Heat replaces shaft power as the driving input.

A refrigerant is absorbed into a solution.

A heat source separates it out again.

It then condenses and evaporates as usual.

Steam, hot water, exhaust gas or gas firing will do it.

Because a COP compares it against electrical input.

That is the wrong comparison for this machine.

The input here is heat, not electricity.

The useful question is what energy the site has spare.

Judged that way the economics can be excellent.

Where usable heat is already being rejected.

Sites running a steam main are natural candidates.

So is combined heat and power with surplus summer heat.

So is a site with constrained or expensive peak electricity.

It draws almost nothing from the incoming supply.

Because the machine rejects more heat for the same duty.

The driving heat has to leave as well as the cooling load.

An electric machine of equal capacity rejects less.

Tower and condenser water flow are sized accordingly.

This is a common oversight in early costings.

The working solution has concentrated beyond its limit.

Solid forms in the circuit and flow stops.

The machine shuts down and needs intervention.

Controls are designed to keep it inside its envelope.

It is a maintained condition, not a rare accident.

Slowly, and they prefer steady operation.

Response is not comparable to an electric machine.

Rapid cycling suits them poorly.

A stable base load is the ideal application.

Sizing should reflect that rather than peak alone.

The grade of heat each one needs.

Single-effect runs on lower-temperature sources.

That makes it suited to modest waste heat.

Double-effect requires a hotter source.

It returns appreciably more cooling in exchange.