Installation Manual

16
ElectroMelt System
Design Guide
Supplemental Design
Information
Icing
Virtually any level of power will melt snow if there is a sufficiently deep snow
cover to insulate the surface from convection-heat loss. However, icing prob-
lems may arise once the insulating blanket has been melted and the pavement
is subject to increased heat loss due to wind action on the exposed surface.
Icing problems also arise when water from adjacent unheated areas runs onto
the heated area or when snow and slush are racked onto the heated area by
pedestrians or vehicles. In many situations the expected anti-icing behavior of a
system imposes more severe constraints than the ability to melt snow does.
Snow-melting and anti-icing systems require only enough power to meet the
system performance requirements. Providing excess power increases system
cost and leads to higher energy costs.
In designing an ElectroMelt system it is therefore critical to specify system per-
formance requirements accurately. This means determining both anti-icing and
snow-melting requirements, as shown below.
As shown in the specification example above, a typical performance specifica-
tion specifies the minimum ambient temperature and the average wind speed at
which all surface points must be above freezing. These are the anti-icing
requirements. It specifies the snow-melting requirements as well, in terms of the
percentage of all snowfall hours for which the operating system must keep the
surface essentially clear, and the allowable percentage of all snowfall hours for
which some snow accumulation is tolerable.
The sections that follow should help you determine and specify an application's
anti-icing and snow-melting requirements.
Determining Ambient Temperature
Once you have determined the heating-cable spacing of an ElectroMelt System
you can determine the ambient temperature by referring to Table 3. Simply
locate the row corresponding to the design's heating-cable spacing. Move
across that row to the column corresponding to the average wind speed during
freezing periods and read the minimum ambient temperature at which all points
on the pavement surface will be at or above 32ºF.
Note: This procedure is derived from finite model studies of 4-inch slabs and is
applicable to standard concrete pavement from 4 inches to 6 inches thick
placed directly on grade. If your application involves other materials or con-
structions, contact your Raychem representative.
Sample Performance Specification
Anti-Icing requirements
Minimum ambient temperature 5°F
Average wind speed 10 MPH
Snow-melting requirements:
Surface clear 50% of snowfall hours
Snow accumulation 3% or less
Performance Requirements
Anti-Icing Performance Requirements