Gas engine driven heat pump system with integrated heat recovery and energy saving subsystems

This application is a divisional of application Ser. No. 11/464,060 filed Aug. 11, 2006.

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.

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.

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”).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

By providing cooling of the internal combustion engine\'s combustion air and additional surface area on the outdoor heat exchanger, the refrigeration system becomes ideal for high desert environments.

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.