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Designing an HVAC System for Extreme Utah Weather

Challenge: The homeowners wanted an HVAC system that would accommodate the extreme Utah climate while using as little electricity as possible.

Building in a place as geographically stunning as southwestern Utah, with its vivid orange and red rock formations, one is keenly aware of the need to live lightly on the land. That was the case for Terra Caelo’s owners, former Apple employees who built a permanent residence in St. George’s eco-conscious Kayenta community. Architectural standards dictated that the home be sited and designed in harmony with the existing terrain, resulting in a low, earth-colored structure that virtually disappears into its desert backdrop.

In a climate where temperatures can spike to 114 degrees in July and dip below freezing on January nights, the design team’s top priority was figuring out how to maintain indoor air comfort throughout the sprawling 5,210-square-foot home while using as little electricity as possible. The couple had two objectives for a high-performance heating and cooling system: the ability to control the temperature in individual rooms, and to do it remotely. “Our goal was to have full control so that anyone in any room can choose the temperature they want,” says owner Patrick Fox, “and to be able to shut off areas such as the guest rooms when they aren’t being used.”

Builder Jake Joines, of J2 Construction, St. George, Utah, immediately suggested a multi-zone system using Mitsubishi Electric’s ductless and ducted units. He had installed similar technology in the ceilings of two previous homes, but Mitsubishi Electric’s customizable Variable Refrigerant Flow (VRF) zoning equipment allowed for a more flexible configuration. With no attic space and limited ceiling area to work with, “we felt like Mitsubishi was the most efficient choice for the installation we were trying to do,” Joines says. “We wanted most of the units to sit on the floor in a recessed closet rather than trying to stuff them into a ceiling.”

The technology’s resource efficiencies appealed to the owners, too. “Our house in California is all ducted and takes a substantial amount of money and energy to heat and cool,” Fox says. “The mini-split systems aren’t pushing air around the house but using it in its location; no energy is lost.” Mitsubishi Electric’s MeZO Controller app was another strong influencing factor, especially since the California-based couple was in residence only part-time during the first year. “I can launch the app on my phone and monitor the temperatures remotely, and if guests have just left I can adjust the temperature or shut off a unit from anywhere in the world,” he adds.

Solution: The Mitsubishi Electric VRF zoning system provided precise, energy-efficient cooling and heating that could be controlled remotely.

Ace Mechanical, St. George, Utah, installed a 10-zone system that isolates the one-story home’s different living pods: kitchen/dining, living room, four bedrooms, two offices, a guest room and a gym. The system’s design, for example, allows a small west-facing office, which gets hot in the summertime, to be precisely cooled without a conventional air handler sending cold air to other rooms that do not need it. Most of the units are hidden inside a small closet with an access door, and a few others are recessed in the ceiling. “Mitsubishi is a trusted name, and a leader in the newest technologies,” says Ace Mechanical co-owner Rob Pead. “They’re one of the best companies to work with, especially in this type of application.” And, he says, this system’s units can run at variable speeds, starting out at around 35 percent of capacity and ramping up in small increments as the cooling and heating loads demand, thus increasing their efficiency.

Facts About Terra Caelo:
Terra Caelo uses an average of 1,850 KWh per year, 58% less than the average per capita use in Utah.

The couple, now in full-time residence, closely tracks their home’s energy usage. With energy bills as low as $9 a month, they are pleased with the Mitsubishi Electric system’s performance — consistent indoor air temperatures that can be remotely controlled with the touch of a fingertip and quiet, conservation-minded operation. “Our summertime energy bill peaked at $238 with a house full of people,” Fox says. “Other homes of similar size in the area have bills that easily double that.”

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