Bus Comfort and How to Achieve It
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Some Points from a Paper by Mr. R. Beveridge on the Lighting. Heating and Ventilating of Passenger Vehicles THE second paper read on May 20 at the Scottish Road Passenger Transport Association Conference was " Lighting, Heating and Ventilating of Public-service Vehicles" by Mr. R. Beveridge, of the Scottish Motor Traction Co., Ltd. . The author points out that he is giving his personal views on problems which he considers have received too /ittle attention in the past, or in which the least progress has been made, and that his remarks are not in any idle spirit of criticism. He deals only briefly with lighting, because, technically, it has some connection with his other subjects.
Anxiety to Obtain Maximum Light.
The bus engineer has to consider dynamo output and battery capacity. Consequently, his anxiety is to see that he gets as much light out of each watt as possible; the more so because of the public demand.
The latest vehicles have as many as 21 12-watt lamps, equal to roughly 250 c.p.—fully twice that necessary in a room of similar size. Bus lighting is, however, a different problem. The ceiling of a room is usually light, and the walls never very dark, but in a bus the lights are usually under the parcel racks; consequently, there is not much reflected light from the roof, and windows replace walls.
On the S.M.T. buses the C.A.V.-Bosch D.0.7.X. dynamo with an output of 25 amps. at 24 volts is employed. The batteries are Exide F.M.F.R.H. with 12 cells and a capacity of 180 amp.-hours at the 10-hours rating. All circuits are 12 volts apart from the starter for the oil engine. The dynamo is exceptionally large and absorbs 1 h.p.
Considering heating and ventilating, in the author's view these should be classed together, and it should be taken as an axiom that the air pressure should be higher inside the bus than outside. The first war tanks had extractor fans, which created a slight degree of vacuum. When the guns were fired and the breeches opened, picric-acid fumes were blown into the tanks, to the extreme discomfort of the crews. The system was immediately altered so that the fans blew air into the tanks; then the fumes were forced out wherever there was an opening.
To-day many buses have extractors, and every cubic foot of air removed must be replaced by outside air entering the bus wherever it can do so, and in many cases it will bring fumes and dust. If the air pressure inside the vehicle were somewhat higher than atmospheric, then the current through the openings would be outward and not inward. The only way to have the pressure higher is to blow air into the vehicles, and the passengers will not tolerate this unless the air be heated before entering.
Air-conditioning plant has been used in ships for years and, later, in railway carriages and aeroplanes, and it is time that the road-transport people were tackling the matter.
B46 Heating and ventilating, are more necessary on a bus than on a tram because of the longer journeys, but the difficulties are much greater on the former, especially in the case of oil-engined vehicles, as the heat generated by such engines is considerably less than with the petrol type. The author believes that the problem can be solved only by co-operation between operators and makers.
He considers that it would be essential to obtain most of the heat from the exhaust manifold, but this means a fairly elaborate casting, and particular care is required to see that no exhaust fumes enter the duct conveying fresh air over the manifold. It is important that the pressure in the whole length of the duct should be above atmospheric, which means that the impeller should be at the entrance.
One trouble experienced with this arrangement was that on long down-bill runs with the engine idling, the manifold temperature dropped considerably, and it was found necessary to fit hot-water pipes in addition. The flow of circulating water from the engine to these pipes must, of course, he controlled thermostatically. The water temperature drops at the same time as that of the manifold, but not, nearly so rapidly. Having heated the air, it should be -delivered along ducts running the whole length of the vehicle to make the warmth as uniform as possible. When placed near the floor or roof, they should be insulated from the body Sides.
If Would seem preferable to situate them near the floor, and the air intake must be external; if it be inside it would be simply heating the same air over and over again, ana-this is not ventilating. The ingress of air should be at the front of the vehicle and as high as possible.
Possibilities of Air Conditioning.
So far the author has dealt only with the heating of the air. In summertime this is, of course, unnecessary, and, in fact, in some countries cooling may be required—a difficult problem, as a small refrigerating plant would be necessary.
In a proper air-conditioning plant. air is filtered and brought to the correct degree of humidity, but Mr..Beveridge confesses that he is not a ventilating engineer and can say little about that side. He is afraid that an efficient filter would mean a more powerful fan, and there. is at present little spare current available for this. Consequently, he would be prepared, meantime, -to cut out these refinements and confine the work to obtaining such a combined
heating and ventilating system as he has outlined.