Abstract:
This invention relates to a method and apparatus for energy effective regulation of temperature and ventilation of one or more ventilation units of buildings, where one or more heat-pumps are used to exchange thermal energy between outdoor air and an indoor heat carrying fluid medium and where the heating and/or cooling of each ventilation units are achieved by distributing the indoor heat carrying fluid medium in each ventilation units, in such a manner that the natural short term variations in outdoor temperature due to passages of weather systems and the day/night variations is utilized to give the one or more heat-pumps optimized conditions such that they are only turned on for extracting outdoor heat which is delivered to the indoor heat carrying and distributing fluid medium at the relative warm periods in the case of warming the buildings, or only in the relative cold periods for cooling the heat carrying and distributing fluid medium for removal of indoor heat in the case of cooling the buildings, and that the thermal energy that is exchanged with the outdoor air is partly used to cover the ventilation units actual demand for heading or cooling while the remaining major part of the thermal energy is sent to a thermal store to cover the ventilation units heating or cooling demand during the subsequent periods where the natural weather conditions is less favorable for exchanging thermal energy from outdoor air by use of heat-pumps.

Description:
This invention relates to a method and apparatus for heating and cooling (climate control) of buildings and houses, where a typically 5-15 day thermal storage is integrated with heat-pumps and ventilation to operate in a particularly optimised synergy. 
     BACKGROUND 
     Large geographical areas in the world has a climate that generally goes through a seasonal change from a warm period in the summer to a cold period in the winter. This seasonal variation is naturally greatly dependent the local topography, whether there is an inland or coastal climate and the actual global latitude in question, but will nevertheless usually be of such an extent that buildings/houses needs means for cooling during the warm season and heating during the cold season in order to keep a comfortable indoor temperature of 20-22° C. For example, in Norway the mean temperatures may vary from −5° C. to +20° C. over a year, while Mediterranean countries and large parts of USA may typically see mean temperature changes from 0° C. in winter to +30° C. in summer. Thus, regardless whether one has a cold or warm climate, a substantial amount of energy is needed to keep a comfortable temperature in buildings/houses. 
     For Norway, which has a relatively cold climate and practically no use of air-conditioning, there is estimated that 71% of the energy consumption in living houses is spent on heating and producing hot water. This figure is somewhat lower for commercial buildings due to a larger demand for electric energy to operate technical machinery. The total energy consumption for heating houses and commercial buildings is estimated to 42.5 TWh/year. Pro capita this amounts to about 10 MWh/year for heating purposes, where approximately ⅔ is hydroelectric power. Despite that there is huge variations in energy consumption patterns in different regions in the world, it is nevertheless obvious from these figures that vast amounts of energy is spent in the world on heating/cooling of houses and buildings, and that there is a huge potential for energy conservation in this sector. 
     PRIOR ART 
     It is known that heat-pumps are very efficient tools for extracting heat energy from a low-temperature source and deposit the heat in a relatively high-temperature area. In general terms one might say that a heat-pump works like an inverted refrigerator, and can normally deliver 3-4 times more heat than their required energy input for driving the process. That is, while direct heating systems like gas fired heaters, wood firing, electric heating etc. has a theoretical upper limit of 100% efficiency and a practical efficiency well below this limit, conventionally available heat-pumps normally have efficiency rates which is in the order of 300-400%. Thus by using industrially available heat-pumps, the reduction in the energy consumption for heating/cooling of buildings can therefore for be as much as 70-80%. 
     There are known several types of heat-pumps, which generally can be characterised according to which medium they collect from and deliver the extracted heat to. For buildings and houses the heat will normally be delivered to a medium that is able to distribute the heat in the building, which in practice means water or air that is subsequently circulated in the building. For the heat source of heat-pumps there is a general convention stating that the heat source should have as high a temperature as possible and preferably be relatively stable over the year. This has led to use of heat sources such as a fluid medium circulated in deep drilled holes in bedrock, in buried tubes in the soil, in tubes submerged in fresh water, rivers, sea-water etc. 
     However, there are a number of problems associated with this approach. Rock and soil have a very low thermal conduction, thus the rock/soil needs a substantial amount of time to replace the heat extracted by the fluid medium. Thus one must employ rather lengthy loops and/or drilled holes in order to obtain a sufficiently large thermal store to allow long term extractions of heat without extensive cooling of the heat source. And as a consequence the investment cost often becomes prohibitive for this type heat extraction. The problem with low extraction capacity of the thermal stores can be solved by using open water as the heat source. It is possible to extract large amounts of heat from water at relatively small volumes (short extraction loops) due to a high specific heat capacity of water and the opportunity to replace extracted heat by convection. Also, water will at moderate depths have a stable and beneficially high temperature of 4° C. Thus water is in many respects an ideal heat source. However, there are problems with corrosion and fouling, especially in sea-water, and this solution is strictly restricted to buildings and houses in the vicinity (within 100 m) of open water. The major part of buildings and houses lies outside this reach. 
     Another approach to reduce the high investment costs for heat-pumps is to extract heat from open air and transfer this heat to water or air that is distributed inside the buildings/houses. These heat-pumps may be installed directly it the walls of existing houses and give a point delivery of heat in the form of hot air. Such solutions are very competitively priced, but has a major drawback in that they significantly looses effect when the demand for heat is largest. That is, they loose much of their beneficial heat extraction effect when the open air temperature becomes low (below 0° C.). Also, such solutions have encountered severe problems with freezing up of heat exchanger surfaces when the open-air temperature has fallen below +2° C. Thus this solution is generally considered to be only suited for coastal climates where the temperature seldom falls below 0° C. 
     Another approach for reducing the energy consumption for heating or cooling of buildings is to employ the natural seasonal temperature variations to build up sufficiently large thermal stores which is to be used in the following season to heat or cool the building. An example of such technology is SE 425 576. For instance, the heat resulting from solar radiation can be used advantageously for the heating of buildings and can eliminate the need for energy consuming heating systems. This form of passive solar heat gain is achieved through the architecture of the building by designing the building for optimising the absorption of solar rays over daily and annual cycles. That is, heat is accumulated by allowing the incident solar rays to fall onto a large thermal mass (generally walls or soil in the inside of the building), or is concentrated by various forms of heat collectors, and similarly accumulated. Greater or lesser heating is achieved by varying the amount of shade from the sunlight. The accumulation of heat allows it to be stored and used later when necessary. However, for cold climates the available solar radiation is less than for warmer climates while the need for heat is larger. As a consequence, the thermal stores must be very large in order to contain sufficient heat for a long and cold winter and also require extensive thermal insulation in order to preserve the heat over long periods (several months). Thus this solution is also encumbered with prohibitive costs, and have therefore not found general use. 
     OBJECTIVE OF THE INVENTION 
     The main objective of this invention is to provide a method and apparatus for heating and cooling of buildings and houses that solves the above given problems. 
     It is further an objective of this invention to provide 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a typical example of how the mean day-time temperature varies over a year in an inland climate (city of Oslo), with simultaneous variation in consumption of electric power. 
     FIG. 2 shows a diagrammatic view of the working principle for a device for heating and/or cooling a building according to the invention. 
     FIG. 3 shows a schematic view of a preferred embodiment of a device for heating and/or cooling a building according to the invention. 
     FIG. 4 is a flow sheet which shows the working principle for an auxiliary software for the logic control of the preferred embodiment shown in FIG.  3 . 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     The objectives of the invention may be achieved by the features as set forth in the following description and appended claims. 
     The objectives of this invention can be achieved by exploiting characteristic features of natural temperature variations in the outdoor climate. The outdoor temperature will in many areas go through three typical patterns of natural variation; day/night, passage of weather systems and seasonal changes. An example of such natural variations are illustrated in FIG. 1 which gives the mean day air temperature in the first half of 1999 for the city of Oslo, Norway. It is the temperature variations due to passage of weather systems which typically occurs in 1-15 days and the day/night variation that is of interest, since these can be utilised to extract heat to warm buildings in relatively mild/warm periods, or vice versa, to discharge heat to cool buildings in relatively cool/cold periods, and then accumulate this heat/cold in moderately sized thermal stores with moderate thermal insulation. 
     Thus, in the case of heating buildings/houses in a cold climate, a special beneficial synergy is obtained by employing a heat-pump which extracts heat from outdoor air during these relatively warm periods and then stores this heat in a moderately sized and isolated thermal store which has capacity of storing 5-15 days heat consumption. Such a system will avoid the disadvantages of conventional air-to-air heat-pumps, since operation of the heat-pump at only relatively warm periods ensures optimal working conditions such that a maximum heat extraction efficiency is achieved. Thus the full potential of the beneficial heat-pump technology is ensured at all climates, and at the same time the risk for production interruptions due to frost formation in the fans is minimised since the warm periods will typically give outdoor air temperatures above 0° C., or at least only a few degrees minus. In the case of cooling of buildings/houses in a warm period the situation becomes reversed. Now it is the relatively cold periods due to passage of weather systems and/or at night that is utilised by using a heat pump to build up a sufficient supply of cold matter in the thermal store which can be applied at a later stage to keep the temperature down in the buildings/houses during periods of warm weather. 
     In order to obtain a heat carrying medium for heating/cooling the buildings/houses with an optimum temperature regardless the fill degree of the thermal store, it is preferred that the store is designed as one or several tubes that is filled with coarse particulate matter and that the loading or extraction of heat from the store is performed by sending a heat carrying medium comprising a fluid through the tube(s). In this manner, the thermal store will gain a warm and a cold end since the heat becomes partitioned between the fluid phase and the solid particulate phase according to the working principle of gas-chromatographic columns. That is, as long as a thermal equilibrium between the particulate matter and the heat carrying fluid is substantially obtained within a reasonable time, the transition zone between the cold part and the warm part in each tube(s) will consist of a narrow area with a sharp temperature gradient and where the cold and the warm zone will have a homogeneous (but of course different) temperature (see FIG.  3 ). Thus, by sending the heat carrying medium through the thermal store in one or the opposite direction, one can readily obtain a warm or cold medium for heating/cooling, respectively. Also, the fill degree of the store can easily be measured by detecting the position of the temperature gradient between the hot and cold zone. 
     One advantage with this type of thermal store is that it is possible to re-use construction materials as the solid particulate material, thus reducing the amount of waste disposal from the construction industry. However, all types of solid particulate materials can be used as fill material in the tubes as long as the grading of the particles is sufficiently narrow in order to form voids and channels between the solid particles, and thus to allow the fluid of the heat carrying medium to flow through the particulate fill material without an excessive fluid pressure loss. That is, the size distribution must be sufficiently narrow to avoid that smaller particles fill in the voids between larger particles. The thermal store may be situated under an adjoining outdoor area (e.g. a parking area) or may be incorporated within or underneath a building. It may be operated both horizontally and vertically. 
     Another advantage of the invention is that the heat extraction capacity of the heat-pump may be reduced compared to conventional use of heat-pumps, since there is no longer a need to ensure a heat extraction capacity to cover the heat consumption at the coldest expected weather when the heat-pump also has the lowest heat extraction efficiency. Thus one can employ smaller and cheaper heat-pumps since they are always run at optimised conditions since the extra heat demand at the cold periods are covered by extraction of heat from the thermal store. Another advantage of the invention is that by use of relatively short term climate variations, one can employ relatively small sized thermal stores with moderate insulation means. Especially when compared to systems where the seasonal temperature variations are employed. Thus, the thermal stores according to the invention will be economically very competitive compared to conventional stores. 
     The benefits of the opportunity to employ small scaled heat-pumps and thermal stores can be further enhanced by leading the used air from the houses/buildings to the heat pump for recovery of waste heat. That is, employing the heat-pump as a heat exchanger for reusing the waste heat in addition to the extraction of additional heat from outdoor air. This working principle is illustrated in FIG. 2, and will be thoroughly explained under the following detailed description of the invention. 
     In order to optimise the heat extracting conditions and to ensure that the thermal store has a sufficient supply of hot or cold particulate matter in order to meet the heating or cooling demand in the coming days, it is envisioned that the system incorporates software and regulation devices for making use of weather forecasts for the next 5-7 days to determine if and when the heat-pump should be engaged to fill the thermal store. That is, the regulation system includes sensors that monitor the filling degree of the thermal store, the actual weather conditions (temperature), and the actual drain rate of heat in the building/house, and employs this information together with the weather forecast to decide when the heat pump should be activated and when the heating/cooling demand can be optimally covered by the accumulated hot/cold matter in the thermal store. In this way, the energy consumption for heating/cooling buildings can be further reduced. 
     Thus in sum, the invention provides a very energy efficient and economically viable method and device for heating of buildings and houses, which in principle is analogous to the energy efficient hybrid engine solution for cars where a small sized combustion engine is constantly run at optimised efficiency for production of electric energy at just above the mean energy need for propulsion of the car, and where the surplus electricity is stored in batteries to be used by the electric propulsion engines at periods with extra load. The method can be applied for any type building or house, such as apartment buildings, commercial buildings, office buildings, store houses etc., and can be adapted to heat/cool one or several separate rooms or areas in one or several houses/buildings. For simplicity, each heating/cooling zone will be called ventilation unit (VU) in the following. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be further explained by way drawings and examples of preferred embodiments. 
     The working principle of the invention may be seen from the schematic presentation of FIG. 2, where reference numeral  1  depicts a series of ventilation units,  2  denotes ventilation ducts for suction of used air from each VU,  3  is a duct that leads the used air to a heat-pump  4 ,  5  is a supply line for outdoor air to the heat-pump  4 ,  6  is a duct that leads the fresh heated air exiting the heat-pump  4  into the VU&#39;s via ducts  7  and/or to the hot end  8  of a thermal store  11 . The thermal store also has a cold end  10  and a heat transfer zone  9 .  14  is a second outdoor air intake that is connected via duct  12  to ventilation ducts  13  for supplying cold air to each VU and/or to the cold end  10  of the store  11 . 
     Each VU is supplied with hot air by ducts  7 , and cold air by ducts  13 , when the device is in heating modus. The hot air is, depending on the weather conditions and the fill degree of the thermal store, supplied by extracting hot air from the hot end  8  into duct  6  as long as the fill degree of the store is satisfactory. In this case cold air is sucked in through inlet  15  and sent to the cold end  10  of the store  11 . In the case when the thermal store is less than satisfactory filled in order to meet the expected heat demand the coming period, the heat-pump  4  will be activated and hot air lead to the ventilation ducts  7  by duct  6 . Eventual surplus hot air will then be directed into the hot end  9  of the store  11  for accumulation of heat. The cold air exiting the cold end of the thermal store  11  will be discharged through duct  12  and inlet  14 . 
     Generally, an air-to-air heat-pump will take in cold fresh outdoor air and extract some of it&#39;s heat content and pass this heat over to a separate air-stream that is employed to heat the VU such that the cold fresh air will be further chilled and discharged. Thus, a heat-pump can shift from raising the temperature to lowering it, and by connecting this discharge outlet for cold air to the cold end of the thermal store (not shown in FIG.  2 ), the heat-pump can be employed to build up cold matter in the store and/or to cool the ventilation units  1  directly by leading the cold air into the them through duct  12  and  13 . Thus the principle solution as presented in FIG. 2 may also be employed to cool the ventilation units. In this case, hot air will be discharged through an outlet on duct  6  (not shown), and used air will be discharged from an outlet on duct  3 . 
     Further in this example, the working principle of the invention includes optimised utility of four factors; 
     1. the energy drain/gain by each ventilation unit and the sum of this for all units 
     2. the filling degree of the thermal store 
     3. the weather forecast for the coming 5-7 days 
     4. the micro-climate (local climate) of individual buildings/houses. 
     The energy drain/gain is typically a result of outdoor temperature, time of day and day in week, and is the total sum of settings for ventilation and temperature by the individual ventilation units. Weather forecasts provide two types of information; forecast of expected outdoor temperatures and forecast of expected weather type (overcast, windy, solar heating etc.) for the coming days. Micro-climate parameters such as total energy gain/drain, time of day, day in week, time of year, and outdoor temperature are registered and stored for each ventilation unit in order to provide a statistically sufficient basis for employing the weather forecast to estimate the coming days energy drain/gain. This estimate and the filling degree of the thermal store (as measured by the ratio hot/cold zone) are employed to determine when and for how long the heat-pumps should be engaged. 
     Also, the following factors are incorporated into the operation scheme of the invention; Used ventilation air is normally the cheapest source for heat since it generally has a higher temperature and thus a higher heat content than outdoor air. Used air is therefore the primary heat source while outdoor air is a secondary heat source which covers the additional demand. The heat-pump(s) is/are always employed at optimum (full) load, since there is no need for adjusting the output to the actual drain rate of the VUs as long as the surplus heat can be accumulated into the thermal store. And in the case the thermal store is filled, the heat pump is turned off, and all heat demand will be supplied by the thermal store. Thus one can employ relatively simple heat-pump(s) without capability of regulating the load, and thus gain an economical advantage and optimal operating conditions. 
     The operation of heat-pump(s) and the auxiliary valves and fans for driving the air-streams in the apparatus, is performed by a regulation system that is under control of a software program that determines the operation modus of the apparatus according to estimates of the expected heat/cooling demand the coming 5-7 days and the actual user settings of fresh air and temperature of each VU, Such software way run on ordinary and available PC-type computers. 
     EXAMPLE 1 
     A preferred embodiment of the invention that is particularly versatile and suited for climates with large seasonal temperature variations is schematically presented in FIG.  3 . Here reference numeral  1  denotes a series of ventilation units,  3  is a duct for used air which is equipped with a fan  22  and a two 2-way flow diverter  26  for leading the used air either to a discharge outlet  17  or to a heat-pump  4 . Heat-pump  4  is connected to an inlet duct  5  for fresh outdoor air, a discharge outlet  18 , and a branch of duct  6  for supplying warm fresh air. The duct  6  runs from the hot end  8  of the thermal store or storage  11  to the inlet ducts  7  of each VU  1 , and is equipped with fan  23  and  24 . Duct  6  is also connected to fresh air intake  5  which is equipped with a 2-way flow diverter  27  and discharge outlet  19 . Another branch of duct  6  is connected to a second heat-pump  33 , and is equipped with a 2-way flow diverter  28 . The second heat-pump  33  is supplied with fresh outdoor air from inlet  34  and is equipped with a cold fresh air outlet  16  that in the other end is connected to the supply duct for cold fresh air  12 . Duct  16  is equipped with a 2-way flow diverter  29  and a discharge outlet  20 . Further, supply duct  12  for cold fresh air runs from the cold end  10  of the thermal storage  11  to the inlet ducts  13  of each ventilation unit  1 , and it is equipped with fan  25 , a 2-way flow diverter  10  with fresh outdoor air inlet  14  and a 2-way flow diverter  31  with outlet discharge  21 . 
     Thus, each ventilation unit is given the opportunity to have both the temperature and ventilation (supply of fresh air) regulated. The units may be flats, offices or suites of offices, or individual rooms in these. Each VU is kept close to barometric pressure by balancing fresh air input to used-air removal, and the used-air ducting  3  is always under suction. Heat transfer is achieved by ventilation air. Temperature is adjusted at individual outlets by balancing the streams of warm and cool fresh air. The thermal store  11  consist of one or several tubes filled with granulated concrete with average diameters of 20-60 mm. Typical dimensions are 1-1.5 m in diameter and a length of 3-20 m, preferably 5-10 m. The total amount of granulated concrete should be about 0.5-2.0 m 3  per m 2  floor area of the ventilation units that is to be heated/cooled, depending on the local climate and degree of insulation of the ventilation units. The temperature of the hot zone in the thermal store should be in the range 30-60° C., preferably 35-50°, and more preferably 40-45° C., while the cold zone should be about 5-20° C., preferably 7.5-15° C., and most preferably 8-12° C. The thermal store is depicted on a horizontal position, but can be oriented in any angle against the horizon. Also, there should preferably be provided means for drainage of condensed water. This is especially important for humid and warm climates where the apparatus is mainly engaged in cooling of the ventilation units. This can be provided by simply giving the tubes a slight inclination relative to the horizontal plane and some kind of drainage duct for discharging the condensed water. The linear flow velocity of the ventilation air during passage through the thermal store tubes is preferably about 1-2 m/s or less in order to ensure a rapid thermal equilibrium and moderate pressure losses. A rapid thermal equilibrium is important for achieving a steep temperature gradient (reference numeral  32  in FIG. 3) and correspondingly short transition zone  9  between the hot  8  and cold zone  10  in the thermal store. 
     Also, by using two heat-pumps, a possibility exists for boosting the accumulation speed for filling the thermal store if only a short period of suitable outdoor temperatures is forecast. This feature enhances the overall energy reduction of the invention, since the probability of being forced to run the heat-pumps at less than optimal outdoor temperatures is reduced. 
     As mentioned, the operation of the preferred embodiment is performed in a set of different modes by selected turning on/off of fans and heat-pumps, and positioning of 2-way diverters/valves. It is preferred that the modes of operation are: 
     I. Neutral 
     In this case, there is sufficient heat production from other sources in the building. Outdoor air at  14  passes through fan  25  to VUs  1 , and is discarded via used air fan  22  and diverter  26 . 
     II. Heating 
     IIa: Normal heating mode, warm air supplied to or from the thermal store depending on outdoor temperature. Like mode I, but diverter  26  shifted to pass used air through heat-pump  4 , where fresh air is taken through  5 , heated and moved by fan  24  to VUs  1 . Depending on outdoor temperature heat-pump  4  may deliver more or less air than required by VUs  1 . 
     IIb: If surplus heat produced by heat-pump  4 , AND thermal core full OR mild/warm weather forecast, then heat-pump  4  is turned off, outdoor air admitted at  14 , diverted through thermal store by diverters  30  and  31 , and transferred as warm fresh air by fan  24  to VUs  1 . 
     IIc: If surplus heat produced by heat-pump  4 , AND thermal store NOT full, AND cool/colder weather expected, remainder from heat-pump  4  is transferred to thermal store through 2-way fan  23 , and diverted to exit at diverter  31 . The system may switch between IIb and IIc for minimising load on heat-pump  4 . 
     IId: If mild/warm now, AND cold weather expected, AND thermal store NOT full, then heat-pump  33  is started, taking outdoor air at full capacity and charging thermal store at 2-3 times ordinary flow rate through 2-way fan  23  with exit of cold air at  31 . At the same time, fan  24  delivers warm air to VUs as demanded. 
     III. Cooling 
     IIIa: If warm weather, then warm air enters through  15  and diverter  27  through fan  24  as warm, fresh air to VUs  1 . Warm air through  15  and  27  passes through the thermal store  11 , is cooled, and goes via diverters  31  and  30 , and fan  25  as cool, fresh air to VUs  1 . 
     IIIb: If cool/cold weather, then cool fresh air enters at  14 , passes through diverters  30  and  31  to charge the thermal store, and exit as warm fresh air through 2-way fan  23  and exit via diverter  27 . Some of this air is led through fan  24  to VUs  1  as fresh, warm air, depending on demand from the VUs. 
     IIIc: If lasting warm weather, with the thermal store in danger of being exhausted, then heat-pump  33  is turned on and warm fresh air enters through  34  to be cooled in heat-pump  33 , and then passed through diverter  29  both to fan  25  and to VUs  1  for cooling, and through diverters  30  and  31  to the thermal store  11  for charging, and exits as warm air through 2-way fan  23  and diverter  27 . 
     It is preferred that the software that selects which operation modus that is to be employed consists of six individual modules which co-operate as shown in FIG.  4 . Module one is separate and should be given as an input from the operator of each apparatus, but should preferably be supplied by firms that offer this service as a speciality in order to ensure a sufficiently high hit percent in the predictions. The remaining modules should preferably be run on a local PC or CPU that is connected to the regulation device that controls and regulates the settings of fans, heat-pumps and diverters. The run frequency should be of the order of once per hour, and will typically run for 5-10 seconds each time. 
     In order to make the controlling software compact and fast such that it may be placed in a separate small computing unit that is integrated as a part of the apparatus, it is preferred that the individual modules are made quite simple with the main task determining selection criteria for searching in a first decision table to determine mode of operation (module  4 ), and settings of diverters and fans (module  5 ). Also the last module (module  6 ) should be simple, using standard cards to turn data from the program into actuating voltage for switches. In detail, module  4  determines a set of selection criteria by matching forecast data to demand for heating or cooling, and for whether the thermal core should deliver or store energy. Each criterion sets or clears a corresponding bit in a computer integer word (typically 32 bit length). This word in turn acts as a search profile. 
     The central concept of the software is the decision table, of which an example is shown in Table 1. The table makes it possible to determine in a very fast and easy way what operating mode should be selected for optimal saving of energy under a large set of weather conditions bye use of bits that are set or cleared in appropriate positions. With 30 individual criteria as in the table, some 1 billion alternatives may be specified. In practice some 30-200 is sufficient, depending on local climate peculiarities. Table 1 illustrates a few examples of individual specification for mode IIa, and overlapping modes I and IIIa (e.g. all weekdays are treated the same). 
     The alternatives (corresponding to columns in Table 4) are subsequently treated as integer numbers, and sorted in numerical order in a table with associated operating mode. The proper operating condition is then found by a binary search in this table with the calculated search profile. By ordering the individual selection criteria suitably, similar operating conditions will have similar numeric values, and the search will find the nearest optimal match if the actual value is not in the decision table. As shown in Table 1, the ordering instead groups similar criteria together, for pedagogical purposes. Actual grouping in practice, as well as specific alternatives, may vary according to local climatic conditions, and can easily be developed by a skilled person. 
     EXAMPLE 2 
     This example gives an example of a preferred embodiment of the invention that is suitable for cold climates and in some coastal climates where the need for active cooling is unlikely to occur. This embodiment is exactly similar to the embodiment of example 1, except that heat-pump  33 , the right branch of duct  6  with 2-way flow diverter  28 , and duct  16  with 2-way flow diverter  29  and discharge outlet  20  is omitted. 
     EXAMPLE 3 
     This example gives an example of a preferred embodiment of the invention that is suitable for warm climates where the need for active heating is unlikely to occur. This embodiment is exactly similar to the embodiment of example 1, except that heat-pump  4  with the left branch of duct  6  with 2-way flow diverter  26 , fresh air inlet  5 , and discharge outlet  20  is omitted. 
     Even though the invention has been described by way of examples of preferred embodiments that employs air as the heat carrying and distributing medium, it should be clear that the invention also relates to the general principle of heating/cooling of buildings by utilising natural short term variations in the climate in a combination of heat-pumps and a thermal store. Thus, there might be envisioned many alternative embodiments that is obvious for a skilled person and that falls within the scope of this invention, including other forms and types of thermal stores such as construction parts of the buildings themselves, water-pools, other heat carrying and distributing media such as water, etc. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Example of decision table for specifying modes of operation 
               
             
          
           
               
                 Mode 
                   
                 Heating 
                   
                 Neutral 
                   
                 Cooling 
                   
               
               
                 Condition 
                 IIa 
                 IIb 
                 . . . 
                 I 
                 . . . 
                 IIIa 
                 . . . 
               
               
                   
               
               
                 Now &gt;5° C. below BT 
                 1 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 Now 0-5° C. below BT 
                 0 
                 1 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 Now 0-5° C. above BT 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 Now &gt;5° C. above BT 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 &gt;5° C. below BT in 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 daytime 
               
               
                 0-5° C. below BT in 
                 1 
                 1 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 daytime 
               
               
                 0-5° C. above BT in 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 daytime 
               
               
                 &gt;5° C. above BT in 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 daytime 
               
               
                 &gt;5° C. below BT at night 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 0-5° C. below BT at 
                 1 
                 1 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 night 
               
               
                 0-5° C. above BT at 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 night 
               
               
                 &gt;5° C. above BT at night 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 &gt;5° C. below BT in 3 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 days 
               
               
                 0-5° C. below BT in 3 
                 1 
                 1 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 days 
               
               
                 0-5° C. above BT in 3 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 days 
               
               
                 &gt;5° C. above BT in 3 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 days 
               
               
                 Store empty of heat 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 Store 0-20% of heat 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 Store 20-40% of heat 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 Store 40-60% of heat 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 Store 60-80% of heat 
                 1 
                 1 
                 . . . 
                 1 
                 . . . 
                 0 
                 . . . 
               
               
                 Store 80-100% of heat 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 Store full of heat 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 Monday 
                 1 
                 1 
                 . . . 
                 1 
                 . . . 
                 1 
                 . . . 
               
               
                 Tuesday 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 1 
                 . . . 
               
               
                 Wednesday 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 1 
                 . . . 
               
               
                 Thursday 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 1 
                 . . . 
               
               
                 Friday 
                 0 
                 0 
                 . . . 
                 1 
                 . . . 
                 1 
                 . . . 
               
               
                 Saturday 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . . 
               
               
                 Sunday 
                 0 
                 0 
                 . . . 
                 0 
                 . . . 
                 0 
                 . . .