Abstract:
A gas heat pump system powered by natural gas, propane or similar gaseous fuel is disclosed. The system uses heat recovery and heat addition to manage efficient heating and cooling cycles. In a cooling cycle excess heat is vented to the atmosphere while in a heating cycle, excess heat is used to heat a subject structure and to prevent frost from forming on outdoor heat exchangers. A control system monitors the system&#39;s operation and corrects abnormal operational conditions or shuts down the system until the system can be manually inspected. The costs of system operation are less than electric systems because of the efficiencies and use of natural gas or propane.

Description:
FIELD OF THE INVENTION 
       [0001]    The embodiments of the present invention relate to refrigerant vapor compression heat pump systems (classic Rankine thermodynamic cycle) driven by combustion engine prime movers with a frostless outdoor heat exchanger, multiple refrigeration circuits, integrated heat recovery, engine cooling and auxiliary heating function configured in single or modular units. 
       BACKGROUND 
       [0002]    Vapor compression heat pump systems are widely used to provide heating and cooling air conditioning to residential and, to a lesser extent, commercial facilities. One drawback of the vapor compression heat pump systems is that the heating capacity decreases as the ambient temperature decreases. Thus, during winter months the vapor compression heat pump systems lack efficiency. Moreover, with low ambient temperatures, building heat losses increase such that building temperatures decrease. One well-known solution to the inefficiency problem has been the addition of auxiliary electric heat strips. Unfortunately, the heat strips increase power usage and therefore system cost. 
         [0003]    In recent years, combination air conditioner/heat pump systems have been suggested as a solution to the inefficiencies discussed above. A gas engine driven air conditioner/heat pump system utilizes a natural gas engine, instead of a traditional electric motor, to drive a compressor in the refrigerant circuit. An air conditioner/heat pump system utilizing a natural gas engine is known as a gas heat pump type air conditioner (“GHP”). The GHP uses natural gas, which is less expensive compared to other fuels such that the operating cost of the GHP is less than air conditioner/heat pump system driven by a conventional electric motor (“EHP”). 
         [0004]    One advantage of using a combustion type engine, in lieu of an electric motor, in a heat pump system is the ability to use excess heat of combustion generated by the engine. The excess heat is available for wintertime heat augmentation thereby reducing or eliminating the need for auxiliary heaters. It has been a common practice with combustion engine heat pump systems to recover the excess heat from the engine by conveying a working fluid (e.g., water and ethylene glycol antifreeze) through the cooling and sometimes the exhaust system such that waste heat from the engine is absorbed by the working fluid. The heated working fluid is then pumped to a heat exchanger or radiator located in the air flow leading to the air-conditioned space. 
         [0005]    Another advantage of using a combustion engine is the significant reduction is costs associated with the use of inexpensive fuel sources such as natural gas, propane and similar gaseous fuels. 
         [0006]    While the advantages of using waste heat from a combustion engine are well recognized, the wide range of options for recovering and using the waste heat has required numerous, separate components to facilitate the heat exchange, auxiliary heating, defrosting and heat rejection. The complexity, size and cost of the heat pump systems having desirable heat recovery and use capability have increased accordingly. In addition, the use of small internal combustion engines at high ambient temperatures and at increased altitudes is problematic in that the environmental conditions reduce output horsepower. 
         [0007]    Therefore, the need exists for a heat pump system which recovers and applies wasted heat effectively into the air-conditioned space and minimizes the use of electrical power demand and costs during both the heating and cooling heat pump cycles in high temperature environments. 
       SUMMARY 
       [0008]    Accordingly, one embodiment of the present invention is a gas heat pump system having an engine compressor section, indoor section and outdoor section comprising: one or more refrigeration circuits comprising a refrigeration compressor and switching device, said switching device operable to direct refrigerant into the indoor section during a heating cycle and into the outdoor section during a cooling cycle; said engine compressor section comprising: an engine capable of running on a gaseous fuel; an engine cooling system; a fuel intake system; and an exhaust gas system; said indoor section comprising: an indoor heat exchanger; one or more fans operable to pass indoor air across the indoor heat exchanger; and one or more expansion valves corresponding to the indoor heat exchanger; said outdoor section comprising: a radiator; one or more outdoor heat exchangers; one or more fans operable to pass outdoor air across the radiator and the outdoor heat exchangers; and one or more expansion valves corresponding to each outdoor heat exchanger. 
         [0009]    The embodiments of the present invention satisfy the need providing a system that integrates waste heat recovery, maximizes load efficiency, maintains comfortable indoor air supply temperatures during low ambient outside temperatures while minimizing electricity demand and cost during a heating and cooling cycle. 
         [0010]    The GHP system disclosed herein comprises three primary components: an engine compressor section, an indoor section and an outdoor section. Ideally, the primary components are contained within a single unit. 
         [0011]    In one embodiment of the present invention, the engine compressor section comprises an internal natural gas engine, waste heat recovery components and multiple belt driven scroll type compressors. In this embodiment, engine coolant is pumped through the waste heat recovery components and the engine thereby removing and recovering the waste heat. 
         [0012]    In one embodiment, the indoor, section comprises an indoor heat exchanger containing multiple interlaced refrigerant circuits and an auxiliary heat circuit and an air blower driven by a multi-speed motor. Also contained within the indoor section are thermostatic expansion devices, check and control valves and miscellaneous refrigeration and electrical components. 
         [0013]    In one embodiment, the outdoor section comprises dual outdoor heat exchangers with one heat exchanger dedicated to a separate refrigerant circuit and anti-frost circuit and multiple high efficiency fans driven by high efficiency multi-speed motors. Also contained within the outdoor section are an engine coolant radiator and various valves and controls. 
         [0014]    A refrigeration system of one embodiment of the present invention comprises two complete heat pump circuits driven by a single natural gas internal combustion engine. The refrigeration system is designed and controlled such that system efficiency is maximized by varying the number of running compressors and refrigerant flow rate through the circuits to satisfy the heating and cooling load requirement for the subject air-conditioned space. The refrigerant flow rate is adjusted by varying the speed of the natural gas internal combustion engine. Load efficiency is maximized by interlacing refrigerant circuits within the indoor heat exchanger and by varying the airflow across the indoor and outdoor heat exchangers to match the ambient conditions and load requirements. 
         [0015]    By providing cooling of the internal combustion engine&#39;s combustion air and additional surface area on the outdoor heat exchanger, the refrigeration system becomes ideal for high desert environments. 
         [0016]    When the GHP is operated in a cooling mode, waste heat is removed from the engine and exhaust by coolant which is directed to the radiator where the waste heat is either rejected to the atmosphere or further directed to an auxiliary heating device like a hot water heating system, swimming pool heating system or other domestic water systems requiring heat. 
         [0017]    When the GHP is operated in a heating a mode, waste heat is removed from the engine and exhaust by the coolant which is directed to the indoor and outdoor heat exchangers. Unless the outdoor ambient temperature is below a threshold frost point temperature (e.g., freezing), all the coolant is directed to the auxiliary heat circuit in the outdoor heat exchanger thereby causing all recoverable heat to be transferred from the engine into the subject air-conditioned space. Such an embodiment maximizes the coefficient of performance (COP), where COP is defined as the ratio of the useful heating energy output to the total energy input (fuel and electricity consumed). If the ambient temperature is below the threshold frost point temperature, part or all of the engine coolant is directed to the anti-frost circuit in the outdoor heat exchanger. The COP is once again increased based on the higher inlet air temperature to the refrigerant portion of the outdoor heat exchanger. 
         [0018]    The embodiments of the present invention also incorporate the capability to add additional heat to the system via an auxiliary natural gas heater (AXTHR) to reduce engine warm up time and provide, in colder climates, additional heat to the subject air-conditioned space without the need for auxiliary electric strips. 
         [0019]    Other variations, embodiments and features of the present invention will become evident from the following detailed description, drawings and claims. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  illustrates a schematic diagram of a first embodiment of a gas engine driven heat pump system of the present invention; 
           [0021]      FIG. 2A  illustrates a schematic diagram depicting refrigerant and engine coolant flows during a cooling cycle without an optional hot water waste heat exchanger (HWXGR); 
           [0022]      FIG. 2B  illustrates a schematic diagram depicting the refrigerant and engine coolant flows during a cooling cycle with the optional hot water waste heat exchanger (HWXGR); 
           [0023]      FIG. 3A  illustrates a schematic diagram depicting the refrigerant and engine coolant flows during the heating cycle operating at ambient temperatures above a threshold ambient temperature without an optional cold climate auxiliary heater (AXHTR); 
           [0024]      FIG. 3B  illustrates a schematic diagram depicting the refrigerant and engine coolant flows during the heating cycle operating at ambient temperatures at or below the threshold frost point ambient temperature without an optional cold climate auxiliary heater (AXHTR); and 
           [0025]      FIG. 3C  illustrates a schematic diagram depicting the system with the optional cold climate auxiliary heater (AXTHR) installed. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    For the purposes of promoting an understanding of the principles in accordance with the embodiments of the present invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the inventive feature illustrated herein, and any additional applications of the principles of the invention as illustrated herein, which would normally occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention claimed. 
         [0027]    Reference is now made to the figures wherein like parts are referred to by like numerals throughout.  FIG. 1  shows a schematic diagram of a gas engine driven heat pump system of the present invention generally referred to by reference numeral  50 . The system  50  includes an engine compressor section  51 , an indoor section  52  and an outdoor section  53  divided by lines  54 ,  55 . 
         [0028]    The system  50  comprises two identical refrigeration circuits referred to as circuit A and circuit B. Internal combustion engine  1  runs on natural gas (or propane or other suitable gases) and drives two refrigeration compressors  2 A,  2 B. The refrigeration circuits operate using classic Rankin cycle principals. A Rankine cycle is a thermodynamic cycle familiar to those skilled in the art. 
         [0029]    Combustion air (CA) first enters an inlet silencer device  32  that reduces air flow noise. The combustion air then travels through an air cooler device  33  that, depending on the combustion air temperature, may cool the combustion air several degrees. Reducing the combustion air temperature increases the horsepower output of the internal combustion engine  1 . The cooled air then passes through an air filter  34  that filters any particulate matter. The clean air then enters an air fuel mixture device  35  located on, or in proximity to, the internal combustion engine  1 . 
         [0030]    Engine combustion exhaust gases exit the engine  1  through water cooled exhaust manifold  22  where the gases are cooled by engine coolant circulated through the manifold  22 . The exhaust gases then enter a catalytic converter  36  that reduces NOx and hydrocarbon emissions. The gases then flow through an exhaust air exchanger  21  such that the gases are cooled to approximately 200° by engine coolant circulated through the exchanger  21 . Next, the cooled exhaust gases flow through exhaust separator  19  where any condensed water (a product of combustion) is removed. The remaining exhaust vapors are vented to the atmosphere. The exhaust liquids (e.g., water), which may be acidic, flow to an exhaust liquid filter  36  that neutralizes any acid in the liquid. The neutralized liquid may then be dispensed through a drain. 
         [0031]    Natural gas, or propane, from a gas source first enters the system  50  via safety cutoff device and pressure regulator  16 . The pressure regulator  16  lowers the gas pressure to a suitable and useable level for receipt by an engine carburetor  35  that causes the gas to be mixed with combustion air. In embodiments utilizing an optional cold climate auxiliary heater  23 , natural gas, or propane, is also piped thereto. 
         [0032]    An extended engine life and maintenance cycle (e.g., 10,000 hours) may be accomplished by the addition of an auxiliary oil storage tank  18 . 
         [0033]    Cool low pressure refrigerant vapor is compressed to high pressure by compressors  2 A,  2 B. Pursuant to the principal defined by the ideal gas law (PV=nRT), as the vapor is compressed, its temperature increases. The now hot, high pressure refrigerant vapor flows to oil separators  3 A,  3 B which separate oil from the refrigerant. The separated refrigerant oil is returned to compressor suction line  16 A,  16 B through metering devices  14 A,  14 B,  15 A and  15 B and solenoid valves  13 A.  13 B. Solenoid valves  13 A,  13 B are activated by a control system in response to changing operating conditions to provide optimum oil flow to the compressors  2 A,  2 B. 
         [0034]    The hot, high pressure refrigerant vapor flows from the oil separators  3 A,  3 B to reversing or switching valves  4 A,  4 B, where the vapor is diverted to the indoor exchanger  6  or the outdoor exchangers  11 A,  11 B, depending on whether the system is in heating or cooling mode. 
         [0035]    When the system  50  is in the cooling mode or cycle, the switching valves  4 A,  4 B divert hot, high pressure refrigerant to the outdoor heat exchangers  11 A,  11 B, which, in the cooling mode, act as condensers. Refrigerant from valve  4 A is directed to outdoor heat exchanger  11 A and refrigerant from valve  4 B is directed to outdoor heat exchanger  11 B. Each outdoor heat exchanger  11 A,  11 B contains a refrigerant circuit (A, B) and a heating circuit (C). The heating circuit is used during the heating mode to prevent frost accumulation on the outdoor heat exchangers  11 A,  11 B. The hot, high pressure refrigerant is then condensed to a high pressure liquid and sub-cooled by removing heat from the refrigerant. The heat is removed by drawing cooler outdoor air across the outdoor heat exchangers  11 A,  11 B. Outdoor fans  30 A,  30 B provide the air flow and are adjusted by the control system to provide the optimum flow rate to match the required refrigeration load and outdoor ambient conditions. 
         [0036]    The high pressure sub-cooled refrigerant liquid then flows through check valve devices  10 A,  10 B to thermostatic expansion devices  7 A,  7 B. The thermostatic expansion devices regulate the refrigerant flow which lowers the pressure of the refrigerant as it flows through the device. The pressure reduction causes expansion of the refrigerant liquid whereby a portion flashes into a vapor that, according to the Joule-Thompson effect, causes the temperature of the two phase refrigerant to be reduced. 
         [0037]    The cold two-phase refrigerant then enters indoor heat exchanger  6  which functions as an evaporator in the cooling mode. Warm return air from the subject air-conditioned space is drawn across the indoor heat exchanger  6  by indoor blower  31 . Heat is removed from the return air thereby cooling the air stream. The cool air stream is then returned to the subject air-conditioned space. The heat removed from the air stream is transferred to the cold two-phase refrigerant flowing through the tubes of the indoor heat exchanger  6  causing the liquid refrigerant to boil. After all liquid refrigerant has boiled into vapor, additional heat is added to the heat exchanger  6  causing the refrigerant vapor to become superheated. The amount of superheat is controlled by the thermostatic expansion devices  7 A,  7 B. 
         [0038]    The indoor heat exchanger  6  includes two interlaced refrigeration circuits (A, B) and one auxiliary heating circuit (C) used during the heating cycle. The interlacing of the refrigerant circuits provides optimum heat exchanger  6  efficiency during full and partial load cycle. 
         [0039]    The superheated refrigerant vapor then flows back to the switching valves  4 A,  4 B and then to suction accumulators  5 A,  5 B where any liquid refrigerant that may have condensed is separated from the refrigerant vapor. The refrigerant vapor is then drawn into low pressure inlets of the compressors  2 A,  2 B such that the cycle can be repeated. 
         [0040]    During both heating and cooling cycles, engine coolant is circulated through the system  50  by coolant pump  20 . Warm coolant is pumped through the exhaust air exchanger  21  where the coolant temperature is raised a few degrees by waste heat recovered from the engine exhaust. The coolant then flows to the water-cooled exhaust manifold  22 , located on the internal combustion engine  1 , such that the coolant temperature is additionally raised. The coolant then enters the internal combustion engine  1  where it removes heat from the engine  1 . This portion of the coolant circuit collects waste heat for efficient use during the heating and cooling cycles. 
         [0041]    Now referring to  FIG. 2A , the system  50  is shown operating in a cooling cycle without any optional devices installed. Engine coolant flows from engine  1  to engine temperature control valve  24 . A proportional integral derivative (PID) control loop in the control system maintains an efficient engine temperature by directing the coolant flow either back to the engine  1  or to radiator  27 . Upon initial startup, in order to bring the engine  1  to a proper operating temperature, the coolant is directed by engine control valve to the engine  1 . As the engine temperature approaches the desired operating temperature, the engine temperature control valve  24  directs the coolant to switching valve  25 . During the cooling cycle, the switching valve  25  directs the engine coolant to the radiator  27  where excess engine heat is removed. The excess engine heat is removed from the coolant as the result of outside air being drawn across the radiator  27  by outdoor fans  30 A,  30 B. The coolant then flows to the coolant pump  20  where the coolant cycle begins again. 
         [0042]      FIGS. 2B  shows the system  50  operating in the cooling cycle with an optional hot water exchanger  29  installed. Hot coolant exiting the switching valve  25  flows to a hot water temperature control valve  26 . Hot coolant is then directed to the hot water exchanger  29  where waste heat is used to heat domestic water, swimming pools and the like. A PID control loop in the control system regulates the hot coolant flow to the hot water exchanger  29  and the radiator  27 . Once a pre-established threshold temperature of the heated water is achieved, the remaining coolant flow is directed to the radiator  27 . Coolant exiting the hot water exchanger  29  and radiator  27  flows to the coolant pump  20 , where the cycle begins again. In this embodiment, waste heat in efficiently used thereby increasing overall system efficiency. 
         [0043]      FIG. 3A  shows the system  50 , without any optional devices installed, operating in the heating cycle when the ambient temperature is above a threshold frost point temperature of the outdoor exchangers  11 A,  11 B. The switching valve  25  directs the hot engine coolant to a frost avoidance valve  28 . Since the outdoor ambient temperature is above the threshold frost point temperature, the PID control loop of the control system directs all hot coolant to circuit (C) of the indoor heat exchanger  6 . 
         [0044]    The indoor heat exchanger  6  includes two interlaced refrigerant circuits (A, B) and an auxiliary heat circuit (C). The auxiliary heat circuit (C) is located on the outlet side of the indoor heat exchanger  6  downstream of the refrigerant circuits with respect to the air flow created by the indoor blower  31 . This configuration of the refrigerant and engine coolant circuits provides several primary benefits. First, due to the sizing and arrangement of the outdoor heat exchangers  11 A,  11 B, heat recovery from the outside air is maximized and transferred to the subject air-conditioned space. Second, due to the interlacing circuits (A, B) within the indoor heat exchanger  6 , partial load efficiency is maximized. Third, waste heat recovered from engine  1  is transferred to the subject air-conditioned space and provides significantly higher air temperatures than possible with conventional heat pump systems during low ambient temperature cycle. Moreover, a significant increase in the COP over conventional heat pump systems is achieved. 
         [0045]    Now referring to  FIG. 3B , the system  50 , without optional devices installed, is shown operating in the heating cycle when ambient temperatures are at or below the threshold frost point temperature of the outdoor exchangers  11 A,  11 B. The switching valve  25  directs the hot engine coolant to the frost avoidance valve  28 . Sensors or similar devices located in the outdoor section  53  sense and report when temperatures are such that frost is likely to form on coils of the outdoor exchangers  11 A,  11 B. As temperatures approach the threshold frost point, the PID control loop adjusts the flow through the frost avoidance valve  28  by directing some or all of the engine heat coolant from the indoor heat exchanger  6  to the frost avoidance circuit (C) in the outdoor heat exchangers  11 A,  11 B. The frost avoidance circuit (C) is located on an inlet side of the outdoor heat exchangers  11 A,  11 B wherein the inlet side is upstream with respect to the air flow created by fans  30 A,  30 B. Cooled engine coolant exits the indoor heat exchanger  6  and the outdoor heat exchangers  11 A,  11 B and flows back to the coolant pump  20  where the cycle begins again. This configuration offers two primary benefits. First, the outdoor exchangers  11  A,  11 B never require defrosting thereby eliminating the high energy used by conventional heat pumps to defrost exchanger pipes. Second, even though the hot engine coolant is directed from its primary function of increasing the heat delivered to the subject air-conditioned space, the energy is not wasted since it is reabsorbed into the system  50  by increasing the temperature of the air entering the refrigerant circuits (A, B) of the outdoor heat exchangers  11  a,  11 B which function as evaporators during the heating cycle of cycle. The effect is that the inlet temperature of the outdoor air to the evaporator is increased several degrees, thus raising the overall heating effect of the system  50  and the corresponding COP. 
         [0046]      FIG. 3C  shows the system  50  including supplemental heating for system cycle in climates not suitable for conventional heat pump systems. An auxiliary heater  23  is installed between the internal combustion engine  1  and the engine temperature control valve  24 . Hot engine coolant exits the internal combustion engine  1  and flows to the auxiliary heater  23  where it is heated to a higher temperature by a natural gas burner using the natural gas (or propane) supplied from the combined safety cutoff device and pressure regulator  16 . The engine coolant then flows to the engine temperature control valve  24 . The system  50  continues to operate as described above with respect to the heating cycle. However, since the engine coolant now has a higher temperature, it provides additional heat to the subject air-conditioned space. Another advantage of the auxiliary heater  23  is that it facilitates a shorter startup time for the internal combustion engine  1  resulting in the ability to more quickly heat the subject air-conditioned space. 
         [0047]    An electrical control system including circuitry, logic and related electronic components, is operable to manage the system  50 . A thermostat controllable by a user dictates whether the system  50  is in the cooling or heating cycle and at what temperature level. More particularly, the control system can vary the speed of the engine  1 , indoor blower  31  and outdoor fans  30 A,  30 B and the number of running refrigeration compressors  2 A,  2 B. The control system includes sensors designed to monitor the system  50  for irregular operational conditions. Based on the detection of irregular or abnormal operational conditions, the control system automatically takes steps to correct the irregularities or abnormalities or shut down the system  50  when the irregularities cannot be corrected. The control system further controls coolant flow during the different cycles. Air-fuel mixture is also managed by the control system. 
         [0048]    Although the invention has been described in detail with reference to several embodiments, additional variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.