An Answer for Retrofit Applications

April 30, 2007
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Contractor Dave Yates connects the condensing unit.

Now that the residential and light commercial new construction boom has lost some of its charge, many U.S. home and business owners will invariably turn their attention to remodeling. It’s statistically proven, seen after every surge in new construction. When new construction falters, retrofit steps into the limelight.

In the eyes of Roy Kuczera, ductless mini-split systems are among the best technologies for retrofit applications - whether for additions, whole-home cooling, or to improve interior comfort for spaces lacking sufficient HVAC.

“Rapidly increasing energy costs are another very forceful influence in the push for ductless technology,” said the vice president of HVAC Products, Fujitsu. “These systems today offer efficiencies into the 21 SEER range, a rather amazing leap in system efficiency.”

A key contributor to ductless system energy efficiency has been the introduction of “inverter” technology. Though it’s been in use for two decades or more in Eastern European countries, it’s just now catching on here in the United States.

“Old school, on-off technology for any type of HVAC equipment is rapidly losing its appeal here in the land of plenty,” said Dave Yates, owner of F.W. Behler Inc., York, Pa. “With this old-style technology, it’s like driving your car with the gas pedal glued to the floor and controlling it purely by turning the ignition key on or off!”

It’s why when retrofits come into play, Yates does not overlook what ductless systems have to offer. “The new approach is the use of equipment that systematically changes or modulates its energy production to match heat loss and gain,” said Yates.

ONE RETROFIT EXAMPLE

Not long ago, Yates put a 1-ton ductless system in for the Thomas family of Manheim, Pa. When they built their home six years ago, the Thomases’ were sure that the bonus room above the three-bay garage would be used for storage. But eventually they chose to turn it into a media room.

Because of the room’s size, the challenge of heating and cooling the space above an unconditioned garage, and with so much exposure to western wind and sun, Yates determined the media room had a larger load than the existing equipment could handle without major changes.

Yates compared the cost of a separate ductless mini-split heat pump system with changes that could be made to the home’s existing comfort systems. Working with the equipment already in place, Yates found that he would need to install a zoned damper system, new ductwork to be routed through restrictive attic spaces, wiring, and an extra thermostat.

“Financially, they were almost a coin-toss apart,” said Yates. “But there were many unique advantages to the use of a new mini-split.”

Yates determined that a ductless mini-split heat pump would avoid ceiling registers and the energy losses that come with holes through the home’s R-45 attic insulation. (Attic ductwork insulation values are typically R-8.)

According to Yates, ceiling registers hold the potential for cold drafts in winter and the likelihood, in summer, of ducted hot air blasts following an offcycle. Any alteration of the ducts serving the sleeping quarters would affect airflow with the possibility of throwing the system out of balance.

“Use of a mini-split heat pump would avoid many time-consuming, disruptive, and expensive central HVAC alterations,” explained Yates. “And the family could quickly have a system that would condition the interior space, exactly where and when they most wanted it.”

Yates and two technicians needed only three hours to install the mini-split system in the room. “The room was noticeably cooler within minutes, and water was streaming steadily through the outside condensate line,” said Yates. “But when the homeowners checked on us toward the end of the job, they couldn’t believe the system was running - both the indoor fan coil and outside condensing unit operate so quietly that you have to strain to hear them.”

For Mr. Thomas, this also meant that there would be no noise to interfere with the new surround-sound system.

Mike (left) and Dave (right) Yates place an outside condensing unit near its final destination at a customer’s home.

ADVANTAGES TO INVERTER TECHNOLOGY

When it comes to advantages of inverter systems, Kuczera said there is less need for supplemental heat as the inverter systems provide better heating performance.

Most air conditioning systems are controlled by a thermo- stat that measures the tem- perature variations inside the environment, compares this against the ideal temperature or set point - and, when necessary, starts the compressor.

When the set point is reached, the thermostat stops the compressor and stops the flow of refrigerant to the evaporator. Kuczera explained that when this process occurs the room temperature can exceed the set point, and consequently leads not only to notable swings in temperature, but also results in the compressor starting and stopping repeatedly at full capacity, in turn meaning significant energy consumption.

To avoid this waste of energy and at the same time achieve advantages in terms of thermal comfort and reduced noise levels, an electric device has been designed that varies the frequency of the power supply to the electric motor that drives the compressor. This device, called an inverter, allows the compressor to operate at required reduced capacity, without falling below, explained Kuczera.

As the compressor is stopped less frequently, the desired temperature is maintained more effectively (that is, with minimum swings in temperature) and the energy consumption related to the peak current required to start the compressor each time is eliminated, said Kuczera.

“The systems offer superb air filtration and - because they’re ductless - there’s no downstream concern about contaminated ducts,” he added.

Another advantage to inverter systems is better humidity control, he said.

“The Thomases’ new unit would offer a dry mode setting for dehumidification without altering room temperatures by more than one degree,” said Kuczera.

According to Kuczera, such systems also operate at ambient (outdoor temperatures) as low as 5°F for heating and as low as 0°F ambient for cooling without modification, “depending on the model.”

“At Fujitsu, we believe that our decision to build all of our new systems for use with the significantly more efficient 410A refrigerant and inverter technology is just what the market has been asking for,” said Kuczera. “These systems run at higher pressure, so line set diameters can be smaller - and less expensive,” adding that the new refrigerant compound also permits higher operational efficiency while transferring more heat into or out of the interior living space.

According to Kuczera, the heat pump that Yates installed for the Thomas’ has a Heating Seasonal Performance Factor (HSPF) of 10.55 in the heating mode, and a 21 SEER rating for cooling.

FOR COMMERCIAL APPLICATIONS, TOO

Ductless systems are suited for light commercial application too, said Kuczera. Multi zone systems with just one variable-speed outdoor condensing unit can accommodate up to four indoor units. Each indoor unit can be turned on or off at will and each will communicate with the outdoor unit separately, he said.

“The outdoor unit’s logic module can alter the delivery of refrigerant as needed to serve each of the air handler’s needs,” said Kuczera. “As a result, each indoor unit’s remote control can be set at any level.”

One of the latest advancements to take the stage in the commercial mini-split market is the introduction of variable-refrigerant flow (VRF) technology. With VRF, heat is transferred directly from interior spaces by circulating refrigerant between a remote condensing unit and interior evaporators, explained Kuczera. Wall-mounted ductless or fan coil-type compact ducted units with evaporators are located in or near occupied spaces, he said.

Multiple evaporators can be connected to the system, allowing for temperature control zoning. Just as with traditional ductless systems, heat is transferred via the refrigerant to an outdoor condensing unit.

“These systems can serve a wide range of applications, including nursing homes, restaurants, office buildings, schools, and churches,” said Kuczera.

“This system minimizes the refrigerant path compared to a multizone mini-split by connecting multiple indoor units to a common liquid and suction line through the use of ‘Y’-shaped separation tube assemblies. The shorter refrigerant path allows for greater system performance from the same amount of compressor work.”

Space temperature control in VRF systems is achieved by modulating the flow of refrigerant to each evaporator, using an electronic expansion valve (EEV). Fan speeds are also variable. The variability of “inverter” operation and zone temperature control leads to improved comfort and energy savings, Kuczera explained.

“The heart of a VRF system is a variable-speed compressor,” he explained. “The speed of the compressor - and thus the amount of refrigerant circulated - is varied to match the cooling loads of the indoor units. When compared to the operation and cycling of conventional, single-speed compressors, temperature control is vastly improved.”

In other words, if you haven’t boarded the ductless “minivan,” it’s now a great time to get involved.

Publication date: 04/30/2007

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