Abstract: A parallel-flow heat exchanger composed of a plurality of stacked, substantially flat panels defining between them, in the stacked state, spaces through which are adapted to flow the media intended to exchange heat. In the panels there are provided inlet and outlet openings for each of the media. In the stacked state, the space between the nth and the (nth+1) of the panels is traversed by one of the media, while the space between the (nth+1) and the (nth+2) panel is traversed by the other one of the media. The inlet and outlet openings are located outside of the confines of the major surfaces of the panels and the axes of the openings lie in planes substantially parallel to the general plane of the panels.

Abstract: A solar fluid heater consisting of a solar collector and a storage vessel. The solar collector includes a supply outlet and a return inlet, a supply conduit, leading the heated fluid from the supply outlet to the vessel, and a return conduit, returning the cold fluid from the vessel to the return inlet. The supply conduit comprises two contiguous portions, a first portion substantially exposed to the same night temperature as in the collector, and extending between the supply outlet and a transition zone. The first supply conduit portion takes an altogether descending course from the supply outlet to at least the transition zone, and a second portion is adapted to maintain it at night at a temperature substantially equaling that of the vessel contents and extends from the transition zone to the outlet opening of the supply conduit inside the vessel, whereby, during the night, the temperature of the first return-conduit portion is substantially equal to the temperature of the vessel contents.