Addition Solar Heat Plan

The underfloor hydronic heat in the addition will consist of 3 zones with 4 loops total: basement 1-loop zone, great room 2-loop zone, and under-loft 1-loop zone. Each loop is 300′ 5/8″ PEXa tubing. The expectation is that the great room zone will the most active. The intention is to run each loop at 1.75 gpm, 90°F water in, 75°F out, which should produce 13K BTU/Hr/loop. So the system should produce 26K BTU/hr in “normal” great-room only mode, with an additional 13K each available in the under-loft area and in the basement.

After much research, I have decided to go with this 800 Liter Solar Water Heater System from Duda Diesel. We will be adding the Turn-Key option and upgrading to Freeze Protection tubes so the collectors can handle routine temps below 14°F (which, based on this past winter, I would have to say that we get). The choice between evacuated tube and traditional flat-plate solar collectors was difficult. The reasons why I chose tubes include: lower weight and individual components for easier rooftop installation (we do not have enough non-floodplain sunny areas for ground-based collectors); space between the tubes provides a lower wind resistance; purportedly better performance on cold and/or cloudy days. My concerns are mainly related to the fact that because the outside of the tubes stay cool any frost or snow can take longer to melt than with flat plates. Oh well, a grand experiment awaits!

The heating is a open direct system, with a 211 gallon solar storage tank supplying the underfloor hydronic heat, as well as preheating the water for a standard domestic hot water heater. The 211-gallon solar tank has a built-in heat exchange coil for rooftop solar collectors and an electric heating element for backup. It is not at all certain whether the electric backup, combined with the large thermal mass of our insulated suspended concrete slab floor will be sufficient to keep us warm during extended bad winter weather (but I am quite confident that we will remain at most chilly, not frozen!). Our backup plans include the fact that we still have wood stoves in the old house (our only heat for 17 winters.)

The solar collection side is a closed-loop system with a glycol mixture to prevent freezing. The collectors will mounted on the addition’s east-facing 5/12 pitched (22.62°) metal roof. They will face 11° east of south (the orientation of the house itself) and be tilted up at a 45° angle.

Click on any of the images below to see a larger version:

Solar_heat_schematic

Schematic of the hot water and heating system [Updated 2015-07-22].

RooftopSolarConfig

Location of the rooftop solar collectors. I hope that placing them close to the addition gable end will minimize blocking snow build-up.

solar_elevation_east

Solar heating schematic from the east. Total heat tube (supply plus return) is about 150′.

solar_elevation_north

Solar heating schematic from the north.

underfloor_heat_main

The two-zone, three-loop main floor underfloor heat tubes. I need to re-do the loops to put a couple in the bow window floor area. (Our original plans called for a window seat in that area.)

underfloor_heat_basement

The underfloor heat tubes in the basement. Placing all the equipment in the mechanical room on the right will be tricky. There are two water tanks, two expansion tanks, and two sets of controllers. Plus I want to plan for a battery bank for future PV solar electric, and the bank will go into a vented box (I have a 3″ PVC conduit in place for that.)

Underfloor Heat Components [already purchased unless noted otherwise]

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