Residential Solar Thermal System: McFeeley Residence

Dressel Construction, a high-end Santa Fe custom homebuilder, and AIA architect Rad Acton designed and built the McFeeley residence in the Las Campanas subdivision of Santa Fe. Cedar Mountain Solar had SolarSkies model SS-20 collectors custom-made to meet the demand for a particularly low-profile array installation. These collectors have 10-foot horizontal headers and were mounted in 12 rows of two collectors each.

The design is based on primary and secondary piping, with each heating load and heat source connected to a central loop of insulated copper piping. Solar heat is delivered to the primary loop via a flat plate heat exchanger. The primary loop is connected to the bottom coil in a dual-coil domestic hot water storage tank, allowing for domestic hot water production from either the boiler or the solar array.

Heating loads include 12 radiant heating zones, a custom-built hot tub and domestic hot water. System controls prioritize solar heat over boiler heat for all loads. Two-stage thermostats are installed in every heating zone. Solar generated heat is used to achieve the high set point and boiler heat to achieve the low set point. This allows regulated heat banking in the floor’s mass. The system is designed to cool select zones by circulating heat from the floors through the collectors at night.

"One of this project's greatest challenges was the atypical hot tub management - keeping it at or close to design temperature at all times to best utilize the radiant tubing installed in the masonry of the tub. Racking the collectors without stand-offs on a foam roof was also really tricky as the roof was, by design, not quite level and foam roofs tend to have some variation in their surfaces."

Boaz Soifer, general manager, Cedar Mountain Solar

 

Overview

DESIGNER: Bristol Stickney, partner and technical director, Cedar Mountain Solar, cedarmountainsolar.com
INSTALLATION TEAM: Larry Israel and Jerome Perea, installation technicians; Jeff Stampfer and Louie Vasquez, field supervisors, Cedar Mountain Solar
DATE COMMISSIONED: Nov. 2008
INSTALLATION TIMEFRAME: Approximately 500 man-hours over 15 months from radiant rough-in through controls calibration
LOCATION: Santa Fe, NM, 36.6º N
SOLAR RESOURCE: 6.5 kWh/m2/day
ANNUAL HEATING DEGREE DAYS: 6,092, base 65ºF
RECORD LOW TEMPERATURE: -18ºF
COLLECTOR AREA: 480 square feet
AVERAGE ANNUAL PRODUCTION: 24 MWh (calculated)

Equipment Specifications

COLLECTORS: 24 custom-made SolarSkies SS-20 collectors, 20 square feet each
ARRAY: 24 collectors in parallel, piped in two banks of 12
STORAGE/HEAT EXCHANGER: Oventrop two-coil 115 gallon SDHW tank; Crown flat-plate heat exchanger
PUMPS: Two Laing D5 Strong PV-direct collector circulating pumps, two Taco 007 radiant floor circulators, Taco 007 SDHW production pump, Taco 0010 boiler circulator, Taco 006 SDHW recirculator
CONTROLS: Two Tekmar 155, two Tekmar 152 thermostatic mixing valves, 12 Honeywell 5220 two-stage heating thermostats, two Taco ZVC406 enclosures, Taco SR504, Tripp-Lite ac/dc converter
FREEZE CONTROL: Closed loop antifreeze
COLLECTOR INSTALLATION: Custom-made ballasted racking, foam roof, 189º azimuth, 60º tilt

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