Models of domestic occupancy, activities and energy use based on time‐use data: deterministic and stochastic approaches with application to various building‐related simulations
Joakim Widéna,*, Andreas Molinb, Kajsa Ellegårdc a Department of Engineering Sciences, Uppsala university, P.O. Box 534, SE751 21 Uppsala, Sweden. b Division of Energy Systems, Department of Management and Engineering, Linköping University, SE581 83, Linköping, Sweden c Technology and Social Change, Linköping University, SE581 83 Linköping, Sweden * Corresponding author. E‐mail adress:
[email protected]. Tel.: +46 18 471 37 82.
Abstract
Time‐use data (TUD) have a large potential for improving occupancy and load modeling and for introducing realistic behavioral patterns into various simulations. In this paper previously developed models of occupancy, activities and energy use based on TUD are extended and described in a general framework. Two extensions are studied: deterministic conversion of empirical TUD is extended into a complete thermal load model encompassing both occupancy and various end‐uses and a Markov‐chain approach for generating synthetic TUD sequences is extended to include a model for load management. Three examples of building‐related applications are presented: simulation of indoor climate in a low‐energy building, household electricity load management in response to time‐differentiated electricity tariffs and simulations of load matching in a net zero energy building. The main conclusion is that the extended model framework can generate detailed and realistic behavioral patterns that allow diversity and correlations between end‐uses to be taken into account.
Keywords
Time‐use data, Occupancy, Load modeling, Building energy simulation, Load management, Markov chain Accepted for publishing in Journal of Building Performance Simulation
1
1. Introduction Following the ever more ambitious targets for energy efficiency around the world, research in the field of domestic energy use has become increasingly important and extensive. This research area is represented both in social science and technical disciplines. However, traditionally, the two disciplines have, with few exceptions, been kept apart. In a review of the most important studies of human factors in household energy use, Lutzenhiser (1993) concluded that a general deficiency of the literature was that “[…] it has generally failed to connect, for example, the energy impacts of social action with the physical performances of buildings, technologies, and the natural environment.” Although this observation was made almost two decades ago, it is still very much true today. The point of departure of the research presented in this paper is that technical research and model development in the field of domestic energy use can benefit greatly from integration of research and methods from the social sciences’ efforts in the same field. The end‐user’s behavior is of course central to the success of energy efficiency schemes, but also increasingly important in the study of many emergent, often small‐ scale energy technologies. For example, direct matching between household loads and on‐site solar photovoltaic systems and in turn the economic benefits, depending on the crediting system, are highly dependent on the household’s load distribution (Widén and Karlsson 2009, Widén and Karlsson 2010). Less sensitive, but still important, the performance of domestic solar heating systems is influenced by the load profile (Jordan and Vajen 2001, Spur et al. 2006). In local distribution grids or microgrids with widespread small‐scale power generation and few customers, the individual household’s contribution to the local balance between consumption and generation is larger and it becomes important with more detailed load models for simulations (Thomson and Infield 2007, Conti and Raiti 2007). All of these effects are because the small scale the end‐users’ individual actions are more visible, less aggregated and less averaged and smoothed. Diversity becomes more important, as well as fluctuations and randomness on different time scales. In the case of low‐energy or passive housing the user’s occupancy and energy use also become more influential on the building performance. Internal heat loads from occupants and equipment are relied on as heat sources, which increases the impact of load diversity (Isaksson and Karlsson 2006, Wall 2006). There is a need to include the user’s actions and activities in a realistic way into modeling of these technical systems in order to study their performance. In previous research models have been developed that use time‐use data (TUD) – sequential, high‐resolved activity data from households, usually collected with diaries – to reproduce a realistic user behavior (Widén et al. 2009a, Widén et al. 2009b, Widén and Wäckelgård 2010). A fundamental observation is that occupancy is crucial for the resulting load patterns: people that are at home and active is a prerequisite for energy use within the building. With modeling from TUD very realistic occupancy patterns can be generated, but the main advantage with TUD is that occupancy patterns can be extended to more general activity patterns that dictate, apart from if the individual is at home or not, which end‐uses the occupant is involved in. The developed models include deterministic conversion of TUD into end‐use profiles and a stochastic Markov‐chain model that creates synthetic activity patterns for an arbitrary number of persons over an arbitrarily long time period. Further possible improvements of the model have been identified in previous studies (Widén and Wäckelgård 2010). Firstly, the different end‐use models could be combined and developed into a complete load model, including multiple energy end‐ 2
uses and occupancy. In simulations of the indoor climate in buildings, the model would preserve correlations between different end‐uses modeled from the same activities and hence represent a more realistic user behavior than, e.g., load profiles combined from different sources or a set of standard profiles. Secondly, the stochastic approach could be extended to include modeling of demand side management (DSM), which would make the modeled user actions more dynamic and applicable to more research problems. Furthermore, there is a need to describe the different developed model types in a general framework and to summarize the model developments and applications. In this paper we present implementations of the two developments suggested above. The deterministic approach is developed into a multiple end‐use model and a suggested load management strategy for the stochastic approach is outlined. The developments are described in the context of a general model framework and three application examples are presented. In the first example the deterministic model is applied to simulations of indoor climate in a Swedish low‐energy building to determine the effect of different detailed user activity patterns on the perceived comfort. In the second example the developed load management strategy in the stochastic approach is tested in modeling of active response to time‐differentiated electricity tariffs. In the third example the stochastic model, with the load management option, is used to simulate the temporal mismatch between photovoltaic generation and a net zero energy building’s load profile at a high‐latitude location, and methods to reduce this mismatch. In Section 2 a background on time use research and methodology is provided and previous research on the topic of occupancy and load modeling, both in general and modeling from TUD, is summarized. In Section 3 the general methodology for modeling from TUD is presented, with focus on the two model developments. The three example applications are presented in Section 4 and a concluding discussion is given in Section 5.
3
2. Background 2.1 Time use and everyday life As indicated above, peoples’ daily activities in everyday life are crucial for the use of energy in households. A recent literature review of Nordic research of everyday life by Karlsson et al. (2010) identifies research on everyday life in a wide variety of academic disciplines; sociology, home economics, social anthropology, pedagogy, human geography, occupational therapy and social work, to mention a few. Important concepts in the research on everyday life are for example habits and routines, and the variation between individuals of different socioeconomic groups or cultures is researched. Everyday life studies are often based on deep interviews, focus groups or video‐ recordings of a small number of individuals. Still, not few studies struggle with definitions of what everyday life is (Karlsson et al. 2010). During the past century many social scientists have researched energy use in everyday life. The interest is directed to policy means (Carlsson‐Kanyama and Lindén 2002, Lindén 2004, Palm 2009, Benders et al. 2006) and to peoples’ lifestyles from a sociological and anthropological perspective (Aune 1998, 2007). In several recent studies the hidden character of energy in everyday life is underlined, as is the role of habits and routines in making energy something taken for granted and used without thinking of it as a resource. (Shove 1999, 2003, Karlsson & Widén 2009). Despite extensive research in the social sciences, in many engineering contexts the actions of the end user are still often treated simplistically, averaged and without consideration of diversity, context and time resolution. It is challenging to represent human activities in a numerical model and to make use of the extensive but often too qualitative results of social science, suggesting some connection between the qualitative field of social science and the quantitative field of simulations is needed. The models presented in this paper is based on the timegeographic approach, which originates from and has found the majority of its applications in the social sciences. Time geography is an approach for researching human resource utilization that was developed in order to integrate the fundamental, though often neglected, dimensions of continuity in time and space in social science and also link the social dimension to nature, materiality and technology (Hägerstrand 1970, 1985). In time geography the individual is regarded as a continuant and her time‐space “biography” can be described by the individual path, depicting her movements between places over time (Lenntorp 1976). It ranges from very short to very long time periods. The individual path is useful to describe not only human individuals but also the time‐ space movements of any kind of individual object (living or non‐living, naturally created or artifacts). Hence, tools and appliances used by human individuals in their everyday life as well as the human individuals themselves can be described in the same way. This provides a basis for analyzing a manifold of aspects characterizing everyday life, like when, where and for how long one or more individuals use various resources. However, the strength of the visualization is lost when more than a limited number of individual paths are depicted in a diagram, since the image gets blurred. To overcome this the activityoriented individual path is developed, which in a first step of analysis highlights the sequence of activities and in a second step of analysis also relate activities to the places where they were performed (Hägerstrand 1970, Lenntorp 1976). Examples of individual and activity‐oriented paths are shown in Figure 1.
4
Figure 1. Example of a timegeographic individual path (to the left) and the corresponding activityoriented graph (to the right). The activityoriented path is a projection of the individual path on the time axis. A time‐geographical description of the everyday life of an individual is based on the sequence of activities performed at one or more places during a time period, including transportation. As mentioned in the introduction, these sequences can be collected empirically from diaries in the form of timeuse data (TUD), of which a further description is provided in Section 3.1. At the levels of the household, neighborhoods, residential areas or society many individuals’ activity sequences constitute aggregate activity patterns, i.e. the everyday life in a group or population. The time‐geographic approach is thus a method that holds a place between quantitative and qualitative approaches. For more qualitative studies, time geographic explorations of everyday life can be complemented with interviews in order to find out the arguments used by people to do what they do in different social and geographical settings. On the other hand, the quantitative aspects of the method can be utilized in statistics and modeling, for example in studies of domestic energy use. Results from time‐use studies are usually reported in terms of the average time used for various activities by an average individual in relevant socioeconomic groups in the population. However, both for modeling purposes and for using TUD as a tool for revealing habits and for making people aware of their use of resources in their everyday life, this is not enough. Averages neglect variation, repetition and duration of activities, which all are important properties in analyzing energy use in households. For modeling of occupancy and energy use it is far more fruitful and in many cases necessary to use the activity sequences just as they appear in everyday life. 2.2 Previously developed models and applications The methodology in this paper builds on previously developed models that in various ways construct occupancy and energy use profiles from TUD. Widén et al. (2009a) showed that load profiles for electricity and hot water could be realistically constructed and reproduced from TUD with a rather uncomplicated deterministic conversion model. 5
In short, the model connects a constant power demand to selected activities of each household member, and the individual appliance load profiles thus obtained are added to produce a total load profile for each household. The model was validated against measured load data, which suggested that the modeled profiles were realistic. As the study suggested that TUD could provide an accurate basis for modeling domestic energy use the concept was developed further in Widén et al. (2009b) and Widén and Wäckelgård (2010). In the former study an occupancy model based on non‐ homogeneous Markov chains was used to generate synthetic occupancy patterns and model domestic lighting demand. In the latter study, the approach was extended to activity patterns and used to produce highly realistic and high‐resolved load profiles for household electricity. From a detailed validation against measurements, it was concluded that the stochastic models reproduce all the important features of electricity loads: end‐use composition, diurnal and annual variations, short time‐scale fluctuations, diversity between households and load coincidence. The models have been used in various applications, mainly related to utilization of small‐scale renewable energy. The deterministic conversion model has been used to study utilization of solar photovoltaics in households and options to increase the solar fraction (Widén et al. 2009c) and to determine the impact of different hot water load profiles on domestic solar heating systems (Lundh 2009). The conversion model has also been implemented in VISUALTimePAcTS/energy use, which is a software for visualization of empirical activity sequences and energy use patterns of individuals and groups (Ellegård and Cooper 2004, Ellegård and Vrotsou 2006, Vrotsou, Ellegård and Cooper 2009). The stochastic model has thus far been used to generate load profiles for power‐flow simulations of low‐voltage electricity distributions grids with large amounts of distributed generation (Widén et al. 2010) and for studies of the effect of different crediting systems for on‐site photovoltaics (Widén and Karlsson 2010). 2.3 Similar models of occupancy and energy use Over the years, several related models for generating household electricity load data have been proposed. The most common type is bottomup models, in which a load profile for a household or a set of households is generated by successively combining and aggregating different types of lower‐level data, sometimes down to entities representing single appliances or individuals. Examples include Capasso et al. (1994), Paatero and Lund (2006), Stokes et al. (2004), Stokes (2005) and Armstrong et al. (2009). These models vary in degree of complexity, number of assumptions and amount of input data. Fundamental for all, though, is the prerequisite of occupants being available for use of electrical appliances. Occupancy has been explicitly modeled for this and other purposes by Richardson et al. (2008) in an approach using TUD, similar to the one presented in this and previous papers, and by Page et al. (2008). The approach in Richardson et al. (2008) was extended to a domestic lighting model (Richardson et al. 2009a) and a complete modeling framework for distributed power systems is being developed (Richardson et al. 2009b). Similar models have been proposed by Tanimoto et al. (2008a,b). Stochastic occupancy and behavioral models have also been suggested for modeling of lighting control (Reinhart 2004), shading devices (Haldi and Robinson 2010) and ventilation (Yun et al. 2009).
6
3. Methodology 3.1 Time use data The TUD that the presented models are based on consist of empirical activity sequences that describe, normally with a high time resolution, which activities one or many individuals perform, and within which geographical and social contexts these are taking place. As an example, Figure 2 shows activity sequences for a group of persons visualized with the VISUALTimePAcTS/energy use software. Each individual’s activity sequence is visualized as a continuous sequence and an aggregate activity pattern is revealed when several activity sequences are visualized side by side according to chosen criteria like, for example, gender and age. As an example of extraction of a subset from the software database, Figure 2 shows individuals aged between 22 and 30 years.
Figure 2. Examples of activity sequences in the form of empirical TUD, visualized with the VISUALTimePAcTS software. This sample contains individuals aged 2230 in the SCB 1996 TUD set. Individuals are sorted by decreasing age from left to right for men and women separately. Each individual performs a sequence of activities that bears meaning to him/her. Since the individual can perform only a limited number of activities at the same time and occupy only one place at a time, a diary in which the sequence of activities performed are noted will serve as an excellent means to trace the individual’s activity path. To collect TUD individuals are asked to note their activities continuously during the surveyed days in a simple diary. The diaries contain information about what activities the individual is occupied with, where she has been located, when the activities were performed at different locations and together with whom the activities were performed. (Ellegård 1999) 7
Indirectly more information can be collected from the diaries: some activities are always performed for a specific purpose, telling why the activity is performed. Also indirectly, it is possible to model what kind of tools and appliances are utilized. Being at home means the apartment is occupied, going by car means a car is used and preparing food claims various kinds of white goods and appliances. To process diaries in the models the activities, places and accompanying persons are coded according to a special hierarchical categorization scheme where activities are categorized with increasing degree of specificity (Ellegård 1999). As an example, Figure 2 shows the most general and least detailed activity categories in a color code scheme. The set of raw data used for developing the models presented here (in the following referred to as ‘SCB 1996’) was collected by Statistics Sweden (SCB) in a pilot study in 1996 and has been utilized in all of the previous model publications. In total 463 individuals (50% men and women) in 179 households wrote diaries one week day and one weekend day. The age span is from 10 to 97 years and the individuals live in different geographical areas of Sweden. Although these data are one and a half decade old, no time use survey since then has been performed with this scope and degree of detail and there is no TUD set that has been as extensively tested for consistency and completeness. Most importantly, previous model validations have shown that reproductions of aggregate load data correspond closely to today’s household load patterns and, thus, that there has been no extensive shift in any of the basic activity patterns that the energy‐use modeling is based on (Widén et al. 2009a). 3.2 General model framework The general model framework includes a set of conversion functions for constructing end‐use profiles from TUD. These functions can either be used in a deterministic approach where empirical TUD are converted or in a stochastic approach where the conversion functions are applied to synthetic activity sequences generated by a stochastic process with parameters determined from an empirical TUD set. In the following, we consider a hypothetical household with N members, with a set of activity sequences a1(k), …, aN(k), where k = 1, …, K denotes the time step. As indicated above, information is normally collected about where and with whom activities are performed. This information could also be utilized in modeling. In the following, however, the latter piece of information is not used and it is assumed that only activities performed at home are considered specifically and that at all other locations the individual is considered to be in an “away” state. 3.2.1 Conversion model The fundamental part of the model framework is the method for conversion of TUD into occupancy and end‐use profiles. The exact functions depend on the modeled end‐use category, but some typical generalized conversion functions can be defined. Before applying a conversion function to the activity sequences it is necessary to sort out the activities involved. Depending on the end‐use, the number of activities can be different. With such a subset of activities A, a step function describing whether any of these activities are performed by a certain individual is defined: 0, (1) 1, otherwise This function is equal to one when any of the activities are performed and zero otherwise. In some cases, for example use of TV and other appliances, shared or collective use can be assumed. In these cases it is necessary to consider whether an 8
activity is performed by one or more members or not at all. In this case, a similar function for the whole household is defined: 1, ∑ 1 (2) 0, ∑ 0 From these step functions a number of general conversion functions can be defined, starting from a general function on the form: , 1 ,…, 1 (3) That is, the output depends on the current state and, possibly, on previous states. Very generalized, three typical functions describe how end‐use profiles can be obtained from the TUD. These are also outlined in Figure 3. The first function describes energy use that assumes different levels when the associated activities are performed and when they are not, corresponding, e.g., to active use and standby of an appliance): , 1 (4) , 0
Figure 3. Examples of the conversion functions defined by Equations 46 in (a)(c), respectively. An example of this is outlined in Figure 3 (a). In the second function energy is demanded during the activity but with a predefined profile: , 1, 1 1 , 1, 1 1, (5) 1 ,…, 2 0 , otherwise The value is thus determined by in which previous time step the change to an active state occurred (if so, the difference is equal to 1) and whether the activity has been performed since then ( 1 0 . An example is shown in Figure 3 (b). The third 9
function describes energy use that is performed after an activity is performed (e.g. if the activity is of the type “turning on an appliance”): , 1 1 , 1 2 1, 1 , 2 3 1, , 1 1 (6) ,
1
1,
,…,
2
1
, otherwise If the step function has changed from one to zero (difference = –1) the energy use in subsequent time steps assumes predefined values, provided the activity has not started again ( , … 1). An example of this function is shown in Figure 3 (c) Total end use ∑ for the household is determined as or, in the case of shared end use, by applying the above functions to u(k) instead of ui(k). Below, modeling of some general end‐uses is outlined: Occupancy. Occupancy within the home can be modeled from the ui functions, with the activity subset A containing all activities performed at home: (7) For application in detailed building performance simulations it is also possible to determine occupancy in different parts of a building by connecting sets of activities to different rooms. This requires assumptions that, for example, all cooking activities take place in the kitchen, sleeping in bedrooms, and so on. Household electricity. Household electricity is modeled mainly with the first and third conversion functions (Equations 4 and 6) described above, the former for appliances used during an activity, e.g. TVs and computers, and the latter for washing, drying and dishwashing machines, where the associated activity is “fill and turn on machine”. In most cases the power of an appliance can be assumed constant, while for some end uses the modeling is more complex, for example for lighting, which depends on the daylight level, calculated from solar irradiation data. This procedure is described in more detail in Widén et al. (2009b). Model implementations for household electricity with different degrees of complexity are presented in Widén et al. (2009a) and Widén and Wäckelgård (2010). Domestic hot water. Domestic hot water use is mainly modeled with the first and second conversion functions (Equations 4 and 5). The former is used to describe water being drawn during the entire course of the activity, for example showering. The second one is used in situations where water is drawn during a certain part of the activity, for example bathing water is assumed to be drawn only in the beginning of the activity. Conversion to hot water use has been treated in more detail in Widén et al. (2009a) and Lundh (2009). Thermal loads. Thermal loads, i.e. heat emitted to the surroundings from appliances, hot water use and persons, can be modeled based on the three end‐uses above. It is possible to use less high‐resolved power profiles in the conversion functions, some weighting factor to describe loss of useful heat and it is also in some cases necessary to introduce a time delay between electricity or hot water use and distribution of heat to the surroundings. The power levels in each conversion function have to be determined and defined. Different approaches can be applied for this. Some that have been used previously are adjusting parameters to make load curves match measured data (Widén et al. 2009c) or determining them as averages from appliance tests (Widén et al. 2009a). 10
3.2.2 Deterministic approach In the deterministic approach empirical TUD sets are converted into end‐use profiles with the conversion functions outlined above. The advantages of converting directly from empirical TUD are that the modeling can be very detailed as the studied sets of activities do not have to be limited as in the stochastic approach (cf. Section 3.2.3). The actual sequences of activities are also preserved, which makes the modeling for individual households more realistic. However, the approach requires access to an entire TUD set in detail, and the model output will have the same limitations (number of households and time span) as the original data set. An example of a set of empirical TUD from the SCB 1996 data set is shown in Figure 4 together with an aggregate modeled load curve.
Figure 4. Example of an aggregate load curve for TV deterministically modeled from the TUD in the SCB 1996 data set. In the activity graph to the left all individuals in the data set are sorted by decreasing age from left to right. For application in building performance simulations, a complete deterministic load model that converts TUD from SCB 1996 was developed that encompasses occupancy, electricity use and hot water use and models thermal loads from all of these end‐uses. To be applicable to simulations of a specific building with seven rooms, each activity and its associated equipment were connected to one room. Each room thus receives a thermal load that depends on the occupancy and appliances and other equipment used during each person’s presence. The actual conversion functions and other assumptions are summarized in Appendix A. As the conversion is done deterministically from empirical TUD, the implementation for the SCB 1996 dataset results in daily profiles for 179 households on one weekend day and one weekday. An example of the output that 11
can be generated with the model is shown in Figure 5 for a 6‐person household. When analyzing the generated load patterns or using them in simulations it is possible to sort out households with interesting patterns and, for example, include various extreme behaviors in the same building model to test performance limits. Section 4.1 contains a further description of how the model can be applied to building simulations.
Figure 5. Example of outputs from the total deterministic thermal load model on a weekday for a 6person household from the SCB 1996 data set. Note that the scale of the individual graphs differ to show the dynamics of each pattern. 3.2.3 Stochastic approach From the previous section the advantages of modeling from empirical data are evident. However, in many applications longer data series are needed, as well as the possibility to generate data for an arbitrary number of households with an arbitrary number of members. It is also convenient if it is possible in some way to condense the total amount of data needed for the modeling (a whole TUD set in the deterministic case). In the 12
stochastic approach, the drawbacks of the deterministic approach are avoided by definition of a Markov chain process that generates synthetic sequences of selected activities with parameters determined from the original TUD set. The selected activities are modeled as a finite number of states in a Markov chain with transition probabilities pij(k) for switching between states i and j from time step k to k + 1. The probabilities change with time to reflect daily changes in activity patterns, i.e. the Markov chain is nonhomogeneous. These transition probabilities are estimated from empirical TUD as the number of transitions nij(k) between states i and j, divided by the total number of transitions ni(k) from state i:
(8)
In previous studies, it was found that hourly averaged transition probabilities are sufficient for maintaining a sufficient accuracy of the model (Widén and Wäckelgård 2010). This considerably decreases the total amount of data to have access to in order to perform a simulation. For example, for a database with N individuals, a 5‐minute resolution and two recorded days per person, the total number of data points is 288 × N × 2. Condensing this data set into transition probabilities with n activities and hourly averages, the total number of data points is 24 × n2 × 2. A synthetic activity sequence is generated from the transition probabilities by randomly sampling a transition from these probabilities in each time step. Note that although transition probabilities are hourly averaged the synthetic sequences may be generated on shorter time intervals, e.g. minutes. In this case the same transition probabilities are used during each hour. As found in Widén and Wäckelgård (2010) the resulting activity sequences are similar to the real ones. The conversion model for generating occupancy and end‐use profiles can then be applied to this synthetic sequence in the same way as to empirical TUD. It is possible to determine, in each time step, the aggregate behavior of the stochastic process. With transition probabilities ordered in a transition matrix
(9)
the theoretical distribution of persons in the respective state is: , , 1 (10) The fundamentals of the stochastic approach are treated in more detail in Widén et al. (2009b) and Widén and Wäckelgård (2010). Although estimated from real data, the transition probabilities can, in principle, be altered to reflect changes in activity patterns. In the proposed load management approach the probabilities for transition to certain activities in a given time step are increased on dispense of other transition probabilities. It is assumed that one set of activities is shifted down while another is shifted up, for example activities that involve electricity use and activities that do not. In the following we consider the transitions from an arbitrary state i. Assume that indices j denote states for which the transition probabilities are shifted up and k denote states for which they are shifted down. The probability for switching to any state within the two set of up‐shifted states is: ∑ (11) We now assume that α is the fraction of persons that switch to states j instead of k, assumed equal for all k, i.e. a uniform fraction of the people not switching to the up‐ shifted activities change to doing this in every time step. Then the new down‐shifted probabilities are: ̂ 1 (12) 13
and the increased probability for switching to states j that is to be distributed on the up‐ . This probability could be distributed in various ways on the shifted transitions is up‐shifted transitions, but in general the up‐shifted probabilities are: ̂ 1 , ∑ 1 (13) where the coefficients distribute the down‐shifted probability on the transitions in question. As this bottom‐up approach affects the transition probabilities in a certain time step independently of the other time steps, i.e. without any “memory”, it does not give any guarantees about the resulting shape of the activity frequency pattern over the day or the total time spent in certain states. In this respect, it can be used as a peak clipping or a valley filling strategy, where the demand is lowered or increased in certain time intervals, but not as a load shifting strategy, where exact volumes of load are moved between different times of the day. However, as will be shown in Section 4.2, it can work approximately in this way.
14
4. Examples of applications 4.1 Indoor climate simulations As mentioned in the introduction, thermal loads occurring in low‐energy buildings such as passive houses tend to play a crucial part for the energy use and for the design of installed heating power. In (Wall 2006), it is reported that required space heating power is more than doubled in the Lindås passive houses in Sweden when occupancy is changed from four to no persons, while the energy demand increases by only 30%. Passive houses are limited in the amount of installed space heating power, making thermal loads an important heating source in cold climatic conditions. Using detailed load profiles from TUD provides information about the time and place of the thermal loads and can be used in a building energy simulation (BES) to provide more detailed dynamics of indoor temperatures. In combination with measurements and CFD one can get the whole picture of the physical parameters related to thermal comfort according to ISO7730; air temperature, humidity, air velocity, radiant surface temperatures, human activity and clothing (ISO 2005). When designing low‐energy houses it is important to consider thermal comfort to avoid rebound effects, such as increased indoor temperature preference, which is described in (Greening et al. 2000). However, the rebound effect for building energy efficiency measures, such as low‐energy buildings, is suggested to be valid only until comfort needs are fulfilled (Greening et al. 2000). Using thermal comfort as a requirement in energy calculations could lead to a more realistic picture of the potential gain in energy efficiency measures. One should also note that thermal comfort issues are individual and that ISO7730 presents a general way of finding the percentage of dissatisfied people (PPD) for a large population. One issue that may cause thermal discomfort in Passive houses is the limitation of installed heating power, which in southern Sweden is limited to 12 W/m2 (FEBY 2009). An example is presented here, with the purpose to show the effect on thermal comfort that such a limitation might have. A newly built (2008) residential terraced two storey apartment with a floor area of 105 m2 in Linköping is used as case study object, also previously studied in (Karresand et al. 2009). This building is modeled in the BES software IDA ICE 4 and is shown schematically in Figure 6. It is equipped with Constant Air Volume (CAV) ventilation with heat recycling (HRX) and heating coil. In the IDA ICE model, the heating coil is regulated with thermostatic control on the exhaust air temperature.
15
Figure 6. Sketch of the passive house model used in the example BES. In this example, the deterministic thermal load model presented in Section 3.2.2 is used in BES, where a winter case is studied. The daily distribution of thermal loads, heating, air flows, transmission losses, average indoor air temperature and outdoor air temperature for a 6‐person household in the kitchen/living‐room can be seen in Figure 7, with a 5‐min resolution. Temperature variations correspond to changes in thermal loads. The peaks coming from air flows correspond to opening of the laundry room door, which is assumed to be opened only when there is laundry activity in the laundry room. When the cooking activity is taking place the kitchen fan is also activated, which explains why the losses from air flows increase at this time. Transmission losses increase in the evening when the kitchen/living room is warmer than neighboring zones. Heating is at most times at maximum 12 W/m2, and decreases only at times when the average exhaust air temperatures from all zones is lower than set‐point, which explains why heating does not decrease during the evening high‐load time in the kitchen/living room.
16
Figure 7. Energy balance of the kitchen/living room zone in the passive house model with thermal loads deterministically modeled from TUD for a 6person household and a 12 W/m2 heating coil. When studying installed heating power versus the effect on thermal comfort one low and one high thermal‐load household are chosen; a 2‐person household with minor thermal loads and a 6‐person household with substantial thermal loads. The PPD prediction is calculated from the predicted mean vote (PMV), derived from simulated average air temperature in the kitchen/living room, during occupancy hours 06:00‐ 23:00, on the coldest day of the week (‐15 to ‐20 °C). Moreover, the mean radiant temperature is assumed to be constantly 0.5 °C lower than average air temperature which was measured in one point with Innova 3710‐equipment on a cold day (‐10 to ‐15 °C). Furthermore, mean air velocity is assumed to be constantly 0.05 m/s, which was measured from this single point only when induced by researcher presence. Henceforth, humidity is measured to be 18‐25 %, however without household tenants’ presence, wherefore an addition of 3 g/m3 moisture as an assumed continuous moisture production is added, which results in roughly 30’%, which is used. Additionally, an activity level of 1.2 met (70 W/m2) and a clothing level of 0.9 clo (0.14 m2 K/W) was assumed, corresponding to sedentary activity and indoor winter clothing.
17
Figure 8. Temperature, PPD and space heating demand for different installed heating powers in the 6person and 2person households. The space heating demand is shown as a percentage of 260 kWh, the maximum space heating demand in the 2person household. Figure 8 shows the temperature, PPD and space heating demand as a function of installed heating power, where the space heating demand for high and low thermal load was maximum 141 and 260 kWh during the winter‐case week and the percentage is described in relation to 260 kWh. One can clearly see that the space heating demand increases with installed power only until good thermal comfort is reached (PPD roughly 5‐10% and PMV ‐0.5‐0.5). When using the limitation recommended by FEBY, 12 W/m2 the overall thermal comfort is reduced substantially, especially when a low thermal load household is present, PPD ~50%. The risk when having a limited peak power in the heating system is that other sources such as household equipment will be used more than what they would normally be used just to heat the building. This may, if the heating system uses low exergy sources, result in a higher primary energy use since much of our household equipment is powered by electricity (Isaksson and Karlsson 2006). This example shows an approach where TUD can be used to introduce high‐ resolution thermal loads in detailed calculations of needed heating power. Depending on the thermal loads the needed installed power during occupancy in this example is 15 and 18 W/m2 in order to maintain PPD below 10%, which is suggested by the ISO7730‐ standard, category B. However, a more detailed study regarding local thermal comfort should be performed using CFD, measurements and questionnaires/interviews. 4.2 Load management Demand side management, or DSM, is a method to alter the use of energy at the end‐user site to fulfill certain goals (Beggs 2002, Abaravicius 2007). In the more specific concept of load management the aim is to lower the demand during on‐peak periods and increase it on off‐peak periods in order to reduce the load on the distribution grid and reduce the need for regulating power. One way for a utility to achieve this kind of load‐ shifting measure at the end‐user site is to introduce price incentives. A time‐ differentiated tariff with different buying prices for electricity at low‐load and high‐load periods is one solution that is considered here. With the method presented in Section 3.2.3, a bottom‐up type stochastic model for 18
customer response to a time‐differentiated tariff can be defined. The response to the price signals is then modeled by up‐shifting the probabilities for switching to electricity‐ dependent activities during low‐load pricing while down‐shifting the probabilities for switching to other activities, and vice versa during high‐load periods. It is important to note that as it is the probabilities that change, the response of an individual to the price incentives is not ideal, but the chance of an action in a certain direction taking place is increased or decreased, which ensures a realistic behavior of the model. In this brief example, the load management method is applied to a two‐level time‐ differentiated tariff. No exact price levels are assumed, but during the high‐load period 07:00‐21:00 (period a) the price is higher and during the low‐load period 21:00‐07:00 the price is lower. It is assumed, as in Section 3.2.3, that in each of the two periods a set of transition probabilities are down‐shifted by a constant factor α (see Equation 12). To reflect load shifting, i.e. that if electricity use is decreased during the high‐load period these activities should be performed during night‐time with roughly the same proportion, the shifted probability is distributed on the up‐shifted transitions as: ̂ 1 (14) where is the original fraction of people involved in the up‐shifted activities j on average during the other time period, calculated from the asymptotic distribution of ∑ . activities (Equation 10), and These calculations were applied to the stochastic Markov‐chain model with nine activity states described in Widén and Wäckelgård (2010). As electricity‐dependent activities that are down‐shifted during the high‐load period and up‐shifted during the low‐load period the states 3‐8 (cooking, dishwashing, washing, TV, computer, and audio) were chosen. As complementary activities that are up‐shifted during the high‐ load period and down‐shifted during the low‐load period the states 2 (sleeping) and 9 (other) were chosen. The parameter α was set to 0.01 which means that in every time step 1 % of the persons switching to an down‐shifted activity instead switch to an up‐ shifted activity. Although the α parameter is not explicitly related to an exact price level, this could be implemented. The transition matrix for weekdays for detached houses was transformed with Equations 12 and 14 and simulations were performed for one day as described in Widén and Wäckelgård (2010).
19
Figure 9. Aggregate household electricity load curves before and after DSM for 10 and 200 households in the studied example. Time resolution is 1 min. The results of simulations with a 1‐min resolution are shown in Figure 9. The stochastic nature of the generated patterns is evident and is realistic. There is more randomness in the aggregate load curves for the set of 10 households. Although it is possible to see some effect of the load management scheme in this small set of household loads, the changed pattern emerges more clearly when a larger number of households is considered. For 200 households, the raised demand on nights and mornings and the lowered daytime demand, especially in the evening peak hours, are more evident. Note also that the originally flat demand between 00:00 and 05:00 is now somewhat higher and more variable, due to more people being awake and active. It is clear that the described approach gives a realistic and diverse demand response. By choosing different activities for down‐shifting and up‐shifting and by changing the α parameter, other patterns and effects can be introduced. If necessary, it is also possible to assign different α values to different activities. The signals to which the response is given could also be changed. In the next section a reversed DSM scheme is tested, that potentially increases matching with on‐site photovoltaic generation. 4.3 Load matching in NZEBs A Net Zero Energy Building is a building that has a zero annual balance between on‐site generation and demand. In this example a solar NZEB located in Stockholm, Sweden, is considered. The building is for one family and has on‐site photovoltaic (PV) generation that equals the household electricity demand on an annual basis. NZEBs are generally not supposed to be self‐sufficient in terms of energy, but rather interacting with distribution systems to maintain the annual balance. In this example the building is connected to the electricity distribution grid, so that when on‐site generation is not sufficient the building imports power from the distribution grid and when the on‐site 20
generation exceeds the local demand it exports the surplus. Although the net difference between demand and generation is zero over the year the actual exchange, or mismatch, with the grid can be substantial (Voss et al. 2010), especially at high latitudes where there is a considerable seasonal asymmetry in solar availability (Perers 1999). Massive introduction of NZEBs in distribution grids would, because of this mismatch, have a clear impact on the voltage levels in existing distribution grids (Widén et al. 2010). Figure 10 shows matching on a 1‐min time scale during three summer days for a NZEB generation and demand setup. On the first two cloudy days the highly fluctuating generation pattern is approximately of the same magnitude and randomly coincides with the load, but on the third and sunny day there is a massive overproduction that is fed into the grid.
Figure 10. Examples of PV generation and household electricity load for the NZEB in the example during three consecutive days. Time resolution is 1 min. The load matching capability of PV, and options to increase this, has been studied previously with aggregate load curves generated with the deterministic model in Widén et al. 2009c). It was found that storage was theoretically the most flexible and efficient solution but that also load management could have a considerable impact. However, as is also fundamental to the concept of NZEBs, storage and in particular seasonal storage is currently not a feasible option for many reasons (Voss et al. 2010). There is thus a need to further examine DSM as a way to decrease the mismatch. In this example the base case azimuth angle of the PV system is 0° and the tilt angle is 45°, the setup which maximizes annual production. The studied alternative cases with options for increased load matching are: a) Load management, modeled with the same approach as in the previous section, but with electricity‐dependent activities shifted up during daytime (08:00‐16:00) and down during night‐time (16:00‐08:00) to match the hours with solar energy availability. The α parameter was set to 0.05. b) PV array re‐orientation from the optimum for annual production. Azimuth and tilt angles of 90° were chosen, which maximizes the afternoon insolation and thus shifts the average production curve towards the evening hours. The simulations with and without load management were done for a detached house over eight years, with the same procedure as outlined in Widén and Wäckelgård (2010). 21
The resulting data series were then subject to hourly averaging to match the resolution of an available eight‐year (1992‐1999) set of hourly modeled PV data for Stockholm, based on measured irradiance data from the Swedish Meteorological and Hydrological Institute (SMHI). These PV data were modeled and analyzed in a previous study (Widén 2010).
Figure 11. Load matching results for the simulated NZEB. Annually averaged PV generation and load curves with the different options are shown to the left. To the right the solar fraction is shown for combinations of options. 1: No DSM + 0°/45° orientation, 2: No DSM + 90°/90° orientation, 3: DSM + 0°/45° orientation, 4: DSM + 90°/90° orientation. Figure 11 shows the resulting load matching capability of PV in these cases. To the right the solar fraction, which is the percentage of load covered by PV (on an hourly basis), is shown for the different combinations of options. The conclusion is that combining both load management and optimizing the PV array orientation can increase the solar fraction from 30 % to a bit above 35 %. This estimate, taking into account the stochastic nature of the load in a more realistic way and using a more realistic load management method, thus yields a lower range of impacts than the previous study (35‐ 48 %). This example shows in a number of ways the advantages of stochastic modeling as an alternative to using measured load data in this type of analysis. Firstly, the ability to generate data over an arbitrarily long period of time (eight years in this example) and, secondly, the realistic load management method. A major advantage is the separation of the behavioral factor from the electrical equipment. With the same activity patterns, represented by the Markov chain transition probabilities, it is possible to simulate different sets of household appliances, and conversely, it is possible, e.g. via the load management method, to introduce different use patterns of the same equipment.
22
5. Concluding discussion A main conclusion from the model description and the application examples is that the presented models are capable of generating very detailed and diverse patterns of occupancy, activities and various end‐uses. On the one hand, with a sufficiently detailed TUD set, this provides a virtually unlimited degree of detail in the generated patterns. It is possible to introduce diversity between households and to maintain correlations between different patterns and end‐uses as all are modeled from the same underlying TUD. Compared to measurements of all data that can be generated – occupancy, electricity use, hot water use, thermal loads – the model provides a less costly and less complicated method, provided appropriate TUD are available. On the other hand, this also raises the question of which degree of detail is necessary for different applications. Model complexity, possible simplifications, computation times and time resolution should all be considered in more extensive studies than the three examples covered here. Especially for the stochastic model the differences in computation time can be substantial depending on the number of modeled activities and the time resolution. An important question for the future is the possible improvement of methodologies for surveying TUD. To utilize the full potential of the models presented here the TUD set has to be representative of the studied population and unbiased and the activities have to be recorded with a sufficiently high degree of detail and categorized in a logical and generalized activity code scheme. One possible way of improving diary data reporting is to collect TUD digitally, for example via handheld devices, where categorizations could be made directly either manually or automatically. With up‐to‐date and generalizable TUD sets the presented methodology could be used, e.g., to give recommendations about installed heating power in passive houses.
Acknowledgements
This work was carried out under the auspices of the Energy Systems Programme, which is primarily financed by the Swedish Energy Agency. Patrik Rohdin, Division of Energy Systems, Department of Management and Engineering, Linköping University, Sweden, is acknowledged for valuable comments to the manuscript.
References
Abaravicius, J., 2007. Demand side activities for electric load reduction. Thesis (PhD). Lund University, Sweden. Armstrong, M.M., Swinton, M.C., Ribberink, H., Beausoleil‐Morrison, I. and Milette, J., 2009. Synthetically derived profiles for representing occupant‐driven electric loads in Canadian housing. Journal of Building Performance Simulation, 2 (1), 15‐30. Aune, M., 1998. Nøktern eller nytende. Energiforbruk og hverdagsliv i Norske husholdninger. Thesis (PhD). Norwegian University of Science and Technology, Trondheim. Aune, M., 2007. Energy comes home. Energy Policy, 35 (11), 5457‐5465. Beggs, C., 2002. Energy: Management, supply and conservation. Oxford: Butterworth‐ Heinemann.
23
Benders, R.M.J., Kok, R., Moll, H.C., Wiersma, G. and Noorman, K.J., 2006. New approaches for household energy conservation – in search of a personal household energy budgets and energy reduction options. Energy Policy, 34 (18), 3612‐3622. Capasso, A., Grattieri, W., Lamedica, R. and Prudenzi, A., 1994. A bottom‐up approach to residential load modeling. IEEE Transactions on Power Systems, 9 (2), 957‐964. Carlsson‐Kanyama, A. and Lindén, A.L., 2002. Hushållens energianvändning: värderingar, beteended, livsstilar och teknik. En litteraturöversikt. Fms‐report 2002:176. Stockholm University, Sweden. Conti, S. and Raiti, S., 2007. Probabilistic load flow using Monte Carlo techniques for distribution networks with photovoltaic generators. Solar Energy, 81 (12), 1473‐1481. Ellegård, K., 1999. A time‐geographic approach to the study of everyday life of individuals – a challenge of complexity. GeoJournal, 48 (3), 167‐175. Ellegård, K. and Cooper, M., 2004. Complexity in daily life – a 3D‐visualization showing activity patterns in their contexts. Electronic International Journal of Time Use Research, 1, 37‐59. Ellegård, K. and Vrotsou, K., 2006. Capturing patterns of everyday life – presentation of the visualization method VISUAL‐TimePAcTS. In: IATUR – XXVIII annual conference, 16‐ 18 August 2006, Copenhagen, Denmark. FEBY, 2009. Kravspecifikation för passivhus. Swedish Environmental Research Institute Report A1592. Greening, L.A., Greene, D.L. and Difligio, C., 2000. Energy efficiency and consumption – the rebound effect – a survey. Energy Policy, 28 (6‐7), 389‐401. Haldi, F. and Robinson, D., 2010. Adaptive actions on shading devices in response to local visual stimuli. Journal of Building Performance Simulation, 3 (2), 135‐153. Hägerstrand, T., 1970. Tidsanvändning och omgivningsstruktur. In: Swedish Government Official Report (SOU) 1970:14, Appendix 4, 1‐146. Hägerstrand, T., 1985. Time‐geography: focus on the corporeality of man, society, and environment. In: The science and praxis of complexity. The United Nations University, 193‐216. Isaksson, C. and Karlsson, F., 2006. Indoor climate in low‐energy houses – an interdisciplinary investigation. Building and Environment, 41 (12), 1678‐1690. ISO, 2005. ISO 7730:2005: Ergonomics of the thermal environment – Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. 3d Edition, 2005‐11‐15, ISO Copyright Office, Geneva. Jordan, U. and Vajen, K., 2001. Influence of the DHW load profile on the fractional energy savings: a case study of a solar combi‐system with TRNSYS simulations. Solar Energy, 69, 197‐208.
24
Karresand, H., Molin, A., Persson, J. and Åberg, M., 2009. How passive are your activities? An interdisciplinary comparative energy analysis of passive and conventional houses in Linköping, ranging from household activities and actors reasoning to indoor environment and local energy system. Working Paper 42, The Energy Systems Programme, Linköping University, Sweden. Karlsson, K. and Widén, J., 2008. Hushållens elanvändningsmönster identifierade i vardagens aktiviteter. Tema T Working Paper 330. Linköping University, Sweden. Karlsson, K., Olaison, A. and Skill, K., 2010. Mapping and characterizing Nordic everyday life research. Tema T Working Paper 343. Linköping University, Sweden. Lenntorp, B., 1976. Paths in spacetime environments: a timegeographic study of movement possibilities of individuals. Lund studies in geography, Ser. B, Human geography 44. Lindén, A.L., 2004. Miljömedvetna medborgare och grön politik. Formas: Stockholm, Sweden. Lundh, M., 2009. Domestic heating with solar thermal: studies of technology in a social context and social components in technical studies. Thesis (PhD). Uppsala University, Sweden. Lutzenhiser, L., 1993. Social and behavioral aspects of energy use. Annual Review of Energy and the Environment, 18, 247‐289. Paatero, J.V. and Lundh, P.D., 2006. A model for generating household electricity load profiles. International Journal of Energy Research, 30 (5), 273‐290. Page, J., Robinson, D., Morel, N. and Scartezzini, J.‐L., 2008. A generalised stochastic model for the simulation of occupant presence. Energy and Buildings, 40 (2), 83‐98. Palm, J., 2009. Finding local opportunities for energy efficiency in households. In: 1st European conference on energy efficiency and behaviour, 18‐20 October 2009, Maastricht, The Netherlands. Perers, B., 1999. The solar resource in cold climates. In: M. Ross and J. Royer, eds. Photovoltaics in cold climates. London: James & James Ltd., 20‐29. Reinhart, C.F., 2004. Lightswitch‐2002: a model for manual and automated control of electric lighting and blinds. Solar Energy, 77 (1), 15‐28. Richardson, I., Thomson, M. and Infield, D., 2008. A high‐resolution domestic building occupancy model for energy demand simulations. Energy and Buildings, 40 (8), 1560‐ 1566. Richardson, I., Thomson, M., Infield, D. and Delahunty, A., 2009a. Domestic lighting: A high‐resolution energy demand model. Energy and Buildings, 41 (7), 781‐789. Richardson, I., Thomson, M., Infield, D. and Delahunty, A., 2009b. A modelling framework for the study of highly distributed power systems and demand side management. In: 1st International Conference on Sustainable Power Generation and Supply, SUPERGEN ’09, 6‐7 April 2009, Nanjing, China. 25
Shove, E., 1998. Gaps, barriers and conceptual chasms: theories of technology transfer and energy in buildings. Energy Policy, 26 (15), 1105‐1112. Shove, E., 2003. Comfort, cleaneliness and convenience. Berg: Oxford, UK. Spur, R., Fiala, D., Nevrala, D. and Probert, D., 2006. Influence of the domestic hot‐water daily draw‐off profile on the performance of a hot‐water store. Applied Energy, 83 (7), 749‐773. Stokes, M., Rylatt, M. and Lomas, K., 2004. A simple model of domestic lighting demand. Energy and Buildings, 36 (2), 103‐116. Stokes, M., 2005. Removing barriers to embedded generation: a finegrained load model to support low voltage network performance analysis. Thesis (PhD). De Montfort University, Leicester, UK. Tanimoto, J., Hagishima, A. and Sagara, H., 2008a. Validation of probabilistic methodology for generating actual inhabitants’ behavior schedules for accurate prediction of maximum energy requirements. Energy and Buildings, 40 (3), 316‐322. Tanimoto, J., Hagishima, A. and Sagara, H., 2008b. A methodology for peak energy requirement considering actual variation of occupants’ behavior schedules. Building and Environment, 43 (4), 610‐619. Thomson, M. and Infield, D.G., 2007. Impact of widespread photovoltaics on distribution systems. IET Renewable Power Generation, 1 (1), 33‐40. Voss, K., Sartori, I., Napolitano, A., Geier, S., Gonzalves, H., Hall, M., Heiselberg, P., Widén, J., Candanedo, J.A., Musall, E., Karlsson, B. and Torcellini, P., 2010. Load matching and grid interaction of net zero energy buildings. In: EuroSun 2010 – International Conference on Solar Heating, Cooling and Buildings, 28 September – 1 October 2010 Graz, Austria. Vrotsou, K., Ellegård, K. and Cooper, M., 2009. Exploring time diariesusing semi‐ automated activity pattern extraction. Electronic International Journal of Time Use Research, 6 (1). Wall, M., 2006. Energy‐efficient terrace houses in Sweden: Simulations and measurements. Energy and Buildings, 38 (6), 627‐634. Widén, J., Lundh, M., Vassileva, I., Dahlquist, E., Ellegård, K. and Wäckelgård, E., 2009a. Constructing load profiles for household electricity and hot water from time‐use data – modelling approach and validation. Energy and Buildings, 41 (7), 753‐768. Widén, J., Nilsson, A. and Wäckelgård, E., 2009b. A combined Markov‐chain and bottom‐ up approach to modelling of domestic lighting demand. Energy and Buildings, 41 (10), 1001‐1012. Widén, J., Wäckelgård, E. and Lund, P., 2009c. Options for improving the load matching capability of distributed photovoltaics: Methodology and application to high‐latitude data. Solar Energy, 83 (11), 1953‐1966.
26
Widén, J. and Karlsson, K., 2009. The influence of Swedish households’ everyday activities and electricity‐use patterns on the utilization of small‐scale photovoltaic systems. In: Proceedings of the eceee Summer Study 2009, 1‐6 June 2009 La Colle‐sur‐ Loup, France. Widén, J., 2010. Correlations between large‐scale solar and wind power in a future scenario for Sweden. Manuscript submitted to IEEE Transactions on Sustainable Energy. Widén, J. and Karlsson, B., 2010. End‐user value of on‐site domestic photovoltaic generation with different metering options in Sweden. In: EuroSun 2010 – International Conference on Solar Heating, Cooling and Buildings, 28 September – 1 October 2010 Graz, Austria. Widén, J. and Wäckelgård, E., 2010. A high‐resolution stochastic model of domestic activity patterns and electricity demand. Applied Energy, 87 (6), 1880‐1892. Widén, J., Wäckelgård, E., Paatero, J. and Lund, P., 2010. Impacts of distributed photovoltaics on network voltages: stochastic simulations of three Swedish low‐voltage distribution grids. Electric Power Systems Research, In Press. Yun, G.Y., Tuohy, P. and Steemers, K., 2009. Thermal performance of a naturally ventialted building using a combined algorithm of probabilistic occupant behaviour and deterministic heat and mass balance models. Energy and Buildings, 41 (5), 489‐499.
27
Appendix A The table below summarizes the parameters that define the deterministic model in Section 3.2.2. This model was used for generating the thermal loads shown in Figure 5 and the input data to the building simulation example in Section 4.1. Most of the modeling routines are based Equations 4 and 6, with some exceptions. For cold appliances and additional electricity a constant load is applied. For the end‐uses modeled with Equation 6, a time delay Δt was introduced in the final series to reflect delayed heat emission. Parameter values were either obtained from measurements on the actual equipment in the modeled building or taken from the estimates in Widén et al. (2009a) and Widén and Wäckelgård (2010). Table A. Parameters in the deterministic thermal load model. Activity/equipment
Conversion function
Parameters*
Room
Human presence
Equation 4
P0 = 0 W, P1 = 100 W
Depends on the activity**
Computer Cooking Cleaning Ironing Stereo TV Dishwashing Washing Drying Cold appliances Additional electricity
Equation 4 Equation 4 Equation 4 Equation 4 Equation 4 Equation 4 Equation 6 Equation 6 Equation 6 Constant
P0 = 40 W, P1 = 100 W P0 = 0 W, P1 = 1500 W P0 = 0 W, P1 = 1000 W P0 = 0 W, P1 = 1000 W P0 = 6 W, P1 = 100 W P0 = 20 W, P1 = 200 W P0 = 0 W, P1 ,…,P32 = 216 W, Δt = 60 min P0 = 0 W, P1 ,…,P26 = 138 W, Δt = 60 min P0 = 0 W, P1 ,…,P24 = 980 W, Δt = 15 min 52 W
Kitchen/livingroom Kitchen/livingroom Kitchen/livingroom Kitchen/livingroom Bedroom 3 Kitchen/livingroom Kitchen/livingroom Laundry room Laundry room Kitchen/livingroom
Constant
2 W/m2
All rooms
Lighting
Equation 4
P0 = 0 W, P1 = 40‐120 W depending on the daylight level
Kitchen/livingroom
Lighting
Equation 4
P0 = 0 W, P1 = 40 W
Bathing
Equation 4
P0 = 0 W, P1 = 500 W
Laundry room, bathroom, shower room Bathroom
Showering Equation 4 P0 = 0 W, P1 = 200 W Shower room * Subscripts 1,2,… denote 5‐min time steps. ** For activities other than the ones specified in the table, a person is assumed to be in the kitchen/livingroom if active and in one of the bedrooms 1‐3 if inactive (sleeping).
28