WO2003040631A1

WO2003040631A1 - Solar heating panel

Info

Publication number: WO2003040631A1
Application number: PCT/NO2002/000405
Authority: WO
Inventors: Thomas Wahl GJERSØE
Original assignee: Gjersoee Thomas Wahl
Priority date: 2001-11-06
Filing date: 2002-11-06
Publication date: 2003-05-15
Also published as: NO20015429D0; NO315997B1; NO20015429L

Abstract

A solar heating panel comprising three substantially parallel plates, a front plate (10) a middle plate (12) and a rear plate (13) assembled in distance to each other, where at least the front plate (10) and the middle plate (12) are glass plates and the rear plate (13) is energy absorbing, and where a liquid may flow between the middle plate (12) and the rear plate (13), where a coating (11, 11') that is transparent to visible light and short waved infrared radiation but is reflecting long waved infrared radiation is coated on at least one of the glass surfaces facing into the room between the front plate and the middle plate.

Description

SOLAR HEATING PANEL

The present invention regards an improved solar heating panel, more specifically a liquid based solar heating panel with a coating that is transparent to visible light and short wave infrared radiation, but which reflects long wave infrared radiation (energy coating).

Liquid based solar heating panels have existed for decades. A traditional solar heating panel comprises a heat absorbing surface across which a fluid such as a gas or a liquid flows, either through a piping system or between two plates, e.g. glass plates. The fluid is heated by the rays of the sun and used as a medium for transporting the heat from the solar heating panel to the location where the heat is to be used or stored.

When using a liquid such as water to transport the heat, leaks may quickly become a problem. Even the smallest leak would cause a loss of medium and possibly damage to the building. Thus liquid based solar heating panels have so far been based mainly on circulation of liquid through piping in the solar heating panel.

Furthermore, solar heating panels have mainly been used as a supplement to heating systems. As the requirement for heating is not normally concurrent in time with the heating capacity of the sun, means have been developed for storing heat for a longer or shorter period of time. The storage systems have proven to be relatively inefficient. Moreover, the users of such systems have had to install other heating systems in parallel with the solar heating system. As a result of this, such systems have been very expensive and not very cost-effective.

Solar heating panels having a plurality of plates for insulation of the solar heating panel and prevention of heat loss from the working fluid to the surroundings are known from US 4 038 967.

The idea of coating glass with a so-called "energy coating" that is transparent to visible light and short wave infrared radiation, but which reflects long wave infrared radiation, i.e. heat radiation from a surface having a temperature of 70 - 80 °C and down, has been known for years. Such coatings have been employed to reduce the heat radiation through window panes into or out from the premises inside. In so-called energy glass, the coating is used to reflect and thereby prevent heat radiation from the premises inside from escaping. In a shading window pane with two layers of glass, the outer pane is here dark in order to absorb part of the solar energy. The dark pane is then heated up, and emits infrared radiation which is reflected from the premises by means of a coating on that side of the inner pane which faces in between the panes.

However such energy coatings are susceptible to contamination and humidity. Attempts to use energy coatings in air based solar heating panels have not been very successful, as pollution in the air has deposited on the energy coating, reducing and finally ruining its effect. Humidity and water will also ruin the effect. Therefore, the use of such an energy coating in connection with water based solar heating panels has not been considered previously.

Furthermore, the use of other types of coating in solar heating panels for the purpose of increasing the amount of energy obtained from these, has been described previously. Thus from EP 017 415 there is known a solar heating panel comprising three parallel plates, where the outside of the middle plate has a coating. This coating consists of a reflective layer exemplified by aluminium foil, located nearest the plate. This reflective coating is in turn covered with a light/heat absorbing layer of germanium, which in turn is covered by a layer of carbon. This triple layer absorbs light, converting it to heat. The coating is transparent to heat radiation, so as to allow this into the working fluid behind the middle plate in order to heat it. Thus the coating is an expensive and complex energy absorbing coating, and not a coating that is transparent to light and reflects heat radiation.

From DE 2 454 206 there is known a solar heating panel having a heat absorbing coating on one or more inner surfaces. The coating described therein changes colours at a set temperature in order to avoid overheating of the heating medium, and is not a coating. The object of the present invention is to provide a solar heating panel and a system comprising a solar heating panel, which can cut costs for the user by reducing the need for electricity or other energy carriers for heating of water.

According to a first aspect of the present invention, a solar heating panel is provided, comprising three essentially parallel plates; a front plate, a middle plate and a rear plate are mounted to each other with mutual spacing, where at least the front plate and the middle plate are glass plates, where at least one of the middle plate and the rear plate is energy absorbing, and where liquid may flow between the middle plate and the rear plate, where a coating is applied to at least one of the glass surfaces facing into the space between the front and middle plates, which coating is transparent to visible light and short wave infrared radiation but reflects long wave infrared radiation (energy coating).

Preferably, all the plates are glass plates.

Preferably also, a dye is added to the liquid in order to increase the absorption of energy.

According to a preferred embodiment, the middle plate is energy absorbing.

According to a second preferred embodiment, the rear plate is energy absorbing.

According to a preferred embodiment, the surface of the front plate facing into the space between the front and middle plates is coated with a coating (11, 11') that is transparent to visible light and short wave infrared radiation but reflects long wave infrared radiation (energy coating).

According to a second preferred embodiment, the surface of the middle plate facing into the space between the front and middle plates is coated with a coating (11, 11') that is transparent to visible light and short wave infrared radiation but reflects long wave infrared radiation (energy coating).

According to another aspect of the present invention, a system is provided for heating of water, the system comprising a solar heating panel as specified above, together with a closed circulation system for the water based liquid, which system comprises pipes and a heat exchanger in which the water based liquid exchanges heat with cold water that is to be heated further in a water heater.

In the following, the present invention will be described in greater detail with reference to a preferred embodiment and the accompanying figures, in which:

Figure 1 is a perspective view of a solar heating panel according to the present invention; and Figure 2 shows a section A-A in Figure 1.

Figure 1 is a perspective view of a solar heating panel 1 according to the present invention. Cold liquid is introduced into the solar heating panel 1 through a liquid inlet 2 and heated liquid is extracted through a liquid outlet 3.

Liquid inlet 2 and liquid outlet 3 are drawn as one inlet and one outlet. The outlet and/or the inlet may also comprise several inlets or outlets respectively, distributed along the side edges in order to ensure an even distribution of the liquid flowing across the surface area of the solar heating panel.

The liquid employed as a working medium or heat transport medium in the solar heating panel may circulate through the solar heating panel by convection, but preferably, the liquid is circulated by means of a pump. In order to avoid or reduce the problem of liquid leaking out of the solar heating panel, it is important to maintain the liquid at a low pressure such as from below atmospheric pressure to about 2 atmospheres. Preferably, the liquid circulating through the solar heating panel is water based, e.g. water to which antifreeze solution has been added in order to prevent freezing, and possibly also dye to improve the absorption of heat. However, other liquids may also be used.

The liquid circulates in a closed system comprising the solar heating panel 1, pipes 4, 5 and a heat exchanger 6 in which the hot water from the solar heating panel 1 exchanges heat with cold water. The heat exchanger 6 may be an integral part of a water heater in which the incoming cold water is heated, or it may be a separate unit for heating the water going into a water heater.

Figure 2 shows a cross section of the present solar heating panel, which in a preferred embodiment comprises three glass plates and/or plates, a front glass plate 10, a middle glass plate 12 and a rear plate 13, preferably also made from glass. Preferably, the rear plate 13 and/or the middle glass plate is/are energy absorbing, either by being dark in itself or by being covered by a dark, energy absorbing coating, in order to ensure maximum absorption of solar radiation and thereby heating of the solar heating panel. Preferably, the rear plate is made from glass in order to avoid stresses in the solar heating panel caused by the different coefficients of expansion of different materials. Preferably, the front and middle glass plates and the rear plate are all made from tempered glass.

The glass plates 10, 12 are 13 are kept apart by spacers 5 glued to the glass plates by use of a suitable adhesive. The spacers 15 are adjusted so as to maintain the desired spacing between the glass plates. The distance between the front and the middle glass plates and between the middle and rear glass plates respectively, may as an example be 10 - 20 mm, without limiting the invention to this. A moulding 14 is fitted around the edge of the glass for protection.

At least one of the glass surfaces facing into the space between the front plate 10 and the middle plate 12 is coated with an energy coating 11, 11'. This coating admits visible light and short wave infrared radiation without hindrance but reflects long wave infrared radiation as stated above, preventing this from escaping the solar heating panel.

The energy coating 11 is of the same type as that used for so-called "energy glass". Here, the energy coating is used to keep the heat, i.e. long wave infrared radiation, inside the solar heating panel. Such energy coatings are known to those skilled in the art of window glass, and they will know how such energy coatings are to be obtained and treated. The type of energy coating may vary and, depending on the choice of coating, will reflect and thereby prevent the loss of 85 to 98% of long wave infrared radiation from the solar heating panel.

By indirectly using the solar heating panel to preheat water that is to be heated further in a water heater, either in an integral unit in the actual water heater or in connection with the pipe supplying the water heater with cold water, it becomes possible to utilise the solar heat all year round. There is a requirement for hot water both in summer and winter. This is in strong contrast to air-borne solar heating panels or solar heating panels connected to the heating system of a building. The problem with such systems is that the heating requirements is out of phase with the availability of solar energy for heating. Attempts to store heat over a longer period, e.g. in a bed of rocks under a building or similar, have generally failed.

The indirect heating also makes it possible to maintain a low pressure in the solar heating panel, while water at a higher pressure is heated in the heat exchanger. This reduces the risk of leakage and any consequent damage to the building.

The present solar heating panel can be installed directly on the outside wall, thus forming an integral part of the facade of a building. In order to avoid heat loss from the back of the solar heating panel, the back should be insulated. According to an embodiment, it may be possible to circulate air at the back of the solar heating panel when water heating is not required, thereby to heat air that is passed into the building for heating purposes. Calculations of total solar flux in Oslo for a vertically mounted solar heating panel on a clear day during the various seasons yield the following values, all values at 12 noon. The results of the calculations are as follows:

These calculations show that the solar heating panel may actually contribute significantly to the heating of water during all seasons, also when the sun is at its lowest.

These calculations show the energy yield of a solar heating panel mounted flat on a facade. However, the present solar heating panel may be installed at an angle to the support, if required. Optionally, the solar heating panel may be mounted so as to be free-standing, on a rack on a roof or other support.

Claims

C l a i m s 1.

A solar heating panel comprising three essentially parallel plates, a front plate (10), a middle plate (12) and a rear plate (13) mounted together with mutual spacing, where at least the front plate (10) and the middle plate (12) are glass plates, where at least one of the middle plate (12) and the rear plate (13) is energy absorbing, and where a liquid may flow between the middle plate (12) and the rear plate (13), where a coating (11, 11 ') is applied to at least one of the glass surfaces facing into the space between the front and the middle plates, which coating (11, 11 ') is transparent to visible light and short wave infrared radiation but reflects long wave infrared radiation.

2.

A solar heating panel according to Claim 1, wherein all the plates (10, 12, 13) are glass plates.

3.

A solar heating panel according to Claim 1 or 2, wherein a dye has been added to the liquid in order to increase the energy absorption.

4.

A solar heating panel according to one or more of the preceding claims, wherein the middle plate (12) is energy absorbing.

5. A solar heating panel according to one or more of the preceding claims, wherein the rear plate (13) is energy absorbing.

6.

A solar heating panel according to one or more of the preceding claims, wherein the surface of the front plate (10) which faces into the space between the front and the middle plates is coated with the coating (11, 11 ') that is transparent to visible light and short wave infrared radiation but reflects long wave infrared radiation.

7.

A solar heating panel according to one or more of the preceding claims, wherein the surface of the middle plate (12) which faces into the space between the front and the middle plates is coated with the coating (11, 11') that is transparent to visible light and short wave infrared radiation but reflects long wave infrared radiation.

8.

A system for heating of water, wherein the system comprises a solar heating panel according to Claim 1, together with a closed circulation system for the liquid, comprising pipes (4, 5) and a heat exchanger (6) in which the liquid exchanges heat with cold water that is to be heated further in a water heater.