IES-VE User Forum

Hi, I have a doubt about how simulate a room with mechanical ventilation at constant temperature of 23.5°C during the occupancy period; this is the condition I have to simulate. So initially I configured a template which the Room condition has the heating profile off, the cooling profile with a set point of 23°C during the occupancy period and in the Air Changes options I selected auxiliary ventilation, but in adjacent condition when I want to select a profile with constant temperature, the options are: external air, external air +offset temperature and temperature from profile, and with the last option ( I though is the right one) just let me select constant 0 and I can’t edit that profile. So with this parameters the simulation results are very strange, the air temperature and the resultant temperature are below 23.5 (which it is suppose that is the constant temperature) the same happened me when I selected in the Air change the adjacent condition: External Air
But if I try to select a profile: ‘constant’ and try to create one, the options are Abs( absolute ) with values I’m not sure if is °C or what units they are,
So definitely I’m doing something wrong and I’m confused how I can simulate this situation, so please if someone can help to solve this issue, that apparently is easy. Especially to try to maintain the ventilation with a constant temperature during the occupancy period

Hi there

You seem to be confusing things a bit here.

There are three different temperatures variables at work here:

1) the room heating setpoint
2) the room cooling setpoint
3) the mechanical ventilation supply temperature

If you leave the room condition heating profile off then you basically have no heating (ie, no radiators for example) and so the room temperature has no lower limit. However, you have applied room cooling which sets an upper limit of 23.5C.

On the mechanical ventilation side, you need to decide what the fresh air condition should be. Is it being heated or cooled by the AHU before being supplied to the space or is it being brought in at external condition? If it is being conditioned before being supplied, this is where you need to create and apply your own absolute profile at a constant value. The temperature difference between this supply temperature and the room temperature at any given time will then determine the aux ventilation gain variable under Vista. So, for example, if you supply the air at the same temperature that the room is being held at, the aux vent gain will be zero. However, if you supply at external condition, the aux vent gain will simply be the same as if the air was coming in directly from the outside.

Of course, the aux vent gain is only the room side component of the fresh air; if you have set a supply condition then the plant side component will show up under the systems variables in vista.

It sounds to me that the first thing you need to do is turn your room heating profile on and then experiment from there.

CP