Order! Order! HVAC System Upgrade at the Court Building2024-06-18T15:12:16+01:00

Project Description

Project Overview

The Gibbons HVAC team was tasked with upgrading and maintaining the HVAC system in a high-profile London court building, focusing on Air Handling Units (AHUs) and a fan gearbox on the roof. The project involved replacing AHUs in the probation area and the main plant room, as well as refurbishing a gearbox for fan no.4. Here’s a detailed account of the approach, execution, and outcomes.

Phase 1: AHU 3 Replacement

The project commenced with the replacement of AHU 3, the smallest unit serving the probation area. The steps involved were:

Isolation and Disconnection:

  • We started by electrically isolating and disconnecting the power supply.
  • The coil was isolated and drained to facilitate safe removal.

Removal of the Old Unit:

  • The AHU was unbolted from the ductwork and removed.
  • Due to its manageable size, it was lifted and skated out in one piece.
  • Some ducting was also removed as it was incompatible with the new, slightly larger unit.

Installation of the New Unit:

  • The new AHU was positioned on the slab with anti-vibration Tico pads underneath.
  • Given its longer length, a support foot was fabricated to stabilize the overhanging part.
  • New duct connections were made and fitted.
  • The old pipework was cut back, and new connections were made to the new coil. This involved a pipe freeze to fit new isolation valves due to the absence of dedicated isolation valves.
  • A new Danfoss 3-way valve and actuator were installed.

Final Connections and Testing:

  • New cabling was run and connected to the fan.
  • The unit was tested and operated perfectly without issues.

Phase 2: AHU 1 and AHU 2 Replacement

Following the successful installation of AHU 3, we proceeded to replace AHU 1 and AHU 2 in the main plant room. These steps were:

Removal of AHU 1:

  • Similar to AHU 3, the electrical and water connections were isolated and disconnected, requiring a pipe freeze for new isolator valves.
  • Due to its larger size (approximately 4 meters long), the unit was cut into manageable pieces for removal.
  • The old unit was scrapped on-site.

Installation of the New AHU 1:

  • The new unit arrived in four sections, designed to fit through the plant room doors.
  • Each section was positioned on the concrete slab, aligned for proper ductwork fitting.
  • The sections were sealed with special foam and bolted together to ensure an airtight seal.

Replacement of AHU 2:

  • The process mirrored that of AHU 1, with the old unit cut up and removed.
  • New sections were installed and bolted together.

Final Connections and Testing:

  • New duct and pipe connections were made to the coils.
  • Electrical connections were completed, and the fans were tested, confirming flawless operation.

Phase 3: Fan No. 4 Gearbox Refurbishment

The final phase involved refurbishing the gearbox for fan no. 4 on the roof. The key steps were:

Preparation and Inspection:

  • Arriving on site at 8 am, we signed in at security, received PTW and access passes, and proceeded to the Engie office for briefing.
  • On the roof, scaffolders had erected a lifting frame across the fan to facilitate gearbox removal.

Gearbox Removal:

  • The gearbox was drained of oil and the impeller unbolted for better access.
  • It was discovered that the key from the gearbox end of the prop shaft had fallen out, causing damage to the gearbox shaft and coupling.
  • The gearbox was unbolted, lifted out, and moved to the access hatch for removal.

Installation of Refurbished Gearbox:

  • The refurbished gearbox was lifted into place using the lifting frame and bolted down.
  • Oil lines were reattached, and the impeller was rebuilt.
  • Due to the damaged coupling, the prop shaft was left off pending the arrival of a new coupling from the USA.


The failure to install a new coupling during the previous refurbishment led to wear and the eventual loosening of the key, causing significant damage to the gearbox shaft and coupling. A refurbished gearbox was successfully installed, and a new coupling has been ordered to complete the repair. The project demonstrated meticulous planning and execution, ensuring all HVAC units and components operated efficiently and reliably.

Impeller and gearbox removed
Access to the roof through hatch
New Gearbox installed
Damage to Shaft
Damage to coupling
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