November 2004

It won’t be long before Mother Nature has us onceagain in her cold, icy grasp. Sleet, snow, ice and freez-ing rain will lay down the challenge for safe movement

outside. As plumbing engineers, most of us readily see thevalue of snowmelt systems. Many building and facilityowners, however, have yet to embrace it.

Frequently, a key obstacle to winning their interest isthe up-front cost for snow melt system installation.Certainly, it’s not inexpensive, but there are benefits thatbalance out the equation. These include convenience,environmental enhancements (no salts, cinder and chemi-cal de-icers) and the greatly reduced labor and hardwarecosts that are otherwise needed to do the job. Ice-meltchemicals can kill nearby plants, increase buildingcleanup as they’re tracked inside and, over time, seriouslydegrade concrete and asphalt.

In essence, snowmelting is radiant heat thrown out thedoor. The method of snow and ice removal employs tub-ing buried outside in a mass to gently melt off winter pre-cipitation thereby keep pathways, driveways and otherareas dry and clear. For commercial applications, espe-cially those deemed critical areas – hospital and seniorhousing entry areas, helicopter pads, delivery and handi-cap access ramps, etc. – radiant heat performs a valuable(perhaps life-saving) function.

Another advantage is the proactive heading-off of lia-bility claims and added safety overall. Given today’s liti-gious society, snowmelts don’t cost money, they save it.The cost of the system is more than returned with oneavoided lawsuit, and some insurers recognize the value ofthese systems, rewarding building owners with reducedinsurance rates.

Snowmelt ClassificationsFor the sake of easy reference, snowmelt uses are

grouped into classifications. These allow us to quantifythe level of snowmelting a system is designed to perform.There are two essential systems of classification – “oldASHRAE” (American Society of Heating, Refrigeration andAir-conditioning Engineers) and “new ASHRAE.”

The old ASHRAE classifications split snowmelting sys-tems into three groups: Class I, Class II and Class III.These classes split systems into the amount of snow actu-ally melted at design conditions. Class I systems aredesigned not to melt snow while it is falling, but after-ward. In Class II systems, half the snow is melted duringsnowfall and the rest afterward. In Class III systems, all ofthe snow and ice is melted while falling.

The key to these classifications is the design conditions.If a system were designed as a Class I (no snow melted)for 36" of snow per day, it could act as a Class III systemwith a minor snowfall of 8". Conversely, a Class III sys-tem designed for around 6" of snow per day would act asa Class I system with 36" of snowfall. So, to guide yourdecisions, know your snowfall.

The new ASHRAE standards still keep Classes I, II andIII, but now labels them 0, 0.5 and 1 for the ratio of snowmelted. They also add a new twist, however – a percent-age to quantify how often the maximum amount of snowoccurs. Many professionals (okay, especially we engi-neers) tend to “overdesign” a system to handle a worst-case scenario. The snowmelt percentages, as divided byASHRAE, are essentially classified into 75%, 90%, 95%,98%, 99% and 100%, with 100% being the maximumsnowfall foreseeable for an area.

It takes a lot of energy to melt snow, about five- to six-times the load required to heat a building of similar size.For example, it may only take 30-40 Btu/hr per squarefoot to radiantly heat a structure, but it can take up to 150

Page 2 8/Plumbing Engineer Copyright © 2004 TMB Publishing. All Rights Reserved. November 2004

Warming up to Snowmelt Technology

By Kolyn Marshall, Systems Design Engineering, Watts Radiant

Continued on page 30

As plumbing engineers,most of us readily see the value of snowmelt

systems. Many buildingand facility owners, however, have yet to

embrace it.

The illustration above shows the way an uninsulated slabmight typically look for snowmelt applications.

Btu/hr-square foot or more to meltsnow and ice from a surface. Why isso much energy required? Namely,the components that make up to load.There are five basic parts to asnow/ice melt system.

Sensible Heat: QsThe first load factor is the sensible

heat required to raise the snow or icefrom ambient temperatures to 32°F.The colder the ambient conditions arewhen precipitation is detected, thehigher the sensible load will be.

Heat of Fusion: QmOnce the mass has reached 32°F

the second phase of the snowmeltprocess can begin. This phase iscalled the Heat of Fusion, which isthe amount of energy required tochange states from a solid to a liquid.This phase of the snow/ice melt sys-tem generally requires the most ener-gy.

Heat of Evaporation: QeAs the mass temperature increases

natural evaporation will begin to takeplace directly from the snow to theatmosphere. This phase is generally asmall part of the overall process, butone that must be considered.

Heat Loss to the Atmosphere: QhAtmospheric losses are the fourth

phase of the snowmelt process. Oncewe start melting snow off our system,we will begin to have voids in thesnow cover – areas that may not haveinitially contained as much snow asother areas due to drifting or may beexposed to solar gain effects. Theseareas clear faster, causing clear patch-es to form, allowing for greater loss-es to the atmosphere – the air sur-rounding the snowmelt. The coldatmosphere will literally “suck” theheat from the slab. We must continu-ally provide energy to the slab toreplace energy lost to the atmosphere.

Back and Edge Losses: QbBack and Edge losses refer to loss-

es not directly associated to the melt-ing snow. These include the ground

below the mass, as well as to the side.E n e rgy in a snowmelt systembehaves like any other radiant sys-tem, that being heat will travel from ahot source (the tubing) to a coldsource (the mass). When a snowmeltfirst starts, energy moves in all direc-tions equally, since the surroundingmass is of equal temperature. Thiscondition changes the longer the sys-tem runs. Since the ground is not anexposed surface it will begin to retainenergy, thus allowing its temperatureto rise. Conversely, the exposed sur-face of the mass continuously losesenergy (to the snow and atmosphere).

Back and Edge losses, however,are really negligible when comparedto the other snowmelting factors.Heat loss to the ground is generallyonly 3-5% of the total system load.

Examples of SnowmeltsTypical snowmelts employ tubing

buried in a concrete slab. The mostpopular tubing used is either synthet-ic rubber (EPDM) or cross-linked poly-ethylene (PEX). EPDM is derived fromsynthetic rubber and is cross-linked,much the same way PEX is, in thepresence of a catalyst and heat (lowpressure steam). Both types of tubinghave a long history of performanceand longevity in high-temperatureapplications.

Tubing comes in a variety of sizes,typically 1/2" ID (inside diameter) to3/4" ID will be seen in a snowmelt sys-tem. The tubing ties into the supplyand return piping via manifolds,which have barbs that transition theflexible tubing to copper, stainlesssteel or brass pipe. These manifoldscome in pairs: a supply manifold,where the tubing starts and a returnmanifold, where the tubing stops. Thelayout is usually easiest if these man-ifold pairs are located together next tothe “zone,” or area to be snowmelted.Manifolds can be located away fromthe zone, but then more tubing will berequired to get to and from the mani-fold pair.Tubing lengths vary accord-ing to manifold placement.

The tubing is spaced from 6 to 12"on center and circulates water thathas been heated to 110 to 140°F.Tubespacing is varied according to thedegree of snowmelting required.More snowfall that needs to be melt-

Continued on page 32

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Snowmelt TechnologyContinued from page 28

ed at a faster rate will require closer spacing of tubes.More material over the top of the tubing increases resis-tance to heat transfer requiring a higher supply water tem-perature.

Common Snowmelt ApplicationsHospital helipads are excellent examples of snowmelts.

With space becoming more and more precious, many hos-pitals are forced to install helipads on the building roofs.

These rooftop helipads can become extremely dangerouswhen coated with ice and snow. Snowmelt systems keepthese helipads snow and ice-free.

Convenient and more inviting to passerby, sidewalksnowmelts can increase business and decrease liability.Customers are more likely to shop stores with clear side-walks, free from ice and snow and chemicals.

Stairs are always viewed as slippery and dangerous. Bysnowmelting stairs, pedestrians can travel in relative com-fort and safety. The spacing of tubes for stairs variesaccording to application, but they are usually installedwith two lengths of tubing in the tread and perhaps onelength in the riser.

Water is always present in car washes. Using snowmelt,property owners can keep car washes open and ice-free.Tubing for car washes is always installed in a concreteslab. The control strategy for car washes is simple. Eitherair temperature or slab temperature can be monitored. Ifthe temperature of the slab or the air drops below 35 F, thesystem is turned on. When the temperature rises above 35F, the system is turned off.

Because they are usually considered Class III systems,tube spacing for hospital entrance ramps are usually setclosely at 6" OC. Further, these systems are idled, or oper-ated at a reduced output, to decrease system lag time (thetime required for the system to reach operating tempera-ture and start melting snow). When the sensors detect pre-cipitation, the system is then operated at full output.

Snowmelting systems ensure cars driving in off thestreet can safely negotiate up and down parking garageramps. One note of caution: be sure to place sensors forthese controls where they can detect snowfall, or precipi-tation and temperature. The sensors are usually placed

away from the ramp.Moving the goods is the motto of many a shipping com-

pany. Trucks can easily get into and out of loading docks,often depressed and slippery. Snowmelting systemsensure that the goods can be moved in and out of yourfacility.

Instead of melting the entire area, sometimes too largeand cost prohibitive, smaller areas are melted where thesnow can be shoveled off and piled on. Used with airportrunways and large parking lots. Large snow piles take upvaluable parking spaces and creating dangerous runoff.Typically, tubing for hot pad slabs is spaced at 4" to 6" OC

to accommodate a large amount of snow. Remember, 6" ofsnow from a runway or parking lot will be collected anddeposited on the pad. It’s not uncommon to have a hot padof perhaps 30' by 30' with snow piled 4 to 6' high!

Hot pads are usually operated manually, activatedwhenever the need arises. Twist timers can be used inplace of on-off switches so the operator doesn’t have toremember to switch the system off. No doubt, facility

owners wouldn’t appreciate seeing the gas bill for a hotpad (or pads) left on accidentally for several weeks.

Principles of OperationSome snowmelts are operated only when there is ice or

snow. These systems are operated in the presence of pre-

Page 3 2/Plumbing Engineer Copyright © 2004 TMB Publishing. All Rights Reserved. November 2004

Continued from page 30

Snowmelt Technology

Continued on page 34

Skiers and other guests move about easily at this resortwhere many of the walkways are snowmelted.

Helipads are commonly snowmelted areas where snowand ice threaten the safe landing of emergency flights.

cipitation when the ambient temperature is below 35 F.While less costly to operate, these system take longer tostart melting ice and snow because they have to increasethe temperature of the slab first.

Controls provide simple temperature and precipitationsensors to sense precipitation when the temperature isbelow 35°F to 38°F. Because these controls are relativelysimple, their cost is also relatively low when compared toother snowmelting controls.

After precipitation and temperature conditions are met,the system will operate until the precipitation stops. Mostcontrols will continue to operate the snowmelt for a peri-od of four to six hours after precipitation has stopped,ensuring the surface is free of ice and snow.

Twist timers can also be used in parallel with thesnowmelting control allowing some manual control overthe system. If it is known that a winter storm is approach-ing, the system can be manually started several hoursbefore with the manual twist timer to reduce system lagtime. Or, conversely, if snow happens to drift onto thesnowmelting surface, but does not engage the precipita-tion sensor, the system can be manually started with thetwist timer.

In order to help systems respond faster, some systemsare idled, or operated at a reduced output until precipita-

Page 3 4/Plumbing Engineer Copyright © 2004 TMB Publishing. All Rights Reserved. November 2004

About the A u t h o rKolyn Marshall is a systems design engineer for

Springfield, Mo.-based Watts Radiant. He has been with thefirm for 10 years. His responsibilities include radiant heat andsnowmelt system design, customer service and the conductingof professional seminars regionally and nationally.

Continued from page 32

Snowmelt Technology

tion is sensed with a temperature below 35° - 38°F, whenthe system is operated at full output. These systems allowfor a faster system response. No snow or ice builds up onthese systems. These systems are crucial when the surfacemust be kept free and clear of ice and snow at all times.

Sophisticated controls that sense slab temperatures, out-door temperatures and precipitation are used. These con-trols are generally more costly than on-off controls due totheir complex nature, but allow for much greater systemcontrol. Controls usually have settings for warm-weathershutdown, slab idle temperature and cold-weather shut-down. Cold weather shutdown is necessary becausesnowmelt systems cease to be effective below about 0°F.We simply cannot provide enough energy below 0°F toeffectively provide snowmelting. Yet, this is rarely trou-blesome because snow below 0°F contains very littlewater.

Snowmelts themselves are not that expensive to oper-ate, since they usually only run a few times a year. Thebiggest cost incurred with a snowmelt system is the up-front cost. Glycol antifreeze is required for all systems,since the system fluid is either dormant or could go dor-mant for a period of time. Relatively large pumps could berequired to move the slushy water-glycol mixture on ini-tial system start-up. Larger boilers are required to deliverthe 100-300 Btu/hr-sq.ft. Supply and return piping isrequired to get the energy from the boiler to the manifoldsfor the tubing buried in the slab. With all these factors,including larger heat source, a snowmelt system can typi-cally cost between $6 - $12 per square foot, depending.

The cheapest system to operate is an on-off snowmelt.These systems are only used five to 10 times per year. Asan example, a Class II system in Buffalo, N.Y., may onlycost about $0.21 per square foot per year. The same sys-tem in Chicago may only cost $0.12 per square foot peryear. Minneapolis or St. Paul may only cost $0.25 persquare foot per year.

Idled systems, because they operate any time the tem-perature is below 38°F, cost more to operate. These sys-tems typically consume up to 100 Btu per hour per squarefoot whenever they are idling and up to 300 Btu per hourper square foot whenever they are operating. Hospitalsmay have waste heat from steam or condensate that maybe readily available, greatly reducing or eliminating ener-gy needs.

So, whether you’re seeing an occasional need to elimi-nate snow in Springfield, or warming an emergency roomentrance in Gnome, a snowmelt system, properlyinstalled, will readily answer the call.