A TESTING AND HVAC DESIGN METHODOLOGY FOR AIR-TO-AIR HEAT-PIPE HEAT-EXCHANGERS

Air-to-air heat pipe hear exchangers were tested wing ASHRAE Standard 84-1991 as a guide. Some changes are introduced for the test facility and methods of calculating effectiveness. ASME PTC 19.1-1985 is used a s a guide for uncertainty analysis. Tests were done for a range of mas s flux [1.574 to 2.912 kg/(m(2).s)], ratios of mass flow rates (0.6 to 1.85), supply air temperatures (-10 degrees C to 40 degrees C), and h eat exchanger tilt angles (-8.9 degrees to 11.2 degrees). Because humi dity changes in the exhaust and supply air streams were negligible, on ly the effectiveness of sensible and of total energy was considered. M easured and calculated results show significant variations in the effe ctiveness of sensible and of total energy, and uncertainties with each independent variable. For balanced exhaust and supply flow rates at - 10 degrees C supply air temperature and 1.574 kg/(m(2).s) mass flux, t he measured effectiveness for sensible and total energy was calculated to be 0.48 and 0.44, respectively, with uncertainties of 0.057 and 0. 052. These measurements decreased to 0.42 and 0.37, with uncertainties of 0.016 and 0.018 for a mass flux of 2.912 kg/(m(2).s). Because wate r vapor condensation effects were small or negligible, the difference between the effectiveness for the sensible and total energy was within the overlapping uncertainty range of each. Based on counterflow heat exchanger theory and convective heat transfer equations, expressions a re presented to extrapolate the effectiveness data between and beyond the measured data points. These effectiveness equations, which represe nt the variation in effectiveness with several independent operating v ariables, are used for HVAC design that is aimed at achieving minimum life-cycle costs.