Introduction

Variable refrigerant flow (VRF) systems offer numerous advantages in K-12 school applications. These systems allow individual temperature control for rooms, which is particularly beneficial for classrooms. Additionally, they provide opportunities for heat recovery and efficient operation. However, VRF systems also present challenges, particularly concerning installation and maintenance. This article explores two case studies from high schools in the U.S. Midwest, highlighting the successes, challenges, and lessons learned in applying VRF systems in educational settings.

Case Study One: High School Renovation

Project Overview

The first case study involves the complete renovation of a high school originally built in the 1950s. The project included replacing nearly all HVAC systems, retaining water-cooled chillers, and installing new condensing hot water boilers. The school features limited ceiling space, poorly insulated perimeter walls, and numerous glass windows.

VRF System Implementation

Most classrooms were equipped with VRF fan coil units, utilizing a combination of ceiling cassettes and concealed ducted fan coil units. Ventilation air was supplied from roof-mounted dedicated outdoor air system units (DOAS) with energy recovery wheels, DX cooling, hot gas reheat, and natural gas burners.

Challenges and Solutions

During an extreme cold spell, the VRF systems struggled to maintain indoor temperatures, revealing a discrepancy between cataloged heating capacities and actual performance under harsh conditions. An emergency heating mode was implemented, utilizing DOAS units to supplement VRF heat. Another issue involved cooling on some DOAS units shutting off due to clogged condenser coils. Preventive maintenance was established to address this.

Outcomes

Despite the challenges, the school district appreciated the individual temperature control offered by the VRF systems and found the maintenance of ceiling cassettes straightforward. The renovation was considered successful overall.

Case Study Two: New High School Construction

Project Overview

The second case study focuses on a new high school construction, featuring a three-story education wing, two-story athletics wing, and two-story performing arts wing. The building, spanning approximately 365,800 square feet, was equipped with around 350 VRF fan coil units.

VRF System Implementation

Ventilation air was provided by indoor DX DOAS units tied to VRF heat pump condensing units. The project encountered numerous compressor failures, prompting an investigation.

Challenges and Solutions

The investigation revealed discrepancies between the installed refrigerant piping and the manufacturer's shop drawings, leading to incorrect refrigerant charges and subsequent compressor failures. Recommendations included strict adherence to shop drawings, field measurements of piping, and installation of bypass suction filters on systems with compressor failures.

Outcomes

The implementation of corrective measures aimed to ensure long-term reliability of the VRF systems. The case highlighted the importance of proper installation practices and rigorous field quality assurance.

Conclusions and Recommendations

VRF systems offer significant benefits for buildings requiring individual room zoning. However, successful implementation hinges on meticulous installation and adherence to manufacturer guidelines. Key recommendations include:

1. Only allowing factory-trained and certified installers to perform installations.
2. Ensuring certified installers are on-site during piping installation.
3. Purging pipes with inert gas during brazing to prevent oxidation.
4. Adhering strictly to manufacturer’s shop drawings and adjusting refrigerant charges accordingly.
5. Implementing strict field quality assurance practices.

Commercial general contractors must emphasize the importance of these requirements to ensure successful VRF system installations. By following these guidelines, the potential advantages of VRF systems in K-12 schools can be fully realized.

Source: Cramm, Kelley. "Applying VRF In K-12 Schools: Case Studies And Lessons Learned." ASHRAE Journal, vol. 64, no. 11, Nov. 2022, pp. 14+