What You Can Calculate
Before buying equipment, you should be able to estimate three numbers: the heat recovered (kW), the effectiveness needed, and the simple payback period. The tools below help with each.
Spreadsheet Checklist
- Supply and exhaust airflow in m3/h or cfm
- Indoor and outdoor design temperatures
- Air density and specific heat (use 1.2 kg/m3 and 1.006 kJ/kgu00b7K for air)
- Electricity price and annual operating hours
Core Formula
Recovered power Q = m_dot * cp * DeltaT * effectiveness, where m_dot is mass flow. For a 10,000 m3/h stream at a 20 K difference and 70 percent effectiveness, that is roughly 46 kW of heating load removed from the fresh-air load.
Online Calculators
Our comparison and sizing pages embed the same formulas so you can change inputs and watch the payback move. Use the spreadsheet when you need to document the calculation for an audit or a client report.
Common Mistakes
- Using peak airflow instead of the part-load average
- Forgetting fan energy added by the extra pressure drop
- Ignoring frost protection energy in cold climates
Before You Start
A successful Heat Recovery Calculation Tools & Spreadsheets project begins with measurement. Record the supply and exhaust airflow rates, the temperatures on each side, and the hours the system runs per year. Note any contaminants in the exhaust and the available space for the core and ductwork. These figures decide both the type of exchanger and whether the payback makes sense.
Step-by-Step
First, choose the exchanger type from the air cleanliness and recovery target. Second, size the core using the measured airflow and the log-mean temperature difference, leaving margin for fouling. Third, lay out the duct path so the exhaust is filtered before the core and the supply side has drainage if it may condense. Fourth, add a bypass for free cooling and wire the fans to a simple control. Finally, commission the unit and record baseline temperatures.
Verification
After startup, compare the pre- and post-installation supply temperatures at the same outdoor condition. A steady recovery of 50 percent or more confirms correct sizing. Re-check each season and clean the exhaust side when the recovered temperature begins to fall, because fouling quietly erodes performance over time.
Frequently Asked Questions
Do I need a bypass? In most climates yes, so the system can free-cool when outdoor air is mild. How is sizing done? From measured airflow and the log-mean temperature difference, not from estimates.