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Snow and Ice Melting with Infrared Heaters
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The Fostoria Multi-Mount (UL listed for completely exposed/unprotected outdoor applications) is frequently used for snow and ice melting. They have quartz lamp heaters which are less susceptible to heat loss from wind and they reach high temperatures. The quartz lamps have less mass to hold heat which can be lost to a rise in temperature of the air crossing it. The following is a case study prepared by Fostoria, showing a general comparison of using infrared or other types of systems.
Comparative Study of
Snowmelt Systems Mechanical/Electrical
Section Facilities Engineering, MTA
CONTENTS
This study demonstrates that: (a) the Shoveling with chemical treatment snowmelt approach is more costly to operate and less effective than the automatic approaches, and (b) that the automatic snowmelt systems facilitate drier and slip-free pavement more consistently. The objective of a snowmelt system is to keep the pavement dry and safe for commuters. It is widely recognized that corrosive chemicals used to slowdown pavement refreeze have caused serious and rapid deterioration of metro station infrastructure and capital equipment. Engineering studies have shown that the life of concrete is reduced by 50% when exposed to the chemicals over a short time. A recent survey of entrance escalators revealed numerous corrosion and deformity of crucial components attributable to exposure to these chemicals. The study indicates that the estimated annual cost of using the shoveling with chemical treatment approach is 88,000. This cost is 22,400 more than the most expensive automated system.
Equal
to the task of building and presenting an argument for automatic
snowmelt systems, this report also compares and presents the strengths
and weaknesses of four snowmelt techniques.
Effectiveness and costs rank these techniques. The platform at
Owings Mills metro station was the test site.
In terms of estimated annual cost and maintenance requirements,
the infrared technique appears to come out on top.
However, the need to find suitable mounting locations for
infrared fixtures limits the effect and the infrared methods for
platform applications has strong potential efficiency and cost savings
benefits. SNOWMELT SYSTEMS
Each snowmelt system is briefly described
in a section below. The
strengths and weaknesses of the systems were gleaned from studies of
technical manuals, engineering handbooks, and interviews with systems
manufacturers, and MTA Facilities Maintenance personnel.
The findings are summarized in a table for quick reference.
The Appendix section of the report presents details on the
derivation of the estimated annual cost for operating each system.
The choice of system is based on the comparative analyses of
strengths and weaknesses and estimated annual operating costs. 2.0
Shoveling with Chemical treatment Use of corrosive chemicals to delay re-freezing of pavement has damaged vital escalator components, accelerating the deterioration of the platform, and threatens the substructure of the stations. See Table 1 for summary of the system’s strengths and weaknesses and comparison with other systems. The costs and effects of the chemicals on the station structure and capital equipment are often over looked. This is because the deterioration process is not immediately evident. The American Concrete Institute classifies an environment where deicing agents are present as a severe environment. Typically calcium or sodium chloride is used as the chemical agent. The chloride ions react with and break down the binding agent, cement paste, of the concrete. Due to the relatively small size of the chloride ions, the deterioration moves through the concrete with each wet and dry cycle. Eventually the chloride ions reach the reinforcing steel and rapidly consume it. Once the adhesion is lost between the sand, gravel, and the reinforced steel, the concrete fails structurally. The only solution left is to replace the concrete. The impact of corrosive chemical on concrete structures is demonstrated by the rate of deterioration of parking garages. Parking garages are not treated with snowmelt chemicals. However, these chemicals are tracked on to the premises by incoming vehicles. The garages are generally constructed using a low water-cement ratio (f>45000psi), fly ash, and epoxy coated reinforcement to reduce the effects of salt. Even with these precautions, the time to major repairs ranges from 7 to 15 years. The major repairs include replacement of floors, beams, and columns. Without this chemical exposure the life expectancy of the concrete is approximately 40 years. MTA’s platforms are subjected to far more salt than parking garages and are less resistant to chloride ion penetration. As a consequence, our platforms have to be repaired more frequently and suffer more rapid decline in structural integrity. There are other chemicals sold as deicing agents that have even more destructive effects on concrete than salt. MTA once used such chemicals, which resulted in structural failure in concrete members. Capital equipment such as elevators and escalators are similarly affected by deicing agents. Elevators and escalators at station entrances deteriorate from the bottom up. A recent survey of these escalators exposed damaged base supports, and rust build-ups, resulting in deformation of crucial support members, and, in a few cases, actual shifting of the entire escalator assemblies were observed. Thus, the total annual cost of using this method to clear snow and ice must include the hidden costs of major repairs or replacement of the infrastructure, inconvenience patrons suffer, and accidents. Using our 10 freezing event for
Baltimore, we estimate the annual cost to clear ice and snow at Owings
Mills to be 88,000. Details
of this estimate are outlined Appendix, A.10.
Infrared
fixtures are typically installed overhead.
Without a completely covered platform, a large number of fixtures
would have to be mounted on poles.
The number of poles required could compromise space and the
aesthetics of platform. This
is one of the drawbacks to the infrared approach.
See Table 1 for a summary of the system’s strengths and
weaknesses and a comparison with other systems.
Another weakness of this approach is its high electric power
demand. For the Baltimore
area, the system is required to output 90W/sq.ft to provide the desired
result. The total annual
cost of using this method to clear snow and ice is estimated at 47,108.
See Appendix A.20 for cost derivation. 4.0
Embedded System Approach 4.1 Direct Buried Cable
Correcting any fault in the buried cable would require
jackhammering the concrete. One
weakness of this system, relative to the infrared system, is that much
energy is expended to raise the pavement temperature before snow melting
begins. Other weaknesses
include high installation cost and the potential for high repair cost.
Additional attractive features of this system include; low annual
operating cost, very little maintenance requirements, and lower electric
power demand than the infrared system.
The total annual cost of using this method to clear snow and ice
is estimated at 44,340.
See Appendix A.30 for cost derivation. 4.2
Skin-Effect Heating System
One
weakness of this system, relative to the infrared system, is that much
energy is expended to raise the pavement temperature before snow melting
begins. The biggest
drawback to this system is its initial cost.
At 50/sq.ft this system is the most expensive on the market.
This cost does not include pavement demolition and
reconstruction. Another
weakness is the potential for high repair cost.
Additional attractive features of this system include; low annual
operating cost, very little maintenance requirements, and lower electric
power demand than the infrared system.
See Table 1 for a summary of the system’s strengths and
weaknesses and a comparison with other systems.
The total annual cost of using this method to clear snow and ice
is estimated at 65,640.
See Appendix A.40 for cost derivation. 5.0
Conclusion The analyses also showed that the infrared system could be the method of choice based on its instantaneous heat production, lower annual cost than the skin-effect system, and low maintenance cost and requirement. The advantages of the infrared systems outweigh its relatively high power demand. The primary drawback to the total use of infrared in platform application is the requirement for additional poles to mount the heat fixtures. This problem would be eliminated if the platform were totally covered. Of the two embedded systems discussed, the Skin-effect system would be the better choice for platform application. The higher initial cost for the Skin-effect is compensated for by the fact that probable cable faults are much less costly to repair with the Skin-effect system. The Direct Buried system falls short as an option because exception is taken to the prospect of jackhammering the platform to fix a cable fault. Although our analysis suggests that
automatic systems would be ideal for snow and ice control, they are not
widely used in the Transit industry.
The current systems installed in the MTA are yet to receive
unanimous acclaim within the MTA. WMATA
is still in the process of evaluating its needs.
Personal Rapid Transit, PRT, in Western Virginia, employs a
hydronic system installed in 1971.
Reports indicate that the system is working well.
However, annual operating costs for the hydronic system range
from 75,000 to 250,000. Chicago
Transit Authority, CTA employs infrared and other systems for snow and
ice control. The extent of
the application of these systems could not be confirmed at this time. 6.0
Recommendations:
7.0
Summary of Cost Analysis Table 1
APPENDIX
A.11
Direct Cost A.12
Indirect Costs:
Estimated
added annual cost per escalator for service and refurbish
A.20
Derivation of annual cost for Overhead Infrared Estimated # of fixtures required =
12150sqft/79sqft/fixture = 154 Fostoria: Multimount 343-30-THSS-480V.
A.21
Direct Costs: Installation and Operation
Estimated
Annual Operations Cost:
A.30
Direct Buried Cable:
A.31
Direct Costs: Installation and Operation
Assume
8” loop spacing
Estimated
system installation cost:
Annual
Operations Cost:
A.40
Skin-effect:
A.41
Direct Costs: Installation
and Operation: Annual
Operations Cost: Estimated annual operating cost: (10 x 306) + 2(600 x 8.32) = 13,044 Estimated life of system, approximately 20 yr. Assumed annual cost of demo. Platform due to cable fault = 15,000 Annual depreciation = 608,000/20 = 30,400 Annual maintenance cost = 200/hrs @ 36/hr = 7,200 Estimated total annual operating cost: = 65,640 Back to top |
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