A plain-language reference for the core ideas behind a chilled-water plant: what the numbers mean, what you can control, and where the energy goes.
How much heat a chiller can move — not how much electricity it uses.
Cooling capacity is measured in tons of refrigeration (TR). One ton is a fixed amount of heat-removal rate:
So a 100 TR chiller can pull 351.7 kW of heat out of the building every second.
Two ways of expressing the same idea: heat moved per unit of electricity.
Electricity consumed per ton of cooling produced.
Meaning: it takes 0.70 kW of electricity to make 1 TR of cooling.
Cooling output divided by electrical input (both in kW), so it's a pure ratio with no units.
Meaning: every 1 kW of electricity produces about 5 kW of cooling.
A typical at-a-glance view, and the vocabulary behind it.
| Term | Unit | What it means |
|---|---|---|
| Plant cooling capacity | TR | Maximum heat the plant can remove |
| Plant power consumption | kW | Electricity the plant draws right now |
| Plant efficiency | kW/TR | Electricity per ton of cooling (lower = better) |
| kW (thermal) | kW | Heat — 1 TR = 3.517 kW |
| kW (electrical) | kW | The electricity the chiller draws to move that heat |
| Cooling load | TR / kW | The heat the building currently needs removed |
| ΔT (delta-T) | °C | Difference between return and supply chilled water |
| Flow rate | L/s | How much water is being circulated |
| CHWR | °C | Chilled-water return — warm water coming back from the building |
| Pump power | kW | Electricity used by the circulating pumps |
Control levers can be set manually or by an AI optimizer; environment and demand are given.
Pump speed
CHWS setpoint (chilled-water supply temperature)
Cooling-tower fan speed
Cooling load (building heat)
Outdoor wet-bulb temperature
The chiller absorbs the building's heat and its own compressor's electrical work, then rejects the sum. For a 100 TR chiller drawing 70 kW:
Where the electricity goes, and the knobs that move the numbers.
The chiller itself contains the evaporator, compressor and condenser. Of the whole plant, the compressor dominates the electricity bill, which is why anything that eases the compressor's job (lower lift, better staging) saves the most.
(1) the chilled-water loop from the AHU, and (2) the condenser-water loop in and out of the cooling tower.
Colder condenser water lowers the compressor's lift and its power. These factors control it:
In rough order of impact for most plants.
How heat travels from the rooms all the way out to the sky.
The building generates heat (people, machines, sunlight). The AHU fan pulls that warm air across a cooling coil; cold water inside the coil absorbs the heat, so cool air returns to the rooms and the water leaves warm. The CHW pump sends that warm water to the chiller's evaporator, which chills it again — the difference between leaving and returning water is ΔT.
Inside the chiller, the compressor moves the absorbed heat from the evaporator to the condenser. Condenser water flowing through (driven by the CW pump) absorbs that heat and carries it to the cooling tower, which releases it to the atmosphere. Then the cycle repeats.