Chilled Water Loops
CT, MRI, linac, and high-power interventional X-ray require chilled-water supply for gradient / klystron / generator / tube cooling. The chiller / cooling-loop is the upstream constraint that gates many "scanner thermal limit" service events.
Typical specs
- Supply temp: 6–15°C depending on modality (MRI gradient cooling is typically 18–24°C; linac and CT generator cooling is colder).
- Flow: 20–50 gpm depending on equipment.
- Delta-T across equipment: ~5°C typical.
- Pressure: per-OEM-spec; typically 30–60 psi.
- Water quality: closed-loop deionized water preferred; chemical treatment (corrosion inhibitor, biocide) required for non-deionized loops.
Modality-specific cooling needs
- MRI — gradient amplifier (GPA) cooling, RF amplifier cooling, cold-head compressor (separate loop or split system). Flow alarm = stop scanning immediately; clearing the alarm and continuing risks expensive damage.
- CT — tube and HV-generator cooling. Long fluoroscopy and high-mA cardiac runs stress the loop; chiller undersizing trips thermal limits at peak load.
- Linac — klystron / waveguide cooling, target / collimator cooling. Critical safety interlock; loss of flow stops the beam.
- Interventional X-ray — tube cooling, particularly on biplane high-duty-cycle programs (cardiac, neuro long fluoro).
Failure modes
- Chiller capacity undersized → scan-time thermal limits hit during long protocols. Symptoms appear during peak load, not testing.
- Flow alarm → scanner stops (correctly). Do not bypass.
- Water quality — particulates clog heat exchangers; biological growth fouls flow paths; corrosion releases metal into the loop.
- Chiller compressor end-of-life — capacity drops over years; routine cycling tests catch it before clinical-impact failures.
Refurb / relocation gotchas
- Existing chiller may not match new equipment specs — refurb installs with different cooling demands sometimes need chiller upgrade as part of the deal.
- Loop water quality in older buildings is suspect; refurb installs benefit from closed-loop replacement when feasible.
- Climate-zone affects chiller sizing margin — hot climates push chillers harder year-round.