Diffuse daylight reflectance of glasses

chen.fz@otm.sg Testing , 0 Comment
Related services Glass optical & thermal properties, Daylight reflectance

As discussed in the glass daylight reflectance page, the diffuse daylight reflectance of a glass is negligible, with the following two relationships:

Diffuse daylight reflectance = 0
Total daylight reflectance = Specular daylight reflectance

In the test report, we will report the glass daylight reflectance only. Below is an example:

There is only 1 result, without the separate total/diffuse/specular reflectance components.

If the result above is expressed in the conventional total/diffuse/specular daylight reflectance format, it would be:

  • Total daylight reflectance = 0.088 (8.8%)
  • Diffuse daylight reflectance = 0.000 (0.0%)
  • Specular daylight reflectance = 0.088 (8.8%)

The diffuse daylight reflectance is negligible, but not exactly 0. It is related to the haze level of the glass. The haze level of typical glasses is less than 0.5%. The diffuse daylight reflectance can be calculated as 0.088 × 0.005 = 0.00044 (0.044%) ≈ 0.000 (0.0%)

In practice, the instrument is not able to accurately measure (or resolve) the diffuse daylight reflectance of a glass. The test method of measuring glass diffuse reflectance is also not defined in the standards.

Therefore, there is only 1 result in the test report, without 3 separate components. The diffuse daylight reflectance of a glass can be estimated theoretically, but cannot the determined by an instrument.

LoRaWAN data logging system for micro-climate monitoring

chen.fz@otm.sg Instrumentation , 0 Comment
Related instruments Temperature & humidity, Wireless & web data loggers

Shown in the photo below is a LoRaWAN data logging system for micro-climate monitoring (soil temperature, air temperature & humidity), deployed in a public garden in Singapore:

The following instruments were used:

There are two LoRaWAN data loggers in the system:

  • LR35W1NTC temperature & humidity LoRaWAN data logger: this data logger supports 1 combined temperature & humidity probe
  • LR35WH general purpose data logger: this data logger supports 4 general input channels. In this installation, 4 PT100 temperature probes were connected.

The battery life of both loggers is longer than 2 years.

A few outdoor-type LoRaWAN gateways with 4G connectivity were deployed to provide network access. The signal coverage is around 1 km in an environment without tall buildings (with trees and other structures). The signal strength is reliable, based on the first few weeks of operation.

The data are automatically uploaded to the Delta OHM cloud. The end users can review the results online in real-time. The cloud service is free of charge.

OTM supplied all instruments and provided installation and maintenance services for this project.

Glass substrate for window film optical & thermal property testing

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Related services Glass optical & thermal properties

For window film optical & thermal property testing, the window film must be applied onto a glass substrate, and it is not practical to test the window film as a standalone film.

If the objective is to obtain the performance data of the window film on a specific type of glass, the film needs to be applied to the known glass type for testing. The glass substrate could be a single glazing glass (e.g. a laminated glass) or a double-glazing unit (DGU).

If the objective is to generate the general performance data of a window film, the following glass substrates are recommended in NFRC 304:

  • Applied films are measured with transparent glass with a solar transmittance greater than 0.820 (Tsol > 0.820) and a visible transmittance greater than 0.890 (Tvis > 0.890).
  • Glass that meets this criterion includes 3mm clear glass, 3 mm low-iron glass, 6 mm low-iron glass.

In practice, we recommend using 3-6 mm clear or low-iron glasses as the substrate.

Instrument for outdoor micro-environment measurement

chen.fz@otm.sg Instrumentation , , 0 Comment
Related instruments Temperature & humidity, Air speed & wind, Thermal comfort

Shown below is a system integrated by OTM for outdoor micro-environment measurement:

The system consists of the following components:

  • HD52.3DP17: ultrasonic anemometer for wind speed, wind direction, temperature, humidity, and solar irradiance measurement
  • TP876.1.I: 50 mm globe thermometer
  • HD33MT.4: data logger supporting 4G communication

At the customer’s request, we also customized a stand for the system. A similar system was customized by OTM before. The new system has castor wheels and it is easy to move the system around for measurement.

The power consumption of the system is very low. With the internal 3.4 Ah battery, the system can run for around 5 days without charging. The data can be directly downloaded via a USB cable. With a 4G SIM card, it is possible to connect the data logger to the cloud.

Substrate for paint/coating material SRI testing

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Related services Solar reflectance index (SRI)

For paint/coating materials, we cannot directly test the wet samples. The paint/coating needs to be applied onto a substrate material for testing.

For thin paint/coating layers, they are translucent to solar radiation and shown below is an example. Some solar radiation can penetrate through the thin paint/coating, reach the substrate material surface, and be reflected or absorbed by the substrate.

Example of a translucent coating layer

The substrate material has some influence on the SRI test results, though the influence is a secondary factor and weak in general.

For paint/coating on building exterior wall or roof, we recommend using cement board as the substrate, as this material is easy to obtain and is close to the plaster layer on the wall or roof.

On the other hand, due to the weak influence, it is okay to use other plate materials as the substrate (e.g. aluminium plate, gypsum board, glass plate). For typical paint/coating layers with a few hundred micrometers of thickness, the influence is close to negligible.

There is no specific requirement on the paint/coating thickness. Technically, we can test any flat surfaces, regardless of the paint/coating thickness. The manufacturer’s instructions should be followed so that the sample tested is close to the actual installed materials.

Digitally signed test reports will be issued by OTM

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We are pleased to announce that digitally signed test reports will be issued by OTM, with the following benefits:

  • More secured
  • Faster delivery
  • Better image quality
  • Smaller file size

Our digital signature is auto-trusted in Adobe Reader. The signature certificate can be verified by simply clicking the signature.

During the transition period, we will still provide manually signed hardcopy reports by default. After the transition period, only the digitally signed test reports will be issued, and manually signed hardcopy reports will be provided on request only.

Wireless data loggers for construction site dust level monitoring

chen.fz@otm.sg Instrumentation , , 0 Comment
Related instruments Wireless & web data loggers, Air quality sensors

Shown below are two wireless data loggers for PM1.0, PM2.5, and PM10 measurements and they will be deployed by a construction company for construction site dust level monitoring:

The instruments are:

The model HD35EDWPM is an upgraded version of the system shown in this post. The new model integrates the sensing part and the data logging part into a single unit.

Shown below is the software screenshot:

The system can be deployed for construction site dust level monitoring. The data logger is rain-resistant and can be deployed outdoors. A clamp is included for each unit and the mechanical mounting is very easy. If the data logging interval is set to 5 min or 10 min, the internal memory can store years of measurement data.

Glass U-value and glass tilt

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Related services Glass optical & thermal properties

We were asked why the U-value of a glass is different when the glass is installed horizontally.

There are 3 heat transfer modes: conduction, convection, and radiation. The convection part is dependent on the glass tilt and it affects the glass U-value.

By default, we evaluate the U-value of a glass with the vertical tilt, which is the most common position of glasses. For a horizontally tilted glass, the U-value is significantly greater than the U-value of the same glass with the vertical tilt.

Besides the dependency on tilt, the U-value is also dependent on the glass height. Other thermal properties (e.g. SHGC) are dependent on the tilt too.

However, it does not mean that the glass U-value shall be evaluated with different tilts. There are primarily two applications:

  • Glass performance rating
  • Fenestration performance rating

For glass performance rating, it is sufficient to evaluate the glass U-value with the vertical tilt only. With this standardized tilt, fair comparisons can be performed conveniently.

For fenestration performance rating, the glass tilt is considered in the evaluation by default.