Abstract:
A controller for an energy management system that controls the amount of light allowed into an area is provided. The system comprises a louver assembly and a light sensor contained within a light well. The light sensor is in communication with a controller that manages the position of the louvers in the system and controls the amount of light allowed through the system. The system further comprises thermal sensors in communication with the controller, which allow for management of the louvers&#39; position to maximize energy efficiency.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims benefit of U.S. Provisional Patent Application Ser. No. 61/703,330 entitled “SKYLIGHT ENERGY MANAGEMENT SYSTEM,” filed with the U.S. Patent and Trademark Office on Sep. 20, 2012 by the inventor herein, the specification of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to radiant energy management, and more particularly to controllers for use with systems for capturing solar energy to manage illumination and temperature within a defined space. 
     BACKGROUND OF THE INVENTION 
     Human thermal comfort is the function of both the air conditions (that is, temperature and air velocity) as well as the radiant environment of the occupants. Alternative types of heating systems, known as radiant heating systems, that use fluid circulated in the floors and/or walls of a building instead of forced hot air are common. Higher floor and/or wall temperatures provide a warm, radiant environment for the occupants which allows the same degree of comfort with a lowered air temperature. Each degree of setpoint temperature reduction can save 2 to 5% of the heat required for a building. In addition, the power required to circulate fluid through tubes in the floor is less than the power required to circulate warm air to deliver the same amount of heat. Further, the circulating air makes the occupant feel colder, negating some of the warming effect. 
     The most common method of radiant heating, via hydronic fluid circulation, has drawbacks. First, the necessary fluid lines must be embedded in the floor of the space, at significant expense. Retrofit applications of radiant heating are much more expensive, because retrofitting the tubes requires either replacement of the floor, or the addition of a new layer of concrete in which to embed the tubes, which adds further costs and construction complexities. Second, the thermal energy is delivered by conduction through the floor structure, and so the entire mass of the floor must be heated, leading to a large time lag between the initiation of heating from the system and the temperature rise of the floor—typically 30 minutes to one hour. This makes it impossible for the thermal control system to respond to many normal changes in the heating load or changes in the desired temperature of the room. Finally, common floor coverings and furnishings such as rugs, carpets, furniture and cabinets act as insulators to conduction of heat from the floor, which reduces the effectiveness of the heating and further increases the time lag in responding to changes in load and set point. Thus, there remains a need in the art for applications of radiant heating that avoid such disadvantages of previously known systems. 
     Further, skylight systems have been provided for illuminating a space below a skylight unit. However, there are a number of practical problems regarding the control of illumination levels with current skylight practices. For instance, most existing skylights have no active control elements at all. The control of illumination levels in the space is completely dependent on adjusting the levels of artificial illumination. Further, current skylight systems that use other modulation techniques such as shades or dampers also suffer drawbacks. For instance, modulation consists of reflecting or blocking the undesired levels of light. The excess light is either reflected back to the sky, which causes it to be wasted, or is absorbed by the modulating surface, which can overheat the skylight. Further, modulation by shades or dampers requires either movement of the shade surface by a significant fraction of the cross-section of the skylight area, or a large angle deflection of the dampers. Consequently, for practically sized motors and drive mechanisms, it is impossible to effect changes in the illumination levels in the time scale of less than one second. Still further, none of the existing systems that are known to the inventor herein are self-contained such that the skylight measures its own delivered illumination levels and adjusts its own dampers accordingly. Modulation of the lighting levels is performed by external systems tied into building system controls which increases system cost and complexity. Thus, there remains a need in the art for controlling the amount of illumination provided by skylight systems that may be more easily implemented than previously known systems. 
     SUMMARY OF THE INVENTION 
     A skylight module preferably including an energy management system that controls the amount of light allowed into an area is described. In one embodiment, the system comprises a louver assembly and a light sensor contained within a light well. The light sensor is in communication with a controller that manages the position of the louvers in the system and controls the amount of light allowed through the system. 
     In another embodiment, the system further comprises thermal sensors in communication with the controller, which allow for management of the louvers&#39; position to maximize energy efficiency. The controller is configured to set the louvers&#39; position so that the difference in temperature between the two thermal sensors is as small as possible. 
     In yet a further embodiment, the system comprises both the light sensor and the heat sensors and the controller is programmed to manage the position of the louvers to maximize light and energy efficiency. In one further embodiment, the system also comprises an occupancy sensor that allows the system to know whether a room is occupied in order to adjust the light requirements and louver positions of the system to maximize energy and light efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of the system described herein. 
         FIG. 2  is a perspective view of two louvers in accordance with one embodiment of the present invention. 
         FIG. 3  is a close-up view of the energy conversion module in accordance with one embodiment of the present invention. 
         FIG. 3   a  is a side view of a graphical representation of the energy conversion module in accordance with one embodiment of the present invention. 
         FIG. 4  is a side view of a thermal receiver in accordance with one embodiment of the present invention. 
         FIG. 5  is a perspective view of a thermal receiver in accordance with one embodiment of the present invention. 
         FIG. 6  is a graphical representation of the louver action as a fraction of incident energy and heat. 
         FIG. 7  is a representation of the trajectory of light reflected from one louver to another in one embodiment of the present invention. 
         FIG. 8  is an electrical diagram of the configuration of a heat sensor for controlling heat collection in accordance with one embodiment of the present invention. 
         FIG. 9  is a perspective view of an alternative configuration of heat sensors on the louver in accordance with another embodiment of the present invention. 
         FIG. 10  is a side view showing the reflection of light in an alternative configuration in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description is of a particular embodiment of the invention, set out to enable one to practice an implementation of the invention, and is not intended to limit the preferred embodiment, but to serve as a particular example thereof. Those skilled in the art should appreciate that they may readily use the conception and specific embodiments disclosed as a basis for modifying or designing other methods and systems for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent assemblies do not depart from the spirit and scope of the invention in its broadest form. 
     Disclosed herein is a control system suitable for use with skylight assemblies, and particularly with skylight energy management systems as described in copending and co-owned U.S. patent application Ser. No. 13/749,053 titled “Skylight Energy Management System,” the specification of which is incorporated herein by reference in its entirety. 
     The system described herein can deliver radiant heating in the form of light from enhanced aperture skylights. The same heating from skylights that is undesirable in the cooling season can also be put to use in the heating season. One hundred footcandles of lighting provided as daylight is equivalent to 1 W per square foot of heating. The enhanced amount of lighting that is possible with the enhanced aperture modulated daylighting system set forth herein can deliver up to 300 footcandles of light on a bright winter day. This is enough to provide 50 to 100% of the daytime heating load. The heat is delivered at 100% efficiency, and it avoids the disadvantages described above with previously known systems. No modifications are required to the floor or wall structures, there is almost no time lag in the delivery of the heat, and radiant heat from above heats the upper surfaces of furnishings, as opposed to the lower surfaces, which enhances the radiant effect on the occupants. It also lowers the required air temperature in the building to provide the same level of comfort. 
     In addition to the positive effects of daylighting on productivity for the occupants of a commercial building space, heating with radiant light has additional specific benefits that are realized by the system set forth herein. The negative psychological consequences of the prolonged reduction of natural daylight during winter has been well documented. Seasonal affective disorder (SAD) is a medical condition that is caused by low natural lighting levels over a long period of time such as can occur in mid- to higher latitude regions in winter. Such conditions can be likely ameliorated by exposure to high levels of natural light such as can be achieved with the control system described herein. 
     A number of advancements are described herein relating to controls for an energy harvesting skylight.  FIG. 1  shows a perspective view of an exemplary skylight module (shown generally at  100 ) which may incorporate the control system set forth herein. The skylight module  100  is configured for installation in, for instance, the roof of a building, such as a commercial building. The module is configured to provide approximately 50-70 percent more daylighting than standard daylighting solutions, as well as generating thermal heat at temperatures of up to 300 F. This is accomplished by providing a higher skylight to floor ratio (SFR) than typical skylight installations. The larger aperture is used to provide full interior illumination during cloudy, morning and afternoon periods. The solar energy that is in excess of that required for illumination is captured by a single axis micro-concentrating collector embedded in the skylight, making the energy available to offset building thermal loads while relieving the building cooling system of the solar heat load that would be coming through such a large roof opening. 
     The louvers  200  of a module include a thermal receiver  300  ( FIG. 2 ) on the back of the louvers that is preferably relatively small in size, such that it is possible to have a high degree of focus of the mirror system. A small thermal receiver (as described herein) has a proportionally reduced heat dissipation rate for the same heat input, and thus increases the efficiency of the thermal collection, and consequently increases the peak collection temperatures up to about 220 F. The heat collected from such assembly may be put to various uses, including service water heating, space heating, and some process heat applications including driving single effect absorption chillers for air conditioning. 
     With particular regard to the skylight energy management system shown in  FIG. 1 , the system provides the means to seamlessly vary the amount of lighting delivered by each skylight module  100  in real time, with the balance of the solar energy not going into daylighting being captured in the form of thermal heat. Moreover, and again with particular regard to the system shown in  FIGS. 1 and 2 , louvers  200  may be provided with a thermal receiver  300  that increases the collection temperature to the range of 275 F to 300 F, thus providing more high-value applications of the heat, such as double effect chillers with up to double the cooling value per unit of heat input, and also power generation using organic Rankine cycle or Kalina cycle turbine/generator systems. Alternatively, improving the collection efficiency in the 200-220 F range greatly improves the economics of thermal process heat applications such as single effect chillers. The system shown in  FIG. 1  incorporates improved optics which provides a concentration ratio of 10 to 15, resulting in a smaller thermal receiver area and temperatures high enough to drive these higher value loads, and greater efficiency at lower temperatures. Being able to drive loads that provide efficient cooling and power generation vastly expands the number of applications for the system, because many more buildings have need for cooling and power than more application-specific process heat uses. 
     With reference to  FIGS. 1-3 , the monitor  116  (skylight) provides 1) structural support to the energy conversion module/louver assembly  220  (ECM), 2) thermal insulation between inside air and the outside, and 3) direction and diffusion for the light from the sky into the space below. The ECM  220 , mounted on the south face of the monitor  116  (assuming the south face is facing the sun), is a micro-concentrating thermal collector and light managing device. A controller board  130  and a small electric stepper motor  132  control the angle of the louvers  200  to deliver the desired amount of light through the ECM  220 , while converting the excess light to high grade thermal heat. Fluid lines  134  circulate coolant directly through each louver  200  to pipes located on the roof or in the ceiling space below the skylight modules  100 . 
     The louvers  200  are moved by stepper motor  132  and linkage  136  which is located on, for example, the west end of the ECM  220 . The controller board  130  is preferably connected to a central control unit and sends commands to the stepper motor  132  which is connected to an actuation bar  137  of linkage  136 . The actuation bar  137  is joined to each louver  200  by link arms  138  that connect preferably to the last inch of the west end of the louver  200 . The action of the linkage is shown in the schematic views of  FIG. 3A  with a cross section of four louvers. The actuation bar  137  moves left to right with a small vertical component as the link arms  138  swing in a circular motion as the louver  200  pivots around a slot pivot  202  on the back of each receiver tube. In an exemplary embodiment of the invention, the receiver tubes do not articulate. This allows for fixed fluid connections to the fluid lines  134  that connect the thermal receivers, an improvement from prior designs that required dynamic fluid seals between the receiver tubes and the fixed fluid tubes. 
       FIG. 2  shows cross sections of two louver sections to show additional detail. The mirror  204  of louver  200  can be either continuously curved or have a faceted shape. The facets are much easier to fabricate with simple sheet bending equipment; the continuously curved design requires custom tooling and high-force hydraulic presses to fabricate. The radius of curvature of the mirror  204  varies along its length to optimize the focusing of light on the thermal receiver  300  and secondary reflecting surfaces (described in greater detail below). The portion of the mirror  204  near the top is generally farther away from the adjacent receiver/reflector surfaces and so requires a larger radius of curvature (less curved shape). The portion of the mirror  204  near the bottom is generally presented with a shorter distance to the adjacent receiver and so requires a smaller radius of curvature to focus the light. In an exemplary embodiment of the invention, the mirror  204  is attached to a pivot bar  206  that runs the length of the mirror  204  (or alternatively may consist of short sections to reduce thermal conductivity and losses). The pivot bar  206  has a linear bulb that fits into a slot  208  on the back of the receiver tube  300  to provide a pivot point for rotation. It is important to minimize the thermal conductivity between the hot receiver tube  300  and the mirrors  204  to keep the mirrors  204  from becoming cooling fins. Therefore, the pivot bar  206  is preferably attached to the mirror  204  with silicone foam tape which has a low thermal conductivity but can withstand the high temperatures of the thermal receiver  300 . In addition, the outer surface of the linear bulb may be coated with Teflon or other high-temperature insulating plastic to minimize thermal conduction from the thermal receiver tube  300  to the pivot bar  206 . 
     As best shown in  FIG. 2 , and again in accordance with an exemplary embodiment of the invention, also attached to the pivot bar  206  is the reflecting diffuser  222 . The reflecting diffuser  222  directs the rays of sunlight that strike it into the space below. The reflecting diffuser  222  (as well as the secondary mirror on the thermal receiver tube  300 , discussed below) is made of specialty lighting reflector sheet that is partially specular and partially diffuse. Such specialty lighting reflector sheet material is readily commercially available, and may comprise, by way of non-limiting example, ALANOD 610G3 available from ALANOD GMBH &amp; CO. KG, or ACA 420AE/DG available from ALUMINUM COIL ANODIZING CORP. The material reflects incoming light rays into a 20 degree cone which provides more diffuse projection into the space below while maintaining the directionality of the light. A purely diffuse reflector, such as a white painted surface, while providing soft light to the space below, would waste light by reflecting some of it back towards the primary mirror. A purely specular reflector, such as a polished reflector, would direct all of the light efficiently into the space, but would require secondary conditioning to avoid harsh glare spots. The shape of the reflecting diffuser  222  can either be curved, as shown in  FIG. 2 , or straight. The main criteria in configuring the reflecting diffuser  222  is that the reflecting diffuser intercept preferably all light rays that come from the primary mirror  204  at the shallow angle so that they do not get re-reflected back to the primary mirror  204  and lost. 
     The details of the thermal receiver tube  300  in accordance with such exemplary embodiment are displayed in the cross-sectional views of  FIGS. 4 and 5 . The main body of the thermal receiver  300  is preferably formed of extruded aluminum. To the base extrusion, three features are attached using high-temperature epoxy adhesives: a thermal baffle  302 , a thermal collector  304 , and a secondary mirror  306 . The operation and further details of such assembly are set forth in full in U.S. Patent Application Publication No. US2013/0199515, and are thus not discussed further here. 
     Light exiting from the bottom of the skylight module  100  is sensed using low-cost light sensors that feedback into the controller board  130  mounted in each skylight module  100 . The optics are designed such that at every sun angle, the amount of light that comes through the energy conversion assembly  220  is a monotonic function of the angle of louvers  200 . That is, moving the louvers  200  at an angle more open to the sky always increases the amount of light coming through, and moving the louvers  200  to an angle more closed to the sky always reduces the amount of light coming through. Therefore, a simple proportional integral control loop can be employed by controller board  130  to keep the light levels at a desired set point. Secondly, the excess light is captured for useful thermal energy. Finally, and with reference to the chart of solar energy allocation versus louver angle depicted in  FIG. 6 , because of the degree of concentration of the optics, the fraction of incident direct solar energy that is converted into illumination goes from 0 to 100% in a louver deflection of less than 3°. This very small deflection can be executed in less than one second, such that the bandwidth of the lighting control can be faster than the disturbances, such as varying sunlight levels. Because of this, the skylight optics combined with a moderately sized motor  132  and electronics processing power of controller board  130  can maintain a very precisely controlled and constant amount of illumination into the space below. 
     This precise control of illumination coming from the skylight module  100  can be used to effect a number of efficiencies and functional enhancements. For instance, in many retail environments such as grocery stores, illumination levels are precisely controlled in order to present merchandise in the best light. Different kinds of merchandise such as produce or dry goods are presented at different lighting levels which have been found to produce optimal sales results. By using skylight modules  100  to maintain a precisely controlled illumination level throughout the day even under varying sky conditions, the inventive energy managing skylight described herein can provide these precise lighting levels with no artificial illumination. It is even possible to vary these control lighting levels as a function of the time of day. For interior spaces that are only intermittently occupied, it is possible to place an occupancy sensor at the base of each skylight module  100 . When the sensor does not detect the presence of occupants, it can be programmed to deliver no illumination and maximize the amount of thermal heat collected. When the sensor detects an occupant, the lighting levels can be raised to the required illumination level faster than the time it takes for many commercial lighting fixtures to turn on. 
     Because each skylight module  100  has its own intelligent controller board  130 , it is a very low cost option (e.g., $20) to add a wireless communication module that can directly control the light fixtures in the vicinity of the module that have a similar low-cost (e.g., $50) wireless receiver. The lighting controls can either be on/off, or modulating which provides a continuously dimmable output of the associated lighting fixtures. This has a number of advantages compared to the current state-of-the-art. Current state-of-the-art in automatic daylight harvesting systems for flat roof commercial buildings is to install an array of sensors 5 to 10 feet above the floor of the space. The sensors measure the total illumination reaching the floor from both the skylights and the artificial lighting. This information is fed back to a central controller, and the artificial lighting is either turned on or off or dimmed to reach the desired setpoint. Combining the control logic for both the skylight module  100  and the artificial light illumination levels in the skylight module  100  itself has several advantages. First, for periods of time when the skylight modules  100  are providing more than the desired lighting levels, the controller can attenuate the amount of light coming from the skylight module  100 . Second, because the skylight module  100  has a knowledge of the amount of light that it is putting out, the array of sensors near the floor of the space is unnecessary. Finally, there are a number of factors that can confuse a floor illumination sensor. The sensor is generally incapable of distinguishing light which is coming from the skylights, the artificial lights, or reflected light. Objects which pass temporarily through the field of view of the sensor which might for example reflect additional light onto the sensor would cause the lighting in that zone to be dimmed unnecessarily, causing a dark zone. The light sensors employed in the system described herein are in the light well of the skylight, and are thus not susceptible to such disturbances. The “light well” is the space that exists between the bottom plane of the skylight module  100  and the open area at the bottom of the roof curb to which the skylight module  100  is attached for mounting to a roof. 
     When the system controller is calling for very low or zero illumination levels, the controller cannot use light sensors as feedback to determine the optimal louver position.  FIG. 7  shows the light path for a louver  200  that is delivering 100% heat and no illumination. It is desired that all of the incoming light be projected onto the two thermal absorbing surfaces. Previous versions of the energy managing skylight product used open loop control in which the optimal angle was calculated based on time of day location and orientation of the module. While conceptually a low-cost approach, a significant amount of programming is required to set up the tables which determine the optimal angles for each installation. A system that uses purely feedback control requires little or no upfront programming and is more robust in the presence of disturbances in the field. 
     In general, it is difficult for a control loop designed to maximize the controlled variable to use the controlled variable directly as feedback because when the system is actually producing at its maximum value, there is no error signal to feedback to the controller. It is necessary to “dither” the signal by intentionally introducing disturbances by perturbing the system from its optimal setting. In systems with a significant amount of time lag between errors in input and output, this dithering technique is difficult to employ. The significant thermal mass of the receiver does produce a significant time lag between the presence of errors in pointing and changes in the temperature of the tube. Also, an issue is the fact that the temperature of the tube is also a function of the temperature of the fluid going through it. Changes in the incoming fluid temperature due to changes in other parts of the system could therefore confuse a feedback controller based on the receiver to temperature. 
     For these reasons, it is preferred to measure and minimize the “spilled” or lost energy, not the captured energy. One approach to measuring the spilled energy is to directly measure the light using a light sensor near the receiver tube. A sensor that measures the amount of concentrated light falling onto the surface would be difficult to use because the focused light is concentrated by a factor of 10 to 15 and saturation or overheating of the light sensor is hard to avoid. 
     Thus, an approach using two temperature sensors to control thermal heat collection, which addresses all of these issues, is shown in  FIG. 7 . Two temperature sensors  402  and  404  are mounted on a sensor bracket  406  which is attached to one of the receiver tubes  300  (because all of the mirrors move in concert, it is only necessary to instrument one of the tubes). The sensor bracket  406  is placed in such a position that is completely shadowed by the adjacent mirror so that no direct sunlight strikes the bracket. The sensor bracket is made of a thin metal sheet which is thermally isolated from the receiver tube  300  upon which it is mounted. The thermal insulation  408  is important to decouple the temperature sensors  402  and  404  from both the thermal lag of the receiver tube  300  to, and the temperature disturbances coming from, the fluid itself. The face of the sensor bracket  406  that faces the concentrated light is painted a medium gray color with a light absorbance factor of about 0.3. If the mirror  204  is perfectly focused and all of the light is falling on the receiver tube  300 , the temperature of the upper and lower temperature sensors  402  and  404  will be equal. As the sun moves across the sky or something else causes an error in the pointing, some of the concentrated light will either spill high or low from the receiver tube  300 . The light that then strikes either the upper or lower region of the bracket  406  will cause a differential heating of the bracket  406  in that area. If the bracket  406  is sufficiently thin, there will be a negligible amount of heat conduction between the two ends of the bracket  406 . Temperature sensors  402  and  404  mounted on the opposite side of the bracket  406  will then measure this differential in temperature and generate a signal to the controller proportional to the difference in temperature in a direction which drives the temperature differential to zero. The sensor that is receiving no stray light will be at the ambient temperature inside the skylight module  100 . The other sensor, which is receiving stray light, will be at a temperature that is proportional to the amount of light striking it and the optical reflectivity of the bracket  406 . Therefore, the temperature that the sensors reach, and therefore the gain of the controller, can be controlled by essentially the color of the bracket  406 . Because the controller only looks at the temperature difference between the two sensors  402  and  404 , and not the absolute temperature, it is insensitive to common mode disturbances such as ambient temperature variations. To compensate for errors in the calibration of each sensor  402  and  404 , the temperature of the two sensors can be sampled at nighttime when there is no solar energy present to drive a temperature difference. The static temperature difference between the two sensors  402  and  404  can then be taken out of the calculation for feedback control. 
     An alternative sensor configuration for controlling thermal heat collection is shown in  FIG. 8 . A possible drawback of using temperature sensors to determine the position of the light beam is the time lag between the impingement of the light on the absorber and the increase in temperature sensor. An alternative approach is to use a sensor  410  ( FIG. 8 ) that measures the light beam directly. The concentration of the light striking the thermal absorber and consequently the spillover light sensor can be as high as 7 to 10 times ordinary sunlight. Light sensors to measure this level of flux are not commercially available. A light sensor  410  as shown in  FIG. 8  is able to operate in the extreme temperature and illumination environment required for this sensor. 
     With continued reference to  FIG. 8 , a photovoltaic cell  412  is mounted on a small circuit board  414  with a shunt resistor  416 . The shunt resistor  416  dissipates the power generated by the PV cell  412 , and the voltage across the resistor  416  is directly proportional to the total light energy striking the sensor  410  over a wide range. Two sensors  410  can be put in series to accurately determine the total light flux high or low of the thermal absorber  304 . Silicone based photovoltaic cells are able to withstand temperatures as high as 180° F. and so are most suitable for this application. As shown in  FIGS. 9 and 10 , the two sensors  410  in series may be attached to a bracket  418  that in turn is attached to receiver tube  300 , reaching above and below the thermal absorber  304 , can thus provide immediate and accurate feedback to the controller for any louver and sun position ( FIG. 10  showing the impact of various sun angles on an array of sensors  410 ). 
     Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications of the embodiments herein shown and described will obviously occur to those skilled in the art upon becoming familiar with said underlying concept. It should be understood, therefore, that the invention may be practiced otherwise than as specifically set forth herein.