It is the objective of this investigation to design and simulate multiple-coil run-around systems under a wide range of operating conditions from cold weather heat recovery to hot weather operation with high cooling loads. A computer program has been developed to simulate any number of supply and exhaust coils in a run-around heat recovery system. The simulation enables the rating of a run-around system based on known physical parameters of each coil, the supply and exhaust air flow rates, inlet supply air temperature and humidity levels, and inlet exhaust air temperature and humidity levels. The simulation program is used in two different manners - it can be used for a specified system, to determine yearly costs and savings by using hourly weather files; and to determine the least objective function based on the life-cycle cost of the system to select design parameters for the run-around system. The yearly simulation uses hourly weather data to determine hourly operating costs and savings, all liquid and air temperatures, and pressure drops in the system. The results show that the performance of an optimised system with two coils is basically the same as the performance of a four coil optimised run-around system with the same total air flows as the two coil system. For the typical building application studied, the life-cycle cost of the optimised systems is 13% less than the life-cycle cost of an original installed run-around system. With evaporative cooling, the life-cycle cost of an optimised system is 24% less than that of the original installed system. For all the heat recovery systems analysed, the payback period is less than 3.4 years.

KEYWORDS: year 1995, designing, run around coils, heat exchangers, air change rate, modernising, heat recovery, computer programs, calculating, rating, performance, payback period, air flow rate, service life, costs, economics, sizing, optimisation, comparing