Critical to designing hydronic snow and ice melting (SIM) systems is selecting the appropriate Snow-Fee Area Ratio and Frequency Distribution. To provide that and other relevant design guidance, the Plastics Pipe Institute Inc. (PPI) has issued a new document about determining appropriate performance levels for various types of SIM applications. Recently published to the PPI Building & Construction Division’s website, Recommendation J "Recommended Hydronic Snow & Ice Melting System (SIM) Performance Level Selections for Residential, Commercial, and Institutional Applications” includes suggested Snow-Free Area Ratio and Frequency Distribution values for 29 common outdoor applications.

According to PPI, unlike in an indoor heating system where the methods to calculate heating loads are well defined, an outdoor SIM system is subjected to fluctuating environments. The non-profit industry group advises that the designer and customer should collaborate to select the capability of a system based on factors such as the type of outdoor area, its exposure, and customer requirements and expectations.

Part of the design process for hydronic SIM systems includes selecting an appropriate Snow-Free Area Ratio (Ar) and Frequency Distribution (FD)  for a given system. These terms are defined in the ASHRAE HVAC Applications Handbook, Chapter 52 “Snow Melting and Freeze Protection”. Designing systems to maintain outdoor surfaces 100 percent snow free in all weather is unrealistic for most applications and requires much larger heat sources, circulating pump(s), pipes, and other mechanical equipment. The new PPI Recommendation J is intended to help manage customer expectations and construction costs.

According to the association, after recent harsh winters and growing concerns about liability, the popularity of hydronic SIM systems is expected to increase. Recommendation J provides design targets for types of outdoor areas, such as private and commercial walkways and driveways, public buildings, schools, airports, hospitals, and more. Guidance is based on the experience of an advanced team of PPI members who collaborated on this document.

“With proper design and installation, benefits of hydronic SIM systems include safety, convenience, reduced liability, minimized environmental impact, and reduced snow removal costs. This document is intended to help clarify the design process for SIM systems and to set appropriate customer expectations for performance,” said Lance MacNevin, P. Eng., director of engineering for PPI's Building & Construction Division.

MacNevin continued, “Selecting the snow-free area ratio for each SIM system is a critical design choice. Although having the SIM area completely free of snow during the snowfall is typically preferred, maintaining a snow-free area of 100% requires that the system melts all snow on contact and requires far more energy than if a thin layer of snow is allowed to accumulate on the surface during the snow event. For a private driveway, an Ar value of 0.5 with a FD value of 75% is likely suitable, whereas a hospital entrance probably should use values of 1.0 and 98%, for example. PPI has consolidated our recommendations into one concise table.”

In addition to the table with recommendations for 29 outdoor area types, four distinct examples are provided to help guide users on reasonable design choices.