[BLDG-SIM] eQuest Dbl Skin Sim

Graham & Megan hamnmegs at ozemail.com.au
Fri Jan 30 20:25:53 PST 2004


I agree with David's advice on approach.  There are many tools that will
allow you to gain some insight into double skin facades, but you need to
understand first principles so that you know when you are stretching your
analysis tool beyond its capability ...  Your tool(s) of choice will depend
on whether you are talking about internally or externally ventilated
facades, whether the facade is used as part of a natural ventilation system,
and whether you want to look at just the energy impact or thermal comfort
aspects as well ... based on this you may find a DOE-2 sunspace gives you
some of the direction you are looking for or alternatively you can start to
look at TAS (by EDSL) or Apache (by IES) to look at energy / comfort to
allow you to draw some broad conclusions on what the value of the facade is
and the critical variables.

With respect to the discussions on cost, a double skin facade will never
stack up if viewed as an energy efficiency measure in isolation.  There are
the obvious opportunities for architectural expression, but teh key drivers
will always be the improvements in thermal comfort and the additional system
options that emerge by knocking out 90%+ of the solar load.  Chilled
ceilings are not feasible at the perimeter unless the solar is controlled.
Similarly the capacity of passive chilled beams will be stretched unless the
skin load is adequately taken care of.

Lend Lease's new head office in Sydney (The Bond) will feature passive
chilled beams with the dominant western facade facing over the harbour
protected by operable external blinds.  The blinds retract during high winds
so don't require the second skin.  Many double skin applications have
effectively been a wind buffer allowing the use of cavity blinds in summer
(wind or no wind) and closing the cavity in winter to buffer temperatures
and increase the insulation value of the glazed portion of the facade ...
Regards,
Graham
Bovis Lend lease

----- Original Message ----- 
From: "Callan, David" <dcallan at syska.com>
To: <BLDG-SIM at GARD.COM>
Sent: Wednesday, January 28, 2004 4:45 PM
Subject: [BLDG-SIM] eQuest Dbl Skin Sim


There are no commercially available energy simulation tools, I am aware of,
that will simulate the complexity of a double skin façade.  The performance
of these systems varies dramatically with the type of façade and its
interaction with the building's HVAC system.  At best, I would suggest you
dig into the research and publications to determine what kind of system you
wish to model, then begin to develop a set of assumptions you can use in the
analysis. When modeling an advanced façade, one should go back to first
principles.  Best of luck!


David P. Callan, MS, PE, CEM
Senior Associate
LEEDTM Accredited Professional
Syska Hennessy Group, Inc.
Email:dcallan at syska.com
http://www.syska.com


-----Original Message-----
From: stvgates at pacbell.net [mailto:stvgates at pacbell.net]
Sent: Tuesday, January 27, 2004 8:36 PM
To: BLDG-SIM at GARD.COM
Subject: [BLDG-SIM] eQuest Dbl Skin Sim

See comments imbedded below ........

----- Original Message ----- 
From: "Kevin Krudwig" <kdk_71 at yahoo.com>
To: <BLDG-SIM at GARD.COM>
Sent: Saturday, January 24, 2004 8:26 PM
Subject: [BLDG-SIM] eQuest Dbl Skin Sim


> Hello,
> Can anyone tell me:
>
> Is it possible to simulate a double skin façade with
> eQuest?
> If so, how to?

I am not aware of an accurate way to simulate a double skin facade in
eQUEST, but a quick back-of-the-envelope analysis may suffice to draw
conclusions about this concept:

1.  Assume your building costs $150/sq.ft. to build, and that the
double-skin is 10% of that cost, or $15.
2.  Assume that energy for the building costs $1.25/sq.ft./year, and that
the double-skin saves 25% of the total energy budget, or $0.31/sq.ft./year.
(In many buildings, lights and plug loads comprise about half the energy
cost, and this analysis assumes the double-skin has no impact on either.  So
this guestimate is based on the double skin saving 50% of the HVAC costs,
which seems quite optimistic.)
3.  The simple payback is then $15/$0.31 = 48 years.  This assumes an
opportunity cost of 0%, and no additional operating and/or maintenance
costs. If the actual interest rate is 5%,
the annual interest cost is $15*0.05 = $0.75/year; or more than twice the
energy savings.  Given the interest cost, the double-skin would have to
eliminate ALL of the HVAC energy, and a portion of the lighting as well.

So, is a double-skin facade worthwhile?  Unless the assumed cost of the
double skin is high by a factor of at least 3, this concept does not appear
worth considering.

Does anyone have any better information on construction costs and energy
savings of an actual building using a double-skin facade?  To me, this
concept is so far out in left field that I don't understand why there is so
much interest in it.

>
> Is it possible to simulate a dynamic façade with
> eQuest?

I'm not sure what you mean by a dynamic facade.  In regards to dynamic
shading in eQUEST, you can define a schedule that modifies the transmittance
of a building shade.

> One that incorporates Photovoltaics?

Yes, eQUEST simulates photovoltaics.  The PV modules can be mounted
stand-alone, or incorporated as part of a building shade.  Be sure to use a
recent version, as the photovoltaic algorithms were upgraded last fall.
Study the PV-MODULE and ELEC-GENERATOR sections in the DOE-2.2 Dictionary.
>
> Thanks
> Kevin K.
>
>
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