CHAPTER X OPERATION OF ICE REFRIGERATORS. Temperature. — The usual method of solving the household refrigeration problem is by the use of ice in any of the standard type refrigerators. The refrigerator using ice will have a temperature in the food storage compartments 20 to 30 degrees lower than room temperature. <Callout type="important" title="Critical Rule">A temperature difference of about 10 degrees between the coldest and warmest part of the food storage compartments is necessary to insure good circulation of the enclosed air.</Callout>. The better type refrigerators with very good insulation will approach the 30 degree temperature difference when there is a good supply of ice. A temperature difference of about 10 degrees between the coldest and warmest part of the food storage compartments is necessary to insure good circulation of the enclosed air. This heat transfer is mostly by convection, the circulating air acting as the carrier. The coldest part of the food storage space is the lower part directly under the ice compartment. <Callout type="tip" title="Pro Technique">The melting-ice, of course, is always at a temperature of 32° F.</Callout> The temperature in the warmest part of a refrigerator should never be higher than 50° F. for the proper preservation of food. The temperature of the coldest air dropping into the food compartment is usually between 40° and 50° P., depending upon the amount of ice, the type and construction of the box and the temperature of the air entering the top of the ice compartment. <Callout type="warning" title="Safety Hazard">Melting ice has a temperature of 32° and the best circulation which can be obtained will not keep the warmest part of the food compartment at a temperature less than 50° in a room of 90°.</Callout> Circulation of Air. — There is a constant circulation of air in refrigerators as long as the ice lasts. For the preservation of food, it is equally as necessary to have good air circulation as it is to maintain a low temperature in the food compartment. No matter how cold the air is, it will not preserve the food properly unless the air is in active circulation. <Callout type="risk" title="Risk of Failure">A gain in efficiency can be made by having the warm air flues against the exterior wall getting the path of the cold air in the center of the box.</Callout> This will make an appreciable saving in the amount of ice used. It is advantageous to have the ice compartment so constructed that the ice will never project above the lower level of the warm-air opening into this compartment. Careful tests have shown that there is a real gain in efficiency by doing this.
Humidity. — Humidity is the water vapor in the air. Atmospheric air always contains a certain amount of water vapor mixed with it. Air at a certain temperature and pressure can contain a definite amount of water vapor. When this amount is exceeded, the excess water vapor will condense. Perfect refrigeration depends as much upon dryness as it does upon cold. It is very essential to have a circulation of so-called 'dry' air in order to properly preserve food in a refrigerator. <Callout type="important" title="Critical Rule">It is just as important that the humidity be low as it is that the temperature be low.</Callout> A practical example is the poor results obtained by keeping foods in the ordinary ice chest where there is considerable moisture and poor air circulation.
Example: Suppose atmospheric air at 80° F. had a relative humidity of 60 per cent. The amount of water vapor in each 100 cubic feet of air would be 60 X 0.1564 or 9.384 pounds 100. The relative humidity inside a refrigerator is highest where the cold air drops out of the ice compartment. The relative humidity is lowest at the top of the food compartment where the warm air enters the ice compartment.
Air Circulation Tests.— A simple method of measuring the rate of air circulation is to place an anemometer in a flue opening in various positions to find the average velocity. Knowing the velocity of the air through this opening and its area, the amount of air circulating can be calculated. <Callout type="gear" title="Specific Equipment">A heat balance method is sometimes used to determine the approximate rate of circulation.</Callout> The heat loss through the walls is determined by an ice-melting test. It is then assumed that this loss is due to the circulating air carrying the heat by convection from the walls of the cabinet to the ice.
Humidity Test. — This test was made on a well-insulated cabinet, cooled with a brine tank. The temperature of the brine during the test varied from 18° F. to 22° F. Several tests similar to this one indicate that the relative humidity of the food compartment can be approximately determined by computation. It is only necessary to know the temperature of the cooling element and the temperature of the food compartment.
Desirable Humidity Indoors, — Humidity control in homes is important for preserving food quality.
Key Takeaways
- Maintain a temperature difference of about 10 degrees between the coldest and warmest parts of the refrigerator to ensure proper air circulation.
- Ensure good air circulation for effective food preservation, as cold air falls while warm air rises.
- Keep humidity levels low in refrigerators to prevent bacterial growth and spoilage.
Practical Tips
- Regularly check and adjust the temperature settings to maintain a consistent environment for food storage.
- Use an anemometer or other tools to measure air circulation rates, ensuring efficient cooling.
- Keep the ice compartment well-insulated to minimize ice usage and reduce energy consumption.
Warnings & Risks
- Be cautious of high humidity levels in refrigerators as they can lead to bacterial growth and spoilage.
- Ensure proper insulation around warm-air openings to prevent heat from entering the food storage area.
- Monitor temperature differences between compartments to avoid hot spots that could compromise food safety.
Modern Application
While the techniques described in this chapter are rooted in historical practices, they still offer valuable insights for modern survival preparedness. Understanding basic refrigeration principles can help in setting up emergency cooling systems during power outages or in remote locations. The importance of air circulation and humidity control remains crucial for preserving food quality.
Frequently Asked Questions
Q: What is the ideal temperature difference between the coldest and warmest parts of a refrigerator?
The chapter recommends maintaining a temperature difference of about 10 degrees between the coldest and warmest parts of the food storage compartments to ensure proper air circulation.
Q: How can I measure the rate of air circulation in my refrigerator?
You can use an anemometer placed in a flue opening to find the average velocity, or you can calculate it using the heat balance method by determining the heat loss through the walls and assuming this is due to circulating air.
Q: Why is humidity control important in refrigerators?
Humidity control is crucial because high humidity levels can lead to bacterial growth, spoilage, and poor preservation of food. The chapter emphasizes that it is just as important to maintain low humidity as it is to keep the temperature low.