Transcript SNOW MELTING

Snow Melting Systems
08 April 2015
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Why Snow Melting ?
Safety
 Garage ramps, driveways
 Sidewalks, bldg. entrances
 Emergency exits
 Reduced maintenance cost
 No shoveling, no plowing
 No salting
Extended surface life
 Carpets and tiles in the buildings
 Concrete, interlock stones
 Surrounding landscaping
NO LITIGATIONS
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Snow-Melt Design/Performance
CL1 Residential (Ar = 0)
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120 Btu/sqft/hr load
Semi-auto / manual controls
9” o.c.
CL2 Type Commercial/Public (Ar= .5)
 150 Btu/sqft/hr load
 9” o.c.
 Automatic controls
CL3 High safety areas (Ar = 1)
 upper range of 200 Btu/sqft/hr
 6”o.c.
 Automatic controls /idling option
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Variables Affecting Load Design?
Environmental Factors
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Snow fall rate
Wet or fluffy/dense snow
Snow temperature
Outside temperature
Wind conditions
Per ASHRAE Applications
 Heat Flux for City
 To 95% of heat flux
 Snow free area ratio 1, 0.5, 0.0(0=snow cover=no
wind effect)
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Snow Melt Heat Balance
q= qs+qm+Ar(qh+qe)
q heat flux required at surface
qs sensible heat flux
qm latent heat flux (melting snow)
Ar snowfree area ratio
qh convective and radiative heat flux, after snow
has melted
 qe evaporative heat flux
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Snowmelt Design
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p.41
1- Identify the outside air temp. and wind speed
2- Identify Delta T for system design
3- Select design surface temp.
4- Determine btu/sqft
5- Determine supply water temp.
6- Identify the installation area
7- Determine btu/h requirements (boiler sizing)
8- Determine type and size of tubing
9- Determine the amount of tubing
10- Determine active loop lengths and # of loops
11- Determine total loop length with leader
12- Select percentage of glycol
13- Determine gpm
14- Determine system gpm
15- Determine system pressure drop
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Design parameters
Appendix A – worksheet p. 61
• Design temp. = 5F
• Wind speed = 10 mph
• Surface temp. = 38F
• 1700sqft driveway
• 5/8 MultiCor
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Snowmelt design
• Step 1- Identify the outside air temp. and wind
speed
• Step 2- Identify Delta T for system design
• Step 3- Select design surface temp.
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Snowmelt design
• Step 4- Determine btu/sqft/hr
• Step 5- Determine supply water temp.
Appendix C – Page 66
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Snowmelt design
• Step 6- Identify the installation area
-Ex. Sidewalk
17ft x 100ft = 1,700 sqft
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Snowmelt design
• Step 7- Determine btu/h requirements (boiler sizing)
Ex. Sidewalk
-126 btu/sqft x 1,700 sqft = 214,200 btu/h
• Step 8 - Determine type a size of tubing
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Snowmelt design
• Step 9- Determine the amount of tubing
1.33 x 1,700 = 2,261
• Step 10- Determine active loop lengths and # of loops
2,261 / 200 = 11.3 loops ( ~12 loops)
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2,261 / 11 = 206 ft per loop
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Snowmelt design
• Step 12- Select percentage of glycol
Ex. Sidewalk we selected 40% glycol
mixture
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Snowmelt design
• Step 13- Determine gpm
206 ft x 0.0081 = 1.67 gpm per loop
Appendix C, p70
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Snowmelt design
• Step 14- Determine system gpm
1.67 gmp/loop x 11 loops = 18.37 gpm
• Step 15- Determine system pressure drop
0.03090 x 226 = 7.0 ft of head
Appendix E, p85
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System Design
TYP. SYSTEM
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Outdoor Air Temp - 0 °F
Wind Speed - 10 mph
Fluid Temp Drop 25 °F, (25-30 °F)
Tube Spacing 6-9” o.c.
Surf Temp 38 °F, (36-45 °F)
Fluid Max 150 °F
200 Btu/sqft/hr
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Mechanical Components
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Snowmelt typical loop layout
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Architectural Considerations
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Installation Methods
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