Busting Four Myths About Absorption Cooling


Absorption chillers have been around for more than 75 years, with several thousand chillers operating successfully all over the world today. Yet myths about cost, operation and performance surround this technology, particularly in North America. Look beyond the myths and you’ll discover absorption cooling technology can be efficient, cost-effective, flexible and reliable.

YORK double-effect, direct fired absorption chiller

A YORK® double-effect, direct fired absorption chiller.

 

Myth 1: Absorption Chillers are Inefficient

The facts say otherwise. In the right applications, these chillers can be more cost-effective.

The coefficient of performance (COP) for an electric chiller is typically 6 to 6.5; for an absorption chiller, it can range from 0.7 to 1.4. Some people automatically rule out absorption chillers because of this huge difference — but it’s not an apples-to-apples comparison because:

  • COP is calculated differently for the two chiller types: An electric chiller is driven by electricity purchased from the grid, while an absorption chiller is driven by available waste heat or low-cost natural gas.
  • The electric chiller’s COP does not account for losses of 60 to 70 percent in electricity generation, transmission and distribution process.

In short, COP alone is not a sufficient basis for comparison. For example, let’s use the typical chiller COP values:

  • Electric centrifugal chiller: 6.50
  • Direct natural gas-fired absorption chiller: 1.20
  • Double-effect steam absorption chiller: 1.40
  • Single-effect steam absorption chiller: 0.70

And looking at typical operating costs based on cents/ton-hours assuming that natural gas is $5/MMBTU, electricity is $0.15/kWh, and steam is $4 per 1,000 lb.:

  • Electric centrifugal chiller: 8.12
  • Direct natural gas-fired absorption chiller: 5.00
  • Double-effect steam absorption chiller: 3.43
  • Single-effect steam absorption chiller: 6.86

It turns out the chiller with the highest COP — the electric chiller — does not necessarily yield the lowest operational cost. The direct gas-fired absorption chiller and the two-stage steam chiller are more appropriate choices.

Of course, utility costs vary and, in many cases, an electric chiller makes more sense. The point is that it’s worth considering absorption chillers, especially if electricity costs are high or rising, demand charges are in effect, or natural gas and waste heat costs are low. For example, here are a couple of applications where an absorption chiller makes sense:

  • A commercial building in New York City where the absorption chiller runs from 8 a.m. to 8 p.m., Monday through Friday, April to September.
  • A hybrid application where the absorption chiller runs during the day and the electric centrifugal chiller runs at night.

 

Myth 2: Absorption Chillers are Expensive

This is not always the case. In the right applications, they can deliver the highest payback.
Absorption chillers may be the most cost-effective option considering utility costs and the availability of waste heat. Even without waste heat, absorption chillers can use low-cost natural gas as an energy source. With these factors, as well as initial capital expense and COP, you will find that absorption chillers deliver a higher payback compared to chillers driven by electricity.

 


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