Some aspects of the energy cost linked to the IAQ. Impact of free-cooling and heat recovery in office buildings.

CLIMA 2000 (.1997.BRUSELAS)Increasing air exchange rate to improve IAQ may increase energy consumption, but this increase may be compensated for by strategies such as free cooling and heat recovery. The frame of the proposed paper is the examination of the potential at a regional level (the Iberian peninsula) of the different strategies mentioned above in typical office buildings. Based on a set of reference building morphologies, studies are conducted to evaluate the impact of increasing air ventilation rates for different orientations, quality of the envelope (opaque walls and glazing), operating schedules and indoor set-point temperatures. Then, the impact of the increased air ventilation rates is corrected by introducing the effect of free-cooling, air-to-air heat recovery devices of different types and finally, the combined effect of both energy savings strategies. The research provides Maps allowing: 1. To identify zones when heating or cooling regimes are dominant, in terms of both, peak load conditions and energy requirements. 2. To compare the expected performance of the two energy saving strategies at a certain locality. 3. To compare the potential benefit of applying a given strategy at different localities. 4. To indicate regions of recommendable application of the strategies and the expected energy savings achievable

A cross-country review on energy efficiency drivers

Energy efficiency remains as the main mitigation factor to slow down the growth of energy consumption and related CO2 emissions, undoubtedly the major responsible for climate change. Gaining insights into the driving forces that make efficiency change is a keystone to define energy policies and examine pathways to sustainable development. To this aim, this paper proposes a pyramidal approach for the analysis and decomposition of energy intensity, the main global efficiency indicator, using the LMDI method. First, the effects related to supply and demand sides of the energy system are separated in Primary Energy Factor and final energy intensity, respectively. Then, supply side is further decomposed to progressively reveal structural effects associated to transformation processes and fuel types. The approach is applied to the most emitting and consuming nations (China, United States, European Union, India, Russia, Japan) to provide a meaningful cross-country analysis over the period 1995–2017. Results show that energy intensity gains have been mainly driven by widespread demand side efficiency improvements from 25% to 61%. Regarding the supply side, unfavourable structural changes due to electrification, up to 12% in China, have only been offset by transformation efficiency gains about 6% in developed countries. Consequently, emerging economies have worsened their energy sector efficiency as they thrive. Changes in fuel mixes have generally contributed to energy intensity reductions (up to 4%) mainly due to shifts from coal and nuclear power towards gas and renewables plants. The proposed methodology could help stakeholders to effectively analyse the energy system and to develop policies to reduce its environmental impact

Revisiting Kaya Identity to define an Emissions Indicators Pyramid

The impact of energy use on the planet due to related CO2 emissions is continuously increasing, despite the adoption of efficiency and decarbonisation policies and widespread environmental awareness. Climate change mitigation will only succeed if the driving forces of consumption and emissions are deeply analysed, and effective means are provided to reverse their trends. To this aim, the Kaya Identity framework is revisited to classify indicators and decomposition studies in the literature. A comprehensive pyramid approach is proposed for the progressive disaggregation and discussion of energy and emissions changes. The approach is applied to the OECD and non-OECD to provide meaningful regional analysis of past trends and future projections according to stated policy intentions. Results show that a hopeful change has already begun in the developed region due to a sustained decrease of the energy intensity and a promising reduction of the carbon intensity. Emerging economies follow the performance of developed nations since 2013, held back by later economic development. Activity slowdown, energy conservation, renewable electrification, efficient power plants and coal phase out appear as the keystones for decarbonisation. As a result, emissions stabilisation could have already been achieved as rises in emerging countries are offset by drops in developed nations. However, more stringent climate policies, especially targeting carbon drivers, are urgently needed to enable emissions reductions compatible with a global temperature increase of 1.5°C

A review on buildings energy information: Trends, end-uses, fuels and drivers

Buildings are a major contributor to climate change, accounting for one third of global energy consumption and one quarter of CO2 emissions. However, comprehensive information is lacking for the development, evaluation and monitoring of mitigation policies. This paper discusses the remaining challenges in terms of reliability and consistency of the available data. A review of energy use in buildings is presented to analyse its evolution by building types, energy services and fuel sources. Residential buildings are the most consuming, although tertiary expansion requires further analysis to develop sound specific indicators. Heating Ventilation and Air Conditioning (HVAC) systems concentrate 38% of buildings consumption, calling for strengthened standards and incentives for retrofitting. Electrification is rapidly increasing, representing a potential tool for climate change mitigation, if renewable power was promoted. However, energy use in buildings will only curb if global cooperation enables developing nations to break the link between economic growth, urbanisation and consumption. To this aim, efficiency gains both in construction and equipment, decarbonisation of the energy mix and a global awareness on energy conservation are all neededComisión Europea Horizonte 2020 76857

Energy-efficiency-oriented gradient-based economic predictive control of multiple-chiller cooling systems

Cuenta con otro ed.: IFAC-PapersOnLine Incluida en el vol. 53, Issue 2 Article number: 145388The growing use of air conditioning systems has become one of the main drivers of energy consumption in buildings. Many efforts are being made to develop new designs and control strategies to improve energy efficiency and minimise electricity consumption. In this work, a model for a case study of multiple-chiller-based cooling system is presented, based on surrogate models derived from information provided by manufacturers, and the study of the economic performance index. Then, an economic predictive control strategy will aim to operate the system optimizing the efficiency of the plant. Instead of the classical two-layer economic predictive control structure, where the reference to be tracked by the controller is given by a real-time optimizer, here we consider a single-layer control strategy where the gradients with respect to the manipulated inputs of the economic performance index are included in the cost function of the model predictive controller. The resulting optimization problem to be solved on line is a QP, which considerably eases the optimization problem, while also avoiding discrepancies between layers that could lead to loss of feasibility.Feder (UE) DPI2016-76493-C3-1-R

Thermal modeling of existing buildings in high-fidelity simulators: A novel, practical methodology

Optimizing efficiency in the operation of the HVAC system of existing buildings requires the construction of a thermal dynamic model of the building, which may be challenging because architectural metadata may be missing or obsolete. Based on a suitable set of measured data, this paper presents a novel practical methodology to create and automatically derive thermal models of existing buildings in high-fidelity simulators for energy management. To this end, the philosophy of grey-box strategies is followed to simplify the modeling and avoid the requirement of architectural metadata, facilitating and expediting the process. First, a building model with a highly reduced number of parameters is constructed by exploiting the existing similarities in the materials of the buildings and simplifying their elements to a simple one-layer parameterization. Then, the parameters of the derived model are iteratively updated while minimizing the error between the real temperature evolution and that generated by the model being identified. For this purpose, data of the room air temperature, estimated occupancy, weather conditions, and variables of the HVAC system are assumed to be available in suitable zones of the building to apply the creation and identification processes of the model, allowing that a whole digital twin of the building is constructed. The methodology is presented by its application to a real case study: the Nimbus Research Centre building at Munster Technological University, located in Cork (Ireland). The high-fidelity simulator software TRNSYS is used for the modeling task, together with the GenOpt optimization program. The results demonstrate that the proposed methodology yields a highly accurate model of the building, capable of representing reality with RMSE values consistently below during open-loop validation periods of up to four days. The findings suggest that this methodology may outperform other modeling techniques reported in the literature. Importantly, the proposed technique is less complex and time-consuming to implement than many of the alternatives

Creation of study cases for building energy management of HVAC control systems in buildings based on TRNSYS

[Resumen] El desarrollo de sistemas de control para la gestión eficiente de sistemas de climatización es una tarea compleja que requiere el uso de modelos dinámicos que permitan emular de forma realista la evolución térmica del edificio. El objetivo de este documento es presentar una metodología para construir casos de estudio de sistemas de climatización realistas orientados al desarrollo de sistemas de control edificios usando TRNSYS. Además se describen los bloques funcionales de TRNSYS necesarios para modelar una instalación realista. Los modelos desarrollados permiten que los sistemas de control se puedan implementar en Matlab, lo que facilita el prototipado del controlador. Esto se valida con un caso de estudio basado en el control de un edificio de prueba.[Abstract] The development of control systems for the efficient management of heat, ventilation and air conditioning (HVAC) systems is a complex task that requires the use of dynamic models that show thermal evolution of the system with a high degree of fidelity. The objective of this document is to present a methodology to create simulation models of realistic HVAC installations oriented to test control systems implemented in Matlab. The topology of the installation and the blocks needed for its implementation are presented. This procedure has been validated with the model of a simple benchmark used in the literature to be controlled with a PI in Matlab.Ministerio de Economía y Empresa de España; DPI2016-76493-C3-1-

Activity and efficiency trends for the residential sector across countries

The residential sector is a major contributor to climate change, accounting for almost a quarter of global energy consumption and a fifth of CO2 emissions in 2019. Since 2000, residential consumption has grown at a sustained rate of 1%/year, driven by the development of emerging economies, despite stagnation in developed countries. The increasing demand for living space, energy services and comfort levels seems difficult to curb, especially in the developing world on its fair attempt to reduce inequality. To understand these trends, this paper analyses the trajectories of key indicators of activity and efficiency in this sector, for emerging and developed regions, as well as for major consuming nations, mainly China, United States, European Union, Russia, India, Japan and Brazil. Despite data limitations, meaningful cross-country comparisons are presented for fuel mixes, energy services and dwelling types. Heating, ventilation and air conditioning (HVAC) systems account for a third of residential consumption and will grow rapidly as increasing wealth in emerging economies allows for satisfying the thermal comfort demand. Economic development will naturally increase housing size and equipment level and reduce household size, and could close the per capita consumption gap between developing and developed regions. Efficiency improvements could reduce the energy use intensity to around 10 koe/m2 but will not be enough to curb residential consumption. International cooperation, policy support and funding are essential to accelerate development and efficiency gains in developing countries without compromising environmental targets. In the meantime, politicians should focus on decarbonising the energy mix and promoting energy efficiency, while citizens focus on energy conservation to avoid irreversible environmental damage

Modeling of Refrigeration Systems for Control and Energy Efficiency

[Resumen] La climatización en edificios es una de las aplicaciones más importantes de los sistemas de refrigeración y su uso supone hasta un 20% de la energía consumida en países desarrollados. Actualmente, los ingenieros de control dedican grandes esfuerzos a mejorar la eficiencia energética de estos sistemas. Uno de los mayores obstáculos en esta línea de investigación es la obtención de buenos modelos, debido a la complejidad de las máquinas de refrigeración comerciales. En este artículo se presenta un modelo para un caso realista de estudio donde se incorporan máquinas reales para el estudio de técnicas de control para la mejora de la eficiencia. Además, se expone un ejemplo donde se aplica control predictivo basado en modelo con seguimiento de temperaturas.[Abstract] Building air conditioning is an important application of refrigeration systems, and its operation consumes up to 20% of the total energy in developed countries. Currently, control engineers are expend time and effort to find new methods that improve energy fficiency. However, obtaining proper models is a difficult task due to the complexity of comercial chillers and business confidentiality. In this paper, data-based identification is proposed to obtain non-linear models of real machines. Furthermore, a case study is presented with the application of model predictive control for temperature tracking.Ministerio de Economía y Empresa; DPI2016-76493- C3-1-