Analysis of Design Factors for Power, Heating, Ventilating, and Refrigeration Systems: Encyclopedia Arctica 2b: Electrical and Mechanical Engineering

CONTENTS

PHOTOGRAPHIC ILLUSTRATIONS

With the manuscript of this article, the author submitted 8 photographs for possible use as illustrations. Because of the high cost of reproducing them as halftones in the printed volume, only a small proportion of the photographs submitted by contributors to Volume I, Encyclopedia Arctica , can be used, at most one o ^ r^ two with each paper; in some cases none. The number and selection must be determined later by the publisher and editors of Encyclopedia Arctica . Meantime all photographs are being held at The Stefansson Library.

ANALYSIS OF DESIGN FACTORS FOR POWER, HEATING, VENTILATING, AND REFRIGERATION SYSTEMS FOR ALASKA

I. STEAM POWER AND HEATING PLANTS

The design of steam power and steam-heating plants for use in the Arctic and Subarctic will differ from that for similar plants in the ^ United^ States ^ —^ only insofar as the designs are influenced by factors peculiar to the climate, geology, and location of the region in which the plant is to be constructed. Following is a review of these general conditions and of the factors to be considered in designs for Alaskan plants.

Climate . Alaska with its lofty mountains, glaciers, snow fields and broad alluvial plains, presents a great variety of climate, controlled largely by the mountain ranges and the modifying effect of the Japan current.

Climatologically, Alaska is a land of extremes; temperatures of 100° F. in the summer and −78° F. in winter have been recorded at Fort Yukon. Pre– capitation varies widely also; an average annual maximum of 155.52 inches (7-year record) was recorded at View Cove in the south coastal area, while Barrow in the northern region has an average annual minimum of 4.34 inches (23-year record). However, as a whole and particularly north of the Alaska Range, it is a relatively arid country as is the case in most arctic and subarctic regions.

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From the standpoint of engineering design, Alaska may well be divided into four climatic areas, although it should be understood that conditions within these areas vary widely in some respects.

From Cook Inlet southerly along the coast, the climate is comparable to that of north coastal New England except for annual precipitation which averages 150 inches in some localities. Here, temperatures range to 75° F. in the summer and rarely drop below 0° F. in the winter. High winds are prevalent throughout the year.

In the area north of Cook Inlet and south of the Alaska Range, the climate is comparable to that of north-central United States. Average annual precipitation is approximately 14.5 inches, snow is light and powdery, averaging about 4 feet. Temperatures run from a maximum of 90° F. to a mini– mum of −40° F. for regions with established records. Areas within this general region probably exist in which minimum temperatures range lower than −40° F. Low wind velocities are the rule, although gust velocities of 60 to 70 miles per hour are sometimes attained and velocities in excess of 100 miles per hour have been recorded.

The long Aleutian chain has a climate somewhat different from the coastal region. In this area a considerable range of wind velocity prevails, with less differential prevailing for the temperature and precipitation aspects. The general situation can be described as follows: The general average annual precipitation does not exceed 50 inches, with far more rain than s h ^ n^ ow as the ^ —^ rule. Temperatures range from 67° F. average maximum to 35° F. average mini– mum. Wind velocities are high and range to 100 miles per hour or better for extreme gusts, with a general maximum range of about 60 to 69 miles per hour.

In the region north of the Alaska Range and south of the polar areas,

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precipitation will vary from an annual average of 13.63 inches (38-year period) at Tanana to the extremely low annual average of 4.34 inches at Barrow. Temperatures range from the extremes of 100° F. to −78° F. The low temperatures generally occur in the interior. Winds are usually light.

The various physical phenomena resulting from these climatic conditions and from which much of the design criteria are evolved are reviewed herewith.

Permafrost . The term “permafrost” refers to the permanently frozen soils occurring at various depths below the earth’s surface in those rela– tively arid regions where mean annual temperatures are below freezing. It may take the form of a continuously frozen layer several hundred feet in depth, in alternate and relatively shallow layers of frozen and unfrozen materials or in islands. The surface layer in a permafrost area is, of course, subject to alternate freezing and thawing with the seasons, and is the so-called active layer. The layer separating the active zone from the permanently frozen mate– rial is defined as the permafrost table. Ground temperatures in permafrost vary but little the year round, ranging from 26° to 30° F. near the surface, and stabilizing, in the Fairbanks area, at a depth of about 100 feet. As approximately 80% of Alaska is in the permafrost belt, it is a factor which should be thoroughly investigated prior to the development of final designs.

The extent to which this condition will affect designs is dependent on the type of the formation, the depth at which it occurs below the ground surface, the height of the ground-water table and the nature of the soils. At locations where p a ^ e^ rmafrost is composed of well-graded granular particles ^ —^ which are stable when either thawed or frozen, its presence will have little effect on foundation designs. Where conditions of instability are met in the form of high ground water table and fine-grained soils, suitable design criteria must be adopted to eliminate the possibility of future settlement.

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If the stratum of fine-grained soils is shallow, it may be removed entirely and replaced with a mat of coarse, but well-graded and thoroughly compacted sand and gravel.

In all investigations of this nature, it should be remembered that disturbing the ground surface by removing or altering the depth of its vegetal covering or excavating for foundations may change the relative posi– tion of the permafrost table quite appreciably, and the possibility and probable extent of such an occurrence should also be studied carefully.

In conclusion, with respect to permafrost and its relation to power plants, the principal point to consider is the need for a thorough subsurface investi– gation of the site or several sites if conditions warrant and, after careful study and analysis of all factors, to develop a set of design criteria appli– cable to the particular conditions encountered. The importance of such studies leading to the development of adequate design criteria can be readily appreciated when considered in the light of the disastrous consequences bound to follow structural failure.

Ice fog is a condition prevalent in cold regions and generally occurs in relatively low areas. It is formed by extremely cold air “flowing” down from the mountains into the valleys, displacing the warmer air, and condensing out moisture in the form of tiny ice particles that remain in suspension. It is a natural phenomenon that will occur and be dispelled by changes in atmospheric conditions and can be sufficiently heavy to close down air operations completely.

The most carefully designed power plants will give off gases and dust to some degree, thus aggravating f ^ t^ he ice-fog condition and it is, therefore, ^ —^ essential that some thought be given the matter, with particular regard to location. In this respect, the ideal arrangement would be to locate the air

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strip on the highest elevation, residential areas at a slightly lower eleva– tion, and the industrial area and power plant at a still lower elevation. This, as mentioned, is an ideal layout, but physical conditions are rarely such as to permit its accomplishment. Accordingly, where the steam power plant and its cooling water facilities must be set at the same elevation as the air strip, they should be located to leeward if at all possible. The plant should be provided with automatic combustion control and fly-ash precipitators. Exhausting steam and vapors to the atmosphere should be eliminated insofar as it is economically possible.

Snow . The heavy snowfalls prevalent in the south-central area of Alaska not only require heavier structural designs, but must be recognized as a con– dition contributory to halting or delaying transportation and, as a consequence, emphasizing the need for adequate fuel reserves.

Earthquakes . Many sections of Alaska are subject to periodic earthquake shock. (See also “Earthquakes in the Arctic Area.”) The areas in the vicinity of Anchorage and Fairbanks have experienced frequent quakes. The disastrous consequences of earthquake damage are readily appreciated; therefore, all structures must be designed to reduce to a minimum the possibility of damage occurring through this medium. Design criteria in this connection have been established by the Pacific Coast Building Officials conference and is pub– lished in their Uniform Building Code, 1946 Edition.

Location . Alaska comprises the northwestern extremity of North America west of the 141st meridian, a strip of coastal land extending south to 55° N. latitude, and all adjacent islands. Its most northerly limit extends to Point Barrow, about 300 miles north of the Arctic Circle. Total land and water area is approximately 591,000 square miles. By and large, Alaska is a particularly isolated country. Shipping, except for a few ports along the

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south coast, is restricted to the summer months. Rail facilities are limited and, with all due respect, hardly on a par with operating lines in the United States. Natural resources are relatively undeveloped, local manufacturing negligible, and skilled labor is available in relatively limited numbers only. These several factors impose an economic condition equally unfavorable to all types of construction. Aside from this more or less universal condition, location affects power-plant designs largely through the factor of transportation. Rail service is frequently disrupted and delayed by excessive snowfall, earthquakes, landslides, and flood, and, as a consequence, abnormally large fuel storage facilities must be provided.

Fuels. It is axiomatic that coal of the highest quality obtainable at ^—^ a relatively reasonable price results in a more economical and efficiently operating plant. Losses sustained in burning low-grade coal are not limited to the loss in heating value alone. More fuel must be transported and handled and larger grates are needed to burn it in order to obtain the heat required by the boiler. Greater quantities of ash must be handled and the percentage of unburned coal in the ash will run higher. The greatest loss in the use of low-grade fuel comes about through the inefficient heat absorp– tion in the boiler as a result of the lower furnace temperatures obtainable. This is very important since a large part of the heat available to the boilers is radiant heat obtained directly from the furnace, and the higher the furnace temperature the better the heat absorption. The high furnace temperatures conducive to efficient operation cannot be obtained from low-grade coal. Coal is mined in Alaska and, although of low grade (for purposes of design it is assumed to have a heating value of 9,000 B.t.u. per pound), it is probably the most economical fuel to use. Oil is not produced in Alaska and

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would have to be imported if used. Too, the heavier and cheaper grades of oils ordinarily used for fuels are extremely viscious and do not flow readily at Atlaskan winter temperatures. This necessitates insulating and equipping pipelines with steam tracers, increasing the cost appreciably. On the other hand, the less visc i ous fuel oils, although more expensive, can be handled ^ —^ by pipeline without undue difficulty and at far less cost than that afforded by rail facilities. If and when the synthetic production of liquid fuels from coal becomes a commercially economical enterprise, it should be thoroughly investigated for exploitation and development in Alaska. However, until that time comes, the locally mined coal will in all probability prove to be the more economical and dependable fuel.

Coal Handling . Aside from outside reserve storage, this phase of the design involves several units. Coal on route from the mines during the cold weather invariably arrives at its destination frozen solidly in the car and, as a consequence, thawing facilities must be included in the plant design (Fig. 1). This involves furnishing a structure enclosing a spur track of sufficient size to accommodate one to several cars. Heat for thawing may be provided by a system of steam coils arranged on the wall along either side of and parallel with the car or cars and unit heaters overhead, or by a series of open flame pits located under the track and between the rails at specified intervals which throw off an intense radiant heat, melting the ice and snow in a comparatively short time. It is, of course, obvious that an adequate drain– age system will be required in connection with either system.

After thawing, the cars are dumped in a track hopped where the coal is carried by a suitable conveyer to the crushers and reduced to the proper size. After passing through the crusher it is carried by elevator conveyer to a head house where it can be disposed to any one of three points as required:

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( 1 ) by horizontal conveyer to the stoker feed hoppers, ( 2 ) by gravity and horizontal conveyer to covered and heated storage bins, ( 3 ) by gravity to an exterior truck-loading port for return to outside storage reserves. This last mentioned would be used only in the event heated storage bins and the stoker feed hoppers are full. Coal can be taken from the heated storage as and when required, by horizontal conveyer back to the elevator conveyer, up to the head house, and into the stoker feed hoppers (Fig. 2). The heated storage bins should be of ample size to permit storage sufficient to meet anticipated emergencies.

Outside reserve storage areas should be located as close to the plant as conditions will permit. Coal so stored will freeze solidly and, unless some mechanical means is adopted to aid in the thawing process, it must be blasted and broken to a fineness such that it will enter the crushing equipment. Probably the most satisfactory method to use in this instance is a grid of steam pipes buried under the stockpiles, installed in conveniently sized and individually controlled sections for the sake of economy.

Condensing Water Facilities . An ample supply of condenser cooling water must be available. If the plant is located near a river or pond having an adequate year-round supply, a satisfactory system may be had by the installa– tion of suitably sized intake and discharge lines. Pipelines of this nature will not freeze even if laid in the ground and uninsulated, because the water gains some heat from the condenser and is in constant circulation.

Water from a natural source is not always conveniently or economically available, in which even it may be practicable to construct an artificial pond in the immediate vicinity of the plant. Surface area is the controlling factor in an artificial cooling pond and depth is of small consequence.

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Cooling ponds of this type will require approximately 150,000 square feet of surface areas for every 1,000 kilo/ [: ] ^ watts^ of turbogenerator capacity. If the required area is not available, similar and equally satisfactory results may be had by reducing the pond area to that required for winter use and installing spray devices to gain the additional surface area required for summer use. The use of a spray pond during the winter is not desirable as it would tend to aggravate the conditions of ice fog prevalent in the cold regions.

The most compact method of cooling condenser water is provided by the ^ Fig. 3^ cooling tower (Fig. 3); however, experience has indicated this to be not entirely satisfactory in winter operations, because of icing difficulties. The fans blow a fine spray at the entrance which freezes and builds up ice to the extent that the fans are no longer operable; this reduces cooling capacity so much that the generator must operate at reduced load. Inasmuch as winter is normally the season of heaviest electrical loads, loss of potential generating capacity at this time becomes a serious problem. Obviously then, this method of cooling condenser water should be discarded.

Intake Air Heaters . In consideration of the low temperatures likely to be encountered in Alaska, it is necessary to provide some means for heating intake air. In many localities within the United States, air heaters can frequently make use of stack gases and thus operate more economically. Where extremely low temperatures are the rule, it becomes necessary to adopt some other means of supplying the intake air heaters, as extreme care must be taken not to reduce stack gases below a temperatures at which condensation will occur in the heate e ^ r^ or the stack, as the resulting erosion would quickly ^ —^ destroy these items of equipment. Danger from this source can be eliminated

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by using steam heat o ^ e^ rs. Insulation must be provided at that portion of the ^ —^ air intake exposed to the atmosphere as otherwise frost and ice will accu– mulate inside the duct work. Insulation must also be provided around the exposed surfaces of boiler stacks to prevent possible condensation and subsequent corrosion.

The effect of extreme cold in such cases must be seen to be appreciated. A bolt passing through the side of a building results in a heat loss diffi– cult to realize. The head of the bolt will become coated with frost and ice to a considerable thickness even insi [: ] ^ d^ e a heated building. It is there– fore, essential that all pipes, ducts, and other metal devices that are exposed to extremes of temperature be adequately insulated.

Space Heating . In the development of a steam plant to serve the dual purpose of providing central steam for space heating and as a source of power in the production of electrical energy, the most economical over-all design embraces the use of turbine exhaust steam for space heating. By so doing, power can be generated at low cost. In order to balance the steam required ^ 4^ for heating purposes with that available from the turbogenerators (Fig. 4), extraction-type turbines are normally used. This type of equipment permits taking steam from the turbine at any desired pressure from zero to full extraction with the balance of the steam not required for heating purposes going into the condenser. From time to time it may happen that more steam is required for heating than is available from the extraction turbines, in which event it can be obtained by passing the high-pressure steam from the boilers through a reducing valve set to furnish additional steam at the pressure required by the heating system. This arrangement is quite simple and is generally used in the design of dual-purpose plants. When all of

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the turbine exhaust steam is to be utilized for heating, the turbine exhaust is piped directly to the steam distribution system. This turbine is termed the “back pressure” type.

Temporary Plants . Approximately three years are required to design and construct a steam power plant of the size ordinarily required by a per– manent military establishment in Alaska, although steam for heating can be had from the boilers in approximately half of this time. In the meantime both steam for heating and electrical power are required for use during the construction period and to service post facilities as they are completed. This, of course, necessitates the erection of plants of a temporary nature. As this procedure involves a considerable item of expense from which there is small return, design and construction schedules should be so planned as to hold the demand for plants of this type to a minimum. Many military units require stand-by service of this nature as a matter of military necessity. Advance planning should, therefore, consider this factor with a view to incorporating the temporary plant in part or in its entirety into the perma– nent over-all layout, possibly as a stand-by.

Both power and heating plants are required for servicing mobilization– type construction which, while not of a strictly temporary nature, would hardly be classified as permanent-type units. In general, capacity require– ments for mobilization-type plants will be less than for permanent type, and many of the structural and mechanical refinements essential to the economical and efficient operation of a permanent plant can be eliminated entirely.

Design of a plant for strictly temporary purposes should consider the use of packaged-type steam boilers and power-generating equipment, as these units can be placed in service in a very short time after delivery to the

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site. Too, if the ultimate in mobility is desired, they can be set up on flat cars or motor trailers, where suitable rail or highway facilities are available, and moved about as needed with relative case.

Over-all design should be of extreme simplicity, embodying only those features assuring structural soundness and a reasonable degree of mechanical efficiency consistent with the purpose for which the plant is to be used.

Interchangeability . Consideration should be given to standardization of equipment and parts within a plant. It is an advantage to standardize plants and methods as much as possible for the interchange of equipment and personnel. Particularly is this true of military installations which may be destroyed or crippled and require the transfer of operators from one plant to another during an emergency, or for any other reason. It should be borne in mind that in such an isolated section, with transportation difficulties, expert servicing is not readily available. All of which points to the need for simple, rugged equipment. Also, plants should be so designed as to facilitate expansion to handle additional loads due to constantly changing military requirements and strategy.

II. STEAM DISTRIBUTION SYSTEM ^ S^ ^ —^

The mechanical features of steam distribution systems in Alaska are, in general, identical with those for such systems in the United States, except that provision must be made for extremes of climate, permafrost, and earthquake conditions which have been described in Section I. Too, over-all design will be dependent on whether it is to be a permanent or a temporary installation. Although this article frequently mentions the e ^ d^ esign factors specifically in ^ —^ relation to military installations, these same factors are applicable to other industrial structures of similar size.

General Design Factors . Facilities within a military reservation are frequently laid out in widely dispersed units. To hold steam distribution pipe sizes to economical diameters where the pipes extend to distances up to 10,000 feet from the central station, distribution pressures of about 200 p.s.i. should be maintained. Reducing stations must be provided in each area served, where the main line pressure is dropped to about 60 p.s.i., this latter pressure being reduced still further within the various buildings to anywhere from 2 to 15 p.s.i. dependent on the needs of the particular building. Pipes are sized in accordance with the quantity of steam to be delivered and the pressure required at the end of the line. A 10% allowance for condensation is usually added to the demand quantity of steam.

Pumped condensate returns are considered to be more satisfactory than a gravity system, as the former may be installed without regard to slope. Manholes should not, in general, be spaced in excess of 500 feet unless condi– tions are unusually favorable. Such a condition is encountered occasionally in the form of a long, straight run with downgrades in the direction of steam flow. Manholes will contain condensate pumps, control valves, expansion joints, traps, and other items of equipment necessary to the prop [: ] ^ e^ r operation of the ^ —^ system. Steam supply mains should be provided with double standard-thickness insulation. Return lines may or may not be insulated, depending on the parti– cular circumstances. This is usually governed by the economies involved and will generally mean that high-pressure-condensate returns will be insulated and the low-pressure returns will not be insulated. Duplex condensate pumps should be provided as a guarantee of continuous service. They should be auto– matically controlled for interchange and picking up the load one from the other, in the event one unit should fail, through motor or mechanical trouble.

Expansion joints must, of course, be installed at specified intervals, together with the necessary anchors. These may be either the compact, accordion-type joint, or a suitably sized loop. Selection between types is also a question of economy. In the larger sized mains, the accordion type is the more economical, whereas from eight inches down there is very little difference in cost. If the steam mains are carried in an underground pipe gallery along with sewer and water mains, the accordion-type joint will probably be the more economical regardless of pipe sizes.

Types of Installations . Either one of two general methods may be adopted in the installation of steam distribution mains. The main can be buried in the ground, carried on posts just above the ground surface, carried on a pole line sufficiently high in the air to clear all ordinarily anticipated vehicu– lar traffic, or it can be installed in an underground pipe gallery or tunnel in company with water supply and sewage collection mains. (See also “Arctic Sanitary Engineering.”)

^ —^ If the steam main is buried in the ground (Fig. 5), it must be insulated and jacketed to assure watertightness. There are several patented mains of this type on the market. On some of these, the supply main and condensate returns are made up as a single insulated and metal-jacketed unit in the smaller sizes. In the larger sizes, the supply and condensate mains are made up as individual units. This type proves to be quite satisfactory where it can be installed in the trench above the ground-water table and in the absence of permafrost. However, if installed below the ground-water table, corrosion eventually causes the metal jacket to leak allowing moisture to work into the insulation, the moisture is vaporized by the heat from the main, and, in some cases, will build up a head of steam sufficient to rupture the

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metal jacket and blow out the insulation. Even if this does not happen, the accumulation of moisture in the insulation destroys its effectiveness and results in excessive heat losses.

Installing the main on posts just above the ground surface while satis–factory under certain conditions is inconvenient if the route necessitates crossing highways and railroad lines, as the main must be depressed under or carried over such traveled ways.

The overhead pole-line type of installation has its merits under certain conditions and, as in the previous method, requires no trench excavation and is open to inspection at all times. It does, however, establish limiting clearances at highway crossings and does not appear to be entirely suitable for a military installation.

In those regions where extremely cold temperatures are the rule or perma– frost is encountered, some means must be adopted to prevent water and sewer mains from freezing. Heat lost from the steam mains, if in close juxtaposition with the water and sewer mains, will permit maintenance of the required above– freezing temperatures. The type of construction best adapted to this method of installation consists of a suitably sized buried conduit containing shelves, hangers, or other devices required in supporting the several utility mains. This buried conduit or pipe gallery is the so-called “utilidor.” As inferred above, it will vary in cross-sectional dimensions to suit the size and number of pipes to be carried and, as a consequence, may be of the larger “walk-through” type (Fig. 6), the “crawl-through” type (Fig. 7), or the minimum-sized service structure. In most cases a sewer will be among the utilities carried. A study of the entire system will determine the relative economies of gravity flow and pumping in total or in part. Proper manhole placement and ability

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to remove covers on the utilidors is a prime requirement to take care of major repairs and overhaul work. This design feature is particularly important for crawl-through type and minimum-sized units of utilidor con– struction. It should again be stressed that all important factors that need periodic attention, such as condensate or other pumps, expansion joints, traps, motors, and controls, should be located at manhole openings in the crawl-through type where they are most readily accessible for check and repair. Furthermore, in crawl-through type of utilidors, special care must be taken that, in the design and construction, full regard for further proper access for inspection and minor repair is given. Unless this point is stressed, installation people will so block the areas with supports and hangers that it becomes almost impossible to inspect the lines.

If it is anticipated that permafrost will be encountered along the route of a proposed utilidor system, test pits should be excavated to determine soil types and their suitability as foundation material and the possible need for waterproofing the exterior of the structure. Should explorations indicate that the subsoil will be somewhat unstable when thawed, provision should be made for removing it to a minimum depth of two feet below the foundation and replacing it with a thoroughly compacted layer of well-graded granular material. This will not only provide a suitable foundation, but will serve, to a certain degree at least, as an insulating blanket in preventing excessive thawing in the permafrost.

Should the permafrost be extremely fine grain, the bulk of which passes 200-mesh sieve when thawed, it may be impossible to provide a suitable founda– tion for the utilidor except by means of piles. Such an installation might be so costly that overhead steam lines will result in the most practicable solution.

The material from which it is constructed should be such as to insure a long-lived structure impervious to the infiltration of ground water. A reinforced-concrete structure appears best to satisfy these requirements. Various cross sections may be developed to suit the needs of the particular project. These may be rectangular, semicircular. circular, or parabolic in shape. The rectangular design has invert and side walls of poured-in-place concrete and a precast sectional cover. The invert and side walls to the spring line of the semicircular sections are of monolithic concrete con– struction, while the removable top is nothing more than a half section of centrifugally spun concrete pipe of standard length. The full circular design is standard centrifugally spun concrete pipe split along the hori– zontal diameter. These split sections can be manufactured with standard pipe plant equipment requiring only slight alterations to the forms. The parabolic section has a poured-in-place invert and a precast cover of vacuum– processed concrete. The semicircular, circular, and parabolic sections are each constructed in part or wholly of precast units. This has one definite advantage in that the various units may be constructed during the winter months when outside work is not possible and reduces to an appreciable degree the field labor contingent. However, they require a considerable plant invest– ment and, unless a number of miles of an identical size structure are involved, the unit cost per foot of each will exceed the unit cost per foot of the rec– tangular section. Dimension and cross-sectional area of the latter may be enlarged or decreased as required without regard to plant investment.

Temporary Utilidors . The above considers permanent types only. During the construction period or where mobilization-type structures are used, it is often necessary to provide an installation of temporary or semipermanent

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design. For strictly temporary use for one or two seasons, a surface-laid, insulated wooden utilidor will, in all probability, prove to be the most economical type of structure. For mobilization-type construction, the utilidor might be a combination of concrete and treated timber, resulting in a design comparable in durability to the buildings served. In a case of this kind, the distribution system also would be designed with a minimum of refinements consistent with general requirements.

Central Steam Distribution vs. Individual Space Heating . The initial investment required for the installation of a steam power plant and utilidor distribution system is high. The only alternative lies in the installation of separate heating units for each individual structure. A careful review of the facts in the case, i.e., additional operating and maintenance labor required and means to keep the sewer and water supply systems in operation, indicates the pattern to be followed. If for some reason or other, central steam distribution is not provided for a particular area, the water and sewer mains can be carried in a much smaller utilidor heated by steam tracers fed by a small boiler plant provided for this express purpose. This is a perfectly satisfactory system mechanically; however, studies will probably show the annual cost of service of such a system will exceed the annual cost of service of an installation including central steam distribution and, in general, indicating the economic advantages and desirability of a central steam heating and distribution plant.

Radiant Heating . While the detail of heating distribution is now recognized as having an important place in space heating, its use in the subarctic is of even greater importance than might at first be suspected. Pioneering in its use has been accomplished. For large g ^ h^ angars, warehouses, ^ —^

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shops, and such structures, careful consideration must be given to its use. A problem arises in those regions where permafrost exists, but generally by careful treatment of the individual case, a solution can be found.

III. VENTILATING AND REFRIGERATION SYSTEMS

Ventila f ^ t^ ing Systems ^ —^

Experience has shown that adequate ventilation of dwellings located in arctic or subarctic regions is an important factor in maintaining the good health and comfort of the occupants and is of particular importance in bar– racks, mess halls, hospitals, schools, and other permanent-type structures where large numbers of people assemble.

Ventilation may be defined briefly as a process by which air is supplied to and removed from an enclosed space by natural or mechanical means. In the former, activation is by means of wind forces and the temperature differential between the inside and outside air. Operating efficiency is variable in accordance with the activ [: ] ^ a^ ting forces. ^ —^

Manually controlled ventilation systems for the smaller barracks, ware– houses, shops, or industrial buildings can be effected by the same means as those commonly used in more temperate regions; windows usually fitted with adjustable storm sash, roof vents, and simple fans are adequate for the purpose. Screens for all such openings are just as much a necessity in the Far North for insect control as elsewhere. However, for the more scientifically designed larger structures — barracks, mess halls, shops — the use of such elementary ventilation in the Arctic or Subarctic is generally limited to providing a proper circulation of air in unheated attic or similar spaces and thus

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minimizing the possibility of moisture accumulating in these areas through excessive condensation. A system of mechanical ventilation is, as the name ’ ^ —^ implies, so designed as to be efficiently operable in entire independence of natural forces and may consist of any number of refinements up to the point where it may be more applicably called “air conditioning.” As considered here, it will consist of intake and discharge vents, supply and exhaust fans, air heaters, humidification equipment, and all necessary controls. Air cooling will, in all probability, be required for limited use in some hospital rooms for summer use; however, this can be treated as a special problem and its control can be effected by packaged units independent of the main ventilating system.

The various factors serving as a basis for the design are the climatological conditions described in Section I, the location and orientation of the building, its type of construction, and the purpose for which it is to be used, all of which introduce a number of interrelated variables. In general, these factors differ in no way from those encountered in the States, except for the extremes in temperature, and, accordingly, designs should be developed along similar lines.

Barracks, mess halls, kitchens, and other buildings all require air changes at varying rates. Barracks should have a minimum of 4 changes per hour with 25% fresh air or 10 c.f.m. per person with 25% exhaust. Large mess halls will require 10 changes per hour with 50% fresh air, and kitchens 10 to 20 changes per hour of 100% fresh air. During periods of extreme cold with an outside temperature of, say, ^ −^ 50°F., the heat required to warm the ^ —^ cold air to a room temperature of 70°F. is substantial and a heavy load is placed on the heating system. This condition can be alleviated by the simple expedient of recirculating the air and cutting the fre x ^ s^ h air intake to 5 to 10%. ^ —^

EA-I. Potter: Power, Heating, Ventilating, and Refrigeration Systems

As temperatures rise, fresh air intake may be increased to normal.

To insure indoor atmospheric conditions conducive to good health and comfort in cold climates, the ventilation system should be designed to include delivery of air with the proper moisture content. In a temperate climate, 30% relative humidity at 70°F. is the generally accepted minimum requireme u ^ n^ t; ^ —^ however, during extended periods of extremely cold weather, relative humidity should be lowered to 20% to prevent excessive condensation, but should not be allowed to go below this point in ^ the^ interests of good health. With atmos– ph a ^ e^ ric temperatures of −50°F., the relative humidity of outside air may be ^ —^ as high as 80 [: ] ^ o ^ r 90%, but, due to the low vapor pressure at this temperature, ^ —^ actual moisture content of the air for all practical purposes is nil. Air taken into the ventilation system at this temperature and warmed to 70° F. without moisture being added will have a low relative humidity, probably less than 5%. Humidification of the ventilating air, therefore, is an essential factor in a ventilating system designed for cold countries. Hospital operating rooms require special attention and should be provided with a complete year– round air conditioning, permitting a minimum of 12 changes of air per hour and a relative humidity of 55%. Maintaining the humidity at this point tends to reduce explosion hazard and is found to be more satisfactory for the patient. Conversely, during the summer months, cooling and dehumidification will be required at times. In all of these rooms where high relative humidities are maintained, double-glazed sash will be necessary to prevent condensation.

In this connection, it is pointed out that ordinary building materials are vapor permeable and, because of the wide difference existing between vapor pressures at ^ +^ 70°F. and −50°F., there is a natural tendency for these ^ —^ un h ^ b^ alanced pressures to equalize. The warm interior, having the higher vapor ^ —^ pressure, loses moisture at a rate in accordance with the vapor permeability

EA-I. Potter: Power, Heating, Ventilating, and Refrigeration Systems

factor of the wall structure. This condition may be eliminated by incur– porating a vapor barrier in the building design. This is nothing more than a layer of highly impervious material installed on the warm side of the exterior, usually directly under the plaster, wallboard, or other interior wall finish. In the absence of an effective vapor seal, moisture will con– dense and freeze within the walls and under roofs of buildings in frigid climates; alternate freezing and thawing causes the buildings to deteriorate rapidly.

Refrigeration Systems

On first thought the need for providing refrigerated storage in arctic or subarctc or subarctic climates appears ridiculous; however, a hasty review ^ —^ of the factors and conditions involved will readily read just any such impression and bring out the realization that refrigeration facilities are quite important in the storage of foodstuffs in the Far North as in the tropics. It is true than an individual might make u a ^ s^ e of the natural conditions obtaining in the ^ —^ permafrost regions or where glaciers are available, and many instances of such use can be cited. So far as can be determined, the planned use of the permanently frozen soils of the North for refrigeration purposes was first seized upon by Europeans. The Eskimos and other northern natives were accustomed to diggin s ^ g^ shallow pits for storage of food down to, but not into, ^ —^ the permafrost; cold cellars of this type provided only partial refrigeration, retarding but not preventing decay. (See “Natural Cold Storage.”) Ice houses to keep food chilled during warm seasons have in isolated communities been employed for winter storage as well; a common sight in the North is the trapper’s cache wherein he keeps his fresh meat frozen and safe from roaming animals throughout the winter. Root cellars (Fig. 8), frequently used on farms in the northern states, are also a common means of winter storage for vegetable crops.

However, in view of the close temperature and humidity control required in storing large quantities and varieties of foodstuffs over variable periods of time, it is commonly believed ^ considered^ that adaptation of natural conditions on a ^ —^ large scale is not a practical method of approaching the problem. ^ (But see general article “Natural cold Storage.”)^ As a ^ —^ consequence, in all established communities and camps, cold-storage plants and their operation are a common facility, as a result of the importance of ^ —^ fish and gam s ^ e^ as food to Alaskans, together with the need of bulk buying ^ —^ for economy reasons. Probably a [: ] ^ g^ reater percentage of people in the Territory ^ —^ have frozen-food lockers than elsewhere. (There are dissenters to this ^ —^ pessimistic view of the adaptability of natural conditions to large-scale ^ —^ refrigeration — see “Natural Cold Storage.”)^ —^

Refrigerated storage must provide both freezer space and cold rooms with control ^ l^ ed temperatures of 0° to 10° F. and 30° to 40° F., respectively, and ^ —^ should include facilities for manufacturing ice. The design should have adequate floor area and hea r ^ d^ room to insure proper cold-air circulation. ^ —^ Stored products should not be stacked closer than 12 inches to the walls of the room or to an adjacent pile, and no higher than 3 to 4 feet from the ceiling. Deducting aisle space and column areas further reduces the net usable storage area to about 40% of the gross room area. Factors affecting the design include climate, transportation facilities, and the quantities and types of foodstuffs to be refrigerated. These factors are basic and must be considered regardless of location. In Alaska the uncertainty of transportation facilities and the need for importing foods will in all probability have the greatest effect on design in the matter of quantity storage and space requirements. Auxiliary heating facilities must be provided for cooler rooms in arctic installations to insure against freezing during extremely cold weather. Other than the above,

EA-I. Potter: Power, Heating, Ventilating, and Refrigeration Systems

designs for refrigerated storage in Alaska will be identical with those for use in the United States.

Humidity control is of extreme importance in any cold-storage plant. Excessive humidity will cause the stored products to mold and too little moisture in the air will dry them up. Experienced packers and cold-storage operators have found that the best humidity is obtained when the temperature of the evaporator coils in the cooler rooms is held from 4 to 5 degrees below the room temperature. Increasing this difference will dry up the air, and decreasing the difference will increase the humidity.

Different foods require different temperatures and humidities if they are to be held in good condition over long periods of time; consequently, separate individually controlled cooler rooms should be provided. Of course, it is not feasible to hold to this design criterion literally. Those foods whose optimum storage temperatures vary but little may be stored together and the cooler room held at a compromise temperature and humidity without adverse effect.

Where refrigeration of a greater capacity than that afforded by the mobile “reefer” or “walk-in” unit is required as a servicing facility for temporary or mobilization-type units, it is believed that a prefabricated– type structure warrants every consideration. They can be designed to meet all ordinary refrigeration requirements and can be erected and placed in operation in a matter of days.

The use of material available in any specific locality is very desirable, both for helping in the developing of the region and also for effecting saving in transportation. Several important materials that have interesting possi– bilities [: ] as insulating materials are the pumice or volcanic-ash deposits found in certain regions and the tundras or muskegs that cover the land.

EA-I. Potter: Power, Heating, Ventilating, and Refrigeration Systems

The latter material is the natural food of vegetation-eating wild life, but it is abundant and has excellent value as an insulation. It has been observed that under several feet of snow and several feet of such vegetation, unfrozen ground water has been found during a time when temperatures for a period of over three weeks ranged from minus −50° to −70° F.

William Everett Potter