We use cookies to provide you with a better experience. By continuing to browse the site you are agreeing to our use of cookies in accordance with our Cookie Policy.

logo
  • Engineers & Specifiers
  • Contractors & Installers
  • Wholesalers & Distributors
  • Sign In
  • Create Account
  • Sign Out
  • My Account
Free Subscription
  • Sign In
  • Create Account
  • Sign Out
  • My Account
  • PRODUCTS
    • Bath & Kitchen
    • Fire Protection
    • HVAC
    • Hydronics/Radiant
    • Plumbing
    • PVF
    • Tools
  • PROJECTS
    • Commercial
    • Green Building
    • MRO/Retrofit
    • Remodeling
    • Residential
  • HOW TO
    • Design
    • Fire Protection
    • Legal Matters
    • Management
  • BUSINESS
    • Buying Groups
    • Technology
    • Associations
  • CODES & STANDARDS
    • ANSI
    • ASHRAE
    • ASSE
    • Regulations
    • Green Building
    • IAPMO
    • ICC
    • NFPA
  • RESOURCES
    • Media Kit
    • Advertise
    • Contact Us
    • Classifieds
    • Digital Editions
    • Behind the Wall
    • Webinars
    • AHR Live 2023
  • PODCASTS
  • DIGITAL EDITIONS
Home » Snowmelt Design: The Art of Best Guess
Feature Story

Snowmelt Design: The Art of Best Guess

Why designing snowmelt systems is a mix of art and science

October 5, 2018
No Comments
pe10_18_vastyan

There’s a saying I like to use when it comes to designing systems, “Engineering is the art of best guess.”

This seems a bit contradictory. Engineering to most is the art of absolutes, the science of definitive measures. When building a skyscraper, one would hope the science behind the engineering would be pretty exact. The reality is that engineering is an art form that takes a known condition and makes it repeatable. 

A steel beam bent eventually breaks. We bend enough beams we begin to create a method to predict when that beam fails. This is engineering. But, what happens when the conditions we are trying to predict are constantly changing?

This is where the art of the best guess comes in. Nothing fits this philosophy better than when trying to design a snowmelt system.

The Art of Constant Change

The only thing constant in this world is change. Mother Nature is fond of showing us this on a daily basis. Meteorologists are all too familiar with how hard it is to try and predict what the weather will bring. This ever-changing element is one of the factors behind the guess.

When an engineer sets out to design a snowmelt system, one of the first things they do is look at the weather data for a given area. How cold does it get? How much snow usually falls? What’s the density of this snow? What was the largest snowfall possible? 

The data they find will make a Jackson Pollock painting look organized. He’s the guy who, back in the 40s and 50s, splashed oil paint all over giant canvases. This was all to the adoring praise of art critics worldwide. I’m guessing it’s not the sort of art that many engineers take a shine to.

Because Mother Nature rarely plays by any single set of rules, it has become necessary for designers of snowmelt systems to be – shall we say – creative in their approach. 

Confidence

When designing a heating system, the conditions are pretty straight forward. Consider the coldest day of the year, evaluate the construction profile, and perform the necessary calculations. Very little changes. 

This is not the case with a snowmelt design. One of the most common variables to contend with, as illustrated earlier in the chart of data provided by NOAA and the National Weather Service, is the actual amount of snow that will fall. Snowfall amounts can range from a few inches to a few feet in any given area, but not for every event.   

So, how are these swings in snowfalls managed? Well, with what’s referred to as a confidence factor. Historical data allows us to get a fairly good feeling of what a typical snow fall amount is with the periodic five-year, 10-year, and 100-year oddity. The confidence level, set between 75 percent to 100 percent, indicates how confident the designed level of snowfall will actually occur.

For example, if the snowfall amount set by ASHRAE for a given area is 12 inches, but we know that is a five-year event, we may design for a 90 percent confidence. 

Counter to this, if we feel the 12-inch snowfall happens pretty regularly, then we may bump this to 98 percent or even 100 percent. The higher the confidence level, the higher the calculated load.

Snowmelt classifications

For the sake of easy reference, snowmelts are grouped into classifications. These allow designers to quantify the level of snowmelting a system is designed to perform.  

There are two essential systems of classification: old ASHRAE, and new ASHRAE. ASHRAE categorizes snowmelt systems into three main groups:  Class 0, 0.5 and 1. 

These refer to the amount of snow which will actually accumulate during the melting process. A Class 0 will generally allow for full accumulation before melting while a Class 1.0 will try to stay up with the rate of snowfall providing a completely snow free area all the time. Performance needs generally drive the classification. Residential will be either a Class 0 or 0.5. Light commercial will generally be a Class 0.5 while areas deemed critical, such as hospitals or loading docks, will be a Class 1.0.

 

Performance variables

Let’s now assume that the design is complete and the engineer made their “best guess.” What now? How does reality stack up to the guess? 

In truth, pretty well. Even though we’ve identified a wide range of unpredictable variables, snowmelt systems generally perform as desired. So, what changes from snowfall to snowfall?

One of the design factors not discussed thus far is time. When a system is designed, the loads calculated are based on a certain amount of snowfall in a given time period. 

Likewise, the melting process is also calculated over a given amount of time. For simplicity, let’s assume one hour. 

For a snowfall amount of 12 inches in 24 hours, we would have about a snowfall average of 0.5 inches per hour. Even though, in reality, it can be anywhere between 0.25 inches to two inches an hour. The calculations are based on what it would take to melt that snowfall in one hour. Let’s say the load calculated is 100 BTU/hr. As the rate of snowfall varies, our BTU delivered does not. So, what changes? 

Time changes. If the rate of snowfall is the designed 0.5 inches, the 100 BTUs of delivered energy will melt the snow in an hour. If the rate is less, the melting takes place faster. If the rate of snowfall is greater, the melting will take place over a slightly longer period of time. 

In this example, if the rate were actually 0.75 inches of snow it may take the system 1.5 hours to melt instead of the designed one hour. The system still works and the snow is still removed. These variations are generally not even noticed as long as the objective of a clear driveway, ramp or walkway is achieved.

Controls make the difference

Control strategies go a long way in reducing the time factor even more. With today’s smart controls, such as tekmar’s latest snowmelt control, melt time is reduced by allowing the system to start before the snow falls. 

The Wi-Fi Snow Melting Control 670 includes a smart feature that checks the local weather forecast based upon a zip code and then anticipates snow falls by pre-heating the slab in advance of a snow fall. This smart feature virtually eliminates the risk of snow accumulation on the slab, while also significantly reducing energy costs compared to snow melt systems that pre-heat continuously throughout the winter season.

The art continues

Every year, we gain a little more understanding on how snowmelt systems perform and how Mother Nature behaves. With each season, we get a few more points to add to our graph, allowing for our guesses to be a bit more accurate.

Kolyn Marshall is a System Engineering Manager with Watts who specializes in developing integrated system designs.

Engineers & Specifiers Engineering Hydronic Piping Systems Hydronics/Radiant
  • Related Articles

    Snowmelt Design: The Art of Best Guess

    Prevention is the Best Medicine for Hospital Snowmelt

    The Art of Design

  • Related Products

    The Wholesaler

    Directory Listing - Premium

  • Related Events

    Council for Research on Distributor Best Practices “Digitizing the Sales Process” Consortium

You must login or register in order to post a comment.

Report Abusive Comment

Most Popular

  • Chicago Plumber’s Union Dyes Chicago River Green for St. Patrick’s Day 2023

  • Six Truths About New DOE 2023 HVAC Efficiency Standards

  • Everything You Wanted to Know About Orangeburg Pipe (But Were Afraid To Ask)

  • The Basis for Most Plumbing Codes

Featured Video

Caleffi video thumb

The Gold Standard: Separation with NO Compromise

Industry Events

  • 26Mar

    MCAA 2023 Annual Convention

    Phoenix, AZ
  • 29Mar

    2023 SFPE European Conference & Expo

    Berlin ,
  • 11Apr

    ASA ELEVATE2023

    Charleston, SC
More Events

Subscribe to our newsletters & stay updated

Subscribe & Learn More

  • Tw03 2023 cover
    Learn More
  • Pe03 2023 cover
    Learn More
  • Phc03 2023 cover
    Learn More
  • Es 2022
    Learn More
Subscribe

More from PHCP Pros

  • Editorial Team
  • Home
  • Contact Us
  • About
  • Advertise

Follow Us

© 2023 All Rights Reserved

Design, CMS, Hosting & Web Development | ePublishing