Multizone beginnings

Multizone units have been a staple in HVAC systems since the 1960s. They were particularly popular in schools, banks, multi-story buildings, and other locations. While VAV systems have become more common in recent years, multizone units were once the predominant choice.

Energy Efficiency and Code Changes

In the earlier decades, energy efficiency wasn’t as much of a concern as it is today. Older multizone units were often constructed with draw-through cooling, blow-through heating, and bypass units. These units provided comfortable spaces by cooling and dehumidifying the air, then reheating it as needed to maintain the desired temperature. However, in the 1970s and 1980s, codes were introduced against multizone units and simultaneous heating and cooling. As a result, they were labeled as energy hogs and fell out of favor among design engineers.

Limitations of Older Units

In addition to energy efficiency concerns, older multizone units lacked the modulation and capacity control of modern heating and cooling systems. Their construction was often subpar, with single-wall construction and minimal insulation.

Major Manufacturers of Multizone Units

Many HVAC manufacturers produced package multizone units. Notable brands included:

  • Carrier (48MA and 50Me units)
  • Trane (SLZB model unit)
  • Lennox (DMS units)
  • McQuay (RMZ units)
  • Nesbitt (RMA units)
  • Acme
  • American Air Filter

Advantages of Multizone Units

One significant advantage of multizone units over traditional VAV systems is that most maintenance can be performed on the roof, eliminating the need for technicians to access occupied spaces. This can be particularly beneficial in sensitive environments like hospitals or schools.

Comparison to VAV Systems

For retrofit applications, multizone units offer several advantages over VAV systems:

  • Direct Fit: Multizone units often fit directly on the curb, eliminating the need for curb adapters.
  • Minimal Modifications: Existing gas and electrical connections can usually be matched closely, reducing installation time.
  • No Ductwork Modifications: Unlike VAV systems, multizone units do not require changes to ductwork, which can be time-consuming and costly.

Ideal Applications

Multizone units are well-suited for projects where time is of the essence. Their ease of installation and minimal modifications make them ideal for retrofits in schools, banks, hospitals, and other facilities where disruptions must be minimized.

In conclusion, while VAV systems have gained popularity, multizone units still offer a viable and efficient solution, particularly for retrofit projects and applications where ease of installation and minimal disruption are essential.