The mechanics and economics of snow melting systems in a retail environment — an alternative to conventional snow removal.
By Earle Mott
In contrast to conventional snow removal by shoveling or plowing, snow melting systems can eliminate the problem without any external intervention or lengthy delay. You do not have to be at the mercy of an independent contractor or employee to begin snow removal after it has stopped snowing.
Snow melting systems come in many different forms: from simple overhead infrared heaters or electric cable systems to sophisticated automatic hydronic systems, which can precisely match performance to need and do so economically. Hydronic snow melting systems are also relatively non-polluting due to the use of environmentally friendly food grade antifreezes. The green side of snow melting is that chemical deicers that kill vegetation and damage pavement, automatic doors and interior floor finishes are eliminated along with wet entry mats, fans and warning signs.
Electric cable and hydronic systems utilize flexible heating circuits (wire or pipe) embedded in or just below the pavement in which a current or solution of warm antifreeze is passed, heating the entire surface to melt snow or ice. Effective snow melting requires delivering the heat to the surface in an evenly distributed manner in order to avoid cold spots, as only partially melting the snow is far worse than not attempting to melt it at all. This can happen when the surface temperature is insufficient or uneven and the snow refreezes or bridges over between warm spots, causing uneven icy surfaces and potentially hazardous conditions. Poorly designed and low performance systems avoid this by utilizing a cold weather cut off (CWCO), which prevents the system from operating when outside conditions exceed the ability of the system to maintain the surface above freezing.
There are three basic methods of operating systems: (1) manually turned on and off; (2) continuous operation, typically called “idling”; and, last, (3) those that automatically operate only during snowfall. Manually operated systems might seem like an inexpensive choice by eliminating most of the controls, but forgetting to turn the system off just once will usually eliminate any potential initial savings with the increased operating costs. Forgetting to turn the system on or turning it on too late may require shoveling or plowing to catch up.
Continuously operating hydronic systems are often referred to as “idling” or “idle mode” systems. In operation, these systems are anything but idle. They are usually activated when air temperatures fall below 38˚ to 45˚F and constantly circulate the antifreeze, adding only enough heat to maintain the pavement at or just above freezing. The benefit to these systems is that the surface is always warm when snow begins; however, the penalty for this can be extremely high operating costs as these systems operate 24 hours a day during winter and must use energy to maintain the surface above freezing even when it isn’t snowing. Most of the energy used is wasted and they can’t be turned off because there isn’t sufficient capacity in the heating equipment to warm the system up quickly enough to respond to any snowfall. These systems are usually lower performance and are unable to maintain the surface temperature above freezing when the ambient temperature falls below 20˚F or during snowfall when rate exceeds 0.5-inch to 1-inch per hour and again, when wind speed exceeds 10 mph. You will often hear designers of these systems claim that it can’t snow below 17˚ to 20˚F in defense of having to turn the system off.
A variation on this method of operation which works quite well is idle/melt mode. This is much the same as an idling system with the exception that when snow is detected the antifreeze supply temperature is raised to a “melt” set point, raising the surface temperature of the pavement to respond to falling temperatures and increased wind speed that normally accompanies a snow storm. Operating costs in excess of $2.00 per square foot per season are common for these systems. Consequently many systems are deemed too expensive to operate after the first month or season and are turned off or operated only after conventional shoveling or plowing has been completed to dry the surface.
Automatic systems activate only when a snow sensor indicates the presence of snow and the outdoor air temperature is below set point usually 34˚F. Only then is any energy used to heat the surface. It must be applied quickly enough to prevent snow accumulation but not so quickly that the pavement is subject to thermal shock. More sophisticated systems use sensors in the pavement or infrared sensors to monitor the surface temperature to balance energy consumption with sufficient surface temperature to clear and dry the pavement. By their nature of requiring a quick response, these types of systems must provide higher levels of performance and therefore do not need to shut down during extreme snow or cold weather. One might assume that these systems are extremely expensive to install and operate due to the higher performance. The reality is that, when properly designed, these systems can use 80% less energy to operate than other types of systems with only slightly higher initial installation costs. One that is usually recovered from the first or second season energy savings.
The real trick to economical snow melting is providing sufficient heat to the surface soon enough but only long enough to melt the snow or ice. Start too late and/or provide too little heating capacity and snow and ice conditions just get worse. Having to hire a contractor to push the snow under those conditions just adds insult to injury.
— Earle Mott has been in the radiant heating industry for the last 37 years and is currently president of Snow Technologies, Inc., a Livonia, Michigan-based firm specializing in commercial and industrial snow melting systems. Email the author at earle@snow-tech.com.