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The Intelligent Use of Energy: Cut Heat Losses With Insulation
Richard R. Vaillencourt, PE, Canterbury Engineering Associates LLC


Editor’s Note: This is the fourth in a series of articles on intelligent energy use in buildings by consulting engineer Richard Vaillencourt. We hope you’ll find them helpful as you work to optimize your building’s energy use.

GInsulation is the least expensive but most important part of your energy equipment. Unfortunately, it is also often the most ignored. Any money spent on energy that doesn’t get to where it is supposed to go is wasted. Anytime the energy that you bought doesn’t hang around, but quickly exits the building, you are spending more money than you need to.

Paradoxically, insulation does not stop heat flow! But it does present a major restriction to the flow of heat. No matter how much insulation is in place, heat will always be lost. If lost heat isn’t replaced by your heating system, the inside temperature eventually will equal the outside temperature. The temperature will remain constant only if you replace energy in the space as fast as it is lost. Having insulation slows the rate of energy losses and therefore the rate at which energy needs to be replaced. Your goal should be to lose the least amount of energy possible over time.

The most important thickness of insulation is the first inch. Adding a covering of 1-inch-thick fiberglass insulation to a bare steam pipe will have an amazing effect on heat loss. A bare 4-inch pipe carrying 15 psig steam at 250 degrees F will lose about 530 Btu per hour per linear foot. Add just 1-inch-thick fiberglass pipe insulation, and the heat loss drops to 57 Btu/hr per linear foot. This is a heat loss reduction of 473 Btu/hr per linear foot – or close to 90 percent. Adding a second inch of thickness will bring the heat loss down by only 20 more Btu/hr per linear foot to approximately 37 Btu/hr per linear foot.

Insulation is equally effective on flat surfaces. If the temperature is 70 F on one side of a wall and 0 F on the other, a wall without insulation will lose approximately 117 Btu per hour per square foot. Adding 3.5 inch of fiberglass insulation (R-11) will reduce that heat loss by about 95 percent down to only 6 Btu/hr per square foot. Adding an additional 2 inches to R-19 will bring the heat loss down by only 2.5 more Btu/hr per square foot to about 3.5 Btu/hr per square foot.

These examples should bring home two truths about insulation:

1. Always insulate.

2. If you can only afford to use thin insulation, do it.

Straight pipes are the easiest and cheapest to insulate. But don’t just insulate the pipes: insulate all the fittings, valves, etc. (except steam traps). The irregular shapes of fittings and valves dramatically increase the heat losses. As a rule of thumb, the heat loss from a 4-inch valve will be two to three times greater than that from one foot of 4-inch pipe.

In the past, insulating fittings was a very expensive thing to do. The insulation was custom-made from rigid, castable insulation for each valve or fitting. This made the insulation hard to remove when maintenance was required on the fittings and easily damaged every time it was handled. The current practice is to purchase a blanket that is very flexible, durable, wire-tied around the valve or fitting and is easy to remove and reinstall.

Once insulation is in place, there is almost no maintenance involved. All that is necessary is to protect it from damage. Insulation works by creating multiple layers of air spaces. These air spaces can be lost if crushed or filled with water. Do not let anyone walk on insulation – whether on pipes, ducts or just in the ceiling. If the insulation gets wet from roof or pipe leaks, it is virtually useless and must be replaced.

So the bottom line is insulate. No matter what you do, it is going to make a difference.

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