Comparison of natural convection heat exchangers for solar water heating systems
Thermosyphon heat exchangers are used in indirect solar water heating systems to avoid using a pump to circulate water from the storage tank to the heat exchanger. In this study, the authors consider the effect of heat exchanger design on system performance. They also compare performance of a system with thermosyphon flow to the same system with a 40W pump in the water loop. In the first part of the study, the authors consider the impact of heat exchanger design on the thermal performance of both one- and two-collector solar water heaters. The comparison is based on Solar Rating and Certification Corporation (SRCC) OG300 simulations. The thermosyphon heat exchangers considered are (1) a one-pass, double wall, 0.22 m{sup 2}, four tube-in-shell heat exchanger manufactured by AAA Service and Supply, Inc., (the Quad-Rod); (2) a two-pass, double wall, 0.2 m{sup 2}, tube-in-shell made by Heliodyne, Inc., but not intended for commercial development; (3) a one-pass, single wall, 0.28 m{sup 2}, 31 tube-in-shell heat exchanger from Young Radiator Company, and (4) a one-pass single-wall, 0.61 m{sup 2}, four coil-in-shell heat exchanger made by ThermoDynamics Ltd. The authors compare performance of the systems with thermosyphon heat exchangers to a system with a 40 W pump used with the Quad-Rod heat exchanger. In the second part of the study, the effects of reducing frictional losses through the heat exchanger and/or the pipes connecting the heat exchanger to the storage tank, and increasing heat transfer area are evaluated in terms of OG300 ratings.
Design of A Solar Thermophilic Anaerobic Reactor for Small Farms
A 10 m(3) completely stirred tank reactor has been designed for anaerobic treatment of liquid cow manure under thermophilic conditions (50degreesC), using a solar heating system mounted on the reactor roof. Simulation models for two systems have been developed. The first system consists of loose components and in the second system the components are integrated. Each of the two systems includes a heat recovery unit to heat the influent by extracting heat from the effluent. The integrated system includes an extra chamber for the pumps and the heat recovery unit, which are in the same insulating cover as the reactor and the solar collector. The control system is based on simple on/off strategy. An auxiliary heater, operated with the produced biogas, can be used during cold months. The measured and calculated design parameters are presented. The simulation results show that the temperature fluctuation of the reactor during the night is less than VC, which is too small to harm the microbial activity. The results show that an annual net thermal energy production and overall annual energy efficiency of 100 and 95%, respectively, could be obtained from the integrated system. (C) 2003 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.
Comparison of Experimental and Simulated Thermal Ratings of Drain-Back Solar Water Heaters
Short-term experimental tests of drain-back solar water heaters are compared to ratings obtained using TRNSYS to determine if computer simulations can effectively replace laboratory thermal ratings of solar domestic hot water heating systems. The effectiveness of TRNSYS in predicting changes in rating due to limited changes in collector area, collector flow rate, recirculation flow rate, storage tank volume, and storage tank design is validated to within [plus minus]10 percent. Storage tank design is varied by using a stratification manifold in place of the standard drop tube. Variations in other component sizes and operating factors are based on current industry standards.