Chilled water and air systems
HVAC is usually the largest controllable load in a hospital and the one with the most clinical risk. Measure the plant, fix control faults first, then upgrade equipment.
Last reviewed: November 5, 2026. Informational guidance written by Tariq Khurshaidi; see the terms of use.
Matching tools: chilled water efficiency, chiller retrofit sheet, AHU fans sheet, pump VFD sheet.
Who owns it
The plant or MEP manager owns the work, with the controls contractor, the infection prevention team (for any air-side change), and clinical leaders for areas that cannot lose conditioning, such as operating rooms, pharmacy compounding, isolation rooms and the sterile processing department.
Data you need first
- Plant kW per ton measured over at least a month: chiller, chilled water pump, condenser water pump and cooling tower fan power, with cooling delivered (flow and delta-T).
- BMS trend logs for supply and return temperatures, valve and damper positions, static pressure, and schedules.
- Zone pressure and air change data for every area governed by ASHRAE 170, from the latest commissioning or balancing report.
- Equipment age and refrigerant type for each chiller, because refrigerant rules affect replacement timing.
Sequence
- Fix control faults first. Simultaneous heating and cooling, stuck dampers and valves, failed sensors and overridden schedules are cheap to fix and often account for double-digit savings. Prove each fix with before and after trends.
- Measure plant efficiency and compare with typical ranges. The chilled water calculator gives kW/ton, COP and a read on whether to investigate or leave alone.
- Sequence chillers on measured efficiency, not habit. Use chilled water supply temperature reset and condenser water reset where the load and the dehumidification needs allow it.
- Add VFDs to pumps and fans where the load varies, and remove throttling valves that waste the saving. Set a minimum speed that keeps required flow and airflow.
- Schedule and set back air handlers only in areas with no pressure or air change requirement, using occupancy data. Leave pressure-controlled areas to a documented clinical risk assessment.
- Then consider equipment replacement. Model the retrofit on whole-plant efficiency, with maintenance, degradation and financing in the life-cycle cost.
Worked example
A plant delivers 8,000,000 ton-hours a year at 0.85 kW/ton. A retrofit proposal promises 0.65 kW/ton on the same boundary. Electricity falls by 8,000,000 × (0.85 − 0.65) = 1,600,000 kWh/yr. At $0.15/kWh that is $240,000 a year, and at the U.S. national average grid factor of 0.348 kg/kWh about 557 tCO₂e. Check the plant first in the chilled water calculator, then test the investment in the life-cycle cost calculator and the chiller retrofit sheet.
The usual failure
Chiller savings, pump savings and air handler savings overlap, so adding them up overstates the total. Another is trusting a vendor figure measured at the chiller only, while the guarantee should cover the whole plant: chillers, pumps and tower. A third is reducing air changes or relaxing humidity in an area that looks empty on the schedule but is governed by a pressure relationship.