WO2006038791A1

WO2006038791A1 - Cooled light source unit

Info

Publication number: WO2006038791A1
Application number: PCT/NL2005/000664
Authority: WO
Inventors: Johannes Van Tilborgh
Original assignee: Johannes Van Tilborgh
Priority date: 2004-09-10
Filing date: 2005-09-12
Publication date: 2006-04-13
Also published as: NL1027017C2

Abstract

A light source unit (2) comprises a housing (6) which accommodates at least a light source (7), a light transmission member (9) disposed in an opening of the housing (6) such that it receives at least a part of the light from the light source (7), which light transmission member (9) is transparent for at least a part of the light which it receives, and a unit cooling system (8) which is connectable to an external cooling circuit (3) in which a cooling medium can be circulated. The unit cooling system (8) includes a cooling member (15) which is connected to the light transmission member (9) for cooling it when the light source unit (2) is in operation and a cooling medium is circulated through the unit cooling system (8). The light source unit (2) is applicable in a space (1) such as in a greenhouse so as to provide growth light to products, while heat production by the light source units (2) is minimized.

Description

Cooled light source unit

The present invention relates to a light source unit comprising a housing which accommodates at least a light source, a light transmission member disposed in an opening of the hous¬ ing such that it receives at least a part of the light from the 5 light source, which light transmission member is transparent for at least a part of the light which it receives, and a unit cool¬ ing system which is connectable to an external cooling circuit in which a cooling medium can be circulated.

Such type of light source unit is known in the art. One

LO of the known units is described in the US patent 3,869,605. The document shows a light source unit which can be cooled by a cooling fluid which flows behind a light reflector of the unit. The disclosed light source unit comprises thermal insulation to minimize heat transfer from the inner side to the outer side of

L5 the unit.

It is an object of the present invention to provide a light source unit which emits at least a part of the light from the light source with reduced heating of the environment of the unit.

20 To obtain this object, the unit cooling system includes a cooling member which is connected to the light transmission member for cooling it when the light source unit is in operation and a cooling medium is circulated through the unit cooling sys¬ tem.

25 Due to the invention the light transmission member is cooled directly so that heat radiation from the light transmis¬ sion member during operation is reduced.

A preferred embodiment is a light source unit in which the light transmission member includes a light filter, which is

30 transparent for light of wavelengths within a predetermined range, whereas the light filter absorbs at least a part of the . light of wavelengths outside said range. This has the advantage that only light of a desired wavelength is transmitted through the light filter. Due to the invention the light transmission 5 member is cooled so that the heat which is generated by absorp- tion of a part of the light will be transferred from the light filter to the cooling medium.

A more preferred embodiment, in particular for use in a greenhouse, includes a light filter which is transparent for PAR light, i.e. having wavelengths between 400 and 700 nm. PAR means Photosynthetic Active Radiation, which is the range of light wavelength which stimulates the growth of products in a green¬ house such as plants and flowers and the like. Light of wave¬ lengths outside said range would lead to a temperature increase of the environment because that part of the light is converted to heat in the greenhouse. It is an advantage when only the de¬ sired PAR light is available in the greenhouse while the outer side of the entire light source unit remains cool.

An alternative embodiment is a light source unit, in which the light filter includes one or more wavelength-selective mirrors which are able to reflect light of wavelengths outside said range. This has the advantage that the heat generation in the light filter is reduced. The heat of the reflected light will be generated elsewhere in the light source unit where the reflected light is absorbed. This is beneficial because it is generally easier to cool elsewhere in the light source unit than the light filter, because the cooling member connected to the light filter should preferably not obstruct the light emission from the light source unit. The advantage of a light filter which has thermal con¬ ducting properties is that the heat transfer to the cooling mem¬ ber is facilitated.

An alternative embodiment is a light source unit, in which the light transmission member includes an insulation win- dow, which is located in front of the light filter viewed from outside the light source unit, forming an insulation chamber be¬ tween the insulation window and the light filter, said insula¬ tion window which is at least transparent for light of wave¬ lengths within the predetermined range. The insulation chamber serves to reduce heat transfer from the light filter to the in¬ sulation window so as to keep the insulation window at a low temperature.

An embodiment in which the insulation chamber communi¬ cates with the cooling member so as to cool a fluid which is in the insulation chamber, which fluid is transparent for light of wavelengths within the predetermined range has the advantage that heat transfer from the light filter to the insulation win¬ dow is further reduced. A preferred embodiment of the cooling member includes a heat exchanger for effective heat transfer and separation of the cooling medium and a local cooling fluid which cools the light filter.

The light source may comprise an electric lamp, but an alternative light source comprises a hot surface, heated by a flame such as a ceramic foam burner, which is generated by burn¬ ing a fuel. The fuel is preferably a gaseous fuel as this is of¬ ten available near greenhouses, for example. The advantage of this alternative light source is its higher efficiency with re- spect to an electrical lamp, because it lacks the conversion of fuel to electricity.

In case the light source comprises a hot surface, heated by a flame, it is advantageous when the cooling medium comprises air and the unit cooling system includes a line con- nected to the light source so as to enable supply of combustion air to the flame. Thus, it is not necessary to introduce an ad¬ ditional combustion air supply line.

The invention also provides a building structure such as a greenhouse comprising a space, in which light is emitted by light source units described above and said space includes a cooling circuit to which the light source units are connected, said cooling circuit is adapted such that heat generated by the light source units is transferable by the cooling medium through the cooling circuit to a collector. The advantage is that such a space is illuminated by light within a desired wavelength range only, whereas the light source unit has a reduced contribution to heating of the space.

These and other aspects and advantages of the invention will be apparent from the following description with reference to the drawings. In the drawings:

Fig. 1 is a schematic perspective plan view of a space, such as a greenhouse which is provided with light source units according to the invention. Fig. 2 is a cross sectional view of an embodiment of a light source unit according to the invention.

Fig. 3 is a cross sectional view of an alternative em¬ bodiment of the light source unit.

Fig. 1 illustrates a space 1 such as in a greenhouse in which (not shown) products like plants, flowers, vegetables or the like are grown. Generally, such a growth chamber is provided with a large number of light source units 2 in order to supply growth light to the products, further called PAR light (Photo- synthetic Active Radiation) . PAR light stimulates the growth of plants and other products and has a wavelength in a range be¬ tween about 400 and 700 run. Light having a wavelength outside this range is not necessary for growth of the products in the greenhouse and leads to undesired temperature increase in the space 1. Besides, the light source units 2 become hot during op¬ eration, so that they will heat the environment by convection and radiation. A too high temperature in a greenhouse adversely affects the growth of products. In Fig. 1 each light source unit 2 is connected to a cooling circuit 3, which cooling circuit 3 is connected to a collector 4. The cooling circuit 3 is filled with a cooling me¬ dium, which is circulated through the cooling circuit 3 by a pump 5. The cooling medium which is heated by the light source units 2 is transferred to the collector 4. The heat collected there can be used for other energy users such as steam produc¬ tion for an electric generator, for example. The cooling medium has a low temperature when it leaves the collector 4 and flows in the direction of the light source units 2. The collector is preferably located in an other space than the space 1 in which the light source units 2 are located so as to avoid that the space 1 is heated by the collector. The heat can also be di¬ rectly converted in the light source unit 2, such as for steam production. Such a cooling system 3 for light source units 2 is particularly beneficial for a greenhouse in periods of high am¬ bient temperature when still light within the specified range is required but heat radiation should be avoided. When the cooling circuit 3 and the light source units 2 are applied in a green- house the cooling circuit lines should be integrated in building profiles between windows or frames of the greenhouse as much as possible so as to minimise sunlight obstruction. Besides, the lines of the cooling circuit 3 in the space 1 should be thermally insulated. Alternatively, the lines of the cooling circuit 3 can be located below the products in the space 1, for example, subterranean. In that case the dimensions in terms of light obstruction are less critical.

In Fig. 1 it can be seen than one group of light source units 2 is connected to the cooling circuit 3. It is possible to extend the system by more groups in the space 1. Each group of light source units 2 can be connected to main lines of the cool¬ ing circuit 3, which main lines collect the heated cooling me¬ dium from the different groups and transfers it to the collector 4. A temperature control device may control the flow of the cooling medium through the cooling circuit, possibly per group of light source units 2.

If different groups of light source units 2 are cooled at the same time a simple temperature control system may be ap- plied. The cooling circuit can be designed such that the pres¬ sure drop over each group of light source units 2 is equal and the cooling circuit 3 can be constructed according to the Tichelmann system. This way of constructing the cooling circuit 3 provides an equal distribution of the cooling capacity over the groups of light source units 2.

If lines of the cooling circuit 3 are located within the light beam from the light source unit 2 they should reflect light such as to minimize possible absorption.

Fig. 2 shows an embodiment of a light source unit 2 ac- cording to the invention. The light source unit 2 comprises a housing 6. The housing 6 accommodates a light source 7, in this embodiment an electric lamp, a unit-cooling system 8, a light transmission member 9, a reflector 10 and a thermal insulation 11. The unit cooling system 8 of this embodiment is con- nectable to the external cooling circuit 3 by an inlet and out¬ let opening 12 for the cooling medium. The cooling medium, which is preferably a liquid such as water, is circulated through the unit cooling system 8. In the embodiment shown in Fig. 2 the unit cooling system 8 is provided with three heat exchangers 13, 14 and 15. The heat exchanger which is denoted by 13 in Fig. 2 cools a chamber in which a socket of the electric lamp 7 is dis¬ posed. This chamber may also be provided with electrical devices for operating the light source 7, such as a transformer or a starter, for example. The heat exchanger which is denoted by 14 in Fig. 2 cools the reflector 10. The heat exchanger 15 is con¬ nected to the light transmission member 9 and envelopes the light transmission member 9 viewed in a direction perpendicular to the plane of the light transmission member 9.

In the embodiment of Fig. 2 the light transmission mem¬ ber 9 includes a light filter 16 which is divided into two por¬ tions so as to form a chamber for a cooling fluid between the two portions. The light transmission member 9 also includes an insulation window 17, forming an insulation chamber 18 between the light filter 16 and the insulation window 17.

The light filter 16 is transparent for light of wave lengths within a predetermined range. For a greenhouse this range is preferably between 400 and 700 Nm. The light filter 16 absorbs at least a part of the light of wavelengths outside said range. As a consequence of the light absorption the light filter temperature will increase. In the embodiment of Fig. 2 the light filter 16 is cooled by a cooling fluid between the two portions of the light filter 16, which cooling fluid is circulated along the heat exchanger 15. The heat exchanger can be shaped as a tube enveloping the light filter 9, located preferably at a higher level than the space between the two portions of the light filter 9 in order to stimulate natural convection of the cooling fluid such as shown by arrows around the heat exchanger 15 and in the light filter 16 in Fig. 2. Circulation of the cooling fluid can also be forced by a pump (not shown) . Due to the heat transfer from the light filter 16 to the cooling fluid the temperature of the light filter 16 can be kept low. If the heat exchanger 15 comprises a tube and this is exposed to the light source the tube should at least reflect PAR light on the portion which faces to the light source. As the light source unit 2 also comprises insulation 11 at the inner side of the housing 6 the temperature of the outer side of the light source unit 2 will stay at a low level. Of course, the cooling fluid between the two portions of the light filter 16 should be trans¬ parent for light of wavelengths within the PAR range. The cool¬ ing fluid is preferably a liquid because of better heat conduc¬ tion properties than a gas. Note that the cooling fluid in the 5 light filter 16 may be a different fluid with respect to the cooling medium in the cooling circuit 3. Nevertheless, the cool¬ ing fluid may also be the same cooling medium of the cooling circuit 3 when eliminating the heat exchanger 15. In the latter case the cooling medium flows between the two portions of the

.0 light filter 16. This is allowable as long as the cooling medium is transparent for PAR light.

In a preferred embodiment the light filter 16 is made of a conductive material, such as Perspex or an other material containing conductive elements such as diamond, and the heat ex-

.5 changer 15 is directly communicating with the light filter 16. This has the advantage of an effective cooling, because heat is directly transferred from the light filter 16 to the heat exchanger 15, whereas the filter may be single-walled.

Fig. 3 shows an alternative embodiment of the light

10 source unit 2. It comprises an electric lamp as light source 7 and a wavelength-selective reflector 10. This reflects PAR light and is transparent or absorbs light which has a wavelength out¬ side the range of PAR light. The light filter 16 is a wave¬ length-selective mirror which is transparent for PAR light and

!5 reflects light outside the PAR light range. In Fig. 3 a light beam containing PAR and non-PAR light originating from the light source 7 is indicated by the line 19, the reflected PAR light beam is indicated by the line 19' and the transmitted PAR light beam through the light transmission member 9 is indicated by the

!0 line 19' ' . Another light beam containing PAR and non-PAR light is indicated by the line 20, the reflected non-PAR light beam by the line 20' and the transmitted PAR light beam by the line 20'' . The reflected non-PAR light indicated by 20' is absorbed by the reflector 10 or the material behind the reflector 10

!5 viewed from the light source 7. The generated heat in and behind the reflector 10 viewed from the light source 7 is transferred to the heat exchanger 14.

Alternatively, the reflector may comprise near infrared photocells which absorb at least a part of the non-PAR light and convert at least a part of the received light energy into elec¬ tricity.

In the embodiment of Fig. 2 and 3 the light source 7 comprises an electric lamp. An alternative embodiment of the light source 7 may be a hot surface, heated by a flame, which is generated by burning a fuel. A gaseous fuel is preferred as this is often available at a greenhouse. In that case an additional line for combustion air supply can be mounted to the light source unit 2. It is also possible to use air as a cooling me- dium in the cooling circuit 3 and to make a line between the unit cooling system 8 and the light source 7 so as to supply combustion air to the light source 7. The exhaust gases of the flame can be cooled by the cooling medium as well (not shown) . In an embodiment in which the light source unit 7 is a hot sur- face, heated by a flame, it is important to keep the surface temperature at a high level so as to generate sufficient PAR light. This can be optimised by a reflector 10 which reflects light over a broad radiation spectrum and a light filter 16 which reflects wavelengths outside the PAR range. This means that the non-PAR light is reflected to the light source 7, thereby increasing its temperature. As less fuel has to be sup¬ plied the efficiency of the light source unit 2 has increased.

From the foregoing it will be clear that the invention provides a light source unit 2 which is able to emit light within a predetermined wavelength, preferably between 400 and 700 nm as growth light for products in a space 1 such as in a greenhouse, whereas the light source unit 2 internally absorbs and/or reflects light of wavelengths outside this range. The heat which is generated inside the light source unit 2 is trans- ferred via a cooling circuit 2 to a central collector 4 for col¬ lecting heat to be used for other purposes. Due to the features of the light source unit 2 a high efficiency, low-temperature light source unit is created.

The invention is not restricted to the above-described embodiments as shown in the drawings, which can be varied in several ways without departing from the scope of the claims. For example, the heat exchanger 15 adjacent to the light transmis¬ sion member may be extended by more heat exchangers. Further- more, the cooling medium may be a liquid or a gaseous cooling medium, for example.

Claims

1. Light source unit (2) comprising a housing (6) which accommodates at least a light source (7), a light trans¬ mission member (9) disposed in an opening of the housing (6) such that it receives at least a part of the light from the light source (7), which light transmission member (9) is trans¬ parent for at least a part of the light which it receives, and a unit cooling system (8) which is connectable to an external cooling circuit (3) in which a cooling medium can be circulated, characterized in that the unit cooling system (8) includes a cooling member (15) which is connected to the light transmission member (9) for cooling it when the light source unit (2) is in operation and a cooling medium is circulated through the unit cooling system (8) .

2. Light source unit (2) according to claim 1, wherein the light transmission member (9) includes a light fil¬ ter (16), which is transparent for light of wavelengths within a predetermined range, whereas the light filter (16) absorbs at least a part of the light of wavelengths outside said range.

3. Light source unit (2) according to claim 2 for use in a greenhouse, wherein the light filter (16) is transparent for PAR light, i.e. having wavelengths between 400 and 700 nm.

4. Light source unit (2) according to claims 2 or 3, wherein the light filter (16) includes one or more wavelength- selective mirrors which are able to reflect light of wavelengths outside said range.

5. Light source unit (2) according to claims 2 - 4, wherein the light filter (16) has thermal conducting properties.

6. Light source unit (2) according to one of the claims 2 - 5, wherein the light transmission member (16) in- eludes an insulation window (17), which is located in front of the light filter (16) viewed from outside the light source unit (2), forming an insulation chamber (18) between the insulation window (17) and the light filter (16), said insulation window (17) which is at least transparent for light of wavelengths within the predetermined range.

7. Light source unit (2) according to claim 6, wherein the insulation chamber (18) communicates with the cool¬ ing member (15) so as to cool a fluid which is in the insulation chamber (18), which fluid is transparent for light of wave-

5 lengths within the predetermined range.

8. Light source unit (2) according to one of the pre¬ ceding claims, wherein the cooling member (15) includes a heat exchanger.

9. Light source unit (2) according to one of the pre- 10 ceding claims, wherein the light source (7) comprises an elec¬ tric lamp.

10. Light source unit (2) according to one of the claims 1 - 8, wherein the light source (7) comprises a hot sur¬ face, heated by a flame, which is generated by burning a fuel,

L5 preferably a gaseous fuel.

11. Light source unit (2) according to claim 10, wherein the cooling medium comprises air and the unit cooling system (8) includes a line connected to the light source (7) so as to enable supply of combustion air to the flame.

20 12. Building structure comprising a space (1), such as a greenhouse, in which light is emitted by light source units (2) according to one of the preceding claims and said space (1) includes a cooling circuit (3) to which the light source units (2) are connected, said cooling circuit (3) is adapted such that

25 heat generated by the light source units (2) is transferable by the cooling medium through the cooling circuit (3) to a collec¬ tor (4) .

13. Building structure according to claim 12, wherein cooling circuit lines and/or electric wires for the light source

30 units (2) and/or the light source units (2) are integrated in the building structure, particularly in a greenhouse in profiles between windows so as to minimize sun light obstruction.