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).
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.