ice-e info pack 17 temperature control

8/12/2019 ICE-E Info Pack 17 Temperature Control

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Temperature control strategies for smarter energy use

Sector Focus of electricity saving strategiesTemperature-related heuristics

for quality preservation

Refrigeratedstorage

For frozen products:

Peak avoidance techniques Sub-cooling of the warehouse during

weekends

Intelligent matching of load (variable and fixedcompressors capacity)

Adaptive defrost

For chilled products (dedicated storage):

Peak avoidance techniques (see heuristics)

Intelligent matching of loads

For controlled atmosphere storage:

Increasing evaporation temperature above therecommended storage temperature is apossibility (see heuristics)

For frozen products:

Peak avoidance and sub-cooling techniques shouldmaintain product temperatures within8 and25 oC

For chilled products:

Sub-cooling to temperatures below 0 oC is notrecommended for horticultural products (or otherssusceptible to freezing damage)

Sub-cooling to2 oC can be well tolerated by somedairy products (e.g. milk, butter, cheddar cheese)

In controlled atmosphere storage, tolerance ofcommodities to temperatures above therecommended storage temperature needs to beinvestigated experimentally. No temperature toleranceguidelines have been fully established for controlledatmosphere storage

Temperature is generallyconsidered asthe singlemos t impo rtant factor

determining the food qual i ty

and safety.

This definition means that a lot of other

process parameters or storage conditions

may more or less influence upon the food

product in different industrial situations, but

the temperature is the only physical value

whose importance is always enormous.

Hence, we will never be wrong to say that a

proper temperature control, temperature

control and again temperature controlis the

prime simple receipt for the success of every

food processor and retailer (Fikiin, 2003). The

temperature-controlled cold supply chain for

refrigerated processing, storage, distribution,

retail and household handling of foods is

ICE-EINFORMATIONPACK

therefore of paramount importance for

guaranteeing safety, quality, wholesomeness

and extended shelf-life of perishable

commodities (Fikiin, 2003; Cleland, 2010).

Reducing energy consumption throughout the

cold chain (and more specifically during cold

storage) is vital since about 40% of the global

food output require refrigeration, while 15% of

the electricity consumed worldwide is used

for refrigeration (including 8 % for industrial

refrigeration). Proper temperature control is a

key factor for achieving an economical use of

energy in the cold storage sector.

From the viewpoint of product safety and

quality, the Golden Ruleis that storage

temperature must be maintained as constant

as possible. In that context, numerous

product-specific data for the practical storage

life of different chilled and frozen

Table 1. Electricity saving strategies for refrigerated storage (Estrada-Flores, 2010)


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commodities, kept at the well known constant

storage temperatures, are published in the

specialized literature (ASHRAE, 2010; Fikiin

2003). However, as Table 1 implies, the

Golden Rulesand strategies for energysavings might often contradict the safety and

quality related requirements. For instance,

the so-called 'passive' Thermal Energy

Storage (TES) involves artificial temperature

fluctuations to accumulate cold in the

refrigerated products, when excessive and

cheap energy is available, and to release this

accumulated energy at the time of peak

loads, when the energy demand is higher

(Altwies and Reindl, 1999; Van der Sluis,

2008). Such approaches are very intuitive

and proven in real practice for many years.

The need for additional investment to build

real activeTES systems is thus avoided.

Recent achievements in information

technologies and automatics make it possible

to implement sophisticated temperature

control strategies for intelligent energy use.

This Info Pack focuses on a comparatively

simple strategy called Night Windafter the

name of FP6 Project No. 020045 Grid

Architecture for Wind Power Production with

Energy Storage through Load Shifting in

Refrigerated Warehouses(Night Wind),

where it was developed (Van der Sluis,

2008). The Night Windstrategy combines

the advantages of using a passiveTES

principle and a way to involve renewable wind

energy when covering the electricity demand

of cold stores on local level or Europe-wide.

The Night Windconcept

Distributed renewable energy resources

(such as wind and solar energy) have asubstantial potential for energy supplies and

reducing CO2emissions in Europe but have

been difficult to integrate so far because of

their intermittent contribution. The integration

of wind power into the national or EU energy

supply systems becomes more complicated

with increasing the production capacity of

Figure 1. Refrigerated foods are used for thermal energy storage as accumulators

of cold (Frozen foods are employed as a phase-change material.)

The Champion:

Potatoes / French

fries the mostrobust Night Wind

friendlyproduct

Passivethermal

energy storage

involves artificial

temperature

fluctuations to

accumulate cold

in the refrigerated

products, when

excessive and

cheap energy is

available, and

release of thisaccumulated

energy at the time

of peak loads,

when the energy

demand is higher


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installed wind turbines, because of the

mismatch of supply and demand of energy.

The wind energy is generated at random

times, whereas the energy use pattern shows

distinct demand peaks during day time and

office hours, and low consumption during the

night. Refrigerated warehouses are constant

power consumers (day and night), where

electricity is converted by the refrigeration

plant into artificial cold stored in chilled or

frozen products. The use of a refrigerated

warehouse for storing renewable wind energy

affords economic benefits from the cost

difference between low and peak-hour

electricity tariffs and permits to offset

undesired peaks in the electrical grid, as

shown in Figure 1 (Van der Sluis, 2008;Fikiin, 2011; Fikiin et al., 2009, 2010).

Energy is stored by producing more cold than

necessary (thereby refrigerating the products

below the prescribed temperatures), while

turning off the refrigeration plant releases

virtual energy matching the difference

between the average and the zero cold store

demands (and letting foods warm up back to

the recommended temperatures of storage).

For example, if the temperature of stored

frozen products throughout EU is permitted tovary by 1 C only, all refrigerated warehouses

can act as a giant battery on the gridthey

could store twice the planned EU's wind

power production for 2010 (Van der Sluis,

2008). While balancing the wind power

production by fossil fuel power generation is

inefficient, such balancing by refrigerated

warehouse load management is a

sustainable (environmentally friendly and cost

effective) alternative with reduced running

costs for the cold chain operators (Van der

Sluis, 2008; Butler, 2007; Fikiin, 2011).

Quality attributes offrozen foods undergoingtemperature fluctuations(freeze-thaw cycles)

Special attention is to be paid to the

refrigerated food quality as affected by the

Night Windtechnology. For that purpose,

quality attributes of selected frozen foods

undergoing temperature fluctuations (freeze-

thaw cycles) have been investigated.

Figure 2. Frozen storage at constant temperature (classical)

Figure 3. Frozen storage at variable temperature (Night Wind)

The quality of some frozen foods is less

affected by temperature fluctuations, while

it substantially deteriorates for more delicate

products, which require strictly constanttemperatures of storage


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Parallel tests have been conducted with 10

different food samples of identical type,

shape and size, stored during 8 months at

constant and variable temperature regimes

(Fikiin, 2011; Fikiin et al., 2009, 2010). The

samplesmeat (bacon), fish (smoked

Mackerel fillet), bakeries (fruit pie), fruit

(strawberries), vegetables (tomatoes, melons

and peppers), potatoes (blanched/semi-

grilled French fries) and ice cream have been

wrapped in plastic bags and boxes,

evacuated and frozen at a constant air

temperature of19 o as well as at a variable

temperature (with day-night cycles) ranging

from16/18 o down to 26/28 o, as

shown in Figures 2 and 3 (Fikiin, 2011; Fikiin

et al., 2009, 2010).

After 3 days, and 2, 4, 6 and 8 months of

frozen storage, the samples have been

thawed in air ambience up to a temperature

in the product centre of 20-22 o. Thus, a

number of quality attributes have periodically

been evaluatedtexture (by penetrometric

measurements), colour (by the method of

Gardner) and drip losses. Sensory evaluation

has also been carried out (with the aid of a

taste panel) to estimate the product appearance,

colour, flavour and consistency. Dataobtained have been summarised in the form

of tables, graphs and predictive equations

(Fikiin, 2011; Fikiin et al., 2009, 2010).

This study revealed that the quality of frozen

products subject to fluctuations of storage

temperature is generally acceptable but, as

expected, inferior in comparison with food

maintained at a constant temperature (in

compliance with the established food

refrigeration standards and good practices).

However, for many products this quality

decay is rather negligible and can be offset

by the obvious economic and sustainability-

related advantages of the emerging Night

Windtechnology (Fikiin, 2011; Fikiin et al.,

2009, 2010). In that context, potatoes (French

fries) appeared to be the most robust Night

Windfriendlyproduct (Fikiin, 2011; Fikiin et

al., 2009, 2010).

Night windcontrol

The aforementioned Night Wind concept

needs optimal strategies for fine control of the

cold store operation, based on economic

Electricity tariffs for corporate industrial users(valid for the Sofia regio n sin ce 01.07.2007, CEZ Electro B ulgaria Ltd .)

Price without VAT and tax(BGL / kWh)Subscription plan Time zones

Medium voltage Low voltage

Peak charge 0.106 0.116

Day 0.060 0.056Three-tariff plan

Night 0.032 0.018

Day 0.081 0.085Two-tariff plan

Night 0.032 0.018

Flat rate All the time 0.077 0.079

1 EUR = 1.95583 BGL, Low voltage: 230/400 V, Medium voltage: 6.3/10.5/21 kV

Figure 4. Electricity tariff depending on the subscription plan

Figure 5. Electricity tariff variation on the stock market


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The work associated with this information pack has been carried out in accordance with the highest academic standards and reasonable endeavours have been made to achieve the degree of reliability andaccuracy appropriate to work of this kind. However, the ICE-E project does not have control over the use to which the results of this work may be put by the Company and the Company will therefore be deemedto have satisfied itself in every respect as to the suitability and fitness of the work for any particular purpose or application. In no circumstances will the ICE-E project, its servants or agents accept liability howevercaused arising from any error or inaccuracy in any operation, advice or report arising from this work, nor from any resulting damage, loss, expenses or claim. ICE-E 2012

For more information, please contact: Kostadin Fikiin ([email protected])

References

Altwies J.E. and Reindl D.T.(1999).Passive thermal energystorage in refrigerated warehouses.Proceedings of the 20th IIRInternational Congress ofRefrigeration, Sydney, Australia

ASHRAE (2010).ASHRAEHandbook: Refrigeration.

Butler D. (2007).Fridges could savepower for a rainy day. Nature News.Available at:http://www.nature.com/news/2007/070205/full/news070205-9.html

Cleland D.J. (2010).Temperaturecontrol and energy efficiency in coldstorage. Proceedings of the 1st IIRInternational Cold Chain Conference,Cambridge, UK.

Estrada-Flores S. (2010).Achievingtemperature control and energy effi-ciency in the cold chain. Proceedingsof the 1st IIR International Cold ChainConference, Cambridge, UK.

Fikiin K.A. (2003).Novelties of FoodFreezing Research in Europe andBeyond. Flair-Flow Europe SyntheticBrochure for SMEs No.10 (ISBN: 2-7380-1145-4), INRA: Institut Nationalde la Recherche Agronomique, Paris(France), 55p.

Fikiin K.A. (2011).Refrigeratedwarehousing as a smart tool to storerenewable energy for improving the

food chain and power supplysustainability. Proceedings of the 6thInternational CIGR TechnicalSymposium "Towards a SustainableFood Chain", Nantes, France

Fikiin K., van der Sluis S.,Paraskova P., Iserliyska D. andTsokov L. (2009).A sustainablecold chain technology for storingrenewable energy in refrigeratedwarehouses and its implications onfood quality. Proceedings of theEFFoST Conference "NewChallenges in Food Preservation",Budapest, Hungary

Fikiin K., van der Sluis S.,Paraskova P., Iserliyska D. andTsokov L. (2010).Sustainabilityenhancement of refrigeratedwarehousing by using frozen foodsas a phase-change material to storerenewable energy. Proceedings ofthe 9th IIR Conference on Phase-Change Materials and Slurries forRefrigeration and Air Conditioning,Sofia, Bulgaria

Van der Sluis, S. (2008).ColdStorage of wind energyNightWind. 4th International Congress forSouth-Eastern Europe EnergyEfficiency and Renewable Energy

Sources, 4-9 April, Sofia, Bulgaria.

criteria (e.g. balance between the

instantaneous wind energy production and

actual electricity demand, predicted

dynamic/stochastic variations of electricity

tariffs on the stock market, etc.), along with

engineering and food quality requirements.

For that purpose, a control system has

been created to manage in real time the

wind power integration, depending on the

store refrigeration demand, the intermittent

availability of wind energy, the stepwise or

stochastic variations of electricity prices on

the stock market (Figures 4 and 5), and other

factors (Van der Sluis, 2008; Fikiin, 2011).

The control system (Figure 6) can serve: (i)

as a decision-support information system to

assist the cold chain operator when taking

decisions on the most profitable pattern of

energy use, or (ii) as an expert system

embedded in the hardware and software for

fully automated control of the store.

Economic benefit andprecautions

The Nigh Windtemperature control

strategy has been demonstrated at the

store of Partner Logistics BV (at Bergen op

Zoom, the Netherlands)one of the largest

frozen food stores in Europe (for 680 000

pallets). This refrigerated warehouse stores

basically French fries, whose quality

remains almost the same after daily

temperature fluctuations and freeze-thaw

cycles. Van der Sluis (2008) reported a very

substantial real profit from implementing the

Night Windtechnology at Partner Logistics.

Let us remind the reader that load-shifting

TES strategies do not save energy as awhole, but dramatically reduce the peak

energy loads, save money and balance the

electricity grids, thereby contributing to the

overall energy related sustainability of the

EU economy.

If you want to try the Nigh Windtechnology

at your own cold store, this should be made

with extremely high attention, care, due

diligence and compliance with the

established food standards and regulations.

Please be aware, that small errors mightbadly damage all your stored produce. The

best way is to contact competent food

technologists, food refrigeration experts or

directly the Night Wind coordinator

(http://www.nightwind.eu ). Many delicate

products are not at all suitable to endure

temperature fluctuations, so that a careful

and detailed examination of your own

products is needed before any dangerous

industrial exercises with large quantities of

expensive produce.

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Optimal switchingsequence

Prediction of wind energy

Energy price forecast APX NWCS

Cold store model

Figure 6. The "Night Wind" control system
http://www.nature.com/news/2007/070205/full/news070205-9.htmlhttp://www.nature.com/news/2007/070205/full/news070205-9.htmlhttp://www.nature.com/news/2007/070205/full/news070205-9.htmlhttp://www.nightwind.eu/http://www.nightwind.eu/http://www.nightwind.eu/http://www.nightwind.eu/http://www.nature.com/news/2007/070205/full/news070205-9.htmlhttp://www.nature.com/news/2007/070205/full/news070205-9.html

ice-e info pack 17 temperature control

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