Boiler Plant:
Three Weil McLain Ultra 310 condensing boilers with a combined boiler input of 930,000 btu/hr. Also includes boiler circulators, isolation valves, and flue and combustion air piping.
Ice Prevention/Snow Melt System:
Includes a copper secondary loop with a Grundfos wet-rotor circulator. The secondary loop contains thermometers, an air purger, wye strainer and isolation valves. The distribution system consists of copper piping that runs to four Rehau Pro Balance manifolds. Approximately 9,000 linear feet of Rehau 3/4” PEX tubing is installed on 9” and 12” centers in the wash bays, sidewalk and entry pad.
Controls:
The boilers are controlled by a Tekmar 265 Modulating Boiler Controller. A Tekmar 090 snow/ice sensor and Tekmar 665 (utilizing the idle feature) controller provide a heat demand to the Tekmar 265. The system is also equipped with redundant protection devices in order to protect the system and meet local codes. Each boiler has its own high-limit control (outside of those in the boiler control). A low-water cutoff is present on the secondary loop along with a pressure switch and a high-limit aquastat. In addition, an emergency shunt trip is located inside each door to shut down the boilers in the event of a crisis.
Miscellaneous: The system is charged with 40 percent aluminum-safe glycol for freeze protection. Also 3/8” foam/foil/foam insulation is installed underneath the slab.
Design Notes:
The system was designed to deliver approximately 110 btu/hr/square foot. The secondary loop flow rate was designed around a 20-degree delta T. The PEX tubing lengths were kept below 350’ in order to minimize head. The distribution piping was sized large enough to keep velocities below 5 ft/s (this also helped keep the head down). The system was set up to provide 130-degree F water out to the system. The Tekmar 265 modulates and controls the boilers to increase efficiency. The slab idling temperature was set at 39 degrees F while the cold weather cut-out is set at 5 degrees F.