Heat Pump and Rooftop Solar Puts Northeast Radiant on Path to Net Zero
Solar At Work | June 21, 2012 | Posted by Fred Greenhalgh
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The rising cost of oil and gas has spurred Mainers’ interest in heating alternatives. A new generation of heat pump technology and falling costs of solar electric modules have combined for a vision that many would not have believed feasible: affordable electric heat offset entirely by solar power.
Leading this charge is Northeast Radiant Technologies (NRT), who recently installed a 14.4kw solar electric array on the open south-facing roof of their Gardiner, Maine offices, alongside a Daikin Altherma air source heat pump.
Being full service heating system design professionals, NRT knew intimately the full range of heating options available. Their choice to go with solar and an air-source heat pump was based on a commitment to environmental responsibility and an exciting vision: a heating system powered solely by the sun.
The Power in Going Solar
“The ability to go Net-Zero with a PV array for a small business like ours was really attractive,” says NRT Co-founder Rob Brown, “With our competitive grant, our time to pay back the system cost is less than 7 years and even with just the base tax credit it’s about 13. We felt if we could really tread that lightly on the earth for that kind of a price it was well worth it to us. And of course, in the end it’s an economic winner as well.”
NRT was able to take advantage of a suite of rebates including a $2,000 Maine state rebate (recently increased to $4,000 for businesses), a 26% Federal Investment Tax Credit, Accelerated Depreciation Benefits, and an Efficiency Maine grant.
Unlike a choice to invest in fossil fuels, NRT knows that in the future their cost of energy will never increase. The solar electric system will produce a little over 18,000 kWh of power a year – a savings of close to $3,000 annually at today’s prices.
The solar electric panels are long-lived, with an expected life span of 30+ years, and contain no moving parts. Whenever the sun is out, clean electricity is generated and either used immediately in NRT’s offices, or exported to the grid.
A Wood Shed That Stacks Itself
The heart of NRT’s heating/cooling is the Daikin Altherma, an air source heat pump that extracts heat from the outside air and transfers it inside through refrigerant piping to supply heating.
Unlike traditional resistive electric heat, electricity is used to move air, rather than heat it, which makes it 2-3 more efficient than resistive electric heat (this is called a COP of 2-3). The system can extract heat from ambient air as low as -4°F! In addition to heating the building, the Altherma also provides cooling – all without the well-drilling or excavation requirements of a geothermal system.
The cooling is a significant aspect for NRT, who is a “peak load contributor” during the warm summer months, which, conveniently, is when their solar electric system will be at peak production. During the times NRT’s system produces more electricity than is consumed in their building, they will bank power with the utility company in the form of a credit. These credits can be used to offset electricity costs in the winter when their electricity will go towards their heating load. As one ReVision staffer remarked, a solar-powered heating system is kind of like a wood shed that stacks itself.
Space Heating Design Makes a Difference
Even with the solar photovoltaic project and Daikin Altherma, NRT’s offices wouldn’t be near reaching their net-zero goal without an elegant radiant distribution design (their specialty, of course!)
NRT’s building is very tight, and unlike most homes in Maine, their cooling loads are equal to their heating loads. For optimal comfort year round, they use three different systems: a hyper-efficient UltimateAir ERV (50 watts), a chilled water coil to dehumidify (25 watts), and a radiant distribution pump (25 watts). That’s 100 watts of total distribution consumption, in contrast to the hundred of watts used in most ducted systems.
This combination of efficiency and renewable energy generation makes for a perfect situation for NRT: “We love watching the array generate juice,” Brown says, “It’s made limiting our power usage here to reach the net zero goal a fun game we all like to play. We really feel like we’re making a difference.”
Full disclosure: NRT and ReVision have collaborated on dozens of space heating projects over the years, so we took a special delight working on this project, as did NRT. Rob adds, “We love working with ReVision. You just can’t beat working with other professionals who not only believe in what they doing but who can do their jobs with the utmost professionalism and technical acumen. Having your staff here at our site was a blast.”
Feeling’s mutual, Rob. Enjoy that sunshine!