You don’t even know what I’m talking about yet but right, up front, I’m joking.
Customers may wonder if there is an air conditioner which is as expensive to install as a central air system, but still uses the same big clunky boxes as window ACs like some air conditioning Reese’s Peanut Butter Cup? Thankfully, yes there is. The ductless mini split air conditioning systems combine unattractive wall mounts with excitingly expensive installation fees. Hooray!
Like I said, I’m joking. Somewhat. Ductless split systems can be more expensive to install and have historically been dogged with less than aesthetic room fixtures (they got better). However, they do have real benefits in terms of space, efficiency, and ease of zoning.
What is a Ductless Split System
A ductless split air conditioning system like many things is right there in the name. It is an air conditioning system split between the indoors and out which does not use ducting to move cold air.
Side note: See this article for the basics of how air conditioning systems work.
The condenser is outside the building and evaporators/circulating fan units are installed in each room that will be cooled. Instead of ducting moving cooled air through the house, electrical wiring and lines with refrigerant connect the interior and exterior units. There are considerable advantages in eliminating the bulky, inefficient ducting.
Ease of Installation – While I compared central systems with window ACs mostly, here I’ll focus on comparing ductless systems with fully ducted central systems. In this phase, ductless systems are easier to install.
Normal central air systems have either an exterior condenser with an interior evaporator hooked to a duct network or a combined system in an interior mechanical room (connected to the ducts).
Ductless split systems eliminates all the duct work but has multiple interior mechanical installations. So you’ve added some mechanical complexity but eliminated a ton of bulky ugly aluminum tubes.
Cost of Installation– For the same reason mentioned above, we have the opposite result. A ductless split air conditioner eliminates the bulky aluminum ducting. Less expensive! But replaces it with an evaporator/fan unit in every room. Much more expensive!
In 2011, the DOE estimated that ductless split systems cost up to 30% more than a comparably sized standard central system (allowing for regional variations and contractors).
Cost of Operation – While the individual units can vary in efficiency ratings, ductless system present some major conceptual gains over standard central systems.
First is that air ducts are a notoriously inefficient way to move cooled air. Leaks and poor insulation can significantly elevate energy use. Heat is absorbed into the ducts, forcing the air conditioner to work that much harder.
The second plus is that the AC controls of a ductless split system can change by room very easily. Newer duct systems have some ability to do this, but split systems can be programmed by room, allowing the target efficiency of a window unit.
Efficiency– Efficiency closely parallel’s cost of operation for the same reasons. Having multiple room units increases the mechanical complexity and electrical components but eliminating the duct work enormously improves the transport of the cooling load. The room units can be controlled individually, allowing the homeowner to zone and program by room. This targeted cooling that gives window mounted ACs and ductless split ACs their advantage in use.
Cooling Capacity – Like central air systems, ductless split systems can be scaled up a considerable size. Unlike standard central air systems, the evaporator/fan needs to be sized per room rather than for the whole building.
The individual cooling units need to be properly sized, centrally located in the room and hopefully easily accessible for cleaning and maintenance and that it matches the room’s aesthetic.
This creates some challenges compared to standard central systems that are sized for the entire building, a much simpler task.
Space– Ductless split systems take up much less space since they eliminate the duct work. Simple enough. Ducted systems usually run their ducts through either the basement or attic. This avoids gobbling up too much living space but exposes the ducts to unconditioned air if outside the insulation. (with the potential for condensation).
Ductless split systems connect the interior evaporator/fans with the exterior condenser via electrical and coolant lines. These can be run through interior walls, insulated and generally kept out of sight.
Noise– Ductless systems take a bit of a knock here. Where a central system could locate it’s mechanical bits far away from prying human ears, the ductless system locates the fan/evaporator in the room being cooled. Where standard systems can be so quiet, homeowners can forget to turn them off vs. fans in the room.
Zoning– Because the electric controls can be attached directly to the room unit, ductless systems can be easily and flexibly zoned.
Ductless mini split air conditioning systems are more expensive and the cooling units can be not so attractive. But if cooling costs are a concern, the efficiency advantages can make the investment worthwhile.