Single Zone VS Multi Zone Ductless Mini Splits (Part 1)

Written by: 
Robert Lewis

A question that I'm frequently asked when meeting with folks to design a mini split system for larger spaces is whether to use several single zone systems or one multi-zone system with a few indoor heads.
For the example shown in Figure 1, an area having four clearly designed heating / cooling zones, the install could be designed with four single-zone units or two multi-zone units (each having two indoor units).

Picture of Multi Zone Vs Single Zone Ductless Mini Splits

Demonstration of Multi Zone Vs Single Zone Ductless Mini Splits

When considering the two approaches above, which is the better design? Is there a better design? As with many design considerations, the cliché “it depends” is probably the correct answer. While an answer suited to the particular application is best answered after a thorough site evaluation, several criteria help to understand the dynamics to consider when evaluating one approach versus another. EFFICIENCY: In general, single-zone mini splits are more efficient than multi-zone mini splits, meaning that you will use less electricity to run a system using single-zone units than you would to run a comparable system using multi-zone units. The amount of savings depends on your particular application and choice of equipment. In the case of the aforementioned systems where each zone requires a 9000 btu unit, the equipment could be specified as: Single Zone Design—four ea. of the Fujitsu 9RLS3 with a SEER rating of 33 and an HSPF rating of 14.2. Multi-zone Design—two ea. of the Fujitsu AOU18RLXFZ with a SEER rating of 18.0 and an HSPF rating of 9.3. In this particular case, the use of Single-zone units will reduce the annual heating energy consumption by approximately 11% and the annual cooling energy consumption by approx. 45%. COST: While system costs vary according to equipment and installation requirements, Multi-zone installations usually cost less than installations that use single-zone mini splits. Any installation cost savings from choosing a multi-zone design need to be traded off with the savings that would be realized if a single-zone design were implemented. A subsequent blog will discuss addition factors such as layout and reliability in considering single-zone versus multi-zone design.

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