Patent Application
20200386447
THE invention pertains to the application of electric powered heat pumps for building cooling and heating with dual heat sources/heat reservoirs or with single air heat reservoir.
Sadi Carnot (1824) invented the idea of reversible machines, which can operate as a heat engine and, in opposite operational direction, operate as a heat pump. William Thomson in 1852 conceived the application of heat pumps for both heating and cooling of space. Electric powered heat pump was instantly successful in cooling application and it, after its 1852 conceptual introduction by Thomson, has gained in quick succession universal acceptance for refrigeration and space cooling.
One hundred and sixty-seven years after Thomson's conception, however, heat pumps' application for space heating is still limited in scope. The most common heat pumps, air source heat pumps (ASHPs), face operational challenges: their efficiency and capacity drop during extreme weathers just when demand is the greatest. This is the result of decreasing coefficient of performance (COP) under large temperature lip as well as requirement of de-frosting and the mismatching between machine capacity and building load. These challenges are sufficiently serious that another-type heat pumps based on a different heat-source, ground source heat pumps (GSHPs), have become widely popular. GSHPs use the earth as a heat source or a heat sink taking advantage of the moderate temperatures in the ground-earth to boost efficiency and reduce the operational costs of heating and cooling.
Because of GSHPs' high COP, they have been successfully adopted in Sweden and Switzerland. This success is a remarkable reflection of the advantage of GSHPs, in particular, an evidence that wide adoption of GSHPs does not exacerbate peak load problem for a national power grid system.
Their popularity in general and small examples of success in particular, however, do not translate into their universal market adoption supplanting the common ASHPs. In a 2009 study-report prepared for EERE of US DOE, [1] Navigant concluded that GSHPs' market penetration in US is limited as result of three barriers:
All three are the direct consequence of earth being poor heat transfer medium and, as a result, GSHPs adoption is costly in capital and demands economic conditions and well-established service-infrastructure that do not prevail in US—while individual adoptions are possible as in Sweden and Switzerland, such adoptions cannot be scaled up in US or worldwide.
Yet another-type heat pumps, solar assisted heat pumps (SAHPs) or combined solar and heat pump systems, have received considerable attention. In a position paper by Solar Heating & Cooling Programme, IEA,[2] it noted, “Solar and heat pump systems (S+HP) are a combined technology that represent a market share in the building heating and cooling segment due to their following advantages . . . . The market share of S+HP systems could reach 100% for new houses in many countries where the heat pump technology is well-established and solar is mandatory for domestic hot water . . . .”2 SHC, IEA_“Solar and Heat Pump Systems Position Paper,” TASK 44/Annex 38 Solar and Heat Pump Systems
Perhaps, the case for SAHPs was put best by Chu and Cruickshank (2014),[3] “the use of solar thermal and heat pump technology together has the potential of alleviating the limitations each system experiences individually in cold weather.” Stand-alone solar cannot ensure meeting the heating load requirement during coldest days and nights, nor does stand-alone ASHP deliver necessary capacity just when heating demand is the greatest. The logic of the system approach by combining the two units is, therefore, in searching for synergy in the combined systems transcending the limits of stand-alone units. In particular, one of the challenges stand-alone units face is peak-load problem: both stand-alone units necessitate significant auxiliary heating that exacerbates peak-load demand. 3 Chu and Cruickshank (November, 2014) “Solar assisted heat pump systems,” Journal of Solar Energy Engineering 136 (041013): 1-9
The schematics of parallel version and series version are shown in
We have carried out performance study of both SAHPs as depicted in
This analysis can be recapitulated to be that an ideal heat pump system that can capture synergy of solar and heat pump should meet both the criterion of (1) high machine COP so that its wide adoption will not exacerbate peak-load of a power grid and the criterion of (2) high system COP by availing itself of dual heat sources. Moreover, it should always meet the criterion of (3) an engineering solution that is scale-up-able. ASHPs fail both criteria (1) and (2); GSHPs meet both criteria but fail criterion (3); parallel SAHPs fail criterion (1); series SAHPs meet criterion (1) but not criterion (2) because of heat pump starvation resulting from failing to avail themselves of dual heat sources (despite its high machine COP, exacerbating peak-load remains a problem).
An additional comment is added here with regards to a known method for partially mitigating large temperature lift problem, which leads to inferior COP. The method, multistage compression refrigeration system or, two-stage vapor-compression refrigeration with a flash chamber, [5] breaks both compression step and throttling step into two respective steps as shown in
It turns out that if a series SAHP is transformed into a dual-heat-sources system for overcoming heat pump starvation it can potentially meet all three criteria. It is the objective of the invention to provide a method of using heat pump for heating with the dual heat sources of air and solar with synergetic coordination in the extractions of heat from both sources. It is also the objective of the invention to provide an apparatus serving as the centerpiece for managing and coordinating heat extractions from both sources. It is furthermore the objective of the invention that the application of the method and the apparatus does not exacerbate peak-load problems of grids. Yet another objective of the invention, which was unexpected, is to provide a method of using said apparatus for managing cooling with single air heat reservoir without exacerbating peak-load problems of grids during summer.
The use of heat pump for heating has not been widely adopted. Prevalent heating and cooling equipment are an odd mix of air-conditioner, i.e., heat pump which is electric powered, for cooling and combustion boiler, which is fired by fuels, for heating. It is our aim to develop a single, electric-powered heat pump system for the multi-function of water heating, space heating/cooling that performs heating function better than all existing heat pump apparatuses. In particular, we have reached the verdict on the existing combined solar and heat pump systems that they are unsuccessive in transcending the limitations of individual solar unit and heat pump unit. One objective of the invention is to provide a method of using heat pump for heating with dual heat sources of air and solar with synergetic coordination in the extractions of heat from both sources. Another objective of the invention is to provide an apparatus serving as the centerpiece for managing and coordinating said heat extractions from both sources. Specifically, in the managing and coordination, the heat pump unit of the apparatus, which comprises a TES unit and an eHeatPump unit, operates in two modes, a TES discharging mode (either discharging heat by heat extracting or discharging coolness by heat dissipation) and a TES charging mode, in such a manner that the timing of the pre-charging operation is flexible for avoiding peak load as controlled by model predictive control (MPC) as well as for scheduling pre-charging during lowest power cost period. The two objectives together aim for transcending the limitations of individual solar unit and heat pump unit. A further objective of the invention is to provide a method of using the apparatus for managing cooling with single air heat reservoir.
An apparatus for building heating and cooling, comprising a thermal energy storage of water tank; an eHeatPump heat extraction means having two operational modes, discharging Mode 1 and charging Mode 2; said eHeatPump being in communication, in Mode 1, with said water tank extracting heat from which and a building space delivering heat to which, while, in Mode 2, in communication with an outdoor fan/heat exchanger unit extracting heat from which and said water tank delivering heat to which; in this Mode 2 operation the temperature of water in said water tank is precharged for anticipated requirement of building space conditioning; whereby the objective of such interactions and communications among the water tank, the eHeatPump, the outdoor fan/heat exchanger unit, and the building space being to breaking a single heat extraction process over large temperature lift during cold periods into two steps of smaller temperature lifts, the first being the Mode 2 operation precharging the water tank and the second being the later Mode 1 operation meeting building space heating load. The apparatus is also known as two-phase compression heat pump system with a thermal energy storage (TES) unit (
A method of managing low-grade-heat for water heating and space heating and cooling, comprising (a) providing exact heat extraction means via the use of a device for heat pumping, known as eHeatPump, in combination with a device for thermal energy storage (TES); (b) means for extracting low-grade heat of solar irradiation for maintaining the thermal condition of said device for thermal energy storage; (c) means for extracting low-grade heat of air enthalpy for pre-charging the thermal condition of said device for thermal energy storage, thereby mitigating heat pump starvation resulting from the prolong operation of heat pumping or absence of solar irradiation. Whereby, a low-grade-heat managing heat pump (LMHP) system operating as a managing means by storing heat/cold and extracting heat rather than as an energy conversion means, and the managing means has access to dual heat sources with eHeatPump operating in two operational modes; the timing of operating the charging Mode 2, when it is operated as a precharging mode, has the flexibility as controlled by MPC to avoid power peak load period, i.e., to take place during off-peak period taking advantage of low cost power; thereby, the dual-sourced LMHP system transcends the limitation of stand-alone ASHP and stand-alone solar system.
Another method of applying the apparatus of two-phase compression heat pump system with a TES for building cooling and refrigeration, comprising (a) providing exact heat extraction means via the use of a device for heat pumping, known as eHeatPump, in combination with a TES device for thermal energy storage; (b) means for cooling-conditioning of space by discharging heat into TES; (c) means for pre-conditioning (precooling) the thermal condition of said TES; whereby with eHeatPump operating in two modes, conditioning Mode 1 and precharging or preconditioning Mode 2, and the timing of operating the precharging Mode 2 has the flexibility as controlled by MPC to avoid power peak load period as well as take advantage of low-power-cost period.
FIG. 1_A parallel solar assisted heat pump (SAHP)
FIG. 2_A series SAHP with electric resistive element
FIG. 3_A two-stage compression refrigeration system with a flash chamber
FIG. 4_Schematic of heat pump management of dual heat sources for building heating
FIG. 5_A two-phase compression heat-pump system with a thermal energy storage (TES) unit
FIG. 6_Another embodiment of the two-phase compression heat-pump system with a thermal energy storage (TES) unit
FIG. 7_Embodiment as shown in
FIG. 8_Embodiment as shown in
FIG. 9_LMHP for heating and cooling depicted in heating operation with dual heat sources
FIG. 10_LMHP for water-heating and space heating&cooling depicted in heating operation with added Grid Integrated Water Heater with resistive element and GIWH control unit, as well as space-heating-and-cooling grid-integration control unit, which controls the operation of compressor and four control valves
FIG. 11_LMHP for heating and cooling depicted in cooling operation with reversing valve in cooling position and solar collectors de-activated
FIG. 12_A two-phase compression air-conditioner/refrigerator with a TES unit; the method can also be used for heating with a single air heat source—in which case, the heat pump reversing valve is set in heating position and the outdoor heat exchanger 10 works as heat extractor in charging phase operation
FIG. 13_Cooling system electric demand profile during three days in summer, which demonstrates the cost and moderate-peak-load advantage of the two-phase compression air-conditioner with a TES unit
It is our aim to devise a single, electric-powered heat pump device for heating and cooling. For that aim the invention has the following objectives. One objective of the invention is to provide a method of using heat pump for heating with dual heat sources of air and solar with synergetic coordination in the extractions of both sources. Another objective of the invention is to provide an apparatus serving as the centerpiece for managing and coordinating said extractions of both sources. Specifically, in the managing and coordination, the heat pump unit of the apparatus, which comprises a TES unit and an eHeatPump unit, operates in two modes, a heating mode and a pre-charging mode, in such a manner that the timing of the pre-charging mode operation is flexible for avoiding peak load as controlled by model predictive control (MPC). A further objective of the invention is to provide a method of using the apparatus for managing cooling with single air heat reservoir.
The method for heating and cooling of this invention is called low-grade-heat managing heat pump (LMHP). Low-grade-heat here refers to heat in an air heat reservoir, or both heat in an air heat reservoir and heat collected by solar thermal panels. Air heat reservoir can serve as a heat source or a heat sink.
In this invention, TES means a thermal energy storage unit, one embodiment of which is a water tank. In this invention, heat pump means an electric powered, vapor-compression-cycle device.
In the context of heat pump cycle, a Carnot heat pump is identified as a perfect heat extraction device. Correspondingly, a vapor-compression-cycle heat pump if it is operating under moderate temperature lift is identified as an “exact heat extraction” device (as an approximation to the perfect heat extraction device) whereas a vapor-compression-cycle heat pump operating under large temperature lift is said to be not meeting the criterion of “exact heat extraction” approximation. Therefore, the heat extraction means that this invention introduces for keeping the “temperature lifting of heat extraction operation” from becoming excessively large by breaking the step into two steps is called exact-heat-extraction HeatPump (short for eHeatPump); the breakup into two steps is assisted with TES.
In both apparatus and method, the eHeatPump operates in two modes or two phases, which will be referred to as either first mode/second mode or first phase/second phase, or mode one/mode two or phase one/phase two. The first mode/phase will be referred to as TES discharging mode/phase, while the second mode/phase as TES charging mode/phase. In the first mode/phase, TES will be considered as the “source” for the eHeatPump operation, i.e., in the case of heating application, TES is the source of heat (a heat source) for eHeatPump, while, in the case of cooling application, it is the source of coolness for eHeatPump in the sense that it serves as a heat sink for eHeatPump enabling the eHeatPump to remove heat from chilled space.
This invention considers the option of hydronically distributed heat, which then activates radiant surfaces for space heating or/and cooling. The method is called thermally activated building systems (TABS).
It is a universally accepted truism that all changes in nature (including methods or processes of efficient operations or devices) can be understood in terms of energy conversion, with those of efficient energy conversion being energy conversion that involves small energy degradation. Note that energy conversion is fundamentally a description of dyadic relation of cause and effect between high-grade energy and low-grade energy, eventually becoming heat. As dyadic relations in the narrow sense of the term, energy conversion, strictly speaking, cannot capture the true meaning of efficient methods.
The energy conversion truism, together and the mechanical theory of heat from which the truism was derived, has been rejected by Lin-Shu Wang. [6] The mechanical theory of heat is supplanted by the predicative entropy theory of heat. In place of energy conversion, truly efficient processes are described in terms of triadic relations (or, the triadic framework) and the ecosystem of triadic relations. For building energy problems, efficient methods are understood in the triads of e-powered managing means, extraction of low-grade-heat, and building space conditioning. That is, the truly efficient methods for building conditioning involve the use of e-powered apparatus such as heat pump/thermal storage system for storing heat/cold and extracting heat, i.e., as low-grade heat managing means, for achieving the desired space conditioning, rather than as energy conversion means. Furthermore, overall efficiency is greatly amplified with individual building triadic relations as components in the triadic ecosystem of individual buildings, power grid, and renewable solar/wind farms. 6 L-S. Wang (July, 2019) A Treatise of Heat and Energy (Springer_Mechanical Engineering Series)
The schematic of one embodiment of the apparatus 30 is shown in
Mode two of eHeatPump is the TES (40) charging mode: valves 64 and 66 are switched to connect the inlet of 60 to refrigerant line to evaporator 2, unit 54, and the outlet of 60 to refrigerant line to condenser 2, unit 58. The operation of 50 in Mode 2 thus extracts heat, through the circulation of anti-freeze liquid, from air heat via unit 10, and, as shown in
For the cooling-conditioning application, reversing valve 62 is set in the other position from that shown in
An important difference of the apparatus 30 shown in
An alternative embodiment of the apparatus 30 is shown in
A schematic of the heating operation of LMHP method is shown in
A compromise for preventing heat pump starvation is proposed here that is structurally identical with SAHP, but with a difference in its operational control, as shown in
Another charging option of using Mode 2 operation, instead of recharging, is precharging of 40. Sensors monitoring 80 and 40, and weather prediction are inputted to a model predicative control (MPC) controller to determine the required thermal condition of 40 for predicting charging need of TES 40 in addition to what is being inputted from 20. If a decision for such charging need is made, eHeatPump switches to Mode 2, the pre-charging mode, which follows exactly the same steps as the recharging steps: valves 64 and 66 are switched to connect the inlet of 60 to refrigerant line to evaporator 2, unit 54, and the outlet of 60 to refrigerant line to condenser 2, unit 58. The operation of 50 in Mode 2 thus extracts heat, through the circulation of anti-freeze liquid, from air heat via unit 10, and, as shown in
The heating application of LMHP method is further refined by adding water heating to the space heating/cooling by adding a smaller water heater 42 to the existing TES 40, as shown in
A schematic of the cooling operation of LMHP method is shown in
The same kind of grid integration in the application and control of GIWH is designed/developed in the application and control of LMHPs. In the application of LMHP method, as shown in
This leads to the application of two-phase compression heat pump with a TES unit to air-conditioning application, as well as the application of LMHP method for cooling and heating with single air heat sink and air heat source, respectively. This is an unexpected use of the apparatus, which was originally conceived as dual source heating of solar and air, stressing the synergy of dual sources transcending the limitations of individual sources. As the case depicted in
One example of utility rate schedule is that of Con Edition of NYC: Its summer peak hours are between June 1 and September 30, and daily from 8 AM to midnight with peak rate of 21.8 cents/kWh. Its off-peak rate is 1.54 cents/kWh, a difference of 14 times. With the effective use of MPC, in this instance, LMHP can operate in Mode 2 each night for the precooling of 40, which is extremely cost effective, whereas with 40 being adequately precooled so that LMHP operates in Mode 1 as needed in the daytime with moderate temperature lift so that the daytime peak-load rated energy expenditure can be minimized. The criterion of what constitutes best precooling scheduling will obviously not be a pure matter of “total” quantity of energy consumed but a matter of the “timing” of each part of energy being consumed. The scheduling or timing has to be “custom-tailored” dependent on each case of rate schedule.
A simulation of air-conditioning operation shows, in
For heating application in this case, not shown, the reversing valve 62 is switched to heating position. Air heat is the single heat source. What distinguishes LMHP from ASHP is the preheating of TES 40 with eHeatPump 50 operating in Mode 2 so that eHeatPump 50 operating in Mode 1 can deliver heat to 80 with moderate temperature lift because of the thermal condition of 40, an important advantage especially during extreme low ambient air temperature. With the effective use of MPC, peak load can be mitigated and the preheating of 40 can be done during attractive power rate period.
In sum, the apparatus of two-phase compression heat pump with a TES provides two modes of heat extraction operation that, by breaking up the weather-imposed large heat-extraction-step into separate charging phase and depleting or conditioning phase, brings about superior operational efficiency as measured by both machine COP and system COP, and flexibility in the timing of pre-charging phase that results in significant operational cost benefit. In its heating application using dual heat sources of solar and air via heat pump heat extraction, LM heat pump system (LMHP system) transcends the limitations of individual solar system and individual AS heat pump system.
The above description and examples should be not construed as limitations on the scope of the invention. Many other variations are possible. Accordingly, the scope of the invention is determined by the claims and their legal equivalents.
