Heating and cooling are provided by two Bosch 2 ton ground-source heat pumps connected to a horizontal ground loop system. One heat pump is a Bosch water-water model and the other a Bosch water-air model. The water-water unit is solely devoted to heating the ten zone radiant floor system on two floor levels, a Runtal hydronic towel warmer/radiator in the master bath, and the 198 gal Bosch/Buderus PL750/2S Solar DHW/Space Heating Combi Tank. The solar tank is kept at a minimum of 100 deg F by the heat pump during periods of poor weather. The water-air heat pump serves a single upper level ducted distribution system that has operable adjustment dampers in the ductwork to allow the owner to create both warm and cool spaces. The upper level air system is controlled by a centrally located “smart” Ecobee thermostat and a mechanical room Ecobee control panel, which is also accessible on-line via a PC or smart phone app, to provide both heating and cooling control at all times. Nine of the ten radiant zones are controlled by simple heat only wall thermostats, and the largest open space 1st floor zone is controlled by the Ecobee thermostat which decides how best to heat that zone (i.e. - capable of running both heat pumps simultaneously).
The envelope of the house is super-insulated with R40 value upper walls, R27 value lower walls, and R60 value roofs. The upper walls are double 2x4 at 24” on center, wood stud walls separated by a 3.5” cavity. The outer wall and cavity have 7” of dense pack cellulose insulation and the inner wall is insulated with 3.5” of rockwool insulation. The lower walls are 8” Logix ICF concrete walls with 2-3/4” of high density foam on each face. The roof trusses have a minimum of 24” of blown-in cellulose insulation. Under the lower level 4” slab-on-grade is 6” of EPS foam insulation which is R22+.
Domestic hot water is generated by a 9 panel (28,000 btu/day/panel capacity) Bosch/Buderus Logasol SKS 4.0 flat plate collector solar system that stores energy in the 198 gallon Bosch Combi storage tank in the lower level mechanical room. Whenever the solar hot water is below 120 deg F, a Seisco on demand electric water heater boosts the water coming from the hot water tank to approximately 135 deg F before reaching a final tempering valve. The solar panel system panels are also utilized to form a solar-geothermal “hybrid” system, such that once the solar storage tank reaches peak temperature (160 deg F in summer), the hot glycol coming from the panels is diverted through a stainless steel heat exchanger via a Bosch/Buderus TR0603 Solar Controller to heat a small buffer storage tank up to 120 deg F. The buffer storage tank is also heated by the 2 ton water-water geothermal heat pump and serves the radiant floor heat system on both levels. The buffer tank temperature is automatically maintained by the heat pump to between approximately 90-110 deg F, based upon the outdoor temperature. When the buffer tank is in active heating mode during the winter season, the BTU’s from the solar glycol go directly into the space heating needs of the radiant floors when not heating the solar tank’s domestic hot water supply. If the buffer tank reaches its maximum heat setting of 120 deg F, the hot glycol feed is then diverted into (13) 300’ long horizontal ground loops that dispense BTU’s into the 12” deep, saturated sand geothermal bed to boost the energy available in the bed. The (13) 300’ long geothermal ground loops are separated vertically from the glycol loops by 4” of wet sand. When the glycol temperatures (usually lower than 115 deg F) are too low to either heat up the buffer tank or solar tank, flow is automatically diverted into the sand bed (“solar dump”).
100% of the electric power consumed in the house is generated by a 13.8 kW DC (12.0 kW AC) photovoltaic system comprised of 60-230W DC panels from BP Solar. All the panels are located on the south side of the detached carriage style garage. Three 4,000W AC Solectria inverters are connected to the PV array, and then through a by-directional smart meter (net metering) to the utility grid. A bank of 16 DC, 60 amp-hour batteries are also connected to the PV system through two 3,600W DC Outback inverters and can supply up to 7,200W of back-up emergency power if the utility grid goes down. During the winter, all the power generated on a monthly basis is utilized on site. Daily levels flow back and forth to the utility through the “net” metering station. During the other three seasons, excess power from the PV system is taken by the local electric utility company and fed back into the grid daily. Once a year, at the end of the first quarter, the net excess energy (if any) is calculated and can either be paid out to the owner or banked for later consumption. The system generated a total of 16,220 KWH during its first 12 months of operation.
Home Energy Rating (HERS) Index: 2
Air Leakage: 0.60 ACH at 50 Pascals (454 CFM on a volume of 45,740 CF of conditioned space)
Lighting Power Density: 0.38 watts/sf