![]() The outdoor unit was noisy and only operated at one speed, but the real noise came from where the water lines penetrated the house. In contrast, we did have some noise issues with our Unico Unichiller air-to-water heat pump at our Seattle house. The outdoor units also operate at multiple speeds, thanks to their inverter technology, and are practically silent. Kudos to the Panasonic engineers for getting this right! Even when the fan is running on high, it is practically silent. The air baffles can be set to swing silently in four directions to circulate air throughout the room without having to raise the fan speed. The fan speed adjusts automatically, so during normal operation, it is quite low. As soon as we turned it on for the first time after installation, I realized that there was nothing to worry about there. We wondered if we would be annoyed by the sound of the Panasonic's fan. One of the benefits of an in-floor radiant heat system is its nearly silent operation. True, it doesn't feel as toasty on your toes as the floors in the Seattle house, but the floor temperature is barely even noticeable, even with bare feet. There is enough rigid foam under the slab to keep it well insulated from the ground, and the concrete floor eventually reaches the same temperature as the indoor air (usually about 69° F). Now that the house has been operational for a year, I can say that our worries were unfounded. We were worried that if we built a house with unheated concrete floors that they would feel cold and uncomfortable on our feet. One thing we really loved about our Seattle home was the warm radiant-heat concrete floors. Many less technologically advanced models only work when the outside temperature is 25° F or above, which simply wasn't good enough for our cold Eastern Washington winters. Dave, who did our energy modeling, chose this particular model for several reasons, notably that it was one of the most energy-efficient available (SEER 28.5) and that they can keep producing heat even when the temperature drops to 0° F. As part of our Artemisia Lab program, Panasonic of North America provided two of their EXTERIOS XE - Single Split System, Low Ambient Wall Mounted Heat Pumps. When we built Artemisia, we tried a different approach. The first one had an air-to-water heat pump connected to a radiant heat system in the concrete floors, which consisted of loops of PEX tubing placed under the concrete slab before it was poured. We have built two zero-energy houses over that last decade. Our experience with Panasonic mini-split heat pumps They are typically much more expensive to install, but they are the most efficient option and can heat effectively in the coldest outside temperatures. Instead of pulling heat out of the air, geothermal heat pumps use the ground as a heat source. See also: Air-to-Water Heat Pumps Geothermal heat pumps This is what we used in our Seattle zero-energy house. These are similar to standard air-source heat pumps, but the outdoor unit has a heat exchanger, which heats an antifreeze solution that circulates through the home via an in-floor radiant or wall coil-and-fan system. Mini-splits do not hook into your existing ductwork. If you have a large home, you will probably need multiple units. These are smaller units that also pull heat out of the air, usually with a single indoor air handler or head. The indoor unit is generally hooked into an air duct system, so they can heat and cool a larger home. These generally look like a large air-conditioning unit outside, but they can create heated as well as cooled air. If you are dedicated to using electric heat pumps, there are several types of system to choose from. Some definitions of net-zero-energy allow for one to use gas heat and calculate the equivalent amount of solar electricity to make up for it, but I like the elegance and simplicity of an all-electric home. If you are shooting for net-zero-energy, your choices are mostly limited to high-efficiency electric heat to supplement the passive-solar design of your home, and that means some form of heat pump. However, as a homeowner looking to build a new home or replace the heating system in an existing home, it's important to have a general idea of your preferences before you discuss your needs with the home's designer. If your energy-saving goals are ambitious, choosing the type and size of a heating system usually requires some expert guidance, probably even some form of energy modeling. HVAC systems can be among the most complicated in a house, and that's usually even more true in an ultra-efficient zero-energy home.
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