Introduction

The present invention relates to a method for chilling a building as well as a building chilling system using solar thermal energy. The invention aims at providing an improved solar absorption cooler while reducing resource consumption.

Background for the invention

In warm climate regions or spaces which due to externally or internally heat sources increase in temperature above acceptable conditions, the need for cooling arises. The cooled spaces may be homes, offices, schools, hotel spaces, bungalows, storages rooms, process areas and applies where condition of space, processes or goods are required. Therefore, to avoid temperatures that exceed the comfort zone or ac- ceptable temperature range, a building may have an air condition unit installed. The most common air condition unit is a chiller operated by electricity which converts electricity into a supply of thermal cooling (typically air or chilled water). Where simultaneous presence of the sun and the demand for cooling is present, an attractive way of providing cooling is to use a solar chiller unit. A solar chiller system applies the solar radiation (thermal energy) as main energy input to produce a chilling effect. The collection of solar thermal energy is typically performed by a solar thermal panel attached to the solar chiller system via a heat exchanger. The present day solar cooling units require a relative large material consumption due to heat/cool storage, moving parts, multiple fans/circulation pumps, multiple heat exchangers, or the need for evapo- ration tower as well as dry cooler. Each of these components is associated with loss of temperature or loss of energy. Specific examples of prior art attempts to produce building chilling systems are disclosed in WO 2009/093979 Al, US 6539738 B2, JP 57073347 A, US 2003041608, US 2005183450, EP 2244039, US 2010251749, and WO 2011/028186 A2.

It is the object of the present invention to provide a method and a chilling system, which reduces the temperature and energy loss, e.g. by reducing the amount of unit operations and material use, thereby increas- ing the system efficiency and reducing the system cost.

Summary of the invention

The present invention relates to method for chilling a building comprising the steps of:

a. Heating a working solution contained in a solar panel using solar radiation,

b. Separating the heated working solution in vapor and a concentrated working solution,

c. Condensing the vapor to liquid refrigerant,

d. Evaporating the liquid refrigerant

i. in a building to be chilled or

ii. outside a building to be chilled, wherein the cooling obtained by evaporation is transferred to a cooling liquid outside the building and transported to the building to be chilled for delivery of the cooling,

at an evaporation temperature of 6-20°C,

e. Absorbing in an absorber the vapor in the concentrated working solution, and

f. Returning the working solution to step a.

According to the present invention, the working solution is heated in the in the solar panel by radiation from the sun. The working solution is pre- ferably LiBr/H ₂ 0 but other working pairs such as LiCI/H ₂ 0, CaCI/H ₂ 0, NH3/H2O or similar are applicable and substances for enhancement of heat and mass transfer or corrosion inhibitors may be added. The supply of heat generates vapor from the working solution which results in a concentrated working solution. The vapor is condensed into liquid refrigerant and the energy produced may either be used in another process or removed as waste heat to the environment. The condensed refrigerant may be distributed to a location (space or industrial process) which needs cooling and the refrigerant is evaporated at a pressure corres- ponding to an evaporating temperature of 6-20°C which provides the cooling of the environment, industrial process, or space. Alternatively, indirect cooling may be used in which the liquid refrigerent is evaporated outside the building cooling a second liquid to be transported to the building for delivering to coolness. The evaporated refrigerant is then absorbed into the concentrated working solution and returned to the solar panel for reheating in the solar panel. The method of the invention has the advantage of being simple and effective thereby reducing loss of energy and temperature in the cooling system. Preferred embodiments of the invention include that the heat generated by the condensing and the absorbing step is removed by a single fan. A volume corresponding to or larger than the volume in the solar panels of the first step a) in the process description above may be integrated into the volume of the absorber acting as a reservoir as the volume of the absorber is sufficiently large to contain the content of working fluid in panels, pipes, heat exchangers. The volume of working fluid in the solar panel may be drained to the reservoir of the absorber during inoperabili- ty of the system. The solar panel may be arranged in a position above the reservoir of the absorber to allow gravity to transfer the working flu- id to the reservoir of the absorber. The concentrated working solution in the absorber may be distributed by a liquid distributor through one or more tubes to the absorber tubes where a liquid/vapor counter flow allows for absorption of vapor into the working fluid. The internal area of the absorber tubes may be enhanced by grooves in the absorber tube inner wall or by inserts in the absorber tubes for a further inner surface area enhancement. The inserts may be a single plate strip, a cross inserts or other shapes fitted into the tube. The working fluid will not fill the absorber tube completely and a liquid film is ideally formed on the inner surfaces of the absorber tubes. The fan may be positioned to deliver an air current to the one or more tube(s) to obtain a cooling. The absorber liquid distributor may have internal elements for distributing of a liquid film to the absorber tubes. The liquid distributor may be constructed such that the flow of liquid is distributed by a tube with one or more exits for optimal liquid flow over a dista nce. The exits may be pointing upwards, side wards or downwards. A refrigerant vapor distributor may be integrated with the reservoir of the absorber. The liquid volume of the condenser may be drained to the evaporator. The working solution may be a solution of lithium bromide, ammonia or other salts in water, lithium bromide being presently preferred. The amount of lithium bromide may be 45 to 65 % by weight. The absolute pressure of the system may be 8 to 120 mbar for lithium bromide and similar aqueous solutions. The temperature of the working solution in the upper part of the solar panel may be 60-95°C, suitably 70-90°C. The temperature of the vapor produced by the evaporation of liquid refrigerant may be 6- 20°C, such as 8-16°C, suitably 10-14°C, and optimally around 12°C. The evaporation may be performed using forced or natural convection around the evaporator. The solar panel is primarily powered by solar radiation but may optionally be assisted with a different heating source. The heating source may be powered directly or indirectly with conventional fossil fuels, renewables such as biomass, district heating or recovered waste heat or other combustibles.

The invention also relates to a building chilling system, using solar ther- mal energy, comprising

- A solar thermal panel containing an working solution to be heated by solar radiation, thereby separating the working solution in a vapor and a concentrated working solution, - A condenser for condensing the vapor to liquid refrigerant,

- Pressure reducing means capable of decreasing the evaporation pressure to a pressure corresponding to an evaporation temperature of 6-20°C,

- An evaporator positioned

i. in a building to be chilled,

ii. or outside a building to be chilled, wherein the cooling obtained by evaporation is transferred to a cooling liquid outside the building and transported to the building to be chilled for delivery of the cooling, and

- An absorber for absorbing the vapor from the evaporator in the concentrated working solution.

Preferred embodiments of the invention include that the condenser and the absorber are arranged in a common entity, which may be cooled by a single fan. The condenser and the absorber in the common entity may be positioned adjacent in parallel for the use of a single fan or the con- denser and the absorber in the common entity may be positioned adjacent in series for the use of a single fan. A funnel may be installed between the fan and the common entity to concentrate the air current.

The chilling system of the invention may comprise a liquid-liquid heat re- covery heat exchanger arranged in the system for cooling the concentrated working solution from the solar panel, whereas the working solution from the absorber towards the panels is heated.

The absorber may contain a reservoir having a volume capable of con- taining the amount of working fluid in the solar panel as well as pipes. The solar panel may be arranged at a position higher than the reservoir of the absorber to allow for drainage by gravity from the solar panel to the reservoir of the absorber. The absorber may comprise a liquid distributor for the concentrated working solution and a vapor distributor connected by one or more tubes arranged to allow for the concentrated working solution to flow from the liquid distributor through the tube(s) by gravity towards the vapor distributor in counter-flow with the vapor. The one or more tubes may be essentially vertical and the fan may be arranged so that the air current is directed towards the one or more tubes for allowing a cooling to take place. The one or more absorber tubes may be having inserts for enhancement of internal absorption area. The liquid distributor may have a tube with exit(s) facing upwards, sidewards or downwards for flow distribution over a length of internal elements for distributing the liquid in an optimal way. The reservoir of the absorber may be integrated with the vapor distributor.

The evaporator may be connected to the pressure reducing means and/or the absorber with pipework of a polymeric material. Further pipework and also components in the system where a diffusion impervious material is required or advantageous may be prepared of a polymeric material. The polymeric material may be cross-linked polyethylene (PEX). The condenser may be positioned at a height above the height of the evaporator to allow for the condenser to be drainable by gravity. A hermetic pump may be used for returning the working solution from the absorber to the solar panel. A hermetic pump does not contain a shaft sealing. The pressure reducing means may be a throttle valve, solenoid valve, capillary tube or orifice. One of the main barriers for commercial breakthrough of solar cooling is the production cost of the solar chiller system. The present invention offers an option for lowering the cost. In addition the weight and footprint of the solar chiller is reduced. The chiller system and the method of the invention may optionally comprise one or more of the following characteristics:

A. Reducing fan power for coolers

B. Working fluid in solar panels C. Drain-back functionality of panels with working fluid

D. Integration of drain-back storage with absorber unit

E. Option for evaporating of refrigerant in indoor chiller module

F. Alternative materials in construction of solar coolers

G. Condenser for refrigerant is drainable by gravity

H. Use of hermetic pump

I. Use of inserts in the absorber tubes

Ad. A. The power consumption of auxiliary equipment such as fans is pa- rasitic in relation to the chiller operation and are as such decreasing the electrical COP (Coefficient Of Performance) of the system. It is therefore desirable to reduce the system electrical power consumption for an efficient chiller operation. The power consumption of a fan is related to the flow rate of the air being transported and to parasitic fan losses. Reduc- ing the latter increases the chiller electrical COP. Furthermore each fan reflects an increase in system component count and hence system cost. In an aspect of the invention it relates to a reduction of the number of dry cooler fans for the condenser and absorber by an appropriate arrangement of said heat exchangers. The embodiment of the invention comprises an arrangement of the condenser and absorber adjacent in either parallel or in series, which allows for using a single fan for cooling of both units instead of separate fans for each. This embodiment furthermore reduces the energy loss associated with fans and allows for reducing the footprint due to a condensed arrangement.

Ad. B. Conventionally, the solar thermal energy received by the solar panels is transferred to the solar chiller system by a liquid heat exchanger by which the solar thermal panel volume is separated from the chiller volume. The use of a heat exchanger causes a temperature loss and use of additional components such as heat exchanger and a circulation pump. In an embodiment of the invention it relates to a reduction of the number of units required for transferring solar thermal energy into the system as well as removing the undesired temperature loss. The embodiment of the invention comprises an integration of the solar ther- mal panel volume into the system volume by having the working fluid led directly into the panel, thereby transferring solar thermal energy directly to the solution in the solar panel. This allows for a removal of the liquid heat exchanger and the associated temperature loss and hence a decreased material consumption and associated component cost.

Ad. C. The solar thermal panels are positioned outside and are subjected to the ambient conditions. That means that during sunshine and inope- rability of the system, the energy transfer to the panels require energy to be removed from the panels to avoid overheating of the panels. This situation can lead to damage and increased downtime of the system. The invention relates in a certain aspect to the use of drain-back of the working solution from the solar thermal panels, thereby removing the fluid when the attached solar unit is not in operation. The invention comprises the system design to allow for a drain-back by gravity from the solar thermal panels to avoid overheating during warm seasons during system shut-down as well as protection of the panels during cold periods where the system is not in operation. This design feature allows for omitting the antifreeze agents or other additives, which reduces the component count and hence reduces material consumption.

Ad. D. The working solution of the solar panel, especially when the solar thermal panel is integrated into the system volume, may drain back to one or more reservoirs. The reservoir(s) can be of temporarily use solely or the reservoir may have an operational functionality. The invention relates in an aspect to an efficient design of the absorber as a part of the drain-back system. The absorber comprises in this embodiment a liquid distributor attached to tubes, in which the absorption process takes place, with a liquid reservoir at the lowest point of the absorber. The liq- uid reservoir acts also as a gas distributor for the vapor entering the absorber from the evaporator. This allows for the absorber to function with multiple functionalities, hence reducing the amount of dedicated components and reducing the material consumption. Ad. E. Conventionally, the solar chiller cooling unit positioned in the air conditioned space is a separate circuit that interacts with the solar chiller system via a heat exchanger. The separate circuit has a circulation pump attached for the transport of cooling media. In an aspect of the present invention it relates to the reduction of heat exchanger numbers, auxiliary equipment in the design of the evaporator, and of a cooling circuit that circulates cooling fluid to the air conditioned room. In an aspect of the invention it comprises a direct evaporation unit integrated into the system volume positioned in the room. This allows for the saving of the cooling circuit heat exchanger, attached circulation pump, and expansion vessel. The invention furthermore reduces the temperature loss associated with a heat exchanger.

Ad. F. The materials used in solar chillers are typically stainless steel type metals, copper, brass, and similar alloys. These metals are high priced materials and therefore the world metal market pricing is highly influential on the cost of a solar chiller, and the chiller cost is hence sensitive to the metal pricing trends. The invention relates to alternative material choice for components used in solar chillers. The alternative materials can be plastic or composite materials for reservoir, valves, and heat exchanger pipework and casings. According to the present invention it is suggested in an embodiment to use polymeric materials with or without diffusion barrier as a substitute of metal piping or other system parts. This allows for a reduced sensitivity towards the metal pricing trend and reduced corrosion issues associated with metals. It also reduces the material consumption for welding and soldering of tubes and components during assembly and installation.

Ad. G. The efficiency and performance of the solar chiller depends on system pressure leaks and pressure losses through the individual components. Change in pressure due to non-process related pressure loss will increase evaporation temperature and thus reduce the COP. The invention relates to a condenser design that allows for the condenser to be drainable by gravity whereby the gravity assists in reducing the required pressure for transport of liquid from the condenser unit. The natural gravity driven flow of the condensed liquid is hence assisting in maintaining a high system COP which also ensures low material consumption. The drainable design of components protects the system components during the cold seasons.

Ad. H. The solar chillers that operate under vacuum, such as the subject for this invention, are sensitive to any leakage that imposes an increase of the absolute pressure in the chiller system. Any pressure increase is reflected as a decrease of chiller COP. The chiller vacuum system is hence desirably tight and any objects reaching from vacuum volume to surroundings are undesirable. An undesired pressure increase of the chiller system is subject to service or maintenance of the chiller. In an aspect, the invention relates to a reduction of the system leak rate by the use of a hermetic pump for the solution circulation. By avoiding shaft sealings, the leak rate is reduced, hence the chiller COP is not severely affected and the frequency between chiller services is potentially reduced. Ad. I. The flow of solution liquid is ideally a liquid film on the absorber tubes inner walls. A high liquid area aids the mass absorption and in some cases extra absorber tubes have been used for ensuring only sufficient absorption area. To enhance the inner wall area of the absorber for mass absorption, inserts in the absorber tubes can be used. The inserts can be straight plates, bend plates, cross plates, star shaped plates or other geometries. Grooved tubes are an alternative. The inserts are ideally touching the tube wall, but need not and the inserts can be fixed in position by choice.

Brief disclosure of the figures

Fig. 1 shows an overview of the complete absorption cooling system including solar thermal panels, Fig. 2 shows an arrangement of the condenser and the absorber with a single fan,

Fig. 3 shows an arrangement of the condenser and the absorber with a single fan and a funnel,

Fig. 4 shows an absorber with liquid distributor, absorber tubes and reservoir, and

Fig. 5 shows a schematic evaporator to be positioned in-house.

Fig. 6 shows a schematic of the absorber tube inserts. Detailed disclosure of the invention

Figure 1 : The figure shows a schematic display of a single effect absorption solar chiller cycle. The solar chiller is powered with solar thermal energy (1) or other sources of heat source and produces cold liquid refrigerant for air conditioning. The evaporator (5) shown as a unit with separated tubes can be located near to the solar thermal panels (1) or at a distance as appropriate. The system can be located underneath or adjacent to the solar thermal panels.

The solution may be added corrosion inhibitors, mass transfer accelera- tors, or other chemical substances for improving the performance and lifetime of the equipment or for reducing the need for maintenance. In cases where the working fluid consists of lithium bromide and water, the concentration of the solution may be in the range of 45 to 65 %, preferably 50 to 63% and optimally 54 to 60% mass of Libr. The system oper- ates under vacuum at an absolute pressure corresponding to an evaporation temperature of 6-20°C.

The energy supply to the system is provided primarily by solar radiation (thermal) through the solar panel which is an integrated part of the sys- tern. The temperature of the fluid in top of the solar panel is approx. 75- 90°C but may vary to 60-110°C depending on operating and ambient conditions. The panels are preferably integrated into the chiller volume allowing for the solution to flow into the panels. Alternatively a separate flow circuit for the panels connected to the chiller volume by a heat exchanger can be used. The solar panel (1) may be assisted with a backup heat source. The heat source may be powered directly or indirectly with fuels, renewables such as biomass, district heating or recovered waste heat from various sources where available.

The concentrated working solution is directed into a liquid-liquid heat recovery heat exchanger (2) for the improvement of the cycle COP and to decrease the temperature of the solution in preparation for downstream process, producing low temperature concentrated working solution. The pressure of the concentrated working solution is adjusted to that from the evaporator by means of a pressure reduction device (3).

The produced vapor is condensed by removing energy, thereby produc- ing liquid refrigerant. The condensing process is ideally performed at constant pressure but a deviation in pressure over the condenser (8) corresponding to a temperature shift of up to 20% through the condenser in degree Celsius is acceptable. The absolute pressure of the condensed refrigerant is decreased to a target pressure corresponding to the desired evaporation temperature. The pressure reduction is provided by means of a pressure reduction device (4). The pressure reduction device may be a valve (4), capillary tube, orifice or other means allowing the reduction of pressure to target the required evaporation temperature.

In the evaporator (5) the liquid refrigerant is evaporated by adding energy at ideally constant pressure. The evaporation temperature is in the range of 5-20°C, preferably 8-16° optimally 10-14°C and preferably at 12°C. The evaporation pressure in the evaporator is fully determined by the evaporation temperature. The process creates cool refrigerant vapor and the evaporation energy is used for cooling either as a direct evaporation in an in-house positioned unit or as an indirect liquid cooling circuit with the evaporator positioned separate from the cooled location or process.

In the absorber (7) the concentrated working solution and the vapor from the evaporator is combined in an exothermic absorption process producing a weaker working solution. The absorption process is normally cooled. The cooling is performed using ambient air driven by a fan (9) or by cooling the component with cooling liquid or heat recovery device. The weaker working solution is increased in pressure, producing a solution at elevated pressure, using a circulation pump (6).

The weak working solution is directed to liquid-liquid heat exchanger (2) for the exchange of energy with the concentrated high temperature working solution for the improvement of cycle COP by increasing the weak solution temperature. A weaker high temperature working solution is produced. The weak high temperature working solution is transferred to the solar panels or to a alternative energy supply in case the panels do not provide heat input (e.g. at no operation at night or the absence of solar panels). The closed cycle has returned to the point of beginning. Figure 2: The condenser and absorber (22) are positioned adjacent, either in parallel or series and supplied with air by a fan (21). By arrangement in series, one unit will be positioned upstream of the other which will increase the cooling temperature for the downstream unit. Preferably the absorber is cooled by the fresh non-heated ambient air, but either unit may be cooled with the fresh non-heated ambient air. By arranging the heat exchangers in parallel, each heat exchanger will be cooled with the same air temperature. The fan is powered by electricity and provides air for cooling of the condenser and the absorber. Figure 3: To increase pressure fan (31) efficiency for arrangement in parallel, a funnel (32) may be installed between the condenser/absorber and the fans. The funnel assists in guiding the cooling air to increase flow distribution and/or to avoid false air intake. The funnel can be of any converging shape. Preferably the funnel is aerodynamically shaped for low pressure loss.

Figure 4: The absorber may be a multipurpose component. The top of the absorber is a liquid distributor (41) to which the concentrated work- ing solution is directed. The liquid distributor distributes the working solution to the absorber tubes (44) in which the solution flows internally. These tubes act as a heat exchanger. The liquid distributor may or may not have a liquid level above the tubes. The inner of the tubes act also as an absorber in which vapor is absorbed into the working solution. The absorber tubes are vertical and the design is self-draining, but deviation from vertical to up to 88° in all directions is acceptable. The process is an exothermic process requiring cooling. At the bottom of the absorber, the solution enters a liquid reservoir (43). The liquid reservoir acts as a reservoir for the solution during operation, as drain-back reservoir when the unit is not in operation and as vapor distributor for the vapor from the evaporator. The drain-back reservoir is important for the collection and storage of the working solution e.g. when the solar chiller is shut down. The solution preferably drains back from the solar panel due to gravity and is collected in some of the lower positioned volumes of the absorber. The reservoir may or may not have a working solution level stored during operation as the solution may flow directly to the pump. The absorber reservoir is suitably designed to allow the collected working solution to flow by gravity towards the pump. The absorber reservoir, position, or technical means should ensure that solution does not flow into the evaporator for contamination reasons.

Figure 5: The evaporator (51) is for directly or indirectly evaporation of refrigerant. For directly evaporation the evaporator is positioned in the space that requires cooling. The evaporator may then be connected to a fan (52) for forced convection or operate without a fan for natural convection.

For indirectly cooling, the evaporator cools another media such as chilled liquid (may be water) (53) in a configuration that allows for superheat- ing of the vapor and the evaporator may be positioned in proximity to the solar panels, absorber and particular preferably is below the condenser to allow refrigerant to flow to the evaporator without a circulation pump.

Figure 6: The internal area of the absorber tube(s) (61) where the absorption of vapor into a liquid film occurs can be enhanced by adding inserts in the tube(s). The number of inserts in one tube may be one, but are not restricted to that. The inserts can have any form and shape, pre- ferably a prolonged shape that allow for the insert to reach from tube entrance to tube exit. In the lower part of the figure cross-sections of 3 different tubes with insert are shown. The insert form can be a cross (62), single straight slap (63), a bend slap (64), or any other shape that will fit into the tube.