Gasketed plate heat exchanger in its blue frame with tie bars and flanged ports, circulation pumps in front of it

Exchanger, close — Inzonex Modular Insulation, hot-water skid

Heat exchangers / Types

Heat exchanger types

The first question is not the size. It is whether it can be opened.

Two families cover almost all hot-water duty. A plate unit stacks thin corrugated sheets and pushes the two fluids through alternate channels. A shell-and-tube unit runs one fluid through a bundle of tubes and the other around them. The plate unit transfers far more per square metre and takes a fraction of the floor. What separates the plate types from each other is not performance but whether the pack comes apart. That decides every maintenance decision made afterwards.

The two families

Plate against shell and tube

Plate

Corrugated sheets clamped between two heavy end frames, with the fluids in alternate channels. The corrugations force turbulence, so the heat transfer coefficient is several times that of a plain tube and the unit is small for its duty. It is what a hot-water plant room has.

Shell and tube

A bundle of tubes inside a cylindrical shell. Bigger and heavier for the same duty. It takes dirty fluids and high pressure differences that would close a plate channel, and it can be re-tubed rather than replaced.

Why the size matters here

A shell-and-tube unit is a large cylinder holding its charge at line temperature, with heads and a shell to insulate. A plate unit is a compact block. Its edge faces and both end frames are still hot metal standing in still air, and they are routinely left bare.

Plate types

Gasketed, brazed, welded

Gasketed

Every plate carries a gasket and the pack is held by tie bars. It can be opened, cleaned plate by plate, re-gasketed and re-tightened, and plates can be added or removed to change the duty. It is the only type that can be opened twice. It dominates building services.

Brazed

The plates are vacuum-brazed into one sealed block with no gaskets and no frame. Compact, cheap and rated for higher pressure. It cannot be opened, so when it fouls it is chemically cleaned in place or thrown away.

Welded and semi-welded

Plates laser-welded in pairs, with gaskets only between the pairs. It takes fluids that attack elastomer gaskets while still coming apart on one side. It is a specialist choice and it is priced like one.

On the skid

What the type changes for insulation

A gasketed unit will be opened

The pack is stripped for cleaning and re-gasketing on a cycle, so this is certain rather than likely. Insulation glued or wired to the frame is cut off the first time, and the unit runs bare for the rest of its life.

The tie bars are the constraint

The pack is closed by pulling the tie bars to a dimension on the nameplate. Anything that fouls a tie bar or hides the plate-pack dimension gets removed, so the module is cut clear of both.

A brazed unit has no such excuse

It is never opened, so there is nothing to work around. It is still usually found bare, because nobody made a cover for a block that shape.

Reference

Type against duty

Type	How it is held together	Can it be opened	Where it belongs
Gasketed plate	Tie bars and gaskets	Yes, plate by plate	Building services, DHW, district heating
Brazed plate	Vacuum brazed, sealed	No	Compact skids, high pressure, small duty
Semi-welded plate	Welded pairs, gaskets between	One side only	Refrigerants and aggressive fluids
Shell and tube	Bolted heads, tube bundle	Yes, and re-tubable	Dirty fluids, large pressure difference

Type · How it is held together · Can it be opened · Where it belongs

Asked about heat exchanger types

Questions.

Answers distinguish modelled heat-loss estimates from equipment selection and service guidance.

What is the difference between a plate and a shell-and-tube heat exchanger?

A plate unit stacks corrugated sheets and runs the fluids through alternate channels. A shell-and-tube unit runs one fluid through tubes and the other around them. The plate unit transfers far more heat per square metre and is a fraction of the size. Shell and tube survives dirty fluids and large pressure differences that would block a plate channel.

Can a brazed plate heat exchanger be opened and cleaned?

No. It is one vacuum-brazed block with no gaskets and no tie bars, so there is nothing to undo. It is cleaned chemically in place, and when that stops working it is replaced. If a unit will need stripping, it has to be a gasketed one.

What is a semi-welded plate heat exchanger for?

Fluids that attack elastomer gaskets. The plates are laser-welded in pairs so the aggressive fluid only ever sees metal, and gaskets sit between the pairs on the other circuit. It comes apart on one side only, and it costs accordingly.

Which type is used for domestic hot water?

A gasketed plate unit, almost always. It carries the duty in a small footprint, and it can be opened, cleaned and re-gasketed. That matters because a DHW exchanger scales and will be stripped more than once in its life.