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Fundamentals of Hydronic Design

Snow Melting


Fundamentals of Hydronic Design Portions of this presentation are copy written by others, acknowledgments, credits

and references as noted.

Materials copy written © 2005, by the American Society of Heating, Refrigerating and AirConditioning Engineers, Inc. Reprinted with permission from ASHRAE

Applications Handbook. These materials can be purchased from the ASHRAE bookstore, www.ashrae.org

This material may not be copied nor distributed in either paper or digital form without permission. Some slides contained animations in the original .ppt format which have

been eliminated in the conversions to images or Adobe’s .pdf format.

If you wish to use this presentation for non commercial use, please contact [email protected] for details and restrictions.

This educational material was assembled and copy written © by Robert Bean, R.E.T., All Rights Reserved.

It is provided for “not for profit” educational purposes.



Courtesy of American Iron and Steel Institute



Seminar Objectives:

Design and Performance Considerations for Snow Melting Systems.

Boston Aerial Highway 1958 © The Aberdeen Group, All Rights Reserved



• Why Snowmelt? • Convenience, Safety and Security • Ensure access to buildings and services

• Piles of snow, snow drifts, ice etc. • Restricted access during removal by other means • Adds a dimension of “personal security” while at home or away.

• Eliminates other methods • Sand, salt, light or heavy gas powered snow removal equipment • Noise, fumes, safety of pedestrians including children and seniors.

• Reduces winter damage and spring clean up • Surfaces, stairs, landscaping, street cleaners etc.



Image Source: Development of a Two Dimensional Transient Model of SnowMelting Systems, and Use of the Model for Analysis of Design

Alternatives, ASHRAE 1090RP, 2001



• Surface Conditions • Dry • Wet • Dry Snow • Slush • Snow & Slush • Solid Ice • Solid Ice & Water Source: A Simulation Tool for the Hydronic Bridge Snow Melting System

Xiaobing Liu Jeffrey D. Spitler, Submitted to the 12th International Road Weather Conference, Oklahoma State University, School of Mechanical and Aerospace Engineering,



• Consider • Client • Control • Construct • Calculations




Client




• Client • Typical

• Residential • Commercial • Institutional • Industrial • Agricultural



• Client • Who is the client? • What are the expectations? • Where is it required? • When is it required? • Why is it required? • How Much?

• Capital, Operation, Maintain

The lowest cost snow melt system is available each year around spring time.

Words of Wisdom From John Barba

[;@)



• Client • Expectation

• Old Method • Class 1 • Class 2 • Class 3

• Current Method • Frequency Percentile



• Client • Frequency Percentiles • Percentage of time required snow melting load does not exceed the reported value. • 75, 90, 95, 98, 99 and 100 %.

• % of time Flux ≤ The Design for a Snow Free Area Ratio •Heliport vs. Residential Driveway • 100% @ Ar=1.0, 170˚F • 75% @ Ar=0.5, 140˚F


Fundamentals of Hydronic Design Percentage of time required snow melting load does not exceed the reported value.

Ex. If the system was designed for 90% it means 10% of the time the load would be exceeded for that specific Area Ratio.

Source: Development Of Snow Melting Load Design Algorithms And Data For Locations Around The World, ASHRAE 926RP Final Report



• Client • Area Free Ratio • Ar = A f /A t , where •A f = equivalent snowfree area, ft 2

•A s = equivalent snowcovered area, ft 2

•A t = Af + As = total area, ft 2

• Ar = 1.0, No snow accumulation • Ar = 0.0, Complete coverage (no heat or evap. losses) • Ar = 0.5, slush (50% coverage)



• Client • Area Free Ratio • Expectation

• Influences • Temps • Spacing • Depth • Insulation • Striping • Bridging



Controls




• Controls • Response • Storm Characteristics

• Climate/Geography • Consumption

• Heat Release • Production

• Heat Generated



Time

Copyright 2004, American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc. and Oklahoma State University.



• Controls • Question Is… • How to Respond to Unknown Storm Characteristics • Think Performance & Operating Cost

• Manual – “Reactive” • On/off

• Automated – “Proactive” • On/Off • Idle/on/Idle



• Controls • On/off • “Heat fluxes up to five times greater than those indicated by steadystate analysis need to be delivered to the slab in order to keep its surface clear from snow during the early hours of the snowfall when the heating system is just starting to operate.” Source: Development of a Two Dimensional Transient Model of SnowMelting Systems, and Use of the Model for Analysis of Design Alternatives, ASHRAE 1090RP, 2001



• Controls • Idle/on • Reduce pick up loads • Increases “stand by” losses • Improves performance • Can be impractical for some applications

• Warm weather shut down • Cold weather shut down

“Without idling, very high fluxes are required to raise the slab temperature

sufficiently at the start of the storm.”



RPA Guidelines for the Design And Installation of Radiant Panel Heating and Snow/Ice Melt Systems (2004 Edition).

All Rights Reserved.

• Controls • Monitor

• Outdoor Temp • Precipitation • SIM Supply / Return • ∆t • Plant Supply / Return • P + I Controls • PID Available



Construction



• Construction • Thermal “Capacitor” • Reduce Back and Edge Loss • “Power” Draw at Surface •Wind •Precipitation • Phase Change • Liquid • Vapor

Edge Loss: Think Retainer For Sand Box




• Construction • Sub Grade •Structural Loads •Live and Dead Loads •Soil Stability •Compaction/Compression •Moisture/ Water Table • Insulation



• Construction • Sub Grade •Excavation •Undisturbed •Compacted •Drainage



• Construction • Moisture •Water Table •Run Off •Melted Snow •Splash



Source: National Radiant Design Center

• Construction • Insulation

• Think Moisture • Think Freezing • Think Soil Expansion • Think Heaving/Swell • Think Collapse/Shrink

•Do Control Heat •Do Control Moisture



• Construction • Insulation •Asks where do you want heat to flow, when and how fast?

Source: 2000 ASHRAE Handbook, Systems and Equipment copy written © 2005, by the American Society of Heating, Refrigerating and AirConditioning Engineers, Inc. (www.ashrae.org).

Reprinted with permission from ASHRAE Applications Handbook.




• Construction • Structure • Compacted Base • Reinforcement • Air Entrained Concrete Sloped ¼” per Ft • 4000psi @ 28 days • .50 h 2 o to cement



• Construction • Structure • Compacted Base • Reinforcement • Air Entrained Concrete Sloped ¼” per Ft • 4000psi @ 28 days • .50 h 2 o to cement Curing Temperature, ˚F

40 60 80 100 120

6

5

4

3

2

1

0 Com

pressive Stre

ngth, 1000 psi At 28 Days

At 1 Day

Design and Control of Concrete Mixtures, Portland Cement Association, 2003




• Construction • Structure •Control Joints •Lesser of • Min 2 x width or every 15ft • ∆ in direction or elevation

•Tube Placement & Pattern • Critical • Influences • Pick Up & Back Loss




• Construction • Surface •Bull Floated •Surface Water Evaporated •Depth of Control Joints • 25% of slab thickness



• Construction • Joints • Control, Expansion, Construct



Calculations



• Calculations • Academic Exercise • Ensures equipment and construction can deliver when called upon if and when the “predicted” event happens.



• Calculations • Is the System for Protection • Is the System for Convenience • Both • Load Calculation ( See Heat Loss to Head Loss, R.Bean, R.E.T., RPA Report) •Thermal Calculations •Hydraulic Calculations •Energy Estimate Calculation



• Calculations • Convective • Evaporation • Conductive • Radiative

Wet Dry

Earth

Conduction

Fire

Radiation

Hot

Cold

Air

Convection

Water

Evaporation



• Calculations • Convective & Evaporation •Wind Velocity •Characteristic Dimension • Shorter slabs have higher convective losses •Wind blown parallel to the long dimension has less load than if the wind blows perpendicular to the longest length.

•Elevation



• Calculations • Conductive •Slab Temperature at the Start of Melting •Snow Density •Rate of Snow Fall



• Calculations • Radiative •Effective Sky Temperature • Dry Bulb Air Temperature • Humidity • % of cloud cover



• Calculations • Radiant Loss •Cloud Cover Temperature •standard lapse rate • 3.5°F per 1000 feet •@10,000 ft = 35 ˚F

•assumed to be opaque



• Calculations • Back Losses •Depends on: • On/off • Idle/On • Ground Temps • Construction • Insulation • Tube Placement

•As high as 50%



• Calculations • Wind •Reduces melting capacity •Direction and slab dimension •10 Mph may add 50% to load •Causes drifting snow • Is the slab on? • Is it idling? • Is it off?

•System Performance



• Calculations • Snow Density • Weather Bureau • 90% of Snow Fall • Occurred between 10˚F and 35˚F



Outdoor Temperature, °F.

Weight (lbs/ft 3

)

0 8 10 12 14 16 18 20 22 24 26 28 30 32 34 2 4 6 0

7

6

4

3

5

8

1

10

2

9



• Calculations • During Snow Fall • q o =( q m + q s ) + ( Ar x ( q h + q e )) • q o ,Power per unit area • q m, ,Intensity of heat of fusion (phase change, snow to water) • q s ,Intensity of sensible heat transferred to snow (snow to 32˚F) • Ar ,Area ratio (how much surface area is permitted to accumulate snow) • q e ,Intensity of heat of evaporation (natural evaporation of melted snow) • q h ,Intensity of heat loss to atmosphere (from snow free areas)



• Calculations • After Snow Fall • q o = q ha + q ea • q ha = Intensity of surface heat loss to atmosphere after snowfall • q ea = Intensity of heat of evaporation after snowfall

• During Idling • q o = q i ( Idling load where qe≈0)



• Calculations • Fluid Temperature •Variations w/in Literature •Adlam / Kilkis / Spitler et al •ASHRAE / IBR •Software • From Research Projects • Manufactures • 3 rd Party Developers



• Calculations • Fluid Temperature •Adlam/ASHRAE for ¾” steel pipes @ 12” o.c., 2” depth •Flux / 2 + t f ˚F = t avg • t f ˚F = film temperature ≈ 33˚F •Example •(140 Btu/h/ft 2 ÷ 2) + 33˚F = 103˚F avg. •t s = (∆t/2) + t avg = (25˚F/ 2) + 102˚F ≈ 115˚F supply



• Calculations • Fluid Temperature • t f = [ρ×c p ×Q j ×∆t/c] 1/n + t a

• t f , Fluid temperature • ρ, Fluid density, • c p , Specific heat • Q j , Volumetric fluid flow rate in branch • ∆t, Temperature drop • c, Unit heating capacity • n, Power of the equipment heating capacity • t a , air temperature wetting the heat transfer surface

Reference Source: An Analytical Algorithm for Hydronic Circuit Analysis and Assessment of Equipment Performance

Birol Ì. Kilkis, Ph.D., Fellow ASHRAE



• Calculations • Fluid Temperature •FEA Software

Source: Development of a Two Dimensional Transient Model of SnowMelting Systems, and Use of the Model for Analysis of Design Alternatives, ASHRAE 1090RP, 2001



• Calculations • Software •Weather •Construction •Expectations •Controls




American Iron and Steel Institute

• Calculations • Example •2” Tube Depth •5/8” PEX •8” Spacing • Insulated •130˚F Average




< Mass of Ice

Height of Snow> Free Area Ratio >




Temperature,˚F Heat Flux, Btu/h ft 2


Fundamentals of Hydronic Design Applications Other Than Snow


Fundamentals of Hydronic Design Copyright / References/ Acknowledgements •Graphic, American Iron and Steel Institute, © Copyright, All Rights Reserved. Graphic, National Radiant Design Center, © Copyright, All Rights Reserved. •Graphic, Building Science Corporation, © Copyright, All Rights Reserved. •Graphic, Boston Aerial Highway 1958 © The Aberdeen Group, All Rights Reserved •Modern Hydronic Heating, J. Siegenthaler, © Copyright, All Rights Reserved. •RPA Guidelines for the Design And Installation of Radiant Panel Heating and Snow/Ice Melt Systems (2004 Edition). © Copyright 2004, All Rights Reserved. •Development of a Two Dimensional Transient Model of SnowMelting Systems, and Use of the Model for Analysis of Design Alternatives, ASHRAE 1090RP, 2001, Spitler, Rees, Xia, Chulliparambil, American Society of Heating, Refrigerating and AirConditioning Engineers, Inc. and Oklahoma State University. Reprinted by permission from ASHRAE. © Copyright 2004, All rights reserved •A Simulation Tool for the Hydronic Bridge Snow Melting System, Liu,Spitler, Submitted to the 12th International Road Weather Conference, Oklahoma State University, School of Mechanical and Aerospace Engineering, © Copyright, All Rights Reserved. •An Analytical Algorithm for Hydronic Circuit Analysis and Assessment of Equipment Performance Kilkis, copy written © 2005, by the American Society of Heating, Refrigerating and AirConditioning Engineers, Inc


Fundamentals of Hydronic Design Snow Melting, Adam, Napier, T, 1950

Heat Requirements of Snow Melting Systems, Chapman, W.P., Katunich, S., 1956

Snow Melting Calculation and Installation Guide, S40 for Residences, Hydronics Institute, 1991

Design of Embedded Snow Melting Systems Part 1 & 2, ASHRAE Transactions, Kilkis, 1994

Updating the Tables of Design Weather Conditions in the ASHRAE Handbook – Fundamentals, ASHRAE 890RP, 1998

Development of Snow Melting Load Design Algorithms Volume I, ASHRAE 926RP, 1999, Ramsey, Hewett, Kuen, Petersen, Spielman, Briefer,

Updated Design Guidelines for Snow Melting Systems, ASHRAE Transaction CH99172, 1999

Transient Analysis of SnowMelting System Performance, ASHRAE Transactions 4591 (RP1090), 1999, Spitler, Rees, Xia, Chulliparambil

Development of a Two Dimensional Transient Model of SnowMelting Systems, and Use of the Model for Analysis of Design Alternatives, ASHRAE 1090RP, 2001, Spitler, Rees, Xia, Chulliparambil

Wirsbo Snow & Ice Melting Design Manual, 2003

Copyright / References/ Acknowledgements: con’t w/ chronological resources



Radiant Based HVAC Systems

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