0022] solar collector system 10 simply strikes the loose and flaccid inner glazing film 26 and the solar absorber plate 20. This significantly increases the heat transfer conductance between the solar absorber plate 20 and the ambient air, which prevents the solar absorber plate 20 from overheating. The air may or may not circulate in cavity 30 that depend upon the temperature difference across the cavity 30 and the cube of its gap distance 30. The temperatures of the solar absorber plate 20 and the inner glazing film 26 are not necessarily equal to the temperature of the cavity 30 whose temperature varies across the gap 30 from the temperature of 26 to the temperature of 18. Once the circulation of the fluid through the heat collector 22 commences, the temperature in the solar collector system 10 will lower and the inner glazing film 26 move away from the solar absorber plate 20 and becomes taut thereby returning the solar collector system 10 to its normal operation.
Experiments with the [0023] solar collector system 10 of the present invention have revealed that when the experimentally measured solar absorber plate 20 stagnation temperature was approximately one hundred and sixteen (116° C.) degrees Celsius, the outer glazing temperature was approximately fifty (50° C.) degrees Celsius. If the inner glazing film 26 were not properly engineered so that it had remained taut, the stagnation temperature of the solar absorber plate 20 would have an estimated temperature of approximately one hundred and sixty-six (166° C.) degrees Celsius. Therefore, the solar collection system 10 of the present invention passively decreased the stagnation temperature of the solar absorber plate 20 by approximately fifty (50° C.) degrees Celsius.
The performance of solar collectors that utilize inexpensive, but low temperature materials, for the solar absorber plate [0024] 20 (such as plastics) must be downgraded to limit the solar collectors' maximum operating temperature. In conventional solar collectors, this is accomplished by using a system with no glazing, a single glazing, and/or a non-selective radiation surface. The solar collector system 10 of the present invention is engineered to passively, reliably, and inexpensively transform a double glazed system to a single glazed system for elevated no-flow, stagnation temperatures thereby extending the range of possible absorber materials that can be used without decreasing performance.
The foregoing exemplary descriptions and the illustrative preferred embodiments of the present invention have been explained in the drawings and described in detail, with varying modifications and alternative embodiments being taught. While the invention has been so shown, described and illustrated, it should be understood by those skilled in the art that equivalent changes in form and detail may be made therein without departing from the true spirit and scope of the invention, and that the scope of the present invention is to be limited only to the claims except as precluded by the prior art. Moreover, the invention as disclosed herein, may be suitably practiced in the absence of the specific elements, which are disclosed herein. [0025]

Claims

What is claimed is:

1. A solar collector system, the solar collector system comprising:

a frame member;

a top plate supported by the frame member, the top plate being transparent to solar energy;

a membrane supported within the frame beneath the top plate;

a solar absorber plate supported within the frame beneath the membrane; and

at least one collector for removing heat from the solar absorber plate, the at least one collector having a fluid selectively flowable through the at least one collector;

wherein upon the membrane achieving a first temperature within a predetermined operating temperature range, the membrane becomes substantially taut within the frame and spaced from the solar absorber plate; and

wherein upon the membrane achieving a second predetermined temperature, the membrane becomes substantially flaccid and contacts the solar absorber plate thereby maintaining the solar absorber plate below a second predetermined temperature.

2. The solar collector system of claim 1 wherein the temperature of the solar absorber plate decreases by at least approximately fifty (50° C.) degrees Celsius.

3. The solar collection system of claim 1 wherein the membrane is constructed from a Teflon material.

4. A system for collecting solar energy, the system having a solar absorber plate for absorbing solar energy and heat collectors for collecting the solar energy from the solar absorber plate during flow conditions, the system comprising:

means spaced from the solar absorber plate during flow conditions and contactable with the solar absorber plate during no-flow conditions for reducing the temperature of the solar absorber plate.

5. The system of claim 4 wherein the means comprises a membrane constructed from a Teflon type material.

6. The system of claim 5 wherein the membrane becomes flaccid at a predetermined temperature and contacts the solar absorber plate.

7. The system of claim 6 wherein the membrane approaches the absorber plate temperature during no-flow conditions.

8. The system of claim 4 wherein the maximum stagnation temperature of the solar absorber plate is reduced by approximately fifty (50° C.) degrees Celsius.

9. A solar collector having a double-glazed configuration, the solar collector comprising:

means for transforming from a double-glazed configuration into a single-glazed configuration upon occurrence of a predetermined event.

10. The solar collector of claim 9 and further comprising a solar absorber plate for absorbing solar energy.

11. The solar collector of claim 9 wherein the means is a membrane, the membrane contactable with the solar absorber plate at a predetermined temperature.

12. The solar collector of claim 9 and further comprising at least one collector alternatable between a flow condition and a no-flow condition, the at least one collector reducing the temperature of the solar absorber plate during the flow condition.

13. The solar collector of claim 12 wherein the predetermined event is the no-flow condition.

14. A method for transforming a double-glazed solar collector system into a single-glazed solar collector system, the method comprising:

providing a membrane;

supporting a solar absorber plate beneath the membrane;

moving the membrane into substantial contact with the solar absorber plate upon the membrane reaching a predetermined temperature.

15. The method of claim 14 and further comprising:

providing at least one collector; and

absorbing heat from the solar absorber plate with at least one collector;

16. The method of claim 14 wherein the membrane becomes flaccid and sags onto the solar absorber plate.

17. The method of claim 14 and further comprising:

constructing the membrane from a Teflon material.