±0.001 rounding discrepancy in specular daylight reflectance calculation

Related services Daylight reflectance

In the daylight reflectance test, the specular daylight reflectance is calculated as:

Specular daylight reflectance = Total daylight reflectance – Diffuse daylight reflectance

Due to the rounding operations, the reported specular specular daylight reflectance could be:

Specular daylight reflectance = Total daylight reflectance – Diffuse daylight reflectance ± 0.001

Shown below is an example result set, with this ± 0.001 discrepancy:

  • Total daylight reflectance = 0.216 (21.6%)
  • Diffuse daylight reflectance = 0.200 (20.0%)
  • Specular daylight reflectance = 0.015 (1.5%)

Some customers expect that the specular daylight reflectance should be 0.216 – 0.200 = 0.016 (1.6%) and suspect that there is a typo in the test report.

Our daylight reflectance test reports are generated by in-house software automatically. The ±0.001 discrepancy is not due to a calculation mistake or a typo, but due to the rounding operations, as illustrated in the table below:

Before roundingAfter rounding
Total daylight reflectance0.21560.216 (21.6%)
Diffuse daylight reflectance0.20040.200 (20.0%)
Specular daylight reflectance0.01520.015 (1.5%)

Weather monitoring with Delta OHM HDMCS-100 all-in-one weather station

Related instruments Weather stations

Shown below is a Delta OHM HDMCS-100 all-in-one weather station installed at a construction site for weather monitoring.

The instrument measures the following 6 quantities:

  • Wind speed
  • Wind direction
  • Temperature
  • Humidity
  • Pressure
  • Rainfall

The data are automatically uploaded to Delta OHM cloud via 4G. The end users can conveniently view the results with a web browser.

The initial hardware wiring and software configurations were performed by OTM and the end users just needed to do some simple last-step mechanical mounting.

Preparing samples for luminance contrast test

Related services Luminance contrast

The luminance contrast test is always in terms of two samples in a pair, typically one bright color sample and one dark color sample. There are two scenarios for sample preparation:

  • Side-by-side flat surfaces
  • TGSI studs on a flat surface

Side-by-side flat surfaces

For side-by-side flat surfaces, two flat-panel samples need to be submitted. Shown below is an example:

The preferred sample size is 100 mm x 100 mm or slightly smaller. The maximum sample size is 300 mm x 300 mm. Only 1 pair of samples (2 pieces) are needed and it is optional to provide additional samples as the backup.

TGSI studs on a flat surface

For Tactile Ground Surface Indicator (TGSI) studs on a flat surface, it is possible to submit the samples as either integrated samples or loose samples.

Integrated samples

Shown below is an example of an integrated sample of TGSI studs on a flat surface:

The preferred sample size of the integrated sample is 100 mm x 100 mm or slightly smaller. The maximum size is 300 mm x 300 mm. Only 1 sample is needed and it is optional to provide additional samples as the backup.

Loose samples

It is possible to submit TGSI studs and flat surface samples separately, without fixing them. Shown below is an example.

It is recommended to provide 2 – 5 loose TSGI stud samples.

For the flat surface sample, the preferred sample size is 100 mm x 100 mm or slightly smaller. The maximum size is 300 mm x 300 mm. Only 1 sample is needed and it is optional to provide additional samples as the backup.

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.

HD2003 3-axis ultrasonic anemometer

Related instruments Weather stations, Wireless & web data loggers, Air speed & wind

Shown below is a Delta OHM HD2003 3-axis ultrasonic anemometer (undergoing testing in our office):

The instrument measures 3 velocity components (u, v, w velocity components) and 3 additional quantities (temperature, humidity, and barometric pressure), and calculates a number of derived quantities (wind speeds and directions, sonic temperature, and wind gust), as shown in the screen capture below:

In this application, the data collected by HD2003 is logged by Delta OHM HD35EDW-MB wireless data logger with MODBUS-RTU input.

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.

Acceptance criteria for solar reflectance index (SRI)

Related services Solar reflectance index (SRI)

We are often asked, “can the SRI of my material pass the requirement?”. This post aims to answer this question.

There are no universal acceptance criteria for SRI. In practice, there could be 3 types of acceptance criteria:

There might be other types of acceptance criteria depending on your objective (e.g. if you want to certify your products under SGBP Certification, SGBC has their own requirements).

Project-specific SRI requirements

Please check with the buyer (e.g. architect, consultant or owner) for the project-specific SRI requirements.

USGBC LEED SRI requirements

Please refer to this page for the requirements in LEED.

Singapore Green Mark requirements

Please refer to this document for the requirements in Green Mark (please search “SRI” in the PDF document).

Remarks

The information listed above may be outdated. Please check with your LEED or Green Mark consultant for the latest requirements.

Additionally, 3 SRI results are presented in our test reports (low-wind, medium-wind, and high-wind, as shown below). If it is not explicitly stated in the requirement, the medium-wind SRI result shall be used in the evaluation by default.

KSJ MG6-F1 gloss meter

Related instruments KSJ gloss meters

For general applications, KSJ MG6-F gloss meter is recommended. Listed below are the key specifications:

  • Angle: single-angle (60°)
  • Range: 0 – 199.9
  • Resolution: 0.1 GU
  • Beam size: 10 mm × 20 mm

More information is available in the following documents:

For more details, please expand one of the blocks below.

Battery

The gloss meter uses 1 piece of AA-size battery. The typical battery life is around 58 hours (alkaline battery; without backlight and BlueTooth).

Basic operations

There are just 3 simple steps to perform gloss measurement:

  1. Power on
  2. Calibration
  3. Gloss measurement

1. Power on

Long press the “ON/OFF” button to switch on the gloss meter

2. Calibration

There is a calibration board in the base holder of the gloss meter (shown above). Mount the gloss meter to the base holder and buckle it properly.

Short press the “Calibration” button. While the “CA” symbol is flashing, short press the “Calibration” again. The “CA” symbol disappears and the gloss meter is calibrated.

3. Gloss measurement

Take out the gloss meter from its base plate. Attach the measurement port (at the bottom of the gloss meter) to the surface to be measured. The gloss result is displayed on the screen, without pressing any button.

Good practices

The following good practice practices are recommended:

  • Keep the calibration board and the lens in the measurement port clean.
  • Re-calibrate the gloss meter frequently.
Smartphone controlled gloss measurement

It is possible to perform online gloss measurement with a smartphone (both Android and iOS) via BlueTooth connection and store the gloss measurement results in the smartphone.

Refer to the user’s manual for the details.