Heat Pumps

A Stirling engine may be used in relation to a heat pump in two ways:

(a) as the heat pump itself;

(b) as the prime mover driving a heat pump.

When the Stirling engine is used as the heat pump it accepts heat at a low (probably) ambient temperature and rejects the heat at a higher temperature to a heating system. Such an arrangement is shown diagrammatically in Fig. 19.1. The system is illustrated by reference to the ideal Stirling cycle P-V diagram and a single-cylinder, piston-displacer. single-acting, Stirling engine. Heat is absorbed during the expansion process at ambient temperature (TH) from an external source (shown as a lake or river). The heat is rejected from the engine during the compression process and is carried off to perform a useful heating function in the building.

Of course work must be supplied (equal to the shaded area on the /' V diagram) to allow the Stirling engine to work in this way. This external work may be supplied from any power source, including an electric motor or a heat engine, perhaps another Stirling engine.

The arrangement of a Stirling engine acting as a prime mover producing power to drive another Stirling engine acting as a heat pump of a cooling engine is illustrated in Fig. 19.2. This may be called the duplex Stirling arrangement or the Stirling-Stirling arrangement. Laboratory versions of such a combination have already been constructed (see Chapter 11) and commerical applications arc anticipated in the foreseeable future.

Stirling Engine Heat Pump
Fig. 19.1. Stirling-engine heat pump

Expansion space Compression spacc Expansion spacc

Healer if for prime mover

Ksgcncraior ouipul Regenerator

Fig. 19.2. Duplex Stirling-engine arrangement. A Stirling engine acting as a prime mover drives a Stirling engine acting as a cooling engine.

Energy flows in the duplex Stirling heat pump are illustrated in Fig. 19.3. Starting at the left of the diagram, air and fuel combine in the combustion chamber to produce high-temperature combustion products. The products leave the system passing through the air preheater where they heat the incoming air and also through a further heat exchanger incorporated in the building heating system.

Meat from the hot combustion products is transferred in the heater of the prime mover to the working fluid. Some of the heat is converted in the Stirling engine prime mover to work and the remainder is rejected in the cooler to the building heating system.

The work produced by the prime mover is consumed to drive the heat pump. The heat pump operates as described above absorbing heat from a thermal source at ambient temperatures and rejecting heat to the building heating system at a higher temperature.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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