Abstract
A performance comparison is presented for a domestic space and hot water heating system with a conventional gas boiler and an air source heat pump (ASHP) with latent heat storage, both with solar thermal collectors for a typical UK climate, to demonstrate the potential of phase change material based energy storage in active heating applications. The latent heat thermal storage system consisted of 10 modules with RT54HC comprising a total storage capacity of 14.75 kWh that provided 53% extra thermal storage capacity over the temperature range of 40–65 °C compared to a water only store. The simulations predicted a potential yearly CO2 reduction of 56%, and a yearly energy reduction of 76% when operating the heat pumps using the economy 10 electricity tariff i.e. a low tariff between 00.00 and 05.00 and 13.00–16.00 with current grid emission values compared to the conventional gas boiler system; successfully offsetting the electrical load to meet the required heat demand. Due to the high capital costs of the heat pump system with latent heat storage, its levelized cost of energy was 117.84£/MWh, compared to 69.66£/MWh for the gas boiler, on a 20-year life cycle.
Highlights
18% of the UK’s final energy consumption in 2016 was used for domestic water heating, mainly through the use of natural gas boilers [1], totalling 26 773 mtoe
A performance comparison is presented for a domestic space and hot water heating system with a conventional gas boiler and an air source heat pump (ASHP) with latent heat storage, both with solar thermal collectors for a typical UK climate, to demonstrate the potential of phase change material based energy storage in active heating applications
The numerical model developed to evaluate the replacement of conventional gas fired boilers with heat pumps coupled with a Phase change materials (PCMs) thermal store to offset heat pump operation from peak electrical demand periods in a semi-detached dwelling, predicted that yearly CO2 emissions could be reduced by an average of 58% using current grid emission values
Summary
18% of the UK’s final energy consumption in 2016 was used for domestic water heating, mainly through the use of natural gas boilers [1], totalling 26 773 mtoe. The CO2 emissions associated with each generation profile were calculated based on the emission coefficients obtained by Hawkes [4] To effectively decarbonize this sector, heat pump CO2 emissions should be less than the currently used conventional gas burning domestic heating systems (around 204 g CO2/kWhth [4,5]), and operated during off peak electrical load times to minimise both carbon intensity and peak electrical load. The numerical model assumed isotropic heat propagation within the PCM, having temperature-dependent thermal conductivity and volumetric heat capacity [J/m3 K] with no volume changes occurring during phase change. The model employed backward spatial discretization for the water flow, and unidirectional radial and axial heat propagation among the copper tube and PCM, as it is presented schematically in Fig. 3C and D. Matlab uses a Gauss-Seidel iterative solver to obtain the new temperature distribution in each time step
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