Refrigerated Vehicle Standards
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" THERE is a need for a British stan dard to govern the level of heat transfer through a refrigerated vehicle and to determine the refrigeration requirements," said Mr. P. A. Thompson, transport manager of Birds Eye Foods Ltd., in a paper given to the International Convention on Frozen Foods and Refrigeration at Earls Court, London, recently:
Such a standard was necessary, he said, to protect three groups: (a) The casual user of refrigerated transport, who would be able to specify, by requesting a particular category of vehicle, exactly what standard he required. In the event of his having to provide the refrigeration (e.g. solid carbon dioxide) he would know exactly what level of refrigeration to apply. At present, with no set categories, the casual hirer of refrigerated transport did not know the vehicle's• thermal efficiency, and was not able to determine precisely what level of refrigeration to apply; (b) The buyer of vehicles; (c) The vehicle builders themselves, who would be protected against unfair competition brought about by the use Of inferior materials and workmanship.
After considering various methods by which one could set a standard for permitted heat transfer, Mr. Thompson said Birds Eye had concluded that the right course was to follow the method established on the Continent, where the standard was based upon the "U" value of the vehicle, i.e., the heat transferred through each sq. ft. of the surface area of the vehicle per hour per degree F. of temperature differential between inside and outside the vehicle,
The Continental standard was 0-0716 B.T.Ufhourift2/°F. This was agreed for low temperature vehicles three, years ago and, with the introduction of new con
structional methods and new insulated materials. he believed that Britain should aim for a higher standard.
Currently it was possible to obtain vehicles with guaranteed " U " values of less than 0-04, and it was desirable that a standard should, in fact, be set at a " U" value near to 0105. This meant that a vehicle insulated with 5-in. polystyrene of a " K " value of 0-2 would need to be 80 per cent thermally efficient in order to achieve the standard. A vehicle insulated with 5-in, polyurethane at a "K" value of 0'16 would need to be only 64 per cent thermally efficient.
There were three methods for testing insulated vehicles for heat transfer, namely cooling by the use of dry ice, cooling by the use of brine, and heating. The brine cooling method was preferred because body stabilityCould' be achieved before the test took place. (The criticism against the drY ice method was that stability was difficult to achieve.) Brine cooling also simulated operating conditions, in that the temperature differential was in . the. -right direction—cold inside the vehicle and warm outside.The criticism against the heat method was that this differential was reversed. Facilities for brine testing did not exist in Britain, and would need to be specially constructed. Mr. Thompson said.
There was a problem in determining the level of refrigeration which should be applied. However, the standards arrived at for practical application and which followed the pattern of Continental standards were:—
(a) Long Distance Vehicles—the vehicle should pull down to and hold 0°F. in an ambient temperature of 90°F. for a period of 24 hours.
(b) Delivery vehicles making fewer than 25 deliveries per day—should be capable, of holding a temperature of 0°F. in a 90°F. ambient temperature for 18 hours.
(c) For, more than 25 deliveries per day—the period should be extended to 24 hours.