Overheating with natural ventilation

[Cedric]

Hi,

I am trying to simulate natural ventilation for cooling during heating period due to internal gain which can be very important (90 W/m²). So, for that I have created a profil to activate natural ventilation when "ta>26 & to>16". My set point heating is 20°C.

So, when cooling start with natural ventilation during heating period, the software "see" natural ventilation like a negative gain and start overheating load. That's not I am waiting. How can I tell to VE that natural ventilation is just for cooling ?

Thank you for your reply.

Cedric

[PCully]

Hi Cedric,

You need to specify the conditions in your controls, I assume you are modelling the nat vent via an air exchange/MacroFlo, you already have controls based on internal and external air temperature which should do a good job of controlling when the windows open but the profile you defined is instantaneous so the windows will open/close immediately that the conditions are met, a ramp profile can build in some deadband to make the pattern more realistic.

If it's a real problem you can't get round then you could define a profile specifying the windows are close din winter months and on your formula control in summer months, that would give you ultimate control but removes some of the automation from the simulation since you will have to decide yourself what seasons you want the windows to operate

Phil

[Cedric]

Hi Phil,

In fact, I manage the nat. Ventilation in air exchange from my template system in apache module. So I just would like to stay to VE that when nat. ventilation is activate (condition is : ta>24.C & to>14.C all over the year, it is my freecooling) heating is not necessary ( consigned heating = 20.C). But when I explore results in VistaPro, I observe abnormal heating load due to temperature of external air from the nat.ventilation. I don't understand why VE start heating even if ta>20.C. Just for information, I have entered a maximun flow of nat. ventilation egal to 6 vol/h for a huge room (5000 m2). I hope that you have an idea to fix that. Thanks. Cedric

[PCully]

The simplest heating control is just a threshold room air temperature, if your controls for the free cooling are too drastic and you flood the room with cold air then the temperature will drop quickly and trigger the heating to switch on.

You can set a variation profile for the heating and/or a Timed profile to specify different setpoints at different times so you could relax the heating setpoint so it doesn't switch in at this threshold when you are bringing in the outside air or control the air exchange more strictly so that it reacts to dramatic temperature drops

Phil