Interim Report (PDF) September 2002
Experiencing an average 9400 heating degree days per year, the town of Hailey, Idaho is an ideal location to evaluate the performance of two residential heating systems and a residential mechanical ventilation system. Here, the NAHB Research Center teamed up with Thad Farnham, a small custom homebuilder based in Ketchum, Idaho who has been in the building and remodeling business for 22 years. In August 2002, Thad Farnham Construction put the finishing touches on a 2,642 square foot, single-family home in Hailey, Idaho that is the subject of this PATH Field Evaluation.
The primary evaluation for this project will focus on a comparison between forced air heating and radiant floor heating. Both systems are now installed in the home and, to the greatest extent possible, the systems have similar characteristics (efficiency ratings, zones, thermostats, etc). The two heating systems will be operated independently for three week periods throughout the 2002-2003 heating season, while the CO2 ventilation system will be enabled full-time. Monitoring devices will capture all pertinent information including, but not limited to outdoor air temperature and relative humidity, indoor subfloor and air temperatures, and energy use.
radiant heat system features a gas-fired high efficiency boiler with a 92% efficiency rating. The boiler, named "The Munchkin", is manufactured by Heat Transfer Products, Inc. Quiet, compact, lightweight, and Energy Star approved, the boiler comes with a 12-year warranty. The system is broken down into four zones, two for the first floor and two for the second. Zone control electronics treat the system as a two zone system, sending heat through both first floor loops each time there is a first floor thermostat heat call and through both second floor loops each time there is a second floor call for heat. Approximately 3000 feet of Wirsbo 1/2" AQUAPEX tubing was used throughout the four zones. This cross-linked polyethylene tubing has a 25-year warranty.
The forced air system employs a Carrier MXA gas-fired furnace with a 95.5% efficiency rating (the efficiency rating for this unit is expected to drop to about 92% at the installed altitude). The MXA is an Energy Star approved appliance. The forced air system has two zones, one on each floor. A zone-controlled damper ensures that supply air is delivered to either the first floor or the second floor individually, but not both simultaneously. The controller is configured to give primary importance to the first floor thermostat's heat call and secondary importance to the second floor thermostat's heat call.
Two thermostats, both Honeywell T8401s, are used to operate the two systems. The T8401 allows the user to set the number of cycles per hour, allowing for a higher level of control during the evaluation.
The second part of the project involves testing and evaluating a CO2
controlled ventilation system. Fresh air ventilation systems have received a great deal of attention recently and may even become mandatory for new construction in some regions. The CO2 controlled ventilation system is expected to be an efficient, low cost method of providing fresh air to occupants. Unlike many ventilation systems that provide a constant flow of outdoor air to the indoor envelope, this system will only ventilate the home when CO2 levels exceed a predetermined limit. Initially, this limit will be set at 1000 ppm.
A Ventostat CO2 sensor is positioned on the divider wall between the kitchen and great room and will be used to monitor CO2 levels and initialize ventilation. When CO2 levels reach the established set point, the Ventostat unit relays power to the central blower and simultaneously opens a normally closed damper in an 8" intake duct connected to the furnace's return plenum. In this way, cold outdoor air is mixed with warm air in the return plenum before being delivered to the house. Though the ventilation system uses the furnace's central blower to deliver outdoor air to the home, it operates independently of both heating systems. That is, the CO2 ventilation system never places a call for heat.
Monitoring of the system is accomplished through a network of thermocouples, power meters, current sensors, and pressure transducers. These sensors have been installed to collect information on energy use, volume of air infiltrated, and Btus of heat lost due to infiltration.
February 2003 Press Release
Data collection on the heating and ventilation systems began in January 2003 and will continue to the end of the 2002-2003 heating season. At the conclusion of the heating season, data will be examined to determine if it is sufficiently robust to end the study.
To this point, the ventilation system has operated as programmed (with a trigger setpoint of 700 ppm of CO2), but less frequently than might be expected. CO2 levels recorded at the sensor location between the kitchen and great room have averaged about 450 ppm in the first four months of 2003.
See the project profile for construction photos and status.
Content updated on 11/20/2006