A two-stage harmonic reciprocating Stirling engine has a primary heater and a pair of regenerators with an intermediate heat exchanger disposed in the fluid flow between the two regenerators. High temperature heat above 5000.degree. F. is supplied to the heater head of the engine while lower temperature, otherwise wasted, heat between 500.degree. F. and 1500.degree. is supplied to the intermediate heat exchanger. The lower temperature heat can be from exhaust gases of the primary burner, or can be waste heat from another process for use in a cogeneration installation.

An externally heated engine is provided which has at least two pistons. The first piston has a first side (working side) and a second side opposite the first side. The first side of the first piston and the first cylinder define a first working chamber containing working fluid. The second side of the first piston and the first cylinder define a first opposite chamber containing an opposing fluid. A heater heats the working fluid in the first cylinder. Preferably, the cylinder is heated by a heat source so that the working fluid has a temperature of no more than 500.degree. Fahrenheit with a temperature difference between the heat source and the working fluid of less than 5.degree. Fahrenheit. The second piston reciprocates within a second cylinder, and has a first side (working side) and a second side opposite the first side. The first side and the cylinder define a working chamber containing working fluid. The second side of the piston and the cylinder define a second opposite chamber containing an opposing fluid. The working fluid in the second cylinder is cooled to a temperature of below 35.degree. Fahrenheit.

A hot gas engine, such as a Stirling engine, which comprises a displacer portion and an expander portion with a heat exchanger connected therebetween. The expander portion has an expander piston which is operatively connected to and rotates an expander crankshaft. In like manner, the displacer portion is provided with a displacer piston which is also operatively connected to and rotates with a separate displacer crankshaft. The two crankshafts are synchronized with respect to each other, preferably by means of an idler gear. Banks of displacer pistons can also be provided for operation on a common displacer crankshaft and banks of cooperating expander pistons also can be provided for operation on a common expander crankshaft.

A refrigerated cold beverage merchandiser (10) includes an enclosure defining an insulated, refrigerated display cabinet (25) and a compartment (30) heat insulated therefrom wherein a compressor (40) a condenser (50) and a condenser fan (60) are disposed. The condenser (50) is formed by a plurality of in-line tube banks (52). Each tube bank (52) is a serpentine tube formed a plurality of unfinned, straight tube segments (54) extending in parallel rows (55) between a pair of spaced, opposed end plates (58) and elbow turns (56) connecting neighboring straight tube segments (56) in a conventional manner. Each successive tube bank (52) is arranged with the other tube banks so that respective parallel tube rows (55) are disposed in-line from the front to the rear of the condenser (50) or with each successive tube bank being offset in a slightly staggered arrangement.