Many of you have experienced a somewhat counterintuitive phenomenon where our modeling shows negative kWh savings for doing certain improvements like air sealing and insulation. This is largely due to increased heating loads that are mostly noticeable during the shoulder seasons where the outside air temperature is mild. Our modeling has always assumed that if you’re heating and cooling a home, that the homeowners never actually open the windows and that the HVAC system is always active throughout the year.​

In February of 2017, we added a field to the window section for both the base and improved sides that asks you if the homeowners open their windows when the temperature is mild outside. If you choose yes, this will help eliminate the negative savings as cooler outside air is allowed to enter the home through windows and eliminate the need for the cooling system to operate.

This is especially helpful for our customers in Arizona and California and even New York City where a significant number of hours have mild outdoor temperatures. In these climates, air sealing and insulation traps additional heat in the home when the outside temperatures are mild and the cooling system isn’t necessary at all if the windows are open. If the windows are closed during the mild temperatures, these improvements can often show an annual negative savings, since there isn’t enough winter heating load to compensate for the extra cooling.

When this is checked, we assume that the users keep the windows open as long as doing so keeps the temperature between the cooling setpoint and the midpoint of the heating and cooling setpoints and maintins an acceptable humidity level. The hour-by-hour determination will depend on temperature (in and out), wind speed, solar gains, etc. Because of this calculation method, adjusting the thermostat setpoints will have an affect on the total amount of window venting applied.

NOTE: This feature is set to No by default. The default setting will not affect modeling. If you have already submitted a job to a utility program for a test-in scenario before the launch of this feature, you will need to be sure to keep the setting at No. Only use the Yes setting on new jobs that have not yet been submitted to your program.