Overview
This facility improvement measure (FIM) focused on upgrading an outdated constant air volume (CAV), multi-zone air handler into a modern, energy-efficient variable air volume (VAV) system. The conversion was designed and implemented through a collaboration between Siemens and Moses Engineering, culminating in a full set of construction drawings and a customized retrofit strategy.
Project Background
The subject air handler, originally installed in the 1960s, served the third floor of the building across 13 individual zones. It was the only remaining unit of its kind in the facility, as all other air handlers had already been retrofitted or replaced. The existing system used a constant-speed fan and mixed hot and cold air downstream of the fan to regulate zone temperatures through a hot/cold deck configuration. This setup led to significant inefficiencies, including continuous fan operation and simultaneous heating and cooling.
Retrofit Strategy
– Replacement of the single large fan with a fan wall consisting of ten smaller fans, providing redundancy and adjustable airflow.
– Demolition of the existing hot and cold deck configuration.
– Installation of a new chilled water coil and replacement of internal components to support draw-through airflow.
– Implementation of VAV terminal units with hydronic reheat coils at each zone to replace existing mixed-air dampers.
– Installation of new return and outside air modulating dampers.
– Integration of new Siemens DDC controls and zone thermostats for precise control.
– All modifications were made inside the air handler to avoid disrupting occupied spaces.
Energy Modeling and Savings Analysis
Due to the lack of existing BAS trend data (the original system was pneumatic), temperature and humidity data was collected using data loggers during fall 2022. A test and balance report provided air flow baselines.
To estimate savings, two energy models were developed:
– Baseline Model: Represented the constant volume, multi-zone configuration.
– Proposed Model: Simulated the redesigned VAV configuration with variable airflow and decentralized reheat.
Energy Performance Table
| Metric | Baseline | Proposed | Savings | Units |
|———————-|——————|——————|——————|————-|
| Cooling Energy | 5,226,862 | 3,561,815 | 1,665,047 | MBH |
| Heating & Reheat | 1,629,127 | 1,929,787 | (300,660) | MBH |
| Fan Energy | 144,899 | 31,466 | 113,433 | kWh |
Conclusion
This air handler conversion from a constant volume, multi-zone system to a variable air volume system exemplifies a high-impact HVAC retrofit. By modernizing equipment, introducing redundancy, and optimizing energy use through system design and controls, the project achieves a meaningful reduction in energy consumption while enhancing building functionality and resilience.
