Ceramic insulation coating can provide energy savings of 20%-30% depending on ambient temperature, contents, weather conditions and application thickness. According to test data and results from applications, efficiency is higher in conditions with exposure to convection-based cooling compared to uninsulated surfaces. Efficiency in convection-based cooling conditions is roughly comparable to conventional materials. The difference is that coating-based insulated equipment will experience a faster heat drop and faster recovery compared to a slow heat drop and slow recovery in a conventionally insulated structure.
The graphic above shows surface temperature measurements on ferrous and stainless steel coupons, showing a 38% difference between a bare coupon temperature of 196F and the 122F coupon coated with 120 mils (3mm) of insulation coating. The nature of the coating is that each additional thickness contributes less and less to overall efficiency. That's common for all insulation. For this temperature range of 200F, a coating thickness of 80 mils (2mm) would typically be recommended for energy conservation and 40 mils (1mm) recommended for personnel protection.
Where is Insulation Coating Used?
Ceramic-based insulation coatings are used on oil storage tanks, heat exchangers, steam lines, refinery process towers, boilers, retork cookers, steam drums, ship structures, buildings and other equipment for retaining heat and saving energy. The typical upper service ceiling for this material is generally 320F/160C to 400F/208C. Ceramic-based coating is particularly useful on exposed equipment that has complex geometry and is more expensive to insulate with traditional materials or where conventional materials cannot be kept dry from rain or free from moisture and high humidity. It's not so much that the coating outperforms conventional materials' rated insulation values when measured at "0" relative humidity and at 70F. It's that conventional insulation is subject to failure due to moisture entrapment and cannot maintain it's rated value, while coating maintains insulation value over a long term, prevents corrosion under insulation and allows visual inspection.
How Does It Work?
Coating relies primarily on radiant heat blocking while conventional material slows down heat transfer with dense mass. The coating's high saturation of ceramic particles provides very low emissivity and transmittance characteristics that block radiative heat transfer. While there is some conductive heat transfer blocking, that's a smaller contribution compared to radiative blocking. A good analogy for low emissivity is "Low E" window coatings that also work by blocking solar radiation wavelengths' heat transfer. The low transmittance characteristic analogy is to compare drinking coffee out of a ceramic cup versus a metal cup. The ceramic cup transmits less thermal energy than the metal cup. These two heat transfer characteristics are very important in understanding how the thin coating blocks transfer of radiant heat energy.
Conventional insulation material's heat transfer rating test is conducted at 0% humidity & 70F. However, in the real world material becomes saturated with moisture at least up to the volume of relative humidity of surrounding air. Not a problem in very dry conditions. However, in most of the world that translates to 40-60+% relative humidity and simply a matter of time before almost all mass-based insulations are saturated to the local relative humidity level. At only 30% moisture content, rock wool's heat conductivity is reduced almost to that of water at 140F/60C and very close to window glass at 176F/80C. The advantage of coating is that it will not accept moisture and retains low heat transfer characteristics indefinitely.
Where Coating Does Not Work
And just as conventional insulation has a point of diminishing return when it comes to thickness, ceramic coating's effectiveness also becomes marginal beyond certain thicknesses at varying temperatures. Because radiant barriers react with thermal energy, they're useful when you have a heat source and do not store the heat energy to maintain a thermal battery as do mass-based conductive materials. This means that coating is very effective on heated equipment and much less so on unheated equipment applications such as preventing cold water lines from freezing. Insulation coating is effective in cold spaces with condensing surfaces based on it's low transmittance characteristics that essentially "take the chill off" and raise them above the dew point. Overall, insulation coating has many proven application in the field and can also be combined with conventional materials for solutions that leverage the best qualities of both.