Zoning systems can be extremely beneficial to both homeowners and the HVAC contractors who install the systems. However, their complexity can sometimes lead to confusion, and perhaps avoidance among contractors.

A new standard developed by the Air Conditioning Contractors of America (ACCA Manual Zr, Residential Zoning Design) aims to help contractors with zoning design to improve the installation and operation of zoned systems.

According to Don Prather, technical services specialist for ACCA, “The standard was developed to address the complex issues related to zoning and to provide HVAC system designers with consensus, industry guidance for making good design and application decisions.”

He added, “Manual Zr provides the zoning industry and HVAC contractors with a common platform for developing design and sales tools for various types of zoning approaches and customer needs.”

With the release of Manual Zr, Prather said, HVAC contractors will benefit from having an ANSI-recognized standard to use “as the definitive tool to aid them in the numerous, often complex considerations they must make when selecting and designing zoned HVAC systems.”


According to Prather, the standard has been under development for over a year. ACCA has completed the development process and Manual Zr is being released for an ANSI public review period; the 45-day comment period is to start by mid-May.

Upon completion of the ANSI public review period, resolution of received comments, and subsequent public review of any resulting substantive changes, the finalized manual will become available as an ANSI-recognized standard before year-end.

Manual Zr is being written to reflect “sound industry practices and design approaches,” stated an earlier announcement from the association.

According to ACCA, “Residential zoning and VAV systems … achieve their full potential and benefit when properly designed.” The new manual will address:

• Benefits and cost (comfort, energy, installed cost).

• Load calculations for zoned systems (peak block load for equipment size; peak zone load and peak room load for air distribution; glass performance, internal and external shading issues).

• Zoning strategies and protocols (diversity issues; MJ8 block load output flags for zoning, and room load output flags rooms that have large load peaks; multi-level construction; glass direction; bonus rooms in attic, in basement, or above garage; open floor plan versus isolated spaces; variation in room and zone cfm for winter and summer; personalized temperature control; internal loads for hobby rooms; continuous fan option).

• Types of zoned systems and attributes (local baseboard or duct coil heating, multiple furnaces or refrigeration cycle units, central heating-cooling with VAV dampers, split coil refrigeration cycle with multiple indoor coils).

• Equipment options and attributes (electric or hot water baseboard, or local duct coil; window units; PTAC and PTHP; central furnace with cooling coil; central air-source or water-source heat pump; split coil equipment).

• Controls and control strategies (bypass air issues for VAV; types of VAV dampers; VAV damper sizing; multispeed or variable speed; airflow management by microprocessor logic).

• Manufacturer performance data and equipment sizing procedure (governed by Manual S).

• Supply and return grille selection (constant-volume versus VAV device).

• Duct airway sizing (governed by Manual D).

• Energy and operational cost issues.

• Additional design procedures, reference tables, equations, and a glossary.

For more information, visit www.acca.org.

Publication date:05/16/2011