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New York Home Centers on Sustainability

ACHR News - May 2012

   
           
 
 

Energy-Efficient Operation

To optimize energy efficiency, the hydronic circulators used in conjunction with the ground-source heat pumps provide heating and cooling by pulse width modulation duty cycle and variable speed control.

The first four circulators are 15-58FC zone pumps, operating on medium speed at 60-80 W with a 50 percent duty cycle for December through February, and July through August; and a 25 percent duty cycle for other months. The next circulator is also a 15-58FC pump that is controlled as a variable-speed injection pump operating at a 20-60 W maximum.

Another circulator is boiler heat backup, 15-58FC, on medium speed at 80 W, only running about 20 percent duty cycle January through February. A final pump, 26-99FC, operates on medium speed 179 W and is for direct-coupled ground-source radiant cooling only operating in the summer at 50 percent duty cycle. This combination heat pump flow control uses about 480 W to heat and cool the structure.

Rowe’s home also features in-floor radiant heating and cooling. The system is embedded in concrete for each floor, as the basement is slab on grade, and the second and third floors are poured concrete over ICF decking. The concrete thermal mass construction acts as a thermal energy flywheel to offset overnight peak loads, so the mass stores energy and regulates temperature fluctuations.
“Bill Cotton, of Cotton’s Concrete in Athens, Pennsylvania, and his team had to work very closely with Aaron on the installation of the tubing into the LiteDeck floor slabs,” said Rowe. “It was a pleasure working with some great contractors who I knew I could trust, and they did not let me down.”
The home’s swimming pool is also a key component, acting as another geothermal heating/cooling source. When the heat pump is operating for air conditioning, and the pool is in heating mode, controls divert the energy normally transferred from the home to the Earth, instead from the home to the pool. Geothermal heat exchange efficiency is somewhat less going to 80F pool water rather than 55F ground; however, the compromise is beneficial as the pool heating becomes a byproduct of air conditioning.

When the pool heat is off, controls divert back to using the vertical ground loops as needed for air conditioning. This design required a properly sized close approach flat plate heat exchanger made of titanium to endure the saltwater pool treatment system.

For radiant cooling, the ground-source heat pump system reverses from heating mode to cooling, charging the 120-gallon buffer tank with chilled water instead of hot water. A variable-speed mixing pump controls the water temperature from the buffer tank to the radiant floor cooling system.
The ERV provides 253 cfm intermittently (11 hours/day) to meet ASHRAE Standard 62.2.

With sensible recovery efficiency of 67 percent and total-recovery efficiency of 46 percent, the energy recovery ventilator is in line with most equipment efficiencies, but uses a significant 490 W during run time; fortunately, it also doubles as a bathroom local exhaust.

The home is monitored and controlled via an Automated Logic building automation system, which can access all 16 zones through remote sensors that are Internet accessible.

“Aaron has a rare passion for technology and all things involving HVAC,” said Rowe. “He guided me through our joint vision for a highly energy-efficient house comprising a geothermal energy source, radiant heating and cooling, insulating spray foam, and web-enabled monitoring and control systems. I had to trust him, and it paid off.”

 
       
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