Unlike heating, Snugg Pro does not require cooling loads on homes to sum to 100%. There are primarily two circumstances where this would be the case, and we'll cover those here. Then, we'll discuss how to identify partial loads, how to adjust inputs, and potential impacts on energy savings results.
It may be optimal for some dwellings with central AC's to enter partial loads into Snugg Pro. While the central AC can cool the entire home, the residents choose to only cool the whole home occasionally out of personal preference.
This occurs most often when residents only use the central AC system during extreme heat or humidity. There are generally three steps to determine whether this might be the case. First, users will see significant 'negative' bias error in the cooling calibration. Second, experienced users may notice the summer electric usage is lower than anticipated or what's seen in similar houses. Third, with those two pieces of evidence, the residents can confirm directly whether they choose only to use the central AC system intermittently.
If the residents advise they only use the central AC intermittently, then it's up to users to determine how much to derate cooling load percentage; but from experience, it would be unusual for the load for an occasionally conditioned home to be more than 30%. The entry for such a unit would look something like this:
If an improvement to the central AC is a recommendation, changing the cooling load percentage will impact modeling results. Changing cooling load from 30% base to, for example, 70% in improved, means more cooling thus more electric consumption. If residents indicate they do not plan to change how they choose to cool the dwelling, still only using it during extreme conditions, then it's a reasonable practice to set the base and improved cooling loads equal even if recommending more efficient equipment.
Another way in which there may be partial loads is with room/window air conditioners. It's relatively common for a window unit or several window units to cool only parts of the home, like bedrooms or living rooms. In these circumstances, start with the approximate percentage of the square feet of the rooms that are air conditioned to the entire conditioned square feet.
For example, take an 11x14 ft bedroom in a home with 1400 sqft of conditioned area. The bedroom is the only room that has air conditioning. Multiplying 11 by 14 means the bedroom is 154 sqft; dividing 154 by 1400 is 11%. So the entry for this unit would look something like this:
For dwellings with multiple window units, it's permissible to add together their load percentages and cooling capacities into a single system. We recommend annotating the cooling measure in Refine > Cooling with notes indicating the system represents several units.