California Association of Building Energy Consultants

Ductless Mini-Split Systems — The Good and the Bad

The Good:

Ductless Mini-Split Systems are being seen more and more in residential applications. These systems are efficient and designed for heating and cooling small spaces. They take up only a small amount of space and are generally quiet.

The Bad:

There are many applications in Title 24 compliance when a ductless mini-split system is part of the energy features that meet compliance. However, it is not always an efficient choice in the mix of energy features for a building to meet California's Title 24 Energy Compliance budgets.

Here is why a ductless mini-split system may be a hindrance in meeting Title 24 Energy Compliance. It has to be modeled with minimum efficiency ratings (established by the federal energy commission) … per this paragraph from the CEC's 2016 Residential Compliance Manual, Section 4.7.9.

4.7.9 Nonducted Systems

Several manufacturers offer equipment that does not use air distribution ducts to heat or cool spaces. These systems use either refrigerant or water that has been heated and/or cooled to condition the space. Besides not using duct work, these systems have advanced controls and full range multispeed compressors that will allow for optimal performance through a wide range of conditioning loads without losing efficiency.

These systems must be modeled as though they were minimally efficient units. The Energy Commission expects that the manufacturers will apply for a compliance option in the near future that will allow for the development of appropriate modeling rules to be included in the performance calculation approach.

As with all other high-performance systems, the Energy Commission recommends that all associated HERS verified measure be conducted to assure that all the efficiency of this equipment is captured.

In most new residential projects the efficiencies of the HVAC system specified in the compliant Title 24 Documentation exceed the minimum federal energy rating requirements, thereby helping the project meet Title 24 Energy Compliance. An efficient HVAC System is key to meeting and exceeding the 2016 Title 24 Energy Requirements.

As always, I am available to discuss the process of meeting the California Energy Code for any building project. Contact me …