A residential split system typically includes a gas indoor furnace and an outdoor condensing unit and has been used in small commercial designs for years. Even so, residential split systems have limitations in commercial applications, and those limitations have increased due to the 2012 International Energy Conservation Code (IECC) requirements.
2012 International Energy Conservation Code impact
Several code changes have impacted the use of residential split systems in commercial designs. For starters, systems equal to or greater than 33,000 British thermal units per hour (btu/h) require economizers, but split systems do not come standard to these specifications. To meet code requirements, a third party manufacturer would be needed to install an economizer. In addition, a third duct sized for the same capacity as the outside air intake louver needs to be added, which may compound ceiling space requirements. Lastly, a system to relieve additional air needs to be added via a relief opening or exhaust fan.
Before considering using residential split systems for your next commercial office build-out, doctor’s office or church classroom, consider these factors:
- Almost all commercial designs require mechanical ventilation. A split system’s capacity and manufacturer’s warranty can be compromised by adding unconditioned outside air. Outside air quantities above 10 percent approach the risk of shocking heat exchangers and leading to poor humidity control. Therefore, the outside air may need to be preconditioned.
- The indoor unit, whether a gas furnace or fan coil unit, takes up valuable real estate. In addition to the physical unit, there are extra building components that must be incorporated into the design such as floor drains, service clearances and vent chases.
- Sizes are limited to five tons (60,000 btu/h) of cooling and 120,000 btu/h of heating.
- A split system fan unit is located indoors, so noise transmission needs to be considered.
Pros and cons of using a residential split system versus a packaged rooftop unit
- Split systems use both indoor and outdoor space whereas a packaged rooftop unit only takes up outdoor space, which is usually not much more than a condensing unit.
- Split systems require multiple electrical connections while a packaged rooftop unit only needs one.
- Split systems work well when equipment cannot be mounted on the roof.
- A split system has a higher up-front cost than a packaged rooftop unit when you take into account the extra electrical connections, adding a third party economizer, adding ducted outside air, building a mechanical room/closet, extra controls and additional labor to install the add-ons.
- The split system has the ability to be more energy efficient than a packaged rooftop unit at +96 percent annual fuel utilization efficiency (AFUE) verses 81 percent AFUE on the heating side and 17+ seasonal energy efficiency ratio (SEER) on the cooling side.
Even though there are both pros and cons to using a residential split system, the biggest advantage is that they offer higher efficiencies, especially on the heating side. Plus, they prevent you from having to place heavier, larger equipment on a roof.