HVAC energy consumption. A control chart to monitor the installation of a new heating, ventilation, and air conditioning (HVAC) system for a clothing store in Panama City, FL, was presented in Mathematics (Vol. 58, 2020). Energy consumption (kilowatts) was measured hourly for 44 consecutive days. The quality characteristic of interest was the depth of the daily consumption measurement distribution, where depth is measured as the median of the distribution. Low depths indicate a problem with the installation. The control chart is shown below, where the dotted red line represents the lower control limit.

a. Is the process “out of control”? Explain.

b. An investigation of the HVAC system discovered the following: On Sep.11, there was a decline in the air conditioning consumption at about midday. On Sep. 21, 22, and 30, the shopping center was closed and thus there was no energy consumption and the temperatures remained high. Do these events represent special (or assignable) causes of variation? Explain.