Energy conservation in environmentally controlled facilities R. L. Opila

Economies d'6nergie dans les installations environnement contr616 On examine/es facteurs ayant une incidence sur /e coot de/'#nergie dans /'exploitation des entrep6ts frigorifiques. La demande d'#/ectricit6 doit #tre limit4e pour obtenir /es tarifs /es plus bas dans /es

conditions du contrat avec /a compagnie de distri- bution #/ectrique. L'entrep6t frigorifique doit #tre agenc~ pour I'entreposage Iogique des produits dans /es diff#rentes zones de temperature. La de- mande de froid est maintenue ~ un niveau bas non seulement en utilisant I'#paisseur optimale d'iso/ation mais en apportant une attention #ga/e I'entrbe de vapeur d'eau et b /'infiltration d'air. Le choix du materiel est essentie/ aussi, ainsi qu'un entretien satisfaisant.

Factors governing energy costs in the oper- ation of refrigerated warehouses are dis- cussed. Electrical demand must be controlled to achieve the cheapest rates within the conditions of the electrical supply contract. Cold store layout should be designed for logical storage of material between different

temperature zones. Refrigeration demand is kept low not only by using the optimum thickness of insulation but by equal attention to water vapour inflow and air infiltration. Equipment choice is also crucial, together with good maintenance.

Six years ago, when many of the facilities operating today were already built, energy was very cheap. It is not news that this situation has changed. This paper deals wi th ways to conserve energy and thereby lower operating costs. It wil l be restricted to the design of new facilities and the selection of equipment, but many of the points discussed can also apply to existing units.

Study ing the e lectr ica l p o w e r c o n t r a c t

If we are going to be effective in reducing the cost of energy, then a good place to start is the electrical power contract. The way electrical power is gene- rated and used results in several complicating factors in how we pay for power.

The first is the fuel adjustment factor by which the uti l i ty company adjusts its charges as fuel costs change. Fuel costs can vary on a daily basis and the electrical uti l i ty wil l then pass on these variations in fuel cost to the consumer by the fuel adjustment factor. This avoids the very time consuming nego- tiations required to change the base rate for power.

A second factor is the demand charge which is a result of the fact that most industry begins work at about the same time, and the electrical uti l i ty must have the generating capability to handle the extreme demand placed on their power generating stations between 7.00 am and 9.00 am when all the elev- ators in the office buildings are funct ioning at maximum capacity and when motors in many

The author is the President of the Globe Engineering Company, 222, North Dearborn Street, Chicago, Illinois 60601, USA. Paper received 2,6 May 1980

industries are starting up and drawing high starting currents. The demand charges appearing in the usual contract can cause payments far above the base power charge.

A third item encountered is power factor wherein we pay for the inefficiencies of electrical c o n - sumption when we do not operate motors at, or near, unity power factor.

A fourth factor coming into play today includes a t ime-of-day usage charge. In some cases, a one power charge is made for power consumed be- tween, for example 7.00 am and 11,00 pm, and a far lower charge is made for between 11.00 pm and 7.00 am. These rates can differ by as much as four times.

A fifth rate adjustment used by the uti l i ty companies is that of having different charges for electrical consumption in summer as compared to winter. Because of the high power requirements currently experienced in the summer months to handle air condit ioning equipment, uti l i ty companies are promoting a summer-winter differential in the power charge.

Due to these various types of charges a reduction in electrical power charges can result if warehouse layout, operations and equipment are considered jointly.

W a r e h o u s e design

Any warehouse layout can be seen in two ways. The first of these is on a tonne-ki lometer basis so

0140-7007/80/050299-03S02.00 Volume 3 Num@o 5 Septembre 1980 © 1980 IPC Business Press Ltd and IIR 299

that the distance travelled is minimized when stocking the warehouse and dur ing order fitling. The 80-20 rule, or a variation thereof, is useful in estab- lishing the basic warehouse design where 80% of the volume results from only 20% of the items stored in that warehouse. The other aspect of layout involves areas where environmental control is needed. These areas should be arranged in a logical fashion to minimize the temperature differences between adjacent spaces. Once the layout has been finalized, then the specifics of warehouse and equipment selection can be developed.

In the case of environmentally cÙntrÙÁÁed wa- rehouses, three major concerns exist. These are: the amount of heat loss or gain through the walls by conduction; the amount of water vapour passing through openings in the insulation and vapour barrier system; and the infiltration of air.

Insulation is one of the better understood areas of energy conservation. It is quite obvious that as power costs increase, greater thicknesses of in- sulation are justified. The transmission of water vapour through building walls and membranes can also cause much energy to be wasted as it conde- nses and changes to ice,

Probably the least understood area is air infiltration and this can cause large additional loads on an environmentally controlled warehouse. Window and door requirements and placement, and the provision of air-locks, are key factors in conserving energy. Where high infiltration occurs in a freezer wa- rehouse, air units should be located to the back of the room and should blow towards the opening doors or air lock. This wil l keep floors dry and reduce defrosting.

Selection of equipment

Where the temperature has to be maintained at 5- 10°C, fan coil evaporator units operating with wet coils can be used. These wil l provide 10% more capacity than a frosted coil and wil l not have to be defrosted, thus saving approximately another 10- 15% in capacity. Rooms operating below 5°C require fan coil evaporator units with frosted coils. The fin spacing used on evaporator coils can have a substantial bearing upon the 0nit's ability to provide adequate refrigeration. The most common spacing is about 6 mm between fins, and increasing it extends the time a f in-coi l evaporator unit may be operated before requiring defrosting.

If blast freezers are needed, evaporators with fewer rows of coils and higher air movement capacity wil l produce the best results. It is especially important that air is directed by baffling to insure that it wil l pass through the product as many times as possible.

When selecting refrigeration compressors, the compressors should be sized to take full advantage of the condit ions imposed on the system by all Operations, including those periods of lowest

demand. The motors driving the refrigeration com- pressors should be operating as close to capacity as is practical under the range of conditions. When installing a new refrigeration system, it is important that oil separators are installed in the discharge of booster and high-stage compressors to make sure that the oil is removed before it can coat the inside of the heat exchange surface - - w h i c h , in turn, reduces overall operating efficiency. It is also very important to make sure that the piping installed in the entire refrigeration system is large enough to maintain low pressure drops.

Maintenance of the equipment

Once installed, a refrigeration system should be maintained in peak operating condit ion, including frequent inspection of hot gas defrost solenoid valves to make Sure that they are not bleeding hot gas when they should be closed. Liquid line check- valves and suction solenoid valves should be closed when units are being defrosted. Recirculating rates should be checked, evaporator unit coils should be inspected to make sur e they are completely de- frosted, evaporator unit fans should be inspected to make sure that they are operating and non- condensible gas should be purged from the system in accordance with the manufacturer's instructions.

During defrost the evaporator fans should be shut off conserving, not only the energy required to run the fan, but the sensible heat generated in the room from the running fan. A 3.71 85 kW (5 HP) fan motor is equivalent to 3.51 685 kW (1 ton of refrigeration). When underfloor heating systems are used they should be watched carefully and the temperatures should be monitored so that they may shut down whenever possible.

Further energy conservation can be obtained by util izing the heat from the refrigeration system's condensing equipment to heat water used for clean- up or washing purposes, or it can be used to heat areas within the warehouse or warehouse office.

Lighting in refrigerated areas can be a very large source of inefficiency. You pay not only for the electricity to light the plant, but also for the re- frigeration needed to then overcome the heat created from the lighting. If possible, high pressure sodium, metal halide, fluorescen't l ighting or mercury vapour l ighting should be installed instead of incandescent lighting. Area l ighting should be used where possible and minimum light levels should be designed for the balance of the warehouse. Obviously, l ighting should be used only when needed and should be turned off at all other times, consistent with the accelerated wear caused by frequent starts. If at all possible, the ballasts required for the various types of l ighting fixtures should be situated outwith the refrigerated space to reduce the load on refrigeration equipment.

Minicomputers can be applied successfully to overall plant operation through load shedding programs which wil l reduce demand charges, and

300 International Journal of Refrigeration

by optimum scheduling of stocking and order- picking~

Conclusions

The reduction in cost of energy begins with a thorough understanding of the electrical contract for

each facility, followed by the development of the lowest operating cost by the combination of oper- ational considerations and equipment selection Each situation requires separate study since no two situations are identical. Too often, these responsibi- lities a r e left to maintenance personnel who are not trained to evaluate the overall performance of a system

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CRYOGENICS Handbook edited by, Beverley Law

Published in association with CRYOGENICS, the Cryogenics Handbook is an international directory of equipment, manufacturers and research at low temperature. Compiled from information supplied by manufacturers and researchers from all parts of the world this book will prove an invaluable aid to project planning as well as providing a general awareness of the cryogenics industry.

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The Cryogenics Handbook will prove to be an indispensable companion to all those concerned with engineering at low temperatures. July 1980 0 86103 21 4/cloth/352 pages/£15.00 net in UK only

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Volume 3 Number 5 September 1 980 301