Air Cooled Chiller Evaporators Explained
Holden Shamburger
Air Cooled Chillers
3 minute read
Evaporators can range a bit on air cooled chillers.
There are several options available to choose from.
The compressor being used, size of system, efficiency target, and pricing decide which is the better choice.
Let’s start with the least common of all.
A tube in tube evaporator is a small and cheap option.
You will find these in mostly older process chillers.
Not the most efficient but can maintain an 8-10F approach.
These are literally a big tube with a smaller tube inside to separate the water & refrigerant.
Second is a braze plate.
These are great because they are small heat exchangers for their tonnage.
They don’t scale very well before their to big and expensive compared to others.
It is several stainless steel plates brazed together with internal chambers that separates the water from refrigerant. Even circuit from circuit.
An 8-10F approach is normal at high loads.
The third on our list is DX shell & tube.
The DX stands for direct expansion. This is the way we differentiate it from the other shell & tube options we'll get to in a second.
These are large steel cylinders with copper tubes inside.
This style the water is on the shell side and refrigerant is in the tubes.
These are very cost effective for larger tonnage machines but lack the efficiency of its counterparts.
Expect 8-10F approach with these at high loads.
The fourth is flooded.
This is in the shell & tube family.
It is built just like its DX brother but the refrigerant is on the shell side and the water is in the tubes.
How I find it easy to tell them apart is the piping.
Flooded the refrigerant piping connects on the side of the shell and the water pipes connect at the end bell/waterbox. A DX would be the opposite.
The liquid refrigerant in these will be enough to cover the tubes.
Typically the top of the shell is open cavity for suction gas.
.5-3F approach is typical at high loads. Great heat transfer efficiency.
The fifth and final is falling film.
The other brother in the shell & tube family.
These work very similar to a flooded with a couple of changes.
There is less refrigerant needed because we don’t fully submerge the tubes.
Part of the tubes will be submerged but not all.
We achieve very similar efficiency as flooded with less refrigerant.
You can tell them apart from a flooded by where the metering device feeds into the evap.
If on top then falling film, if on bottom then flooded.
Just like flooded, a .5-3F approach with load is expected.
These are the main types of evaporators used on air cooled chillers.
MTT
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