194_voltage reduction in supermarkets

7/28/2019 194_Voltage Reduction in Supermarkets

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Voltage reduction

in

supermarkets

Feb 2012

Martin Braun


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Voltage reduction in supermarket

Abstract

A few decades ago experiments were conducted to see if a reduction in voltage also reduced the demand for

energy. Interest in this approach has increased over recent years in different quarters including supermarkets.

This project examines the potential for energy savings for supermarkets by reducing the supply voltage and

focused on two of their major consumers of electricity: Lighting and centralised refrigeration. It was found that

for lighting energy savings depends on the actual light fittings installed and that for centralised refrigeration no

energy savings could be verified.

1. IntroductionThe idea of saving energy by reducing voltage is not new.

For instance in the 1970s and 1980s, there were various

trials conducted in the US to prove its feasibility [1-3].

Therefore it is not surprising that now, when the

reduction of electricity consumption is an important topic,

this approach is being investigated again. Generic

guidance is available on the appropriateness of voltage

management [4] and specific appliances have also been

examined (e.g. domestic appliances [5]).

The investigation here focuses on the retail sector in the

UK, which uses about 3% of total electrical energy [6], in

particular on supermarkets. Therefore more efficient use

of electricity will not only benefit this industry, but the UK

at large. Hence this sector is looking at various ways to

achieve this end. For example, Morrisions expects to

reduce the total store energy demand by up to 7%

through voltage optimisation [7].

The scope of the experiments includes two of the major

categories of electrical equipment found in a supermarket:lighting and centralised refrigeration. How they were

tested and their test results are described in the sections

Lighting and Refrigeration, but, first, an introduction to

the idea of voltage optimising is given. The section on

conclusions discusses the findings and puts them into the

wider context.

2. TheoryThe consumed electrical energy is the time integral of

power. Hence, to reduce energy consumption, either the

time or the power (or both) needs to be reduced while, at

the same time, the other component must not increase

proportionally (or even disproportionately).

Voltage reduction as a means of saving energy in the UK

relies on the large voltage tolerance of 10% (i.e. from

207V to 253V) [8]. For historic reasons, the voltage is

frequently considerably above the lower limit [4] at which

CE marked equipment should be able to operate.

Therefore reducing the voltage may also lower the power

consumption as power is a function of voltage, current

and the power factor. However, as these three factors are

load-dependent, they may not be independent of each

other. Hence the load has to be investigated to get the

real picture.

3. LightingThe lamps examined here include different types of

fluorescent lamps, i.e. with an external ballast and

compact lamps. The compact lamps came from three

different brands (including one unbranded CFL). The

experiments also examined metal halide and LED lamps

(see Table 1).

Technology Description

Fluorescent 58W linear with inductive ballast

Fluorescent 58W linear with electronic ballast

Fluorescent 3 x 24W linear with electronic ballast

Fluorescent Compact 9W





Metal Halide 4 x 35W with inductive ballast

Metal Halide 1 x 35W with electronic ballast

Metal Halide 1 x 70W with electronic ballast

LED 10W tube

LED 22W tubeTable 1: Lamps examined

Remarks: Blue lines - test leads,

Black lines - Power to lamp

Figure 1: Test set-up Lighting

The schematic of the test set-up in Figure 1 shows that the

voltage was varied through an autotransformer. Multi

meter No 2 logged both the voltage and the power (multi

meter No 1 was used for indication only). The lux meter

measured any relative change in light output. In addition,

the current and voltage wave forms were recorded with a

storage oscilloscope.

1.1 Results External ballastFor ease of comparison the lamps tested here are broken

down into three different categories. The first relates to


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fluorescent and metal halide lamps with external ballasts.

The graphs in Figure 2 indicate that there is virtually a

linear relationship between the relative voltage and

relative power for the inductive ballast and no

dependence on the input voltage for the electronic ballast

(all values are normalised to 230V). The same relationship

also holds for metal halide lamps. In addition to this, one

finds that illuminance behaves essentially the same as thecorresponding power.

Figure 2: 58W linear fluorescent lamp Power consumption

The power consumption of lamps with an inductive ballast

is 10% (metal halide) to 16% (58W linear fluorescent)

higher than the equivalent lamp with an electronic ballast.

1.2 Results Compact fluorescent

Figure 3: Compact fluorescent lamps - Power consumption

Based on voltage-power graphs compact fluorescent

lamps can be sub-divided into those around 10W (i.e. 9W

and 11W) and the higher power lamps. The lower

powered devices behave in a very non linear way as can

be seen in Figure 3. At some point below 230V (100% of

voltage) the power consumption rises as the voltage is

reduced. This behaviour is not observed with the

remaining three lamps with a higher power rating. They

show a relative linear relationship.

Looking at the test results further it can also be seen thatcompact fluorescent lamps consume about 30% more

than their rating at 230V. Additionally, the data also

reveals that, for compact lamps, the illuminance falls

linearly between 0.67 (9W) to 1.35 percentage point (21W)

per 1 percentage point of voltage reduction.

1.3 Results LED lampsFigure 4, relating to the two LED lamps, shows not only

the power graphs, but also includes the plot for the

illuminance of the 10W lamp and shows that the light

output is independent of voltage (this is also true for the22W lamp). Furthermore the figure shows that for the

smaller of the two lamps the voltage reduction results in a

reduction in power demand below 230V. The power

consumption of the larger lamp exhibits virtually no

dependency on the input voltage.

Figure 4: LED lamps - Power and illuminance

4. RefrigerationThis section describes the experiments performed on a

centralised refrigeration plant installed in a training facility;

therefore the cooling load is smaller than would be

expected for a system of this size (under unforced, normal

condition the plant uses about 25% of its maximum power.

Maximum means all compressors and fans running). As

Figure 5 shows, for this series of experiments, the electric

part of the system was fed through a voltage optimisation

system which allows control of the voltage between 220V

and the mains voltage level. The set-up has two main

meters (9F08 for all compressors and 912 for the fans)

and three sub-meters, one for each compressor.

Compressor No 3 is supplied through a variable speed

drive; the others are directly fed.

The test programme included three parts which lead to

three data sets relating to:

1. Time intervals before and after the installation of thevoltage optimisation equipment.

2. The variation of the voltage at normal operationconditions.

3. The variation of the voltage under full loadconditions (i.e. all three compressors and all four

fans running simultaneously).

As meter 908 did not read I3 correctly after the

installation, only the power consumption of phases 1 and2 were examined to see if there was a reduction in energy

consumption. With this in mind the energy consumed

75%

80%

85%

90%

95%

100%

105%

110%

115%

120%

125%

90% 95% 100% 105% 110%

Relativepower(%)

Relative voltage (%)

Inductive ballast Electronic ballast

75%

80%

85%

90%

95%

100%

105%

110%

115%

120%

125%

90% 95% 100% 105% 110%

Relativepower(%)

Relative voltage (%)9W 11W 18W 20W 21W

75%

80%

85%

90%

95%

100%

105%

110%

115%

120%

125%

90% 95% 100% 105% 110%

Relativepower

,illuminance(%)

Relative voltage (%)

10W - Pow (%) 10W - Illu (%) 22W - Pow (%)


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before and after installation was compared and the

results are summarized in Figure 6. Although the data is

not entirely consistent, it does not support a claim of

reduced energy demand. The case for the fans metered

through 912 is similar so that no overall energy savings

were found.

Remarks: Black lines: Power

Blue lines: Measuring total through 908 or 912Purple lines: Sub-metering components

Figure 5: Test set up Refrigeration

As meter 908 did not read I3 correctly after the

installation, only the power consumption of phases 1 and

2 were examined to see if there was a reduction in energy

consumption. With this in mind the energy consumed

before and after installation was compared and the

results are summarized in Figure 6. Although the data is

not entirely consistent, it does not support a claim of

reduced energy demand. The case for the fans metered

through 912 is similar so that no overall energy savings

were found.

Time Average Energy 1 Average Energy 2

27 Jan 07

9:00-12:00 1.01kWh/h 0.94kWh/h

15:00-18:00 1.23kWh/h 1.07kWh/h

Change (%) 22.14% 14.01%

11:00-12:00 1.19kWh 1.12kWh

16:00-17:00 1.27kWh 1.08kWh

Change (%) 6.71% -3.81%

26 Jan 02

16:00-17:00 1.09kWh 0.98kWh

Change (%) 16.5% 10%Figure 6: 908 - Comparing before and after

To verify these findings the data set relating to the voltage

variations under normal conditions was also analysed and

the data is visualised in Figure 7. This figure displays the

star voltages and the energy meter reading. If the gradient

of the energy reading is constant, then there is no change

in energy consumption, which is the case not only for 908

(average energy consumption per phase: 1.5kWh/h), but

also 912 (not displayed here, average energy consumption:

0.8kWh/h).

Finally, the system was tested under full load conditions

by adjusting the refrigeration plant settings accordinglyand then increasing the voltage from 220V to about 240V

in 5-Volt steps. At each step the power readings were

taken and then the system was allowed to recover before

proceeding. The top ten power readings in each interval

were averaged and then analysed. It was found that the

overall power consumption drops slightly when the

voltage is reduced. The graphs for the individual motors

are displayed in Figure 8. This figure that the VSD driven

motor is essentially voltage independent, the fans seem to

consume less power at reduced voltage (r=0.8) and thatpower demand of compressor No 1 increases as the

voltage drops, but that the behaviour of compressor No 2

is not so clear.

Figure 7: Energy reading under normal load conditions for 908

Figure 8: Power vs voltage graph of components

5. ConclusionsHere, the question of whether a reduction in voltage on

lighting and centralised refrigeration saves energy in a

supermarket was investigated. The findings show that for

lighting it depends on the actual light fitting (see Table 2)and that for the refrigeration plant no energy savings

were observed.

The colour coding in Table 2 helps to break down the

results with regards to saving potentials. Highlighted in

green are light fittings which show a reduction of about 2

percentage per percentage of voltage reduction. These

findings also agree with guidance given in [4].

Furthermore it was found that, not only is the power

demand of the actual lamp voltage dependent [9], but

also the inductive components add to the power

consumption. For the fluorescent lamp and the metal

halide they add 16% and 10%, respectively. The savings ofthe higher rated CFLs are greater than observed in [5]

which may be because the components of the actual CFLs

95%

100%

105%

110%

220 225 230 235 240

P

ower(%)

Voltage (V)909 910 911 912


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tested might have been different. Incidentally, the power

ratings of CFLs were about a third below their real power

consumption (at 230V) measured during the experiments

here.

The yellow shaded rows indicate small savings or a more

complex case. For instance, the power demand drops for

the 10W LED tube below 230W by just over one

percentage point for every percentage point of voltagereduction whilst keeping its light output virtually constant.

Such a relationship is to be expected because the light

output of an LED depends on the drive current (for an

example see [10]). A less straightforward case is the lower

rated CFLs where, unlike their higher powered

counterparts, the power demand can actually increase

with voltage reduction. The difference may stem from

different values of the circuit components. If, for example,

all CFLs used the VK05CFL IC, then some of the

component values would be different for the lower power

CFLs.

Technology Description

Fluorescent 58W linear with inductive ballast


Metal Halide 4 x 35W with inductive ballast



LED 10W tube



Fluorescent 58W linear with electronic ballast

Fluorescent 3 x 24W linear with electronic ballast

Metal Halide 1 x 35W with electronic ballastMetal Halide 1 x 70W with electronic ballast

LED 22W tubeTable 2: Result Lighting

Finally, pink denotes that power demand is voltage

independent and therefore voltage optimisation measures

are not effective. Apart from the 22W LED tube, these

light fittings use relatively sophisticated external

electronic ballast, which, not only makes the light fitting

voltage independent, but also corrects the power factor

so that an almost pure current sine wave is produced.

During the second set of experiments relating to the

refrigeration plant no energy savings were observed

through voltage reduction. If this plant can be treated as a

thermostat controlled device, then the findings here are

consistent with [4] and [5]. Thermostat controlled devices

can be thought of as consuming the same energy even if

the input power is reduced as energy is not necessarily

proportional to the power input. (One notable exception

is where the load is permanently on; as frequently is the

case with lighting).

To verify these findings it would have been ideal to

conduct the same experiment more than once, but,

because of time constraints, is was not possible. It was

also unfortunate that the data normally stored in the

voltage optimisation equipment could not be retrieved.

The examinations of the individual compressors and fans

showed that the behaviour of a given motor depends,

amongst other things, upon its load and mode of control.

The power demand of compressor No 3, for instance.

which is controlled through a VSD, is independent of the

input voltage [4]. On the other hand, for compressors No

1 and No 2, which are directly mains fed, the power

consumption actually increases as the voltage is reduced(albeit it that the relationship is relatively weak for

compressor No 2). A possible explanation is that these

compressors have to deliver the same mechanical output

power regardless of its input voltage. So, as the voltage

drops the current increases driving up the electric losses

in the motor disproportionately (as Ploss = I2

* R).

The case for the fans is different again. Here both the fan

speed and fan torque are reduced with decreased voltage

(the relationship between load torque and speed is

relatively complex) [11], (page 206). Therefore, as the

output power is proportional to torque and speed, the

power demand drops as the voltage is brought down.

Acknowledgments

The author wishes to gratefully acknowledge the helpful

guidance of Dr David Stone, University of Sheffield, as well

as Mr Keith Bertie and Mr Matthew Maaer, Oaksmere and

the staff from iVolt for their help.

References

1. Scalley, B.R. and D.G. Kasten, The effects of distribution

voltage reduction on power and energy consumption.

IEEE Transactions on Education, 1981. 24(3): p. 210-

216.2. Gustafson, M.W., Residental End Use Load Affected by

Voltage Reduction. IEEE Transactions on Power

Apparatus and Systems, 1981. PAS-100(11): p. 4381-

4388.

3. Kirshner, D. and P. Giorsetto, Statistical Test of Energy

Saving Due to Voltage Reduction. Power Apparatus

and Systems, IEEE Transactions on, 1984. PAS-103(6):

p. 1205-1210.

4. Trust, C., Voltage management, 2011, Carbon Trust:

London.

5. Hood, G.K. The effects of voltage variation on the

power consumption and running cost of domestic

appliances. in Australasian Universities Power

Engineering Conference. 2004. Brisbane, Australia.

6. Tassou, S.A., et al., Energy consumption and

conservation in food retailing. Applied Thermal

Engineering, 2011. 31(2-3): p. 147-156.

7. Morrisons, Corporate responsibility review 2011/11,

2011.

8. BSI, BS7697:1993 Nominal voltage for low voltage

pulbic electricity supply systems, 2003, BSI: London.

9. Simpson, R.S., Lighting control : technology and

applications2003, Oxford Focal.

10. Mobicon, Data sheet for 5mm super white LED,

Surplustronics, Editor, Surplustronics: Auckland City.

11. Hughes, A., Electric motors and drives. 3rd ed2006,

Oxford: Elsevier.

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