While Jean is correct about an interior shade/curtain action for solar gain (I think you can find this in ASHRAE Fundamentals as well), you asked about night
heat loss/gain. For heat loss, the blind creates an additional air layer between the interior of the glass and the shade. The added resistance of this layer is degraded by air leakage from the air space to the room, but there is and added thermal resistance.
If the shade is also insulated, there is even more resistance, but there is still air exchange with space between the shade and the glass unless this is some type of special, air sealed curtain system. Conductive heat gain should be reduced at night as well,
but the gap air leakage still degrades things.
Under solar gain conditions, interior shades are not that effective on over all loads. They adsorb much of the solar load, just in a different place, and they
are not able to effective reflect it back out. They are somewhat beneficial when the window heat is contained and directed to the exhaust/return for the mechanical system, and they will improve comfort for those in the direct beam path. EnergyPlus can probably
calculate a comfort benefit, but likely just adds the gain to the total room load with minimal benefit to a mechanical system.
LBL WINDOW has incorporate shades into window calculations. You can perhaps find more references and papers there.
As an aside, earlier this month I looked at a humidified house when it was about 10 deg F outside. All small windows with interior blinds had heavy condensation
on the interior side due to the thermal insulation of the blind and the lower glass temperature. The main area of the residence (a very high end home) was floor to ceiling (20 ft) curtainwall. The curtain wall has exterior blinds that were closed, and there
was no condensation anywhere. The exterior blind, even though it was individual slats, was enough to reduce heat loss on the exterior side of the glass due to wind and the creation of an additional air space.
Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
On Behalf Of jeannieboef@xxxxxxxxx
Sent: Thursday, January 23, 2014 5:59 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Cc: <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Subject: Re: [EnergyPlus_Support] The effect of window curtain on heat loss/gain
Sean,
The folks at Transolar (whilst I was doing a training on TrnSys) told us of research that suggested using internal blinds was close to useless in repelling solar heat gain. Whilst I've not read a paper on this,
it makes sense intuatively. I would assume a curtain is similar if deployed on the inside.
Mit freundlichen Grüßen- Sent from my iPhone (excuse the brevity)
i. A.
Jean Marais
b.i.g. bechtold
Tel. +49 30 6706662-23
On 23.01.2014, at 15:34, <seanking.1970@xxxxxxxxxxx> wrote:
Hi,
I would like to explore the effect of applying night window curtain on heating loads comparing to the one without night curtain.
Could anybody advise if this is a reasonable practice by using E+? What is the principle if it does generates difference? In my understanding, the blocking of radiation to the sky would be the primary effect (reduce internal air temperature and cool the inside thermal mass as a result), and of course in practical, the curtain will add extra thermal resistance to the window assembly, together with retarding heat convection maybe?
Therefore, I would like to make clear, when adding curtain (I mean applying curtain), does E+ add extra thermal resistance to window assembly and is there any definition/calculation of reducing heat convection effect?
I am sure there won't be a very big change for heating loads, especially when window to wall ratio is small and internal thermal mass is light.
Any comments on above are welcomed.
Sean
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