WO2016016892A1

WO2016016892A1 - Solar air heater construction unit

Info

Publication number: WO2016016892A1
Application number: PCT/IL2015/050783
Authority: WO
Inventors: Ofer ZVULUN
Original assignee: Zvulun Ofer
Priority date: 2014-07-31
Filing date: 2015-07-30
Publication date: 2016-02-04

Abstract

A solar air heater that comprises enclosure with a front transparent or translucent sun-facing wall, a rear wall, and side walls between the front and rear walls; an inlet section by which air is introducible to said heater; an outlet section from which air heated by solar energy is dischargeable; and a heating element interposed between the front and rear walls and across which the introduced air is flowable. The heating element comprises a plurality of three dimensional, multi-directionally sloping protrusions made of a thermally insulating material each of which is coated with a layer made of a heat resistant, dark-color material for maximizing transfer of solar energy to the introduced air to increase the temperature of the solar heated air. The heating element is an expanse of identical protrusions that protrude from the rear wall, that is made of the thermally insulating material, and are directed towards the front wall.

Description

SOLAR AIR HEATER CONSTRUCTION UNIT Field of the Invention

The present invention relates to the field of solar heat. More particularly, the invention relates to a solar air heater construction unit.

Background of the Invention

Solar air heaters of various types are known in the art. Various methods for converting the solar energy into heat and for transferring that heat to treated air are known in the art. Such heaters suffer, typically, from low total efficiency due to a low conversion ratio from sunlight to heat and due to heat transferred to the heater structure instead of to the heated air.

Various types of solar air heater constructions are known in the art. Most of them form a kind of an elongated box or container having at least one of its sides transparent, i.e. the one facing the sun, and means for urging cooler air through this box from one end of the box, typically a lower end, to the opposite end, typically the higher end. The capacity of absorption of heat by the air may be influenced by various variables, such as the temperature developing in the heater, the rate of flow of air through the heater, and the required temperature at the output port of the heater versus the ambient temperature.

A solar air heater is required that has small heat losses during the transfer from sun heat to heated air, with low heat losses to the heater structure and with high heat transfer capacity. Further, the heater is required to form a constriction element that fits into a construction such as a building or hall.

Many solar heaters are known from the prior art, such as US 2010/0186734, WO 2012/026901, US 7,631,641 and CN 203310135. For example, US 2010/0186734 discloses a heat absorbing element located between the front and back panel, which is wave-like to increase its surface area and is covered by a dark color to increase the absorption of thermal energy from the sunlight. The air is guided into a first flow passage inside the front translucent or transparent panel so as to be subject to heat from the sunlight, enters a second flow passage in the space between the front panel and the heat absorbing element, and then enters a third flow passage in the space between the back panel and the heat absorbing element. Although the heat absorbing elements of the prior art are effective in absorbing solar energy, they are nevertheless subject to thermal losses as a significant portion of the absorbed thermal energy is not transferred to the air circulating within the solar heater.

It is an object of the present invention to provide a solar air heater that increases the heat transfer efficiency relative to prior art devices from sunlight to heat.

Other objects and advantages of the invention will become apparent as the description proceeds. Summary of the Invention

The present invention provides a solar air heater, comprising an enclosure comprising a front transparent or translucent sun-facing wall, a rear wall, and side walls between said front and rear walls; an inlet section by which air is introducible to said heater; an outlet section from which air heated by solar energy is dischargeable; and a heating element interposed between said front and rear walls and across which said introduced air is flowable, wherein said heating element comprises a plurality of three dimensional, multi- directionally sloping protrusions made of a thermally insulating material each of which is coated with a layer made of a heat resistant, dark-color material for maximizing transfer of solar energy to said introduced air to increase the temperature of said solar heated air.

In one aspect, the heating element is an expanse of identical protrusions, e.g. pyramidal or conical, which protrude from the rear wall and are directed towards the front wall. The rear wall may also be made of the thermally insulating material, e.g. polyurethane foam. In one aspect, the air heater further comprises a flow control element by which the flow rate of the introduced air through the air heater is controllable. In one aspect, the air heater further comprises one or more conduits through which the introduced air flows from the inlet section to the outlet section, wherein each of said one or more conduits is provided with the heating element. In one aspect, the one or more conduits is integral with a wall or roof of a building having a room, or remotely spaced from a room, to be heated by the heated air.

In one aspect, the discharged heated air is in heat exchanger relation with a body of water to be heated.

Brief Description of the Drawings

In the drawings:

Figs. 1 and 2 schematically illustrate a solar air heater construction (SAHC) unit in front view and isometric view, respectively, according to an embodiment of the present invention;

Fig. 3 is a front view of two attachable segments of the air heater of Fig. 1 ;

Fig. 4 is a perspective view of a heating element which is a part of each segment of Fig. 3; Fig. 5 is a schematic illustration of a solar air heater unit, according to another embodiment of the invention;

Fig. 6 is a schematic illustration of a building comprising an air heater according to an embodiment of the invention, with two sloping walls;

Fig. 7 illustrates another embodiment that comprises two sloping walls, a short wall and a long wall, with a snow flap therebetween;

Fig. 8 shows in an expanded view of a section of the embodiment shown in Fig. 7, where the snow flap is in a first position allowing warm air to flow over a heating element in the long wall;

Fig. 9 illustrates in expanded view the same embodiment, but the flap is in a second position allowing warm air to flow into a front wall or panel of the solar heater in the long wall, and Fig. 10 shows another view of the embodiment with the flap in the same position. Detailed Description of Preferred Embodiments

Reference is made to Figs. 1 and 2, which schematically illustrate a solar air heater construction (SAHC) unit 10 in front view and isometric view, respectively, according to an embodiment of the present invention. SAHC unit 10 may comprise inlet section 12, outlet section 14 and heating section 22. Inlet section 12 may be adapted to provide a continuous or intermittent air supply into SAHC unit 10. The air may be taken from the ambient of SAHC unit 10 or from other sources, as described in detail below.

Heating section 22 may be formed, generally, as two main walls 24 and 26, substantially, but not necessarily, parallel to each other, enclosing an internal space within which air heated by solar energy is able to circulate. Front sun-facing wall 26 may be made of a transparent or translucent material which is adapted to allow sunlight rays 5 to pass therethrough into the internal space. Rear wall 24 may be made of almost any desired material which provides structural strength to the heating element, which may be placed entirely or partially in abutment with the inner face of rear wall 24. The internal space may be confined also by side walls (not shown, substantially parallel to the plane of the page) and at the other ends by inlet section 12 and outlet section 14. It will be noted that SAHC unit 10 may be built in any desired size. Accordingly SAHC unit 10 may be built in sizes that fit into constructions of buildings as external panels, substituting regular panel sections or roof panel sections. The panel may be mounted on a frame member, or any other interface member associated with a building portion, such as a wall or roof.

Typically SAHC unit 10 may be located, with respect to an external reference frame, e.g. the horizon, tilted by a tilting angle a, to set a desired sun ray impingement angle β. The sun ray impingement angle β may preferably be set as close as possible to 90° to enhance the heat transfer rate. However, this angle may be subject to other considerations, such as those dictated by the construction of a building with which SAHC unit 10 is a part. The elevation of inlet section 12 may typically be lower than the elevation of outlet section 14 in order to take advantage of the spontaneous flow of heated air inside the internal space. Yet, other configurations may be utilized. In configurations where the spontaneous flow of air is not sufficient for the intended use of SAHC unit 10, the flow of air via SAHC unit 10 may be urged by fan/blower 15, which may be located within or close to outlet section 14, as illustrated, or at other locations on the air-supply or heated-air path.

The rate of air flow through SAHC unit 10 may be controlled, for example via control of the rotational speed of fan 15, so as to ensure compliance with one operational parameter such as maximum heat transfer efficiency, constant outlet temperature, maximum temperature inside SAHC unit 10, and the like. It will be noted that by the controlling of the air flow rate via SAHC unit 10, the momentary heat flow into SAHC unit 10 by sun rays 5 may be balanced against the temperature of air provided via inlet section 12, or balanced against the temperature at outlet section 14, or against a temperature setting inside SAHC unit internal space 22C. The specific temperatures at the various locations may be measured using any desired type of temperature sensor, the rotational speed of fan 15 may be controlled using any desired speed control unit, the comparison of the control parameters so as to comply with the control equation may be done using any control unit. However, these aspects and elements of SAHC unit 10 are not part of the invention described in this application.

Heat exchangers heated by sunlight rays typically convert the energy received by the sun rays into heat by either exposing to the sun rays to a surface of material painted with a dark color, typically black, or by concentrating the rays using reflectors, lenses and the like onto a fluid conduit, such as a pipe. Such heat exchangers suffer from energy losses when the energy is in the heat phase due to the need to heat the material of which the heat exchanger or the conduit containing the heated fluid are made. The amount of lost heat energy depends on the type of material from which the heater is made, and the nature of the isolation of that heater from its ambient. The higher the specific heat of the material from which the heat exchanger is made, the higher is the heat energy absorbed in bringing the heat exchanger to its working point. Also, as the heat conductivity of a material is increased, the higher will be the heat transferred therefrom to another structural element of the air heater and not to the circulating air. For example, the specific heat of aluminum is 210 calories per degree Celsius and its heat conductivity is 220 W/m*K, of iron is 110 calories per degree Celsius and its heat conductivity is 80 W/m*K, and of copper is 92 calories per degree Celsius and its heat conductivity is 390 W/m*K. In contrast to the prior art construction of heat exchangers, SAHC unit 10, according to embodiments of the present invention, employs thermally resistive materials with a high specific heat value and with a very low heat conductivity that form the heat exchanging material underneath the heat

5 exchanging surface. For example, rigid polyurethane foam (PUR/PIR) has a specific heat of 334 calories per degree Celsius and a heat conductivity of 0.025 W/m*K. Alternatively, other thermally resistive materials may be used, such as glass fiber or rock wool.

Reference is now made to Fig. 3, which illustrates two segments 35 and 36 of the rear wall 10 24 of Fig. 1, according to an embodiment of the present invention. Each segment of rear wall 24 is configured at its two sides with a male portion 37 and a female portion 38, respectively, which facilitate coupling with adjacent rear wall segments. A perspective view of one of the segments is shown in Fig. 4.

15 A trapezoidal coupling member 39 may be used to secure together the upper straight edge 33 of each of male portion 37 and female portion 38. The coupling member 39 comprises a body 46, two angled legs 47a and 47b and four spacers 29a, 29b, 29c and 29d. A first leg 47a of coupling member 39, angled relative to the body 46, is placed on a complimentary angled wall of a male portion 37 and a second angled leg 47b is placed on a complimentary

20 angled wall of the female portion 38 adjacent to the male portion, thus the adjacent male and female portions are secured together by coupling member 39.

A multi-layered front wall is shown to be formed by two rectilinear portions 26 A and 26B, e.g. made of polycarbonate, but it will be appreciated that the front wall may comprise any 25 other number of layers.

The four spacers 29a, 29b, 29c and 29d perpendicularly extend from the body 46 of coupling member 39 distal to the legs 47a and 47b, such that there is a gap between the spacers and the legs, defining internal space 42 within which air heated by solar energy is 30 able to circulate. Furthermore, the spacers 29a and 29b, and 29c and 29d, are distanced from each other to allow the front wall to be engaged therebetween. The coupling member 39 and the male- female portions thus together serve as a skeleton for robust modular building of SAHC units 10. The heating section may comprise a heating element 32 that protrudes from the inner face 27 of lower wall 24. Heating element 32 formed as an expanse of identical multi- directionally sloping protrusions 41, such as small pyramids or cones, may be formed of an insulation material having a very low heat conductivity value, such as rigid polyurethane foam. Protrusions 41 may also be configured with any other shape having a large surface area, such as lamellae, scales, leaves, or an amorphous shape, whether smooth or roughened, for improved sun ray absorption and improved thermal conversion. Lower wall 24 may also be made of the same insulation material from which protrusions 41 are made, for a simplified manufacturing process. With respect to prior art air heaters having two dimensional protrusions, this specific form of heating element 32 provides an enlarged area of contact of the three dimensional, multi-directionally sloping protrusions 41 with the heated air flowing thereon. Additionally, the non-linear surface of heating element 32 enlarges the turbulence in the air flowing over heating element 32, thus enhancing the heat transfer value from heating element 32 to the heated air. An exemplary configuration of the protrusions 41 may be such that the angle A defined by the sloping wall of two adjacent protrusions is 30 degrees in any direction, the height of a protrusion above lower wall 24 is 49.5 mm, and the spacing between the narrow upper surface or apex of adjacent protrusions is 55 mm in one direction and 50 mm in another direction.

Protrusions 41 are painted or coated with a thin layer of heat resistant, dark paint 43, e.g. black. Paint 43 may be aluminum or copper based. The sun rays that heat the thin layer of dark paint 43 are converted into heat and raise the temperature of the paint layer. The insulation material on which the layer of paint is applied almost completely prevents the heat from being transferred to the back wall of the air heater, thus providing excellent insulation to that direction. The amount of the substance/material, e.g. paint, applied to darkened layer 43 that needs to be heated by the sun rays before the heat is transferred to the air flowing over protrusions 41 is very small. As a result, the heat losses involved in heating the heating element material are minimized and the heat conversion efficiency is enhanced. The temperature of the air circulating within the heating section is therefore to increase to a relatively high value, being dependent upon the thinness of the applied darkened layer 43.

When air is flowing over the heating element 32 at a rate that keeps the temperature of the heating element within working conditions, i.e. so as to prevent continuous damage thereto, this means that all of the extra heat is delivered to the flowing air. Accordingly, even if the temperature developing within the paint layer 43 is high, it is regulated by the rate of air flow over it, and this way heat conversion is maintained within long term operational conditions. Because the actual temperature of the air coming out of the heater is, for example, within the range of about 30-100°C, for a heater having an operational heating area of 8 square meters and an air flow speed of about 8.5 cubic meters per minute, the temperature difference between the heated air and the ambient air is kept moderate, and the heat losses, expressed by:

E_dis ~ ΔΤ * H_Conductivity, (Equation 1)

where Edi_s is the heat energy dissipated due to losses of heat conductivity;

ΔΤ is the temperature difference between the temperature inside the air heater and the temperature on the other side of the insulation material; and

H_conductivity is the specific heat conductivity of the insulation material,

are minimized. It will be apparent that the higher is the temperature difference, the higher are the heat losses. The inventor of the present invention has discovered that as the flow rate of fluid, such as air, over heating element 32 is increased, the heat transfer efficiency will be higher. A heat transfer efficiency of about 75% was able to be measured and calculated. Heat transfer efficiency HTEFF is defined as:

HTEFF = Pin / Pout x 100 (Equation 2)

= (P_sun / Qairout x ΔΤ x C_air) xl00, (Equation 3)

where P is the heat flux, Qairout is the flow rate of air out of the air heater, and Cak is the specific heat of air. Exemplary values include a sun-derived heat influx P_sun of 550 J/sec-m ,

3 3

an air flow rate Q_ai_r0ut of 0.065 m /sec, an air density of 0.168 kg/m , a temperature difference ΔΤ of 70 °C, and a specific heat C_air of 1000 J/kg-°C. Reference is now made to Fig. 5, which is a schematic illustration of a SAHC unit 400, according to another embodiment of the present invention. SAHC unit 400 comprises a heating section 402 with a heating element 432 formed similarly or identically to heating element 32 of Fig. 4 and provided with protrusions configured as small pyramids or cones. Outlet section 410 may be similar or identical to outlet section 14 of Fig. 1. Inlet section 422 may be located at the lower section of SAHC unit 400; however, the air inlet into this section is received via air supply conduit 420 located next to, and preferably under, lower wall 401 of heating section 402. This arrangement enables locating the air inlet 418 close and adjacent to air outlet 41 OA, which enables easy installation of SAHC unit 400 as part of a heating arrangement in which SAHC unit 400 may be used as part of a roof or a wall 450 of a building. The air heated thereby may be circulated into and out of that building via a single opening 452. It will be noted that the temperature of the outer face of lower wall 401, which is typically very close to that of the ambient around SAHC unit 400 due to the high level of thermal insulation provided by heating element 432, even without the additional insulation provided by air supply conduit 420, will be between the temperature of the air supplied to SAHC unit 400 and the ambient temperature, ensuring a very small temperature gradient across lower wall 401 and conduit 420 and, as a result, very low heat energy losses in that path. In order to maximize the thermal efficiency of SAHC unit 400, the front wall 440, which is transparent, may be formed using double glazing as seen in detail 445, providing enhanced thermal insulation through this wall.

The heated air SAHC unit 10 or 400 may be used for various goals, such as for heating of the internal space of a home, building or workspace, for the contribution of heated air to heat pumps used for heating swimming pools or other bodies of water, for drying air within spaces such as a home, building or workspace by using means such as a desiccant drum, for use of the heated air for heating external wall or a roof to melt accumulated snow, for use of heated air as a source of heat for cooling purpose by means of an absorption refrigerator, for accumulating heat energy by heating a material with a specific heat value, such as water, for later use, and for any other use and embodiment requiring heated water at working temperatures of 60-95°C. Reference is mow made to Fig. 6, which is a schematic illustration, in a cross-section view, of a portion of building 500 comprising air heater 480, which incorporates some elements of air heater 400 of Fig. 5. Air heater 480 is integral with a roof of building 500, and is 5 attached to one of its side walls 503 and ceilings 504.

Air heater 480 may comprise heated air outlet conduit 493, which may be formed to supply heated air to desired locations inside of building 500. Air heater 400 may further comprise air inlet section 482 through which air received in inlet section 482 from a room of building

10 500 flows and is heated. The air heated by heating element 432 is discharged from outlet conduit 493 attached to side wall 503. As described above with respect to air heater 400 of Fig. 5, the construction of the air heater provides heat insulation at its lower wall, and the continuous flow of air delivered by inlet section 482 between the heating elements 432 of air heater 400 and the roof of building 500 ensures enhanced heat insulation at the location

15 where air heater 400 is installed.

One added benefit of this installation is the possibility to operate air heater 400 without requiring the use of an air filter, since the air circulated through air heater 400 is taken from the inside of a closed building. Thus, an air heater such as air heater 400, when installed as 20 part of the roofing of a building, such as building 500, may provide heat insulation between the outside ambient and the inside of building 500 substantially as good as a regular roofing element, while providing heated air into building 500 through outlet conduit 493.

It will be appreciated that air heater 400 may be formed integrally with other parts of a 25 building, for example a single external wall. Air heater 400 may comprises any number of conduits to suit the requirements and needs.

Fig. 7 illustrates another embodiment 600 that comprises two sloping walls 687, 688 with a snow flap 660 therebetween.

30

In general the longer wall 688 has a gentler slope and is better oriented in relation to the sun to heat air. The shorter wall 687 essentially connects the longer wall 688 to the floor of the house 500. However, the shorter wall 687 also contains air heating means. In some environments, seasons and locations, in particular in cold countries, the orientation of the sun to the house is such that the amount of heating by the shorter wall 687 is significant and may surpass the heating capacity of the longer wall 688 per unit area. Moreover, the short 5 wall 687 has an important role in improving the heating capacity of the longer wall 688, as will be explained below.

As shown in an expanded view of a section of the embodiment 600, in Fig. 8, each wall 687, 688 comprises a heating element 632 and front panels 645. The heating elements and 10 front panels of the two alls are separated by the flap 660. The flap 660 comprises a handle 662 and a shutter 664.

When the flap 660 is orientated as in Fig. 8 air from the short wall 687 can freely flow to the long wall 688, essentially passing over the heating element (not shown) of the long wall 15 687.

However, as shown in expanded view Fig. 9, importantly the front panel 645 of the long wall 688 comprises long passages 646 extending through the panel 645 so that heated air from the short wall 687 can pass through the panel 645 to a pipe 694 that extends from the

20 long wall 688 to inside the house 500. The flap 660 is oriented to direct the shutter 664 to block passage of air from the short wall 687 to the heating element of the long wall 688 and allow that air to entirely pass through the front panel 645. This positioning allows heating of the front panel, which can be very useful to help melt snow from the long wall 688. Snow will generally not accumulate on the short wall 687 because the wall is close to

25 upright, and thus the short wall 687 serves together with the flap 660 to allow releasing snow from the more horizontal long wall. The melting of the snow may allow the long wall to resume heating air, and may also stop the absorbance of heat from the house by the snow.

Expanded view Fig. 10 also shows the flap positioned, by control of the lever 662 of the 30 flap 660, to allow air into the front panel. Optionally there is a fan, blower or other means 691 to help draw/direct/distribute the heated air into the house 500. The heated air con vector 691 may help convey the heated air to a heat exchanger or storer 695, that may for example utilize some of the heat to heat some water.

While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried out with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without exceeding the scope of the claims.

Claims

1. A solar air heater, comprising:

an enclosure comprising a front transparent or translucent sun-facing wall, a rear wall, and side walls between said front and rear walls;

an inlet section by which air is introducible to said heater;

an outlet section from which air heated by solar energy is dischargeable; and a heating element interposed between said front and rear walls and across which said introduced air is flowable, wherein said heating element comprises a plurality of three dimensional, multi-directionally sloping protrusions made of a thermally insulating material each of which is coated with a layer made of a heat resistant, dark-color material for maximizing transfer of solar energy to said introduced air to increase the temperature of said solar heated air;

wherein the heating element is an expanse of identical protrusions that protrude from the rear wall and are directed towards the front wall, and

wherein the rear wall is also made of the thermally insulating material.

The solar air heater according to claim 1 , wherein the protrusions are pyramidal or conical.

The solar air heater according to claim 1 , further comprising a flow control element by which the flow rate of the introduced air through the air heater is controllable.

The solar air heater according to claim 1, wherein the thermally insulating material is polyurethane foam.

The solar air heater according to claim 1, wherein the thermally insulating material is glass fiber or rock wool.

6. The solar air heater according to claim 1, further comprising one or more conduits through which the introduced air flows from the inlet section to the outlet section, wherein each of said one or more conduits is provided with the heating element.

7. The solar air heater according to claim 6, wherein the one or more conduits is integral with a wall or roof of a building having a room to be heated by the heated air.

5

The solar air heater according to claim 6, wherein the one or more conduits is integral with a wall or roof of a building remotely spaced from a room to be heated by the heated air.

The solar air heater according to claim 1 , wherein the discharged heated air is in heat exchanger relation with a body of water to be heated.

The solar air heater according to claim 1 ,

wherein the rear wall comprises segments, each segment comprising a male portion and a female portion;

wherein the front wall comprises rectilinear portions;

wherein the heater further comprises a plurality of coupling members, each coupling member comprising a body two angled legs and four spacers, and

wherein:

20 the first leg of coupling member is angled relative to the body, and is placed on a complimentary angled wall of a male portion and a second angled leg is placed on a complimentary angled wall of a female portion, whereby adjacent male and female portions are secured together by coupling member, and

the four spacers perpendicularly extend from the body of coupling member distal to

25 the legs, such that there is a gap between the spacers and the legs, defining internal space within which air heated by solar energy is able to

circulate; and the spacers are distanced from each other to allow rectilinear portions to be engaged therebetween.

30 11. A system for heating air for a house, the system comprising: a short slanted wall of the house; a long slanted wall of the house, and a flap therebetween; wherein the short slanted wall is upright relative to the the short wall; the short wall and long wall each comprising the solar heater of claim 1 ;

wherein the sun-facing wall of the long wall has passages therethrough;

wherein the flap is configured to allow in a first position warm air to flow from the short wall through the sun-facing wall of the long wall and in a second position warm air to flow over the heating element of the long wall.