System Type
Chillers
Oversized chillers built from DX refrigerant circuits short cycle at part load, tripping nuisance alarms and lockouts and never holding a steady chilled-water temperature. Rawal Devices modulates each DX circuit to the real load, for chilled-water-like part-load performance without replacing the plant.
Two ways to modulate a chiller
A chiller can use either the mechanical APR Control or the electronic APR‑E Valve. The right choice depends on how precise the leaving-water temperature control must be for the job, which is why the best next step is to talk to a Rawal Devices Engineer for the selection.
Chilled-water performance on DX
Chiller dreams on a DX budget.
What It Covers
This applies to chillers built from DX refrigerant circuits. The APR Control works on air-cooled and water-cooled chillers with reciprocating or scroll compressors, and on screw compressors in some cases. Modular chillers, which combine multiple DX circuits, are a sweet spot. It does not apply to centrifugal chillers.
The Problem At Part Load
An oversized chiller rarely sees full load. At part load its DX circuits short cycle, throwing low-pressure and low leaving-water-temperature alarms, tripping nuisance lockouts, and struggling to hold a steady chilled-water temperature.
Runs Instead of Cycling
Each DX circuit modulates to the real load, so the chiller runs steadily at part load rather than cycling on and off.
Ends the Lockouts
Steady operation holds leaving-water temperature and clears the low-pressure and low-leaving-water alarms behind the nuisance lockouts.
Proof: A Modular Chiller In Washington D.C.
A Japanese restaurant in Washington D.C. ran a badly oversized modular chiller, four 30-ton compressors, 120 tons total, short cycling with low-pressure and low-leaving-water-temperature alarms and lockouts. An APR Control on each circuit modulated it from 30 tons down to 10, about 67% turndown. The short cycling and lockouts stopped, and the owner avoided a costly rebuild of storage tanks, pumps, and re-piping.