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What a tired chiller plant costs in the UAE
Most chiller plants in the Gulf were commissioned well and then left alone. We costed the drift for a 1,000-ton plant.
US$120,000
a year from the same chillers, run better
- 1,000,000 kWhof electricity saved each year
- 404 tof CO₂e avoided each year
The problem
In the UAE, cooling makes up about 60% of national peak electricity demand, and close to 70% in Dubai. Most of that cooling comes from chiller plants in malls, offices, hotels and district cooling networks.
A plant is usually efficient on the day it is handed over. Then the years go by. Condenser tubes foul. A setpoint gets changed to stop a complaint and nobody changes it back. Chillers start in whatever order the building management system was set up with, which may not be the order that uses the least power. A plant designed for 0.8 kW per ton of cooling ends up drawing 1.05.
We took a 1,000-ton plant cooling all year, about 4,000 equivalent full-load hours, on DEWA's top commercial slab plus the fuel surcharge.
The working
Each line follows from the one before it. The inputs and their sources are listed further down, so you can redo it with your own numbers.
Electricity per ton of cooling
1.05 kW per ton
Today
0.80 kW per ton
After tuning
The efficiency gap
efficiency today − efficiency after tuning
= 1.05 − 0.80 kW per ton
= 0.25 kW per ton
Electricity saved
capacity × full-load hours × gap
= 1,000 tons × 4,000 h × 0.25 kW
= 1,000,000 kWh a year
Money
electricity saved × (tariff + fuel surcharge) ÷ exchange rate
= 1,000,000 kWh × (AED 0.38 + AED 0.06) ÷ 3.6725
= US$119,809 a year
Carbon
electricity saved × DEWA grid intensity
= 1,000,000 kWh × 0.4041 kg CO₂e/kWh
= 404 t CO₂e a year
The fix
None of this needs new chillers. Most of the gap closes in the controls, by sequencing the chillers so each one runs near its best load and letting the condenser water temperature fall when the weather allows. The rest comes from cleaning the tubes on a schedule instead of when someone complains.
The data to find the gap usually sits in the building management system already, logged every few minutes and rarely read. We pull a few months of it, work out the plant's real kW per ton hour by hour, and compare that with what the equipment should manage at the same load and weather. The difference is the saving, and it shows which change wins most of it.
What would change the answer
Tariff slabs and the fuel surcharge change from month to month, so check your own bill. Plants with newer chillers or variable primary flow may already be closer to 0.8.
A hotter year adds cooling hours and raises the figure.
Inputs and sources
- Chiller plant capacity1,000 tons of coolingAssumption for a typical site
- Equivalent full-load hours4,000 h a yearAssumption for a typical site, cooling all year
- Plant efficiency today1.05 kW per tonAssumption for a typical site, ageing water-cooled plant
- Plant efficiency after optimisation0.8 kW per tonAssumption for a typical site, sequencing, condenser water reset, cleaning
- DEWA tariff, top slab0.38 AED/kWhDEWA slab tariff
- DEWA fuel surcharge0.06 AED/kWhDEWA; varies monthly
- AED per USD3.6725 AED/USDUAE dirham peg
- DEWA grid carbon intensity0.4041 kg CO₂e/kWhDEWA Climate Change Report 2021
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