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Learning to Automatically Identify Home Appliances

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Appliance load monitoring (ALM) is a technique that enables increasing the efficiency of domestic energy usage by obtaining appliance specific power consumption profiles. While machine learning have been shown to be suitable for ALM, the work on analyzing design trade-offs during the feature and model selection steps of the ML model development is limited. In this paper we show that 1) statistical features capturing the shape of the time series, yield superior performance by up to 20 percentage points and 2) our best deep neural network-based model slightly outperforms our best gradient descent boosted decision trees by 2 percentage points at the expense of increased training time.
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Learning to Automatically Identify Home Appliances
Dan Lorbek Ivanˇ
ciˇ
c1, Blaˇ
z Bertalaniˇ
c1,2, Gregor Cerar1, Carolina Fortuna1
1Jozef Stefan Institute, Ljubljana, Slovenia
2Faculty of Electrical Engineering, University of Ljubljana, Slovenia
E-mail: dl0586@student.uni-lj.si
Abstract. Appliance load monitoring (ALM) is a
technique that enables increasing the efficiency of domes-
tic energy usage by obtaining appliance specific power
consumption profiles. While machine learning have been
shown to be suitable for ALM, the work on analyzing
design trade-offs during the feature and model selection
steps of the ML model development is limited. In this
paper we show that 1) statistical features capturing the
shape of the time series, yield superior performance by
up to 20 percentage points and 2) our best deep neural
network-based model slightly outperforms our best gradi-
ent descent boosted decision trees by 2 percentage points
at the expense of increased training time.
1 Introduction
Household energy consumption accounts for a large pro-
portion of the world’s total energy consumption. The first
studies, conducted as early as the 1970s, showed that as
much as 25% of national energy was consumed by our
domestic appliances alone. This figure rose to 30% in
2001 [1] and continues to increase with an exponential
rate. Some researchers even predict that these numbers
will double by 2030 [2].
In support of rationalizing consumption, appliance load
monitoring (ALM) has been introduced. It aims to help
solve domestic energy usage related issues by obtaining
appliance specific power consumption profiles. Such data
can help devise load scheduling strategies for optimal en-
ergy utilization [2]. Additionally, data about appliance
usage can provide useful insight into daily activities of
residents which can be useful for long-distance monitor-
ing of elderly people who prefer to stay at home rather
than going to retirement homes [2]. Other applications
include theft detection, building safety monitoring, etc.
The two different ways of realizing ALM are intru-
sive load monitoring (ILM) and non-intrusive load mon-
itoring (NILM). While ILM is known to be more accu-
rate, it requires multiple sensors throughout the entire
building to be installed which incurs extra hardware cost
and installation complexity. NILM, however, is a cost-
effective, easy to maintain process for analyzing changes
in the voltage [3] and current going into a building with-
out having to install any additional sensors on different
household devices, since it operates using only data ob-
tained from the single main smart meter in a building.
The obtained data is then disaggregated and each individ-
ual appliance and its energy consumption are detected.
One promising approach to ILM for automatic iden-
tification of home appliances is the use of machine learn-
ing (ML). For instance, in [4] they used ML to find pat-
terns in the data and extract useful information such as
type of load, electricity consumption detail and the run-
ning conditions of appliances [4]. More recently, [5] fo-
cused on the study of design trade-offs during the fea-
ture and model selection steps of the development of the
ML-based classifier for ILM. In their study they consid-
ered various statistical summaries for feature engineering
and classical machine learning techniques for model se-
lection. We complement the work in [5] by extending
the feature set with additional shape capturing values and
considering deep learning (DNN) and gradient boosted
trees (XGBoost) as promising modelling techniques. The
contributions of this paper are as follows:
We explore a variety of different statistical features and
show the ones capturing the shape of the time series,
such as longest strike above mean, longest strike be-
low mean, absolute energy and kurtosis yield superior
performance by up to 20 percentage points.
We show that our best DNN based model slightly out-
performs our best XGBoost by 2 percentage points at
the expense of increased training time. We also show
that our models outperform the results from [5] by 5
percentage points.
The paper is organized as follows. Section 2 summa-
rizes related work, Section 3 formulates the problem and
provides methodological details, Section 4 focuses on the
study of feature selection trade-offs, while Section 5 dis-
cusses model selection. Concluding remarks are drawn
in Section 6.
2 Related Work
Existing work that uses machine learning for ALM, such
as in [6] investigates the performance of deep learning
neural networks on NILM classification tasks and builds
a model that is able to accurately detect activations of
common electrical appliances using data from the smart
meter. More complex DNNs for NILM classification tasks
are presented by the authors in [3], where they introduce
a Long Short-Term Memory Recurrent Neural Network
(LSTM-RNN) based model and show that it outperforms
the considered baselines. In [7] they approach a simi-
lar problem by proposing a convolutional neural network
based model that allows simultaneous detection and clas-
sification of events without having to perform double pro-
cessing. In [8] authors train a temporal convolutional
neural network to automatically extract high-level load
signatures for individual appliances while in [9] a fea-
ture extraction method is presented using multiple par-
allel convolutional layers as well as an LSTM recurrent
neural network based model is proposed.
3 Problem formulation
Our goal was to design a classifier that when given an
input time series T, it is able to accurately map this data
to the appropriate class C, as shown in equation 1.
C= Φ(T)(1)
where Φrepresents the mapping function from time
series to target classes and C is a set of these classes,
where each class corresponds to one of the following house-
hold appliances: computer monitor, laptop computer, tele-
vision, washer dryer, microwave, boiler, toaster, kettle
and fridge. The appliances and measured data illustrated
in Figure 1 available in the public UK-Dale dataset are
used. The UK DALE (Domestic Appliance-level Elec-
tricity) contains the power demand from 5 different houses
in the United Kingdom. The dataset was build at a sample-
rate of 16 Hz for the whole-house and 0.1667 Hz for each
individual appliance. Data is spread into 1 hour long seg-
ments, each dataset sample contains a time series with
600 datapoints as depicted in Figure 1.
For realizing Φ, we perform first a feature selection
task followed by a model selection one. For selecting the
best feature set, we perform feature selection in Section
4. For model selection, we go beyond the work in [5] and
consider deep learning architectures enabled by Tensor-
flow and advanced decision trees that use on optimized
distributed gradient boosting technique available in the
XGBoost open source library as detailed in Section 5.
4 Feature selection
As can be seen in Figure 1, the time-series corresponding
to each device has unique shape and patterns, therefore an
intuitive approach to feature selection is to extract statis-
tical properties of the time series that would capture the
unique properties of the signals. For instance, a summary
such as the peak-to-peak value is able to capture the dif-
ference between the maximum and minimum value in a
time series signal while one such as skewness is able to
describe the asymmetry in the distribution of datapoints
in a particular sample. A good combination of such fea-
ture would be able to inform the model with relevant in-
formation about the power consumption of each appli-
ance, making it easier to find patterns in the data and per-
form classification task more accurately. Recently, stan-
dard tools for computing a large range of such summaries
Figure 1: Selected appliances, showing power in relation to time
over a 1 hour interval.
are provided by dedicated time series feature engineering
tools such as tsfresh 1.
Following an extensive evaluation of combinations of
time-series, we report the results for a representative se-
lection of three feature sets as follows:
FeatureSet1 - This feature set consists of the raw
time series, containing 2517 time series samples, each
with 600 datapoints. It is used as a baseline to see the
performance achieves with the available data.
FeatureSet2 - This feature set consists of: mean
value, maximum, minimum, standard deviation,
variance, peak to peak, count above mean, count
below mean, mean change, absolute mean change,
absolute energy. The count above and below mean counts
the numbers of values in each sample that are higher or
lower than the mean value of that same sample and helps
quantifying the width of a pulse such as the ones for the
toaster and microwave from Figure 1. The mean absolute
change gives the mean over the absolute differences be-
tween subsequent time series values. The absolute energy
represents the sum of squared values, calculated using
formula shown in equation 2 and provides the informa-
tion on whether a specific appliance has large consump-
tion profile or not.
E=
n1
X
i=0
x2
i(2)
FeatureSet3 - After taking a deeper look into the fea-
tures from FeatureSet2, we noticed that minimum is re-
1https ://tsfresh.readthedocs.io/en/latest/text/list of
features.html
dundant as it is usually zero in every sample and peak-to-
peak is in most cases equal to maximum value due to the
lowest value mostly being zero. This feature set consists
of: maximum, standard deviation, mean absolute
change, mean change, longest strike above mean,
longest strike below mean, absolute energy, kurtosis,
number of peaks in each signal. The longest strike
above and below mean returns the length of the the longest
consecutive subsequence that is higher or lower than the
mean value of that specific sample. The kurtosis is an-
other metric of describing the probability distribution and
measures how heavily the tails of a distribution differ
from the tails of a normal distribution.
Table 1: Feature comparison using the best models.
Model Feature set Precision Recall f1
DNN3 FeatureSet1 0.638 0.595 0.573
XGB3 FeatureSet1 0.799 0.769 0.779
DNN3 FeatureSet2 0.918 0.885 0.889
XGB3 FeatureSet2 0.869 0.864 0.867
DNN3 FeatureSet3 0.931 0.898 0.902
XGB3 FeatureSet3 0.888 0.889 0.889
DNN3 best[5] 0.893 0.887 0.888
XGB3 best[5] 0.861 0.860 0.861
SVM[5] best[5] 0.851 0.835 0.834
4.1 Results
The results of the feature selection process are listed in
Table 1 for the two techniques considered in this paper.
As can be seen from the second column of the table en-
titles instances, the dataset is balanced. From columns
3-5 it can be seen that for the baseline FeatureSet1, the
f1 score is 0.57 for the CNN and 0.77 for XGB. By using
features that better capture the shape of the time series
such as in the case of FeatureSet2, an improvement of
up to 20% can be seen as follows: the f1 of the CNN
model increasing to 0.89, the precision 0.92 and recall to
0.88. The XGBoost model also performed better with an
f1 of 0.87, precision of 0.87 and recall of 0.86. Finally, it
can be seen from the table that FeatureSet3 performs the
best with the f1 of 0.90, precision of 0.93 and recall of
0.90 for the CNN model and f1 of 0.89, precision of 0.89
and recall of 0.89 for the XGB model. FeatureSet3 per-
formed better than FeatureSet2 because its features had
much less correlation between each other as well as all of
the redundant features from FeatureSet2 were removed.
For FeatureSet3, a variety of different feature orderings
were also tested but the results remained more within 1%
accuracy variance.
To gain insights into the per class performance of Fea-
tureSet3 with the two techniques, we present per device
f1 score breakdown in Table 2. It can be seen that com-
puter monitor, microwave and kettle are classified worst
by all three models, as their similar consumption profiles
make it difficult for the models to distinguish between
them. Nevertheless, the CNN classifies all three the best
due to its superior pattern recognition ability.
Table 2: Per class performance, FeatureSet3 vs best [5]
Class Inst. CNN f1 XGB f1 [5] f1
monitor 300 0.827 0.833 0.780
laptop 276 0.983 0.932 0.838
television 300 0.992 0.976 0.941
washer/dryer 226 0.941 0.912 0.804
microwave 300 0.688 0.620 0.687
boiler 300 1.000 0.968 0.940
toaster 215 0.949 0.940 0.806
kettle 300 0.756 0.722 0.739
fridge 300 1.000 0.983 0.970
5 Model selection
For analyzing the performance of DNN and XGBoost for
our problem we conducted extensive performance eval-
uations. We started by developing a deep learning se-
quential model, which at first consisted of three dense
layers, each with an arbitrarily chosen number of neu-
rons. By trying different combinations of hyperparame-
ters such as number of neurons, loss functions, optimiz-
ers, batch size, number of epochs, number of layers and
learning rate, we came closer to finding the best suited
model for our problem. For optimizing certain hyperpa-
rameters we took advantage of the automatic hyperpa-
rameter optimization framework Optuna 2. We then ap-
plied similar optimization techniques on the XGB model,
although it’s default parameter configuration already gave
good results. All the experiments were ran on Google
Colab using an instance with Nvidia Tesla K80 GPU and
12.69 GB of RAM.
In this section we present and analyze three represen-
tative models from each class, DNN and XGboost respec-
tively.
5.1 Deep neural network
DNN1 - This model consisted of three fully con-
nected dense layers. The first two had 32 neurons each
as well as ReLU (rectified linear unit) activation function,
while the output layer had nine neurons, each correspond-
ing to one of the nine possible appliances and Softmax
activation function.
DNN2 - For this model we took the DNN1 model and
added an additional dense layer with 64 neurons as well
as changed the activation function to linear in the penulti-
mate layer. With this additional complexity we expected
to see better results.
DNN3 - For this model we introduced two 1D con-
volution layers, first with 128 filters and second with 64.
Then we used a flatten layer to reduce the dimensionality
of the output space, and make the data compatible with
the following dense layer, followed by another (output)
dense layer.
2https ://optuna.org
5.2 XGBoost
XGB1 - This is the model with standard configura-
tion, i.e. maximum depth of 3, 100 estimators and learn-
ing rate of 0.1.
XGB2 - In this model we increased the maximum
depth to 4 as well as first reduced learning rate by 50%
(to 0.05) and then increased the number of estimators by
50% (to 200). Doing this gave slightly better results.
XGB3 - For this model we decreased the maximum
depth to 2, increased number of estimators to 500 and
learning rate to 0.25.
Table 3: Model performance on FeatureSet3.
Model Precision Recall f1 Comp. time
DNN1 0.866 0.851 0.846 10.972s
DNN2 0.900 0.887 0.889 21.026s
DNN3 0.931 0.898 0.902 21.124s
XGB1 0.876 0.863 0.864 1.126s
XGB2 0.884 0.881 0.882 2.518s
XGB3 0.888 0.889 0.889 3.225s
SVM [5] 0.878 0.852 0.852 0.301s
5.3 Results
5.3.1 Classification performance
The classification performance of the models is provided
in Table 3. It can be seen that the best performing models
are DNN3 with an f1 score of 0.90 and XGB3 with an f1
of 0.88. However, the computation time of XGB3 is only
3.23s while for DNN3 it is 21.12s. The XGB classifier
using classical machine learning performed only about
1 percentage point worse than the CNN model, while at
the same time being much less complex and able to com-
plete the entire training process about 18 seconds faster
than the CNN. In addition, the XGB model is much eas-
ier to optimize since it has no hidden layers and a pre-
arranged hyperparameter configuration that usually re-
quires no further optimization at all. From the last line of
the table it can be seen that the SVM-based model from
[5] performs 5 percentage points less than DNN3 on Fea-
tureSet3.
5.3.2 Computation time
The superior performance of the DNN model comes at a
cost of increased algorithm complexity and hence longer
computation time. As depicted in Table 3 the first DNN
model took 10.97 seconds to complete the training pro-
cess and the best (most complex one) took 21.12 seconds.
XGBoost, on the other hand, was much faster with XGB1
taking only 1.12 seconds. The added depth for the XGB2
caused a slight increase in computation time to 2.52 sec-
onds, which further increased to 3.23 seconds due to the
high number of estimators used in XGB3. Finally, the
state of the art was the fastest to complete the training
process taking only 0.3 seconds but scored the worst in
terms of performance.
6 Conclusions
In this paper we investigated the design trade-offs during
the feature and model selection steps of the development
of the ML-based classifier for ILM. After formulating our
problem, we first show that by extracting various statis-
tical features from raw time series data and then training
our models with these features, we were able to improve
f1 score by up to 20 percentage points.
Second, we propose two different ML techniques and
our process of developing the proposed models using these.
We show that optimizing hyperparameters to better suit
our specific problem can improve their respective perfor-
mance by around 4 percentage points. However, choos-
ing the right features that better capture the shape of the
data has a much greater impact on the end results than op-
timizing the models. We also show that classical machine
learning model does not perform significantly worse than
the deep neural network based one, while at the same time
being less computationally expensive.
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An empirical study on energy disaggregation via deep learning
  • W He
  • Y Chai
W. He and Y. Chai, "An empirical study on energy disaggregation via deep learning," Advances in Intelligent Systems Research, vol. 133, pp. 338-342, 2016.