Designing an air-conditioning system to handle an Arizona summer
According to Greek legend, the phoenix was an unimaginably beautiful bird that after a long life died in a fire of its own making, only to rise again from the ashes.
It’s an enduring symbol of death, rebirth and the aspirations of humankind.
An early white settler, gazing at the remnants of a long-gone Native American settlement where modern-day Phoenix lies, envisioned the rise of a great metropolis in the same location.
And 150 years later, the Phoenix area is home to 4.6 million people and the scorching heat is as much a factor now as ever. In July, average high temperatures crest 106°F, typically falling into the double-digits overnight.
“If you talk to an old-timer, they’ll tell you that Phoenix has gotten hotter,” said Aaron Sharp, founder of Sharp Air Conditioning & Heating LLC. “Most attribute it to the quantity of pavement in the valley.”
Sharp is an HVAC construction contractor that focuses on high-end residential work, and most of that takes the form of service and retrofit. Given the mild winters in the Sonoran Desert, heating is a smaller consideration than the need for reliable air conditioning, though still necessary.
In Phoenix, the key challenge is dealing with incessant heat and huge solar gain. And with rising electrical rates, the need for energy efficiency is very important, too.
Across all six branches in the region, Ferguson officials say they have seen high-efficiency products gaining popularity with installers, and Sharp is no exception.
“We’ve recently made a push into green energy and high-efficiency retrofits,” Sharp said. “For most of our clients, comfort and efficiency trump upfront cost.”
It’s meant that Sharp’s service technicians are doing a few less in-kind replacements of air-conditioning units each year. Sometimes they use a solar-ready approach, where new condensers are installed along with the components necessary to connect to a dedicated photovoltaic panel. Other times, they’re finding ways to get creative with condensers and zoning, adding efficiency while improving comfort and controllability.
A recent air conditioner replacement in a single-story, 4,000-square-foot home prompted Sharp to inquire about one of Ferguson’s newest lines: the light variable-refrigerant-flow J-II system made by Fujitsu.
Technicians were removing a 15-year-old, 12-seasonal energy-efficiency ratio air conditioner and gas-fired furnace. After discussing his options — with special consideration made for the homeowners’ requests — Sharp decided to replace the existing equipment with a 5-ton J-II condenser. He also planned to add three zones.
“Once you max out the mechanical efficiency of available options, you need to find other ways to reduce power consumption,” Sharp said. “By adding zones to the house, we’re not only improving the controllability of the space, but increasing efficiency. It’s something few people realize before we speak with them about it.”
The family’s two children had moved out, leaving large parts of the house unused. Because the entire ground floor was on a single zone, some rooms were much more comfortable than others. The full, finished basement was a second zone and suffered similar problems, though not as bad.
The owners were adamant that the new system not “blow” cool air forcefully across the room, making them feel quite cold near a supply grille, and too warm anywhere else.
Sharp’s plan was to use the 19-SEER J-II for its ability to support up to nine zones. This way, the unused floor-space could be set back from the rest of the home, and the master bedroom and common areas could be controlled individually. In addition, smaller zones meant lower static pressure in the ductwork.
To make sure his plan checked out, Sharp brought his layout to Ferguson’s design team and had it checked for performance and compatibility standards in Fujitsu’s design simulator. Since Ferguson is the exclusive Fujitsu VRF distributor in the Western U.S, the company was able to quickly determine if the plan needed any changes.
After his design was OK’d, Sharp technicians put the plan to work.
“The upstairs trunk line was removed, and three smaller branches were added, each with their own fan coil,” Sharp explained. “This took a little more work than simply connecting the condenser to wall-hung evaporators, but it was well worth the effort.”
The living room return was reused. New return boxes were cut in for the master bedroom and the childrens’ rooms, and individual thermostats were added.
A new fan coil was installed for the basement zone, but supply and return ducts were left unchanged. A 12,000-British thermal unit ceiling cassette was installed in the theater room, which always got too hot when occupied. With its own thermostat, the room now responds rapidly.
“The J-II provides the flexibility of a full VRF system, but doesn’t require three-phase power,” Sharp said. “With the four fan coils and the ceiling cassette, we have a combined 78,000-Btu maximum load connected to a 60,000-Btu condenser or 130 percent of capacity.”
VRF condensers can be undersized because it’s rare that all evaporators would be required to run at the same time. And in such an instance, the electronic expansion valves on each of the evaporators will throttle to maintain operation of all indoor units.
Aside from the use of refrigerant headers instead of branch boxes, the J-II VRF system installs much like a multizone mini split. But longer line sets and the ability to accommodate many more zones make it a far more capable solution. With sizes between 3 and 5 tons, the systems fit the bulk of Sharp’s job sites.
“There are a lot of high-SEER, conventional AC units on the market,” said Sharp. “Many offer variable speed and inverter compressors. The difference is that we’re zoning with refrigerant circuits here instead of zone dampers. Closing down entire circuits when not in use provides a comfort and efficiency advantage.”
The homeowners recently told Sharp that they’re the most comfortable they’ve ever been in the home. Maybe that says something about being an empty nester, but it probably has to do more with the retrofit.
Those complaints of being blasted with cold air? Now a thing of the past.
For Sharp AC & Heating, the new system is a growing option for light commercial applications, or when retrofitting a residential heating and cooling system.