• Energy Research

Vertical ground-source heat pump systems (GSHPSs) use the ground’s undisturbed relative constant temperature as a source for space heating of residential and commercial buildings. The design of GSHPSs is focused in finding the optimal depth and amount of boreholes and also the connected power requirement like the amount and size of heat pumps. In this paper a mixed-integer nonlinear programming (MINLP) approach to solve the design problem of a vertical GSHPS is presented. The resulting mathematical model includes the calculation of the total annual costs (TAC) and the coefficient of performance to obtain estimates of both economic and ecological relevance to design an optimal equipment set-up. For desired constraints the numerically optimal values of the design parameters (borehole depth, mass flow rate, number of boreholes, type and number of the heat pumps) were calculated. Two numerical solution alternatives are investigated, namely Generalized Reduced Gradient (GRG2) and evolutionary algorithm. The GRG2 approach provides a more stable and faster optimal solution. Calculated results are presented through a validation example. The evaluation of the proposed objectives and studied sensitivity effects present the applicability of the model. This method was able to improve the TAC about more than 10%.

Proactive, comparative environmental hazard assessment of LOHC systems based on alkylcarbazoles, quinaldine, benzene and toluene including H2-rich, H2-lean and partially hydrogenated forms.

This paper presents the first account on the ecotoxicological profile of some potential LOHC structures.

Structured open-cell foam reactors are promising for managing highly exothermic reactions such as CO2 methanation due to their excellent heat transport properties. Especially at low flow rates and under dynamic operation, foam-based reactors can be advantageous over classic fixed-bed reactors. To efficiently design the catalyst carriers, a thorough understanding of heat transport mechanisms is needed. So far, studies on heat transport in foams have mostly focused on the solid phase and used air at atmospheric pressure as fluid phase. With the aid of pore-scale 3d CFD simulations, we analyze the effect of the fluid properties on heat transport under conditions close to the CO2 methanation reaction for two different foam structures. The exothermicity is mimicked via volumetric uniformly distributed heat sources. We found for foams that are designed to be used as catalyst carriers that the working pressure range and the superficial velocity influence the dominant heat removal mechanism significantly. In contrast, the influence of fluid type and gravity on heat removal is small in the range relevant for heterogeneous catalysis. The findings might help to facilitate the design-process of open-cell foam reactors and to better understand heat transport mechanisms in foams.

Abstract Shallow vertical ground-source heat pump systems (GSHPSs) have become a popular alternative to conventional heating systems. Typically more than one vertical ground heat exchanger (GHE) is required along with an increasing heat demand. The higher the number of GHEs, the more a system may benefit from optimal design and operation strategies that focus on costs and efficiencies. However, an optimisation of the heat and fluid flows in these systems, based on discretised models, can be computationally time-consuming and sometimes infeasible. To meet this challenge, one might apply simplified models and identify suitable constraints. In this work an analytical finite line source (FLS) model is compared by RockFlow, a finite element approach. The average absolute difference for a long-term investigation between these approaches is obtained at only approx. 0.2 °C, which was evaluated as sufficient. Subsequently, the FLS model is successfully applied to demonstrate the existence of borehole-specific heat flux distributions. For all case studies optimal solutions were found. These results confirmed the useful application of novel optimisation methods. The impact of the GHE specific heat flux distributions on the time-dependent and spatial temperature course in the vicinity of the GHE is impressively shown. The investigation of the soil and heat pump cycle revealed the system efficiency potential and costs. The efficiency improvement potential, caused by different optimal heat flux distributions, was approx. 2%. The best energy extraction improvement was nearly 20%, which equated to a monetary saving of 12%.