GO GREEN - Case Study
Energy Efficiency Use and Indoor Air Quality Evaluation A Palm Springs Home Built In 2002
May 31, 2015
- GREEN heating and air conditioning system upgrades have resulted in a 4.3% reduction in energy use (year one, year-over-year electric bill comparison).
- Indoor environmental comfort has improved significantly due to the ‘right-sizing’ of the air duct system plus installation of electronic damper controls and energy efficient programmable thermostats.
Image: Air Duct System Bid Specifications
- Improve the home’s energy use efficiency, and as a result, reduce electric bills. Primary homeowner concerns related to the energy used by the home’s multi-zone air conditioning system which resulted in high electric bills.
- Improve the interior air flow and circulation as well as the resulting air quality.
Image: New Bryant 4-Ton Air Conditioner Condenser For Bedroom Zone
The home was built in 2002 and measures approximately 3,200 square feet. Two 3-ton split heating and air conditioning systems with an attic ducting network servicing each of the two zones are installed. One of the two zones services the bedrooms (a master and ensuite guest bedroom), the laundry room and library. The second zone services the remaining living spaces including the kitchen, dining room, living room, powder room and connecting hallways. The heating and air conditioning systems are each composed of an indoor furnace and evaporator coil with outside condensers.
Evaluation - Home Inspection By A Certified Home Energy Star (HERS) Rater
1. Hired Energy Management Services (EMS) - a professional GREEN Home Energy Star, energy efficiency consultancy. Contracted with EMS to complete a comprehensive evaluation of the home’s wall and ceiling installed insulation presence, existing multi-zone air conditioning and heating systems and air ducting, with a focus on improving energy use efficiency, interior air quality and air distribution flow. EMS prepared detailed bid specifications of their recommended HVAC system improvements and upgrades which included Certified Energy Plans (prepared by EMS’s Certified Energy Plans Examiner – CABEC). These bid specifications were used to obtain bids from three HVAC HERS-rated contractors. From these bids, one HVAC contractor was selected to perform the recommended work.
Image: New Robert Shaw Programmable Thermostats
2. Deployed (by EMS) were a variety of techniques to diagnose the home’s current energy use efficiency and air flow systems:
- Walked the entire home and filmed the installed wall and ceiling insulation presence with a Thermography Camera to pin point any insulation gaps/‘hot spots’ and determine the overall thermal insulation quality.
- Gauged the energy use and overall operating performance of the existing two-zoned air conditioning and heating systems.
- Determined the duct static pressure/degree of leakage from the existing air ducting system. Determined each of the two existing 3-ton systems’ capability to handle the assigned square footage per the EnergyPro load calculation that was performed.
- Evaluated the effectiveness of the current air flow ducting network and air supply and return registers.
Image: New Ceiling Mounted Register Grill
3. Identified issues impacting the home’s energy use efficiency:
- The entire bedroom zone air duct system needs help. The system duct static pressure was confirmed to be very high (total static readings of 1.07”wc, which is twice as high as the normal design static of 0.5”w). This high static pressure is hard on the indoor fan motor servicing this zone (requires the motor to stay on continuously) and causes reduced air delivery to all of this zone’s rooms.
- In addition, the Temperature Difference (TD) across the indoor cooling coil is too low. The actual TD was 15.1 degree F. vs. the required TD which should approximate 23.5 degrees F. Thus, the existing bedroom zone’s 3 tons of cooling capacity is actually operating at only 64%. In effect, the homeowners are paying to run a 3 HP compressor and only getting 2 tons of delivered cooling.
- The existing 3 ton air conditioner and condenser serving the home’s 1,285 square foot bedroom zone, based on the EnergyPro load calculation that was performed, is undersized to service this volume of space.
- Only one thermostat was installed to service the entire bedroom zone vs. having a programmable thermostat located in each of the bedrooms. Also, there were no powered dampers installed to provide for the individual control of each bedroom’s air flow and temperature.
- Surprising was the lack of ‘voids’ or hot spots found in the installed insulation in the walls and ceilings.
- An undersized (duct diameter size) air flow ducting distribution system serving the home’s bedroom zone.
- All supply air registers installed were sidewall registers and not ceiling 3-way registers as required. The sidewall registers do not promote good aspiration of the cool air and warm air mixing.
Only one return air grill was installed in the bedroom zone. This is insufficient for the space serviced by this zone’s system. With all bedroom, library and laundry room doors closed, two thirds of the return air is effectively being cut off and is causing the entire system to overwork (on both the air and the refrigerant sides).
Solutions and Results
- Installed a new energy efficient 15.5 SEER 4 ton air conditioner and condenser serving the home’s bedroom zone.
- Replaced the existing bedroom zone’s air ducting (more than 40 feet in length) with a properly sized and sealed duct flow system. Duct leakage specified was not to exceed 6% - HERS verification required confirmation to meet Title 24 requirements.
- Installed new supply and return air ducts - curve blade supply grills and bar type return grills.
- Installed Honeywell Zoning Controls with Arometric and powered dampers resulting in each bedroom having individual air flow controls.
- Installed new programmable thermostats in each of the bedrooms for operating the new Honeywell powered dampers, thus providing capability to control individual room temperature and air circulation.
Energy Use Efficiency Results -- Improved the home’s overall energy use efficiency. Reduced year one, year-over-year electric bills by 4.3%.