Generic Thermal Model of Electric Appliances Integrated in Low Energy Building Herie PARKa,c,*, Marie Ruellan", Nadia Martajb, Rachid Bennacerb and Eric Monmassona aSATIE CNRS UMR8026, University of Cergy-Pontoise, Cergy-Pontoise, France bLMT CNRS UMR 8535, Ecole Normale Superieure de Cachan, Cachan, France cDep. of electrical engineering, Yeungnam University, Gyeongsan, Gyeongbuk, Korea (herie.park, marie.ruellan, eric.monmasson)@u-cergy.fr, nadia
[email protected],
[email protected] _
Abstract- This paper presents a generic thermal model of electric appliances
as
consumption
an
auxiliary
buildings.
The
heat electric
source
in
appliances
low are
energy firstly
classified into four categories by their heat and mass transfers. The mathematical model and its electric equivalent circuit are proposed based on the first law of thermodynamics and the thermal-electric analogy. Then the correspondence between the proposed
model
and
the
ARX model is
presented
for
a
parametric identification. To illustrate this study, two electric appliances of the closed-heating category, a monitor and a refrigerator, are selected. Each model has been experimentally tested and identified in a well-insulated building. They are implemented
in
a
simple
RC-Iumped building
model
and
simulated using Matlab/Simulink. Both experimental data and simulation results are compared.
I.
INTRODUCTION
Nowadays, the concept of low energy buildings is focused on achieving low environmental impacts of buildings. It is especially related to the amounts of energy consumption and of CO2 emission. In order to reduce the environmental impacts and realize high energy efficiency of buildings, many countries strengthen their building regulations and codes. In addition, many researchers have also worked on analyzing the energy performance of buildings and integrating the renewable energy technologies into buildings [1]. In the field of building, the energy is used for space heating/cooling, lighting, equipment/appliances operating and water heating. The energy demands for heating and cooling system are more than a third of the energy used in both of residential and non-residential (or commercial) buildings [2]. These demands depend on the exterior characteristics of buildings, the physical properties as well as the types, and the energy efficiencies of inner sub-systems of buildings. Therefore, the thermal analysis of buildings based on this information is important to assess the building energy performance. Furthermore, the analysis permits to predict thermal responses, design sub-systems, calculate heating/cooling loads, and control these sub-systems of buildings. It is helpful to achieve the energy efficiency and the thermal comfort of buildings. During the past few decades, building energy simulation tools have developed for such a thermal analysis. The most representative simulation tools of them are ESP-r, TRNSYS, EnergyPlus, SPARK and SIMBAD. These are based on fundamental laws of energy, heat and mass transfer [3-4].
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With the help of the validated building simulation tools, energy performance of a building could be evaluated during its life cycle. It is obvious that the results of the evaluation differ from building components. Among the components, there are internal heat gains caused by solar irradiation, operations of electric appliances and occupant's behavior in a building. These gains have been taken into account for the heating/cooling loads calculation. In low energy building, which thermal insulation is reinforced, the internal heat gains become decisive factors on the building energy consumption and the thermal comfort of occupants. However, because of their uncertainties it is not easy to predict the gains. Thus, ahnost of the simulation tools have been used the past weather information and the pre determined profiles of electric load usages and the occupancy. These uncertainties of heat gains have been caused retrofit errors between the simulation and the validation of energy analysis of buildings [5-6]. Moreover, as more reliable results and accuracies are expected, the simulation time interval tends to be shorter than an hour. In intra-hour simulations, the models of a building and its sub-systems have to be more accurate in order to catch the highest dynamics. Even though many researchers have worked on solar irradiation models [7-8], both deterministic and stochastic models of occupant's behavior and lighting usages [9-10], metabolic heat gains by occupants [11] in buildings, there are only a few works on the modeling of heat gain of electric appliances [12-13]. Therefore, the objective of this paper is to propose a generic thermal model of electric appliances. It is especially applied in low energy consumption buildings. It permits to calculate the temporal heat gain of electric appliances and predict the indoor temperature of the building. For this, we firstly classify electric appliances regarding their power characteristics. In section III the generic model are introduced based on the first law of thermodynamics and the thermal electric analogy. A parametric identification method of the proposed model using ARX model is presented. In section IV the proposed model is applied to two actual cases: a monitor and a refrigerator. Then the parameterized models are integrated in a simple building model implemented on Matlab/Simulink. Simulated temperature evolutions and heat flux of each model are compared to measured experimental results. The last section concludes the work.
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II.
CLASSIFICATION OF ELECTRIC ApPLIANCE
Tn order to establish a generic thermal model of electric appliances, it is necessary to characterize the systems from a thermal point of view. An electric appliance needs electrical power, Pelee(t) for its operation. Then, the electrical energy of the appliance, Eelee(t) is converted into other forms of energy, namely, heat and work. Basically, all of electric appliances produce heat by Joule heating effect. So part of, Eelee(t) is converted to Joule heat. Moreover, when work is produced by translational or rotational motion, some irreversibility is unavoidable as a mechanical friction (non ideal efficiency). Tn this case the mechanical equivalent heat is produced. For example, an electric fan, a refrigerator and a washing machine generate mechanical equivalent heat as the results of the work of electric motor. In addition, there is also a part of energy which is converted into acoustic (pressure work) or electromagnetic waves. These forms of energy are also fmally converted into heat. Thus, the appliances for which Eelec(t) is totally converted into such kind of heat are classified as 'Heating Systems (HS)'. However, there are few appliances which part of Eelec(t) is also converted into work such as comminuting (crushing or grinding) or volume expansion in quasi-adiabatic process. In this case, the fmal form of the work is not heat. Therefore, these appliances, which fmal forms of energy are not only heat, but also work, are classified as 'Working Systems (WS)'. After that an appliance has been classified as a HS or a WS, it is then identified as one of the thermodynamics systems: 'Closed Systems (CS)' or 'Open Systems (OS). These defmitions are based on the exchange of energy and mass. Both CS and OS exchange heat with an outside system. However, the OS additionally exchanges its mass with an outside system. Almost of electric appliances only exchange their heat through the boundaries but without mass transfer. These are so called as CS. There are some examples of CS: a refrigerator, a television, a computer, an electric convective heater, a microwave and a hair dryer. Conversely, the appliance, which is classified as OS permits to transfer both energy and mass across its boundary. For example, a washing machine and a dish washer exchange their mass (water) with outside systems. According to above classifications, electric appliances are categorized into four groups: 'Heating-Closed Systems (HCS)', 'Heating-Open Systems (HOS)', 'Working-Closed Systems (WCS)' and 'Working-Open Systems (WOS)'. The power flux of an electric appliance regarding to the classifications are shown in Fig. 1. Pmech(t) is the mechanical power [W], c]Jopen(t) and c]JheatCt) are the mass flux [W] and the heat flux[W] across to the boundary of the electric appliance, respectively. The power flux characteristics of each group and some examples are also detailed in Table I. From this classification, we propose a generic thermal model of electric appliances in next section. The model would cover all categories of appliances shown in this section.
Fig. I. Power flux diagram of an electric appliance TABLE T CATEGORIES OF ELECTRIC APPLIANCES Characteristics
Examples
es
Pmcch(t)=O
