Heating and cooling systems account for nearly 50 percent of a house's energy consumption, so 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.
Performance values
To reduce a house'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's a 30 percent increase in efficiency over the previous 10-SEER minimum—but also about a 30 percent increase in cost, according to manufacturers.
Now that 13 SEER is the industry standard, you need to move up an efficiency level or more to maintain a competitive edge as well as to meet the new Energy Star program minimums of 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 keep in mind that higher-SEER units also can cost anywhere from 40 percent to 100 percent more than a base 13-SEER system.
Recently, the DOE issued new standards for gas- and oil-fueled furnaces, upping efficiency ratings from the previous 78 percent annual fuel utilization efficiency rating (AFUE). The new minimum is set at 80 percent AFUE for gas furnaces and 82 percent AFUE for oil furnaces. (The new standards will go into effect in 2015.) High-efficiency furnaces with AFUE ratings up to 95 percent and 96.7 percent 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 percent and 83 percent, respectively.
Efficiency Versus Cost
Except for some high-end builders, most pros 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 percent 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.
Size Right
Choosing energy-efficient heating and cooling units isn't enough; they 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 air conditioning 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 effect 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 percent or more, and also leads 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," points out Mickey Smith, product manager for York.
Estimating heating and cooling needs based 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 "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.
Seal Tight
Finally, no discussion of high-performance HVAC would be complete without emphasizing the importance of duct sealing. According to Energy Star, sealing and insulating the ducts can improve the efficiency of a house's heating and cooling system by as much as 20 percent, potentially more. Leaving ducts unsealed and uninsulated allows conditioned air to leak into unconditioned spaces, which wastes energy and creates the potential for hot and cold spots.
"You could spend several thousand dollars to get the highest-efficiency HVAC system put into a home, but if your walls are full of spots where air can leak out, or if the ductwork is not installed properly, that system is not going to be very efficient," says Robert Smart, vice president of construction for Cary, N.C.-based Anderson Homes. "You can't look at one piece independently. You have to think of the whole house as a system." BP
Fresh Look
Despite the energy-saving advantages, tightly sealed houses mean less natural ventilation. Properly designed, mechanical ventilation can bring fresh air into the building and exhaust polluted or stale indoor air out to maintain air quality.
The American Society of Heating, Refrigerating, and Air-Conditioning Engineers recommends an air exchange rate of one-third per hour for most houses, meaning that one-third of the air inside a house is replaced with fresh air from outside every hour. Mechanical ventilation controls the introduction of fresh air while diluting pollutants and removing 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 outdoor air for stale indoor air. The heat exchange provides about 70 percent 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.
Natural ventilation through windows uses one-third the energy of mechanical ventilation, according to Larry Brown, NAHB's program manager for energy efficiency. However, mechanical ventilation is automatic; windows require a homeowner to open and close them.
—S.L.M.
--This article originally appeared in Green Products and Technology magazine.
Luxaire Acclimate HL8B Series Split-System Heat Pump
Luxaire. The Luxaire Acclimate HL8B series 18-SEER, 10-HSPF split-system heat pump features a two-stage compressor that operates at two levels to provide maximum efficiency. The compressor is isolated from the rest of the components and protected by a composite bulkhead, reducing sound and vibration. A high-pressure relief valve and temperature sensors protect the compressor against adverse operating conditions. The unit uses R410A refrigerant. 800-589-2473. www.luxaire.com.
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Coleman Echelon Split-System Heat Pump
Coleman. Echelon split-system heat pumps, available in four models in 2- to 5-ton sizes, are designed to provide efficiencies up to 10 HSPF and up to 18 SEER. 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. It uses R410A refrigerant. 877-726-5362. www.switchtocolemanac.com.
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Bryant Hybrid Heat Packaged HVAC System
Bryant. The Hybrid Heat system pairs a gas furnace and a heat pump, allowing homeowners to 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 with R410A refrigerant and an Evolution Plus 95i gas furnace with 95 percent AFUE. 800-428-4326. www.bryant.com.
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York Affinity YZH Series Split-System Heat Pump
York. The York Affinity YZH series 18-SEER, 10-HSPF split-system heat pump utilizes 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." It uses R410A refrigerant. 800-910-9675. www.yorkupg.com.
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Carrier Infinity IdealComfort System Modulating Gas Furnace
Carrier. The Infinity IdealComfort System modulating gas furnace offers up to 95 percent AFUE and 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 percent of the time, blowing a nearly continuous flow of warm air. The system also provides control over humidity, air quality, fan speed, and ventilation. 800-227-7437. www.carrier.com.
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Trane Energy Star-Qualified XV95 Gas-Fueled Furnace
Trane. The Energy Star-qualified XV95 gas-fueled furnace features two-stage operation that delivers high-efficiency performance of 96.7 percent AFUE. 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. 608-787-2000. www.trane.com.
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Comfortmaker SoftSound SXT+ Two-Stage Split-System Air Conditioner
Comfortmaker. SoftSound SXT+ two-stage split-system air conditioners are available in 2- to 5-ton cooling capacities and provide up to 18-SEER efficiency. A Copeland scroll compressor and two-speed fan motors provide for quieter operation by operating in the quieter, lower stage most of the time, the company says; sound jackets and a sound-reducing fan orifice also reduce noise. The units also feature corner posts with grille panels for added strength and vibration and noise reduction, and LED fault indicators for easier service diagnosis. 931-359-3511. www.comfortmaker.com.
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Whirlpool Gold W4GC6 16-SEER Air Conditioner
Whirlpool. The Gold W4GC6 16-SEER air conditioner features a Copeland Scroll UltraTech two-stage, high-efficiency compressor that the company says provides improved temperature control and greater energy savings versus standard compressors. The model also includes the Comfort Alert II diagnostic model for more efficient servicing, a heavy-duty sound jacket, and aluminum fins and copper tubing that maximize heat transfer and air flow. Refrigerant is R410A. 800-253-1301. www.whirlpool.com.
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Hallowell Acadia All-Electric Heat Pump
Hallowell. The Acadia all-electric heat pump is a single system designed to comfortably and efficiently heat and cool homes regardless of weather; the unit's Opti-Cycle booster allows for efficient operation in temperatures as cold as -30 degrees F, according to the firm. The unit, which is 300 percent efficient, offers a SEER rating of 16 following recent upgrades. Details include an acoustically isolated compressor compartment and self-diagnostic control features. 877-322-2342. www.gotohallowell.com.
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