Grantville Gazette, Volume 40 (34 page)

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What can go wrong? On the large scale, thaws and rains can melt the ice crop, and snow has to be shoveled or planed off. On the small scale, a worker can fall into the icy waters or be injured by an unexpected movement of one of the 200
–
400 pound blocks. Tools can be lost or broken.

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A potentially more dangerous means of obtaining ice was to chop it off an iceberg. In August 1819, Captain Hadlock of the brig Retrieve succeeded, but the enterprise was nearly a disaster. On the first attempt, his sailors had to take shelter from a sudden storm. On the second, the inexperienced iceberg hackers caused the iceberg to topple over and damage the ship. They pumped their way to Martinique, and I hope Hadlock thought that his $1,700 fee was worth the trouble. (Weightman 92). On the other hand, in the twentieth century a Dane stated that it was "quite customary to use iceberg ice for drinking water" and "if you know icebergs, you know which ones are going to tip around." (David 327).

In Sitka, an ice crop failure forced the Alaska Ice Company to cut ice from Baird Glacier (Carlson 58).

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A small-scale operator can avoid much of the labor of harvesting ice by setting out bins of water and allowing them to freeze overnight. The resulting ice blocks are then freed from the bins and stored.

Mass Ice Storage

In the late-nineteenth century USA, ice was usually cut in January-March and consumed in May-October. (Hall 6). That was, of course, in part because ice was needed most when temperatures were high. However, the ice was not shipped south as soon as it was cut. The very conditions that made it easy to harvest ice also made it difficult to transport it. Ice was therefore harvested in the winter and stored until spring. The waste during this storage period was typically 10
–
25%. The ice would then be shipped to a distribution center and stored again until it was sold. The typical total waste, from harvest until arrival in the hands of consumers, was 40
–
55%. (Hall 9).

Natural caves
. Caves are cooler than the surface in summer, but warmer in winter; a great mass of earth and stone has thermal inertia, a fancy way of saying that it changes temperature only slowly, so cave temperatures are virtually constant year-round. The depth in meters at which the annual temperature change is only 1
^o
C is 3.18 * natural logarithm of the temperature change at the surface; that works out as 10.8 meters for a 30
^o
C summer-winter surface difference. The average cave temperature is primarily a function of latitude and altitude; temperature (
^o
C) = 0.6 * latitude (degrees) -0.002 altitude (meters). (A cave will be cooler than this formula predicts if it has a snowmelt-fed stream running through it during the spring.) (Moore 27ff).

Some caves contain ice year-round; either they are at a high enough altitude so the average surface temperature is below freezing, or they are "cold traps." The latter have a bottle shape; cold air flows in during the winter and blocks the ingress of warm air during the summer, reducing the average temperature by about 10
^o
C relative to the predicted value. Cold traps are usually lava caves.

Underground storage is probably more advantageous in temperate regions, which have cold winters and hot summers, than in the tropics, where temperature variation is small.

Artificial caves
. In Italy, Buontalenti constructed the Grotto Grande for the benefit of the PittiPalace, and used it for ice storage. In Francesco Redi's epic poem, Bacchus in Tuscany, Bacchus orders, "bring me ice duly, and bring it me doubly/Out of the grotto of Monte dei Boboli. . . . Redi 18). It's likely that Buontalenti also made use of simple ice pits.

The traditional English icehouse was mainly underground, and lined with brick or stone (Weightman15). With regard to the 1619 "snow well" at Greenwich, contemporary accounts state that it was a "brick-lined well, 30 ft (9.23m) deep and 16 ft (4.92m) in diameter, covered by a thatched timber house with a door." (PastscapeMonument 761486).

Above-Ground Mound
. At Walden Pond, the ice-harvesters didn't bother to build an ice house. "They stacked up the cakes thus in the open air in a pile thirty-five feet high on one side and six or seven rods square, putting hay between the outside layers to exclude the air. . . . At first it looked like a vast blue fort or Valhalla; but when they began to tuck the coarse meadow hay into the crevices, and this became covered with rime and icicles, it looked like a venerable moss-grown and hoary ruin. . . . This heap, made in the winter of '46
–
7 and estimated to contain ten thousand tons, was finally covered with hay and boards. . . ." Despite the lack of a proper roof, it survived the summer of 1847 and indeed "was not quite melted till September, 1848." This was called "stacking."

Above-Ground Ice House
. The ice-houses of the American "ice belt," used to hold the ice until it could be shipped south, were usually above-ground buildings. A medium sized one held 10,000 tons of ice, and was built using 175,000 feet of lumber. It was perhaps 30 feet high and sometimes divided into "rooms" holding perhaps 700 tons each. One ton of ice required 42.5
–
45 cubic feet. A large ice house might hold 60,000 tons and feature rooms holding several thousand tons apiece. (Hall 9).

In 1880, the cost of large ice houses, with machinery (20 hp steam engine-driven elevator chains), was $0.75
–
1.00/ton capacity for wood construction and $2/ton for brick. (Hall 10). Ice can be fed to an "elevator" by one man at a rate of 175 tons/hour, and 20 men would be needed to stow the ice away at that rate. (Id.)

Small ice houses will be more expensive than large ones because materials cost is proportional to surface area. In 1905, for a wood creamery ice house holding 15,000 cubic feet, Cooper (506) quotes $1044.70, and the brick equivalent was about 30% more expensive.

Waste varies according to how long the ice is stored, how large and well insulated the ice house is, and how warm it is outside during the period of storage. In Maine, the waste at the large ice company houses was about 20%. (Hall 23). That said, ice could last in a well-designed and operated ice house for 2
–
3 years.

A few up-timers may have their own farm ice houses or have at one time seen or read about such. I have documented the existence of an at least partially above-ground ice house on Sandridge farm, in Audra, West Virginia. (Sandridge). There was also one on Lost Creek farm in North central West Virginia, although nothing is now remembered about its construction. (Lost Creek). In Leesburg, Virginia, there was a late-nineteenth century above-ground ice house with stone walls and straw insulation. (Leesburg). The USDA Farmers' Bulletin 913 (Dec. 1917) contained a detailed description on how to build a small wooden ice house (pp. 29
–
39). I am sure that farmers in Grantville received the Farmers' Bulletin and I suspect that some of them are pack rats who never throw away anything unless they run out of space. Or the Grange may have the bulletin.

What about ice houses in warm climates? Tudor's first Havana icehouse was an above-ground wooden structure, a cube twenty-five feet on each side. The sales office was directly above the ice store, and the ice was brought up through a trap door. The structure was double walled, with sawdust and peat packed in the interstitial space. This meant that the insulating material remained dry. Meltwater escaped through a drain. (Weightman 65ff). At first, Tudor was losing 56 pounds ice/hour. He found that covering the ice with blankets, rather than sawdust, reduced the loss to 18 pounds/hour. (Id.)

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What can go wrong in ice house operation? If there's a gap in the insulation, melting may be excessive. If the ice is packed improperly, the ice can slide toward the outer walls and bring them down. (Cooper 494). Lightning can strike the house (did you remember to provide lightning rods?) and set it on fire. For that matter, a fire can originate in the insulating material, as occurred at WenhamLake in 1873.

The Physics of Keeping Cold

The enemy of ice is heat, and heat is transferred in three different ways: conduction (molecules in contact), convection (gas or liquid molecules in motion),and radiation (molecules not involved, can even cross a vacuum). Heat travels to the outside of an ice house by convection and radiation through the air, and conduction through the ground. It then travels through the insulation by conduction (and, if air spaces are provided, convection and re-radiation).

The first thing we need to recognize is that there are definitely economies of scale. Since heat transfer occurs at the surface of an object, that the rate of transfer is proportional to the exposed surface area. But the increase in temperature as a result of that heat transfer is going to be inversely proportional to the volume. Large masses of ice have a lower surface area/volume ratio than small ones, so they will lose a smaller percentage of their volume to melting in a given time, with equal protection.

Secondly, heat flows from hot to cold, and the rate of conductive heat transfer is proportional to the temperature difference. So it's advantageous to store the ice up north and ship it down south only just before summer begins; you'll lose less ice that way.

Thirdly, the rate may be reduced by insulating the inside from the outside. In considering insulating materials (next section), bear in mind that a small ice storage requires better insulation than a large one, and that the price of the delivered ice sets a cap on what can reasonably be spent on insulation. Also, it may be cheaper to use a great thickness of a decent insulator rather than a small thickness of a great one.

Insulation must be more than resistant to heat flow, we also have to worry about the effects of mechanical damage, ultraviolet radiation, fire, moisture, fungi, vermin, etc. Insulation is often a composite of different materials to take advantage of their different properties.

For some situations, the thermal mass (heat capacity) of a material is also important. The thermal conductivity measures the steady rate at which heat passes through a layer, i.e., the rate if the temperature difference between inside and outside is maintained. The thermal mass measures how much a given quantity of heat will change the temperature of a bulk material; the greater the thermal mass, the smaller and slower the change. This makes a difference if you're in a part of the world in which there is a big change in temperature from daytime to nighttime. Some heat is drawn back out of the massive material before it has a chance to penetrate to the interior. The materials with the highest thermal mass include, in descending order: water (4186 kJ/m
³
K); concrete (2060), stone (1800), rammed earth (1675), brick (1360), adobe (1300), wood (904), and fiberglass (6.7). (
http://myhouseinthewoods.com/htm_wood.htm
)

The advantage of underground construction is not that earth is a good insulator (conductivity ~4) but rather that it has a relatively high thermal mass.

Note that thermal mass is not necessarily a good thing. Professor Mapes warned that stone is the worst material for an ice house because, if the walls are heated by the sun, they retain the heat day and night. (Robinson 296). The key questions are whether the walls are thick enough so that the heat doesn't penetrate during the daytime and does the heat flow reverse at night.

Reflectivity
. A reflective surface can reduce heat transfer by radiation to the outside of an above-ground ice house, or across a vacuum or air gap. Tin (let alone aluminum) foil is likely to be too expensive, but American "ice belt" houses were painted a "glaring white." (Hall 9).

Drainage
. If outside temperatures are above-freezing, then, inevitably, there will be some melting. It's essential to drain away this meltwater. The heat conductivity of water is much higher (0.58 W/m-oK) than that of air (0.024), so it becomes a corridor for the delivery of more heat to the remaining ice. (ETB). If the soil is porous (gravel or sand), that may be sufficient; if a drain is constructed, it provides a path for warm air to enter. (Cooper 525).

Condensation
. Water vapor condensing on the warm side on the warm side of the insulation will compromise it; so you will want a vapor barrier, such as kraft paper or asphalted felt. (Marks 19-15).

Ventilation
. I have found a lot of contradictory statements made about ventilation. Weightman (65) says, "as ice melts, it releases latent heat, which creates a warm and therefore rising draft of air." He explained that traditional ice houses had domes in order to provide ventilation, dissipating this warm air. But Weightman is wrong; it takes heat to melt ice, and latent heat is released when ice freezes.

Cooper envisions the ice house as having a loft, separated by a plate floor from the actual ice storage. Ventilation is needed, he says, in the loft area, to counteract heating by radiation. "Above the plate, plenty of air; below it, none whatsoever." (527).

Professor Mapes says that ventilation is needed only if the ice is in a cold storage, to keep the food from fouling. If the ice is just being preserved for use elsewhere, it will last longer if there's no ventilation. (Robinson 297).

Above-ground versus below-ground
. All else being equal, below-ground storage provides more insulation. Larsen reported the results of some experiments in South Dakota. Of 15 tons stored in 12x12 foot pile above ground, with a foot of straw under and over, and boards on top to keep out the rain, only 10% could actually be used. A second lot was stored in an equal-sized pit, with similar protection, and of that 30% survived. Later experiments featured an ice house with, I believe, a partially underground construction. With straw insulation, 30% of 8 tons survived. The next winter, with sawdust insulation, 47% of 10 tons survived.

Nonetheless, according to Ballard's 1892 report on the Maine ice trade, above-ground is better because a "cooler and dryer atmosphere can be maintained during the summer, with the use of sawdust and shavings of wood or meadow hay as dunnage. Evaporation is more gradual, which is necessary in order to keep ice from forming a solid mass in the houses."