r 
4 
, 
. 
REFRIGERATION AND REFRIGERATOR INSULATION ON BOARD SHIP. 153 
The difference between the heat inflow through the insulation and the total 
heat actually absorbed by the melting of the ice is the amount of heat entering the 
box from other sources than through the insulation. This excess of heat ordina- 
rily occurs during the daytime only, 7. e., when the box is being opened, since at 
night the box remains closed. A machine, to be of sufficient capacity to produce 
the temperatures actually obtained with ice, therefore, must be large enough to ob- 
sorb the heat inflow through the insulation and also the additional heat entering 
during the daytime from other sources, 7. e., to take care of this entire load during 
the day. Stated in another way, the machine must be large enough to absorb, dur- 
ing the daytime part of its run, half of the total insulation loss plus all of the bal- 
ance of the loss. 
Fourth, a further fact to be taken into account in determining the proper size 
of machine is that the temperatures which are obtained with ice are not satisfac- 
tory. If they were satisfactory, one of the greatest reasons for putting in cooling 
machinery would be void. Where a temperature of 55° can be obtained with ice, 35 
to 45, will be demanded of mechanical cooling. Therefore the machine size must be 
further increased in proportion to the number of degrees difference of temperature 
required. For instance, if the outside temperature is 71° and the temperature desired 
is 35 , where the ice temperature has been 55° the machine size must be increased in 
the proportion of 71 minus 35, divided by 71 minus 55, or 2% times. 
Fifth, furthermore, if the cooling machine were installed in accordance with 
these figures it would handle average summer weather conditions, but would be in- 
sufficient for extreme hot weather, the most important condition to be met by refrig- 
eration. It is necessary, therefore, to further increase the size of the machine in 
the ratio of the difference between the maximum summer temperature and 35 and 
the average summer temperature and 35 . 
Sixth, one further allowance should be considered, namely, the fact that in 
many cases, for one reason or another, it is either impossible or undesirable to oper- 
ate the machine except during certain parts of the day. The machine size must, there- 
fore, be increased by as much as may be required to produce the desired amount of © 
refrigeration in the short time available. 
Seventh and finally, if the machine is not placed directly beside the box to be 
cooled, allowance must be made for the heat inflow into the insulated cold main. 
The amount of heat entering from this source is often of considerable import- 
ance, particularly with small machines. 
When one comes to apply these figures to an individual case the size of machine 
is apt to work out so large as to be rather startling. There are so many elements 
that are entirely uncertain, such as the kind of workmanship in the insulation, the 
amount of leakage through doors, the kind of care the refrigerator will be given, the 
probability of the doors being left more or less ajar; there are, in fact, such a multi- 
tude of very uncertain elements that considerable leeway ought to be allowed in the 
size of machine. 
Where the amount of refrigeration is large, as in a good sized storage ware- 
