Air-to-Air Heat Exchanger

Understand how the air-to-air heat exchanger works. Explore component overviews, measurements, and additional resources.

Overview

Air-to-air heat exchangers transfer energy between two airstreams that must be at different temperatures for sensible heat transfer and different moisture contents for latent heat transfer.

In a building, an air-to-air heat exchanger can be used to recover latent or sensible heat either during the cooling or heating season. Recovering energy from the exhaust stream lessens the energy load on the air handling plant. Typical air-to-air heat exchangers include fixed plate heat exchangers and rotary wheel heat exchangers, with the former typically only recovering sensible heat.

How do I…

Quantify Electricity Usage (kWh)

The measurement strategy for an air-to-air heat exchanger is to measure the heat transfer (Btu/h) from airstream to airstream within the heat exchanger, as well as any energy consuming components associated with the heat exchanger, such as the energy wheel motor.

info Rotary Wheel

Some air-to-air heat exchanger models do not include a rotary wheel, there is no electrical consumption in those models.

Measure Motor Power Draw

Directly measure the three-phase power of the supply and return fan motors of the ERV. This measurement will also capture the hours of operations of the fan motors.

How to Measure

Click any measurement below for detailed setup, data collection, and troubleshooting instructions.

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Hourly True RMS Power Draw (kW)

Use this technique to measure the hourly three-phase power of the motor.

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Total Operating Run-time (hrs)

Use this technique to measure hourly motor runtime of the motor.

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Measurement Locations

Assess Component Performance

The performance of an air-to-air heat exchanger is determined by quantifying the thermal energy transfer across the supply and return air streams. Below is a summary of measurements needed to quantify the annual energy transfer and operating characteristics of an air-to-air heat exchanger.

Measure Air Temperature and Flow Rate

Directly measure the air temperature and relative humidity of the various air streams in the air handler. Also measure the supply air flow rate, so the data can be used to estimate how much heating or cooling is provided to the served space.

How to Measure

Click any measurement below for detailed setup, data collection, and troubleshooting instructions.

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System and Outdoor Air Relative Humidity (%)

Use this technique to measure the average hourly system and outdoor relative humidity.

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System Air Temperature (°F)

Use this technique to measure the average hourly system air temperature.

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True RMS Power Draw (kW)

Use this technique to measure the average hourly true RMS power (kW) of the supply and exhaust fan motors.

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Air Flow Rate (CFM)

Use this technique to measure the average hourly supply and return air flow rates.

Measurement Locations

Further Reading

ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 1. HVAC SYSTEM ANALYSIS AND SELECTION. I-P Edition.

ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 26. AIR-TO-AIR ENERGY RECOVERY EQUIPMENT. I-P Edition.

CenterPoint Energy (2022). “Runaround Loops.” Energy Recovery Systems. https://www.centerpointenergy.com/en-us/Services/Pages/Runaround-loops-MN.aspx?sa=MN&au=bus

Heatex (2022). “Heat Exchanger Basics.” https://www.heatex.com/knowledge/heat-exchanger-basics.