Air-Conditioning Options For Hydronic Heating Systems
October 28, 2010
Your customer has a state-of-the-art hydronic heating system, including radiant floor heating, which he loves. But after such a hot summer, he wants to install some kind of central air-conditioning so his family won’t melt away next summer. He dreads the idea of ripping open his home’s walls to install large ducting for a traditional central air-conditioning system. So he calls you, begging for a less-intrusive alternative.
Two alternatives to bulky ductwork are available for this customer or homeowners who live in older homes - high-velocity systems and mini-split or mini-ductless systems. Both will require some degree of cutting into walls, floors and ceilings, but no major remodeling compared to installing large ductwork for a traditional system.
Small Ducts, High-VelocityA high-velocity system has an air distribution system different from conventional ducted air-conditioners. The fan coil and air-handling unit are typically installed in attics, garages or crawl spaces of homes not designed for forced-air circulation heating or cooling.
The system uses small, 2-inch insulated, flexible tubing to supply cooled air (or heated air in winter) to any room in the house. The tubing requires about one-tenth the space of conventional central air-conditioning, says the National Association of Home Builders Research Center’s ToolBase Services. The small diameter and flexility allow it to be fed through ceiling joists, wall cavities and around obstructions. Air passes through sound-suppressing tubing at the end of a duct run before entering the room through a plastic collar-like cover plate. These plates can match the surrounding paint color or woodwork, which make them difficult to detect, thus preserving the structure and design of the room.
The main supply trunk is either a rectangular or round duct that forces high-pressure air through the small ducts; about 1 1/2 inches of static pressure. “This creates a high-pressure zone as it enters the conditioned space and a low-pressure zone around that,” says John Baldasaro, national sales manager for SpacePak. “You now have a continous blending effect called aspiration, which allows a temperature differential in the room of less then two degrees from floor to ceiling and wall to wall within that room.”
The high-velocity air pushed through the small-diameter tubing mixes or blends room air more efficiently and reduces “temperature stratification” - the tendency of warm air to rise to the ceiling while cooler air settles to the floor. Add the removal of 30 percent more of a room’s humidity than conventional systems, which allows the homeowner to turn the temperature up three to four degrees and still be comfortable, and you get a 10 to 15 percent energy savings in a year, Baldasaro adds.
Sizing the system is important for any system, but for mini-ducts it is important to install the correct number of vents per room for maximum comfort, explains Ted Brown, SpacePak’s business development manager. Systems that are too big or too small will result in customer complaints and callbacks.
“You can’t satisfy the customer if you can’t satisfy the thermostat,” he adds.
High-velocity systems have been strong in the retrofit market when coupled with a hydronic or radiant system, Brown notes. But now architects, engineers and interior designers are designing smaller homes with very little wall and floor space. SpacePak is now providing design services for loads, layout, zoning, etc., of its systems for these customers so they can be installed in new construction.
No DuctworkThe primary benefit of a mini-ductless or mini-split system is, obviously, no ductwork. “The average American home loses 30 percent of its energy through conventional ducts,” says Bill Hick, Northeast regional sales manager for Fujitsu. “Really good ductwork may be 15 SEER [Seasonal Energy Efficiency Ratio] in the lab, but delivers only 11 SEER. Mini-ductless air-conditioning systems are rated at 26 SEER.”
SEER ratings are determined by the cooling output in Btu during a typical cooling season divided by the total electric energy input in watt-hours during the same period. The higher a unit’s SEER rating, the more energy-efficient it is.
Several mini-ductless models are Energy Star-qualified and meet the requirements of the 30 percent federal tax credit for installation of high-efficiency equipment. (As of press time, the energy-efficiency tax credits were due to expire Dec. 31 of this year.) And many states and utilities have rebate programs for energy-efficient heating and cooling systems.
“The challenge for manufacturers is to get contractor buy-in first,” Hick explains. “They can, in turn, relay the energy-efficiency information to homeowners.”
He adds that contractors do seem to be catching on to the technology, as it is a low-cost, high-tech product. Fujitsu’s mini-split business has grown about 50 percent each year over the last 10 years, except in 2009. Some of that growth can be attributed to the federal, state and utility tax credits and rebates.
Mini-ductless system manufacturers are the first in the industry to fully use inverter compressors. “The compressor is the heart of the system, pumping the refrigerant,” Hick notes. “Inverter compressors can pump 100 percent capacity down to 20 percent capacity or any one of thousands of points in between. Temperature sensors throughout the system know exactly what’s going on in the space being maintained. Computers control the variable-speed compressor to the precise point to minimize electrical consumption, then convert that energy into Btus for more or less cooling or heating as efficiently as possible.”
The condensor and compressor are located outside the home, much like conventional central air-conditioning systems, for quiet operation indoors. To eliminate the ductwork, thin copper tubing is run up the outside wall, through a 2 1/2-inch opening and connected to a wall-mounted blower inside the room. The copper tubing can be installed through walls and joists to minimize wall destruction. Refrigerant is cycled through the lines from the outdoor condensor to the indoor unit.
Each room to be cooled would have its own wall unit. Contractors can create up to four zones with a timer and optional wired remote for better temperature control. The same unit can be used in cooler months for heating.
The evenness of temperature can be a challenge with such systems, Hick admits, but with proper zoning it becomes less of a problem. Open floor plans are better equipped for this technology, allowing for much more flexibility in installing units.
To determine your customer’s air-conditioning needs, talk to him or her and review the rooms in the home to be cooled. Review the options with the customer to find the best system to provide the best comfort and save the most energy.
Regional HVAC Energy-Efficiency Standards ProposedLast October, HVAC manufacturers and organizations signed an agreement with energy-efficiency groups for new, regional energy-efficiency standards for central air conditioners, furnaces and heat pumps. The standards would raise the minimum efficiency of residential air-conditioning systems by about 8 percent for three climate regions - north, south and southwest - recognizing that appropriate investments in heating and cooling efficiency depend on usage.
In the north, most furnaces would be required to have a 90 percent efficiency, up from the current 78 percent. In the south, central air conditioners would be required to have a SEER of 14, up from the present 13 SEER. Heat pump and oil furnace standards would rise on a national basis. Efficiency standards for through-the-wall and small-duct high-velocity systems would be reviewed to see if changes were needed.
The signatories agreed to submit their agreement as a legislative proposal to Congress for inclusion in energy legislation that, as of press time, was still under consideration in Washington. They are working hard to get Congress to pass the legislation before they adjourn for the year, says Francis Dietz, vice president of public affairs for the Air Conditioning, Heating and Refrigeration Institute, because the Department of Energy is also working on rules for air conditioners, heat pumps and furnaces. The industry does not want to take a chance on what the DOE would consider appropriate efficiency standards for these technologies.
“Another reason for passage is that the legislation contains language allowing building codes for new construction to provide an option for efficiency levels higher than the federal minimum, as long as there is also an option for just meeting the minimum,” Dietz explains. The DOE does not have the authority to enact such a change in building codes, so it could not include such a provision in its regulations.