Absorption Chiller vs Electric Chiller: Annual Energy Cost Calculator

This calculator compares the annual energy and water cost of a gas-fired Thermax absorption chiller with an electric chiller of the same cooling capacity. With the default settings (1,000 kW, air conditioning 5 months a year, electricity at RUB 7.5 per kWh, gas at RUB 8.5 per m³), the electric chiller costs RUB 3.19 million a year and the absorption chiller RUB 1.01 million, including cooling tower make-up water. The difference is RUB 2.18 million, or 68%.

It is useful when a site has gas and the question is whether an absorption chiller is worth looking at at all. The calculator answers that in a minute and shows how every figure is derived. How the machine works and where it fits, I covered in What Is an Absorption Chiller.

The calculator works in Russian rubles (RUB), with Russian tariffs as defaults. Enter your own prices to see your own result.

How do I use the calculator?

1. Pick a mode. "Air conditioning" is 5 months a year at 12 hours a day. "Industrial process" is 12 months at 24 hours. The mode changes only months and hours; load is set separately.

2. Enter the cooling capacity in kW and the prices of electricity, gas and make-up water. Type a number or move the slider.

3. Set the average load in percent. The default is 70%: a machine rarely runs a whole season at full capacity.

4. Under "Coefficients and operating mode" you can change the COP of both machines, the gas calorific value, the specific tower make-up, and the number of months, hours and days.

5. If you are comparing with a water-cooled chiller, tick "Electric chiller also uses a cooling tower". Otherwise it is treated as air-cooled and uses no water.

6. Read the cost cards, the bar chart and the green savings panel. The "How each figure is derived" block breaks the calculation down step by step.

What assumptions are built into the model?

Operating hours = months × days per month × hours per day. Air conditioning gives 5 × 30.4 × 12 = 1,824 hours a year, industrial process 12 × 30.4 × 24 = 8,755 hours.

Annual cooling = capacity × load × operating hours. Average capacity is used, not peak.

Electric chiller. Electricity = cooling ÷ COP. The default COP is 3.0: 1 kWh of electricity gives 3 kWh of cooling. Cost = electricity × tariff. If the chiller has a cooling tower, the tower takes the cooling load plus compressor work: cooling × (1 + 1 ÷ COP).

Gas-fired absorption chiller. Driving heat = cooling ÷ thermal COP of 1.4. Gas = heat ÷ calorific value of 9.3 kWh/m³. The tower takes both the cooling load and all the driving heat: cooling + driving heat. This is why an absorption chiller uses noticeably more water than a water-cooled electric chiller.

Water. Make-up = heat to the tower × 1.8 L/kWh ÷ 1,000. That is about 1.5 L of evaporation plus blowdown. Water costs RUB 45 per m³, water supply only, without sewerage charges.

Savings = annual cost of the electric chiller − annual cost of the absorption chiller. Share = savings ÷ electric chiller cost.

Default parameter	Value
Cooling capacity	1,000 kW
Electricity	RUB 7.5 per kWh
Gas	RUB 8.5 per m³
Make-up water	RUB 45 per m³, excl. sewerage
Load	70%
Electric chiller COP	3.0
Absorption chiller thermal COP	1.4
Gas calorific value	9.3 kWh/m³
Cooling tower make-up	1.8 L per kWh of heat rejected

Reduced to one kilowatt-hour of cooling at these tariffs, the electric chiller spends RUB 2.50, the absorption chiller RUB 0.65 on gas and RUB 0.14 on water, RUB 0.79 in total.

What does a worked example look like?

"Air conditioning" mode, 1,000 kW, everything else at default.

1. Hours: 5 × 30.4 × 12 = 1,824 h. Average capacity: 1,000 × 70% = 700 kW. Annual cooling: 700 × 1,824 = 1,276,800 kWh.

2. Electric chiller: 1,276,800 ÷ 3 = 425,600 kWh. At RUB 7.5 that is RUB 3,192,000 a year. The chiller is air-cooled, no water.

3. Absorption chiller: driving heat 1,276,800 ÷ 1.4 = 912,000 kWh. Gas: 912,000 ÷ 9.3 = 98,065 m³, or RUB 833,548.

4. Absorption chiller tower: 1,276,800 + 912,000 = 2,188,800 kWh of heat. Make-up: 2,188,800 × 1.8 ÷ 1,000 = 3,940 m³, or RUB 177,293.

5. Absorption chiller total: 833,548 + 177,293 = RUB 1,010,841. Savings: 3,192,000 − 1,010,841 = RUB 2,181,159, or 68%.

If the electric chiller is also water-cooled, it rejects 1,702,400 kWh and uses 3,064 m³ of water for RUB 137,894. Savings rise to RUB 2,319,053, or 70%.

In "Industrial process" mode the same 1,000 kW runs 8,755 hours. The electric chiller costs RUB 15.32 million a year, the absorption chiller RUB 4.85 million (RUB 4.00 million of gas and RUB 0.85 million of water), and the savings are RUB 10.47 million.

What are the limitations?

This is an energy cost calculation, not a cost of ownership.

• Machine prices, installation, cooling tower and grid connection are not included. Capital cost for an absorption chiller with its tower and for an electric chiller differs, so payback is calculated separately.

• Electricity for pumps, tower fans and absorption chiller auxiliaries is not included for either machine.

• COP is constant all year and at any load. In reality it changes with outdoor temperature and load.

• A COP of 3.0 corresponds to an air-cooled chiller. If you compare with a water-cooled one, enter its COP: it is noticeably higher, and the absorption chiller's savings shrink.

• Sewerage charges are not included in the water price.

• The calculator does not check gas supply limits or connection. Without gas on site, the comparison does not apply.

FAQ

At what gas price does the absorption chiller stop paying off?

By the calculator's formulas, with everything else at default, costs are equal at a gas price of about RUB 30.7 per m³. If electricity changes instead, the break-even point is about RUB 2.38 per kWh: below that, the electric chiller is cheaper. Enter your own tariffs and the savings panel shows which machine wins.

Why is the absorption chiller's COP 1.4 and the chiller's 3? Does that make it worse?

These are different ratios. The thermal COP of an absorption chiller shows how much cooling it gives per 1 kWh of heat from gas. A chiller's COP shows how much cooling it gives per 1 kWh of electricity. At the default tariffs, a kilowatt-hour of heat from gas costs about RUB 0.91 (8.5 ÷ 9.3), while a kilowatt-hour of electricity costs RUB 7.5. So the lower ratio still produces the lower bill.

Why does the absorption chiller use more water?

Its cooling tower rejects both the cooling load and all the driving heat. In the example above that is 2,188,800 kWh against 1,702,400 kWh for a water-cooled chiller, hence 3,940 m³ of make-up against 3,064 m³.

Does the calculator include equipment cost?

No, only annual gas, electricity and water costs. Capital cost, installation, grid connection and the 10-year cost of ownership are covered by the four cooling options calculator. What makes up lifetime cost, I covered in Chiller Total Cost of Ownership.

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