Thermal comfort is a critical aspect of building design, and as defined by ASHRAE 55, it is “that condition of mind that expresses satisfaction with the thermal environment”. This satisfaction is influenced by six key factors: metabolic rate, clothing insulation, surface temperatures, air speed, temperature, and relative humidity. As occupant comfort becomes increasingly important, especially in healthcare and residential facilities, the direct impact on productivity, physical and mental health, and overall satisfaction cannot be overstated.
In this blog, we explore how Baumann Consulting is deploying retro-commissioning (RCx) and computational fluid dynamics (CFD) to improve thermal comfort at the Illinois State Veterans Home in Manteno, IL.
Project Background: Addressing Thermal Comfort Challenges at the Illinois Veterans Home
The Illinois Veterans’ Home at Manteno, established in 1986, is a dedicated facility providing comprehensive care and support to veterans. The Veterans’ Home is based on a 122-acre campus in Kankakee County, which comprises five major nursing care units and two ancillary service and support buildings. The home accommodates up to 304 residents with skilled nursing care. Many veterans in the facility are elderly or disabled, with conditions like diabetes and arthritis, which require proper thermal comfort to obtain a satisfactory living environment for people who served the country.
The veteran’s home is undergoing a renovation of four residential buildings to improve occupant thermal comfort. These buildings–R1 and R2 (one-story residential buildings) and S1 and S2 (one-story support buildings)–serve as both living and communal spaces for veterans. R1 and R2 are one-story residential buildings with wings of bedrooms, nurse stations, dayrooms, and gathering areas, while S1 and S2 house kitchen, dining, and food prep spaces, assembly halls, and physical therapy areas. All buildings have full crawl spaces where the vast majority of the HVAC and electrical equipment is located.
This project is being led by the Illinois Capital Development Board (CDB) and replacing decades-old air handlers across these buildings. For decades, the air handlers have been the subject of ad-hoc HVAC system expansions, many of which ignored the whole-system implications.
The Chief Facility Engineer reported ongoing issues with poor thermal comfort, particularly in the winter months. He suspected that the malfunctioning VAV box’s electric resistance heating coils were to blame. These coils were failing to operate due to low-flow safeties triggered by improperly installed ductwork. Despite previous upgrades to direct digital controls (DDC) and a building automation system (BAS), thermal comfort issues persisted.
To address these issues, the design team was retained to perform a scope of work consisting of the replacement of HVAC equipment in each building and the replacement or retrofit of variable air volume (VAV) terminal units located above the first-floor ceiling areas. Any existing pneumatic controls will be replaced with new DDC controls connected to an expanded BAS. Piping and ductwork modifications as dictated by the equipment replacement and by existing conditions will be designed as required.
Utilizing RCx to Identify HVAC Issues
The first step in diagnosing these thermal comfort issues at the Veteran’s home was performing RCx on the AHUs and associated VAV boxes. Baumann conducted this assessment to determine whether the existing HVAC systems could achieve safe supply airflow to prevent the electric resistance heating coils from tripping. Baumann also measured VAV box airflows using a flow hood to collect measured data for use in simulation calibration.
During the RCx process, Baumann measured VAV box airflows using a flow hood to gather data for use in simulation calibration. Functional performance tests were conducted on the air handlers and VAV boxes in the vacant West wing of Building R-2, while a thorough inspection was carried out across all four buildings.
Several issues were identified during the inspection:
- Poor VAV box duct connections, including insufficient duct lengths and inappropriate use of flex duct.
- Malfunctioning or improperly mounted air flow safety switches, many of which needed replacement.
Leveraging CFD for System Optimization
Following the RCx assessment, Baumann conducted a CFD study of the existing duct conditions in the two buildings R2 AHUs (AHU-R2-NW and AHU-R2-SW), where the team performed detailed functional testing and took airflow measurements with calibrated test equipment.
The CFD process was conducted in two phases: pre-design and validation.
Pre-Design CFD Modeling Process
The Baumann team completed the pre-design phase in January 2025. The pre-design phase had three goals:
- Create a computer model of the existing conditions at the two studied AHUs in Building R2 that is calibrated to match the measurements taken at Baumann’s previous RCx testing to validate the computer model’s predictive capability.
- To identify the pressure losses in the VAV box downstream ductwork that may be contributing to the current airflow issues.
- To determine the reduced supply fan static pressure required to achieve the measured airflow if the ductwork were modified to best practices.
The geometry of the AHU-R2-NW and AHU-R2-SW supply duct distribution systems was modeled based on the current condition as-built drawings, supplemented by Baumann’s field observations. The geometry of supply ducts from terminal units to diffusers was not included in the model. The two AHUs’ supply fan discharge static pressures are as-balanced.
The pre-design CFD simulation was calibrated with the supply airflow that Baumann measured at each box during RCx testing. The initial CFD simulation results with the VAV box downstream duct pressure drop set at 0.25” were anticipated to overestimate supply airflow.
Pre-Design CFD Simulation Results
The CFD simulations revealed that the AHUs were overestimating the supply airflow achieved at the VAV boxes by 50%-80 % when simulating 0” VAV box downstream duct pressure drop. The supply fan discharge static pressure had to be reduced by 0.9-1.2” WC from the starting value, the presently-balanced static pressure, to achieve a simulated VAV box supply airflow within 5% of the measured value.
Similarly, the AHU simulation overestimated the supply airflow achieved at the VAV boxes by over 30% when simulating a 0.25” VAV box downstream duct pressure drop. The supply fan discharge static pressure had to be reduced by 0.7-0.9” WC from the starting point to achieve a simulated VAV box supply airflow within 5% of the measured value. Additionally, the average VAV box downstream pressure drop had to be increased to 0.96” WC instead of the pre-assumed 0.25” to achieve a simulated VAV box supply airflow within 5% of the measured value.
Design Validation Phase CFD Plan
Once the project team completes a mechanical check set containing the revised duct design and new air handling unit, Baumann will undertake the design validation phase. In this phase, the CFD model will be updated to reflect the new design, with the following primary goals:
- Create a computer model of the new air handlers and revised duct conditions to validate the design and demonstrate that the new supply fan and duct design can achieve the scheduled design supply airflow rates.
- Quantify the increased supply fan static pressure needed to achieve the scheduled design supply airflow rates, if necessary.
Conclusion
The integration of RCx and CFD modeling offers an innovative and effective approach to diagnosing and optimizing thermal comfort in veteran housing. By addressing airflow inefficiencies and leveraging advanced modeling techniques, Baumann Consulting is helping improve the living conditions for residents at the Illinois State Veterans Home. As the project progresses, these solutions will not only improve thermal comfort but also enhance overall energy efficiency and system performance.
Experiencing issues with thermal comfort in your facility? Reach out to us to discover how our team can assist you.
