Heating and cooling systems account for nearly 50% of a home’s energy consumption, so your choice of equipment and the way it is installed are keys to success for any green builder. And as the focus on energy efficiency has led to improved building shell performance (including high-performance insulation packages and passive solar heating), selecting HVAC components that match the projected energy requirements will ensure that you optimize the system and meet the occupants’ comfort needs and expectations.
To reduce a home’s energy usage, opt for high-performance HVAC units that exceed the required minimum standards when budget allows. Since 2006, the minimum allowable seasonal energy efficiency rating (SEER) set by the U.S. Department of Energy for residential air conditioners and heat pumps is 13. (The higher the SEER rating, the higher the unit’s energy efficiency.) That 30% increase in efficiency over the previous 10-SEER minimum is matched by about a 30% increase in cost, according to manufacturers.
And now that 13 SEER is the minimum industry standard, you’d need to increase the efficiency level to maintain a competitive edge as well as to meet new Energy Star program minimums. Energy Star’s minimum requirement now is 14 SEER for air conditioners and 14 SEER/8.0-8.2 HSPF (heating seasonal performance factor) for heat pumps.
Air conditioners and heat pumps with SEERs ranging as high as 21 have been available for a few years, but with the added costs ranging between 40% to as high as 100% more than the 13 SEER units.
Recently, the DOE issued new efficiency standards for gas- and oil-fueled furnaces, increasing efficiency ratings from the previous 78% annual fuel utilization efficiency rating (AFUE) to new standards of 80% AFUE for gas furnaces and 82% AFUE for oil furnaces. (The new standards will go into effect in 2015.) High-efficiency furnaces with AFUE ratings up to 95% and 96.7% have been available for several years as well; to meet Energy Star requirements, gas and oil furnaces must have AFUE ratings of at least 90% and 83%, respectively.
Efficiency Versus Cost
Except for some high-end builders, most home builders still offer base-level HVAC systems because they are the least expensive and deliver adequate efficiency. According to Brett Sailors, vice president of sales for renewable energy solutions provider New Point Energy, return on investment (ROI) becomes a bit negligible when installing units higher than 16 SEER because of their higher initial cost.
In regions where cooling days are few, such as the northern states, there may be little value in installing a higher-SEER air conditioner or heat pump. It’s true that a 13-SEER unit will use more energy than a higher-rated unit, but if the system doesn’t run constantly or frequently, it will take much longer to see an ROI. In low cooling-demand areas, 13 SEER may provide adequate efficiencies and comfort, especially if combined with ventilation and dehumidification systems.
Reshetar Custom Homes in Pipersville, Pa., has value-engineered the base HVAC system offered in its new green-built community—Springtown Knoll in Bucks County—to provide the best ROI. The houses, which will meet both Energy Star and Keystone Green Building Initiative guidelines, are built standard with 92% AFUE furnaces and 14-SEER air conditioners, along with whole-house humidification systems and heat recovery ventilators.
Local energy codes that preempt federal energy codes may require builders in some states to install HVAC units with higher-than-minimum efficiency ratings or to take additional building-envelope and duct-sealing steps when using minimum-rated units.
Choosing energy-efficient heating and cooling units isn’t enough. They also must be sized correctly. “If you design the system to fit the house and its level of tightness, it will run more efficiently,” says Brian Stamm, purchasing manager for Colorado green builder McStain Neighborhoods.
Improperly sized HVAC systems not only suck up more energy, they also can lead to comfort issues. An oversized AC unit, in particular, can cause uncomfortable conditions, such as hot and cold spots or poor air quality, says Jeff Hurt, brand manager for Coleman Heating & Air Conditioning.
Too much capacity also can lead to short-cycling, which will prevent the system from drawing moisture out of the air, so the home is cool but clammy. This leads homeowners to lower cooling set-points in an effort to make their homes more comfortable, which increases energy use, say Energy Star experts. Short-cycling can decrease energy efficiency by 30% or more and lead to more wear and tear on the air conditioning unit, decreasing the life of the system.
On the other end, “If it’s undersized, it will run all the time because it can’t keep up with the home’s demands,” says Mickey Smith, product manager for York.
Estimating heating and cooling needs solely on square footage will not yield the most accurate HVAC sizing. HVAC subs also will need “every scrap of information on the house: the type, size, and number of windows; whether they’re insulated; how the house is insulated,” says Reshetar Custom Homes president Shawn Reshetar.
Refer to the Air Conditioning Contractors of America’s (ACCA) Manual J8 to calculate heating and cooling loads and properly size home HVAC systems, or employ an HVAC engineering firm that has experience with optimizing more efficient systems.
No discussion of high-performance HVAC would be complete without emphasizing the importance of duct sealing. According to Energy Star, sealing and insulating ducts can improve the efficiency of a house’s heating and cooling system as much as 20%, potentially more. And while most residential energy experts recommend running all ductwork within conditioned space, many builders still run ducts through unconditioned attics and crawl spaces, which can really affect performance. Leaving ducts unsealed and uninsulated lets conditioned air leak into unconditioned spaces, which wastes energy and creates the potential for hot and cold spots.
“You can’t look at one piece independently. You have to think of the whole house as a system,” says Robert Smart, vice president of construction for Cary, N.C.-based Anderson Homes.
You or your HVAC contractor should use the ACCA’s Manual D (or a similar method) to design and size ducts, supply registers, and return grilles. Once all ducting is installed and sealed, perform a duct-blast test to identify areas in ducting where leaks may persist. A blower-door test can help identify leaky areas in the rest of the building envelope.
“It’s very difficult to make leakage zero, but you want to get losses down as low as you can, typically less than 10%,” advises Randy Scott, Trane’s vice president of product management systems. Most green building programs have fairly low tolerances for duct leakage; the Energy Star program, for example, allows no more than 6%.
Despite the energy-saving advantages, tighter homes may require mechanical ventilation because you’ve reduced the natural ventilation typically found in less efficient homes. Properly designed, mechanical ventilation can supply fresh air into the building and exhaust polluted or stale indoor air out to maintain air quality.
The American Society of Heating, Refrigeration, and Air Conditioning Engineers recommends an air exchange rate of one-third per hour for most homes. Mechanical ventilation controls the introduction of fresh air and not only dilutes pollutants but also removes excess moisture. Depending on the type of ventilation installed, the system also can condition incoming outdoor air before mixing it with indoor air, helping to maintain temperatures and efficiencies.
Installing one or more heat recovery ventilators (HRVs) in a cold climate helps save energy while exchanging fresh air for stale air. The heat exchange provides about 70% efficiency, according to Energy Star, offsetting the energy used to condition the fresh air during the process. HRVs also retain indoor air’s moisture, incorporating it into incoming air.
In warm, humid climates, installing energy recovery ventilators (ERVs) works in much the same way, but removes humidity from incoming air during the fresh-air exchange while conditioning it with cool air from inside the house.
Stephani L. Miller is associate Web editor/news for Custom Home, residential architect, Architect, and Architectural Lighting magazines.
Glossary of Terms
SEER (seasonal energy efficiency rating)—the measure of cooling-process efficiency for air conditioners and heat pumps. Higher SEER numbers equal higher efficiencies and greater energy savings.
HSPF (heating seasonal performance factor)—the measure of heating-process efficiency for heat pumps. Higher HSPF numbers equal higher efficiencies and energy savings.
AFUE (annual fuel utilization efficiency)—the measure of efficiency for gas- and oil-fueled furnaces, given as a percentage that reflects how much of the fuel produces heat and how much is wasted. Higher AFUE numbers equal higher efficiencies.
R22—a chlorine-containing, hydrochlorofluorocarbon-based refrigerant that is being phased out of production and use because of its impact on the ozone layer when released into the environment.
R410A—a new non-chlorine, environmentally friendly refrigerant that does not affect the ozone if released into the environment. Will become the industry standard once R22 is phased out in 2010.
DOE Office of Energy Efficiency and Renewable
DOE EERE Building Energy Codes Program:
Energy Star: www.energystar.gov
Environmental Protection Agency: www.epa.gov
North American Technician Excellence:
Partnership for Advancing Technology in Housing:
Coleman. Echelon split-system heat pumps are available in four models in 2- to 5-ton sizes. The heat pump delivers discharge temperatures above 98.6 degrees F when heating to eliminate “cold blow,” says the maker. An isolated compressor compartment, swept-wing fan, and high-efficiency compressor reduce sound during operation to as low as 71 dBA in cooling mode and 72 dBA in heating mode. Efficiency rating: 10 HSPF/18 SEER. Refrigerant: R410A. 877.726.5362. www.switchtocolemanac.com.
Trane. The Energy Star–qualified XV95 gas-fueled furnace features two-stage operation that delivers high-efficiency performance. The Comfort R variable-speed motor provides warmer startups during the heating season and better humidity control during the cooling season, the firm states. The XV95’s insulated blower door and cabinet help save energy and reduce noise during operation. Efficiency rating: 96.7% AFUE. 608.787.2000. www.trane.com.
Lennox. Designed to introduce fresh air into the HVAC system, Healthy Climate heat recovery ventilators (HRV) and energy recovery ventilators (ERV) perform frequent air changes throughout the day. An aluminum heat-exchange core in the HRV recovers up to 78% of heat from indoor air, while the same core in the ERV operates at three speeds to improve airflow and air quality and reduce humidity, the maker says. 800.954.6669. www.lennox.com.
Luxaire. The Luxaire Acclimate HL8B Series split-system heat pump features a two-stage compressor that operates at two levels for maximum efficiency. A composite bulkhead protects the compressor, which is isolated from the rest of the components, reducing sound and vibration. A high-pressure relief valve and temperature sensors protect the compressor against adverse operating conditions. Efficiency Rating: 10 HSPF/18 SEER. Refrigerant: R410A. 800.589.2473. www.luxaire.com.
York. The York Affinity YZH Series split-system heat pump uses a microprocessor with a demand defrost-control system that allows defrosting cycles only when necessary for increased comfort and efficiency. An anti-short-cycle timer helps extend the compressor’s life and improve efficiency by preventing short-cycling. The system’s hot heat-pump technology reduces the feeling of “cold blow.” Efficiency rating: 10 HSPF/18 SEER. Refrigerant: R410A. 800.910.9675. www.yorkupg.com.
Broan. Ideal for houses from 3,001 to 4,500 square feet, the HRV100H heat recovery ventilator replaces stale indoor air with fresh air. Outgoing indoor air tempers incoming air without cross-contamination, the maker says. The HRV provides 64 to 146 cfm of whole-house balanced ventilation and features the Smart Defrost system that prevents ice buildup. 800.558.1711. www.broan.com.
Whirlpool. The Gold W4GC6 air conditioner features a Copeland Scroll UltraTech two-stage, high-efficiency compressor that the company says offers better temperature control and greater energy savings versus standard compressors. It includes the Comfort Alert II diagnostic module for more efficient servicing, a heavy-duty sound jacket, and aluminum fins and copper tubing that maximize heat transfer and air flow. Efficiency rating: 16 SEER. Refrigerant: R410A. 800.253.1301. www.whirlpool.com.
Bryant. The Hybrid Heat system pairs a gas furnace and a heat pump, letting homeowners use gas or electricity depending on what is most economical for the weather and fuel-cost conditions in their area, the company says. The unit combines an 18-SEER Evolution 288ANA heat pump and an Evolution Plus 95i gas furnace with 95% AFUE. Refrigerant: R410A. 800.428.4326. www.bryant.com.
Carrier. The Infinity IdealComfort System modulating gas furnace maintains indoor temperature within 0.3 degrees F of the thermostat setting, the firm claims. Instead of cycling on and off, the furnace operates at low speed 83% of the time, blowing a nearly continuous flow of warm air. The system also provides control over humidity, air quality, fan speed, and ventilation. Efficiency rating: 95% AFUE. 800.227.7437. www.carrier.com.