I have recently received a number of inquiries regarding VLI (ventilation load index) data and how it should be applied. In short, the VLI represents the energy required "at the coil" to heat, cool, and humidify 1 cfm of OA to a defined constant condition for one month. That defined leaving air condition used to calculate the VLI data reported in the "Weather Report" each month is 55 degrees F, a commonly used leaving air temperature setpoint.
Individual sensible and latent cooling and heating VLI components are calculated hourly, and then totaled for the month. The sensible cooling ventilation load index (VLIcs in Ton-hrs/cfm) is calculated for every hour that the outside air dry bulb temperature is above 55 degrees.