• Energy Research

Las universidades españolas tienen un papel fundamental en la aplicación de la Agenda 2030. La CRUE ha manifestado un compromiso decidido por la incorporación de las competencias relacionadas con los objetivos de desarrollo sostenible (ODS) en la universidad. En este artículo se analiza el contenido impartido en la asignatura de Climatización, dentro del grado de Ingeniería Mecánica de la Escuela Técnica Superior de Diseño con el objetivo de determinar aquellos ODS y metas que se trabajan en la asignatura. Algunos de estos contenidos también se imparten en asignaturas relacionadas de otros grados y másters, de modo que este análisis es útil para más asignaturas.

[EN] The fact that the popular head loss coefficient concept, may become negative in branched junctions, is a symptom that something is not correctly managed. The paper makes a review of recent works which have sought new models based on physical concepts, as a way to avoid speaking about "negative losses". Herwing and Schmandt [1], showed that the origin of the negative sign was a diffusive shear work exchange between the two streams of a branched junction. Traditionally, the head losses at the branched junctions are neglected, but definitely it cannot be done in HVAC air-duct networks. Firstly, the paper illustrates how, by ignoring this "negative loss" contradiction, traditional duct network analysis may encounter unexpected numerical difficulties. Secondly, it shows that the Minimum Energy Dissipation Principle (MinEDP) can be successfully applied to analyze the steady-state of any flow network (not necessarily HVAC ductworks), with or without shear work at junctions. Moreover, the new method does not need to know the latter, beforehand, although the nature of the solution is very different in either case. Finally, the paper includes a practical example of an HVAC ductwork to illustrate the outcomes. The new method works smoothly and quickly and does not need any ad hoc modification to cope with an eventual "negative" head loss. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

[EN] Eliminating the use of natural gas for non-domestic heat supply is an imperative component of net-zero targets. Techno-economic analyses of competing options for low-carbon heat supply are essential for decision makers developing decarbonisation strategies. This paper investigates the impact various heat supply configurations can have in UK supermarkets by using heat recovery principles from refrigeration systems under different climatic conditions. The methodology builds upon a steady-state model that has been validated in previous studies. All refrigeration integrated heating and cooling (RIHC) systems employ CO2 booster refrigeration to recover heat and provide space heating alongside various technologies such as thermal storage, air-source heat pumps (ASHPs) and direct electric heaters. Seven cases evaluating various technology combinations are analysed and compared against a conventional scenario in which the building is heated with a natural gas boiler. The specific combinations of technologies analysed here contrasts trade-offs and is a first in the literature. The capital costs of these projects are considered, giving insights into their business case. Results indicate that electric heaters are not cost-competitive in supermarkets. Meanwhile, RIHC and ASHP configurations are the most attractive option, and if a thermal storage tank system with advanced controls is included, the benefits increase even further. Best solutions have a 6.3% ROI, a payback time of 16 years while reducing energy demand by 62% and CO2 emissions by 54%. Such investments will be difficult to justify unless policy steers decision makers through incentives or the business case changes by implementing internal carbon pricing. This research was supported by funds provided via the Imperial-Sainsbury's Supermarkets Ltd. partnership. This work also was sup-ported by the UK Engineering and Physical Sciences Research Council (EPSRC) [grant numbers EP/P004709/1, and EP/R045518/1] . Emilio J. Sarabia gratefully acknowledges financial support from Universitat Politecnica de Valencia Fellowship. Data supporting this publication can be obtained on request from cep-lab@imperial.ac.uk.

[EN] The target of the paper is to study how to devise an efficient discrete-event model for the yearly energy simulation of buildings. Conventionally, software tools use time-driven schemes and many components must be computed at every sampling time-point. Event-driven simulation aims at lowering this burden, by calling only those components whose state is evolving quickly. The article explores a model based on DEVS formalism and Quantized State Systems (QSS) techniques. Within this paradigm shift, our strategy was to reuse as much widely accepted knowledge as possible. One immediate difficulty was, that the well-known conduction heat transfer function (CHTF) of multi-layered walls is not suitable for DEVS in its traditional form since it is constrained to sample at a fixed time step. Instead, the paper introduces a non-conventional method: the Successive State Transition method (SST). Its distinguishing traits are: it allows variable time steps, has high accuracy and its computational workload adapts to the elapsed time between transitions. Unfortunately, although we found that SST and QSS work well together, the paper shows that the aforementioned transfer function is not adequate for event-driven simulations. Based on the paper outcomes, we propose a workaround for further research: a new transfer function, relating the conduction heat flux (input) to the time derivative of the wall superficial temperature (output) (recall that the traditional input-output relationship: superficial temperature and conduction heat flux, respectively).

[EN] The objective of this article is to compare the behaviour of the most representative domestic hot water systems (DHW) in single-family buildings. The study evaluates the energy consumption, equivalent CO2 emissions and cost for each system over a 15-year life period. This analysis is carried out in four cli- matic zones across Europe to observe the influence of climatic conditions on the results. The four climatic zones are located in the cities of Athens, Madrid, London and Berlin. The analysed systems are: a) natural gas-fired instantaneous water heaters, b) electric storage water heater, c) solar thermal system with gas- fired instantaneous, d) solar thermal system with electric storage water heater, e) air-source heat pump, f) photovoltaic system with electric storage water heater, and g) photovoltaic system with air-source heat pump. This range of technologies covers the most likely solutions to be implemented across domestic buildings in Europe.The heat pump system (HPWH) with PV considering self-consumption shows the lowest environmen- tal impact in all zones, but is not an attractive investment in the coldest zones due to lower natural gas prices. Thermal solar systems have a high purchase and maintenance costs which do not compensate their energy savings. The PV HPWH system has a greater reduction of emissions and a lower cost than HPWH across a 15-year life. The gas boiler system has the lowest cost in a 15-year period in the coldest areas, despite having a greater environmental impact than the heat pump.(c) 2023 Elsevier B.V. All rights reserved.

[EN] This paper compares and quantifies the energy, environmental and economic benefits of various control strategies recovering heat from a CO2 booster system in a supermarket for space heating with the purpose of understanding its potential for displacing natural gas fuelled boilers. A theoretical steady-state model that simulates the behaviour of the CO2 system is developed and validated against field measurements obtained from an existing refrigeration system in a food-retail building located in the United Kingdom. Five heat recovery strategies are analysed by modifying the mass flow and pressure level in the condenser. The model shows that a reduction of 48% in natural-gas consumption is feasible by the installation of a de-superheater and without applying any advanced operating strategy. However, the CO2 system can fully supply the entire space-heating requirements by adopting alternative control strategies, albeit by penalising the coefficient of performance (COP) of the compressor. Results show that the best energy strategy can reduce total consumption by 32%, while the best economic strategy can reduce costs by 6%. Findings from this work suggest that heat recovery systems can bring substantial benefits to improve the overall efficiency of energy-intensive buildings; nevertheless trade-offs need to be carefully considered and analysed on a site by site basis before embarking on such initiatives. This research was supported by funds provided via the Imperial-Sainsbury's Supermarkets Ltd. partnership. This work also was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) [grant number EP/P004709/1]. Emilio J. Sarabia gratefully acknowledges financial support from Universitat Politecnica de Valencia Fellowship. Data supporting this publication can be obtained on request from cep-lab@imperial.ac.uk