A comparative study of district and individual thermal energy systems providing heating, cooling, and domestic hot water for low-energy residential community applications

Many countries are setting ambitious goals for their residential energy sectors, reflected in progressively stricter building codes. Much progress has occurred in improving household energy efficiency but achieving a further energy reduction in this sector is particularly challenging since the cost-effectiveness of efficiency measures are often compromised by increasing marginal cost with decreasing overall energy use. District systems providing thermal services to a group of low-energy dwellings, can potentially meet household demand at a lower site energy use compared to conventional individual systems. Moreover, due to economies of scale, central systems may allow the use of local renewable resources such as geothermal and solar energies that would not otherwise be economically feasible.;This study analyzes the potential benefits in terms of site energy and levelized cost of thermal service for a domestic hot water grid providing heating, cooling and domestic hot water to a small community of low-energy dwellings, located in Northern California that currently has access to electricity only.;A set of two district-system-based scenarios, are compared against a business as usual individual-system-based scenario. In all scenarios, thermal systems are sized for a reference low-energy residential community. Models for all scenarios were constructed using Transient System Simulation (TRNSYS) software. Weather data were used for a typical meteorological year in Sacramento, California. These data were used to run simulations on the models and to obtain a set of values for site energy use and levelized cost of service. The baseline scenario is served by individual electric space heaters, air-to-air air conditioning units and storage-type electric water heaters. The two district energy alternatives are served by a ground source heat pump and an electric boiler with individual air conditioners respectively.;The results indicated that for 3 dwellings with a total annual thermal energy demand of 14.22 MWh and a peak load of 12.7 kW, the most efficient system is a district ground source heat pump. In terms of levelized cost however, the business as usual system is the cheapest. Two parameters were identified as the main causes for higher levelized costs of the district configurations studied: capital cost and system size. While only up to a 30% decrease in capital cost was considered in this study, results suggest that in order to have lower LCOE than BAU, the capital cost of the two district scenarios would need to be 5 times lower than the one considered. With respect to sizes, LCOE decreased by 80% and 60% for the BAC and GHP respectively as the size increased from 3 to 12 dwellings. Again, no breakeven point was observed for the sizes considered, but results suggest that the district scenarios may present lower LCOE than BAU for systems of approximately 36 dwellings.