Two plate heat exchangers seen from the side, tie bars running the full length of each frame, ports on the fixed end plates

Exchanger, port side — Inzonex Modular Insulation, hot-water skid

Heat exchangers / Cleaning

Cleaning a plate heat exchanger

It tells you it is fouled long before it stops working.

Fouling is gradual, and it announces itself in two numbers before anybody notices the building is cool. One is the temperature the secondary reaches against the primary going in. The other is the pressure drop across the unit. Those two are the condition monitoring on an exchanger, and both come off gauges that are already there.

The symptoms

What fouling looks like from outside

The approach opens up

The gap between the primary inlet and the secondary outlet is the cleanest signal there is. On a clean unit it is small and steady. As a film builds on the plates that gap widens, and it widens long before anyone complains about the hot water.

Pressure drop climbs

Fouling narrows the channel, so the same flow costs more pressure. A rising differential across the unit at unchanged pump speed is the second half of the picture. It separates a fouled unit from one that is simply undersized.

What is actually on the plates

On hot water it is usually scale from hardness, and it forms fastest on the hottest plate. On a circuit taking make-up or on an open system it is sludge and corrosion product. The strainer and the dirt separator upstream are part of the exchanger maintenance.

Clean in place

Without opening the unit

When it is enough

Scale in a closed loop that has not been left for years responds to a circulated cleaning solution. Pump it in the reverse direction to normal flow, then flush and neutralise. Nothing comes apart and the unit is back in service the same day.

When it is not

A pack with hard deposit, with a blocked channel, or with a gasket already weeping will not come back chemically. Circulating acid through a unit with a failing gasket makes the leak the next problem.

It is not a substitute for looking

Clean in place tells you nothing about the state of the plates. On a unit with a long service life the pack is opened periodically whether or not the chemistry has been keeping up.

Opening the pack

What the strip-down involves

Measure before you slacken

The closed plate-pack dimension is on the nameplate and it is what the unit gets tightened back to. It is recorded before anything is undone, because a pack closed to the wrong dimension either leaks or crushes the gaskets.

Plates come out in order

The plates alternate in orientation and they go back in the same sequence. They are numbered or marked on the edge as they come off, and they are hung rather than stacked so nothing is bent.

Then the gaskets

Gaskets are inspected and, on anything but a young unit, replaced while the pack is open. Clipped gaskets come off by hand; glued ones need the old adhesive off the groove before the new one will sit.

Closing it

Tie bars are pulled evenly, diagonally opposite pairs together, down to the nameplate dimension and no further. The pack is checked square as it closes, and it is pressure tested before it goes back into service.

The insulation part

Why a fixed cover never survives this

Everything above happens on a cycle

Strip, clean, re-gasket, close, test. Insulation that has to be cut to reach the tie bars is cut once. After that the unit runs bare and the loss is permanent.

The module comes off first and goes back last

It is cut clear of the tie bars and the nameplate. The strip-down is not slowed by it, so there is nothing to justify leaving it off.

Reference

Symptom against cause

Symptom	What it usually means	First check
Approach temperature widening	Film building on the plates	Compare with the commissioning figures
Pressure drop rising at the same flow	Channels narrowing, or a blockage	Differential across the unit, both circuits
Output falls off suddenly	Blocked channel or a strainer loaded up	Strainer and dirt separator first
Both circuits contaminating each other	Cracked plate or failed gasket	Isolate and pressure test each side

Symptom · What it usually means · First check

Asked about cleaning a plate heat exchanger

Questions.

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

How do I know if my plate heat exchanger needs cleaning?

Two numbers say it before anyone notices the building. The approach temperature - the gap between the primary going in and the secondary coming out - widens as a film builds on the plates. The pressure drop across the unit rises at unchanged flow. Either on its own is worth investigating; both together is a fouled pack.

How do you clean a plate heat exchanger?

Either in place or by opening it. In place means circulating a cleaning solution, usually in the reverse direction to normal flow, then flushing and neutralising. Opening it starts with recording the plate-pack dimension. Then slacken the tie bars, take the plates out in order and clean them individually. Re-gasket, and close back to that dimension.

What causes fouling in a heat exchanger?

On hot water it is mostly scale from hardness, deposited fastest on the hottest plate. Where the system takes make-up or is open to air it is sludge and corrosion product instead. The strainer and dirt separator upstream exist to catch that.

How tight should the plate pack be?

To the dimension stamped on the nameplate, and no tighter. That figure is recorded before anything is slackened. Tie bars are pulled in diagonally opposite pairs so the pack closes square. Over-tightening crushes the gaskets and the unit leaks as soon as it is up to temperature.