Electric System Design

The design of an electrical system follows the same general principles as a hydronic system, but some of the particulars are obviously different.

Things to keep in mind with electrical systems include the following:

• Energy: The electrical equivalent of 130–170 BTUs per square foot is between 38 and 50 Watts per square foot. The electrical power, circuiting, and distribution needs should be designed accordingly.
• Temperature: Electrical systems use a fixed wire temperature of about 140 degrees Fahrenheit. This temperature is not changeable during operation.
• Wire size: No special wiring is required for electrical distribution wiring from the control panel to the snow-melting system, based on code requirements. The electrical snow-melting system itself will use the manufacturer’s standard wiring products.
• Insulation: No insulation is needed.
• Wiring layout: The length or run of the snow-melting system wiring/cables needs to be considered. Generally, these cables come from the manufacturer in a fixed length and cannot be extended.
• Wiring spacing: Wiring spacing needs to be closer than hydronic piping spacing and should be 3–4 inches on center. Wider spacing will cause striping and be less effective.
• Wiring depth: Wiring should also be closer to the surface than hydronic piping. The minimum depth below the surface is 2 inches, with an ideal depth for performance and protection at 3 inches.

Keep in mind that all the design parameters indicated here for hydronic and electrical systems are for typical buildings and sites. It is always best to consult with manufacturers for recommendations related to specific project conditions and requirements.

Photos courtesy of Watts

Main control boards are compact, based on electronic technology, and straightforward to use by maintenance staff and homeowners alike.

Snow-Melting Controls

The key to the successful operation of any mechanical or electrical system is the means to control it. Recognizing this, manufacturers offer particular control devices and systems specifically designed for snow-melting systems. The controls are essentially the same for both electrical and hydronic system types, meaning that they use the same components and just control different things. A hydronic system uses the controls to turn on and off or regulate the pumps, mixing valves, boiler, etc. Electrical systems use the controls as basically an on/off control regulating the time when a system, or zones within it, comes on and goes off.

All snow-melting control systems include several aspects with products, software, and manufacturing support available. These include the following:

• Main control boards: A central or convenient location can be selected to install the control board. This could be in the mechanical room where the boiler, manifold, electrical panel, or other equipment are located, or it could be somewhere else. Typically, the control board is a small device, no bigger than a shoe box, and mounted on the wall. The control operates on 120 V electricity and then engages the corresponding-sized contactor for the application. This may be anywhere from 120 V to 277 V depending on the application or product used.

  One of the appealing features of the control board component is that it is the programmable “brain” of the system. This means that it can be used to help optimize the way the system runs. For example, the design professional or operator can get a bit creative and use the controls to cycle different zones of the system. If this is addressed in the design phase with the intent that not all zones need heat at once, then perhaps the boiler in a hydronic system can be smaller.

  Since control boards are essentially all electronic devices, they can take advantage of interfacing with other electronic systems. Some controls can communicate with building automation systems (BAS) using BACnet or Modbus. This allows for things like alert notifications, remote monitoring, and full adjustment capability to be carried out through the BAS. Some controls can even be connected to a mobile phone app, allowing facility managers or maintenance staff the ultimate flexibility in when, where, or how they receive information or initiate commands to operate the system.

• Control sensors: The means for providing input to the control panel is to use automatic sensors that detect moisture and temperature. There are two common types of sensors: those installed in the ground and those installed on an aerial mount above ground. In-ground sensors automatically detect snow or ice on a driveway or walkway, which means that they need to have snowfall to discern conditions. In-ground sensors are also used to monitor the slab or pavement temperature. In-ground sensors are used for a wide range of systems on a variety of building types. Aerial sensors are used when the use of in-ground sensors simply is not practical. This means that they can be a good option for remodeling projects or sites that have other restrictions interfering with the in-ground sensor installation.

  The installation of automatic snow-melting sensors is simplified through the use of some common but sophisticated technology and features. For example, some controls are Wi-Fi enabled, giving them access to weather data and allowing for remote access. Other control options can “daisy chain” together to identify up to 12 zones with different priorities in each zone, allowing the control board to respond accordingly.

• Sequencing: The control sequence is an important part of snow-melting systems, just like any other mechanical/electrical system. The basic elements here are automatic and manual operations, with the ability for a manual override if needed. Typically, the start function is automatic based on information from the in-ground or aerial sensors. An on-demand start is typical, meaning that the system turns on when one or more sensors are activated. Otherwise, the system remains in the “off” mode. There is the option for an anticipator function, which is a Wi-Fi enabled feature connected to weather information or an operator. This allows for a preemptive start of the snow-melting system prior to actual snowfall so the surface is warm and begins melting as soon as the snow starts to hit it. Some operators find that a manual override to start up a system is also helpful for conditions that are not directly related to a snowfall, such as drifting snow or black ice formation.

The system should turn back to “off” based on an automatic function, such as a timer or separate interlink. This keeps the system from running longer than needed and helps reduce energy use and operating cost. It is also a requirement of the International Energy Conservation Code (IECC) in Section C403.13.2 (2021 edition), which states: “Snow- and ice-melting systems shall include automatic controls configured to shut off the system when the pavement temperature is above 50 degrees Fahrenheit (10 degrees Celsius) and precipitation is not falling, and an automatic or manual control that is configured to shut off when the outdoor temperature is above 40 degrees Fahrenheit (4 degrees Celsius).”

In addition to a straight “on” or “off” situation, some critical areas (helipads, emergency room entrances, etc.) may engage in a control sequence known as idling. This is a condition that maintains a constant slab condition whether it is snowing or not but turns off when the outdoor temperatures are reached as cited in the IECC above. Idling options can be permanent or temporary but are typically intermittent based on weather conditions. Idling was used where deemed necessary in the past, but this practice has been mostly replaced by the availability of anticipator systems.

For insight into the significance of controls, Dave Raabe, a tekmar Control Systems sales representative with ROI Marketing, says, “Controls operate hydronic and electric snow-melting systems, with options for fully automatic operation, remote access, and equipment protection. The latest controls improve efficiency through coordination and allow for remote access using a Gateway, WiFi access, and mobile app access options.”

Photos courtesy of Watts

In-ground/in-slab sensors (left and middle) recognize temperature and moisture and are wired back to a main control board. Aerial sensors (right) are used where in-ground sensors are not practical.