A HEAT PUMP SYSTEM USING WATER AS THE THERMAL FLUID

A heat pump system using water as the thermal fluid

Technical field of the invention

The present invention relates to heat pump systems using water as the thermal fluid, and in particular to heat pump systems capable of producing binary ice.

Background of the invention

A heat pump is designed to move thermal energy opposite to the direction of spontaneous heat flow. Hence, heat is absorbed from a cold space and released to a warmer one.

The general architecture of a classical heat pump system includes a circuit of a thermal fluid that changes between its liquid state and its gaseous state. The thermal fluid in its gaseous state is pressurized and circulated through the system by a compressor. On the discharge side of the compressor, now hot and highly pressurized, the thermal fluid in its gaseous state is cooled in a condenser (heat exchanger) until it condenses into its liquid state at a high pressure and moderate temperature. The heat is thereby released into the warm space. The high-pressure thermal fluid, in its liquid state, then passes through an expansion valve and into an evaporator (heat exchanger). The flow must be limited into the evaporator to maintain the pressure low therein, and to allow expansion of the thermal fluid, in its liquid state, back into its gaseous state. The thermal fluid in its gaseous state then returns to the compressor and the cycle is repeated.

Thermal fluids are capable of evaporating at low temperature at

atmospheric pressure. The thermal fluids commonly used in refrigerating machines do however pose a problem, because they are either dangerous to handle, or are environmentally toxic. It is therefore desirable to provide a heat pump system operating with a safer thermal fluid.

Summary of the invention

The inventors of the present invention have developed a heat pump system operating with water as the thermal fluid. Although this solution may seem obvious, there are severe technical difficulties with handling water in its gaseous state, since the volume expansion is much larger than for traditional thermal fluids. Furthermore, the use of water as the thermal fluid has the advantage that one can utilize water in its different states for different purposes. Hence, there is no need for a system, where the same water moves around in a circuit. The expansion valve is therefore redundant. As an example, binary ice may be produced in the evaporator, and delivered to the end-user, while hot water, at the same time, is produced in the condenser, and delivered to another end-user. New water then obviously needs to be introduced into the evaporator.

A first aspect relates to a heat pump system comprising:

- a unit comprising:

i) an evaporator;

ii) an axial flow compressor; and

iii) a condenser;

- a first heat exchange system in water communication with the condenser of the unit through an inlet and an outlet positioned in the condenser;

- a second heat exchange system in water communication with the evaporator of the unit through an inlet and an outlet positioned in the evaporator.

In one or more embodiments, the evaporator and the condenser are not in water communication with one another through an expansion valve. A second aspect relates to a heat pump system comprising:

- a unit comprising:

i) an evaporator;

ii) an axial flow compressor; and

iii) a condenser;

- a first heat exchange system in water communication with the condenser of the unit through an inlet and an outlet positioned in the condenser;

- a second heat exchange system in water communication with the evaporator of the unit through an inlet and an outlet positioned in the evaporator;

wherein the evaporator and the condenser are not in water communication with one another through an expansion valve.

The unit of the heat pump system comprises an evaporator, an axial flow compressor, and a condenser.

The evaporator is the component of the heat pump system in which a part of the water evaporates into steam, while taking on heat from water from the second heat exchange system.

The second heat exchange system runs from the evaporator to an installation for cooling purposes, and/or to an installation for storing and/or delivering binary ice and/or cold water. New water is then provided to the evaporator; or the same water is returned to the evaporator when it has taken up heat from an area to be cooled. Hence, the second heat exchange system provides heat or heat and water to the evaporator and the evaporator provides cold to the installation for cooling purposes, and/or provides binary ice and/or cold water to an end-user via the second heat exchange system. The heat pump system is operated at low absolute pressure, which may be in the order of 4-15 mbar absolute pressure in the evaporator. The liquid water in the evaporator is not completely evaporated. Rather, a portion of the liquid water evaporates at such low pressure by extracting energy from the remaining liquid water. The remaining liquid water, now cooled, can then be used for another purpose. Depending on the intended use, the liquid water level, as well as the absolute pressure, within the evaporator is controlled.

In one or more embodiments, the heat pump system further comprises a second control system configured for adjusting the level of liquid water in the evaporator to a level within a preset threshold range.

In one or more embodiments, the control system comprises an indicator configured for measuring the liquid water level within the evaporator.

In one or more embodiments, the control system comprises means for moving liquid water in and/or out of the evaporator.

In one or more embodiments, the evaporator comprises a plurality of agitators/mixers in its lower portion. The agitators allows for an improved degree of evaporation from the water present in the lower portion of the evaporator. Using only one agitator results in the formation of a vortex within the water, which result in an inefficient evaporation process. When the system is operated to produce binary ice, the plurality of agitators especially improves the homogenization, such that ice crystals will not grow too large to be transported through tubes and pumps in the second heat exchange system to the end-user.

In one or more embodiments, the lower portion of the evaporator is thermally insulated.

The one or more outlets of the second heat exchange system from the evaporator is positioned in the lower portion of the evaporator, while the one or more inlets of the second heat exchange system to the evaporator may be positioned both in the lower and/or higher portion of the evaporator. When the inlet is positioned in the higher portion of the evaporator, the water from the second heat exchange system may in one or more embodiments be injected into the evaporator in the form of droplets by means of a spray ramp. The water droplets evaporates instantaneously due to the very low absolute pressure prevailing in therein, which may be in the order of 4-15 mbar absolute pressure. In other words, the energy needed to vaporize the liquid comes from the liquid itself, due to an adiabatic process.

Since, the use of water in a low absolute pressure system according to the present invention requires the handling of a volume expansion much larger than for traditional thermal fluids, there is a need for a compressor capable of moving such a volume rapidly enough, while still being capable of compressing the steam entering the compressor from the evaporator. The extend of compression depends on the temperature difference of the water/binary ice to be extracted from the condenser and the water entering the condenser from the first heat exchange system. When producing binary ice in the evaporator, the pressure in the evaporator is 4-5 mbar absolute pressure. When the water entering the condenser from the first heat exchange system has a temperature of about 30 degrees Celsius, the pressure must be 40-50 mbar absolute pressure in the condenser. Hence, the compressor must be capable of compressing the steam from the evaporator by at least 1000%. The inventors of the present invention have found that an axial flow compressor is suitable for this purpose.

The axial flow compressor comprises a plurality of stages, each stage comprising a stator and a rotor. In the axial flow compressor, the water (in the gaseous state, steam) is compressed in a series of stages as it flows axially (parallel with the axis of rotation) through a decreasing tubular area. The steam passes from one stage to the next, each stage raising the pressure slightly. The stator comprises rows of stator airfoils/vanes. The rotor comprises rows of rotor blades. The rotors are connected to a central shaft and rotate at high speed. The stators are fixed and do not rotate. The function of the rotors is to increase the speed of the water (in the form of steam). The function of the stators is to increase the pressure of the steam and to prevent the steam flow from spiraling around the axis of rotation by bringing the steam flow back parallel to the axis of rotation.

In one or more embodiments, the axial flow compressor comprises at least 10 stages, such as within the range of 10-30 stages, e.g. at least 12 stages, such as within the range of 12-28 stages, e.g. at least 14 stages, such as within the range of 14-26 stages, e.g. at least 16 stages, such as within the range of 16-24 stages, e.g. at least 18 stages, such as within the range of 18-22 stages, preferably within the range of 10-15 stages.

The condenser is the component of the heat pump system in which the water steam from the axial flow compressor is condensed into liquid water, while transferring some of its heat to the water entering from the first heat exchange system. The first heat exchange system runs from the condenser to an installation for heating purposes and/or to an installation for storing and/or delivering heated water, and/or to a water cooler. New water is then provided to the condenser; or the same water is returned to the condenser when it has taken up cold from an area to be heated.

Hence, the first heat exchange system provides cold to the condenser, and the condenser provides heat to the installation for heating purposes and/or to an installation for storing and/or delivering heated water, and/or cooled in a water cooler.

The outlet of the first heat exchange system from the condenser is positioned in the lower portion of the condenser, while the inlet of the first heat exchange circuit to the condenser is positioned in the higher portion of the condenser. In one or more embodiments, the water from the first heat exchange system is injected into the condenser in the form of droplets by means of a spray ramp. The water droplets fall towards the lower portion of the condenser while capturing heat from the steam, thereby forcing the steam to condensate.

Since, a continued amount of water is transported from the evaporator, through the compressor, to the condenser, liquid water must be removed from the condenser to avoid flooding.

In one or more embodiments, the heat pump system further comprises a first control system configured for adjusting the level of liquid water in the condenser to a level within a preset threshold range.

In one or more embodiments, the first control system comprises an indicator configured for measuring the liquid water level within the condenser. In one or more embodiments, the first control system comprises means for moving liquid water in and/or out of the condenser.

In one or more embodiments, the first control system comprises means for moving liquid water from the condenser into the liquid water, and below the waterline, in the evaporator.

In one or more embodiments, the first control system comprises means for moving liquid water from the condenser into the first heat exchange system.

The inventors have developed a heat pump that is compact and thus suitable for installation in confined spaces. In one or more embodiments, the axial flow compressor extends into the condenser.

In one or more embodiments, the unit is contained in a confinement enclosure for vapor, and wherein the evaporator and the condenser are configured, respectively, as an evaporation zone and a condensation zone separated by an internal wall within the confinement enclosure.

In one or more embodiments, the axial flow compressor extends from the internal wall within the confinement enclosure and into the condenser, and wherein the suction inlet of the axial flow compressor is incorporated into said internal wall.

In one or more embodiments, the suction inlet of the axial flow compressor is coupled to an inlet casing extending into the evaporator.

In one or more embodiments, the unit further comprises a desuperheater positioned within the condenser.

The high compression of the steam obtained by the axial flow compressor increases the temperature of the steam considerable. The desuperheater makes it possible to recover a part of the heat at the outlet of the axial flow compressor by means of a heat re-use circuit. It will be understood that the desuperheater, when present, will be distinguished from the condenser in that no phase change takes place within it.

Unlike what occurs in the evaporator or the condenser, it is not necessary that the heat exchange implemented by the desuperheater occur by direct contact, nor that the heat-carrying fluid of the heat re-use circuit be water (even if the selection of water is preferred). The desuperheater can thus be a heat exchanger that is conventionally found in the market. Advantageously, the desuperheater is configured to implement a cooling of the steam up to the condensation limit (dew point).

The value of the desuperheater is in using a portion of the heat for diverse applications, such as heating or preheating (of air, of liquid, etc.), via the heat re-use circuit.

In one or more embodiments, the heat pump system further comprises a lubrication circuit for the compressor; and wherein the lubrication fluid is water derived from the first and/or second heat exchange system.

In one or more embodiments, the heat pump system further comprises a compressor cooling circuit; and wherein the cooling fluid is water derived from the first and/or second heat exchange system.

It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention.

Brief description of the figures

Figure 1 shows a system in accordance with various embodiments of the invention.

Detailed description of the invention

Referring to Figure 1 , the general scheme of the invention is shown in relation to both system and method.

Figure 1 discloses a heat pump system 100 comprising a unit, a first heat exchange system 300, and a second heat exchange system 400. The unit comprises an evaporator 210, an axial flow compressor 220, and a condenser 230. The evaporator 210 and the condenser 230 are not in water communication with one another through an expansion valve.

The first heat exchange system 300 is in water communication with the condenser 230 of the unit through an inlet 310 and an outlet 320 positioned in the condenser 230. The water from the first heat exchange system 300 is injected into the condenser 230 in the form of droplets by means of a spray ramp 330.

The second heat exchange system 400 is in water communication with the evaporator 210 of the unit through an inlet 420 and an outlet 430 positioned in the evaporator 210. The inlet 420 is shown positioned below the waterline in the evaporator 210. Alternatively, water may be added through the inlet 422, positioned above the waterline.

The heat pump system 100 also comprises a first control system configured for adjusting the level of liquid water in the condenser 230 to a level within a preset threshold range. The first control system comprises an indicator 242 configured for measuring the liquid water level within the condenser 230. The first control system also comprises means 244 for moving liquid water in and/or out of the condenser 230.

The heat pump system 100 further comprises a second control system configured for adjusting the level of liquid water in the evaporator 210 to a level within a preset threshold range. The control system comprises an indicator 246 configured for measuring the liquid water level within the evaporator 210. The control system also comprises means 248 for moving liquid water in and/or out of the evaporator 210.

The unit is contained in a confinement enclosure 250 for vapor, where the evaporator 210 and the condenser 230 are configured, respectively, as an evaporation zone and a condensation zone separated by an internal wall 270 within the confinement enclosure 250.

The condenser 230 is equipped with an outlet 249 in its upper portion for connection to a vacuum pump (not shown). At startup, the vacuum pump provides the needed low-pressure conditions for the functioning of the system. It may also be suitable for maintaining low-pressure conditions during the operation of the system. A bypass valve (shown in the internal wall 270) makes it possible to circulate steam around the unit during startup. The bypass valve is configured to be closed during normal operation.

The heat pump system 100 further comprises a lubrication circuit 280 for the compressor; and where the lubrication fluid is water derived from the first 300 and/or second 400 heat exchange system.

The heat pump system 100 also comprises a compressor cooling circuit 290; and where the cooling fluid is water derived from the first 300 and/or second 400 heat exchange system.

The evaporator 210 comprises a plurality of agitators/mixers 212 in its lower portion. The agitators 212 allows for an improved degree of evaporation from the water present in the lower portion of the evaporator. When the system is operated to produce binary ice, the plurality of agitators 212 especially improves the homogenization, such that ice crystals will not grow too large to be transported through tubes and pumps in the second heat exchange system 400 to the end-user. References

100 Heat pump system

210 Evaporator

212 Agitator

220 Axial flow compressor

221 Stage

230 Condenser

242 Indicator

244 Means for moving liquid water

246 Indicator

248 Means for moving liquid water

249 Outlet

250 Confinement enclosure

270 Internal wall

280 Lubrication circuit

290 Cooling circuit

300 First heat exchange circuit

310 Inlet

320 Outlet

330 Spray ramp

00 Second heat exchange circuit 20 Inlet

22 Inlet

30 Outlet