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Despite many studies that were found in the literature regarding the modelling of the short-time-step (STS) behaviour of the borehole ground heat exchangers, reported investigations of its effect on the long-term dynamic simulation of a ground-source heat pump (GSHP) system were sparse. Hence, in this study, the dynamic performances of a GSHP system applied to an office zone in Hong Kong over a period of 10 years were compared with both the long-time-step (LTS) and STS approaches for the boreholes. It was found that with the adoption of the more appropriate STS approach, the simulated fluid temperature leaving the ground heat exchanger borefield was lower by at most 1.62 °C over a range of ground and grout thermal conductivities investigated. This also allowed the design borehole length to be reduced by at most 14.4% while the resulting energy consumption was still better than those based on the LTS approach. In this regard, the STS approach should be employed in the long-term dynamic simulation of GSHP systems. [ABSTRACT FROM AUTHOR]

Abstract: Waste heat recovery by means of a Rankine Cycle is a promising approach for achieving significant reductions in fuel consumption and, as a result, exhaust emissions of passenger car engines. This approach is already well established in industrial applications such as gas and steam power plants or ship propulsion systems. While these systems are mainly designed for stationary operation, the behaviour in highly dynamic operating conditions becomes more important when the principle is transferred to a passenger car engine. Knowledge of the dynamic response of the employed heat exchangers plays an important role in performance prediction and control system design of the steam cycle. Hence, a dynamic model of the exhaust gas heat exchanger employing the moving-boundary principle was developed and is presented in this paper. The model describes both design operation and the heat-up procedure of the component. For achieving high model accuracy in the resulting broad range of operating conditions, new approaches for modelling wall temperature distribution and zone switching were developed. Simulations of stationary operating points as well as the response to typical disturbances of the system’s input variables are in good agreement with test bench measurements. The model is used to develop a control system for dynamic operation on the test bench. Further studies of the operating characteristics reveal varying dynamic behaviour depending on the heat flow rate from exhaust gas to working fluid as well as coupling of evaporation pressure and outlet steam temperature. [Copyright &y& Elsevier]

Abstract: A 1 kW solid oxide fuel cell (SOFC) balance of power (BOP) system is analyzed using experiments and simulations to optimize the design and operating conditions. The system consists of an autothermal reformer, combined heat exchanger and afterburner, and dummy stack. Thermolib program is used for the simulations. The system exhibits stable operation during a two cycle on/off experiment. The simulated results obtained by zero-dimensional modeling are similar to the experimental results although a discrepancy appears early in operation owing to the simplified modeling. The system''s characteristics are also investigated in terms of the fuel utilization, presence or absence of internal reforming and external heat transfer coefficient. [Copyright &y& Elsevier]

Abstract: The European Energy Efficiency Building Directive 2002/91/CE, as well as other acts and funding programs, strongly promotes the adoption of passive strategies for buildings, in order to achieve indoor thermal comfort conditions above all in summer, so reducing or avoiding the use of air conditioning systems. In this paper, the energy performances achievable using an earth-to-air heat exchanger for an air-conditioned building have been evaluated for both winter and summer. By means of dynamic building energy performance simulation codes, the energy requirements of the systems have been analysed for different Italian climates, as a function of the main boundary conditions (such as the typology of soil, tube material, tube length and depth, velocity of the air crossing the tube, ventilation airflow rates, control modes). The earth-to-air heat exchanger has shown the highest efficiency for cold climates both in winter and summer. The possible coupling of this technology with other passive strategies has been also examined. Then, a technical-economic analysis has been carried out: this technology is economically acceptable (simple payback of 5–9 years) only in the cases of easy and cheap moving earth works; moreover, metallic tubes are not suitable. Finally, considering in summer a not fully air-conditioned building, only provided with diurnal ventilation coupled to an earth-to-air heat exchanger plus night-time ventilation, the possible indoor thermal comfort conditions have been evaluated. [Copyright &y& Elsevier]

This article compares the performance of geothermal absorption and compression heat pump systems for space conditioning. The comparison is performed on an R-2000 residence for three Canadian locations representing three different climates and energy contexts: Montréal, Edmonton and Vancouver. The analysis is based on simulations carried out using TRNSYS. Results indicate that the required length of the geothermal heat exchanger is significantly different for the two types of heat pumps (compression and absorption). In Edmonton, geothermal absorption heat pump systems have a lower life-cycle cost and emit fewer greenhouse gases than geothermal compression heat pump system. In Montréal, both systems have similar life-cycle costs. Since electricity is mainly hydro-based the greenhouse gas emissions are much lower for the compression system. In Vancouver, the compression system has both lower life-cycle costs and lower greenhouse gases emissions. [ABSTRACT FROM AUTHOR]