Figure 2 (opposite) shows the 2001 Washington outdoor air ventilation utility costs per cfm compared to normal. From this graph we can see the cost impact that the weather had on ventilation utility costs each month. We can also compare the impact of each individual cost component (sensible cooling vs. latent cooling, etc). If the volume of outside air being conditioned is significant, the results should coincide with data from the utility bills. If the weather and utility data do not agree, then a flag should go up to investigate why not. In addition to normal data, similar comparisons can be made to weather and utility data from previous years.
Figure 3 summarizes the total annual ventilation costs for a 250,000-cfm constant volume lab building in Washington. The table shows that the overall net cost reduction for the year was 11%, or $51,004. However, recall that this reduction only represents the impact of weather on ventilation costs. Other factors affected by weather also come in to play such as heat recovery, building envelope heating and cooling, economizer cooling, cooling tower and humidifier water consumption, etc. These will be discussed further in upcoming columns.