A heat exchanger is a device to provide for the transfer of internal thermal energy between two or more fluids, between a solid surface and a fluid, or between solid particulates and a fluid, in thermal contact without external heat interactions. This chapter presents experimental investigations on the thermal performance of various nanofluids in different types of heat exchangers and provides a clearer view of the application of nanofluids in heat exchangers. It explores to communicate some simple lessons about fouling, to which local experience and designs criteria must be added. The chapter presents a brief review of bioheat transfer from the perspective of those aspects, which distinguish it from processes in inanimate systems. It examines the performance of a number of phase change material (PCM)-enhanced building elements and whole-building effects. The chapter discusses several types of thermal bridges which can be spotted at various parts of the building skin and architectural interfaces.