Solar Hot Water Rehab- Shealy

Thirty years ago, Tom Shealy had moved from Massachusetts to Stratham, New Hampshire to set up his own dental practice and enjoy the good life.

The nation was still reeling from the memory of the 1973 OPEC oil embargo and, with emerging solar energy technologies, seemed poised to launch from the fossil fuel age into an era of renewable energy. The Carter administration made renewable energy a priority and homeowners like Shealy were eligible for rebates on solar equipment, such as the technology created by Concord, MA based Acorn Structures.

At the time, Acorn had a passive solar home design using a ‘trickle down’ active solar collector for solar domestic hot water and space heating. Shealy took advantage of the Carter-era programs to invest in an Acorn home, the product of some of the best engineering minds at the time, and a concept that fascinated editors of Popular Science and writers of books on energy efficiency.

How the Acorn Worked

Schematic of Acorn Passive Solar HomeA large amount of roofspace (roughly 480 square feet) would consist of a single-glazed solar hot water collector – basically an aluminum sheet with copper tubes on top, covered with fiberglass insulation to help retain heat. Water would be pumped from a large (2,400 gallon) insulated water tank housed in the basement and up into the collectors, where it would then ‘trickle down’ back into the storage tank. The upper (hottest) water in this storage tank would head into the home’s domestic hot water supply, while water in an inner ‘buffer’ tank would be pumped through the home’s heating system.

While this water-based process was happening, the home would also take advantage of its passive solar orientation. The Acorn homes were built facing-south with large solariums (south-facing rooms with lots of glass) that ducted warm air to a concrete slab below the house. This solar-warmed air would then be blown through an insulated central air shaft, and into the house. Along the way, the air would breeze across a loop from the water-based heating system and whisk heat from the solar-heated water into the home. Due to the unique design of the system, the water only needed to be heated to 70 degrees to contribute to home space heating.

While complex, this combination of active/passive solar combinations was enormously more efficient than relying on #2 heating oil for home heating – and 30 years later, the Shealy household was still using it! However, all good things come to an end, and after nearly 30 years of operation the Acorn home was showing signs of age.

Re-Investing in Solar

Comparison of old and new solar hot water arrays

“We’d been very happy with the Acorn home and our investment in solar,” Tom says, “But we noticed a deterioration in system performance in the last couple years of life. Finally it started leaking, and we knew we needed to do something.”

Tom called us in, and our team of solar engineers worked together to come up with the best way to get the Shealy’s system back into good working order. We discovered that the solar water storage tank and heat exchangers still worked, but that the pumping system and collectors would need to be replaced. We chose Wagner Euro C-20 flat plate solar hot water collectors, which boast an anti-reflex glass with light tranmissivity of 96%. 2.5″ of insulation surround the copper piping in these collectors, which is enclosed in a weatherproof aluminum frame.

The drain-down, ‘trickle’ pumping system was replaced a pressurized, glycol-based heat transfer system that would be more resilient in both freezing and high-heat conditions. We added an external heat exchanger to transfer heat from the pressurized loop to the existing Acorn tank, which continues to operate as it has for decades, pumping hot water up to the taps and blowing warm air into the house.

A Whole Lot Warmer

“The difference was immediately obvious,” Tom says of the installation. “The old collectors had been having trouble getting the tank temperature above 90 degrees the last six years, while the new system is much more efficient.”

Now as he nears retirement, Tom enjoys the peace of mind knowing that the costs of his home are predictable and provided courtesy of the sun. “We’ve enjoyed our solar array for almost 30 years but we also enjoyed seeing how far the technology has come. I hope we see another 30 years of sunshine ahead of us.”