MMA Professor Reduces Oil Use by 1/3 with Solar Hot Water
Residential Projects | December 24, 2013 |Posted by Fred Greenhalgh
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When Marine Transportation Professor Capt. Andy Chase first moved into his home in the early 1990s, he knew he had some work to do. An energy audit confirmed that the 2×4 framed home (located in beautiful Castine, Maine) would benefit from insulation and upgraded windows and doors.
Andy and his wife felt like their house could further benefit by taking advantage of their wide-open, south facing roof, and started looking into solar options. When they talked to ReVision Energy, they discovered that solar hot water offered the best combination of fuel savings and environmental benefits.
“There’s no longer any scientific dispute over the fact that we need to cut down on our production of carbon, or face increasing environmental consequences. I’ve witnessed glaciers receding in the Arctic just from my own experience travelling there as an maritime educator over the last 20 years,” Andy says, “But as homeowners we have to balance the desire to do the right thing with finances. Solar hot water offered a great opportunity to save money and make a significant dent on our carbon footprint.”
Using the Sun to Solve Problems with Oil
Andy’s home, like over 400,000 in Maine, heats with oil and prior to solar was using a high-mass oil boiler to produce domestic hot water. This design – while convenient for the oil company – is one of the least efficient ways to heat water. The oil boiler is controlled to fire multiple times per day, 365 days a year, to keep the water tank heated, even in the middle of summer, and even if the home is unoccupied. With this set-up, approximately 1 gallon of oil each day is wasted in ‘standby’ losses from the oil boiler. When the boiler does run, it is extremely inefficient because larger oil boilers do not have the ability to modulate their burn rate. Instead, these boilers fire up at full capacity and run at an efficiency of around 15%.
Solar hot water, combined with boiler control upgrades, offers an excellent solution to this problem. A set of solar thermal collectors are installed on the roof (either evacuated tubes, as the Chases use, or flat plate collectors) and connected to a special-purpose storage tank installed in the basement.
A pump station uses sensors to regulate the flow of a nontoxic antifreeze solution used for heat transfer. When the rooftop collectors are warmer than the tank, circulating fluid moves to the roof, collects heat, and distributes that heat into the water tank as it passes through a heat exchanger. When the sun sets, the pump shuts down automatically. The pump also has settings to protect the tank from getting too hot.
In Andy’s case, he opted for a solar tank with an electric backup element which removes domestic hot water load from the boiler completely – other set-ups allow you to continue to use the oil boiler for backup, mainly during the colder months when the boiler is likely running for space heating already. Either way, ReVision Energy typically also installs a ‘cold start’ aquastat to the boiler, which allows it to shut down completely when not in use, rather than maintaining a 100+ degree temperature every day of the year.
“I watched it like a hawk at first,” Andy says, “In the first year we calculated it saved us approximately 1/3 of our fuel bill [around 300 gallons of oil]. Once I could see it did what it was supposed to, I stopped paying as close attention. Now it just works – it hasn’t needed any work, it runs very quietly, my hot water is hot, and it’s happily up there in the sun making heat and saving us money.”