A modern household refrigerator seems like a simple device: plug it in and forget it. However, behind the metal walls hides a complex engineering system, the main task of which is to preserve the cold. Thermal insulation plays a decisive role here, because it is the quality of the insulating layer that determines how much electricity the compressor will consume and how long the food will remain fresh during a power outage.
Many owners wonder what it is the material that is located inside the housing, especially when faced with problems such as the appearance of condensation on the outer walls or freezing of the corners of the chamber. Understanding the structure of insulation is necessary not only for general development, but also for a competent approach to repair or restoration of equipment. In this article, we will look at what fills the space between the walls of refrigerators, why some materials are better than others, and what to do if the insulation has ceased to fulfill its functions.
The issue of choosing a material is decided by manufacturers at the model design stage. The energy efficiency class and the final cost of the device depend on this. Polyurethane foam has become an industry standard, but there are alternatives that have been used in the past or are used in specific models.
Main thermal insulation materials in refrigeration technology
Development history refrigeration equipment knows several types of insulation. The oldest models, released several decades ago, often used glass wool or mineral wool. These were bulky structures with thick walls, which could cake over time, losing their properties. Today, this approach is considered archaic and ineffective.
The modern standard is polyurethane foam (PPU). This material foams directly into the cavity between the inner plastic casing and the outer metal casing. In the liquid state, the components mix and rapidly expand, filling all the voids, corners and spaces around the evaporator tubes. After hardening, a rigid foam-like structure with closed cells is formed.
⚠️ Attention: Polyurethane foam releases toxic substances when burned. When dismantling an old refrigerator or disposing of it, it is strictly forbidden to burn the insulating layer over an open fire.
There is also the concept vacuum panels (VIP), which is used in premium models to increase the usable volume with the same external dimensions. They provide better insulation than polyurethane foam, but damage during repairs leads to complete loss of properties. The use of such panels makes the walls thinner, but significantly increases the cost of the structure.
Why polyurethane foam has become the standard
The dominance of polyurethane foam is due to a unique combination of physical and economic characteristics. The main advantage is the low coefficient thermal conductivity. This means that the material transmits heat from the outside very poorly, allowing the compressor to turn on less often to maintain the set temperature.
Pouring technology allows you to create a monolithic layer without seams or joints. Unlike laying sheet materials, liquid foam penetrates into hard-to-reach places and flows around technological holes and fasteners. This eliminates the formation of cold bridges bridges of cold — areas where heat penetrates faster, causing local freezing or condensation.
- 🧊 High adhesion: the material firmly adheres to metal and plastic, creating a single structure.
- 💧 Moisture resistance: the closed cellular structure does not absorb water, which is critical for working in conditions of temperature changes.
- 🛡️ Mechanical strength: hardened foam gives additional rigidity to the case, protecting the internal chamber from deformation.
It is important to note the environmental aspect. Previously, freons were used as a foaming agent, which destroys the ozone layer. Modern manufacturers have switched to cyclopentane and other safe gases, which makes the operation of equipment safe for the environment.
Design features of the insulating layer
The wall of a modern refrigerator is a multi-layer sandwich. On the outside there is a sheet of steel, often with a polymer coating, then there is a layer of polyurethane foam, and inside there is a plastic box made of ABS plastic or polystyrene. The thickness of the insulation varies depending on the model and energy efficiency class.
In budget models, the layer thickness can be 2-3 cm, while in devices of class A++ and higher it reaches 5-7 cm or more. An increase in thickness directly affects the useful volume: with the same external dimensions, a refrigerator with better insulation will have a smaller internal chamber.
| Type of material | Thermal conductivity coefficient (W/m K) | Service life | Moisture resistance |
|---|---|---|---|
| Polyurethane foam (PPU) | 0.022 - 0.028 | 15-20 years | High |
| Mineral wool | 0.035 - 0.045 | 10-15 years | Low (hygroscopic) |
| Expanded polystyrene | 0.030 - 0.038 | 15 years | Medium |
| Vacuum panels | 0.004 - 0.008 | 20+ years | Depends on the shell |
Particular attention is paid to the doorway area. An additional heating element (anti-condensation frame) is often installed here, since this place is most susceptible to the formation of moisture due to the contact of the warm air of the room with the cold end of the housing.
Problems with insulation: wetness and mold
One of the most serious problems is moisture getting inside the thermal insulation layer. This can happen due to mechanical damage to the housing, when the tightness of the internal chamber is broken, or due to a manufacturing defect when pouring foam. Water that gets into the polyurethane foam sharply reduces its insulating properties.
Symptoms of insulation getting wet are:
- 💧 The appearance of “dew” or drops of water on the outer walls of the refrigerator.
- ❄️ Local freezing of sections of the body (for example, the corner freezers).
- 📉 Increased compressor operating time and increased electricity bills.
If water freezes inside polyurethane foam, when it expands, it can rupture the cells of the material, which leads to irreversible destruction of the insulation structure. In the long term, this is fraught with the development of mold inside the wall, the spores of which can get into the food storage chamber.
⚠️ Attention: If you notice swelling of the inner plastic panel or the appearance of yellow rust spots on the outer wall, this is a sure sign that the insulating layer is getting wet and requires intervention.
Can it be replaced? insulation yourself
Theoretically, it is possible to replace polyurethane foam, but in practice this is an extremely complex and labor-intensive process that is rarely economically justified. To do this, it is necessary to completely disassemble the body, removing the old material, clean the surfaces and re-fill with two-component foam.
The difficulty lies in the fact that the polyurethane foam tightly glues the inner and outer shells. Separating them often results in deformation of the plastic or metal. In addition, at home it is impossible to reproduce the technology of factory pressure filling, which ensures uniform distribution of the material.
Alternative restoration methods
Some craftsmen try to drill holes in the case and pump polyurethane foam into it. This is ineffective, since the foam expands with enormous pressure and can simply squeeze out the inner wall of the refrigerator, deforming the chamber.
A more reasonable solution in case of serious violation of thermal insulation is external insulation or replacement of the unit. If the problem is local (for example, the seal has come off or the plastic is cracked), you can try to eliminate the cause of moisture, but it is almost impossible to restore the factory properties of polyurethane foam.
☑️ Diagnosis of insulation problems
The influence of insulation quality on energy consumption
Quality thermal insulation directly determines the energy efficiency class of the refrigerator. The better the material holds the cold, the less often the compressor turns on. In modern models, it is the improvement of insulating materials that has made it possible to achieve consumption rates of 200-250 kWh per year.
If the integrity of the insulating layer is damaged, the load on the compressor increases significantly. The engine wears out, trying to compensate for heat inflows, which leads to its premature failure. Therefore, caring for the case is not only a matter of aesthetics, but also a way to extend the life of the equipment.
It is worth considering that even a small hole in the case, for example, for laying an additional wire or sensor, must be carefully sealed. Any unprotected area will become a channel for the penetration of warm air and moisture.
Frequently asked questions (FAQ)
Why are drops of water protruding from the outside of the refrigerator?
Most likely, the seal of the internal casing is broken, and moisture from the chamber has entered the insulation. Also, the reason may be high humidity in the room and a malfunction of the anti-condensation frame around the door.
Is it possible to use regular polyurethane foam for repairs?
No, household polyurethane foam has a different structure and expansion coefficient. It will not provide the necessary thermal insulation and can deform the body when it hardens. A special two-component mixture for refrigerators is required.
Is polyurethane foam inside the refrigerator harmful for food?
No, after complete polymerization (hardening), polyurethane foam is chemically inert and safe. It is completely isolated from the inner chamber by a plastic box and does not come into contact with food.
What to do if there is a mold smell in the refrigerator?
If the smell is not eliminated by washing, mold may have grown inside the thermal insulation layer through microcracks. In this case, repair is often impractical, since disputes will constantly appear.
How to check if the insulation is wet?
When the compressor is running, carefully touch the outer walls. If individual areas are icy to the touch or condensation appears on them while the rest of the surface is warm, the insulation in this place is broken.