A Science Of Its Own

A Science Of Its Own
< Snow Melting
A Science
Of Its Own
There are several different
options to deal with the
increasingly complex world
of snow melting applications
once you establish what the
customer’s needs are.
BY MIKE MILLER
T
he demand for snow melting is increasing, as are
zoned snow melting systems and the necessity for
multiple automatic snow/ice detectors. Zoned snow
melting systems accommodate higher priority and
lower priority zones, as well as different slab surfaces.
Snow melting systems should never run without a system controller that was developed and designed specifically for that purpose. The reason for this is that most
controls today come with very intense algorithms to make
snow melting as efficient as possible.
The system should have outdoor temperature guided
capability that can override the system from entering snow
melting mode if it is too warm outside and mother nature
could melt the snow for free, or if the outdoor conditions
are so extreme that a given heat source would not have
enough capacity to get the job done. Depending on surface
covering, some snow melting systems may need to control the rate of slab surface temperature rise to avoid damage to a slab caused by tensile stresses from a cold start.
Properly insulated pipe for distribution to and from each
snow melt manifold is in all cases required to ensure heat
gets to where it is needed.
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SYSTEM TYPES
A manual snow melt system is a system that is enabled
and disabled manually by an individual or user. Often, this
is the most cost effective system in terms of product/hardware cost, as it can be achieved with a device as simple as
an on/off switch. On the other hand there are operational
and possibly even safety concerns that could arise from
such a system.
Operationally, this type of system could quickly become
very expensive to operate if disabled too late or worse yet,
forgotten about until the fuel bill is in the mail. If turned off
too early, it could pose a safety threat as any water from
the just melted snow could reform into ice if not completely
removed. When enabled too late, the slab’s pick-up time
will increase, as will the running time. This system definitely requires an attentive user.
A semi-automatic snow melt system is enabled manually,
but disabled automatically based on an adjustable amount
of running time. Most controls on the market have this built
in as a standard feature. The systems are often enabled
by the push of a button on the control or with a momentary
push button located remotely from the control.
The semi automatic system allows a user to melt the
snow as desired and only requires the human interface at
the beginning of a snow melting event. Based on a preset but adjustable running time period, the system would
disable itself when the time has expired. Setting the right
amount of time is the key and often hard to predict. The
same operational or safety concerns exist as in the previous option whereby the system could still turn off too late
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Snow Melting >
or too early. At least its disable is set and even if it is forgotten about, it won’t
run beyond the time set.
A fully automatic snow melting system utilizes an automatic snow/ice detector that enables the system upon detection of snow or ice on its surface and
disables the system when the snow or ice has been completely removed. Its location is very critical. It should be located in an area where it would be most likely
to detect snow accumulation.
The detector usually adds to the initial component cost but it helps run the
system as economically as possible as the snow melt system only runs while
needed. Compared to the manual or semi-automatic snowmelt systems, the
automatic sensor addition often pays for itself within months.
Any of these three different types of systems should run off a slab sensor
embedded in the slab for accurate surface temperature control. Setting the right
surface temperature for a melting event may change how the system performs.
For example, higher melting slab surface temperatures help clear off snow from a
surface more quickly, but are more expensive to operate as the temperature difference of slab surface temperature compared to ambient outdoor temperature
is greater and therefore the load is greater. Lower melting surface temperatures
clear off snow at a slower rate, but the load of the system is decreased as the
temperature difference between slab surface and outdoor air is lower. Melting
surface temperatures that I personally use for snow melting systems are typically
36F residentially and 38F commercially.
APPLICATION SCENARIOS
Some specialized applications are often referred to as snow melting applications but sometimes that may not be the right terminology, as outlined in the first
example.
Carwash Applications
In car wash applications we are often asked to ensure that ice will never form
from the water used in the car wash on a slab surface. It is important that any
run off from the water is directed to a floor drain. In those applications, the water
frequently splashes across a large slab area. This would not be an application
where an automatic snow/ice detector would normally be utilized due to an element of liability attached to the property. Additionally, there is never really a right
place for that sensor to be installed.
Car wash applications are in fact slab warming applications as the surface temperature of the slabs leading to and coming from the wash bays must be kept
above freezing conditions to avoid ice buildup at all times. In those cases, use
a single slab sensor or a set of square number of sensors (e.g. 4, 9, 16, 25…)
for averaging purposes on larger slabs. In the previous examples of the different
types of snowmelt applications, this one could be classified a manual system,
but in reality it would not, as this system is required to run during all business
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< Snow Melting
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hours.
Ideally a timer that is programmed for the business hours
would set the melting, or more accurately called, the slab
warming time periods. This would be referred to as a fully
automatic system specifically for car washes.
or around pools and hot tubs, that would be only run if in
use. In this case, there would be two zones, one with automatic snow/ice detector and one with just a slab sensor
and some sort of push-button enable device.
Residential Properties
Residential snow melting applications can be manual,
semi-automatic or fully automatic, or a combination thereof.
One would chose a manual system if the user wants to be
in full control of the snow melting system. He would need
to be attentive to the operation, as he would be the one
enabling and disabling the system. The concerns mentioned above regarding manual snow melting systems are
true and while the system was the most cost-effective to
purchase, it likely becomes the most costly or more critical
system to operate.
Traditionally, many systems that a customer wants to run
manually, end up being semi-automatic, since most controls have the disable feature built in so the system disables itself after a set amount of running time.
Higher end properties most often suit fully-automatic
systems or a combination of fully-automatic and semiautomatic. The combination system is often utilized where
there is a higher traffic service area or zone, such as driveway and sidewalk that uses an automatic snow/ice detector, and a separate zone of snow melting of a patio or deck,
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HPAC | September/october 2010
On the residential and commercial side, high-end properties often have multiples of fully automatic and possibly
semi-automatic snow melting zones. Fully-automatic zones
may be multiple areas of parking lots, driveways, sidewalks
and different exposures or surfaces. Lower traffic areas,
such as pools and hot tubs, patios or decks, or loading
ramps if commercial, call for for a semi-automatic system.
Before starting the system design it is very important to evaluate the customer’s needs and expectations.
Snow melting can be a science on its own and there are
always other features, functions and benefits to evaluate.
Whatever the application, the manufacturers and suppliers
specializing in this field can assist you in working through
the options. <>
Mike Miller is a controls specialist with experience in the manufacturing, distribution and
contracting sectors of the industry. He can be
reached at mike.miller@uponor.com.
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