Electric heating | EPFL Graph Search

Electric heating is a process in which electrical energy is converted directly to heat energy. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical device that converts an electric current into heat. The heating element inside every electric heater is an electrical resistor, and works on the principle of Joule heating: an electric current passing through a resistor will convert that electrical energy into heat energy. Most modern electric heating devices use nichrome wire as the active element; the heating element, depicted on the right, uses nichrome wire supported by ceramic insulators. Alternatively, a heat pump can achieve around 150% - 600% efficiency for heating, or COP 1.5 - 6.0 Coefficient of performance, because it uses electric power only for transferring existing thermal energy. The heat pump uses an electric motor to drive a reversed refrigeration cycle, that draws heat energy from an external so

Sensitivity analysis on optimization of PV installation with thermal energy storage

Diane Delphine Remmy

The installation of solar panels on building roofs is increasing and considered as a potential solution to decarbonise the current energy system. However, how to make the best use of this energy is yet to be determined. In this project, two already developed optimization algorithms are compared to analyse the synergy between thermal storage and photovoltaic power production. The energy system includes photovoltaic panels, a heat pump and electric heaters. The conducted sensitivity study shows that the simulation of the thermal and electrical fluxes depends on whether self consumption or the minimization of the operational cost is favoured and thus impacts the usage of the produced power.

2020

Competition between cooling and shortwave radiation in shaping near-surface convection in pelagic waters of Lake Geneva

Hugo Cruz

When lake surface waters above the temperature of maximum density 4◦C cools, the verysurface fluid parcels become denser than their neighbours below. The latter process leads to a gravitationally unstable density distribution which may trigger ‘free convection’, i.e. the upper denser waters look for their equilibrium position somewhere down in the water column. This phenomenon usually occurs at night time, when the atmosphere is colder than surface waters. However, during daytime, it may happen that the lake surface cools—releasing heat to the atmosphere—while shortwave radiation penetrates through upper waters. In this scenario, the near surface waters of the photic zone can host an unstable layer due to the net surface cooling, whereas waters beneath it experience radiative heating and gravitational stabilization. Here, we investigate the competition between shortwave radiation and surface cooling when wind is low or negligible. Thus, depending on the relative intensity of surface cooling and shortwave radiation, the upper water column undergoes different gravitationally unstable density distributions and potentially convective regions. The objective of this Master Project is to investigate, describe, and characterise such convective regimes. To do so, the heat equation controlling temperature evolution of the upper water column subject to surface cooling and penetrative radiative heating is investigated. In parallel with in-situ observations, mathematical and numerical modelling allow to understand the phenomenon taking place. The results allow to infer how the relative importance of surface cooling and penetrating shortwave radiation may affect vertical heat and mass transfer within the lake and between the lake and the atmosphere.

2021

Urban Form Optimization for the Energy Performance of Buildings Using Citysim

Jérôme Henri Kämpf

The energy efficiency of the urban texture relies notably on the buildings’ form, which characterizes its capability to take profit of the solar potential as well as its loss of energy through the envelope. Therefore, the general layout at the district scale has a significant impact on the global energy balance in a dense built environment, where the relative position of the adjacent buildings generate shadowing and inter-reflection on a large part of the incoming solar radiation. In the current work, an urban energy simulator named CitySim is used together with a hybrid evolutionary algorithm. The physical model within CitySim features the computation of shortwave radiation including reflections, longwave radiation and a nodal thermal model for the building energy flows. The complete simulation leads to a rather precise evaluation of the annual heating needs, defined as the objective function to be minimized at the district scale. An existing district in Paris is taken as case study: the Bercy park front. Its buildings are disposed in several blocks surrounding courtyards with openings on the park’s side (southwest). This district is recent (1994-2005) and located in a dense area of seven stories buildings. In its original design, the access to sunlight was taken into account by the planner, thus the initial intuition of the architect is compared with optimized configurations. The paper describes a case of urban form optimization, with the formal description of the variables, constraints and objectives of the problem and the definition of the geometrical case for Bercy Front Park. The optimization variables focus on geometrical properties such as the height of the buildings and glazing ratios. The thermal properties of the building (insulation, glazing type) are set in accordance with the French standards of the thermal regulation (RT2005). The urban layouts resulting of the optimization process are analyzed and discussed.

EPFL Solar Energy and Building Physics Laboratory (LESO-PB)2013

Urban Form Optimization for the Energy Performance of Buildings Using Citysim

Jérôme Henri Kämpf

EPFL Solar Energy and Building Physics Laboratory (LESO-PB)2013