Browsing by Author "Sakellariou, Evangelos"

Now showing 1 - 6 of 6
  • Thumbnail Image
    ItemOpen Access
    ENERGETIC STUDY OF A SOLAR ASSISTED GROUND SOURCE HEAT PUMP SYSTEM FOR DOMESTIC HEATING WITH PARAMETRIC ANALYSES VIA SIMULATION
    (De Montfort University, 2020-01) Sakellariou, Evangelos
    In this thesis, a solar assisted ground source heat pump system is energetically evaluated for the UK Midlands climate conditions. The conducted research is supported by an experiment made by De Montfort University. This consisted of seven photovoltaic-thermal collectors and a novel very shallow geothermal heat exchanger, supplying a heat pump used to heat a small house. The detail mathematical model of the system was formulated, and parametric analyses were conducted via simulation. Parametric analyses were carried out by assuming two dwelling types, one new and one refurbished, and by varying the number of the solar collectors and the size of the novel very shallow geothermal heat exchanger (1.5 m deep). Additionally, two potential system configurations and two locations of geothermal heat exchanger had been assumed (the one to be exposed and the other to be beneath the dwelling). The important aspects of the research were: a) to determine the parameter which influence the systems energy performance and to define the energetically better system configuration, b) to identify the heat and electricity independence of the system from conventional energy sources, c) to examine the metrics in which the energy evaluation of the systems can be based on and d) the potential reduction of greenhouse gases emissions against a natural gas boiler-based system and a ground source heat pump system. Within the current work, no economic evaluation of the system has been conducted. The results analysis has shown that the higher ratio of generated to consumed electricity is the index which illustrates the system with the best energy performance. This ratio is a valid approach only if the auxiliary heat required by the systems is added to the consumed electricity, by being assumed to be offered via electricity. By contrast, the seasonal performance factor, which is used widely, was diagnosed as an unappropriated metric to describe the energy performance of the systems. Additionally, the concept of the specific productivity was used to identify improvements on the performance of the systems caused by parameters variation. Based on evaluation made via the studied metrics, the topology with direct use of solar heat was found to get lower efficiency than this without direct use. As regards the heat autonomy of the systems, this was found to be up to 83% for the new dwelling and 73% for the refurbished one. Similarly, the electricity offered by the photovoltaic-thermal collectors achieved a self-sufficient stage for most schemes paired with the new dwelling. However, the system paired with the renovated building did not manage to get more than the 90% of its electricity to be offered by the collectors. A potential solution for greater power coverage from the solar energy may be a more efficient photovoltaic-thermal technology. Though, the key role of the system heat coverage was found to be the size of the geothermal heat exchangers and the area of the solar collectors. Hence, for a totally geothermal system paired with the new dwelling, the fractional heat coverage was estimated to be between 0.33 and 0.69 for the smallest geothermal heat exchanger of 16 and the largest one with 40 borehole heat exchangers (1.5 m deep), respectively. By adding 20 PVTs on the larger geothermal heat exchanger, the factional heat coverage was increased to 0.83 and to 0.70 for the smallest number of borehole heat exchangers. Likewise, the refurbished dwelling with only 16 borehole heat exchangers was found with 0.31 heat coverage and with 0.55 for the largest geothermal heat exchanger. By adding 20 PVT collectors on both borefields the heat coverage was increased to 0.65 and to 0.74 for the smaller and the larger geothermal heat exchanger, respectively. It was found that higher energy performance can be obtained when the geothermal heat exchanger is exposed, instead of being placed beneath the new dwelling. The superiority of the geothermal heat exchanger to be installed at an uncover space instead of being placed beneath the dwelling applies to all the investigated configurations and sizes of the system. Thus, the largest system with 20 PVTs was estimated with ratio between the generated to consumed electricity of 1.9 for the exposed location, against the ratio of 1.5 which was found for the exchanger to be covered by the dwelling. Similarly, for the smallest array of 4 PVTs, the ratio was estimated to be 0.26 and 0.22 for the exposed and the covered by the dwelling choice accordingly. Lastly, the investigated system was found with lower carbon emissions than the natural gas boilers system at all the investigated configurations and for both dwelling types. The gas boiler system was estimated to release 1509.7 kg CO2e year-1 and 3050.9 kg CO2e year-1, when it is installed in the new and the refurbished dwelling accordingly. With the new dwelling, all configurations with more than 12 PVTs were found capable to decarbonize in total the emissions from the natural gas boiler system, while for the energy renovated dwelling the fraction emission savings were estimated up to 0.8. Also, the proposed system was estimated less emissive than the conventional ground source heat pump system for PVT arrays with more than 4 collectors and with more than 8 collectors for the new and the refurbished dwelling, respectively.
  • Thumbnail Image
    ItemOpen Access
    Energy and economic evaluation of a solar assisted ground source heat pump system for a north Mediterranean city
    (Elsevier, 2020-11-27) Wright, A. J.; Sakellariou, Evangelos; Axaopoulos, Petros
    In this study, a PVT based solar assisted ground source heat pump (SAGSHP) system was investigated regarding its energy performance and cost-effectiveness for the city of Thessaloniki (Greece). The SAGSHP system was set up to cover the space heating and domestic hot water needs for a low-rise dwelling. A mathematic model of the system was formulated in TRNSYS was used with the aim to carry out parametric analysis by varying the number of the PVTs. Two of the most important components of the employed model, the PVT collector and the geothermal heat exchanger, have already been validated via experimental data. Simulations were conducted and through the results seven energy metrics were estimated, with the objective to examine the system’s energy performance from various perspectives. The SAGSHP system with 16 PVTs was found capable of covering 73 % of the heating load and to generate 1.22 times more electricity than that consumed by the system. The electricity yield of PVTs was not affected throughout the parametric analysis, and the maximum specific productivity was estimated at 301.5 kWhe PVT-1 per year. The results suggest that a SAGSHP system equipped with about 14 PVTs can reach energy self-sufficiency. As regards the economics of the SAGSHP system, this was compared with a natural gas boiler system via two methods: life cycle cost (LCC) and life cycle savings (LCS). A sensitivity analysis with major economic parameters of the systems was carried out. It was found that the cost-effectiveness of the SAGSHP system is influenced mainly by its capital cost and by the price of the natural gas. Systems equipped with less than 12 PVTs can be cost-competitive by subsiding from 8 % up to 42 % of their capital cost. Also, system with more than 12 collectors were found of more benefit than the smaller ones, in the case where feed-in-tariff schemes are applied, or the bank loan’s interest rate is low. It can be concluded that, the proposed system can be an attractive monetary solution for covering the heating load in comparable dwellings with a similar climate to Thessaloniki.
  • No Thumbnail Available
    ItemOpen Access
    Energy, economic and emission assessment of a solar assisted shallow earth borehole field heat pump system for domestic space heating in a north European climate
    (Elsevier, 2021-06-15) Wright, A. J.; Sakellariou, Evangelos; Axaopoulos, Petros
    The performance of a solar assisted ground source heat pump (SAGSHP) system was evaluated and compared with a conventional gas boiler system using simulation, for a central England location. The earth energy bank was the long-term heat store element of the system and consisted of a very shallow field (1.5 m deep) of borehole heat exchangers (BHE). The mathematical model of the system was formulated, and parametric analyses were carried out by varying the number of BHEs and their spacing. The energy performance was expressed using four energy metrics, while its economy and CO2e emissions were compared with a natural gas boiler (NGB) system via the life cycle cost method and the fractional CO2e savings, respectively. The system can be energy self-sufficient by installing 40 BHEs at 1.25 m spacing or with 32 BHEs at 1.5 m spacing. The NGB system appears more economic than the SAGSHP system, due to low natural gas prices, the high price of the imported electricity, the low price of the exported electricity and the higher capital cost of the SAGSHP system. However, the SAGSHP system was found to have net negative carbon emissions, in contrast to the high positive emissions of the NGB system.
  • No Thumbnail Available
    ItemOpen Access
    PVT based Solar Assisted Ground Source Heat Pump system: modelling approach and sensitivity analyses
    (Elsevier, 2019-09-19) Sakellariou, Evangelos; Wright, A. J.; Axaopoulos, Petros; Oyinlola, M. A.
    A solar assisted ground source heat pump (SAGSHP) system is a promising technology which pairs two widely abundant renewable energy sources, solar and shallow geothermal. In space heating dominated regions, the addition of solar collectors to conventional ground source systems improves their feasibility. There are many aspects which influence the system’s efficiency; but experimentation to optimize these would requires high capital investment and take a very long time. Therefore, mathematical modeling and computer-based simulations are preferable methods to conduct sensitivity and feasibility analyses. In this work, a PVT based solar assisted ground source heat pump system was modeled using TRNSYS program, and sensitivity analyses were conducted. For the PVT collectors, an experimentally verified transient model was utilized, while experimental data were used to validate a novel very shallow borefield. For the heat pump model, manufacturer’s performance data along with a new novel method were combined, and a new component was created in the simulation platform. A single family dwelling with domestic hot water demand was assumed for the heating load, and weather data from Birmingham, West Midlands, UK was used. The simulation results were evaluated by utilizing the annual specific productivity metric rather than the systems seasonal performance factor, which is the current choice for SAGSHP systems. The proposed evaluation approach was found be capable of clarifying, in detail, the effect of the parametric variation on the system’s energy performance. The sensitivity analyses are focused on six parameters on the energy conversion side, with the heat pump’s evaporator as the physical boundary. It was found that the storage capacity and the plate heat exchanger’s effectiveness, contribute the most to the system’s and PVTs’ heat productivity. Whilst heat productivity depended more on the parameters’ variation, the power generation was influenced mainly by the collectors’ tilt. The results of this study are significant for design and operation of these systems.
  • Thumbnail Image
    ItemOpen Access
    Solar and geothermal energy for low-carbon space heating and energy independence.
    (IESD, De Montfort University, 2019-07-04) Sakellariou, Evangelos; Wright, A. J.; Oyinlola, M. A.
    In developed countries, space heating is highly dependent on fossil fuels consumption. Also, the non-renewable fuels combustion emits CO2 which is claimed to impact the most on greenhouse effect. The utilization of Renewable Energy Sources (RES) for space heating, instead of fossil fuels, has been found to be feasible for systems’ greater energy independence and reduction in CO2 emissions. Solar Assisted Ground Source Heat Pump (SAGSHP) systems are a promising technology which can be used to accomplish the above framed target. A mathematic model of a SAGSHP system was built and a parametric analysis for Birmingham which is a city located in the UK’s West Midlands was conducted. Two scenarios based on two different dwellings were investigated, the one was a house recently erected and the other was a refurbished house. As regards the new house, simulation results showed that the utilized energy for space heating and Domestic Hot Water (DHW) can vary from 33% up to 73% RES dependent and, at the same time, electricity generation can be 2.21 times higher than the system’s demand. As regards the energy renovated dwelling, the RES contribution to the delivered heat was found to be between the 33% and 63%, while the electricity generation did not result in any surplus energy from the consumed. Finally, by making use of SAGSHP system instead of a natural Gas boiler, the reduction of CO2 emissions was found to be between 300kg/year and 2,170kg/year for the new building and from 245kg/year up to 3,221kg/year for the refurbished house, respectively. In both cases, SAGSHP systems proved to be a feasible practice for greater energy independence from non-renewable energy sources with substantial positive impact on the greenhouse gasses emissions.
  • Thumbnail Image
    ItemOpen Access
    Thermal Analysis of an Earth Energy Bank
    (University of Nottingham, 2019-09-08) Naranjo-Mendoza, Carlos; Sakellariou, Evangelos; Wright, A. J.; Oyinlola, M. A.; Greenough, R. M.