HVAC forum
Chiller replacement
Building a defensible replacement case from measured load, plant condition, access constraints and whole-of-life cost.
A chiller reaching 20–25 years of service is a prompt for investigation, not an automatic like-for-like replacement. Start with condition, refrigerant leakage, maintenance history and an actual cooling-load profile. Trend electrical demand, chilled-water supply and return temperatures, condenser-water temperatures and flow over a representative cooling season, then compare current selections at full and part load.
Runaround coil
Applying runaround heat recovery where supply and exhaust air streams are separated or cross-contamination must be avoided.
A runaround system connects a coil in the exhaust airstream to a coil in the outside-air stream with a pumped water or water-glycol loop. Because the air streams remain physically separate, it suits hospitals, laboratories, indoor pools and industrial facilities where a wheel or plate exchanger may be impractical or create a cross-contamination concern.
HVAC wire sizing
Coordinating mechanical selections, circuit capacity, voltage drop and protection before equipment is ordered.
Cable sizing for mechanical plant begins with a coordinated equipment selection. Confirm running current, starting method, protective-device requirements and route length, then check current-carrying capacity, voltage drop, fault-loop performance and installation conditions against applicable standards. An equipment schedule based on assumed fan duty is insufficient while system resistance remains unresolved.
Low-load chiller
Keeping chilled-water plant stable and efficient when most operating hours fall well below peak design load.
Many Australian buildings retain central-zone cooling demand through winter while operating at a fraction of summer peak load. If the active chiller cannot unload far enough, it reaches setpoint quickly, stops and restarts soon afterwards. Repeated short cycling reduces efficiency, destabilises temperature control and increases compressor wear.
Chilled water bypass lines
Selecting and sizing decouplers, minimum-flow bypasses, condenser-water bypasses and flushing provisions in chilled-water systems.
A chilled-water bypass may maintain minimum flow through chillers or pumps, hydraulically separate circuits, regulate temperature, protect equipment during changing demand, or isolate delicate coils during flushing. Its correct function depends on system topology and location. An undersized, oversized or poorly controlled bypass can waste pumping energy, create low delta-T problems or leave plant below its safe operating flow.
Supplementary air conditioning
Sizing independent tenant systems for equipment, occupancy and outside-air loads beyond the base-building allowance.
A supplementary air-conditioning system is physically independent of the normal base-building system and serves a specific load created by occupant use. Typical examples include communications rooms, densely occupied boardrooms and tenant equipment areas. It should meet the additional demand without overloading the base system, and lease documents should clarify responsibility for capital cost, maintenance and energy use.
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