Folded Sheet Metal Heat Panels Are Not More Energy Efficient!

We've noticed an increase in the companies offering revolutionary new, brilliantly engineered, masterfully efficient (can you detect my sarcasm yet), roof and gutter ice dam prevention systems. We assumed customers would easily see through their slick marketing and write them off. Most do, however these companies persist in misleading, so we are putting together a series of articles to help educate.

Energy Efficiency

Let's inject some common sense in the discussion - it really seems to be lacking. The basic concept is similar to a heat sink. A heat sink is a structure that transfers heat from a source of higher temperature to an area of lower temperature. Electronics are a good example as they generate heat and that heat needs to be dissipated or it can cause premature failure. This is most often done using a heat sink. They are aluminum structures that have fins which allow for the heat to be spread out into the relatively cooler air. Do a web search and see if you can find a heat sink made from steel. You may be able to, but steel never a first choice.

Steel makes a poor heatsink. Ideally you would try to find a way to use a more suitable material.

Having said that, a poor heatsink is better than no heatsink. But not by much.

Here is a table of the thermal conductivity of certain materials:

Copper - 400 W/(m.K)
Aluminum - 250 W/(m.K)
Brass - 109 W/(m.K)
Iron - 80 W/(m.K
Steel - 43 W/(m.K)

Notice how much worse steel is at transferring heat. Roof and gutter deicing systems are essentially heat sinks. They deliver the heat energy created by the roof heat cable to the snow load on the roof. There is not a compelling efficiency reason to choose painted steel for a roof deicing heat panel product.

True energy efficiency in roof ice prevetion systems can be managed through several avenues.

• Customer management of the roof ice melt system. If the customer actively participates in the operation of the system, greater efficiency can be achieved by turning the system on and off as the need arises.

• High Efficiency Control Systems (DC Sierra). These control systems measure the temperature of the roof ice melt panels and react by adjusting power output. For example, on a mild winter day with little or no wind the Roof Ice Prevention System might only being using 25% of its maximum power -far less than the amount the 'revolutionary, patent pending' single cable option uses. When conditions turn ugly, the Edge Melt System coupled with the DC Sierra has the ability to ramp up its power output to full to keep up. The single cable folded steel sheet metal heat panel quickly becomes overwhelmed and creates ice rather than preventing it.

• Thermostat control. The use of thermostat controllers in the residential market allows for 'window' operation. The heating cables are allowed to operate at temps between 10 and 34 degrees and the controller can be turned off when no snow is present to minimize energy usage.

Do extruded aluminum designs take more power?

The recent claim is that the reason extruded aluminum base panel design uses 2 runs of heating cables is that it 'wastes' the heat energy created by housing the heating cables in an extruded aluminum base. This claim indicates a lack of understanding of how self regulating heating cables work and the principles of heat transfer and the thermal conductivity of different metals. Aluminum's ability to efficiently transfer heat is well documented. It is exceeded by copper (which Edge Melt Systems use) and silver or gold for its heat transfer properties. Most other metals fall far short of aluminum. For example, the use of steel as a bracket to hold a heating cables to a steel roof edge means a system that can be 6 times less efficient - requiring more power to achieve the same results. 

Why is steel used for roof edge heated ice melt systems?

It certainly is not because of its superiority over aluminum, nor is it the result of exhaustive engineering and testing. Maybe the equipment used to make these folded sheet metal heat cable systems is not robust enough to handle thicker aluminum. (Even using .040 prefinished aluminum would represent an improvement). It may also be that when these systems were being developed there were patents still in force that prohibited copying the aluminum extrusion concept. Or, it could be just a cost thing. 

Whatever the reason, a well designed aluminum extrusion based system is always superior to a folded sheet metal heated edge. Stay tuned for the next article in this series. We will detail the physics behind our claims. I know - boring math, but we promise pictures. Oh yeah, facts as well. We think that speaks louder than bluster.

2