SIMPLE DESIGN TOOLS FOR EARTH-AIR HEAT EXCHANGERS
Ralph T. Muehleisen
In the early stages of the design of building systems, the use of simple design tools can help estimate the size and/or impact of system components in evaluating the viability of various technologies. However, such design tools are not readily available to evaluate earth-air heat exchangers (EAHEs), also known as earth-tubes. Furthermore, even though many researchers have developed sophisticated equations to analyze EAHEs, they cannot be easily recast into design equations and must be used by trial-and-error. This paper describes a set of simplified analysis and design equations to support early-stage EAHE design and which are suitable for implementation in a spreadsheet. The equations we have developed allow the designer to quickly determine the length of tubing required for a desired level of heat transfer effectiveness; estimate the pressure drop across the system and required fan power; and estimate the mean monthly temperature of air exiting the tube.
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