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Domestic Hot Water

The hot water heating system relies primarily on solar power with backup from the gas boiler used in the heating system.

Solar Hot Water

The solar hot water system consists of

When the sun heats the water in the solar collectors above the temperature of the storage tank, the differential controller turns on the solar loop circulator. The hot water from the collectors is pumped to the heat exchanger at the bottom of the tank where it heats the water for the house.
The now somewhat cooler water still contains enough energy to heat the downstairs floor. From the tank the water flows to a manifold in the south east wall of the wine cellar. From there it travels through a second set of 1/2" PEX-Al-PEX tubing in the concrete slab to warm the floor. If the floor is getting too warm in summer, you can turn on the diverter valve to bypass the floor tubing.

Boiler Backup

On cloudy days and in the winter, there may not be enough insolation to heat sufficient water so the boiler provides a backup. The system layout is a primary-secondary loop similar to Figure 6-6 "Single Boiler Zoned with Valves" on Page 38 of the Lochinvar Knight Installation and Operation Manual. The high efficiency KBN080 boiler provides heat for both the radiant heating and domestic hot water.

In the boiler loop, the flow goes from the boiler through

  • the pressure and temperature relief valve
  • a pressure and temperature gauge
  • a drain and purge valve
  • a Honeywell PV100 SuperVent air separator with TK300-90 expansion tank and FM911 backflow preventer and fill valve
  • closely spaced tee
  • Grundfos UPS15-58FC circulator with check valve
  • a fill and drain valve
  • back to the boiler

In the domestic hot water loop, the flow goes from the boiler loop supply through

  • a Grundfos UPS15-58FC circulator with check valve
  • a Honeywell FV180A air vent
  • the heat exchanger in the Stiebel Eltron storage tank
  • back to the boiler return line

An aquastat on the east wall of the utility room detects when the hot water tank is too cold. It starts two circulators (for the boiler and domestic hot water), and then fires up the boiler to heat water in that loop. The hot water from the boiler flows through the heat exchanger in the upper loop of the tank to heat the water for house.

Thermostatic Control

On a warm summer day the collectors can easily heat the storage tank to 160 F or more. This provides ample hot water, but the temperature is so high that people could be scalded. For safety a mixing valve on the top of the tank tempers the water to a more reasonable 120 F for use in the house. For further safety and convenience, every shower has thermostatic control valves.

Hot Water Recirculation

The upstairs master bathroom is relatively far from the hot water storage tank. A motion sensor by the doorway detects when a person enters the bathroom. It starts a hot water recirculator to bring hot water to the bathroom as quickly as possible. This is

  • more convenient since you don't have to wait so long for a hot shower
  • saves water since you aren't sending water down the drain while waiting for it to heat up
  • saves energy since the recirculated water takes less energy to reheat than the colder (typically 55 F) city water.

Guesthouse Tankless Hot Water Heater

The guesthouse may see only occasional use, so a tankless hot water heater eliminates standby energy losses. The Takagi T-KJr turns on within a few seconds when you turn the hot water all the way on.