System Performance Comparison of Residential Combination Air and Water Heating Systems in Cold Weather Climates

by Corinne Wichser

Institution: KTH Royal Institute of Technology
Year: 2015
Keywords: Engineering and Technology; Mechanical Engineering; Energy Engineering; Teknik och teknologier; Maskinteknik; Energiteknik
Record ID: 1350614
Full text PDF: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166119


The state of Minnesota has an extreme weather climate, with cold winters and humid hot summers. In a residential building, space and water heating account for about 61% of the total energy consumption. A combination heating system is an innovative idea that integrates the space heating and water heating systems as one unit to achieve improved performance and efficiency over two independent systems. This analysis will focus on air for space heating, as it is a common system used in the applicable location. Benefits of the system include a smaller footprint, simplified installation and maintenance, a single fuel input and exhaust, and increased efficiency. More testing and research is required, however, to make them an economically feasible option. Twenty combination units of varying designs and manufacturers are installed and monitored in qualifying households throughout the Hennepin County area in Minnesota for about eight months to determine the efficiency and performance of these relatively new systems. These results will be extrapolated to a typical year with the goal to define the ideal combination system type by comparing the calculated system performance to the original existing system performance at each site, the load stress on the system (low, average, and high), the performance of the system on a heating design day, the federal regulation criterion for standard systems, and the different combination systems being researched in this study. It is determined that the tankless type 2, with a 7.5 liter (2-gallon) reserve storage tank, is the most efficient combination system during a typical year in Minnesota. Better insulation is required for storage tanks to reduce stand-by losses. System installation guidelines and design packages will improve performance and maintenance issues. The combination system could be improved by implementing other design strategies such as segregating the space heating and domestic hot water loops or introducing renewable energy to replace the natural gas fuel input.