When you’re looking for a way to keep just part of your house cool this summer, you might want to consider a mini split air conditioning system. These systems strike a happy medium between individual window or wall air conditioners and central air conditioning, in terms of size, installation cost and operating cost.

All air conditioners work the same way, whether they’re self-contained in a small window unit or set up in a larger split system. There are three basic components to the system: a compressor, a condenser and an evaporator.

A refrigerant material enters the compressor as a cool, low-pressure gas. In the compressor it is compressed, changing it to a hot, high-pressure gas. It then enters the condenser, where the heat dissipates and the gas changes to a cooler, high-pressure fluid.

It then passes into the evaporator through a tiny hole, causing the liquid’s pressure to drop. The liquid changes back into a gas, and as it does so it absorbs heat from the air around it. Now a low-pressure gas again, it returns to the compressor and the cycle is repeated.

How a mini split system works

Unlike central air conditioning, mini split systems don’t have any duct work. Systems such as these have been very popular in Europe, Japan and other parts of the world for a long time, and are just starting to gain popularity here in the U.S. They can cool one or more interior spaces without the cost of cooling the entire house.

They’re perfect for keeping the bedrooms cool at night without spending energy dollars to cool the rest of the house, or for cooling just the family room, living room, man cave or other areas of the house where a lot of activity takes place.

There are three basic components to the mini split system. An outdoor unit houses the condenser and compressor. It sits on a small poured or prefabricated pad, alongside the house in a location that’s convenient to the location of the interior unit(s). This is also one of the big advantages over window or in-wall air conditions, since it isolates all the noise outside of the house.

Inside the house, there’s an evaporator unit that gets mounted on the wall. Since cool air naturally falls, the evaporator unit is typically mounted fairly high on the wall, usually just a short distance down from the ceiling, so it doesn’t disrupt furniture placement. And unlike window air conditioners, it doesn’t disrupt natural ventilation or views, or create potentially dangerous obstacles to egress in an emergency.

Depending on the size and design of the system, two or more interior evaporator units can be connected to a single exterior condenser unit, and some systems can handle up to four.

For example, in a three-bedroom house you could install one in each of the bedrooms, operated off a single exterior unit. The interior units are whisper-quiet, so they’re ideal in a bedroom environment. And the other big advantage is that the occupant of each bedroom can set his or her own temperature, regardless of the settings of the other units.

The third component of the system is the line set that connects the interior and exterior units. For each indoor unit there are two pipes — one for the liquid refrigerant and one for the gas — plus a condensate drain line, an electrical line and a thermostat line.

All of these are usually bunched together in one 3-inch or larger flexible conduit, which simplifies the installation.

What are the disadvantages?

Nothing’s ever perfect. With the mini split system, the primary downside is the cost. If you already have a central heating system, you’ll probably find that it’s actually less expensive to simply add central air conditioning to your existing system. However, if you’re starting from scratch, these systems should prove less expensive than central air when you factor in all the duct work.

If you’re an avid do-it-yourselfer, you may find this to be another disadvantage. These aren’t really designed with the home handyman in mind. In fact, in some cases doing the installation yourself may adversely affect your warranty.

However, running the line set between the interior and exterior locations can often require drilling, removal of drywall, patching and painting, and other tasks that you might want to undertake yourself to save money. Same with trimming landscaping and pouring the pad for the exterior unit.

Talk with the contractor and see what tasks you can handle on your own, and how much the savings might be.

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