MULTICYCLE SYSTEM FOR SIMULTANEOUS HEATING AND COOLING

Abstract

System that delivers heating and/or cooling to multiple zones using two or more thermodynamic cycles that are tailored specifically to the overall load and in so doing provide a heating or cooling effect at high efficiency using only a single work fluid and a single accumulator connected to two or more external media.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. 371 US national phase application of PCT international application serial number PCT/US2014/030425, entitled “MULTICYCLE SYSTEM FOR SIMULTANEOUS HEATING AND COOLING,” filed on Mar. 17, 2014, which claims priority to U.S. Provisional Application Ser. No. 61/789,668, titled “MULTICYCLE SYSTEM FOR SIMULTANEOUS HEATING AND COOLING,” filed Mar. 15, 2013, all incorporated by reference herein in their entirety.

FIELD OF THE DISCLOSURE

Modern systems for building heating, ventilation and air conditioning (HVAC) are typically sectioned into one or more zones. Each zone might be configured with its own independently controlled HVAC system; or alternatively, the building might be configured with a single, central HVAC system, with separate controls in multiple zones to distribute conditioned air as demanded. Zones can vary in size, and loads within each zone will change depending on the time of day, building orientation, occupancy, productive activity and many other variables. At any given time, some zones could call for cooling, while others could call for heating. For example, in a building with a strong southern exposure and many windows, the morning demand might call for cooling on the south side while the north side still uses heating.

A common means for dealing with such a variety of loads is to operate, at the same time, separate cooling and heating systems running independently of each other. There are times when a zone were to demand cooling, while a heating system might still be used to restore air to a comfortable temperature after it has been chilled for the purpose of dehumidification.

In the particular case of heat-pump systems wherein both heating and cooling are provided simultaneously, equipment costs are high because of the need for multiple sub-systems, each with its own set of cycle components (typically a compressor, accumulator, expander and heat exchangers), each one optimized for the particular mode of air conditioning—heating or cooling—being applied.

In any thermodynamic system that causes heat to move from one location to another, heat exchangers facilitate the absorption of energy from one location and the expulsion of energy to another. In the typical room air conditioner, heat is absorbed by a cold fluid circulating through a coil that is exposed to indoor conditions, thereby cooling the room air. After compression to a higher temperature the fluid is condensed in another coil that is exposed to the outdoors, thereby rejecting heat to an environment that is outside of the room being cooled. The converse is true in the case of the outside air being used as a source of heat for indoor air, in which case the cycle is reversed so that working fluid vaporizes in the outside coil, is then compressed to a higher temperature, and then condenses in an indoor coil to release heat inside a building. The colder the outside air, the harder the compressor needs to work to provide adequate heat indoors.

In applications involving multiple zones, the need could arise for heating in some areas and cooling in others. This is often the case in large buildings, where southern exposures may incur enough solar heat to require cooling, even in winter, while the back of the building is being heated. For situations such as this, a popular remedy is Variable Refrigerant Flow (VRF) systems. Such systems employ a variable flow compressor that responds to changes in the load inside the building. Automated valves in the system direct fluid to the appropriate subsystem for heating or cooling. Valve multiplexers facilitate the movement of heat from one room to another, but overall the system is characterized by a single cycle driven by the compressor of the outdoor unit. The heating and cooling potential in various zones is confined to the limits of temperature and pressure of the cycle.

One way to improve efficiency is to absorb heat from, or to reject heat to, the earth. Such systems are commonly called Ground-Source Heat Pumps (GSHPs). Carbon dioxide can be safely recirculated though ground loops without fear of environmental damage in the event of a leak. A conventional system with carbon dioxide as a working fluid can use a compressor drives the fluid through the outside medium—be it air, water, soil or other “environmentally contaminable” medium—to either lose energy or absorb energy before recycling back to system or transferring heat indoors. Fluid returns to the indoor system either as a gas or a liquid, depending on the air-conditioning mode set indoors.

What is lacking is a system that can deliver heating or cooling to a zone using a thermodynamic cycle that is tailored specifically to the overall load and in so doing provide a heating or cooling effect at high efficiency.

SUMMARY OF THE DISCLOSURE

To that end, it is an object of this invention to heat and cool multiple zones simultaneously by operating different cycles of heating and cooling simultaneously with a single fluid that shares a common point with all the cycles. More specifically, the common point in all cycles is the neutral condition.

It is a further object of this invention, the energy transferred to one of the external media is the net energy duty of all the remaining cycles and such external media is ground, air or water.

By accumulator is meant any means of storing the working fluid and containing it within a defined space, at a state condition known herein as the neutral condition, said space of which may be in the form of a vessel, a collection of vessels or closed channels, be they above ground or below ground.”

By compressor and its root derivatives is meant the impelling of gas to a substantially higher pressure.

By neutral condition is meant a condition of temperature and pressure common to each thermodynamic cycle where the liquid and gas are in equilibrium.

By pump and its root derivatives is meant the impelling of liquids.

By blower is meant a device to drive gas with enough compression that it will flow at the desired flow rate.

By working fluid is meant the substance in either liquid or gaseous state that conveys heat from one point to another within an apparatus and is impelled by a pump, blower or compressor.

By heat sink is meant where energy is absorbed.

By heat source is meant where energy is provided.

By external medium is meant earthen ground, indoor air, ventilation air, outdoor air, water, construction features of a building, liquid or solid phase change material, or a heat-transfer fluid that further transfers the energy to and from another medium, with any of which the working fluid exchanges heat.

By zones is meant external spaces within which there are different demands for heating or cooling.

In the present invention energy is transferred between one or more external media using a single working fluid operating in more than one thermodynamic cycles simultaneously, wherein there exists at least one condition of temperature and pressure in common with each cycle, said condition referred to herein as the neutral condition. The neutral condition is controlled so as to ensure the simultaneous existence of both liquid and vapor states of the working fluid, in thermodynamic equilibrium. In one embodiment of the apparatus of the present invention the neutral condition is held in the accumulator. At the location of the neutral condition, the working fluid can act as a heat source for at least one thermodynamic cycle while simultaneously acting as a heat sink for at least one other thermodynamic cycle. Manipulating the neutral condition, results in an enthalpy change that balances the net energy change of all the thermodynamic cycles.

The fluid is contained and pressurized within pipes, tubing and heat-exchange equipment, collectively referred to as channels, and is driven through them. One preferred embodiment of a driving means is a pump, while other embodiments include such means as a blower or compressor. Heat is transferred through these channels and external media at points along the flow path where a temperature differential exists between the working fluid and the external media.

In another embodiment of the present invention, one of the external media is earthen ground. Other embodiments of the external media include spaces to be cooled or heated. A preferred working fluid is carbon dioxide, although other working fluids may be used as well. Earthen ground can be used as either a heat sink or heat source in case conditions in the accumulator need a decrease or increase in energy, respectively, in order to maintain the neutral condition and adequate amounts of vapor and liquid and to keep the accumulator's liquid level within upper and lower set-point limits.

In one embodiment of the present method, any combination of two or more of the following thermodynamic cycles operates simultaneously to transfer energy, such as heating and cooling. One possibility could be a cycle wherein (i) the working fluid in at least one thermodynamic cycle is liquid in the neutral condition; (ii) the liquid working fluid is impelled from the location of the neutral condition by a mechanical means through an external medium that is a heat source; (iii) the liquid working fluid transfers energy to the heat source and then (iv) returns to the location of the neutral condition. A second possibility is a cycle wherein (i) the working fluid in at least one thermodynamic cycle is liquid at the location of the neutral condition; (ii) the liquid working fluid is depressurized from the neutral condition to a pressure that is less than that of the neutral condition; (iii) the lower pressure working fluid is impelled from the location of the neutral condition by a mechanical means through an external medium that is a heat source; (iv) the working fluid is compressed to a vapor state by a mechanical means to the pressure of the neutral condition. A third possibility is a cycle wherein (i) the working fluid in at least one thermodynamic cycle is gaseous at the location of the neutral condition; (ii) the gaseous working fluid is impelled by a mechanical means from the location of the neutral condition without substantial compression through an external medium that is a heat sink; (iii) the working fluid then returns to the location of the neutral condition. A fourth possibility is a cycle wherein (i) the working fluid in at least one thermodynamic cycle is gaseous at the location of the neutral condition; (ii) the gaseous working fluid is drawn from the location of the neutral condition and compressed to a pressure greater than that of the neutral condition pressure, thereby increasing in temperature; (iii) the working fluid is directed through external medium that is a heat sink; (iv) the working fluid expands to a pressure that is close to that of the neutral condition; and (v) the working fluid returns to the location of the neutral condition.

In another embodiment of the present invention liquid working fluid from the accumulator is impelled by a pump and is channeled through a warmer external medium causing the liquid fluid to absorb heat and evaporate to a vapor within the channel. Liquid working fluid from the accumulator is expanded to a pressure that is less than that of the neutral condition, then channeled through a warmer external medium that causes the liquid fluid to absorb heat and evaporate to a vapor within the channel, then is compressed back to the pressure of the neutral condition. Gaseous working fluid from the accumulator is blown without significant compression and channeled through a cooler external medium that causes the vapor fluid to expel heat and become a liquid. Gaseous working fluid from the accumulator is compressed to a pressure greater than that of the neutral pressure, from which point it is channeled through a cooler external medium that causes the vapor fluid to expel heat and become a liquid, and is then finally expanded back to the pressure of the neutral condition. After emerging from the channels that pass through warmer or cooler external media, the various streams of working fluid return to the accumulator vessel that is maintained at the temperature and pressure of the neutral condition. The net result of these cycles can cause a change in neutral conditions, typically changing the liquid level, pressure and temperature in the accumulator. In order to maintain the accumulator at prescribed conditions of temperature, pressure and liquid level, a separate stream of working fluid is channeled through one the external media acting as a heat sink or heat source, depending on need. This external medium is typically outside air, water, a heat transfer fluid or earthen ground. In a preferred embodiment, an external medium is earthen ground. The amount of working fluid diverted to this medium is sufficient to offset the net difference of the sum of the heat duties of all the other warm and cool external media traversed by working fluid. The energy transferred through the external media is the net energy of all of the thermodynamic cycles. For example, if the net heat duty from the other external media is positive, i.e., an excess of heat, vapor is driven by a blower or compressor from the accumulator and subsequently condensed while being channeled through a heat-sink medium, thus expelling heat. As fluid emerges from the heat sink it is channeled back to the accumulator. If the net heat duty is negative, i.e., a deficit of heat, liquid working fluid is pumped from the accumulator and subsequently evaporated while channeled through a heat-source medium, thus absorbing heat. It then returns to the accumulator.

Another embodiment of the present invention is an apparatus for transferring energy between two or more external media. A single working fluid operates in more than one thermodynamic cycle. One or more means of driving impels the single working fluid through channels to two or more external media. Pressure regulators, orifices, capillary tube, and other commercially available valving is used for pressure control of each thermodynamic cycle. An accumulator maintains the neutral condition of the thermodynamic cycles. In another embodiment, heat from one of the external media is transferred to another external media. The enclosed channels conduct working fluid through heat exchangers for the purpose of transferring heat to or from external media. Valves control the lowest and highest pressures of each thermodynamic cycle operating simultaneously, said valves ensuring that at least one of the highest or lowest pressure of each of the thermodynamic cycles is common to all cycles at the neutral condition, which is held in the accumulator. One or more driving means impels a portion of liquid working fluid that is close to the neutral-condition pressure, while one or more driving means impels a portion of vapor working fluid that is close to the neutral condition pressure. A driving means such as a compressor drives a portion of working fluid that is in vapor state regardless of pressure. The accumulator contains an amount of working fluid in excess of that used to fill the enclosed flow channels, while being controlled to a pressure that is close to the neutral-condition pressure, and in sufficient quantity so as to deliver working fluid in a given thermodynamic state to two or more of the external media and to ensure the availability both of liquid at any pump suction and of vapor for compression. The accumulator connects to channels through the various external media for the purpose of conveying excess energy to at least one of the external media, or absorbing energy from at least one of the external media. This external medium is typically outside air, water, a heat transfer fluid or earthen ground. In a preferred embodiment, an external medium is earthen ground. Channels in the form of pipe or tubing embedded in earthen ground contain the working fluid as it passes through this medium. The preferred working fluid is carbon dioxide, although the present invention is not limited to any one working fluid. Earthen ground can be used as either a heat sink or heat source in case conditions in the accumulator need a decrease or increase in energy, respectively, in order to maintain adequate amounts of vapor and liquid and to keep the accumulator's liquid level within upper (maximum) and lower (minimum) set-point limits. Other external media to which heat is expelled or from which heat is absorbed by the working fluid, may be but are not limited to room air, fresh ventilation air or an intermediate heat-transfer fluid such as water or glycol mixed with water. Liquid pumping and vapor blowing may supplement the work of compressors, thereby improving cycle efficiency.

In the present invention, a single accumulator services the entire system, no matter what the combination of heating and cooling zones that may exist within the building. Liquid and gas are simultaneously fed to the zones. Energy is efficiently traded among cooling and heating systems by means of the unitary accumulator. All systems may be located indoors, except for a loop that is directed outdoors, preferably through earthen ground, for the purpose of either absorbing heat or expelling heat, as needed to keep the accumulator liquid level within acceptable limits. This contrasts with a Variable Refrigerant Flow system wherein a compressor delivers a gaseous working fluid to the indoor systems, and, overall, only one thermodynamic cycle that governs the system, even though a system of valves inside the building redirects both liquid and gaseous working fluid between zones so as to minimize waste heat. The present invention, on the other hand, delivers liquid and gaseous working fluid to the building by different driving means of compression, pumping or pressure relief through an expander so that downstream systems undergo different thermodynamic cycles that are tailored to their particular loads.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 represents the pressure-enthalpy relationship of multiple cycles operating simultaneously;

FIG. 2 shows a generic layout of equipment in a system of the type disclosed herein;

FIG. 3 repeats FIG. 2 but with annotations that related the various devices to the pressure-enthalpy relationship shown in FIG. 1;

FIG. 4 expands on FIG. 3 to show the multiplicity of devices and cycles that is possible in accordance with this disclosure; and

FIG. 5 presents a process flow diagram in support of the Example.

DETAILED DESCRIPTION OF THE DRAWINGS

The ensuing descriptions of the thermodynamic cycles make use of a common chart of pressure and enthalpy, the vapor-liquid envelope of which is denoted by a heavy curved line in FIG. 1. The multiple thermodynamic cycles of the present invention are described in this diagram.

One of the cycles shown in FIG. 1, referred herein as the “pumped cycle,” is represented by the points P₁, P₂, C₄, P₃, and back to C₄ and finally P₁, in that order. In this manner, the pumped cycle is providing supplemental cooling. Working fluid that has been condensed along the return path of P₃ to C₄ while passing through an external medium is available to a pump at a suction pressure denoted by P₁. It is immediately pumped up to pressure P₂, which is still in the liquid region. In practice, the difference in pressure between P₁ and P₂ is slight. From the pump discharge, the fluid traverses a thermodynamic path from P₂ past C₄ to P₃ as it flows through channels that contain it within an external medium, which could be air, water or ground, where it absorbs heat and evaporates. For example, the working fluid could absorb heat from a room, thereby cooling that space. Point P₃ may fall short of the vapor-liquid equilibrium envelope or run past it into the superheated vapor state, depending on the amount of heat to be absorbed and the temperature differential between the fluid and the medium being cooled, but the pressure will remain nearly the same. The segment C₄ to P₃ forms a locus of equal temperature and pressure that is referred to as the neutral condition. The neutral condition is common to all thermodynamic cycles of this invention. It is also the condition of temperature and pressure that exists in the accumulator. From point P₃, the fluid flows to another heat exchanger, where it is condensed at close to the same temperature as evaporation. Point P₁ lies at the liquid edge of the vapor-liquid equilibrium zone, but at a temperature and pressure that is slightly lower in temperature and pressure from the neutral condition.

External air or ground temperature is denoted in FIG. 1 by the dashed line, which marks an isotherm on the pressure-enthalpy chart that is cooler than the isotherm C₄-P₃. For example, a fluid that is evaporated and condensed at 62 F could be evaporated by a room-air medium at 72 F and then condensed by ground at 55 F. As the liquid emerges from the condensation medium, however, it undergoes a slight decrease in pressure at the suction side of a liquid pump.

The conventional cooling cycle, referred to herein as “compressed cooling,” can provide much lower temperatures than pump cooling. This cycle is shown in FIG. 1, where the fluid traversing point C₄ is expanded to point C₁, which is at a lower pressure and temperature than the neutral condition. One advantage of lower temperatures is its ability to dehumidify the air. Once the fluid is completely vaporized, it enters a compressor suction at C₂ and moves to a condition of higher temperature and pressure at C₃. Importantly, the higher pressure is close to that of the pumped liquid so that the compressed fluid can re-mix with pumped fluid, in the accumulator.

Yet another of the cycles shown in FIG. 1, referred to herein as “compressed heating,” starts with vapor from point P₃, at practically the same pressure as point H₂, that is sent to a compressor for boosting to condition H₃, from which the fluid then enters a heat exchanger, located in a different zone, for purposes of heating, rather than cooling, that zone. The fluid may be at supercritical pressure, as indicated in FIG. 1, although it may also pass through a zone of condensation within the vapor-liquid equilibrium area. In the preferred case of carbon dioxide, the fluid would most likely be maintained above the critical pressure, such that it does not change state as it cools. After emerging from the room-air heater at condition H₄, the fluid is then expanded to the H₁. Heat is then absorbed indirectly from higher-enthalpy streams returning from the pumped- or compressed-cooling coils or the ground itself, in the accumulator, before the fluid returns to the compressor for re-circulation in the compressed heating loop.

It is thus demonstrated that a single fluid can progress through each of the three aforementioned thermodynamic cycles simultaneously, and that there is a temperature and pressure in common in all these cycles known as the neutral condition. Pumped cooling is denoted by the path P₁-P₂-C₄-P₃-C₄-P₁. Compressed heating is denoted by the path H₁-H₂-H₃-H₄-H₁. The difference in pressure and temperature between lines H₁-H₂ and P₃-C₄ is not significant. Compressed cooling is denoted by the path C₁-C₂-C₃-C₄-C₁. All three of these cycles pass through at least some portion of the same or common neutral condition of temperature and pressure exhibited by C₄-P₃. This condition of temperature and pressure also exists in the accumulator, and working fluid passes through the accumulator at some point in all of the cycles.

For purposes of illustration, the following descriptions may refer to fluid entering into or emerging from a ground loop of embedded tubing. The ground represents one of several types of external media to which heat is expelled, or from which heat is absorbed. It is the preferred medium for balancing excess or deficit heat in the accumulator according to this disclosure, although this disclosure by no means limits this function to earthen ground. Other media serving this function could be outdoor air, a heat sink of stored energy, water, a zone of hot or cold temperature in a manufacturing area or another non-ambient source.

A simplified example of such a multi-zone heating and cooling system is shown in FIG. 2. At the heart of this process is accumulator vessel 1, which contains an equilibrium vapor-liquid mixture of working fluid. This working fluid flows through various devices for heating or cooling zonal air and then back to the accumulator 1. In the example shown, these devices are shown as fan-blown air handlers, although it is understood that this disclosure is by no means limited to devices of this type alone. Heat can also be exchanged in such devices as water heaters or coolers, solar collectors, waste-heat recuperators, radiant coils and even complete indirect cycles for heating or cooling, as will be explained with subsequent FIGS. 3 and 4. It is further understood that the number of devices need not be limited to four, as shown in FIG. 2. There can be any number of devices, in various combinations of heating and cooling modes, as is typical of a multi-zone system for conditioning the air in buildings.

One of the example devices in FIG. 2 is a heater 2, which can be used to heat room air, and which is serviced by a compressor 3 that heats up the working fluid ahead of it. An expander 4 after the heater 2 relieves pressure back to the neutral accumulator pressure. Another heating device 5 is serviced by a blower 6 rather than a compressor. In this configuration, vapor from the accumulator 1 could be used to pre-heat outside ventilation air if that air is substantially cooler than the temperature of the working fluid in the accumulator. Alternatively, it could be used to preheat water going to a water heater. In the case of a blower, fluid is impelled without substantial pressure change. A slight loss of pressure due to suction at the blower inlet is recovered at the outlet as the fluid pressure returns to that of the common neutral condition. This path is denoted by sequent B₂-B₂-C₄.

A third device 7 can cool and possibly dehumidify zonal air in an exchange of heat with liquid working fluid that is first cooled in expander 8 before reaching air handler 7, where it evaporates to vapor and moves on to the suction of compressor 9. This compressor 9 brings the working fluid back to the neutral accumulator pressure. The fourth device in this example, air handler 10, exchanges heat with liquid working fluid that is pumped from accumulator 1 via pump 11. This liquid also evaporates to vapor in the air handler, but does so at conditions that are close to the neutral condition. A typical application for this type of cooling is to pre-cool incoming ventilation air.

In all of the aforementioned example devices, working fluid goes back to the accumulator 1. All streams return to the neutral condition, but with varying degrees of energy, as measured by enthalpy. The higher the degree of energy, the higher the fraction of vapor versus liquid. They all combine to a single state point, denoted by the letter J in FIG. 1, that fits somewhere on the line of the neutral condition, C₄ to P₃.

Depending on the heating and cooling loads imposed on the system by the air handlers, the instantaneous quality at point J is very likely to differ from the quality of accumulator 1, leading to a change in equilibrium temperature and pressure in the accumulator, which also causes the liquid level in the accumulator 1 to rise or fall. In this way, the accumulator 1 acts as a dynamic heat sink or heat source to balance the overall energy load of the system. The accumulator 1 can only serve this function so long as there exists both liquid and vapor in it. To ensure this condition, and to prevent the liquid level from rising too high or falling too low, working fluid is sent to an external medium, preferably the ground loop 12, in the form of vapor to be condensed if energy must be subtracted from the system, or in the form of liquid to be evaporated if energy must be added. In either case, fluid emerges from the external medium at the neutral condition, now adjusted for proper energy balance. The trigger for moving fluid through the external medium is a liquid level that has drifted far enough from upper or lower set-point limits as to cause the equilibrium temperature to rise or fall enough to provide sufficient temperature differential with the external medium, preferably the ground, as to facilitate efficient heat transfer. Specifically, liquid level is allowed to rise high enough that the equilibrium temperature in the accumulator 1 falls sufficiently low as to facilitate efficient evaporation in the ground loop 12, or the liquid level is allowed to fall low enough that the equilibrium temperature in the accumulator 1 rises far enough to facilitate efficient condensation in the ground loop 12. As shown in FIG. 2, vapor can be driven through the ground loop 12 at moderate pressure drop by a driver 14, which may be a blower or compressor. Liquid is typically driven by pump 13 to prepare it for evaporation in the ground loop 12.

In a perfectly steady-state condition, wherein the loads on the air handlers never vary and the ground acts as a perfect heat sink or source at constant temperature, the accumulator level would remain constant. Flow through the ground loop 12 would likewise hold steady, and the neutral condition would be unchanged. Working fluid would reject heat to the ground, or absorb it from the ground, so as to correct any net energy gain or loss, respectively in the combined working fluid leaving the air handlers. For example, take the hypothetical case of a simultaneous demand profile of 2.0 kilowatts compressed heating, 3.0 kilowatts of compressed cooling and 3.9 kilowatts of pumped cooling using carbon dioxide as the working fluid. The set-point liquid level is 25% of the accumulator height, and pressure is 55 bar. This condition would cause a heat and pressure to build up in the accumulator, leading to the excess being expelled to the ground. Of the total mass flow of fluid in and out of the accumulator 1, close to 30% would have to channel through the ground loop 12 in order to prevent the liquid level from falling further.

Under conditions of surplus cooling duty, as in the example above, it is desirable to maintain a liquid level that is low enough as to maintain a vapor temperature that is sufficiently higher than ground temperature as to ensure adequate condensation in the ground loop 12. Conversely, under conditions of surplus heating duty, it is desirable to maintain a liquid level that is high enough as to ensure adequate evaporation of pumped liquid in the ground loop 12. Between these conditions of suitable temperature differential with other external media, such as the ground, and the working fluid, the accumulator 1 itself acts as the heat sink for surplus cooling duty, or heat source for surplus heating duty, as manifested by changing temperature, pressure, liquid level and enthalpy within its confines.

FIG. 3 takes the example presented in FIG. 2 and annotates it with state points as labeled in FIG. 1. Points C₄, P₃ and H₄, which correspond to the condition of the working fluid at the outlets of the air handlers, are all at the temperature and pressure of the neutral condition. Meanwhile, a blower or compressor 14 pushes accumulator 1 vapor into the ground loop 12 for condensation, or a pump 13 pushes liquid into the ground loop 12 for evaporation, in such manner as to return working fluid to the accumulator 1 at the neutral condition. Under steady state in a properly controlled system, the stream of the working fluid resulting from the mixture of fluid coming from the ground loop 12 with fluid from the air-handling devices will be not only of the same temperature and pressure as the accumulator 1, but also the same vapor-liquid quality, thereby maintaining a steady liquid level. Under transition conditions caused by varying heating and cooling loads, however, the mixture of working fluids from the ground loop 12 and the devices will actually be of a higher or lower quality as the accumulator 1—at the same temperature and pressure—so as to correct the liquid level in the accumulator 1 toward the set point level. Whenever the liquid level remains at a pre-determined level (the “set point”), the system is said to be “static,” i.e., the pressure and liquid level in the accumulator is constant and the liquid level is allowed to change only when net enthalpy changes of the multiple cycles is not zero. To accomplish this, fluid flow rates through the multiple cycles are controlled so as to maintain constant temperature and pressure. The liquid level is accumulator 1 is monitored by a gauge (not shown). When the liquid level exceeds the maximum level of the set point, pump 13 is actuated to pump liquid from accumulator 1 through ground loop 12 to evaporate the fluid (as discussed above). When the liquid level drops below the minimum level of the set point, blower or compressor 14 is actuated to push vapor from accumulator 1 through ground loop 12 to condensate the fluid (as discussed above). The alternative is to allow the temperature and pressure within the accumulator to change. The liquid level within the accumulator may also change, but it is not a requirement. Under this condition, the system is said to be “dynamic.”

The pumped cycle may serve to boost the efficiency of either compressed cooling or compressed heating by pre-cooling or pre-heating incoming ventilation air, respectively. For example, if the outside air is cooler than ground temperature, pumped liquid from the ground can be used to pre-heat ventilation air to a temperature close to that of the ground. Conversely, if the outside air is substantially hotter than ground temperature, pumped liquid from the ground can be used to pre-cool ventilation air. The same principle applies to a secondary working fluid, such as water, which may be used as an intermediate between the primary working fluid pumped or compressed through the ground loop 12, and the external medium of room air. Such a fluid may be heated or cooled by blown vapor or pumped liquid, respectively. Ventilation air can only be pre-cooled or pre-heated at any particular time, depending on the temperature of outside air. But it may still be possible to run both blown vapor and pumped liquid cycles at the same time, so long as they exchange heat with different media. An example could be pre-cooling warm outdoor air with pumped CO₂ liquid while pre-heating water with blown CO₂ vapor.

As was noted above in the discussion of FIG. 2, there can be any number of devices, in various combinations of heating and cooling modes, as is typical of a multi-zone system for conditioning the air in buildings. This is now demonstrated in FIG. 4, which shows a multiplicity of devices in both heating and cooling modes. For simplicity, each of the four basic modes described by FIG. 2 is shown with a pair of zonal cycles, although the actual number of such sub-loops can be greater or fewer, even none. FIG. 4 is annotated with cycle labels in accordance with FIG. 3. Multiplexing junctions 15 are denoted as parallel lines and represent a piping arrangement that directs the fluid to the appropriate indoor system, which may be either direct, as described by subset 16, or indirect, as described by subset 17. A similar multiplexing array follows the indoor system so as to direct the working fluid back to the accumulator 1 via either a compressor, expander or unobstructed pipe, as used by the particular mode of heating or cooling being exercised. In direct heating or cooling (subsets 16), the working fluid from the accumulator 1 exchanges heat with the space being so conditioned, typically a room in a building. The simplified depiction of the multiple cycles shown in FIG. 2 is representative of such direct heating and cooling. In indirect heating or cooling (subsets 17), the working fluid exchanges heat with a second working fluid, which then undergoes a vapor-liquid compression cycle of its own. It is this secondary fluid that exchanges heat with the space being conditioned, rather than the working fluid from the accumulator 1. Such systems of indirect heating and cooling are in fact quite common. Thus, FIG. 4 presents a more generalized picture of a multi-cycle heating and cooling system than the simplified version shown in FIG. 2. Whether direct or indirect, the working fluid of the accumulator 1 eventually comes to the same points labeled as H₄, C₄ and P₃, which occupy the same positions in both FIGS. 2 and 4.

Example. A test set up comprises the direct exchange (DX) geothermal well field employing carbon dioxide (R744) working fluid, compressor-pump skid, and air-handling unit (FIG. 5).

The air handing unit (AHU) has two microchannel heat exchangers (mcHX 20, 22) installed in it. The bottom mcHX 20 is positioned so that it is the first to encounter the return of outside air, which is supplied with pumped R744 refrigerant. The top mcHX 22 encounters air that has passed through (or been conditioned) by the bottom mcHX 20, which is supplied with compressed R744 refrigerant. Both supply streams come from the same accumulator 1. The bottom mcHX 20 is also instrumented with two coriolis mass flow meters to measure the quality of the R744 refrigerant upon entering and leaving.

The test started with the compressed cooling alone. After the system was operating for about 1 hour, pump cooling was operated simultaneously. After a few hours the pump cooling was shut off and the compressed cooling system alone was running.

The average pressure increase across the compressor was 420 psig. Temperature, density and power readings from this test are given in the Table 1 below.

TABLE 1
			Pump and
		Compressed	Compressed
Working fluid CO2	Units	Cooling	Cooling
Power demand:
Compressor	kW	2.2 ± 0.1	2.1 ± 0.2
Pump	kW		0.1 ± 0.1
Heat exchanger inlet:
CO2 Temp	° C.	7.0 ± 0.7	8.5 ± 2.1
CO2 Density	Kg/m3	254.3 ± 10.6	308.8 ± 47.0
Heat exchanger outlet:
CO2 Temp	° C.	18.1 ± 1.3	13.3 ± 4.7
CO2 Density	Kg/m3	98.8 ± 4.6	109.9 ± 14.7
Coefficient of		4.1 ± 0.2	7.7 ± 1.2
Performance

While the disclosure has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the embodiments. Thus, it is intended that the present disclosure cover the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.

Claims

1. A method of transferring energy between two or more external media comprising:

providing two or more external media;

employing a single working fluid operating in more than one thermodynamic cycle simultaneously, wherein each thermodynamic cycle of the more than one thermodynamic cycle has a common neutral condition of temperature and pressure and at least two thermodynamic cycles of the more than one thermodynamic cycle are selected from the group consisting of:

a first cycle wherein (i) the single working fluid is liquid in the common neutral condition; (ii) impelling the liquid working fluid from the neutral condition by a first mechanical device to one of the two or more external media that is a heat source; and (iii) the liquid working fluid absorbs energy from the heat source and returning the single working fluid to the common neutral condition;

a second cycle wherein (i) the single working fluid is liquid in the common neutral condition; (ii) depressurizing the liquid working fluid from the common neutral condition to a pressure that is less a pressure of the common neutral condition; (iii) the liquid working fluid absorbs energy from one of the two or more external media that is a heat source and vaporizes; and (iv) compressing the single working fluid by a second mechanical device to the pressure of the common neutral condition; a third cycle wherein (i) the single working fluid is gaseous in the common neutral condition; (ii) impelling the gaseous working fluid by a third mechanical device from the common neutral condition to one of the two or more external media that is a heat sink; (iii) the gaseous working fluid provides heat to the external media; and (iv) returning the single working fluid to the common neutral condition; and

a fourth cycle wherein (i) the single working fluid is gaseous in the common neutral condition; (ii) drawing the gaseous working fluid from the common neutral condition and compressing the gaseous working fluid by a fourth mechanical device to a pressure greater than the pressure of the common neutral condition pressure and a temperature greater than the temperature of the common neutral condition; (iii) directing the gaseous working fluid to one of the two or more external media that is a heat sink; (iv) the gaseous working fluid provides heat to the external media; (v) depressurizing the working fluid to a pressure of the common neutral condition.

2. The method as described in claim 1, wherein the single working fluid at the common neutral condition is a heat source for at least one thermodynamic cycle of the more than one thermodynamic cycle while the single working fluid is a heat sink for another at least one thermodynamic cycle of the more than one thermodynamic cycle.

3. The method as described in claim 1, wherein at least one external media of the two or more external media is selected from the group consisting of earthen ground, indoor air, ventilation air, outdoor air, water, construction features of a building, and a heat-transfer fluid.

4. The method as described in claim 1, wherein fluid flow rates through at least one of the multiple cycles is controlled such that the common neutral condition is static.

5. The method as described in claim 1, wherein the neutral condition liquid level, pressure and temperature are allowed to vary such that the common neutral condition is dynamic.

6. The method as in claim 1, wherein the energy transferred through one of the external media of the two or more external media is the net energy of all of the thermodynamic cycles of the more than one thermodynamic cycle.

7. The method as described in claim 1 wherein the single working fluid is carbon dioxide.

8. An apparatus for transferring energy comprising:

a single working fluid;

a single accumulator to store the single working fluid and to set a common neutral condition of a plurality of thermodynamic cycles;

a plurality of fluid channels connected to the single accumulator, wherein the plurality of fluid channels being exposed to a plurality of external media define a plurality of zones to transfer energy between the single working fluid and each external media of the plurality of external media; and

at least one single working fluid driving mechanism disposed in each fluid channel of the plurality of channels to determine a thermodynamic cycle of the each zone of the plurality of zones;

9. The apparatus according to claim 8, wherein at least one single working fluid driving mechanisms is selected from the group consisting of pumps, compressors, and blowers.

10. The apparatus according to claim 8, further comprising one or more pressure control devices disposed in the each fluid channel of the plurality of fluid channels, wherein the one or more pressure control devices is selected from the group consisting of pressure regulators, orifices, and capillary tube.

11. The apparatus according to claim 8, wherein two or more external media of the plurality of external media are selected from the group consisting of earthen ground, indoor air, ventilation air, outdoor air, water, construction features of a building, and a heat-transfer fluid;

12. The apparatus according to claim 8, wherein the single working fluid is carbon dioxide.

13. The apparatus according to claim 8, wherein the single working fluid at the common neutral condition is a heat source for at least one thermodynamic cycle of the plurality thermodynamic cycles while the single working fluid is a heat sink for another at least one thermodynamic cycle of the plurality thermodynamic cycles.

14. The apparatus according to claim 8, wherein the common neutral condition is static.

15. The apparatus according to claim 8, wherein the common neutral condition is dynamic.

16. The apparatus according to claim 8, wherein the single working fluid can be simultaneous gaseous and liquid states.

17. The apparatus according to claim 8, wherein at least two thermodynamic cycles of the plurality thermodynamic cycles are selected from the group consisting of:

a first cycle wherein (i) the single working fluid is liquid in the common neutral condition; (ii) the liquid working fluid is impelled from the common neutral condition by a first single working fluid driving mechanism to a first external media of the plurality of external media that is a heat source; and (iii) the liquid working fluid absorbs energy from the heat source and the liquid working fluid returns to the common neutral condition;

a second cycle wherein (i) the single working fluid is liquid in the common neutral condition; (ii) the liquid working fluid is depressurized from the common neutral condition to a pressure that is less a pressure of the common neutral condition; (iii) the liquid working fluid absorbs energy from a second external media of the plurality of external media that is a heat source and vaporizes; and (iv) the liquid working fluid is compressed by a second single working fluid driving mechanism to the pressure of the common neutral condition;

a third cycle wherein (i) the single working fluid is gaseous in the common neutral condition; (ii) the gaseous working fluid is impelled by a third single working fluid driving mechanism from the common neutral condition to a third external media of the plurality of external media that is a heat sink; (iii) the gaseous working fluid provides heat to the third external media of the plurality of external media; and (iv) the working fluid returns to the common neutral condition; and

a fourth cycle wherein (i) the single working fluid is gaseous in the common neutral condition; (ii) the gaseous working fluid is drawn from the common neutral condition and compressed by a fourth single working fluid driving mechanism to a pressure greater than the pressure of the common neutral condition pressure and a temperature greater than the temperature of the common neutral condition; (iii) the gaseous working fluid is directed to a fourth external media of the plurality of external media that is a heat sink; (iv) the gaseous working fluid provides heat to the fourth external media of the plurality of external media; (v) the working fluid is then depressurized to a pressure of the common neutral condition.

18. The apparatus according to claim 8, wherein one fluid channel of the plurality of fluid channels being exposed to an earthen ground external media with a first single working fluid driving mechanism of the at least one single working fluid driving mechanism being a pump, and a second first single working fluid driving mechanism of the at least one single working fluid driving mechanism being selected from the group consisting of a compressor and a blower.

19. The apparatus according to claim 8, wherein one fluid channel of the plurality of fluid channels being exposed to an earthen ground external media with a single working fluid driving mechanism of the at least one single working fluid driving mechanism being a pump.

20. The apparatus according to claim 8, wherein one fluid channel of the plurality of fluid channels being exposed to an earthen ground external media with a first single working fluid driving mechanism of the at least one single working fluid driving mechanism being selected from the group consisting of a compressor and a blower.

21. The apparatus according to claim 8, wherein one fluid channel of the plurality of fluid channels being exposed to only an earthen ground external media with a first single working fluid driving mechanism of the at least one single working fluid driving mechanism being a pump, and a second first single working fluid driving mechanism of the at least one single working fluid driving mechanism being selected from the group consisting of a compressor and a blower.

22. The apparatus according to claim 8, wherein one fluid channel of the plurality of fluid channels being exposed to only an earthen ground external media with a single working fluid driving mechanism of the at least one single working fluid driving mechanism being a pump.

23. The apparatus according to claim 8, wherein one fluid channel of the plurality of fluid channels being exposed to only an earthen ground external media with a first single working fluid driving mechanism of the at least one single working fluid driving mechanism being selected from the group consisting of a compressor and a blower.

24. The apparatus as described in claim 8, wherein the accumulator liquid level, pressure and temperature are allowed to vary such that the common neutral condition is dynamic.