#1155 Whole House fan budgets different between traditional and vent to outside on 2700 plan

[Todd Ferris]

When we change the whole house fan on 2100 single story from a traditional fan to a direct vent design, we see no change in the EDR. When we make the same change on the 2700 two story, the direct vent performs better by 0.2 EDR. If this is an error, we need to get it fixed, if it is for another reason we need to know why so that we can explain it to industry.

[Bruce Wilcox]

There are small heating and cooling compliance results differences between traditional (the Standard Design) and direct Vent (DV) whole house fans in your simulations for both the 2100 and 2700 ft2 prototypes (see the Energy Use Details reports). In both cases the DV case has slightly reduced cooling and increased heating energy use. In the 2100 ft2 case with EDR roundoff the changes cancel. In the 2700 ft2 case they do not quite cancel and the EDR changes slightly.

There is no reason to expect that these 2 models will give identical results. The traditional WHF exhaust air pressurizes the attic zone during operation and the large volumes of room air passing through impact the attic temperature. The DV fan does not directly affect the attic pressure or temperature. WHF damper leakage is also different between the 2 cases as the traditional WHF leakage warms the attic in winter reducing heating load while the DV leakage goes directly outside where it doesn't affect heating load.