Energy Recovery Ventilator (ERV) Simulator

Office buildings and commercial facilities: Large buildings must provide the ventilation rate required by code while keeping HVAC energy down. Energy recovery ventilators are used together with the make-up air unit and pay off especially in meeting rooms, shops and restaurants with high occupancy and a large humidity load. The design sets the airflow from the required ventilation rate and estimates the recovered heat at the peak outdoor conditions (the summer and winter design days).

Residential continuous ventilation: Homes are required to ventilate continuously to control indoor air quality, and heat-exchange ventilation systems are standard in low-energy houses and net-zero-energy homes. The more airtight a house is, the larger the share of heat that moves in and out through ventilation, so the relative benefit of an ERV grows. In cold regions freeze protection is key; in warm regions summer latent recovery drives the selection.

Cleanrooms, hospitals and data centres: Facilities with strict temperature and humidity control draw in large volumes of outdoor air while holding the indoor condition, which makes the HVAC load very high. Pre-cooling, pre-heating and pre-dehumidifying the outdoor air with an ERV lowers the capacity and running cost of the main equipment. To avoid cross-contamination with contaminated zones, however, managing the leakage rate so exhaust does not bleed into the supply is critical.

Energy audits and life-cycle cost evaluation: Building energy retrofits and life-cycle cost (LCC) studies estimate the annual heating and cooling energy saved by adding an ERV. A steady-state calculation like this tool gives the recovered heat at representative outdoor conditions; integrating it over hourly weather data (hourly outdoor temperature and humidity) yields the annual saving and the payback period. Detailed evaluation uses dynamic heat-load simulation software.

The most common mistake is assuming the catalogue effectiveness is reached as-is on site. The catalogue sensible and latent effectiveness are measured at a specified standard airflow and standard temperature/humidity conditions. In reality, raising the airflow lowers the effectiveness (the air passes through the core faster), and an imbalance between supply and exhaust airflow also reduces it. If a clogged filter shifts the airflow away from the design value, the performance shifts too. This tool's calculation assumes the entered effectiveness holds exactly, so on a real unit it is safer to assume a somewhat lower figure.

Next, the belief that latent heat can be ignored. If you only think of dry climates or winter, the latent effect looks small, but in a hot, humid climate the latent load of dehumidifying the outdoor air can equal or exceed the sensible load. If you recover only sensible heat and not latent heat, the supply air stays humid even after you have lowered its temperature, leaving the AC with a residual dehumidification load. Raising the outdoor relative humidity in this tool makes the latent recovery Q_l change sharply, showing that latent heat is not negligible in humid conditions. You need to choose between a sensible-only HRV and a total-heat ERV according to the climate.

Finally, leaving fan power out of the accounting. An ERV adds a pressure drop wherever the air passes through the heat-exchange core, and that raises the fan power consumption. Even if the recovered heat is large, the extra fan power can eat it up, so the unit does not save energy overall. In particular, in the shoulder seasons when outdoor and indoor are close, bypassing the ERV and using the outdoor air directly (economiser cooling) saves more than forcing the air through. Evaluate the real energy benefit as "recovered heat − added fan power", and design with the expectation of switching operating modes by season. This tool covers only the heat-recovery side, so fan power must be assessed separately.