It is only in exceptional circumstances that a food service manager is called upon to express an opinion on the selection of fuel. When she is appointed she usually finds that the nature of the equipment already installed has settled the question for her. Nevertheless, she may at any time be called upon to advise on additional items of equipment, or on the planning or re-planning of a kitchen and the equipment to be installed in it, and the decision on the fuel to be used is of fundamental importance, influencing costs and determining practice for many years ahead. She should therefore be concerned with all aspects of the fuel question, and ready with facts and figures when necessary. Her advice is likely to be based to some extent on practical experience, but it is important that she should not allow familiarity with only one type of fuel to weigh too heavily when she makes her recommendation. It must be realized at the outset that the question is a complicated one because there are so many general factors, such as cost, convenience, performance, etc., each of which must be considered separately in relation to the four main heat sources available, namely, solid fuel, oil, gas, and electricity, all of which again may be used either directly or indirectly in the form of steam. Moreover, although it would seem to be a simple matter to obtain conclusive figures to support the recommendation for the use of any one fuel, it is not easy because there are great variations in the way in which equipment is used even when almost identical kitchens are involved.
Outline of Heat Sources
The term fuel is used somewhat generally to cover the basic sources themselves such as coal and oil and their products gas and electricity. For the sake of clarity it is useful to adopt another term, namely heat sources, and to classify as follows:
Heat Sources used both Directly and Indirectly as Steam:
1. Solid fuel
Heat sources of particular interest to the food service manager are dealt with in some detail below.
The solid fuels which concern the caterer fall into two groups (a) the bituminous coals and (b) the smokeless fuels comprising anthracite, smokeless briquettes and coke, the essential difference between the two groups being in the volatile content. Coals included in the first group may have a volatile matter content ranging from 18% to 45% whereas for anthracite the figure is 4%–10%. Coal with a volatile matter content between 10% to 18% is considered to be a smokeless fuel and is sometimes referred to as steam coal, sub-bituminous (10%-14%) and semi-bituminous (14%-18%). It is interesting to note that about 90% of the annual output of the coal mines in this country falls into the bituminous group.
Bituminous coal, anthracite and coke differ considerably from each other in density, a factor to be considered in relation to storage facilities. Coke requires twice the storage space of an equal weight of coal and needs also a larger fuel bed in the furnace.
Coke is used frequently for steam raising and the production of hot water, and the three main types are gas coke, hard coke and low temperature coke. The first is made during the manufacture of coal gas and is less dense and more porous than hard coke, which is made in coke ovens and is used mainly for metallurgical industries. The process for the production of low temperature coke is similar to that employed for gas coke, but whereas temperatures of up to 1000°C. are used for the latter 600°C. is used to produce the former. The temperature at which coke will ignite depends on the temperature to which it has been submitted during manufacture. Some of the low temperature cokes ignite at temperatures as low as 450°C. whereas a hard coke may not ignite until well over 600°C.
The size of the coke chosen depends on the equipment used and manufacturers will usually make recommendations on this matter.
Briquettes are a useful alternative to coke and anthracite where a smokeless fuel is required, and they have the advantages of low ash content, high density, cleanliness and ease of handling, and consistency of size and quality. They are made by mixing the dust of anthracite and bituminous coal with a smokeless binder and pressing it into blocks and cakes.
Two types of gas are, in the main, available in this country for catering namely Town Gas and Calor Gas. The former is available in all urban areas and is supplied through pipes at a pressure of 2 to 3″ water gauge (i.e. about 0.1 lb. per sq. in.). The latter is supplied in cylinders of two sizes, one of 32 lb. containing approx. 210 cu. ft., and the other 83 lb. containing approx. 520 cu. ft. The cylinder pressure is 18 lb, to 25 lb. per sq. in. at 60°F. which for use in kitchen equipment is cut down by a low pressure regulator to 11″ water gauge (about 1/3 lb. per sq. in.). Owing to the differences in the pressure and composition of the two gases specially designed burners are needed for equipment using Calor gas. Natural gas is now available in some parts of the country and its use is gradually increasing.
Town gas, Natural gas and Calor gas differ in calorific content. Calor gas is 3200 B.Th.U. per cu. ft.; Natural gas 1000 B.Th.U. per cu. ft.; Town gas varies, but over 90% of the gas available lies within the range of 450-500 B.Th.U. per cu. ft. The gas supplied by the N. Thames Gas Board, i.e. the London area, has à calorific content of 500 B.Th.U. per cu. ft.
Although Town gas is supplied to the consumer through a meter which records the quantity supplied in cu. ft., the basis of charge in this country is a unit of 100,000 B.Th.U. which is known as the Therm. Thus if the calorific value of the gas supplied is 500 B.Th. U. per cu. ft., 200 cu. ft. will have a heat energy of 1 Therm.
The use of electricity as a source of heat in the kitchen involves the caterer in none of the problems of variety which surround the use of coal, oil and gas. There are, as we have seen, many kinds of coal with different characteristics and widely different calorific values. To a lesser extent the same applies to oil and gas. With electricity: however, we measure the commodity by the heat it contains a unit of electricity always produces the same amount of heat. The unit of electricity itself, known as the kilowatt hour, is the amount of energy which is supplied when a 100 watt element operates for 10 hours. It is also the amount of energy resulting from using a 1000 watt element for one hour. No matter at what rate the electricity is used the product of watts and time divided by 1000 gives the number of units expended and for each of these units the heat equivalent is 3412 B.Th.U.
A British Thermal Unit is the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit. It is found by experiment that the amount of heal produced by one unit of electricity will raise the temperature of 3412 lbs. of water one degree Fahrenheit and this accounts for the conversion factor quoted above. It is thus possible to compare the amount of heat available from a pound of coal, a cubic foot of gas and a unit of electricity, but obviously this alone is not sufficient; consideration must also be given to the thermal efficiency or the efficiency of heat conversion of the particular appliance under consideration.
For catering purposes the two main types of fuel included under this heading are paraffin or kerosene, and fuel oils which include gas oil, light fuel oil and heavy fuel oil. Paraffin is not used extensively in catering except in certain special cases such as canteens in remote parts where the other fuels more convenient in use are not available. Fuel oil is not used directly for the heating of cooking equipment, but only for steam raising and water heating. Gas oil is the most suitable fuel for this purpose, the other two being used mainly in industry. The calorific values of kerosene and gas oil are 1.5 and 1.6 Therms per gallon respectively.
FACTORS AFFECTING CHOICE
The following are the main factors affecting choice.
Initial Costs Including Installation
One of the first points to be considered when estimating the advantages and disadvantages of the different fuels is the cost of the necessary equipment for each type. Price lists from different manufacturers will show variations in price quoted for comparable items due usually to differences in quality or in the actual design It is usually found when comparing the prices of pieces of equipment which are similar in all respects except the actual fuel to be used, that that designed for steam is the most expensive, and that the cheapest is that designed for solid fuel (excluding the heat storage types which are the most expensive). Those using electricity or gas come between the two with the former usually a little more expensive than the latter. Oil fired cooking equipment is not really comparable with the other types as the models available are limited in scope. In the restricted field in which comparison is possible it will be found that the prices are less than for any other types of equipment.
Comparison of the costs of installing equipment fired by the different fuels can only be made accurately by taking figures for identical layouts equipped with items using the different fuels, but such figures are not easy to obtain. The three main fields to be considered are gas, electricity and steam, and although it is not practicable to equip a kitchen entirely with steam equipment, and therefore to some extent choice is restricted to gas or electricity, in the choice of equipment for other sections of the work, as, for example, boiling, steaming or for heating hot cupboards choice is not restricted. Where such comparisons are possible it is known that installation costs are highest for steam and cheapest for gas. Electrical installation costs are higher than those for gas owing to the high costs of the switchgear required. However, when gas is used the products of combustion will place a heavier load on the ventilation system of the kitchen than is necessary when electricity is used. Any extra expenditure which this necessitates should therefore be added to the installation costs for comparative purposes. The high costs of steam installations are the result of the expensive network of high pressure pipes with the connecting valves and traps, but do not take into consideration the cost of the steam generator itself, since in many cases this has already been installed for the main building served by the kitchen. If, how. ever, this is to be provided specially for the kitchen a considerably higher initial cost will of course result. The installation costs of coal fired equipment are less than any of those already considered, and for oil-fired equipment are non-existent, but as their use is limited comparisons are of little value. A large kitchen using solid fuel appliances only is not a practical proposition and one using oil only would not even be considered.
When considering the running costs of various pieces of cooking equipment the price of the fuel used in relation to its calorific valve is the first consideration. Other factors are the efficiency of the equipment, the degree of skill required to ensure efficient use or the fuel, the amount of labor needed to supply the fuel to the equipment and the maintenance costs. in order to compare costs of fuels it is necessary first of all to work out the price of a unit of heat supplied by each and the following table gives current prices (1969), calorific values and cost per Therm for a variety of common fuels.
Electricity appears expensive but in some pieces of equipment, as for example water heaters where the element is immersed in the water a hundred per cent efficiency can be achieved by lagging to prevent losses due to radiation. Thus it appears that before costs of fuel can be compared another figure must be considered, namely the working efficiency of the appliance. This can be defined as the percentage of useful heat available for the fuel consumed and may be used to determine the cost per useful Therm. Working efficiency figures will vary for the same fuel from one appliance to another according to design. Thus for the heat storage type of solid fuel cooker working efficiencies of up to eighty per cent are claimed, whereas for the non-insulated type of coal-fired range the figure may be as low as twenty per cent and even in modern well-designed equipment never exceeds about forty per cent. Average percentages for the three main fuels are as follows: solid fuel 20-30, gas 50-60, electricity 80-100. Thus, for example, if the working efficiency of gas is taken as 50 and that of electricity as 100 the cost per useful Therm of the former is 57d. and of the latter 57.24. But such figures can only be taken as a very general guide and must be considered carefully in relation to other factors influencing efficiency, such as equipment design and the degree of skill required to ensure efficient use of fuel. This latter point is of considerable importance when comparing real costs of gas and electricity. To obtain the maximum value from the current used in electrical cooking equipment full use must be made of the residual heat remaining after the current has been switched off, and this is not always practicable in catering even if it were possible to obtain staff who are fully appreciative of its importance.
In a discussion of comparative costs of fuels the controversial question of gas versus electricity inevitably arises. Reliable figures on this subject are not easy to obtain since each party tends to quote examples favoring his own side. However, it is agreed that electricity can be used more efficiently for roasting, baking and toasting than for boiling and frying and therefore any comparisons must be made separately for these two groups of operations. Such figures as are quoted are obtained by comparing fuel consumption from comparable kitchens or from kitchens which have used one type of fuel in the past and been converted to use another. It is claimed by one party that twenty units of electricity are equivalent to one Therm of gas and by the other that ten is the equivalent figure. Such figures are used generally to cover fuel usage in equipment for all types of cooking operations but in fact probably refer mainly to roasting, baking and toasting. The figure for the other group of operations is nearer to forty units of electricity to one Therm. However, the limits are at least defined and costs can be compared.
As has already been mentioned, solid fuel is not now used extensively for the direct heating of cooking equipment in large kitchens. There are, however, kitchens serving small numbers of meals where the use of ranges fired by this method is quite satisfactory. Such kitchens are found in country guest houses, school canteens in remote parts, youth hostels, etc. Coal consumption for these ranges varies according to size, design and use. For example, a 6ft. black non-insulated range with two ovens of the type installed in many canteens during the war will consume up to 36 tons of coal a year, whereas the heat storage type of cooker of similar capacity has an annual consumption which does not exceed 10 tons. Thus although a strict arithmetical calculation shows solid fuel to be the cheapest form from the point of view of calorific content, it is obvious that in practice it is the most economical only when the equipment in which it is used has a high working efficiency.
Another method for comparing running costs in terms of fuel used is to calculate the amount per meal served. Such figures are not easy to obtain, partly because the majority of large kitchens are not restricted to one fuel only for cooking, and partly because this is not a calculation required for normal running purposes and would therefore only be prepared for a specific inquiry. It is a useful figure to have for comparative purposes when estimating or analyzing overhead costs. From the figures available it seems that fuel consumption per meal served falls as the output of the kitchen increases.
The gas consumption is higher in the factory canteen because the meal includes soup and tea. For the latter cu. ft. gas per cup is considered to be reasonable, the amount used decreasing slightly as the numbers increase.
Other figures taken from recent American practice are somewhat lower, the average per meal for gas being given as 1800 B.Th.U. which converted to cu. ft. of gas of 450 B.Th.U. per cu. ft., is 4 cu. ft. gas per meal served. The comparable figure for electricity is 0.3 unit a figure which lines up more nearly with those considered by The British Electrical Development Association to be reasonable. In view of the difficulties of ensuring the most economical use of fuel by kitchen staff it is not safe to base estimates on the lower figure.
It is generally agreed that the indirect use of fuels in the form of steam should not be considered for the smaller kitchens. Thus in Post War Building Studies No. 9. Mechanical Installations it is stated that steam is not recommended for kitchens of less than 500 meals unless it is readily available. In his lecture mentioned above J. C. Morris expresses the view that if a steam plant is required for other purposes in a new building, it always pays to increase the size of the boiler to serve the kitchen also. The use of steam in large central kitchens of 1000 to 2000 meals is also recommended even where a special plant is required, on the ground that the increased capital expenditure so incurred will be fully justified. Even when smaller sized kitchens are under consideration the use of steam may be justified where supplies of gas or electricity are unreliable or unobtainable.
Although no supporting figures are available, it would seen from the evidence that steam is not an expensive fuel for catering purposes. Where solid fuel fired boilers are used, this conclusion might be expected for the following reasons. In the first place, if the fuel is used efficiently it is the cheapest form of heat, and secondly, although steam generators may vary in performance according to the way they are handled and maintained, under first class conditions working efficiencies of up to 75% can be expected. Thirdly, steam cooking equipment, i.e. boilers, steamers and hot cupboards, can be considered to have working efficiencies approaching 100%, provided that steam traps and valves are maintained in good working order. Some heat losses must be expected in the transmission system but these are reduced to a minimum by efficient lagging. When all these factors are borne in mind it is clear that steam raised by solid fuel is a cheap source of heat for cooking. Where gas, oil and electricity are used for boilers, working efficiencies are given as 75% for the first two and 98-100% for the third and thus it would seem that from the point of view of the cost of fuel alone oil is the only one which compares at all favorably with solid fuel. Of course, as has already been pointed out in Chapter Eleven the amount of labor required is considerably reduced with gas, electricity and oil, a factor which may be of some importance when considering a particular scheme.
It is inevitable that expense will be incurred for maintenance work on cooking equipment and machines and it is useful to assess at the outset the extent of these costs. They may relate to the replacement of worn or defective parts or to labor charges for work such as scaling of water boilers or cleaning of burners on gas cookers, which is necessary to maintain the apparatus in efficient working order. An examination of the arrangements made by the gas boards and electricity authorities shows that practice varies somewhat throughout the country from one area board to another. Two examples are quoted below, one for gas and the other for electricity, and although they cannot be taken to apply generally in all areas they are typical of satisfactory arrangements which are possible.
The electricity authority recommends making arrangements for regular maintenance rather than waiting until something goes wrong; and states that correct maintenance consists of –
(a) A quarterly routine visit to ascertain that everything is in good working order.
(b) Periodical de-furring of all water boiling apparatus in hard water districts.
(c) Periodic visits to make a thorough inspection of all equipment. The electricity board would be prepared to quote for a fixed number of visits or to charge on a time and materials basis.
Where a caterer has gas appliances on hire (no new hiring arrangements are being made in the area concerned), the appliances are inspected once a year and defects are rectified by the gas board’s maintenance staff without additional charge. A maintenance service for equipment owned by the catering establishment can also be arranged, covering two, three or four regular visits per annum, with charges based on schedule rates for the types of appliance concerned. The charge for a single oven range for example is 22/- per visit including burner and tap maintenance and cleaning and the cleaning of flueways. Charges for the supply of spare parts are extra.
Although the above schemes apply to specific areas of the gas and electricity undertakings, similar arrangements could probably be agreed in other areas. Where difficulties arise in respect of specific items, the makers of the equipment concerned will usually advise or undertake the maintenance work themselves.
In many cooking operations it is necessary to vary the temperature of the heat source from time to time and the speed with which this can be achieved is a measure of the flexibility of the cooking equipment. There is no doubt that gas fired equipment ranks first in this respect for all methods of cooking including baking, boiling, steaming and frying; it can be equaled only in grilling, where electricity is also very flexible. For steaming and boiling, steam ranks second, electricity third and solid fuel fourth. It will of course be realized that boiling in a large kitchen may refer to that done in independent fixed pans each with its own source of heat or in smaller movable pans on boiling tables. The previous statement refers to fixed boiling pans and is only true of the second method of boiling when solid hot plates are used. Where the radiant type of boiling plate is used, electricity and gas are equally flexible for boiling operations. Solid fuel cannot be considered as flexible for roasting and baking, but in boiling on the hot plate its apparent inflexibility can be overcome by altering the position of the pan relative to the main source of heat. Over the whole of the solid top of a cooking range there is a considerable temperature gradient and careful use of this can to a great extent overcome the inflexibility of solid fuel. With solid fuel cookers of the heat storage type, the problem is not so much one of flexibility as of recovery rate. If the cooker is used continuously for both oven and hot plate work, heat reserves are used up and it is not possible to obtain the high temperatures needed for quick boiling or high temperature baking.
If, in addition to flexibility, the speed at which a particular piece of equipment can be brought into operation is also considered, steam for both boilers and steamers ranks first. If a head of steam is already available in the boiler house a steamer can be ready for use within 5 to 10 minutes after turning on the steam cork, whereas 15-20 minutes would be required for a gas fired steamer. And when the time taken to bring to the boil equal quantities of the same liquid in comparable boilers heated by steam, gas and electricity respectively is measured, the first of these is again found to be the quickest.
Other points to consider as influencing the choice are cleanliness in use, ease of use, comfort and convenience and of course the availability of each particular fuel because in certain districts neither electricity nor Town Gas are available and therefore only the other fuels can be considered.
On the score of cleanliness there is no doubt that electricity ranks highest and solid fuel lowest. For even though cooking pans do not nowadays come into direct contact with the fire itself there is always a certain amount of dirty work entailed in lighting fires, removing ashes and cleaning flues. Even where this work is reduced to a minimum, as in the continuous burning types of heat storage cookers, it is still existent and has to be contended with. In actual day to day handling there is little difference between gas and electricity as regards cleanliness. It is in the general effect on the kitchen over a period of time that the difference is noticeable because the products of gas combustion released into the atmosphere during cooking are deposited on walls and ceilings unless special flues are installed to take them direct to the outside. Nor is there much to choose between gas and electricity for ease of use when once the user has fully understood how each particular piece of equipment is best handled. When user reactions to these two particular fuels are taken, they are usually found to be influenced either by the flexibility of the fuel or by experience with one to the exclusion of the other. The first of these has already been dealt with and the second is not of importance when the question is considered as a whole.
The above five items have dealt with the main problems of choice of fuel in normal times. Restrictions imposed daily result, among other things, from the limited supply of solid fuel available. Some of these factors are predictable as in the case of unavailability of particular forms of solid fuel, and plans can be drawn up accordingly. Others, such as electrical power cuts and reduced and fluctuating gas pressure, are the result of events less easy to anticipate. Severe winter weather not only places an increased load on the supply of both electricity and gas but also may interfere with transport and so prevent the delivery of solid fuel in various places.
Variations in Fuel Costs in Identical Kitchens:
It is clear from the evidence already considered that fuel costs will vary from one kitchen to another depending on size, type of fuel chosen, level of maintenance of the equipment, type of meal cooked, and the efficient organisation of the kitchen. What is not always realized is that when these factors are eliminated and identical kitchens using the same fuel and producing similar menus are compared, fuel costs per meal may still show wide variations.