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Specify a rotary heat exchanger when the airflow is large, the duct static pressure is high, or the exhaust is dirty or hot; specify a heat pipe heat exchanger when you need a compact, low-resistance installation that consumes no power — rotary recovers up to 75% of the thermal energy in the exhaust and the ROT-HRW rotor is rated at 79% efficiency at 3.5 m/s and 170 Pa, while a heat pipe exchanger moves heat by gravity with no moving parts, no energy consumption and effectively no maintenance cost.

The underlying mechanism is completely different

These two technologies look interchangeable on a schedule and behave nothing alike. Understanding the mechanism is the fastest way to the right choice.

Rotary — a moving heat-storage matrix

The rotary heat exchanger works like this: the rotor turns continuously at 10 rpm and acts as a heat-storage or cold-storage core. Fresh air passes through one half of the unit while exhaust air passes counter-currently through the other half. The exhaust air releases its heat into the core, and as the rotor turns to the fresh-air side it gives that heat up to the cooler incoming air.

In the total-heat type rotor, moisture transfer happens at the same time. The moisture separated from the airstream enters the moisture-absorbing coating of the heat-storage core and is released when the rotor turns to the other air stream. The recovery efficiency can reach over 75%, reducing the cooling and heating load and the power consumption of the air-conditioning or boiler operation.

Heat pipe — a sealed, gravity-driven working fluid

A heat pipe heat exchanger generally adopts a gravity heat-pipe configuration. When the hot end — the evaporator section — of the gravity heat pipe absorbs heat from the hot airflow passing through it, the high-saturation vapour generated by the volatile liquid inside the pipe flows toward the cold end, the condenser section. The cold airflow absorbs the heat released by the vapour and causes it to condense, and the resulting condensate returns to the hot end.

There is no fan, no motor and no pump anywhere in that description. The working fluid circulates because of gravity and phase change.

Head-to-head comparison

Rotary heat exchanger vs heat pipe heat exchanger

Where each one wins

Choose rotary when

The airflow is large. A single rotary unit can cover 15,000 m³/h and beyond where a plate core would need to be split into multiple sections.

The duct static pressure is high. The rotary core is designed for high-pressure ductwork, where a plate core would need to be much heavier.

The exhaust is dirty or particulate-laden. A rotary matrix tolerates fouling far better than a fine-pitch plate core.

You need moisture recovery. The total-heat rotor transfers latent heat as well as sensible heat, which a heat pipe cannot do.

The exhaust is hot. The ECW high-temperature rotor tolerates exhausts above 120°C, up to 300°C, with cores in magnesium-aluminium alloy or stainless steel foil.

Choose a heat pipe when

You want zero energy consumption. The device contributes nothing to the electrical load and there are no moving parts to wear out.

Installation space is tight. The section fits inside an AHU or a fresh air ventilator rather than needing its own unit footprint.

The exhaust is corrosive or dusty. Copper tube and aluminium fin with a zero-spangle galvanized frame gives better corrosion resistance and effective condensate drainage.

The exhaust is cool and clean. Since a heat pipe transfers sensible heat only, there is little point paying for latent recovery on a dry airstream.

And where the plate exchanger still wins

It would be a mistake to treat this as a two-way choice. The plate heat exchanger remains the default for clean exhaust and anywhere cross-contamination control matters, because it has no moving parts at all and separates the two streams completely. The plate heat exchanger selection guide sets out that decision in detail.

Three-way summary — when to use which core

Published data for both

ROTER rotary heat exchanger — published engineering data

ROTER heat pipe heat exchanger — published structural features

One detail in the heat pipe data deserves emphasis, because it is often overlooked: the unit can also be specified with the evaporator and condenser sections arranged horizontally on either side of the AHU evaporator — the U-type arrangement — connected by copper tubes. Where the coil length exceeds 1.5 m there is at least one central support point, and all cooling coils are mounted on sliding bases so the coil can be drawn out of the unit for external maintenance.

Frequently asked questions

What is the difference between a rotary and a heat pipe heat exchanger?

A rotary heat exchanger uses a rotating heat-storage matrix: the rotor turns at 10 rpm, the exhaust air gives up its heat to the matrix, and the matrix gives it up to the incoming fresh air as it turns. A heat pipe heat exchanger uses a sealed tube containing a volatile working fluid that evaporates at the hot end and condenses at the cold end, moving heat by gravity and phase change. One has moving parts and can also transfer moisture; the other has no moving parts and transfers temperature only.

Which is more efficient?

On a like-for-like duty the rotary is generally the more capable technology: it recovers up to 75% of the thermal energy in the exhaust, and the ROT-HRW rotor is rated at 79% efficiency at 3.5 m/s face velocity and 170 Pa. The total-heat rotor additionally transfers moisture. A heat pipe exchanger has no published rotary-equivalent figure, but it has the advantage of consuming no energy at all, which changes the running-cost comparison considerably.

Which one handles high-temperature exhaust?

The rotary. The ECW type high-temperature rotor withstands exhausts up to 300°C, with the heat-storage core made of magnesium-aluminium alloy or stainless steel foil and a load-bearing steel-plate casing welded inside and out and insulated. A heat pipe exchanger is not suitable for high-temperature duty, though a plate heat exchanger in Series G construction is rated to the same 300°C.

Which is better for a dirty or dusty exhaust?

The heat pipe. Its copper-tube and aluminium-fin structure gives low air resistance, effective condensate drainage and higher corrosion resistance than a rotary matrix, and it has no moving parts that can foul. If moisture recovery is also required, the comparison is closer and the total-heat rotor becomes the stronger option.

Does a heat pipe heat exchanger use electricity?

No. There are no moving parts and no energy consumption, so the device itself contributes nothing to the electrical load. This is the basis of the fast payback usually quoted for this type of exchanger. The fans in the associated AHU still use power, of course — only the heat transfer device is passive.

Can these be used in a combined air handling unit?

Yes, and that is a primary use case. The heat pipe heat exchanger is widely installed in combined air handling units, where it not only recovers energy from the return air but also provides dehumidification and reheat functions according to the functional configuration. It can also be connected directly to the air duct, or installed horizontally inside a fresh air ventilator.

How do I get a quotation and selection?

Send us the airflow, static pressure, exhaust temperature and composition, and the outdoor and indoor design conditions. ROTER returns the sizing calculation, a model selection with the efficiency at your conditions, and a quotation — normally within 24 hours.