Filed under: Enclosure, Materials and Methods | Tags: Architecture, construction, Glass
Ceramic silkscreen painted glass is commonly used for spandrel glass and areas of a facade where a printed design is desired. Paint is applied to clear, tinted, patterned or reflective glass – only pyrolytic glass though. For a glass to be heat treated after coatings are applied, it needs to be Pyrolytic. The paint is applied by silkscreen print, digital printer or roller/curtain. After paint is applied, the glass is then tempered or heat strengthened which fuses the paint to the glass to create an integral and durable coating. The final product might then be laminated for use as overhead glazing. The opacity of frit can improve shading and reduce heat gain. However in comparison to exterior architectural shading devices, frit typically offers only minor reduction in solar heat gain.
Several similar names are used to refer to this process:
- Ceramic Base Painted Glass
- Ceramic Fritted Glass
- Colourclad Glass
- Ceramic Backed Glass
- Opacified Glass
Filed under: Building Enclosure, Enclosure, Materials and Methods | Tags: construction, curtainwall
I recently had the opportunity to get a closer look at the installation of a unitized curtainwall. It is a systematic process of assembling prefabricated parts on the construction site. The following sketch shows the basic concept of curtainwalls. The step by step photos that follow document the installation of a single panel.
The installation shown below is high-rise construction, requiring panel installation from the interior of the building. In shorter buildings, the panels are often installed from the exterior.
Here the panels arrive within the building crated for transportation.
This is the top of a panel before installation. The hook that will engage the anchor in the floor slab is shown clearly.
The Glazier hooks the hoisting device to hoisting points built into the panel.
The panel sits on a rolling cart glass side up to avoid damage. The panel is then lifted out. It will then need to be rotated 180 degrees outside the building.
On the floor above, Glaziers await the panel to be hoisted up.
On the lower floor, Glaziers guide the panel into the correct position.
The lower floor communicates to the upper that the panel is aligned and ready to be set onto the anchor.
The upper floor workers use a variety of tools to force the panel down and into place. They use rubber mallets, pry bars, or in this case.. a size 11 leather boot.
With the panel hooked into the anchor and the stack joint interlocked, the panel is secured.
Here is the typical slab edge anchor with panels installed on the floor below. This anchorage system allows for 3 directions of adjustment to accommodate construction tolerances.
After panels above are installed, firesafing is compressed between the concrete floor and the curtainwall to provide a fire-rated separation between floors.
In exterior wall specifications, several statistics of glass performance show up consistently. Clear descriptions of these properties can be found in the GANA Glazing Manual. Here are summaries of these performance properties.
Visible Light Transmittance is the percentage of visible light in the solar spectrum transmitted through a glass. It’s expressed as a decimal; i.e. 0.90 for clear glass or 0.40 for tinted/coated glass.
Visible Light Reflectance is the percentage of visible light within the solar spectrum reflected by the glass.
Solar Energy Transmittance is the percentage of ultraviolet energy within the solar spectrum transmitted through the glass.
Solar Energy Reflectance is the percentage of ultraviolet energy within the solar spectrum reflected by the glass.
Shading Coefficient is the ratio of the solar heat gain of a particular glass to the solar heat gain through a lite of 1/8” clear glass. 1/8” clear glass is given a value of 1.0
Calculation: S.C. = (Solar Heat Gain of Glass in question) ÷ (Solar Heat Gain of 1/8” Clear Glass)
Solar Heat gain includes the heat directly transmitted through the glass and the solar radiation that is absorbed and reradiated within the interior space.
U-value is a measure of air-to-air heat transmission (loss or gain) due to thermal conductance and the difference in indoor and outdoor temperatures. A lower U-Value means less heat is transferred through the product in question. Glass manufacturers publish center of glass U-values as the edges may have a higher U-value due to the insulating unit spacer. Window manufacturers publish total window U-values.
Expressed as: Btu/hr/ft/°F
R-value is the reciprocal of the U-value. This value measures the thermal resistance of a glazing system. The higher the R-value, the less heat is transmitted through the glazing.
Expressed as: ft²/hr/°F/Btu
Calculation: R-value= 1 ÷ U-value
Relative Heat Gain (RHG) is the amount of heat gain through a material, taking into account the shading coefficient and conductive heat gain.
Expressed as: Btu/hr/ft²
Calculation: RHG = (Summer U-value x 14°F) + (Shading Coefficient x 200)
Solar Heat Gain Coefficient (SHGC) is the ratio of the solar energy entering the space to the incident solar radiation. Manufacturers provide center of glass
Calculation: SHGC = (Solar Energy Gain through Glazing) ÷ (Solar Energy Incident on the Glazing)
Emissivity (e) is the measure of a surface’s ability to emit long wave infrared radiation.
Emmittance is the ratio of the rate of radiant emission. Is a consequence of temperature only.
Coolness Index is the (visible transmittance of a glazing system) ÷ (solar heat gain coefficient). This ratio is helpful for selecting glazing products for different climates. i.e. selecting glass that transmits more heat than light vs. those that transmit more light than heat.
