A heat pump is understood to be a system involving a heat-circulation process of the type wherein a liquid cooling means at +2.degree. C. is evaporated in an evaporator and consequently absorbs the heat from a medium, for example water or air, at a temperature of +10.degree. C. The cooling-medium vapor of +2.degree. C. absorbs here approximately 10 kW. heating efficiency and is then drawn away by a compressor. The cooling-medium vapor is condensed to 15.5 bar in said compressor, is heated to +60.degree. C. and is fed to a condenser while absorbing a further 5 kW. (compressor output). Here the cooling-medium vapor emits again the absorbed 15 kW. at an unchanged high pressure and becomes liquid. The heating water, for example for a heating system of a house of the conventional type, is guided through the condensor and absorbs the heat which is emitted from the cooling-medium vapor, which heat is fed now in the heating water to the actual heating purpose.
The liquid cooling means at +60.degree. C. moves from the condensor on to an expansion valve, expands here and assumes a lower pressure of 3.5 bar at a temperature of +2.degree. C. This cooling means is returned to the evaporator and a new cycle of said means in the heat pump starts. (The aforementioned values are only exemplary values and are provided to aid one to easily understand the circulation processes of the heat pump. The physical principles of a heat pump are discussed in detail for example in "VDI-Statusbericht Warmepumpe" VDI-Verlag, GmbH, Dusseldorf 1976.).
The purpose of the present invention is now to provide a drive unit which is coupled with the compressor in such heat pumps, which drive unit can be operated and serviced easily and without any errors by nontrained persons, for example housewives. This purpose is attained according to the invention by the unit including a fuel-injection internal combustion engine which drives the compressor and a starter associated with said engine being fed power from an electric power line, wherein the starter can be connected to the electric power line by means of a switch.
In the preferred embodiment of the invention, the starter is constructed as an electromagnetic drive motor having a rotor and a stator. The rotor is secured to the crackshaft of the engine and serves at least partially as a flywheel. The stator has coil windings of which current from a three-phase a.c. power-line is fed.
The starting switch can be operated manually in heat pumps of a simple construction. In systems which have a high ease of operation, however, automation will be used, for example a thermostatically controlled relay, which, when falling below a fixed minimum value in the temperature of the heating water for the heating system of the house, closes the starting switch. This automation is preferable in view of the fact that a heat pump is used often only as an auxiliary heating system in a house, which is heated with heating oil, and must be started and turned off many times during changing weather temperatures.
A preferable further development of the invention results when a coupling is arranged between the crankshaft of the engine and the driven shaft of the compressor, which coupling is constructed as a centifugal clutch. The compressor is connected in this manner to the driving fuel-injection internal combustion engine only after same has reached the necessary speed and the predetermined torque.
For the purpose of designing the drive unit as an easily transportable and installable unit, it is preferable to provide a common support frame, on which, with the interpositioning of vibration-damping elements therebetween, the structural components (internal combustion engine, starter, compressor) are secured. An arrangement which is very advantageous with respect to space results when the starter is arranged between internal combustion engine and compressor such that its housing is secured on the one side to the internal combustion engine and on the other side to the compressor.