Project Description
New Construction:
Plumbing, radiant heating, and snow melt at Lake Tahoe, California.
Boiler Plant:
Two Weil McLain Ultra 230 boilers were installed as a heating plant in order to take advantage of load sharing and also to provide redundancy.
Radiant Heating System:
The copper distribution piping was sized to keep the fluid velocity below 5 ft/second. To provide even heating, the tubing was laid in counter-flow spiral patterns, and the radiant pump was sized for a 10-degree temperature drop.
Snow Melt System:
The snow melt tubing was spaced on 9” centers, and the system was designed to deliver 125 btu/sq ft with a 20-degree temperature drop.
Domestic Hot Water System:
The domestic hot water is heated off of the high-efficiency boilers through a double-wall FlatPlate heat exchanger. The domestic hot water is stored in two 120-gallon storage tanks (with electric backup). The FlatPlate heat exchanger was sized to deliver the maximum output with both boilers firing at full fire.
Controls:
The boilers are controlled and reset by a Tekmar 265 modulating boiler controller. Erie VL500 zone controllers control the zone valves. Aprilaire thermostats were installed in the boiler room with remote in-wall sensors located in each zone. A central setback thermostat was installed with a home/away switch to allow the entire house to be easily set back for extended periods of time. A Tekmar 090 snow/ice sensor and Tekmar 665 control the snow melt system. A Tekmar 262 controller sequences and controls the boilers for domestic hot water production. A pressure switch protects the boilers and pumps from a low water situation, and a high-limit aquastat protects the radiant floors from a high temperature excursion.
Miscellaneous:
The system was charged with 40 percent aluminum-safe glycol for freeze protection. An automatic glycol feeder was installed to make up water/glycol mixture to the system and thus ensure that the solution is kept at a 40 percent mixture.
Design Notes:
The boiler piping and controls were set up to maximize efficiency and redundancy. When there is a call for domestic hot water, the Tekmar 262 fires the first boiler to supply 190-degree water/glycol to the heat exchanger. The boiler then turns off its boiler heating pump, turns on its domestic heating pump and supplies 190-degree water/glycol. If the domestic load is light, the first boiler will easily handle the load while the other boiler continues to handle the radiant and snow melt. If the domestic load is large, the Tekmar 262 will call for the second boiler to deliver heat to the domestic system. The advantages of this setup are: 1) Either or both boilers can be used to heat domestic hot water; 2) When only one boiler is heating domestic water, the second boiler can be operating at low temperatures and thus be condensing and operating very efficiently.