New chance for renewable electricity sources managing cooling devices
based on “The minA Concept”
Prof. Péter, FÖLDESI1, Eszter, GYÖRGY2, Richard, ZILAHI3 and Prof. Bojan ROSI4
Széchenyi István University/Department of Logistics and Forwarding, Győr, Hungary
Széchenyi István University/Department of Transportation Engineering, Győr, Hungary
3 Eötvös Loránd University of Sciences/Faculty of Informatics, Budapest, Hungary
4 University of Maribor/Faculty of logistics, Celje, Slovenia
1
2
Abstract— Renewable electricity production has the promise to be able to provide the energy for our
economies on a sustainable way. There is a strong need for “green logistics” solutions worldwide, as
transportation requires “green fuels” (bio-fuels, green electricity and/or hydrogen, etc.), and the facilities
alongside the supply chain (factories, warehouses) require green electricity sources. The availability of these
renewable sources is not predictable, so the integration of renewable energy production into the load levelling
control of the National Grid requires special solutions. There are some technically possible, but not financially
feasible electricity storage options today, and we can also use some DSM (demand side management)
methods we are presenting in our essay.
Keywords: renewable electricity, demand side management, domestic refrigerator
1. Introduction
Electricity-driven cooling is one of the most important consumer profiles – the world is using more
and more electricity for these purposes (residential, industrial). The logistics industry has huge
cooling energy demand as there are many storage locations and transport actions “from the field
to the table”, and there are cooling needs to keep the products in fresh and good conditions
during logistics activities.
Cooling demand has year-by-year growing part in total electricity consumption, especially summer
time. Industrial cooling is not changing as much during the year, but the electrical power need for
the same cooling energy is increasing in this period, because ambient temperature is higher. There
were many new air conditioner installations in residential areas and bureaus, offices, shopping
centres in the previous decade, so the summer peak electricity demand reaches nearly the winter
maximum (Földesi, Bódis, Bajor, 2012).
“The minA Concept” is based on our wire-logistics approach: according to the real nature of the
cooling demand through the supply chain it is possible to provide electricity infrastructure savings.
Applying “The minA Concept” as demand side management technique in modifying the daily
load profile of the electricity network can help system operators in shifting the supply system to a
more sustainable state.
In the actual phase of our research at Szabó-Szoba R&D Laboratory at Széchenyi University Győr
we are focusing on the control of a domestic refrigerator to prove the feasibility of the concept. In
our essay we present the test procedures and the results of the measures.
2. The Unit Commitment Problem
The power and energy industry – in terms of economic importance and environmental impact – is
one of the most important sectors in the world since nearly every aspect of industrial productivity
and daily life are dependent on electricity. Renewable energy provides clean and sustainable
approach to energy production, helps to ensure security of energy supply, and contributes to the
meeting of the Kyoto Protocol objectives.
From the customer side, availability of electrical energy is indispensable - the main function of
traditional electricity supply is to serve the consumer demand with solidly available (security of
supply) and satisfactory (quality of supply) electrical energy (with adequate frequency and
voltage). For the system operator it requests the integration of different sources (the base-load, the
regulated and the non-regulated power stations, the fluctuating renewable wind and photovoltaic
energy and in the future vehicle-to-grid units) and switch to the optimal network topology, in
accordance with changing demands – known as unit commitment problem (UC). (Földesi, Baricza,
Kiss, Vas, Bajor, 2010).
The new challenges in electricity supply, like de-regulation, distributed generation (co-, tri- or multigeneration) and electricity storage needs new theoretical approaches from the viewpoint of
logistics. Decentralized electricity production and the introduction of variable, fluctuating
(renewable) sources and transportation needs (electric vehicles) increase the difficulty of stabilizing
the power network, mainly due to a supply-demand imbalance. It is therefore convenient to
generate the energy, transmit it, convert it, and then store it if need be. Although there are various
commercially available electrical energy storage systems, no single storage system meets all the
requirements today. (Földesi, Baricza, Kiss, Vas, Bajor, 2010).
Unit commitment with renewable electricity sources and electrical energy storage is more complex
than typical UC of conventional generating units, as the number of variables is much higher than in
typical UC problems, and both cost and emission should be minimized. From the measurements of
the available renewable sources it can be clearly seen that the fluctuation of the solar and wind
sources could not have been well predicted. For higher utilization of these sources there is a strong
need for electricity storage solutions, or some new aspects of demand side management
techniques, we are investigating.
National electricity supply grids are constructed and re-engineered for the annual peak
consumption. The results of overdesigning are high infrastructure construction and operation cost,
also unutilized capacity in the same time. Our wire-logistics approach deals with demand side
management and renewable electricity applications to smooth the daily electricity profiles.
3. Using RC, RRC and Smart Metering DSM technologies for balancing
Some distribution system operators (DSOs) - among them all Hungarian DSOs - have installed
extensive demand-side management (DSM) infrastructure in order to be able to perform peakclipping and valley-filling of the daily load curves. These systems rely either on the traditional ripple
control (RC) or radio ripple control (RRC) technology (Dán et. al, 2010).
The Ripple Control system is a telegram based DSM system, where the carrier is the 50 Hz distribution
network. In Hungary the application of the system has been started in 1975, basically for switching
on and off boilers (electric storage water heaters) and high capacity storage space heaters. In the
beginning of the 2000’s the controlled power was approx. 1500 MW, which is one fourth of the
winter peak load. Applying RC system, hundred thousands of customers can be controlled from
one place, as the sending device can be installed on any voltage level from LV to HV. The
addressee can be either only one consumer, or a group of them.
The simple structure of RC could incur some possible problems, which are disadvantageous:
 One-way communication: the DSOs do not have any reply from the addressees whether
they received the message and fulfil the switching order or not?
 The distribution system is planned to transmit 50 Hz waveform: the transmission of other
frequency components is not ideal.
Nowadays the RC system is used for the following purposes in Hungary:
 Basic controlling (Tariff shift, Public lighting
 Customer’s load controlling (Boilers, Electric storage space heaters, Air conditioners)
 Other controlling purposes (Civil defence siren, Factory switching, Building
advertisement lights)
and
The control is based on sending standardized telegrams. The task of the Sender Device is to
generate the message with the proper power and voltage to reach all (including the furthest)
controlled customers. There are some new demands that cannot be realized using the traditional
RC system. In the beginning of 1990’s the Radio Ripple Control (RRC) has been started to realize.
The novelty of RRC (compared with RC):
 The messages are transmitted with long-wave antenna, thus the transmitting is independent
from the topology of the electric network.
 The addressing interval is much wider, it is possible to address millions of consumers with one
telegraph, thus it is enough to have one controlling frequency.
 It is possible to transmit messages to hundreds of kilometres, in some seconds
 The small gas motors and gas turbines are not affected.
Several goals can be set when the DSM is in focus, like daily load curve shaping, load limitation at
system breakdowns, or minimizing of balancing energy (i.e. the minimization of the deviation of the
actual load from the schedule)
There are many different aspects of simulation, like
 Investigation of possible base-cases (rescheduling, control)
 Tariff-based incentive (On the example shown below there is no significant difference in the
daily energy consumption, but he customers achieved some 13.2 % of the total energy cost
of controlled and reschedulable consumers. The morning and evening peak periods had
been reduced, but large gradient changes in the total load can be observed. The reason is
the behaviour of the rational customers: they would like to minimize the negative
consequences of rescheduling, thus they switch on their reschedulable appliances
immediately after the tariff gets lower.)

Direct DSM control (The load redistribution is more significant than in the tariff incentive
case. The steep load slopes can be reduced with DSM program optimization. It can be
concluded that the comfort of the customers have not changed in case of boilers and
deep freezers. The cost saving is much higher because the consumption is possible on a
very low tariff.)
Base case - Controllable
Base Case – Reschedule-able
Tariff incentive - Controllable
Tariff incentive – Reschedule-able
Direct DSM with Smart Metering
Fig.1: Cases of simulation (Dán et al. 2011)
It has been shown that the household customers can be incited with a dynamic tariff system in
order to reschedule their electric devices. This will cause consumption redistribution from the peak
load periods to the valley load period. However in case of system breakdown a fast (but smart)
load shedding can only be achieved with direct DSM. Thus the possibility of direct load control is
essential and should be exploited in Smart Meter systems.
Another reason to apply direct load control is the need to avoid large gradient load changes
observed when simulating customer response to tariff incentives.
It has also been demonstrated that load curve shaping can be performed more effectively if direct
load control is applied for boilers and deep freezers – compared to the case when only a tariff
incentive is applied. A special load control program is necessary for air-conditioners.
4. Domestic refrigerators in operation
Product temperature is a quality and safety determining factor. Some indications show that food is
often stored in domestic refrigerators at temperatures that are too high. In refrigerators without
ventilation, strong temperature heterogeneity is often observed, with warm zones (sanitary risk) and
cold zones (freezing risk) due to very low air circulation. (Laguerre et al. 2007)
Fig.2: Temperature distribution in space (Yang, 2009)
and in time, during the on-off cycles (Björk, 2010)
The most common way to control the cooling capacity in household refrigerators and freezers is by
on-off control (cycling or intermittent operation). The compressor starts as a preset temperature in
the refrigerated space is exceeded (cut-in temperature) and shuts down as a low temperature
(cut-out temperature) is reached. (Björk and Palm, 2010)
Since the compressor efficiency also declines as the ambient temperature rises, a refrigerator's
electricity use is very sensitive to the ambient temperature. Modest changes in kitchen temperature
will have surprisingly large impacts on refrigerator energy use. Electricity consumption varied from
1.25 to 2.6 kWh per day even though the temperature increased only 11 °C (from 17 to 28 °C). The
correlation is so good that it suggests that variations in ambient temperature cause virtually all of
the variations in energy consumption. Just like a house, a refrigerator will use less electricity if its
thermostat is re-set to a higher (warmer) temperature. The energy consumption rose 26% from the
warmest acceptable to the coldest possible settings, when all other test conditions were
maintained at the DOE values (Meier, 1995).
Room temperature varies due to seasons and the thermostat setting varies according to consumer
behaviour. The temperatures of the surveyed refrigerators were: average 6.6 °C, minimum 0.9°C
and maximum 11.4°C. The temperature of 26% of surveyed refrigerators is higher than 8°C, which is
the regulatory temperature for stable foods in France. The difference between the temperature
level during weekdays and weekends is not significant.
There are other parameters influences the energy need: There are results with empty and loaded
refrigerators, between various room temperature and humidity conditions, with different frequency
and length of door openings, thermostat settings, and the introduction of warm food.
It has been identified that the performance of household refrigerator depends strongly on
temperature and air distribution inside the storage chamber (Yang et. al, 2010)
5. Test measures on the field of “The mina Concept”
There are many new development pathways for having smart refrigerator – we can imagine one
that is equipped to sense what products are being put into it, and may even be able to determine
when a product needs to be replenished. The refrigerator may even be able to send alerts when
the food reaches a point where it may be suspect. This alert may be displayed on the refrigerator’s
screen or may be sent to a computer via e-mail. The smart refrigerator keeps track of what is in
stock through a couple of different methods. The method chosen often depends on the
technology available on the food package. Given the fact that the smart refrigerator is still largely
in the experimental stages, the technology is still evolving (for example RFID systems for automatic
recognition and tracking).
There are widely available pure technical developments, like having better insulation or more
efficient compressor unit, what consumes less electricity and performs better between part-load
conditions, etc.
Finally, we were not able to find any investment in the literature dealing with the daily consumption
profile of the domestic refrigerator.
Electricity supply systems suffer from the fluctuation of demand – without or just with little portion of
storage, this super-pull systems have to be agile, from the wire-logistics viewpoint.
On this way, overdesigning the production, transmission and distribution system required to be able
to provide the actual consumer demand moments-from-moments, according to our lifestyle.
Fig.3: The daily load profile of electricity consumption and the role of storage and demand-side management
(Földesi, Hegyi, Bajor, 2011)
When we wake up, maybe the first thing is turn the light on – this need is elementary. After, during
breakfast preparation, we usually open the door of the fridge, generally more than 3 times, and for
more than 2 minutes – and after closing the door, we can realize, that the compressor switched on
(the temperature reached the thermostat settings). As can be clearly seen on the profile, this
period has the highest kinetic challenge – any saving we can reach in this “morning upload and
peak” window provides huge benefit (the operation on the traditional way is very expensive without fulfilling the needs from storage, like hydropower – the national grid’s system operator have
to start expensive additional power plants, etc).
The main idea of “The minA Concept” is to shift this demand to another, GridfRiEENd (grid-friendly)
period (Földesi, Hegyi, Bajor, 2011). Naturally, this type of demand side management technique
can be acceptable, if the limitation not affects the quality of food in the refrigerator.
Applying “The minA Concept” in a case of a simple domestic refrigerator we installed a brand-new
Gorenje RF3184W type fridge in Szabó-Szoba R&D Laboratory. The purpose of the research is to
investigate which type of “variable setpoint strategy” can be able to help in smoothing the daily
electricity profile of households and shift the cooling demand from critical periods to non-critical
intervals. In the actual phase of our investigation we are focusing on to substitute the conventional
"thermostat-driven" control to a "microcontroller-driven, product temperature based" one to prove
the feasibility of the concept.
During the test procedure our Gorenje refrigerator is completed with a York-ISN microcontroller for
monitoring system parameters, like 6 analogue inputs for temperature sensors and additional 2
digital inputs, like
1.
2.
3.
4.
5.
6.
outside air temperature sensor (OUT-AIR),
refrigerator air temperature sensor (RFG-AIR),
freezer air temperature sensor (FRZ-AIR),
vegetable box air temperature sensor (VCM-AIR)
perishable product temperature sensor (PRS-TMP, a piece of bacon),
liquid product temperature sensor (DRN-TMP, a bottle of beer in the middle of the
refrigerator),
7. door opening contact (DOP-STA)
8. refrigerator thermostat status (THR-STA)
The York ISN microcontroller drives the only digital output for starting the compressor. During
thermostat-driven control strategy the microcontroller pass the incoming signal to the compressor
with 10 seconds delay, during peak limitation and minA strategy there are other system parameters
required to start cooling (time window enabled, temperature of the liquid reach a given level, etc).
A laptop computer was connected to the microcontroller to manage the operations and log
measurements in every minute.
FRZ-AIR
PRS-TMP
Fig. 4: The minA test environment
RFG-AIR
DRN-TMP
In the first phase of the investigation we made the test to recognize the thermostat-driven switching
points related to product temperature distribution with different manual settings. As a result we got
the thermostat-driven temperature profile of different settings near a given load (in our further
research we will test the impact of door openings and various loads).
The cooling process has different gradient where we consider different product or air temperature
values, according to different thermal inertia and heat capacity.
Fig.5: Temperature profiles of DRN-TMP at the case of starting the half-load test
In the actual phase of investigations we demonstrate the effect of applying “The minA Concept”
with “microcontroller-driven, product temperature based” control:




the base signal is the DRN-TMP value
setpoint varies during the day with ±0.5°C “switch on – switch off” tolerance
the pre-cooling setpoint is +3.0°C from 0 to 6
the normal setpoint is +5.0°C from 9 to 16 hrs


the emergency cooling setpoint is ±9.0°C from 6 to 9 and from 16 to 21
the peak limitation period is from 18 to 19, when compressor starts are disabled
Fig.6: DRN-TMP daily temperature profile with applying “The minA Concept”
Based on “The minA Concept” it is possible to reduce the number of switching operations, what
can extend the lifetime of the compressor unit and reduce the maintenance cost. Otherwise, in this
case we have to accept wider tolerance in the temperature profile.
Applying “The minA Concept” often request longer operation interval of the compressor unit for
cooling the products in the normal space, but in the same time the freezer can be over-cooled.
TH-Operations
ON
OFF
Minimum time (min)
22.00
6.00
Average time (min)
57.19
59.27
Maximum time (min)
398.00
807.00
Fig. 7: Operation intervals based on the traditional thermostat-control
MC-Operations
ON
OFF
Minimum time (min)
79.00
21.00
Average time (min)
255.72
161.89
Maximum time (min)
583.00
360.00
Fig. 8: Operation intervals based on “The mina Concept”
Fig.9: FRZ-AIR TH4
Fig.10: FRZ-AIR TH6
Based on the results of the test we can offer a possible gridfriend development of household
refrigerators: a balance valve between the freezer and the refrigerator
On this way we can solve the buffering task in 2 steps:
 1st: Buffer the energy of renewable electricity sources using DSM control, or switch off the
device when the electric system is overloaded (using various setpoints is possible not only
with the refrigerators, but all the other heat storage equipments as well, if the system
operator has information about the actual conditions of the device)
 2nd: Transmit the cold air from the freezer part to the refrigerator part when it is necessary
6. Conclusion
We considered the cooling demand (an electricity-driven service) of a domestic refrigerator in our
wire-logistics as a special need what sometimes can be delayed – in „The minA Concept” we
presents an economically and technically achievable, environmentally sustainable way of cooling
unit operations.
We introduced a new pathway in domestic refrigerator advancement based on our special wirelogistics approach – it is possible not just disable, but simple limit the operating conditions, or in the
deep valley periods (before morning peak and uploading, etc) use pre-cooling. Limitation or
disabling can be applicable in warehouses as well – the trucks with vegetables usually arrive in the
morning, unloading takes time, while the doors are open – it is possible not to start the refrigerator
units for cooling the street, etc.
In the successful integration of renewable electricity sources it is possible to use demand side
management control for matching renewable production and electricity-based cooling (RC, RCC,
DSM)
 having information about actual temperature of heat-storage equipment: thermoelectric
sensor and information for the system operator

improve the level of storage based on “The minA Concept”: using control tools instead of
enabling and disabling
From the electric system operator point of view the application of “The minA Concept”, as a tool
has great promises (it is possible to use on the same way, like night charge boilers and electrical
heaters) – there is no need for special infrastructure, the electric network can transmit the
“limitation” or “disabled” signal itself, no additional infrastructure required, only a cheap receivertransmitter electronics in the refrigerator. The question remain: will the producers be opened for this
type of innovations, or people will buy the required electronic equipment for centralized minAcontrol? Which type of tariff system can support these changes?
7. References
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Authors
Eszter, György – BSc student in transportation engineering
Széchenyi István University
Member of the Szabó-Szoba R&D Laboratory
Richárd, Zilahi – BSc student in infromatics
Eötvös Lóránd University Budapest
Member of the Szabó-Szoba R&D Laboratory
Péter, Bajor – electrical eng. Msc., teacher of eng. Msc. (PhD Student)
Széchenyi István University
Assistant Lecturer at the Department of Logistics and Forwarding
Member of the “Szabó-Szoba” Student’s Innovation and Education Development Laboratory
Péter, Földesi CSc – transportation engineer MSc
Széchenyi István University
Reader, Head of the Department of Logistics at Forwarding
H-9026 Győr, Egyetem tér 1. HUNGARY
E-mail: pbajor@sze.hu, Mobile: +36 30 63-73-270