The difference between NFRC winter and summer U-values

Related services Glass optical & thermal properties

Listed in the table below are the standard NFRC winter and summer environmental conditions:

Environmental conditionNFRC winterNFRC summer
Outdoor air temperature-18 °C32 °C
Outdoor wind speed
(convection)
5.5 m/s
(26 W/m2K)
2.75 m/s
(15 W/m2K)
Outdoor sky temperature-18 °C32 °C
Outdoor sky emissivity11
Indoor air temperature21 °C24 °C
Indoor convectionASHRAE/NFRC inside modelASHRAE/NFRC inside model
Indoor room temperature21 °C24 °C
Indoor room emissivity11

These are the standard environmental conditions defined in the NFRC standards and widely used by the industry. It is possible to define local environmental conditions and use them in a specific region.

In the US, the NFRC winter U-value is used (called U-factor and with the imperial unit).

In Singapore, the NFRC summer U-value is typically used, and, in our test reports, both the winter and summer U-values are reported.

For most glasses, the summer condition U-value is smaller than the winter condition Value. The main reason is that the outdoor wind speed in the summer conditions is lower and it results in a lower outdoor side convective heat transfer rate.

Online glass U-value, SHGC & shading coefficient calculator: V2.1.0

Related services Glass optical & thermal properties

We’ve just upgraded our online glass U-value, SHGC & shading coefficient calculator to V2.1.0, with the feature of argon gas concentration specification added.

It is now possible to vary the argon gas concentration to study its impact on glass U-value. The default argon concentration is 95%. Please click the screenshot below to access this online calculator and also read this article on the relationship between gas fill and double glazing unit (DGU) thermal performance.

On-site measurement of wall system U-value

Related services Thermal conductivity, On-site testing & monitoring

We are now able to test wall system U-value on-site. The test method is based on ISO 9869-1, with some improvements for Singapore’s environmental conditions.

The measurement instrument setup is illustrated below:

The following 3 quantities are measured:

  • Indoor side wall surface temperature (by a temperature sensor)
  • Outdoor side wall surface temperature (by a temperature sensor)
  • Heat flux through the wall (by a heat flux sensor)

The instruments need to be deployed on-site for a few days. The thermal resistance (R-value) of the wall system is calculated from the averaged results. The thermal transmittance (U-value) of the wall system is calculated from the R-value and the surface film resistances defined in the BCA ETTV code.

For better measurement accuracy, a surface electric heater of the size 0.5 m x 0.5 m is attached to the indoor side of the wall system to increase the indoor/outdoor temperature difference across the wall system.

Online glass U-value, SHGC & shading coefficient calculator: V2.0.0

Related services Glass optical & thermal properties

We are pleased to introduce our upgraded online glass U-value, SHGC & shading coefficient calculator. The current version is V2.0.0. Click the screenshot below to access this online calculator.

Online glass U-value, SHGC & shading coefficient calculator

Refer to this early post for the features of the V1.1.0 version.

New features added in V2.0.0

  • SHGC and shading coeffcient calculations
    • Note: limited to single glazing systems; this is due to the restriction of the mathematical model in ISO 9050/EN 410
  • More compact user interface
  • Tooltips on glass configuration schematics

Feedback and comments

We will improve this calculator regularly. If you have feebback and comments, please let us know.

Online ETTV U-value calculator: V1.1.0

Related services Thermal conductivity

We are pleased to introduce our online ETTV U-value calculator. The current version is V1.1.0. Click the screenshot below to access this online calculator.

Online ETTV U-value calculator

Features:

  • No download or installation required.
    • The calculator works in all mainstream browsers with javascript enabled.
  • User friendly and responsive
    • In fact, you don’t need to click the “Calculate U-value” button and the results are updated instantly after your changes.
  • Full compliance to BCA ETTV code
    • With built-in ETTV material library and standard conditions for air gaps and surface film resistances
    • Accuracy has been validated with other independent codes.
  • Flexible and powerful
    • User materials can be added and edited conveniently
    • The thermal resistance of each layer is listed clearly
    • Informative tooltips are displayed when the curve is moved over the schematics

Feedback and comments

We will improve this calculator regularly. If you have feebback and comments, please let us know.

Online glass U-value calculator: V1.1.0

Related services Glass optical & thermal properties

We are pleased to introduce our online glass U-value calculator. The current version is V1.1.0. Click the screenshot below to access this online calculator.

Features:

  • No download or installation required.
    • The calculator works in all mainstream browsers with javascript enabled.
  • User friendly and responsive
    • In fact, you don’t need to click the “Calculate Glass U-value” button and the results are updated instantly after your changes.
  • Full compliance to ISO 10292 or EN 673
    • Accuracy has been validated with other independent codes.
  • Flexible and powerful
    • Major factors influencing glass U-value are supported: insulating glazing units, low-e coating, gas fills, laminated glasses.

Future developments

It is planned to include US NFRC U-value calculation in the future. SHGC and shading coefficient calculations may be included too.

Feedback and comments

We will improve this calculator regularly. If you have feebback and comments, please let us know.