HEATING GLASSHOUSES

New Zealand Journal of Agriculture, Volume 73, Issue 5, 15 November 1946, Page 471

HEATING GLASSHOUSES

Comparative Costs of Oil, Coal, and Electricity

By

A. A. POWELL,

-, Cool Storage Officer, Wellington.

TNQUIRIES about the use of electric power for glasshouse heating have been received from growers recently. Though the initial outlay for installing electric heating equipment is comparatively low, the high running cost makes its use at present uneconomical compared with other types of heating.

Glasshouses can be heated electrically either by heating water with an electric element and circulating it in the usual way, or by installing finned units to , heat the air and a properly-designed, system of distribution to ensure circulation of the heated air to all parts of the glasshouse. . The second method should be more efficient, as all .the heat produced is evenly distributed through the atmosphere of the glasshouse.

The greatest drawbacks to the use of electricity for this purpose at- present are the' shortage of power and the high cost of current compared. with coal and fuel oil. The following J comparisons show the amount of heat, calculated in British Thermal Units (8.T.U.), which can be bought for a penny when using electric power, fuel oil, or good-quality coal:— Electricity One unit of electricity (1 kilowatt hour) employing a heater of 100 per cent, efficiency produces 3,412 units of heat. . \

Cost of Current B.T.U. for a Unit. One Penny. Id. 3,412 2d. 4,549 - Id. 6,824 id. 9,099 2d. 13,648

If power can be obtained at id. /a unit, it would probably pay to designa system - using finned heating tubes or elements and forced air distribution to all parts of the enclosure to control the temperature of the air in a glasshouse automatically under the varying conditions which arise from inside and outside influences. The finned heating tubes are obtainable in Ift. 6in. lengths, using 500 watts each. A fan is necessary to force the air over these heaters to prevent them from overheating. ■ Coal The estimated heat in 11b. of best quality New Zealand non-coking coal is TO,OOO 8.T.U., and the average

efficiency of a coal-fired tubular boiler is 65 per cent. Using coal at £2 15s. a ton to heat a glasshouse with a normal hot-water system, one penny would buy 22,060 B.T.U. Oil Fuel«Mj|M||

The estimated heat contained in lib. of fuel oil is 19,000 8.T.U., and the average efficiency of a tubular oil-fired boiler is 65 per cent. Using fuel oil

at its present cost of £9 15s. 6d. a ton to heat a glasshouse using the-normal hot-water system, . one - penny buys 11,792 B.T.U.

It has been suggested that an oil-fired heater of the’ type that heats the air direct, and not with hot water, could be used in a glasshouse., If it were efficiently installed within the glasshouse the thermal efficiency should be up to 95 per cent, instead of 65 per cent, with an oil-fired tubular hotwater boiler outside the . house. The only heat loss would be from the flue above the roof, and that could be reduced to a minimum. Then one penny would buy 17,234 B.T.U. If fuel oil were reduced in price to say £6 13s. a . ton, 25,000. B.T.U. would be bought for a penny, which

would mean that oil would give the same heating value as coal. - The greatest difficulty in applying a direct heat exchanger fired with either fuel oil or coal to \ the heating of * a glasshouse is the temperature difference of about 800. degrees F. between the furnace heating tubes and the atmosphere of the glasshouse. I. B ■ Conclusions Electric Power: If power is available at' reasonable cost, . electric appliances may be ideal for heating the amateur’s glasshouse, where cost of running is not a primary consideration and time and labour saving are of great importance. Though electric power is not at present economical for commercial glasshouse heating, there may be a strong case in some localities for making a partial use-of electricity during peak periods as an auxiliary to the main heating. . ' It has been stated that to maintain a temperature of approximately 20 degrees F. above outside temperatures the loading of electric tubular heaters should be as follows: — ■ ■ Size of Glasshouse Load (cubic feet) (kilowatts) 250 1 to 11 500 2 1,000 3 2,000 4 Coal: The use of good-quality coal in a tubular boiler for the circulation of hot water is by far the most economical method of heating a glasshouse at present. Fuel Oil: Though fuel oil appears at first to be much more expensive than coal, other factors should be taken into account. Labour costs end wastage are less than for csal, and oil is much more easily adapted to use in a thermostatically-operated boiler. Oil, however, still seems to be considerably more expensive than coaL

“Seek, and ye shall find . . .

“Very full of dreams that desert, . . . ”

FOR some time past a familiar feature of booksellers’ displays has been a large blue-bound volume jacketed with a coloured reproduction of the fortress gateway marking the western end of the Great Wall which divides China from Mongolia, and bearing the inscription “The Gobi Desert.” First published in 1942, and now in its eighth edition, this unique work won for its authors the Lawrence of Arabia Memorial Medal (the award of the Royal Central Asian Society) and also the Royal Scottish Geographical Society’s Livingstone Medal. The copy before me as I write has on its title page the signatures of Mildred Cable and Francesca French, who compiled this remarkable record of 15 years’ sojourn in the vast desert of Gobi. For together with 'Eva French, the other member of. their party, the Trio, as they are popularly called, recently visited New Zealand on a lecture tour in connection with the centennial of the British and Foreign Bible Society in this Dominion.

It'was during their stay in the capital that I had the opportunity of meeting these eminent missionaries and explorers. May 1 introduce them to you under their Chinese —Feng ' Precious Pearl, Kai All Brave, and Feng Polished Jade. Loving art and music, and having a talent for languages, Miss Eva French, who is the elder of the two sisters, spent her earlier years on the Continent, thus achieving an education far in

advance, of most English girls of that time. Despite strong opposition she eventually forsook the conventionalism of Victorian society for the perils of life as a pilgrim-preacher in China. My first glimpse of her in her dark-brown coat of Persian lamb wool (purchased from a trader in Tibet) and high-crowned hat happened to be a rear view. When she turned toward me the serenity of her gaze and the strength of her features in repose were indicative of the unconquerable fearlessness of spirit which had enabled her to triumph over the horrors of the Boxer Rebellion, blizzards, brigands, danger, and hardship, that she might fulfil her calling.

I doubt if Miss Cable would be more than an inch over 5 ft. in height; nor did her flat-soled footgear add appreciably to her stature. Nevertheless, her personality was as clear-cut and beautiful as the Lake of the Crescent Moon, which is set like a sapphire among the sand-dunes in the desert of Lob, and on its slender shore stand trees “whose leaves are silver and whose fruit is gold.*’ Her handclasp was firm, her manlier decisive and reassuring. She was simply dressed in dark blue, fastened high at the throat in the Chinese manner, and her small, eloquent hands sometimes toyed with the long, finely-linked neck-chain which sparkled against the sombre silk of her gown. Her voice had the resonance of one used to speaking with knowledg

and authority, yet there was no harshness in her tone, but an all-compelling power to inspire her listeners with the conviction of her belief —a belief to which she has brought the keen mind of the scientist, the disciplined intellect of the student, in conjunction with humour, and a love of beauty which, even as a child, “tipped the balance of pleasure till it touched the index of pain”—a belief in the Word whereby all peoples of the earth may be led in the Way of the Prince of Peace.

On greeting the third of the Trio 1 had the instant impression: here is a person who has a gift for friendship. As I encountered the joyousness of her smile, the kindliness and understanding which are so integral a part of her nature, I could well realise what an outstanding contribution Francesca French has made to this unusual partnership—“a threefold cord is not easily broken.” We talked of the Orient and particularly of China, where the three served for more than 20 years before beginning their trek 'into the desert country beyond. Miss French’s love for the romantic city which constituted her first glimpse of China was apparent in the way she spoke of Peking. (Indeed, the touch of green at the neckline and the gleaming bead-embroidery which softened the severity of her black frock put me in mind of the jade the lapidaries of Peking carve into such precious commodities, commanding high prices in consequence. The coral-headed pin in her upturned hat also struck a distinctly Eastern note, as did her golden furs of Tibetan fox.)

The conversation turned to famous travellers whose literary talents have made their exploits household words; Sven Hedin, foremost of Asian explorers; Kingdon Ward, ethnologist and botanist, whose books on Himalayan flora depict mountainsides of primulas” and forests of rhododendrons in full bloom; Owen Lattimore, a minister’s son with a wonderful understanding of the Chinese people (I have a snap of this cheerful compiler of Mongolian customs and folklore which was taken at the Yosemite Conference by a New Zealand friend But it was of the desert dwellers that Miss French waxed most fluent. Few who formed her audience will forget her description of those whom she and her companions met as they journeyed over the Gobi. For all sought something. Some sought wealth by i selling merchandise which was scarce in the wilderness, receiving payment in gold dust and gradually accumulating a fortune, though not as we estimate one here. Some collected coloured stones and shipped them to Peking, incurring the comment of the nomads: “What a strange country these people come from that they have no stones and must come all this way to collect them.” Some sought refuge from justice, adopting Mongolian manners and attire in an endeavour to change their identity. Botanists came looking for new plants and rare flowers and seeds; anthropologists [Photographs reproduced from “.The Gobi Desert”.: Mildred Cable

searched after early traces of mankind; meteorologists sent up balloons to assist their, study of air currents in readiness for future airways. The Gobi people themselves, were a simpler, more direct folk, who had no hesitancy in discussing spiritual things, and their search was for truth.

The dominant landmark of the desert was the obo, or altar of stones raised to the unknown god. Every wayfarer made some offering at these shrines— silken banner, coins f pretty pebbles, or perhaps a lock'of hair, but the Trio who travelled the ancient trade routes seeking to save the souls of men always left copies of the Scriptures translated into the various languages for those who followed the highways of the desert. ; To these three noble women was entrusted the task of bringing Christianity to the peoples of Central Asia. The Trio have abundantly proved the verity of Christ’s injunction in His sermon on the mount: “ anb ye sfljall finb; knock ant it 1 shall be openeb unto you. jfor ebery one tfjat as&etfj reciebetfj; / anb Ije tfjat seehetlj finbetij....” fl with Francesca French. London. Hodder and Stoughton Limited.]

THE GOOD NEIGHBOUR k —