One of the best ways to reduce the electricity your AC system consumes is to program your thermostat. But if you're building a new green dream home or upgrading your HVAC system, then going with hydronic heat and a multi-split heat pump system may be the most efficient you can get.  If you thought a heat pump was only used for heating, think again (I admit, it's a bad marketing job by whoever came up with the name). As I mentioned in our post on air-source heat pump:

When you see Heat Pump, you only think about “heating”, but it can also be used to cool.  So really, it should be called a Heat/Cool Pump.  The most common form of a heat pump is the air-source heat pump, and that will be the focus of this article.  There are other types of heat pumps, like the geothermal heat pump.

The main thing that a heat pump has than an air conditioner doesn't is a reversing valve.  From the HowStuffWorks article on heat pump:

The key to allowing the air-air heat pump to also cool is the reversing valve. This versatile part reverses the flow of the refrigerant, so that the system begins to operate in the opposite direction. So instead of pumping heat inside your home, the heat pump releases it, just like your air conditioner does. When the refrigerant is reversed it absorbs heat on the indoor side of the unit and flows to the outside. It's here that the heat is released, allowing the refrigerant to cool down again and flow back inside to pick up more heat.

One of the leading blogs I've found regarding split-system heat pumps is Allison Bailes' Energy Vanguard.  They had a post early in 2012 titled "No Duct Losses by 2050? ACEEE Thinks So!":

"The American Council for an Energy Efficient Economy (ACEEE) just released a new report,  The Long-Term Energy Efficiency Potential: What the Evidence Suggests, so of course I had to find out what they wrote about homes. There's a lot of good stuff in there, but one statement jumped off the page as I read:

By 2050, distribution energy losses have been essentially eliminated primarily due to a fairly large shift from duct work to energy delivery in hydronic and refrigerant-based (multi-split) systems."

If you need an introduction to the mini-split heat pump, check out Energy Vangaurd's post on the advantages of mini-split heat pump. In that post, Allison talks about their visit to the Mitsubishi heat pump production facility in our home state of Georgia and says:

Mitsubishi's line of residential ductless heat pumps is called the Mr. Slim. It's a split system heat pump, which means that the compressor and condensing coil are outdoors, and the evaporator coil and blower are indoors. In that regard, it's like your typical 'central' air conditioner or heat pump. You can tell if a house has a mini-split by looking at the outdoor condensing unit. They're thinner and smaller than the typical ducted system condensing unit.  The indoor unit can be mounted on a wall, set into the ceiling, or sit on the floor.

There was also a guest post on Energy Vanguard regarding heat pumps and hydronics, which provides a nice background to reference for the ACEEE report.  From that guest post written by David Butler of Optimal Building Systems in Arizona:

In warm climates with average or better electric rates, the heat pump is hands-down the best heating system. It costs less to operate than a furnace (most markets), and in tight, well insulated homes, a heat pump is actually more comfortable. The lower supply temperature, once considered the bane of heat pumps, is actually preferable in well insulated homes.

Since heat pumps produce less heat as the outdoor temperature drops, supplemental heat is needed in all but the warmest regions. In high a performance home, the need for supplemental heat is dramatically reduced, with a typical balance point (BP) in the mid-twenties. One concept that’s important to understand is that performance doesn’t fall off a cliff below the balance point. At five degrees below the BP, a heat pump will still carry about 75% of the load. If the number of hours below the BP is small, electric supplemental heat is the best option, given its low first-cost.

In moderate to cold climates where a heat pump requires significant supplemental heat, a natural gas-fired hydronic coil is preferable to electric strips. A high-efficiency tankless water heater, such as the Rinnai Ultra, is the ideal heat source for hydronics. The coil, which looks like a radiator, should be sized to handle the full design load. It’s installed between the air handler and the supply plenum (the heat pump coil is on the return side). As with electric strip heat, the hydronic pump is energized when the thermostat senses the heat pump can no longer handle the load.

Regarding hydronic heating, this website has some pretty good information comparing hydronic heating vs. gas forced air heating.

So the multi-split heat pump system can handle heating and cooling, but when more heat is necessary it works in conjunction with the hydronic heating system to keep your home at a comfortable temperature.  That sounds about as efficient as it gets.  What do you think?