I do not know whether I should say anything on this topic. I have done so a few time related to different questions.
As I understand it, the Eplus simulation process does not actually introduce air flow, in the non AFN model.
When an ventilation object is added, the amount of air flow in the object is to determine the amount of heat to be added or subtracted from the zone. OA in and zone air out. All the other HVAC air flow rate may not be affected, because these airflow rates are also only used to calculate the heat transfer amount.
This is also the reason why so many user could not understand what is actually happening in the VAV system. The VAV damper position is calculated from the zone temperature and the supply air temperature difference and the zond demand. When the damper is at the limiting position, extra cooling and heating must be made available, without the set point not met warning. Damper at the mimiting position means that no extra heating or cooling can be picked from the system coils..
Similarly, the OA mixer, etc also uses the air flow rate to calculated heat energy involved. 100% OA means that you have a fixed amont of heating and cooling from OA through the AHU and all of the return air is exhausted through the relief nod of the mixer. A new name is generated, DOAS without heat recovery..
In zone mixing, again the air flow rate is to determine the heat energy to be carraied from zone to the other. When a volume of air is flowed from zone A to zone B, an equal amount is flowing back from zone B to zone A.
This is the reason why, the ventilatin air can be injcted in and exhaust without any openings in a zone.
It dowa not matter, whether you have doors open or not between zones. Opening all doors to a corridor does not mean that the air fill flow through it, unless you declare the corridor as a return air plenum mixer or path for the zones.
When one install a bathroom exhaust fan and leave the door open to the other zone, it does not mean that the air is being exhausted using the air through the door from the zone. If the bathroom is not conditioned, the inlet may be the outdoor air. If the bathroom is conditioned, the exhause fan may cause an unbalance in the system air flow. I do not know the answer to this yet.
I think, the exhaust fan has no meaning. For heat balance, the bathroom air comes from the inlet of the OA mixer. The airflow rate to the bath room can be higher and to be equal to the exhaust fan rate. The temperature of the air entring the bathroom would be that of the suipply air, which can be of a higher temperature, if the thermostat in the bathroom is set to a higher value.
This is why I am using Ventilation object so simulate louvers, instead of using full AFN model. No louvers are acuallyt entered in the IDF. AcH is changed in the different zones to refect the wind direction. My objective is to use natural ventilation, external shades, heat source control, wet utside soil surfaces (eco-roof on the ground.), etc. and study the natural temperature in a residential building. The conclusiong is that no AIr-Conditioning is needed in most situations in the tropical countries.
There seems to have many topics covered. But there is only one, there is no actual air flow in the EPlus zone model when not using the full AFN mode.
If thay are correct, may be some of the experts can confirm that.
If I am wrong, please point them out or ignore them.
Date: Tue, 25 Sep 2012 13:55:11 -0400
Subject: Re: [EnergyPlus_Support] Zone Ventilation : Design Flow Rate
I ran a 1 zone simulation to check for the things that Richard had suggested.
The results seem to say that (based on PTHP supply airflow sizing, zone sensible load predicted) -
the situation with a 55 cfm exhaust (using ZoneVentilation:DesignFlowRate) with 0 infiltration and 0 zone mechanical exhaust is SAME as the situation with a 55 cfm infiltration with 55 cfm zone mechanical exhaust (using Fan:ZoneExhaust)
So I guess the ZoneVentilation:DesignFlowRate object does make up equal amounts of air as it exhausts
On Tue, Sep 25, 2012 at 10:33 AM, Richard Raustad <RRaustad@xxxxxxxxxxxx> wrote:
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