Abstract:
An efficient indirect building cooling system that bypasses a conventional chiller mechanism by connecting the indoor and outdoor intermediate fluid systems when conditions permit. This system includes indoor and outdoor fluid cooling circuits, each of which interfaces with the conventional chiller mechanism. The two fluid cooling circuits are connected together when weather conditions make doing so more efficient.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a cooling system for buildings, and more particularly to a cooling system that uses indirect evaporative cooling with a supplemental chilling mechanism. 
         [0002]    Conventional refrigeration (“cooling”) units used to cool buildings, automobiles and other places in which people, computers or other items dwell at maximum acceptable temperatures utilize the Carnot cycle. In such a conventional cooling unit, a compressor is used to cyclically compress and expand a fluid (“refrigerant”), thereby changing the refrigerant&#39;s temperature, in order to transfer thermal energy (“heat”) from air inside the building to air outside the building. During the cycle, the temperature of the refrigerant is reduced well below the temperature of the indoor air so that heat is transferred to the refrigerant when air is blown across thermally conductive heat exchangers the refrigerant flows through. The refrigerant temperature is next increased well above the temperature of the outdoor air so that heat is transferred from the refrigerant to the outdoor air when air is blown across thermally conductive heat exchangers the refrigerant flows through. 
         [0003]    The conventional Carnot cycle refrigeration mechanism has four main components, as illustrated schematically in  FIG. 1 : an evaporator  10 , a compressor  20 , a condenser  30  and an expansion device  40 . These components are connected by fluid conduits  12 ,  22 ,  32  and  42  that contain the refrigerant in liquid and gas states and convey the refrigerant from one component to the next without permitting significant atmospheric contamination by refrigerant or significant contamination of the refrigerant by atmospheric matter. The components of the refrigeration mechanism, and its operation, are explained below beginning with the evaporator  10 . Although the operation begins with the evaporator, it will be understood that the mechanism is continuous and cyclical, and the explanation below starting with one component does not suggest a “beginning” or “end”. 
         [0004]    The evaporator  10  is a heat transfer device that transfers heat in the warmer indoor air to the cold refrigerant. The refrigerant in the evaporator can cool air directly in the case of an air cooling coil, which is an air-to-refrigerant heat exchanger commonly found in home air conditioning units. Alternatively, the refrigerant in the evaporator can cool the air indirectly using an intermediate fluid, such as water or glycol in the case of water chillers used in skyscrapers and factories. The intermediate fluid of an indirect system&#39;s indoor water circuit  16  can then be pumped to heat exchangers  14  in many locations where the refrigerant can cool the air with air-to-water cooling coils. The warmed water is then pumped by the electric pump  18  to a water-to-refrigerant heat exchanger, such as the evaporator  10 , where the water is cooled when the refrigerant absorbs the heat. In the evaporator  10 , the liquid refrigerant evaporates due to the absorption of heat from the water. 
         [0005]    After the warmed gaseous refrigerant leaves the evaporator, it flows along the conduit  12  to the compressor  20 . The compressor compresses the refrigerant significantly to increase its pressure, thereby increasing the temperature of the refrigerant due to well-known laws of chemistry (e.g., the ideal gas law: PV=nRT). Hot refrigerant exits the compressor and flows toward the condenser  30 . 
         [0006]    The condenser  30  is also a heat transfer device, and the condenser transfers heat from the hot refrigerant to the outdoor air. The refrigerant in the condenser can heat the outdoor air directly in the case of an air-to-refrigerant heat exchanger commonly found in home air conditioning units. In such a direct condenser, a coil is placed outdoors and the outdoor air is drawn over the coil using an electric fan, thereby cooling the refrigerant in the coil. Alternatively, the refrigerant in the condenser can heat the outdoor air indirectly using an intermediate fluid, such as water that flows through an outdoor water circuit  36 , to cool the refrigerant in a water-to-refrigerant heat exchanger, and then is pumped by the electric pump  38  to an outdoor air-to-water heat exchanger  34 . In both the direct and indirect condensers, the refrigerant is cooled sufficiently to cause condensation of the refrigerant to a liquid phase that remains at high pressure. 
         [0007]    The high pressure, relatively cool liquid refrigerant flows through the conduit  32  to an expansion device  40 . The expansion device is typically a valve/orifice that meters the flow of refrigerant through the conduit. That is, the refrigerant cannot flow without restriction through the orifice, but is metered by the viscosity of the fluid and the size of the orifice that cause the pressure on one side of the orifice to be much higher than on the other side of the orifice. The pressure of the refrigerant on the downstream (evaporator) side of the expansion device  40  is significantly lower than on the upstream side of the expansion device. This significant reduction in pressure (prior to the refrigerant entering the evaporator) causes a significant drop in the temperature of the refrigerant, which permits the cold refrigerant to absorb heat when it enters the evaporator  10  and begins the cycle again. 
         [0008]    Outdoor air can be used to cool the refrigerant in the condenser directly by simply placing the condenser coil outdoors and directing outdoor air across it. A variation of this “outdoor chiller” is an evaporative condenser in which the outdoor coil is sprayed with water to further cool the refrigerant. In both of these “direct” configurations, no intermediate fluid is utilized between the refrigerant and the outdoor air. 
         [0009]    Conventional cooling systems used in large buildings use “indirect” cooling for a safer and more efficient system. Using non-toxic water or other fluid pumped in an indoor circuit throughout the building from the water-to-refrigerant evaporator  10 , any or all parts of the building can be cooled safely by connecting a water-to-air heat exchanger  14  to a water line that is part of the indoor evaporator circuit  16 . The cool water is pumped to the room to be cooled, and air is drawn across the coils of the heat exchanger  14 , thereby cooling the room air as the water thus absorbs heat from the room&#39;s air. The water is then pumped back to the evaporator  10  to transfer its heat to the cold refrigerant. When cooling is not required in a particular room or part of the building, the water is not pumped or air is not blown over the water-to-air heat exchanger. 
         [0010]    The condenser  30  is also indirectly cooled using non-toxic water that is pumped from the water-to-refrigerant heat exchanger (the condenser  30 ) to the outdoors where the heat is released. The water is the intermediate media in the outdoor condenser circuit  36  that cools the refrigerant in the water-to-refrigerant heat exchanger (condenser  30 ), and then the water is cooled by outdoor air in the water-to-air heat exchanger  34 . 
         [0011]    There are generally three types of devices used to cool the water with outdoor air in an outdoor condenser circuit. A fluid cooler is a large outdoor coil with a fan. The water flows through the coil and the fan draws air across the coil to cool the water. This operates in a similar manner as a conventional household air conditioning system&#39;s outdoor unit, except that the fluid cooler cools the intermediate fluid instead of refrigerant. 
         [0012]    An evaporative cooler uses the same configuration as a fluid cooler with the addition of a separate water source that sprays water over the coil. The water evaporates, thereby cooling the air, and the colder air is drawn across the coil to cool the water in the coil more effectively. When using an indirect evaporative cooler the water that cools the condenser never comes in contact with the outdoor air because the condenser water circuit is a closed circuit. The water sprayed over the coil is collected, placed in fluid communication with the evaporative cooler&#39;s pump and is sprayed over the coil again. 
         [0013]    The third type of water cooling device is a cooling tower, which uses a box with a large fan and “fill”, which is a medium used to increase the surface area and the time of contact between the air and water. In a cooling tower, water from the condenser is cooled by spraying the water on the fill and using the large fan to cool the water. In a cooling tower, some of the water evaporates, which cools the water further. The cool water is collected in the bottom of the cooling tower (basin) where it is pumped back into the building. 
         [0014]    The water in a conventional cooling tower is directly exposed to the outside air, which means the water becomes dirty and then flows back through the internal fluid conduits in the building. In essence, the water “cleans” outdoor air by trapping particles and chemicals in the air when the two fluids make contact. In most conventional cooling towers, an attempt is made to clean the water because dirty water will foul the water cooled condenser over time and the water-cooled condenser must be cleaned. Even with cleaning of the water, the condenser must be cleaned about once every year. 
         [0015]    In order to avoid dirtying the water of a cooling tower, an intermediate heat exchanger is commonly used to transfer heat between the cold cooling tower water and the indoor building cooling water. These heat exchangers are typically plate and frame heat exchangers, and much care is needed to keep them clean. 
       BRIEF SUMMARY OF THE INVENTION 
       [0016]    The invention contemplates an indirect evaporative cooling system with a supplemental chiller that can be bypassed in the event that the conditions warrant. An integral economizer is made possible by cooling the condenser with water. Under acceptable weather conditions the building can be completely cooled by the evaporative cooler portion of the circuit and the supplemental chiller is shut down. When weather conditions are not favorable for the evaporative cooler to perform all of the cooling, the supplemental chiller is engaged to supplement the cooling of the evaporative cooler. Thus, the building can be cooled when the outdoor conditions are not conducive to cooling by the evaporative cooler alone. 
         [0017]    The evaporative cooler preferably uses a water spray over a closed coil. Air is drawn over the coil and the water evaporates. The evaporating water cools the air, which in turn cools the coil. The water in the coil is thus cooler than using air alone, thereby making the unit more efficient than an air-cooled chiller. The preferred unit is designed to operate with and without the evaporative water sprayed over the coil. When the outdoor conditions permit, the enhanced evaporative cooling allows more hours of “free” cooling without supplemental use of the chiller or of the water spray. This is useful to conserve water when dry outside air is sufficiently cool, and this limits the amount of water that is used by the evaporative cooler. The ability to operate without the evaporative spray also allows the water in the evaporative cooler to be drained during freezing conditions to avoid breakage and to avoid additional evaporation. In the case of a water outage, the unit is capable of running on the hottest day. This eliminates the need for redundant water storage on site or auxiliary wells. 
         [0018]    When the outdoor conditions are capable of producing complete cooling using the evaporative cooler alone, the chiller is turned off. The water from the indoor evaporator circuit that flows through the building&#39;s internal conduits is then directed to the outdoor condenser circuit. The indoor evaporator circuit water is thus cooled by the evaporative cooler and is then pumped back to the indoor water circuit to further cool the building. The outdoor water circuit water preferably also bypasses the condenser. In this way, the water can avoid the condenser when the chiller is dormant. Alternatively, the water can pass through the condenser if it is desired. 
         [0019]    A three-way valve is used to divert all the water in the indoor evaporator circuit to the outdoor condenser circuit. A hydraulic bridge also allows the building&#39;s indoor evaporator circuit water to mix with the water of the outdoor condenser circuit before it either enters or bypasses the condenser. Water preferably only enters the water-cooled condenser when supplemental mechanical cooling by the chiller occurs, but this can be varied if advantages arise. When there is supplemental cooling by the chiller, the water of the indoor evaporator circuit mixes with water of the outdoor condenser circuit to be further heated by the chiller&#39;s condenser and then enters the evaporative cooler outdoors. The evaporative cooler then cools the hotter water by using evaporative cooling and then is returned back to the indoor evaporator circuit, preferably just upstream of the evaporator, where it is cooled further to meet the cooling requirements of the building. 
         [0020]    If the outdoor conditions are not favorable, the valving does not direct the water from the indoor evaporator circuit to the condenser circuit and the evaporative cooler. In this case, no free cooling is provided and the system works like a standard water-cooled chiller. 
         [0021]    The chiller circuit uses large motors to drive the compressor, and these are expensive to operate. It is contemplated to take the refrigeration circuit out of operation when the outdoor heat exchanger is sufficient to cool the water sufficiently to cool the indoor air. This could occur when the temperature conditions outdoors are favorable, and/or when the outdoor humidity conditions are favorable to the outdoor heat exchanger having water (which is not taken from the indoor or outdoor circuits) sprayed onto the outside of the heat exchanger to cool the water flowing through the heat exchanger during evaporation of the water into the outdoor air. A computer detects the temperature, humidity, dew point and other conditions inside and outside the building to determine when to cease operation of the refrigeration cycle and permit the water circuits to bypass the refrigeration circuit. 
         [0022]    This system is unique inasmuch as it utilizes evaporative free cooling without the use of an intermediate heat exchanger. It allows simultaneous free and mechanical cooling, which will reduce the amount of electrical energy being used. It is preferably provided in an assembled package that has all these features built in so that it can replace inefficient air-cooled systems that do not have free cooling. It is designed to limit water use by being able to run without the evaporative spray pumps being energized. This allows safe cold weather operation as well as emergency operation in the case of a water outage. It is also more efficient than an air-cooled chiller because it uses evaporative cooling. At the same time the evaporative cooling is indirect so that airborne contaminants do not enter the condenser circuit water. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0023]      FIG. 1  is a schematic hydraulic circuit illustrating a prior art cooling system. 
           [0024]      FIG. 2  is a schematic hydraulic circuit illustrating a cooling system according to the present invention. 
       
    
    
       [0025]    In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific term so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word connected or terms similar thereto are often used. They are not limited to direct connection, but include connection through other circuit or mechanical elements where such connection is recognized as being equivalent by those skilled in the art. In addition, circuits are illustrated that are of a type that performs well known operations on fluids. Those skilled in the art will recognize that there are many, and in the future may be additional, alternative circuits that are recognized as equivalent because they provide the same operations on the fluids. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 2  illustrates a cooling system  100  that embodies the invention and typically serves a large building, such as a skyscraper, apartment building, school, hospital or any other large building  101 . The cooling system  100  can be housed within the building, outside the building or a hybrid in which some of the components are inside and some are outside. A mechanical chiller circuit  126  includes an evaporator  110 , a compressor  120 , a condenser  130  and a valve  140  connected by a closed loop of conduits  112 ,  122 ,  132  and  142  containing a refrigerant. The chiller circuit  126  operates in a known manner (as described above in relation to the prior art system shown in  FIG. 1 ) to pump heat from the evaporator  110  to the condenser  130  so that the heat can be removed from the building  101  in which the chiller circuit  126  operates. 
         [0027]    An indoor evaporator fluid circuit  116  includes the evaporator  110  and the indoor air heat exchanger  114  connected by a loop of conduit. The indoor circuit  116  is illustrated with a single heat exchanger  114 , but in a typical installation there are dozens if not hundreds of heat exchangers in series and/or parallel along the indoor circuit  116 . Such heat exchangers function substantially identically with the heat exchanger  114 , and therefore only the heat exchanger  114  is described below. Water is the preferred intermediate fluid media that flows through the indoor circuit  116  as impelled by a conventional pump  118  connected to a central computer  200 , but a water and antifreeze mixture or any other acceptable fluid can be substituted for the water. The central computer  200  is preferably a generally programmable computer, such as a personal computer, but could be a specialized computer such as a logic circuit, a mechanical computer or any equivalent. 
         [0028]    An outdoor condenser circuit  136  includes the condenser  130  and the outdoor air heat exchanger  134  connected by a loop of conduit. The outdoor circuit  136  is illustrated with a single heat exchanger  134 , which in a typical installation is an evaporative cooler with a conventional water spray system  8  that can be actuated to spray water onto a coil through which the water that is part of at least the outdoor circuit  136  flows. The sprayed water is part of neither the outdoor circuit  136  nor the indoor circuit  116 . It is preferred that water flows through the outdoor circuit  136  as impelled by a conventional pump  138  connected to the central computer  200 , but the water can be replaced by water including antifreeze or by any other acceptable fluid. Because the fluids of the indoor circuit  116  and the outdoor circuit  136  are mixed during at least some modes of operation of the system  100 , the fluids used in the circuits  116  and  136  are preferably the same. The pumps  118  and  138 , as well any other item referred to herein as connected to the central computer  200 , can be connected thereto by wire or a wireless connection. 
         [0029]    A bypass  150  is formed of the conduits  151 ,  152  and  153  extending from the conduit of the outdoor circuit  136  just upstream of the condenser  130  to the conduit just downstream of the condenser  130 . A valve  155  is mounted at the juncture where the conduit  151  begins and controls whether fluid in the outdoor circuit  136  flows through the condenser  130  or through the bypass  150  as will be described in more detail below. The valve  155  is connected to and is operated by the central computer  200  or through the internal controls of the chiller assembly. 
         [0030]    The bypass conduits  160  and  170  extend between the indoor circuit  116  and the outdoor circuit  136 . The conduit  160  permits water to flow from the indoor circuit  116 , starting at a point just downstream of the heat exchanger  114 , directly to a point in the outdoor circuit  136  that is just upstream of the condenser  130 . The conduit  170  permits water to flow from the outdoor circuit  136 , starting at a point just upstream from the condenser  130 , directly to a point in the indoor circuit  116  that is just upstream from the evaporator  110 . The entry and exit points of the conduits  160  and  170  can be varied. The bypass conduits  160  and  170  are opened and closed to the circuits to which they connect by the valves  162  and  172 , respectively. The valves  162  and  172  are connected to, and are actuated between the opened and closed positions by, the central computer  200 . The term “downstream”, as used herein, refers to a relative position in a hydraulic circuit that is farther along in the direction of fluid flow. The term “upstream”, as used herein, refers to a relative position in a hydraulic circuit that is not as far along in the direction of fluid flow. 
         [0031]    It is preferred that the central computer  200  receives signals from sensors (not illustrated) that detect various conditions within the building  101  in which the system  100  is installed, such as the temperatures in discrete portions of the building, which can be rooms or regions of the building. Furthermore, the computer  200  preferably receives information about the temperature of the fluids in the circuits  116  and  136 , for example from temperature sensors (not shown). The computer  200  also receives signals from weather sensors (not shown) around the heat exchanger  134 , in order to detect conditions, such as outdoor air temperature, relative humidity, dew point, wet bulb, wind speed, wind direction, barometric pressure and any other conditions desirable for the operation of the apparatus. The central computer  200  is also connected to the valves described herein, the compressor  120 , the expansion valve  140  and any other controllable features of the system  100 . The central computer  200  is preferably programmed to receive the condition signals and process them using algorithms to actuate, in a conventional manner, the valves, compressor and other features to which it is connected in order to optimize the operation of the system shown in  FIG. 2 . 
         [0032]    The system  100  of  FIG. 2  is in a state of non-operation. The system is started from a non-operational state by applying power to the central computer  200 , which, once operational, begins receiving building temperature data and weather data. Based upon pre-programmed instructions, the computer actuates the system  100  into one of the modes of operation when the indoor temperature is sufficiently high to require indoor cooling. 
         [0033]    There are three modes in which the system  100  is contemplated to operate, but there could be more than three as will be apparent to a person of ordinary skill from the description herein. First, the system  100  can operate the chiller circuit  126  without any use of the bypass conduits  160  and  170 . In this operating mode, referred to as “high power mode”, the compressor  120  is actuated by the central computer  200  to compress refrigerant in the chiller circuit  126 , and the pump  118  in the indoor circuit  116  and the pump  138  in the outdoor circuit  136  pump water around their respective circuits. It is possible for the water sprayer  8  to operate in high power mode, but it is not required. The most electricity used in any mode of operation is used in the high power mode, and this mode of operation is typical when there is the highest load imposed on the system by the building during the weather that is the least favorable for cooling. This can be, for example, the operating mode used on a hot, humid day with little air movement, and in this mode the system  100  operates in a conventional manner without connecting the indoor circuit  116  and the outdoor circuit  136  to one another via the conduits  160  and  170  or any other fluid connection. 
         [0034]    The second possible mode of operation is the “low power mode” and this mode occurs when the chiller circuit  126  is not operational—that is, when the compressor  120  is not powered. The low power mode includes the opening of the valves  162  and  172  that permit water to flow from the indoor circuit  116  to the outdoor circuit  136  through the conduit  160  and to return through the conduit  170 . The low power mode is the operating mode in which the least amount of electrical energy is used, and is the mode selected when there is a load imposed on the system by the building when the outdoor conditions permit cooling to occur by the evaporative cooling only using the outdoor air heat exchanger  134 . This mode is described in detail below. 
         [0035]    The third mode is the “medium power mode” in which the chiller circuit  126  is operating—that is, when the compressor  120  is powered—and the valves  162  and  172  are open to permit water to flow from the indoor circuit  116  to the outdoor circuit  136  through the conduit  160  and to return through the conduit  170 . The medium power mode is the operating mode in which more electrical energy is used than the low power mode, but less than the high power mode, and is typical when there is a significant load imposed on the system by the building, but when the outdoor conditions permit partial cooling by evaporative cooling using the outdoor air heat exchanger  134  and partial cooling using the mechanical chiller circuit  126 . This mode is described in detail below. 
         [0036]    In the high power mode, all thermal energy is moved from the indoor circuit  116  to the outdoor circuit  136  through the mechanical chiller circuit  126 . Because thermal energy is transferred more rapidly when there is a greater temperature differential between the source of the energy and the destination, the chiller circuit  126  can transfer energy rapidly between the indoor circuit  116  and the outdoor circuit  136 . This comes at a cost, however, because it takes substantial electrical energy to drive a conventional compressor. Nevertheless, this energy input provides the temperature differential when the refrigerant becomes extremely hot so that the refrigerant transfers substantial thermal energy to the water in the outdoor circuit  136  when the refrigerant and water flow through the condenser  130 . Subsequently, when the cooled refrigerant expands in the valve  140 , the refrigerant reaches a very cold temperature to significantly cool the water in the indoor circuit  116  when both fluids pass through the evaporator  110 . This provides a significant temperature differential allowing the refrigerant to receive substantial thermal energy from the water in the indoor circuit  116 . Thus, the high energy mode is very effective at pumping thermal energy from the indoor circuit  116  to the outdoor circuit  136 , but this comes at the price of large amounts of electrical energy. 
         [0037]    As noted above, the water in the indoor and outdoor circuits  116  and  136  is circulated therein by one or both of the pumps  118  and  138 . In the low power mode, the chiller circuit  126  is shut down, and the valves  162  and  172  are opened to allow water to flow into the conduits  160  and  170  from the indoor and outdoor circuits  116  and  136 . Thus, no thermal energy is moved from the indoor circuit  116  to the outdoor circuit  136  through the chiller circuit  126 . This saves electrical energy, because the main consumers of energy in the low power mode are the pumps  118  and  138  (only one of which might be used to further save energy), and these pumps use far less electricity than the compressor  120 . 
         [0038]    During the low power mode when the water flowing in the indoor circuit  116  reaches the valve  162 , the water is diverted to the conduit  160 . This water has just been warmed by passing through the indoor heat exchanger  114 , and the water reaches the outdoor circuit just upstream of the condenser  130 . It is preferred in the low power mode for the water to effectively bypass the condenser and flow instead through the bypass  150 , as diverted by the valve  155 . 
         [0039]    After bypassing the condenser  130 , the water in the outdoor circuit  136  passes through the outdoor heat exchanger  134  and is cooled. The water then flows to the valve  172 , which diverts the water into the conduit  170 . The cooled water exits the conduit  170  by entering the indoor circuit  116  just upstream of the evaporator  110  and just downstream of the valve  162 . It is possible to bypass the evaporator  110  using a bypass similar to the bypass  150 , but this is not necessary. This cooled water is circulated around the indoor circuit  116  and enters the indoor heat exchanger  114  to cool the air inside the building to which the system  100  is operatively connected. This cycle is repeated for as long as the low power mode is called for by the computer  200 , based on the conditions. It is possible during the low power mode for the water sprayer  8  to spray water on the outdoor heat exchanger  134  in a conventional manner to further cool the air that contacts the outdoor heat exchanger  134 , but this is not required. 
         [0040]    The central computer  200  uses pre-programmed algorithms to determine whether the building cooling load requirements can be met by the low power mode in order to save energy. It is contemplated that the system  100  can be switched back and forth between low and high power modes in order to make the system  100  more energy efficient when the conditions permit. Alternatively, or additionally, the medium power mode can be engaged as will now be described. 
         [0041]    In the medium power mode, the system differs from the high power mode inasmuch as the valves  162  and  172  are open to divert the water from the indoor circuit  116  to the outdoor circuit  136  as in the low power mode. Additionally, in the medium power mode, the compressor  120  is powered to compress the refrigerant in the chiller circuit  126 , but it is preferably powered to operate at a lower level than during the high power mode. For example, the compressor  120  can be driven to operate at about one-quarter, one-third, one-half, three-quarters or some other fraction of the maximum amount of compression of which it is capable. In an example, the compressor  120  is actuated to operate at about one-half of the maximum compression. Thus, the medium power mode is a “hybrid” of the low and high power modes. In the medium power mode, thermal energy is pumped from the indoor circuit  116  to the outdoor circuit  136  through the conduits  160  and  170  and through the chiller circuit  126 . The degree of compression can be varied as the system&#39;s requirements change. 
         [0042]    At the outdoor circuit  136 , water enters the circuit just upstream of the condenser  130  via the conduit  160  directly from the indoor circuit  116  and mixes with water flowing around the circuit from the outdoor heat exchanger  134 . Some of the water upstream of the condenser  130  can be diverted around the condenser  130  by the valve  155  and the bypass  150  and some can pass through the condenser  130 . Alternatively, all water upstream of the condenser  130  can pass completely through the condenser  130 . Whether all, some or no water bypasses the condenser  130  is determined by the conditions, as detected by the central computer  200 , in various components of the system  100  and in and around the building. In particular, the conditions in the chiller circuit  126  can be detected to determine whether and how much to bypass the condenser  130 . 
         [0043]    During the medium power mode, as the building load increases and/or as the outdoor conditions reduce the energy efficiency of cooling by bypassing the chiller circuit  116  as in the low power mode, a smaller amount of water bypasses the condenser  130  and the system  100  begins to resemble the high power mode of operation, except that the compressor  120  operates at a lower power level. Similarly, as the building load decreases and/or as the outdoor conditions increase the energy efficiency of cooling by bypassing the chiller circuit  116  as in the low power mode, a larger amount of water bypasses the condenser  130  and the system  100  begins to resemble the low power mode of operation except that the compressor  120  is operating. In this way, the outdoor heat exchanger  134  accomplishes more of the cooling as the outdoor conditions permit, thereby reducing the load on the evaporator  110 . 
         [0044]    It is preferred that in the medium power mode, the water sprayer  8  is used to further cool the outdoor heat exchanger  134 , particularly as the weather conditions warrant. Thus, the medium power mode increases the energy efficiency of the system  100  over the high power mode while pumping larger amounts of thermal energy out of the building than the low power mode. 
         [0045]    As noted, the valves  162 ,  172  and  155  are opened and closed completely or to varying degrees as controlled by the central computer  200  that senses conditions inside and outside the building  101 . When the indoor and outdoor water circuits  116  and  136  are connected by the conduits  160  and  170 , the water in the indoor circuit  116  that has been warmed by absorbing heat from the indoor air flows to the outdoor circuit  136  and flows either through the condenser  130  or bypasses the condenser  130 . Whether the condenser  130  is bypassed is determined by the greatest efficiency in operation. The water flows into the outdoor heat exchanger  134  and releases heat to the outdoors, then flows through the conduit  170  back to the indoor circuit  116  just upstream of the evaporator  110  where the water releases heat to the refrigerant (if the chiller circuit  126  is in operation). The water, cooled in the outdoor heat exchanger, flows through the indoor heat exchanger  114 , thereby cooling the indoor air. This cycle repeats and can be varied based upon changing conditions, electricity costs and/or preferences. 
         [0046]    The pump  118  for the indoor circuit  116  can vary the flow of the heat transfer fluid through the indoor air heat exchanger  114  or the flow can remain constant. The pump  138  for the outdoor circuit  136  can vary the flow of the heat transfer fluid through the indoor air heat exchanger  134  or the flow can remain constant. Flow variation within a circuit can take place by changing the speed of the pumps  118  and  138  or by using separate, variable speed pumps that distribute fluid to the heat exchangers  114  and  134 . Thus, in some circumstances the pumps  118  and  138  do not impel fluid to the heat exchangers  114  and  134 , but the variable speed pumps do. 
         [0047]    Additionally, it should be noted that the fluid flows in the circuits  116  and  136  are typically different, and the pressures in the circuits vary as does the pressure produced by the pumps  118  and  138 . As shown in  FIG. 2 , hydraulic bridges between the connections  160  and  170  at the indoor circuit and the outdoor circuit allow bypassing of fluid flow and pressure so that the pumps  118  and  138  can act independently, if desired. 
         [0048]    This detailed description in connection with the drawings is intended principally as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be adopted without departing from the invention or scope of the following claims.