Ducted Mini Splits Offer Hidden Benefits
Concealed systems offer homeowners and HVACR contractors ductless advantages
Ductless heat pumps have taken the U.S. by storm with sales increasing by double digits over the last few years. That momentum is expected to continue; however, not every homeowner wants to look at wall-mounted units in their living spaces.
Enter the ducted mini-split heat pump, which offers a more aesthetically pleasing option for homeowners who are hesitant about the look of wall-mounted, ceiling-recessed, or other ductless options, according to Michelle Robb, director of residential marketing, Mitsubishi Electric US Inc. Cooling & Heating Division.
And for the majority of homes in the U.S. that already have ductwork in place, the ducted mini split offers a viable alternative to central HVAC systems, as well.
“Having a ducted mini-split option means homeowners interested in ducted systems can have the setup and aesthetic they want while still benefiting from the efficiency, quiet operation, and zoning capabilities that mini splits offer,” said Robb.
In the U.S., most homeowners have central heating and cooling systems that utilize ductwork, and when it comes time to replace that equipment, they usually opt for another central system. However, according to manufacturers, ducted mini splits should be considered as they can increase energy efficiency while taking advantage of a home’s infrastructure. And, depending on the design, ducted mini-split systems can potentially reduce concerns about duct leakage and/or IAQ problems that can occur with forced-air systems.
“Traditional ducts collect dust and dirt over time, including pollen, pet dander, and volatile organic compounds, and these materials are recirculated throughout the home over time,” said Victor Flynn, product manager, Panasonic Appliances Air-Conditioning North America. “In addition, all traditional ducts leak conditioned air to some extent, which reduces energy efficiency and increases utility costs. With ducted mini-split systems, evaporators are generally located close to the distribution point, which leads to a reduced amount of air leakage and dirt build-up in ductwork related to mini-split systems.”
In addition to using existing ductwork, ducted mini-split systems allow users to take advantage of high-efficiency inverter technology, said Terry Frisenda, national accounts manager, air conditioning technologies, LG Electronics USA Inc.
“In some cases, our ducted units operate as high as 18.5 SEER,” Frisenda said. “These systems are also quiet, perform well in cold climates, and allow users to adjust each zone independently. With single-phase heat recovery, consumers even have simultaneous heating and cooling in different zones.”
The amount of energy savings a homeowner may see with a ducted mini-split system can be significant — on the order of 30-40 percent, said Robb.
“Traditional central heat pump systems are also controlled by less sophisticated outdoor units, which shut off when target temperatures are met and then turn back on when the temperature has slipped far enough from the target,” she said. “Our ducted and ductless mini splits are powered by an inverter-driven compressor, which modulates to satisfy space temperature requirements and is significantly quieter in the process.”
Traditional ducted systems use fan motors that draw excessive amperage to overcome the external static pressure of ductwork. Higher amperage draw results in higher energy usage, said Matthew Lacey, senior product manager of single and multi-zone systems, Daikin North America. “Central systems that utilize long ductwork runs and flex ducts may have increased external static pressure and lower operation efficiency. While ducted single- and multi-zone systems experience similar challenges, the efficiencies remain higher as the indoor fan coil unit is located closer to the source and requires less ductwork.”
Contractors can offer homeowners a lot of bang for their buck with ducted mini splits, because a single outdoor unit can connect to up to eight indoor units, and each indoor unit can service one or multiple rooms, explained Robb.
“Contractors determine how many units to use by running load calculations. Mitsubishi Electric makes this easy by providing programs like the Residential System Builder™, an app built for use on tablets that allows HVAC contractors to walk into customers’ homes and provide an accurate estimate of what size and type of system should be used for each home,” she said.
A ducted single- or multi-zone system works similarly to a central heat pump system, except that it is applied as a zone solution with shorter duct runs, noted Lacey. “For example, if a two-story home includes a large game room and three bedrooms upstairs, a load calculation for a traditional system may recommend a 4-ton system with the controlling thermostat in the game room. This traditional system would have one indoor fan coil or furnace with an evaporator coil and a considerable amount of ductwork from the single unit to each of the four rooms.”
With a ducted single- or multi-zone system, it may be possible to reduce the size of the system to a 3-ton multi-zone system with one condensing unit outside connected via copper tubing to four individual fan coils that serve each of the four rooms, said Lacey.
“Each room would have an independent thermostat control for heating and cooling as opposed to a traditional system that may be limited to heating or cooling all four rooms at once.”
Contractors will like the flexibility of ducted mini-split systems, said Victor Perez, national director of sales, Samsung.
“Contractors have the option of utilizing one indoor unit per room or utilizing one indoor unit for several rooms — it’s dependent upon load, fan static pressure, sound generation, amount of ductwork, plenum height, and economics. In addition, the indoor unit can be installed either horizontally or vertically, depending on the application. Either way, the ductwork is attached to the indoor fan coil and then extended into the various locations, as needed.”
Essentially, a ducted mini-split system is laid out very similarly to a unitary system complete with an air handler, said Frisenda; however, unlike a conventional system, the indoor air handler does not require its own power source as it draws power from the outdoor unit.
“One unit can serve multiple rooms and, in some cases, that is preferred. By combining multiple rooms with a ducted mini-split unit, consumers can maximize efficiencies and reduce installation costs to build larger comfort zones, as desired. To ensure proper installation, contractors need to run a Manual J room-by-room load calculation, which will determine the number of indoor units required to appropriately condition the space.”
Ducted mini-split systems can be installed in ceilings, attics, closets, or under the floor, but, as with any heating or cooling system, proper load sizing and installation is key.
“Ducted mini-split systems are designed to be located close to air distribution points and are sometimes fitted with a multi-port flange that allows for two or more distribution points, but it should be noted, due to relatively low static pressure ratings, duct length should be minimized,” said Flynn.
As with any system, ducted mini splits do have their limitations. In extreme climates, for example, supplemental heat may be required, but many manufacturers note that their ducted mini-split systems can offer substantial heating capacity down to minus 13°F. To address IAQ concerns, many ducted mini splits offer advanced filtration options and dehumidification control; however, installing an energy recovery ventilator (ERV) is usually recommended.
Given the flexibility, energy efficiency, and comfort that ducted mini-split systems can offer homeowners, it is no wonder manufacturers are optimistic about their future.
“The acceptance of ducted mini splits continues to grow,” said Perez. “Projections show that demand for ducted mini splits will soon be equal in size with ductless mini splits.”
Publication date: 5/29/2017