[bldg-sim] Insect screens on restricting flow

[Abaza, Hussein]

When I was with Virginia Tech. We built a model of a double skin facade similar to the Commerze Bank in Frankfurt window on a test cell and made field measurements. The air circulation due to temperature difference was not a big factor. 
Dr. H. Abaza

________________________________

From: bldg-sim at gard.com on behalf of Gaurav Mehta
Sent: Thu 1/12/2006 8:53 AM
To: bldg-sim at gard.com
Subject: [bldg-sim] Insect screens on restricting flow


Ian,

 

 

You raised a very good point. Here are some of the things that I would like to share and I would appreciate some input myself:

 

1.    You wrote:

 

[I'm concerned about insect screens affecting the buoyancy driven airflow for a double skin façade.]

 

Dr. Karl Gertis (director of the Fraunhofer Institute of Building Physics in Stuttgart, Germany) provides a critical review of double-skin façades in one of his article and cites some problems in the literature regarding research related to Glass Double Facade e.g. "window insect screens cannot be used with natural ventilation because the airflow is too weak to overcome the pressure loss over the air filter."

 

For more information about the article please go to the following link:

 

http://gaia.lbl.gov/hpbf/perfor_c.htm

 

 

2.    You wrote:

 

[I was wondering if anyone new of some papers that have covered the airflow properties of insect screens or can give me some information off hand.]

 

 

            Jun Tanimoto, Jun and Kimura, Ken-ichi (1997), Simulation study on an air flow window system with an integrated roll screen, Energy and Buildings             26(3): 317-325.

 

 

There are a few sources that also deal with the effect of insect screen on airflow but they are specific to wind driven natural ventilation. 

 

            Swami, M.V. and Chandra, S. (1988), Correlations for pressure distribution on buildings and calculation of natural ventilation airflow, ASHRAE Transactions, Vol. 94, Part 1, pp 243-266.

 

This paper provides a procedure for determining ventilation rates based on the Vickery algorithm (1983), however, assumption inherent in this procedure is that there is no stack effect.

  

            Givoni, B. (1981), Man, Climate and Architecture, New York: Van Nostrand Reinhold.

            

On pp 304 Section 15.8 Givoni discusses the effect of fly-screens on ventilation. He quotes van Straaten, the decrease in total airflow, caused by a 16 mesh, 30 gauge wire screen is about 60% and 50% when the wind speeds are respectively 1.5 and 2 mph and only about 25% when the wind speed is 10 mph.

 

Straateen, J. F. van, (1967), Thermal performance of buildings, Elsevier Publishing Co Ltd

 

 

3.    You wrote:

 

[I'm also wondering how to incorporate their effects on the flow by use of discharge coefficients and pressure loss coefficients.]

 

Andersen, Karl T. (1995), Theoretical considerations on natural ventilation by thermal buoyancy, ASHRAE Trans. 1995, Vol.101, Part 2, Paper number SD-95-14-1, 1103-1117

 

For abstract please visit the following link:

http://resourcecenter.ashrae.org/store/ashrae/newstore.cgi?itemid=17248&view=item&categoryid=452&categoryparent=452&page=1&loginid=1357156 <http://resourcecenter.ashrae.org/store/ashrae/newstore.cgi?itemid=17248&view=item&categoryid=452&categoryparent=452&page=1&loginid=1357156> 

 

In the section 'coefficients of interest' the author discusses velocity, contraction, discharge, and resistance coefficients and may provide insight into the effect of insect screen on airflow, however, the author does not directly relate it to the insect screen.

 

There is a gap in the computation of natural ventilation research especially in terms of discharge coefficients and pressure loss coefficients as Ansyley (1999) and Linden (1999) point out that the computation of natural ventilation lacks experimental data and borrows the discharge coefficient and flow resistance of openings derived from data traditionally used for fluid flow in pipes and resistance values traditionally used in computation of mine ventilation.  

 

Ansyley R. (1999), Unresolved Issues in Natural Ventilation for Thermal Comfort, HybVent Forum'99

 

Linden, P.F, (1999), Fluid Mechanics of Natural Ventilation, Annu. Rev. Fluid Mech. 1999. 31:201-38

 

 

 

 

Best regards,

 

Gaurav Mehta

 

 

	----- Original Message ----- 
	From: Ian Doebber <mailto:Ian.Doebber at arup.com>  
	To: bldg-sim at gard.com 
	Sent: Wednesday, January 11, 2006 15:28
	Subject: [bldg-sim] Insect screens on restricting flow


	I'm concerned about insect screens affecting the buoyancy driven airflow for a double skin façade.  I was wondering if anyone new of some papers that have covered the airflow properties of insect screens or can give me some information off hand.  I'm also wondering how to incorporate their effects on the flow by use of discharge coefficients and pressure loss coefficients. 


	Thanks 

	Ian Doebber 
	Graduate Mechanical Engineer 
	Arup 
	901 Market Street Suite 260 San Francisco CA 94103 
	tel: 415-946-0292 
	fax: 415-957-9096 
	cell: 415-613-4314 
	ian.doebber at arup.com <mailto:ian.doebber at arup.com>  
	www.arup.com <file://www.arup.com>  

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