Reverse cycle air conditioner system

A compression air conditioning system adapted to cool air within the passenger compartment of a motor vehicle can be reversed to function as a heat pump for heating the compartment. The system includes a first heat exchanger located within the compartment wherein the refrigerant is vaporized in the air conditioning mode and condensed during the heating mode. An electrical resistance heater is energized for a short period after starting the engine during which time the various heat sources may be inadequate to heat the passenger compartment air sufficiently. A diverter valve regulates flow through the refrigerant lines so that flow in either the heating or cooling mode is always in the same direction through the lines and the system components. A second heat exchanger located outside the compartment operates as a condenser during the cooling cycle and as an evaporator during the heating cycle. Three sources of heat energy can be used within the second exchanger to heat the refrigerant. The engine exhaust gas and primary engine coolant can be used to heat ambient air, which is carried to the second exchanger to heat the refrigerant when outside temperatures are so low that the refrigerant is not adequately heated from the atmosphere.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a reverse cycle refrigeration system that may 
operate as an automotive heater or air conditioner. More particularly, the 
invention pertains to such a system wherein the waste heat from the 
primary engine coolant and from the engine exhaust gas system are used as 
heat sources during the heat pump operation. 
2. Description of the Prior Art 
The heat pump is a device which uses heat energy absorbed by a refrigerant 
at a low energy state and delivered at high temperature to heat a space 
after having mechanical work applied. It is known from the prior art that 
an air conditioning system can be reversed in operation for heating rather 
than cooling. U.S. Pat. Nos. 3,171,474, 3,141,498, 2,585,748 and 2,806,674 
describe the use of an air conditioning system as a reversible heat pump 
for the purposes of cooling or heating the passenger compartment of a 
motor vehicle. A recognized difficulty with a reverse cycle system is the 
tendency to accumulate frost on the evaporator coils during certain 
periods when atmospheric conditions enhance the possibility of frost 
accumulation. The prior art has been concerned with adapting heat pump 
systems to prevent accumulation of frost by various means. U.S. Pat. Nos. 
2,988,896, 3,444,699, 3,283,809 and 4,102,391 employ various means either 
for preventing the accumulation of frost, sensing its presence or 
dissipating the frost. 
Except in regions of mild winter temperature, the outside winter air is not 
in general a sufficient, low temperature source of heat for a heat pump 
system. In addition to the operating cost for power and maintenance, there 
are fixed costs for the equipment of the heat pump, which substantially 
exceed similar costs for a conventional heating system. Consequently, it 
is difficult to justify these unless there is need of using the same 
equipment for cooling in summer. 
In conventional practice the passenger compartment of a motor vehicle is 
heated by heat taken from the primary engine coolant in a radiator. Within 
the compartment, room temperature air is forced through the heater to 
enhance the efficiency of the heat exchange. It is recognized that small 
passenger vehicles, particularly those having efficient engines adapted to 
deliver high gas mileage, wherein the exhaust gas is recirculated through 
the engine have an insufficient quantity of waste heat from the coolant to 
satisfy the requirements for passenger comfort. For example, it has been 
estimated that perhaps only one-third of the heat load required to 
maintain the compartment at an average 70.degree. Farenheit temperature 
can be supplied from the primary coolant of an engine having the 
efficiency required in future vehicles. 
SUMMARY OF THE INVENTION 
The air conditioning system according to this invention for heating and 
cooling the passenger compartment of an automotive vehicle includes a 
first heat exchanger located within the compartment for transferring heat 
between the refrigerant and the air within the compartment. A second heat 
exchanger is adapted to transfer heat between the refrigerant and the 
ambient outside air or air preheated from the primary engine coolant or 
from the waste heat in the engine exhaust gas system. A compressor is 
driven by an electrical motor from the engine of the vehicle. A diverter 
valve communicates its inlet side with the discharge side of the 
compressor and is adapted to direct refrigerant from the compressor to 
either the first or second heat exchangers. The diverter valve is adapted 
to receive high pressure refrigerant from either the first or second heat 
exchangers and to direct the refrigerant to the suction side of the 
compressor. A second portion of the diverter valve directs the liquified 
compressed refrigerant from the pressure side of the compressor to either 
the first or second heat exchangers depending on whether the system is 
operating as an air conditioner or as a heat pump. When the exterior air 
temperature is so low that the refrigerant cannot receive heat enough from 
this source to maintain passenger comfort during the heating mode of 
operation additional sources of heat may be used. For example, the primary 
engine coolant can be used to preheat ambient air or the engine exhaust 
gas can exchange its heat to the ambient air. Air preheated from either or 
both of these sources is then used either to augment or to replace outdoor 
air as the heat source for heating the refrigerant in the evaporator. 
It is possible during winter use when ambient temperature is so low as to 
inadequately heat the refrigerant and during engine starting conditions, 
and a short period thereafter, that the waste heat available in the 
coolant and the exhaust gas system may also be inadequate to maintain 
passenger comfort. In this instance, the compressor will be underloaded 
and will not require the full capacity of the electrical system to deliver 
electrical energy. The refrigerant delivered to the compressor will be at 
least partially unvaporized and in the liquid state. Therefore, the 
mechanical work done within the compressor is far less than the work 
required if the refrigerant were fully vaporized. The electrical energy 
required to drive the compressor is correspondingly less. When this 
situation prevails, the excess capacity of the electrical system to 
produce electrical current not required by the compressor can be applied 
to energize a resistance strip heater mounted preferably within the 
condensor and across which passenger compartment air is forced to produce 
a heat exchange. In this start-up condition, heat from the electrical 
source adds to the heat derived from the heat pump without requiring that 
the electrical system be oversized in relation to its normal operating 
requirements.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the FIGURE, a compression refrigeration system is shown having 
refrigerant-carrying passages, conventionally of copper tubing, connecting 
various elements of the system. A first heat exchanger 10, which functions 
as an evaporator when the system is cooling the passenger compartment and 
as the condenser when functioning as a heat pump, is shown located within 
the interior of the vehicle. One refrigerant line 12 communicates the 
outlet side of the first exchanger to an inlet of one portion of a flow 
direction diverter valve 14. 
A second refrigerant line 16 communicates the outlet side of the first 
exchanger 10 to the inlet side of a second heat exchanger 18. The second 
heat exchanger, which functions as a condenser when the system is cooling 
the passenger compartment and as an evaporator when the system functions 
as a heat pump, is preferably located externally of the passenger 
compartment. Line 16 first carries refrigerant to an expansion valve or 
capillary 20 before being admitted to the second exchanger. A check valve 
22 interposed between expansion valve 20 and the first exchanger 10 allows 
the refrigerant to flow in the direction from the first to the second heat 
exchangers, but prevents flow in the opposite direction. 
Refrigerant line 24 communicates the outlet side of the second exchanger 18 
with a tee fitting 26 where lines 28, 30 join line 24 and communicate line 
24 with the diverter valve 14 and a second check valve 32, respectively. A 
second expansion valve or capillary 34 is interposed between the second 
check valve 32 and the hydraulic line 36 that carries refrigerant to the 
inlet side of the first heat exchanger 10. Similarly, check valve 32 
allows refrigerant to flow from the second to the first heat exchangers 
18, 10, but prevents the flow of refrigerant in the reverse direction. 
A compressor 38 driven by the engine (not shown) of the vehicle has its 
inlet or suction side 40 connected by a hydraulic line 42 to the outlet of 
that portion of diverter valve 14 that is supplied with refrigerant from 
either refrigerant line 28 or 12. The outlet or pressure side 42 of the 
compressor is connected by line 44 to a second portion of the flow 
diverter valve 14. Diverter valve 14 is adapted to direct the pressurized 
refrigerant delivered from the compressor through line 44 either to 
refrigerant line 46 or 48. Line 46 communicates the outlet side of the 
second portion of diverter 14 to the inlet side of the second heat 
exchanger 18. Heat exchanger 18 may be adapted to have a single inlet 
fitting connected to the outlet side of the expansion valve 20 and 
refrigerant line 46. Line 48 communicates the outlet side of the second 
portion of diverter 14 with the common inlet fitting 36, which is 
connected to the outlet of second expansion valve 34 and the inlet of the 
first heat exchanger 10. 
Diverter valve 14 has two distinct portions, one associated with its outlet 
connected by line 41 to the suction side of the compressor, the other 
associated with the inlet communicating through line 44 with the pressure 
side of the compressor 38. Valve 14 operates with regard to the first 
portion by directing refrigerant carried to its inlet side by either lines 
12 or 28 to the suction side of the compressor. With regard to the second 
portion of diverter valve 14, refrigerant supplied to its inlet side by 
refrigerant line 44 is diverted either to line 46 or 48. Of course, the 
line to which the pressurized refrigerant will be directed or from which 
refrigerant is received in the diverter valve 14 will depend on whether 
the system is operating to heat or to cool the passenger compartment. 
Whether operating as an air conditioning system or as a heat pump, the 
flow of refrigerant through the compressor, the heat exchangers 10, 18, 
the diverter valve 14 and the hydraulic lines is always in the same 
direction. 
Air at ambient outdoor conditions is supplied to and flows through the 
second heat exchanger 18 regardless of whether the system is operating to 
heat or cool the passenger compartment. However, exhaust gas from the 
engine may be diverted from the exhaust system of the vehicle and caused 
to flow through the second heat exchanger 18 when the system is operating 
in the reverse cycle as a heat pump. Heat is taken from the exhaust gases 
in this way in order to augment the heat exchange occurring between the 
refrigerant and the ambient air, particularly when outside air has a low 
temperature insufficient to heat the passenger compartment. 
Alternatively, waste heat from the engine cooling system may be used as the 
heat source. In this instance, the coolant is chilled in a radiator 52 and 
normally exchanges its heat with the ambient air that is allowed to leave 
the vehicle and return to the atmosphere. However, in our system the 
outdoor air after being heated by the coolant in the radiator may be 
carried in an air duct 54 to the second heat exchanger 18 through which it 
flows and in which a heat exchange takes place whereby the refrigerant is 
heated and the air cooled. 
The first heat exchanger 10 is adapted for use during the air conditioning 
cycle to have air from the inside of the passenger compartment pass 
through the exchanger 10 wherein the refrigerant is heated and the air 
cooled. Generally, the air will be forced by a fan driven by a motor 
through the coils of the first heat exchanger in order to increase the 
efficiency of heat exchanger 10. 
An electrical resistance strip heater 56 is located adjacent the coil of 
the heat exchanger 10 and receives electrical power through an electrical 
circuit wherein the resistance heater is in parallel with the motor (not 
shown) that drives the compressor. With the system operating in the 
heating mode when outdoor temperatures are low, there may be insufficient 
heat from the atmosphere to heat the temperature of the passenger 
compartment to the desired temperature. The waste heat from the engine 
whether taken from the primary engine cooling system or from the exhaust 
engine gas may not be a sufficient source of heat for the compartment at 
least until sufficient running time has elapsed and the engine has come up 
to temperature. During this interim period, the compressor is underloaded; 
therefore, electrical energy unneeded to drive the compressor is available 
for other purposes. When our system is operating in the heating mode, a 
compressor amperage coil (not shown) permits the surplus electrical energy 
to be diverted to the electrical resistance heater 56 whereby a rapid 
transfer of heat energy to the refrigerant will occur. As the compressor 
requires additional load causing the electrical motor to draw more 
current, the amperage solenoid disengages thereby opening the circuit and 
deenergizing the resistance heater. After this time, heat from the engine 
coolant or the exhaust system will augment the heat recovered from outdoor 
air and the system will operate in its usual manner. 
When operating in the air conditioning cycle, liquid refrigerant is 
vaporized in the evaporator 10 and thereby absorbing heat from the 
passenger compartment air, which is forced through the heat exchanger 10. 
Low pressure vapor from the evaporator 10 flows through the refrigerant 
line 12 to the diverter valve 14, which is positioned to direct flow to 
the suction side 40 of the compressor 38. In the compressor the 
refrigerant is raised in pressure and temperature and is delivered from 
the compressor through the line 44 back to diverter valve 14. Valve 14 is 
arranged to direct flow of refrigerant through line 46 and inlet fitting 
50 to the condenser 18. Pressure at which refrigerant is delivered to the 
condenser may be approximately 195 psia and the temperature 200.degree. F. 
Ambient air whose temperature may be 100.degree. F. is forced through the 
coil of the condenser 18 whereby an exchange of heat occurs between the 
air and the refrigerant causing the refrigerant to cool to approximately 
120.degree. F., its pressure remaining at 195 psia. In transferring its 
heat to the outside air in the condenser 18, the refrigerant undergoes a 
change of phase to the liquid state. 
The high pressure refrigerant then passes through the hydraulic lines 24, 
30 and through the check valve 32, which is opened during the 
refrigeration cycle to admit flow of refrigerant through the expansion 
valve 34. Within expansion valve 34, the refrigerant throttles to the 
evaporator pressure. In passing through the expansion valve the liquid 
refrigerant cools, perhaps to 40.degree. F., and as a consequence of the 
throttling process its pressure is reduced to about 50 psia. The cold 
refrigerant then enters the inlet fitting 36 which directs it through the 
coil of the evaporator 10. The air within the passenger compartment is 
forced through the coils and a heat exchange takes place whereby the 
refrigerant is heated and the air is cooled. The flow rate of air through 
the evaporator will be about 200 cubic feet per minute. 
Either a dichlorodifluoromethane such as Freon-12, 
monochlorodifluoromethane such as Freon-22, or trichloromonofluoromethane 
such as Freon-11, can be used in our system. The pressures and 
temperatures of the refrigerant throughout the system will, however, vary 
depending upon the refrigerant used, the pressure drops in the system, the 
ambient conditions and the desired temperatures. 
When the system is operating in the air conditioning mode, the first check 
valve 22 is closed. Therefore, refrigerant exiting the evaporator 10 does 
not flow through the line 16, but rather through the refrigerant line 12 
which carries it to the diverter valve 14. 
When the system is operating in the reverse cycle as a heat pump to heat 
the passenger compartment, check valve 22 is opened and valve 32 closed. 
Therefore, refrigerant from the exchanger 18 flows to diverter valve 14 
rather than to heat exchanger 10. Liquid refrigerant leaving the condenser 
10 at approximately 160.degree. F. and 280 psia is carried in line 16 
through check valve 22 to the first expansion valve 20. In passing through 
expansion valve 20 the refrigerant expands into the coil of the 
evaporator. 
Outside air is forced through the evaporator at approximately 1000 cubic 
feet per minute whereby the air is cooled and the refrigerant heated to 
approximately 22.degree. F. at 36 psia. Alternatively, when the 
temperature of the outdoor air is so low that the passenger compartment 
cannot be adequately heated, heat can be pumped from the primary engine 
coolant by circulating the coolant through the radiator 52. Ambient 
outdoor air receives heat from the coolant and instead of being dissipated 
to the atmosphere, is directed in the air duct 54 and forced through the 
evaporator 18. A third potential source of heat for the system is the 
waste heat normally delivered to the atmosphere in the form of engine 
exhaust gases. The system can be adapted to produce an exchange of heat 
between the exhaust gases and the ambient air in a heat exchanger (not 
shown). The air so heated can be delivered through the air duct 54 and 
forced through the evaporator 18. 
The vaporized refrigerant leaves the evaporator 18 through the line 24 
wherein it is directed through the line 28 to the diverter valve 14. Valve 
14 is arranged to direct the flow of vaporized refrigerant through line 41 
to the suction line 40 of the compressor 38. In the compressor, mechanical 
energy is added to raise the pressure and temperature of the refrigerant 
to about 260.degree. F. and 280 psia. The hot refrigerant is discharged 
from the compressor through line 44 which carries it to diverter valve 14. 
Since the system is operating as a heat pump, diverter 14 is disposed to 
direct flow through line 48 through the inlet fitting 36 to the condenser 
10. Within the condenser, the refrigerant gives up superheat and the heat 
of vaporization to the passenger compartment air, which is forced at 200 
cubic feet per minute through the condenser. 
When the outdoor temperature is so low that the refrigerant is not heated 
sufficiently in the evaporator, or if the engine coolant or engine exhaust 
gas temperatures are so low that the refrigerant is inadequately heated, 
the refrigerant will not be evaporated in the evaporator 18 but will be 
delivered to the suction side of the compressor either entirely or in 
large part still in the liquid phase. In this instance, the compressor is 
required to do less work on the refrigerant since a phase change is only 
partially involved. Consequently, the power required to drive the 
compressor is less than if the source of heat were at a higher temperature 
and the refrigerant fully vaporized. When the compressor 38 is underloaded 
in this way, the excess electrical current otherwise drawn by the electric 
motor that drives the compressor can be used to energize the electrical 
resistance heater 56, which may be housed in the same unit as the 
condenser 10. In this case, when the passenger compartment air is forced 
through the condenser the air is heated partially by an exchange of heat 
between the refrigerant and the air and partially by the air passing over 
and drawing heat from the resistance heater. 
In normal operation during the heat pump cycle, the refrigerant leaves the 
condenser 10 at approximately 160.degree. F. and 280 psia at which 
conditions it is delivered back through the check valve 22 and the first 
expansion valve 20.