Simulation of energy use in residential water heating systems




Schneyer, Carolyn Dianarose

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Current federal and provincial efficiency standards for residential water heating are based solely on the tested efficiency of individual water heating devices. Additional energy expended or saved as the water cycles through the home is not taken into account. This research, co-funded by British Columbia’s Ministry of Energy, Mines and Petroleum Resources (MEMPR), is a first step toward the Province’s goal of developing a new energy efficiency standard for water heating systems in new construction. This groundbreaking new standard would employ a “systems” approach, establishing guidelines for new construction based on the total energy used for water heating within the building envelope The research team has developed a Simulink computer model which, using a one-minute time-step, simulates 24-hour cycles of water heating in a single-family home. The objectives of this thesis are to use that model to simulate a variety of water heating technology combinations, and to devise methods of utilizing the resulting data to evaluate water heating systems as a whole and to quantify each system’s relative energy impact. A metric has been developed to evaluate the efficiency of the system: the system energy factor (SEF) is the ratio of energy used directly to heat water over the amount of energy drawn from conventional fuel sources. The CO2 impact of that energy draw is also considered. Data is generated for cities in three different climates around BC: Kamloops, Victoria and Williams Lake. Electric and gas-fired tank water heaters of various sizes and efficiencies are simulated, along with less traditional energy-saving technologies such as solar-assisted pre-heat and waste water heat recovery components. A total of 7,488 six-day simulations are run, each representing a unique combination of technology, load size, location and season. The resulting data is presented from a variety of angles, including the relative impacts of water heater rating, additional technology type, location and season on the SEF of the system. The interplay between SEF and carbon dioxide production is also examined. These two factors are proposed as the basis for devising performance tiers by which to rank water heating systems. Two proposals are made regarding how these tiers might be organized based on the data presented here, though any tiers will have to be re-evaluated pending data on a wider range of technology combinations. A brief financial analysis is also offered, exploring the potential payback period for various technology combinations in each location. Given current equipment and energy costs, the financial savings garnered by the increase in energy efficiency are not, in most cases, found to be sufficient to justify the expense to the homeowner from a purely fiscal perspective. Additional changes would need to take place to ensure the financial viability of these technologies before large-scale adoption of systems-based standards could be employed.



water heating, energy policy, residential, British Columbia, Canada, Energy Factor, DWHR, solar water heating, carbon dioxide emissions, hot water use, energy use, System Energy Factor, water heating system, systems approach, energy efficiency, energy standard