Snow and Ice Melting Systems: Estimating Operating Costs (Part IV)

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If you’ve been reading this series up to now you’re probably thinking, “Wow–I need to incorporate a SIM system in my new driveway/ sidewalk/ramp for my new house/business/office building! But how much will it cost to operate one of these at my home or business?”

 

 

 

Well, that’s a great question, which we can estimate based on some historical weather data and current fuel costs. Our SIM seminars explain the math in detail, but we don’t have space for all of that in a blog post. Instead, we will give a few examples.

 

Much of the information available to SIM designers comes from ASHRAE (American Society of Heating, Refrigeration and Air Conditioning Engineers). As ASHRAE members, REHAU designers have access to this information, some of which is used below.

 

Before we get started, please understand that it is difficult to predict the weather, so it is difficult to predict SIM system operating costs with any certainty. Every effort is made to explain assumptions based on known or assumed data.

 

Example 1:  Residential

 

– Location: Chicago, IL
– Project: 40 ft x 18 ft driveway and 20 ft x 4 ft walkway, with a combined area of 800 ft2
– Ramp is poured concrete 5 in. thick
– Designer selects a system capable of keeping a Free Area Ratio (Ar) of 0.5 (50% snow free) during a 90% Frequency

Distribution snowfall; this requires an output of 77 Btu/ft2 per hour
– With downward losses, the SIM heat load = 74,000 Btuh (output calculated using steps explained in part II of this series)
– Fuel: Natural gas @ $1.15 Therm net fuel cost 1
– Heat source: Natural gas boiler @ 90% combustion efficiency on average 1
– Typical temperature at start of snowfall is 18°F (-8°C)
– Weather data shows that it snows/ices 124 hours per year, and we assume this happens over 12 “events” per year, 10.3 hours of frozen precipitation at a time (12 x 10.3 = 124 hours annually)

 

1 Energy costs and heat source efficiency vary, and so will these results 

 

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Estimate 1:  Fully automatic system, no idling (also applies to semi-automatic electronic control)

 

– Total annual load is made up of the melting load plus the pick-up load
– For this project that adds up to 12 million Btus per year
– How much does it cost to generate 12 million Btus of heat for the ramp?
– Based on the previous assumptions, the net energy cost is US$12.75 per 1 million Btus 1
– 12 million Btus x US$12.75/1 million Btus = US$155/year in fuel*

 

Note: Electrical costs for heat source and circulator not shown, but these are minor in comparison

 

 

 

Compare this reasonable cost with an annual snow removal contract estimated of $100 per snow fall ($1,200 per year) for plowing with a truck-mounted scraper. Afterwards, the homeowner must do the salting and sanding. The hydronic SIM system is 88% less expensive to operate over the winter than relying on mechanical snow removal, which may damage outdoor surfaces with blades, salt, etc. In other words, the SIM system costs one-eighth as much each winter to operate, provides convenience and safety, while protecting outdoor surfaces.

 

 

Example 2: Commercial
– Location: Albany, NY
– Project: Parking garage ramp, 50 ft long x 20 ft wide for a total area of 1,000 ft2
– Ramp is poured concrete 6 in. thick
– Designer selects a system capable of keeping a Free Area Ratio (Ar) of 1.0 (100% snow free) during a 90% Frequency

Distribution snowfall; this requires an output of 125 Btu/ft2 per hour
– With downward losses, the SIM heat load = 150,000 Btu/hr (output calculated using steps explained in part II of this series)
– Fuel: Natural gas @ $1.10 Therm net fuel cost 1
– Heat source: Natural gas boiler @ 93% combustion efficiency on average 1
– Typical temperature at start of snowfall is 18°F (-8°C)
– Weather data shows that it snows/ices 156 hours per year, and we assume this happens over 20 “events” per year, 7.8 hours of frozen precipitation at a time (20 x 7.8 = 156 hours annually)

 

 

We will estimate operating costs for this commercial system twice, using different control strategies.

 

 

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Estimate 2a:  Fully automatic system, no idling (also applies to semi-automatic electronic control)

 

– Total annual load is made up of the melting load plus the pick-up load
– For this project that adds up to 30.5 million Btus per year
– How much does it cost to generate 30.5 million Btus of heat for the ramp?
– Based on the previous assumptions, the net energy cost is US$11.80 per 1 million Btus 1
– 30.5 million Btu x US$11.80/1 million Btu = US$360/year in fuel 1

 

Note: Electrical costs for heat source and circulator not shown, but these are minor in comparison.

 

 

Compare this reasonable cost with an annual snow removal contract estimated at $3,000 per winter for plowing, salting and sanding. And you get to keep the snowbanks in your parking lot at no charge! The hydronic SIM system is 85% less expensive to operate over the winter than using on mechanical snow removal, which relies on people to show up, and may damage outdoor surfaces with blades, salt, etc.

 

 

Estimate 2b:  Fully automatic system with idling activated when not snowing

 

– Total annual load is made up of the melting load plus the pick-up load plus the idling load
– For this project that adds up to 127 million Btus per year
– How much does it cost to generate 127 million Btus of heat for the ramp?
– Based on the previous assumptions, the net energy cost is US$11.80 per 1 million Btus 1
– 127 million Btu x US$11.80/1 million Btu = US$1,500/year in fuel1

 

 

Note: Electrical costs for heat source and circulator not shown, but these are minor in comparison.

 

 

Activating the Idle setting in this project increased the annual fuel cost but reduced pick-up time, resulting in a more responsive, safer system. Many commercial projects will utilize the Idle setting on the control, which can be fine-tuned to save energy.  This hydronic SIM system is still 50% less expensive to operate over the winter than relying on mechanical snow removal.

 

Some facilities generate waste heat which they are trying to reject using chillers or geothermal heat pumps during portions of the year. Some examples are office buildings, factories, hockey rinks, car dealerships with waste-oil boilers.  In these applications, an Always-on SIM system can be an efficient and effective solution for rejecting the excess heat of the building or processes, while providing all the benefits of a hydronic SIM system.

 

REHAU Academy offers several seminars which explain this design process in detail using real-world examples. REHAU’s design department also assists customers and engineers with SIM design work, including generating PEX pipe layout drawings when required.

 

 

By Lance MacNevin