Cooling Load Increases With Envelope Improvement

[Ryan Moore]

Why does the kWh use increase when I improve the envelope of the home?

[Ryan Moore]

The house is in a climate where the cooling load is driven mostly by solar gains. Unless there is extensive voluntary window venting by the occupants (which OptiMiser doesn’t currently model), then there will be many hours during which the outside temperature is lower than the setpoint, but there is still cooling load. During these hours the envelope is actually reducing cooling load and thus improvements to the envelope will increase the cooling load. In some cases this effect will outweigh the savings that the envelope improvement provides during hours when the outside temperature is above the setpoint.

The magnitude of the increase in cooling load will generally be very low and thus not significant from a cost/benefit perspective.

Another thing to consider is that these cases will still usually generate positive demand savings, because peak loads tend to occur during higher outdoor temperatures.

[Gamaliel Lodge]

UPDATE: OptiMiser can now model voluntary window venting. When the occupants vent excess gains during the shoulder season, the effect described above is greatly reduced. You can turn on window venting using check boxes at the bottom of the cooling page.

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