The ROSE Cottage Project
General Energy Use, Strategies and Systems
Energy Use:
The project combines the use of PV panels with a back-up battery bank; solar thermal panels; geothermal heat pumps (2); a hybrid design that integrates excess BTU production from the solar thermal system to boost the effective COP of the geothermal system with both space heating BTU's via the buffer tank as well as a wet sand heat sink below the building; a dedicated air-air HRV for fresh air; and an on-demand electric back-up domestic hot water heater. The HERS rating of the home, before inclusion of the PV system, was calculated to be 35. The project has performed each calendar year (3 total) at zero net for each year of the 3 years, including the use of the outdoor spa which is metered internally for record purposes, and consumes approximately 10% of the PV output.
The Geo-Solar Hybrid system sees an annual ground temperature (recorded) swing from approximately 40 deg F late winter to 75 deg F late summer. The peak COP for the hybrid performance is estimated to reach a max of 5.0.
Energy Strategies:
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).
Zero Net Energy Definition Used
Site Energy Use
Monthly Energy Data and Utilities
Energy Data Type: Modeled, Verified
Electric Utility: Unitil Electric
Other purchased Fuels: Less than 50 gal of propane per year is purchased to supply a gas stove cook top and an architectural gas fireplace.
Datasets and utility bills:
Attachment Size 
2013 (12 month) Summary Performance Data for the ROSE Cottage Project113.5 KB 2014 (12 month) Summary Performance Data for the ROSE Cottage Project 115.24 KB 2015Energy (12 month) Summary Performance Data for the ROSE Cottage Project 276.66 KB Energy Star HERS rating Certificate 401.06 KB Unitil Electric Records 2015 312.46 KB Unitil Electric Records 2014 317.48 KB Unitil Electric Records 2013 364.84 KB Energy Star Label 183.63 KB Energy Star Report 441.71 KB
Datasets and utility bills sources and reliability: Monthly Unitil readings (bills) have been retained since interconnection of the PV system (Dec 2011). Project construction completion (occupancy) occurred in August, 2012. Data taken from the calendar years 2013, 2014, and 2015 have been used for the purposes of this case study.
The ROSE Cottage Project
Renewables and Energy Balance
Renewable Energy Sources: Renewable energy is generated on-site but not on the building (e.g. wind turbine in the parking lot)
Renewable Energy System Description & Details
100%* of the electric power generated comes from 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. *- Net zero energy use is achieved through the ability to net meter with the local electrical utility, taking back "banked" energy during the daily daytime/nightime cycle as well as the annual 12 month cycle of solar energy production levels.
Annual renewable energy generated
15,411 kWh
Annual Renewable Energy Generated Data Type
Measured
Power Rating
Renewable Energy System Type(s)
Source of Annual Production Data
13,800Watts
Photovoltaics
Gross energy production is metered and recorded each month. The three year annual average is 15,411 kwh/yr. The High year was 15,771. The Low year was 15,020
Storage and Installed Capacity
A bank of 16 DC, 255 amp-hour batteries are also connected to the PV system through two 3,600W DC Outback inverters and can supply up to 7,200W and 49kWh of back-up emergency power if the utility grid goes down.
Energy Storage type
THERMAL
Stage 1-A 198 gal solar water storage tank is used to store domestic water supply from the 9 panel roof collectors. Max temperature settings used vary from 130-160 deg F over the year.
Stage 2- Secondary hot water (glycol) is used (from either lower grade heat from the solar thermal panels or high grade heat from the panels above the max set point of the 198 gal tank) to heat the geothermal system's buffer tank up to a max of 110deg F through a stainless steel heat exchanger.
Stage 3- Secondary hot water (glycol) is used (from either lower grade heat from the solar thermal panels or high grade heat from the panels above the max set point of both the 198 gal tank and geothermal buffer tank) is used to heat the geothermal system's wet sand bed located below the sub-slab insulation layer using (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. Measured ground (sand) temperatures vary through the course of the year from approximately 40deg F (winter) to 75deg F (summer) over a 12 month cycle.
9 loops for each system run underneath the 6" eps foam below the lower level concrete floor. 4 loops run underneath 6" eps foam located outside the foundation walls on the south side of the building beneath 8-10 feet of earth fill. During summer cooling mode, the 4 outside loops become dedicated to geothermal cooling via a zone control valve on each system, while the 9 interior loops continue to store excess heat from the solar thermal panels.
ELECTRIC
A bank of 16 DC, 255 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 and 49 kWh of back-up emergency power if the utility grid goes down.
Energy Storage Capacity
7 kW
Annual Energy Import/Export
Electricity amount (imported from grid)
3,740 kWh/year
Net electricity usage (purchased electricity)
-370 kWh/year
Electricity amount (credited or exported to grid)
4,110 kWh/year
General Energy Use, Strategies and Systems
Energy Use:
The project combines the use of PV panels with a back-up battery bank; solar thermal panels; geothermal heat pumps (2); a hybrid design that integrates excess BTU production from the solar thermal system to boost the effective COP of the geothermal system with both space heating BTU's via the buffer tank as well as a wet sand heat sink below the building; a dedicated air-air HRV for fresh air; and an on-demand electric back-up domestic hot water heater. The HERS rating of the home, before inclusion of the PV system, was calculated to be 35. The project has performed each calendar year (3 total) at zero net for each year of the 3 years, including the use of the outdoor spa which is metered internally for record purposes, and consumes approximately 10% of the PV output.
The Geo-Solar Hybrid system sees an annual ground temperature (recorded) swing from approximately 40 deg F late winter to 75 deg F late summer. The peak COP for the hybrid performance is estimated to reach a max of 5.0.
Energy Strategies:
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).
| Zero Net Energy Definition Used | Site Energy Use |
|---|
Monthly Energy Data and Utilities
Less than 50 gal of propane per year is purchased to supply a gas stove cook top and an architectural gas fireplace.
| Attachment | Size |
|---|---|
| 2013 (12 month) Summary Performance Data for the ROSE Cottage Project | 113.5 KB |
| 2014 (12 month) Summary Performance Data for the ROSE Cottage Project | 115.24 KB |
| 2015Energy (12 month) Summary Performance Data for the ROSE Cottage Project | 276.66 KB |
| Energy Star HERS rating Certificate | 401.06 KB |
| Unitil Electric Records 2015 | 312.46 KB |
| Unitil Electric Records 2014 | 317.48 KB |
| Unitil Electric Records 2013 | 364.84 KB |
| Energy Star Label | 183.63 KB |
| Energy Star Report | 441.71 KB |
Monthly Unitil readings (bills) have been retained since interconnection of the PV system (Dec 2011). Project construction completion (occupancy) occurred in August, 2012. Data taken from the calendar years 2013, 2014, and 2015 have been used for the purposes of this case study.
The ROSE Cottage Project
Renewables and Energy Balance
| Renewable Energy System Description & Details |
|---|
| 100%* of the electric power generated comes from 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. *- Net zero energy use is achieved through the ability to net meter with the local electrical utility, taking back "banked" energy during the daily daytime/nightime cycle as well as the annual 12 month cycle of solar energy production levels. |
| Annual renewable energy generated | 15,411 kWh |
|---|---|
| Annual Renewable Energy Generated Data Type | Measured |
| Power Rating | Renewable Energy System Type(s) | Source of Annual Production Data |
|---|---|---|
| 13,800Watts | Photovoltaics | Gross energy production is metered and recorded each month. The three year annual average is 15,411 kwh/yr. The High year was 15,771. The Low year was 15,020 |
Storage and Installed Capacity
A bank of 16 DC, 255 amp-hour batteries are also connected to the PV system through two 3,600W DC Outback inverters and can supply up to 7,200W and 49kWh of back-up emergency power if the utility grid goes down.
| Energy Storage type |
THERMAL Stage 1-A 198 gal solar water storage tank is used to store domestic water supply from the 9 panel roof collectors. Max temperature settings used vary from 130-160 deg F over the year. Stage 2- Secondary hot water (glycol) is used (from either lower grade heat from the solar thermal panels or high grade heat from the panels above the max set point of the 198 gal tank) to heat the geothermal system's buffer tank up to a max of 110deg F through a stainless steel heat exchanger. Stage 3- Secondary hot water (glycol) is used (from either lower grade heat from the solar thermal panels or high grade heat from the panels above the max set point of both the 198 gal tank and geothermal buffer tank) is used to heat the geothermal system's wet sand bed located below the sub-slab insulation layer using (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. Measured ground (sand) temperatures vary through the course of the year from approximately 40deg F (winter) to 75deg F (summer) over a 12 month cycle. 9 loops for each system run underneath the 6" eps foam below the lower level concrete floor. 4 loops run underneath 6" eps foam located outside the foundation walls on the south side of the building beneath 8-10 feet of earth fill. During summer cooling mode, the 4 outside loops become dedicated to geothermal cooling via a zone control valve on each system, while the 9 interior loops continue to store excess heat from the solar thermal panels. ELECTRIC A bank of 16 DC, 255 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 and 49 kWh of back-up emergency power if the utility grid goes down. |
|---|---|
| Energy Storage Capacity | 7 kW |
Annual Energy Import/Export
| Electricity amount (imported from grid) | 3,740 kWh/year |
|---|---|
| Net electricity usage (purchased electricity) | -370 kWh/year |
| Electricity amount (credited or exported to grid) | 4,110 kWh/year |