Planning an HVAC Replacement Without Disrupting Operations

Start with the existing system

A replacement plan begins with a survey of the equipment as it is, not as it was designed. Record the condition and age of each item, its refrigerant, its maintenance and fault history, and the loads it now serves, which may have changed with the use of the building. Systems using R22 can no longer be topped up with that refrigerant in the UK or EU, which often sets the priority.

Measure what matters for the new selection: airflows, water flows, pressures and temperatures under real operating conditions. The survey should also establish what can be retained, such as pipework, ductwork, electrical supplies, controls and structural supports, and what the new equipment will need that the old did not. Where records are incomplete, logging temperatures, flows and power for a period before the design is fixed shows how the plant actually behaves across different loads.

Decide what must keep running

Map how the building operates across the day, the week and the year. Identify spaces that cannot lose cooling, heating or ventilation, such as server rooms, clinical areas, kitchens or guest floors, and agree acceptable conditions during the works with the building operator.

Timing reduces risk. Cooling plant is best replaced in the cooler months and heating plant in summer, while in the Gulf the milder winter period is the usual window for work on cooling plant. Existing standby capacity can allow one unit to be taken out of service while the others carry the load. Agree in advance what happens if a stage overruns or temporary plant fails, and keep portable cooling or heating available for the most critical spaces.

Choose a phasing strategy

Most replacements use one of four approaches, or a combination of them: exchanging units one at a time using existing standby capacity; connecting temporary plant while permanent plant is replaced; installing new plant alongside the old and switching over once it is proven; or replacing distributed systems zone by zone or floor by floor.

Temporary plant needs connection points, electrical supplies and space, which are best designed into the scheme early. Modular equipment delivered in sections through existing openings can remove the need for major building works. Whatever the approach, each stage should be commissioned and accepted before the next section of existing plant is taken out of service.

Access, lifting and working around occupants

Crane lifts may need road closures, permits and weekend working, and the route from delivery point to plant room has to be checked for weight and size. Noise, vibration, hot works on pipework and refrigerant recovery should be planned around the occupants, with isolation, drain-down and permit procedures agreed in advance.

In occupied hotels, hospitals and offices, the building operator needs a programme of works they can communicate to guests, patients or tenants, and a contact for any unplanned impact. Equipment deliveries should be sequenced with the installation programme so each outage window is used as planned.

Controls, integration and commissioning

New equipment has to work with the existing building management system, or with a new one introduced in the same project. Confirm the protocols and points required, and plan how old and new plant will be controlled together during the transition, since interim control arrangements are a common source of problems.

Water and air systems should be rebalanced after significant changes, and plant performance verified under load, ideally in both the heating and cooling seasons. Handover should include updated drawings, operation and maintenance information and training for the people who will run the system. Keep the old plant serviceable until each new stage has been accepted, so there is a fallback if commissioning reveals a problem.

Before work starts

Confirm the following before the first item of plant is isolated.

• Survey of existing equipment and measured duties
• Critical spaces and acceptable conditions during the works
• Seasonal window for each stage
• Phasing strategy and temporary plant needs
• Access, lifting and permit arrangements
• Controls strategy during the transition
• Commissioning and acceptance criteria for each stage
• Communication plan with the building operator