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window heat-balance

asked 2016-09-30 14:11:54 -0500

Niraj Kunwar
31 ●2

updated 2016-09-30 15:38:03 -0500

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

Hi, I need to use window heat balance in Energy plus. In engineering reference there are : 1)different heat balance methods and algorithms given for window, shading, window with gaps,frames,etc. and 2)another heat balance calculation using equivalent fenestration method which uses equivalent layer method for all window and shading layers. Are both methods used at same time for heat balance calculation or the methods are chosen between one of the two depending on the input provided? If they are not used at same time, which model is more feasible based on the data about window and shading we have from window manufacturer and which is better in terms of accuracy ? I'd really appreciate it, if someone could answer my question.

answered 2016-10-03 11:39:42 -0500

Archmage

7185 ●3 ●11

The window model is selected by the type of construction object used to describe the window. A single window is only going to have one model at a time, but the building could have different window models assigned to different windows. The input object "Construction" will trigger the original model in EnergyPlus which is similiar to older versions of the Window program. The input object "Construction:WindowEquivalentLayer" will trigger the ASHWAT model. There is also a third option using the input object "Construction:ComplexFenestrationState."

As to which is better, it depends on how complex the window system is and what kinds of layers you need to model. The original model is fine for plain insulated specular windows. If you have special fabric or screen materials, the ASHWAT equivalent layer model might have some advantages on the ease of input. The complex fenestration can handle bidirectional light redirections.

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Hi Archmage, Thanks for your answer. I am going to model a low-e double glazed window with a internal shading layer. I see the ASHWAT model can be applied for heat balance of CFS taking into account it's angular solar optical properties .

Is there any chance to incorporate angular optical properties of shading layer Roller shades and Venetian blinds in daylighting module?

I think E+ takes into account the angular optical properties of glazing layer in daylighting module but it does not consider angular optical properties for the shading layer. Thanks again.