Mini-split air conditioners and heat pumps have been around for many years. These systems are just like your standard central air conditioning systems, except instead of having ductwork and registers, they place the air handler into your room. Each room where you want heating/cooling, you install a smallish wall unit.
While a central, ducted system makes sense for some homes, they are prone to inefficiencies due to duct losses. Ducts are often leaky and placed in basements or worse, attics, where they spew conditioned air instead of into the rooms where you want it. In fact, studies have shown that most ducted system lose 20%-30% of their efficiency through these losses. So that expensive 18 SEER system is likely only performing like a good 12 SEER system
On top of that, it's very difficult to get an even balance of air distribution in the house. One room might be too warm, another too cold. If you warm a cold room up to comfortable temperatures, the rest may be much too warm.
Finally, it's wasteful to heat and cool the entire house if you spend most of your time in just a few rooms. Many people try to close off unused rooms, but this isn't good for central systems which are designed to work with full air flow. Closing a few registers does little to reduce the energy used by a central system.
With a mini-split, each area has it's own air handler and hence, it's own control. If you don't need to condition a room, you can turn the system off and close the door. It's that simple.
What makes newer mini-split heat pumps much more efficient than older ones is what's called inverter technology. This is a variable speed motor driving the compressor. If a room needs only a little cooling, then the compressor runs slowly, while if it needs a lot of cooling, the compressor can run at high speed. Not only does this save energy, it makes the system much better at properly satisfying the demands of the room and its occupants. The result is a system that is both less expensive to operate and more comfortable.
While other companies, most notably Mitsubishi, makes mini-split heat pumps, the Fujitsu RLS breaks new ground with its incredible energy efficiency. Remember the SEER rating? The cost to run a system is inversely related to the SEER, so a 10 SEER system costs twice as much to run as does a 20 SEER unit. Up until recently, most installed air conditioners were 10 SEER. In the last few years, many have increased to 14 SEER. Top of the line systems were 16 to 18 SEER. In comparison, the Fujitsu 9RLS is 26 SEER and the 12RLS is 25 SEER.
Remember, this assumes perfect ductwork for a conventional system whereas in the ductless mini-split, the efficiency is basically what you get. So if you have a 14 SEER central AC, you're probably getting 10 to 12 real SEER. So the RLS systems cost half to operate as a current central AC. This can add up to hundreds of dollars per year.
What about ground source heat pumps (GSHP)? These systems are known to be extremely efficient, costing much less than other systems to operate. However, even a high-end GSHP system is about the same efficiency rating. Additionally, for homes, these are only suited to central installations, so duct losses still apply. Hence, amazingly, the Fujitsu RLS series in practice operates more efficiently than even a GSHP!
As noted previously, the inverter technology in the RLS mini-splits allow them to match their output to the needs of the room, while most air conditioners are either on or off. Even top of the line systems only have two speeds. A conventional system will barely run at all when it's 75 and humid, leading to very uncomfortable conditions. With its variable speed compressor, the RLS will keep your house comfortable whether it's 75 and humid or 95.
In an effort to rectify this situation, I installed a Fujitsu 12RLS (one ton cooling capacity) system in the living room. While it does require some tweaking of the blower speed for optimal operation, the system works much better than the GSHP. Since it has a much lower capacity than the main system, it runs longer. This is desirable for space heating/cooling as it results in better dehumidification in the summer and more uniform temperatures. I am now able to dial in exactly the conditions called for by the weather. If it's cool but humid, I can operate it in it's "dry" setting, where it acts as a dehumidifier and provides minimal space cooling. If it's mid-day and the sun is blazing down, I can turn it up to max cooling.
As an energy consultant, I'm always measuring my own home's energy usage. On a day where the average daily temperature was 80F, the GSHP runs five to seven hours per day, requiring about 30 kwh of electricity to operate. Now that I've installed the 12RLS, the GSHP typically runs about one hour, and this is only required to cool/dehumidify our bedroom at night. After I install another unit in the bedroom, I won't have to use the GSHP at all for cooling.
Measuring the usage of the Fujitsu is trickier because it doesn't just turn on and off. However, I also track my household electrical usage. Comparing comparable days between previous years and this year, I'm finding that my summertime electrical consumption used for cooling has dropped by about 33% (dropping from 30 kwh to 20 kwh). So, not only does the system keep us more comfortable, it reduces our electric usage.
Keep in mind too that I'm comparing the Fujitsu 12RLS to one of the most efficient ground source heat pumps on the market. A conventional air conditioner would consume about twice as much as the GSHP (about 60 kwh/day on a warm day). In that case, I'd be cutting my electric usage in half!
Now that I have had most of a winter in which to try the heat pump operation, I've found the system to work well. First, the specifications are superb. The 9RLS has a full rated output of 12,000 BTUs/hr at 47F outdoor temperature while the 12RLS is rated at 16,000 BTUs/hr. Both units have an HSPF (heating seasonal performance factor) of 12. Again, this compares very favorably to a GSHP system.
Remember that the performance of conventional (air source) heat pumps drops along with the outdoor temperature, so the heat output of the Fujitsu diminishes in cold weather. However, while a conventional heat pump has a single speed compressor (two-speeds on high-end units), the inverter drive of the Fujitsu allows it to vary the speed of the compressor in order to produce more heat as the demand increases. This allows it to work comfortably at a wider range of temperatures than a conventional air-source heat pump. A ground source heat pump however maintains more output as the outdoor temperature drops because it is not dependent on air temperature. It uses the relatively stable ground temperature.
In this winter's cold weather, with days into the low teens, the 12RLS performed very well. I only have to use the main GSHP for a few hours a day on cold days. The RLS has been keeping the living room cozy at 70F-72F and the bedrooms remain cooler at around 68F at night, which is perfect for sleeping.
In the colder temperatures, I have had to turn on the heating zone for the bedrooms because they don't get enough heat to keep them warm. Even with some air distribution, it's not the same as having a central heating system. In the long term, I will probably add another unit to serve the bedroom.
In the finished basement where our son lives, the 12RLS has been the primary heat source. It keeps that area a steady 68F-70F and hasn't missed a beat, even in a recent cold spell when the temperatures dipped into the teens. For example, on a day when the average temperature was 27F, the 12RLS in the basement consumed 13kwh. For comparison, that's as much energy as a hair dryer would use in about 9 hours.
If you're interested in seeing how much energy is being used by different systems in my house, click this link. There you can the current temperature and the amount of energy these systems are using.
As with any product, there are disadvantages. In the case of any mini-split system, you have to have an air handler in each area where you need temperature control. In most homes, this does NOT mean every room. Typically, you might have one in each occupied bedroom and one or two in the main living space.
With the RLS series, you have one outdoor unit for each indoor unit. Some mini-split systems allow connecting multiple indoor units (up to four) to a single outdoor unit. Unfortunately, these systems are much less efficient than the RLS, so I was stuck with the one-to-one installation.
In most homes, you'll use the mini-split to augment existing systems, reducing the need for many units. However, it is important to keep this in mind. You still want a backup heat source for the coldest days. Baseboard electric or space heaters can satisfy this need. Just remember, they cost several times as much to run as the heat pump, so you only want to turn them on when absolutely necessary.
Another disadvantage is cost, though that's difficult to compare. With a central system, you need to install ductwork, so that has to be compared. On the other hand, if you're upgrading an existing central system, you probably won't be redoing all the ductwork. For comparison, each 12RLS I had installed cost about $3,500, minus a total $1,500 government incentive for high efficiency system upgrade, for a total cost of $5,500 for two systems.
For a retrofit central heat pump, in our area, it costs about $10,000 for a high efficiency unit. That too would qualify for the $1,500 incentive, reducing the cost to $8,500. But this single unit serves an entire zone, usually half or all of the house. In order to fully condition my house that is currently served by the GSHP, I would have to install two to four more units, bringing the totall installed cost to $12,500 to $19,500.
Finally there's aesthetics. I personally don't mind the attractive, white, plastic case (shown at the top of the page). However, many people object to having this mounted on the wall. In any case, it is not as clean or unobtrusive as a small air supply grill in the ceiling.
Overall, I am extremely satisfied with the Fujitsu 12RLS. While it requires some fiddling with settings to optimize it for different weather conditions, it has dramatically reduced my summer cooling bills and made my home much more comfortable. In fact, I was so impressed with it, that I was motivated to write and post this review.
U.S. Dept. of Energy - Heat pumps
This is updated daily and allows a better Q&A interaction than this website.