Solving an engineering problem on a legacy HVAC control system with limited drawings
Asset One completed an offshore survey of the existing HVAC control arrangements on the Ninian Central Platform to support the integration of a replacement chiller system.
With very little design information available for the legacy control system, the objective was to establish what was actually installed, understand how it worked, and provide the verified engineering information needed to develop a practical, minimum-modification integration strategy.
Engagement overview
Nexos Solutions
CNR International
Ninian Central Platform
Offshore Oil & Gas
Equipment Surveys, Brownfield Engineering, Controls, HVAC Systems, Technical Assurance
What needed to be addressed
The existing HVAC control system was legacy, with very little design or as-built documentation available. A replacement chiller package was being introduced, but the relationship between the new equipment and the existing controls was not understood.
The engineering challenge was not simply to replace controls. Working from limited drawings, the requirement was to:
- Understand how the existing control system actually worked
- Trace control loops from panels out to field devices
- Identify actuated equipment and the services they controlled
- Establish the relationship between existing controls and the new chiller package
- Define the minimum interfaces required for safe integration
- Avoid unnecessary modification to operational equipment
- Close the information gaps before detailed engineering
How we approached the work
Asset One carried out an offshore field survey focused on physical verification rather than reliance on incomplete legacy drawings. Activities included:
- Inspection of existing HVAC control panels
- Tracing of control connections from panels to field devices
- Identification of controllers, actuators and associated equipment
- Mapping of controller-to-field relationships
- Review of valve and service arrangements
- Verification of available control interfaces
- Development of an equipment inventory
- Development of a control loop verification register
- Definition of a practical control integration philosophy
- Identification of information required for the next engineering phase
Defined deliverables
HVAC control loop survey
Physical tracing and verification of existing control loops.
Controller-to-field mapping
Documentation of relationships between panels, control connections and field equipment.
Equipment inventory
Structured record of identified controllers, actuators and associated control components.
Loop verification register
A traceable register recording verified control loop information.
Control integration philosophy
Definition of the proposed relationship between the new chiller controls and the retained existing HVAC controls.
Interface requirements
Definition of the minimum signals and interfaces required for safe integration of the replacement chiller.
Design information register
Identification of information requiring confirmation before detailed design.
Technical solution
Replacement Chiller Package
Inputs
- Chiller operating status
- Chiller fault status
- Required permissives
- Process temperature information
Interface
Defined hardwired interfaces
Johnson Controls pneumatic HVAC controls
Existing HVAC controls remain operational and autonomous.
Design Principle
Retain serviceable existing control functionality and introduce only the interfaces required for safe and effective operation of the replacement chiller.
The recommended philosophy avoided unnecessary wholesale replacement of the existing control system. Only the interfaces required for safe chiller operation were introduced, while the existing controls continued to perform their established functions.
What the work achieved
The offshore survey provided:
- 01A verified understanding of the existing HVAC control arrangements
- 02Improved visibility of controller-to-field relationships
- 03Identification of key actuated equipment
- 04A structured control loop verification record
- 05An equipment and control component inventory
- 06A defined minimum-modification integration philosophy
- 07Defined interface requirements for integration
- 08Identification of outstanding information required for detailed design
- 09Reduced reliance on assumptions during subsequent engineering
Relevant capabilities
Planning a brownfield modification with incomplete legacy information?
We survey what is actually installed, establish how it works and provide the verified technical information needed to move engineering forward.