Recovery Is Part of the AHU

Modern air-handling units treat recovery as a built-in module, not a bolt-on. Selecting the right integrated recovery means matching the core or wheel to the unit's airflow, static budget, and control scheme.

Selection Inputs

• Design airflow - supply and exhaust, ideally balanced
• Static pressure budget - what the fans can deliver after the core
• Effectiveness target - set by the energy or code requirement
• Control integration - summer bypass, frost, modulation

Module Choices

Verify

Confirm the module rating at the unit's actual face velocity and that the combined unit meets the fan and frost-control requirements.

Before Installation

• Confirm the core fits the AHU section with clearance for seals
• Verify duct connections align with the core ports
• Plan condensate drainage for sensible cores in cooling mode

During Installation

• Seal all interfaces to prevent airstream leakage
• Support the core to avoid stress on the frame
• For rotary wheels, align the drive and check the seals

Controls

Wire summer bypass, frost protection, and alarms per the manual. Mis-wired frost control is the top cause of winter failure.

After Installation

Balance airflow, commission, and record baseline temperatures and pressure drop for future troubleshooting.

The Design Point Is Not Reality

Equipment runs most hours at part load, not at the rated condition. Sizing only at the peak point overstates savings.

How to Size for Real Use

• Build a load profile across the year (bin method or hourly)
• Compute recovered energy at each load step, not just the peak
• Weight by annual operating hours to get true savings

Effectiveness at Part Load

Effectiveness rises as face velocity falls, so part-load operation is often more effective than design. The fan energy, however, falls too - net the two for a realistic payback.

Verify

Ask for the effectiveness curve, then integrate it over your actual profile instead of quoting a single percentage.

Why Material Matters

The plate material sets cost, corrosion resistance, hygiene, and whether the core can carry moisture.

Options

Selection Criteria

• Airstream corrosiveness (chlorine, grease, chemicals)
• Hygiene rules (food-grade, cleanable)
• Budget and lifecycle cost

What the Media Does

The wheel media stores and releases both heat and moisture. Its coating decides how much water vapour transfers and how the wheel ages.

Media Types

• Aluminium (sensible) - no moisture transfer, lowest cost
• Molecular-sieve coating - strong latent transfer, durable
• Desiccant paper - high moisture uptake, needs careful humidity control
• Polymer / hybrid - corrosion-resistant, good for harsh air

Selection Criteria

• Required latent effectiveness at your humidity ratio
• Air cleanliness (corrosive or particulate loads)
• Pressure drop and wheel depth trade-off

Verify

Use the Eurovent or AHRI 1060 certified latent effectiveness at your operating point, and confirm the media is rated for your airstream.

Step 1 - Audit the Duty

Record supply and exhaust airflow, indoor and outdoor design temperatures, and the allowable supply-air temperature. Confirm the streams are reasonably balanced.

Step 2 - Pick the Technology

• Simple, low-maintenance - crossflow plate core
• Highest effectiveness or humidity - rotary wheel
• Contaminated or separated streams - run-around coil
• Rugged, no moving parts - heat pipe

Step 3 - Check the AHU

• Physical space in or beside the unit
• Fan capacity for the added static pressure
• Controls for summer bypass and frost protection

Step 4 - Install

Slot the core into the AHU section, seal the interfaces, connect controls, and verify drainage for condensate.

Step 5 - Commission

Measure airflow and temperatures on both sides, compute actual effectiveness, and compare with the rated curve. Document the result as the baseline.

The Fluid Does the Work

A heat pipe transfers heat through evaporation and condensation of a sealed working fluid. The fluid must stay liquid at the cold end and vapour at the hot end across your operating range.

Common Fluids

Selection Criteria

• Operating temperature - pick a fluid whose range brackets your duty
• Freeze risk - for sub-zero, use ammonia or a low-temp refrigerant
• Compatibility - fluid must not corrode the tube wall
• Pressure - vapour pressure at hot end must stay safe

Watch-out

Mismatched fluid is the most common heat-pipe failure. Specify the fluid from the coldest and hottest expected temperatures, not the average.

Why Counterflow

In a counterflow core the streams run in opposite directions, so the cold outgoing air meets the coldest part of the incoming stream. This squeezes out more energy than crossflow - typically 70 to 75 percent versus 60 to 65 percent sensible.

Customization Levers

• Plate spacing - tighter spacing raises area but also pressure drop
• Pass arrangement - number of counterflow passes and port layout
• Material - aluminium, polymer, or coated foil per duty
• Core depth - deeper core at lower face velocity lifts effectiveness
• Port size and position - match the AHU ductwork

When to Customize

Custom counterflow cores suit passive-house, low-temperature heating, or tight space where every point of effectiveness counts. For standard commercial jobs, a stock crossflow core is usually sufficient.

Verify

Confirm the customized core rating at your face velocity, not the catalogue nominal, and check the pressure drop against the fan.

Two Forms of Energy in Air

Air carries energy as dry-bulb heat (sensible) and as water vapour (latent). A sensible exchanger moves only temperature; an enthalpy exchanger moves both. The choice changes the whole system design.

Deep Selection Logic

• Dry or cold climate - sensible recovery is usually enough; moisture is not the bottleneck
• Hot, humid climate - latent load dominates; choose enthalpy recovery
• Mixed climate - check the cooling-coil load with and without moisture recovery

How to Quantify

Compute the latent load as the mass of condensate the coil must remove. If that load is large, enthalpy recovery (rotary wheel or membrane plate) typically halves dehumidification demand and shortens payback.

Decision Rule

If the humidity-ratio difference between streams is small, a sensible plate core is the cost-effective choice. If it is large and the cooling coil is oversized, move to enthalpy recovery.

Why Defrost

When exhaust air drops below freezing, frost forms on the core and blocks it. Several strategies exist; pick by climate and device.

Strategies

Selection Note

Set the strategy from the coldest expected outdoor temperature, not the annual average, or the core ices up during the worst week.