Window U Value

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Dear All,

I am tring to model window with 0.9 U-value. When i use 0.9 U value on
model, LV-D reports shows 0.709 U value (frame with = 0 ). What is the
reason it ? Please find attached files.

Thanks for all replies,

Sefa Sahin

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Hello Sefa,

This is a timely question - I needed this as a reminder for a couple active projects!

Anytime the SIM reports are unintuitive/confusing - be sure you're aware of the following resource: Help > Tutorials and Reference > Detailed Simulation Reports Summary

Here, there are a number of clarifying notes concerning report LV-D specifically. To your case, if all frame widths are set to zero, then the difference between inputs and these outputs will be the OA film coefficient for a 7.5 mph (summer) windspeed:

See the table located here in the DOE-2 help files for further information/documentation: Volume 2: Dictionary > Envelope Components > GLASS-TYPE > GLASS-CONDUCTANCE (Table 11)

In summary, do not equate the GLASS-CONDUCTANCE input with the assembly U-value, when using simplified glass type inputs.

If you want to effect U-0.9 for the entire assembly, enter 1.23 for glass conductance in simplified window properties inputs. LV-D should then report 0.9 as the assembly U-value.

At one point - I performed a curve-fit to find the coefficients to interpolate the above-cited table and shared with the list - see the email thread and image copied below. Until assembly U-value becomes an input option for Simplified glass type inputs (feature-request, developers!), you could also calculate/automate GLASS-CONDUCTANCE with the following expression, referencing a global parameter:

0.2535*#PA("ASSEMBLY-UVALUE")**3+0.101*#PA("ASSEMBLY-UVALUE")**2+1.0852*#PA("ASSEMBLY-UVALUE")-0.0117

~Nick

Nick Caton, P.E.

Senior Energy Engineer
Energy and Sustainability Services
North America Operations
Schneider Electric

D 913.564.6361
M 785.410.3317
E nicholas.caton at schneider-electric.com
F 913.564.6380

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

I believe the lower U-value includes the frame. The original number is only center-of-glass.
John R. Aulbach, PE

Hello Sefa, ?This is a timely question ? I needed this as a reminder for a couple active projects! ?Anytime the SIM reports are unintuitive/confusing ? be sure you?re aware of the following resource: Help > Tutorials and Reference > Detailed Simulation Reports Summary ?Here, there are a number of clarifying notes concerning report LV-D specifically.? To your case, if all frame widths are set to zero, then the difference between inputs and these outputs will be the OA film coefficient for a 7.5 mph (summer) windspeed:See the table located here in the DOE-2 help files for further information/documentation: Volume 2: Dictionary > Envelope Components > GLASS-TYPE > GLASS-CONDUCTANCE (Table 11)In summary, do not equate the GLASS-CONDUCTANCE input with the assembly U-value, when using simplified glass type inputs.? ?If you want to effect U-0.9 for the entire assembly, enter 1.23 for glass conductance in simplified window properties inputs.? LV-D should then report 0.9 as the assembly U-value. ?At one point ? I performed a curve-fit to find the coefficients to interpolate the above-cited table and shared with the list ? see the email thread and image copied below.? Until assembly U-value becomes an input option for Simplified glass type inputs (feature-request, developers!), you could also calculate/automate GLASS-CONDUCTANCE with the following expression, referencing a global parameter:0.2535*#PA("ASSEMBLY-UVALUE")**3+0.101*#PA("ASSEMBLY-UVALUE")**2+1.0852*#PA("ASSEMBLY-UVALUE")-0.0117 ?~Nick ? ? ? ?Nick Caton, P.E.
| ? Senior Energy Engineer
? Energy and Sustainability Services
? North America Operations
? Schneider Electric | D??913.564.6361
M??785.410.3317
E??nicholas.caton at schneider-electric.com
F??913.564.6380 | 15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States |
| |

? ? ?-----Original Message-----

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Right: LV-D accounts for both frame effects and outside air film. In this case, Sefa mentioned setting frame widths to zero (knocking out that variable), so I tailored my reply to address mainly the film issue.

Nick Caton, P.E.

Senior Energy Engineer
Energy and Sustainability Services
North America Operations
Schneider Electric

D 913.564.6361
M 785.410.3317
E nicholas.caton at schneider-electric.com
F 913.564.6380

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400