Boiler Insulation System – Material and Jacket Selection

Insulation is what keeps the heat energy of a boiler system from leaking out of the system on its way to the end users. Inspect the condition of your insulation often enough to keep the insulation from becoming seriously deteriorated. This measure summarizes what insulation does, what to insulate, and how to insulate. It also gives you several methods of finding defective insulation, even if it is buried.

Heat Loss of Bare Surfaces

Surfaces lose heat by radiation and convection. If the surface has little insulation value, such as the surfaces of steel pipe and fittings, the rate of heat transfer and loss depends almost entirely on the surface area and surface temperature. Convective heat loss occurs strongly even at low temperatures, but levels off to a maximum rate. In contrast, radiation heat loss continues to increase exponentially with temperature.

Radiation becomes the dominant mode of heat loss from exposed surfaces in high-temperature plants. For example, a bare pipe carrying 15 PSI steam is about 150°F hotter than typical boiler room air, and it loses about 400 BTU per hour per square foot of surface area. By comparison, a bare pipe carrying 600 PSI saturated steam loses about 1,600 BTU per hour per square foot.

The amount of bare surface in a heating plant is usually minor, so bare surface heat loss is not a major consideration. Still, it may pay to insulate localized bare surfaces, as recommended below.

Upgrading Intact Insulation on Boiler

If a surface is insulated, the rate of heat loss is determined primarily by the surface area, the thermal resistance (the R-value, in English units) of the insulation, and the insulation thickness.

The shape or curvature of insulation is also a factor. Insulation that is curved has more outer surface area in relation to its thickness, and hence more heat loss. This is significant in the case of pipe insulation. Because of this effect, a given thickness of insulation is more effective with larger pipe diameters.

Insulation that is kept dry and free of physical damage remains effective indefinitely. In most heating plants, the insulation was installed properly at the time of construction, although certain minor areas may have been neglected. Damage over the years may lead to some loss of insulation, but incidental damage usually does not justify replacing insulation.

If insulation is in reasonably good condition, the remaining question is whether there is enough of it. In many heating plants, the amount of insulation may be inadequate in terms of present economics. It may be economical to supplement the original insulation, or to replace the existing insulation with new material having higher thermal resistance. Upgrading is most likely to be worthwhile in systems that have extensive piping that is easily accessible.

However, upgrading existing insulation usually has a low rate of return. Each additional increment of insulation thickness provides less benefit. Economics favors installing plentiful insulation on new equipment. A large fraction of the cost of insulation is for labor, and it does not require much additional labor to increase the insulation thickness.

Select your insulation quantity using engineering calculations. The principles and formulas are simple. Refer to ASHRAE publications or other books dealing with heating systems.

Heat Loss of Wet Insulation

Moisture is the worst enemy of insulation. If fibrous or open-cell insulation becomes wet, its insulation value falls drastically, and it may be permanently damaged. If buried pipe insulation of this type becomes soaked, it becomes ineffective, and the surrounding soil determines the rate of heat loss. Closed-cell insulation may lose little insulation value if wetted, provided that it is installed snugly. Even closed-cell foam may not keep the pipe itself from becoming wetted, which causes corrosion.

In indoor locations, insulation becomes wet if there is a leak, usually in the pipe or equipment that the insulation is covering. A leak may soak the insulation. Insulation should be installed so that a leak inside the insulation can drain out, but this is rarely done in practice.

The worst moisture damage to insulation occurs in buried pipe. Deterioration of buried insulation is a common, insidious source of major energy waste in large distribution systems. In the past, engineers tended to underestimate this problem, causing many facilities to suffer high heat loss from their underground pipe. Fortunately, piping system designs and equipment that preserve the integrity of the insulation have now become widely available. Unfortunately, replacing underground pipe is very expensive.

In steam tunnels and pipe trenches, the relative humidity of the air surrounding the insulation may remain at 100% if the soil is wet. This does not cause the insulation to become wet, provided that the pipe remains warmer than the air inside the tunnel. The higher temperature of the pipe keeps the relative humidity inside the insulation well below 100%. (Just the opposite situation exists with chilled water piping, which faces a serious problem of waterlogging when it is installed inside tunnels.) If the piping system is shut down at certain times, the insulation may become wet. Whether this is a problem depends on the type of insulation.