Symptom - Falling Effectiveness

• Cause: fouling or airstream leakage
• Fix: clean the core; reseal interfaces; verify duct connections

Symptom - Rising Pressure Drop

• Cause: dust, grease, or frost buildup
• Fix: clean the core; check frost strategy in winter

Symptom - Frost on Core

• Cause: defrost not triggering or set too high
• Fix: lower the defrost setpoint; confirm preheat or bypass works

Symptom - Wheel Noise or Vibration

• Cause: belt, bearing, or seal wear
• Fix: inspect and replace per schedule; re-balance the wheel

Symptom - High Humidity Indoors

• Cause: enthalpy wheel or membrane under-performing
• Fix: verify latent rating; check media condition; confirm rotation

Three Controls That Matter

Recovery units need more than a fan. The right controls protect the core and maximise savings.

Summer Bypass

When no recovery is wanted (free cooling or mild weather), a bypass diverts air around the core so the coil does the work.

Frost Protection

In cold climates, preheat, timed bypass, or recirculation keeps the exhaust above freezing. Set the trigger from the real minimum temperature.

Modulation

Variable-speed fans and wheel speed match recovery to demand, avoiding over-recovery that wastes fan energy.

Alarms

Monitor pressure-drop trend and supply-air temperature; a rising drop or falling effectiveness signals fouling or leakage.

The Building

A school in a hot, humid climate, 8,000 m3/h exhaust, cooled most of the year, dehumidification is the main load.

Step 1 - Duty

Supply and exhaust 8,000 m3/h, outdoor 34 C at 80 percent RH, indoor 24 C at 50 percent RH.

Step 2 - Technology

Choose a rotary enthalpy wheel: it recovers both temperature and moisture, cutting the dehumidification load.

Step 3 - Size

Target 75 percent sensible and 65 percent latent. This removes a large share of the coil's moisture load.

Step 4 - Result

Cooling and dehumidification energy drop markedly; the wheel's motor energy is small versus the saved coil load.

The Building

A refrigerated warehouse, -25 C inside, frequent door traffic, warm make-up air needed for defrost and personnel doors.

Step 1 - Duty

Make-up air 6,000 m3/h, outdoor summer 30 C, indoor -25 C; the load is refrigeration, not heating.

Step 2 - Technology

Plate core sized for low face velocity, with a defrost strategy for the cold intake.

Step 3 - Frost

Below -2 C exhaust dewpoint, add a preheat coil or timed bypass set from the coldest week, not the average.

Step 4 - Result

Pre-cooling incoming air trims refrigeration energy by 10 to 25 percent depending on door traffic and climate.

The Building

An older office, 10,000 m3/h constant-volume exhaust, heated winters, no recovery. Goal: cut the ventilation heating load cheaply.

Step 1 - Duty

Supply and exhaust both 10,000 m3/h, outdoor winter -5 C, indoor 21 C, desired supply at least 16 C.

Step 2 - Technology

Choose a crossflow plate core: simple, low maintenance, no humidity need in this climate.

Step 3 - Size

Target 70 percent effectiveness. At 20 K difference that recovers about 46 kW of heating load.

Step 4 - Fan Check

Confirm the existing fan can handle the added ~120 Pa. If not, plan a fan upgrade.

Step 5 - Result

Ventilation heating load cut by roughly two-thirds; payback within a few heating seasons.

What the Calculator Does

The sizing calculator turns four inputs into recovered power, effectiveness, and payback: supply airflow, exhaust airflow, indoor and outdoor temperatures, and run hours.

Inputs You Need

• Supply and exhaust airflow in m3/h or cfm
• Outdoor winter and summer design temperatures
• Indoor setpoint and allowable supply-air temperature
• Electricity price and annual operating hours

How It Computes

Recovered power Q = m_dot x cp x DeltaT x effectiveness. The tool then multiplies by run hours and price to show annual saving and simple payback.

Using It Well

• Enter part-load average airflow, not peak, for realistic savings
• Add the extra fan energy from pressure drop
• Compare plate, rotary, and heat pipe side by side

Verify

Treat calculator output as a screen; confirm the final choice against an EN 308 or AHRI 1060 rating at the operating point.

Why a SOP

A fouled core loses effectiveness and raises fan energy. A written procedure keeps performance up and warranty valid.

Annual Inspection

• Record supply-air temperature and pressure drop as baseline
• Inspect the core for dust, grease, or condensate buildup
• Check rotary seals, belt, and bearings if fitted

Cleaning Steps

1. Switch the unit off and lock out power
2. Remove filters and vacuum loose dust from the core faces
3. Wash with low-pressure water and a neutral cleaner; never use high pressure that bends foils
4. For greasy exhaust, use a degreaser suited to the media
5. Rinse, dry, and refit; confirm drainage is clear

Rotary Wheels

Clean the media per the manufacturer schedule, inspect seals, and verify the drive. Log every service with the date and readings.