Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
There are several reasons why the building energy consumption would not be proportional with the outside air rate: (1) There are other loads in a building such as conduction, solar, internal heat gain, etc. If you lump those as A and the outside air load as B, would A+B be proportional to A+2B, A+3B, etc.? (2) There may be a deadband in the building thermostat setting, such as heating at 16C and cooling at 28C. If the building floats throughout the day, such as during the swing season, the heat flows due to the fresh air will never appear in the building energy consumption at all. (3) Differences in HVAC sizing relative to the ventilation loads can have a big impact on the building energy consumption. Since you're varying the outside air rate from 0 to 20, the equipment will be sized for the non-ventilation loads in the first case, and maybe completely on the ventilation loads in the second case. On the other hand, the HVAC might not be sized at all for the ventilation load, since many sizing routines don't even consider the ventilation load!
| | 2 | No.2 Revision |
There are several reasons why the building energy consumption would not be proportional with the outside air rate: (1) There are other loads in a building such as conduction, solar, internal heat gain, etc. If you lump those as A and the outside air load as B, would A+B be proportional to A+2B, A+3B, etc.? (2) There may be a deadband in the building thermostat setting, such as heating at 16C and cooling at 28C. If the building floats throughout the day, such as during the swing season, the heat flows due to the fresh air will never appear in the building energy consumption at all. (3) Differences in HVAC sizing relative to the ventilation loads can have a big impact on the building energy consumption. Since you're varying the outside air rate from 0 to 20, the equipment will be sized for the non-ventilation loads in the first case, and maybe completely on the ventilation loads in the second case. On the other hand, the HVAC might not be sized at all for the ventilation load, since many sizing routines don't even consider the ventilation load!
Lastly, have you checked to make sure that the Fresh Air Amount is truly as you've entered?
