Mech ventilation energy

hi
mech ventilation energy in my energy plus result have native amount
does anyone know what is reason ?

@hiwa

- - CORRECTION - -
I just realized that part of my initial post below (currently crossed out) is completely wrong. Mechanical ventilation in Ladybug is reported as a single output, with positive indicating heat gain and negative indicating heat loss, not as absolute ventilation gain/loss values. So the actual answer to your question is that the negative values are just representing heat loss, sorry for the mix up!

Note: I crossed out the incorrect part, but decided not to strike out the section on possible sources of noise in the mechanical ventilation outputs, since while it’s not strictly relevant it’s still accurate.
- - CORRECTION - -

What is the minimum number in your mechanical ventilation output? Assuming you are using an ideal loads air system, if all the negative values are close to zero like the ones in your screenshot, I think you can safely ignore them as simulation noise, and think of them as just zero values.

The noise in the mechanical ventilation outptus from Ladybug is not unexpected, and must be due to the fact that this particular value isn’t a dedicated EP output and is instead calculated by subtracting the total supply energy from the total zone energy. I’m not exactly sure what the source is, but there’s a couple of factors that I think might be the contributors:

  • Zone loads occasionaly exceeding the system heating/cooling capacities by a small amount (which is expected during extreme hot/cool days).
  • System heating/cooling rate not equaling the zone loads at each timestep due to unaccounted-for thermal storage (since the zone air heat balance is a steady-state calculation).
  • Truncation errors that occur during the EP numerical integration. These get averaged out over the course of the entire, cyclical simulation but might show up at timestep scale.

thank you very much for your comment
@SaeranVasanthakumar i have a question about UDI . i mentioned you for another Question .
If you answer me, you have helped a lot

@hiwa,

No problem!

As for UDI, unfortunately I don’t do a lot of work with daylighting simulations so don’t know the answer to your question, but I’m sure someone from the forum will respond soon.