Re: [EnergyPlus_Support] Hygro-regulated opening

Dear lixing,

thank you.

Let's try to explain a little more the real system I want to model:

A low pressure exhaust fan extracts air from several rooms through ducts (and room air outlet fix grilles).
Each room have a hygro-regulated grille that constitute an outdoor air inlet, which opening area is proportional to the indoor relative humidity.
The higher is the indoor relative humidity, the more the inlet grilles open, so that for a given airflow volume (driven by the fan), the outdoor-indoor pressure difference (taken in a given room for example) is lower .
Then, if a regulation system senses this outdoor-indoor pressure difference and orders the fan to increase its speed (or volume, or power) untill this pressure difference matches an ordered pressure difference, the outdoor air entering the room is increased. Therefore, too, if a stack effect creates a sufficient pressure difference, the fan cuts off.

To answer to your questions:
1- Such a ventilation system is produced by a french firm (www.aereco.fr, some large scale experiments were done quite recently)..
2- Grille's opening area is linear with RH (but we can imagine to use several on/off grilles to approach the response).
3- In fact the goal is just to modulate fan's volume according to a pressure difference (and again we could use several constant volume exhaust fans, each one working in a given range of values (of RH ideally) thanks to the Control Mode). Sorry, my third question was not clear at all. So the right question is quite similar that for the grilles: is there a mean to apply a "pressure difference control mode" for the exhaust fan?

I think you already answered to my questions, but if ever you have an idea to by-pass the problem...

Many thanks.

Loïc

From: Lixing Gu <gu@xxxxxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Friday, April 24, 2009 2:55:36 PM
Subject: Re: [EnergyPlus_Support] Hygro-regulated opening

Loic:

Here are my answers below your questions.

1- is it possible to make the surface object variable according to the
relative humidity? (maybe adapting the program?)

No. The program is not designed to have RH control. Do you have real
examples?

2- or is there an other way to make it?

I need to understand your thoughts more. Do you want modulate an opening or
just make it on/off based on RH?

3- given that the goal of the variable aperture is to modulate the air
volume, I would like the fan to be "constant pressure difference": is it
realizable?

The current exhaust fan is a constant volume fan. What is fan performance
for a constant pressure difference fan? Do you have real applications?

Thanks.

Lixing

----- Original Message -----
From: "aburrrrido" <aburrrrido@yahoo. com>
To: <EnergyPlus_Support@ yahoogroups. com>
Sent: Friday, April 24, 2009 4:57 AM
Subject: [EnergyPlus_ Support] Hygro-regulated opening

Hi all,

I am currently trying to model a simple ventilation system based on an
exhaust fan and outdoor air variable aperture paths that open according to
the indoor relative humidity.

As I didn't find any object to directly do this, I am trying to use an
AirflowNetwork: MultiZone: Component: DetailedOpening object and its
AirflowNetwork: multizone: Surface object to model the variable aperture. But
the Ventilation Control Mode of the surface object can only be done via
Temperature or Enthalpy controls (or other not interesting for my purpose),
and not via humidity.

So my questions are:
1- is it possible to make the surface object variable according to the
relative humidity? (maybe adapting the program?)
2- or is there an other way to make it?

A second problem is that doing a simulation with a temperature controlled
variable aperture, it appears that when the exhaust fan is on, the opening
factor of the AirflowNetwork: multizone: Surface object has no influence on
the air volume. It seems logical as the exhaust fan is treated as a constant
volume fan.

So the issue is:
3- given that the goal of the variable aperture is to modulate the air
volume, I would like the fan to be "constant pressure difference": is it
realizable?

Many thanks in advance for your help.

Loïc

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