Tags: Standard

3 Apr 2009, Comments Off

CFC Reviews CMHC Design Report: Window Installations – Achieving field performance

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With proper design and clear specifications, it only remains to confirm that the window is installed properly in the field to make certain that the desired performance is achieved.
First, try to make sure that the windows on site are the ones that were specified. Check window labels (see Figure 4), invoices or shipment waybills for the model and manufacturer, and glazing options. Low-e coatings are impossible to verify just by looking at them, but there are ways to determine whether a window has a low-e coating (even if it is not possible to verify that it is the exact coating that was specified). A commercially available, handheld electronic device can be used to determine if a low-e coating exists and on which surface.
For a low-tech version of the same verification, use a flashlight, butane lighter or other source of light. With the light source held at the correct angle, a reflection of the light source from each surface will be visible. If there are no low-e coatings, the images will be similar, but if a low-e coating exists, the reflection of the light source off that surface will be different.
A low-e coating reduces the amount of energy transmitted in the long-wave part of the spectrum, so more of those wavelengths will be reflected back toward the viewed and the image will appear redder than the others. A black surface behind the window makes viewing easier.
Once the product has been verified as being what was intended, several field tests can verify the performance of the installed product. These include noise transmission, air leakage, ease of operation and water leakage.

Noise transmission

ASTM E966 is the field version of the STC lab test. A decibel meter and calibrated sound source are required. Several measurements are taken from the interior and the exterior, with the decibel reduction computed and converted to an STC rating as per the Standard. The specifications should indicate acceptable levels, recognizing that the fieldmeasured STC will not meet the same level of performance as the lab-rated specimen.
The tests should include the wall-window interface when performed in situ. This will not confirm the window rating, but will demonstrate the actual performance.

Air leakage

Portable air-leakage test units are commercially available. These units contain a vacuumcleaner motor and a calibrated airflow meter. The user must create a chamber to isolate the specimen of interest — this can be a window, or a bank of windows, or some other assembly. The test can isolate the window, or include the wall-window interface, depending on how the chamber is sealed to the wall.
Air leakage required to maintain a pressure difference is measured through the airflow meter. The result can be displayed as a flow (L/s or m3/hr) or a flow per unit area (L/s/m2 or m3/hr/m2, which is more common in door testing), or in the A440 units of m3/hr per metre of crack length. This can then be compared to the A rating, remembering that the field measurement will probably be higher than the lab-rated specimen.
If a small amount of smoke from a smoke pencil can be applied at the exterior, it may be possible to identify leaks, but this is usually easier to do with a blower-door test. The smoke pencil can be used to visualize the locations of leaks, which can then be addressed as needed.

Ease of operation

This parameter is a concern for elderly or physically challenged occupants. The window can be tested by applying a simple spring balance to the operating hardware.
The amount of force required to initiate motion, and to maintain motion, is measured, and must be less than the levels set in the A440 Standard. The Standard also defines where to take the measurements, depending on the window operator type. Ideally, let the occupants try the windows as a supplement to the test measurements.
Often they can give you useful feedback as to the required angle of applied force, as well as the amount of force necessary to open, close or lock the window. Note that ease of operation is usually a contrary requirement to air leakage and water leakage, both of which require the window to be tightly sealed (and therefore, usually difficult to operate). Proper selection of operating hardware can address these conflicts, but the best test occurs on the installed window.

Water leakage

Resistance to wind-driven rain is a particular concern in coastal locations, but water leakage is not welcome anywhere. Thus, installed windows should be properly evaluated in this regard.
The ASTM E1105 Standard is a field version of the E 547 test, used to determine the A440 B rating. Water is uniformly sprayed on the outside of the window at a specified rate and the window is subjected to an air-pressure difference to simulate wind pressures. The pressure is cycled in an attempt to simulate gust loading: A440 requires four cycles of five minutes with pressure “on” and one minute with pressure “off,” while the water spray is continuous throughout the test. The A440.1 User’s Guide gives test air pressures.
These pressures are maintained for the four “on” cycles, so air pressure should be continuously monitored. Before testing, the window should be preconditioned. As defined in E1105, this means opening, closing and locking the window five times, to ensure that the hardware is working and the seals are not over-tightened (which would affect the ease of operation).
The window should be observed carefully for signs of leakage. A clear chamber for testing, made of either polycarbonate or acrylic sheets, will facilitate the review. Note that there is a difference between the A440 pass-fail criteria and that of the E1105 procedure.

A440 defines water leakage as:

water penetrating the window assembly and wetting interior room surfaces;
water passing through the window into the wall below the sill;
OR
water trapped in the window assembly after the test pressure is released.

Any of these three occurrences constitutes a failure under A440. The E1105 procedure only considers the first of these to be a failure, and does not mention the other two modes of failure. It is important to define pass-fail criteria BEFORE the test begins, ideally in the project specifications.
Also, the last of these criteria is somewhat subjective: if the water is still in the assembly, but the weepholes and drainage are clearly working (so that the water will eventually drain out of the assembly), this could be considered a “Pass,” even though water in the assembly after the last oneminute “off ” cycle is, strictly speaking, considered a “Fail.”
Note that the E1105 test equipment must be calibrated, and the calibration is to be repeated every six months to make sure the water spray is constant. Reviewed by Guiseppe Strazzeri.

2 Apr 2009, Comments Off

CFC Reviews CMHC Design Report: Window Installations – Specifying ABC Ratings

Author: admin

The most important thing to recognize about ABC ratings is that they are not intended to represent field performance.

The CSA A440 Standard is intended to be a consumer guide, to allow purchasers to evaluate one window compared to another under standard test conditions. Consider the example of fuel economy ratings for vehicles: they are done under a standard set of conditions to allow the consumer to compare vehicles for fuel efficiency, but we don’t (or shouldn’t) expect to achieve that level of fuel economy on the road. This is because the fuel economy rating is determined under controlled conditions in a dynamometer testing laboratory, whereas actual driving conditions include hills, turns, stop signs, other drivers, and variable weather (to name a few of many considerations).

Similarly, the rated performance of a window in a laboratory test cannot be used to predict field performance. The test is done with a specific size of window, under controlled laboratory conditions, but the installed window is often a different size and will experience a wide range of weather conditions. The tested window is tightly sealed into the test chamber, but the installed window can leak around its perimeter (between the wall and the window frame). The tested window may also be reinforced at the test size, but not at the installed size (or vice versa), which can produce a large difference in performance. Thus, the rating system is valid for product comparison, but must be used cautiously as a design tool.

There are four important points to consider about ratings and field performance:

1. Field performance is generally not as good as rated performance.

The interface between the wall and the window frame provides additional paths for water and air leakage and the window will not be as completely anchored in the wall as it was in the test chamber (in fact, it must not be anchored as rigidly, as some allowance for movement is required in the field installation). The A440.1 User’s Guide is still appropriate to identify the desired ABC ratings for a given location and building size, but remember that this now defines the required field performance. So, if the intent is to verify field performance, test to the A440.1 design value, but specify a window with a higher rating. Thus, if A440.1 suggests a B3 performance level is needed in the field, conduct an ASTM E1105 test (see Section 3) at 300 Pa to achieve the B3 equivalence, but ask for a window that is rated to the B4 or B5 level, to make sure the desired performance level can be achieved.

2. It is important to understand how the window was tested.

The test size, test conditions, actual measured data (as opposed to the A, B or C rating level), and presence or absence of reinforcement all affect the test result, and this information is only available in the full test report. When evaluating the window rating, a professional designer should request the full A440 report for the window. This is issued by a test laboratory accredited by the Standards Council of Canada and contains all information related to the test specimen. The test results should also contain cross-sectional drawings, which are useful for determining how the installed window was anchored and what seals and reinforcing components were in place during the test. It is important to know whether the window was reinforced if energy performance is a consideration. The U-factor of a vinyl window can be greatly reduced by the presence of steel reinforcing bars in the extruded components. This can lead to a dilemma: the designer must choose between the reinforced product (which has a higher U-factor) and the nonreinforced product, which may not meet the A440 minimum levels. Another consideration is that the window may have been tested as part of a combination. This is permitted in the A440 procedure, but each window in the combination must have been evaluated individually. This means that (for example) a window that is halfcasement operator and half-fixed window may quote ABC ratings, but both the casement and the fixed window must have been evaluated separately to show compliance with the A440 Standard.

3. All windows in Canada have ABC  ratings.

All Canadian building codes require windows to meet the minimum A440 criteria of A1 B1 C1. It therefore follows that all windows must have been tested to show that they meet this requirement, before they can be sold. This means that test reports are available for all rated products, and professional designers should insist that this information be provided. If there is no test report, the designer should question the basis for the rated value.

4. All windows are tested under A440 at standard sizes.

The test report will verify the size of window tested, but to comply with the A440 procedure the standard sizes below are used (note: window sizes are always quoted as width x height): Before specifying a requirement for ABC ratings, it is incumbent on the designer to do some homework to make sure that the desired window rating is available for some products. It is not useful to specify A3 B7 C5 (that is, simply choosing the highest level for all parameters) if such a product does not exist.

Moreover, asking for the top ratings without any consideration for cost does not constitute best service to the client, and sends a signal to the contractor that the designer has not taken the time to consider the design requirements. This may have unfortunate consequences when the bids are opened. Reviewed by Jan Luistermans.

2 Apr 2009, Comments Off

CFC Reviews CMHC Design Report on: Condensation potential

Author: admin

Whenever the surface temperature of any part of the window is low enough, the humidity in the room air will condense on the cold surface. If condensation continues long enough, a significant amount of water can build up. This can lead to damage of interior finishes, mold growth and—if the water drains into the wall below the window—perhaps damage to the wall assembly. While many factors affect the formation of condensation (for example, presence of drapes, air circulation in the room, interior humidity levels) the window itself contributes to the problem if the surfaces are too cold. Therefore, it is useful to be able to rate a given window design for its potential to allow condensation.
The CSA A440 Standard describes a method of rating a window’s condensation potential. A window is tested in a hot-box chamber, its surface temperatures are measured at specified locations on the window, and a weighted average interior surface temperature is determined. The “Temperature Factor” is then calculated according to:
TF = (Ts–To) ÷ (Ti–To) x 100 <1> where Ti and To are the indoor and outdoor air temperatures in °C, and Ts is the average room-side surface temperature measured in the test.
For the standardized conditions of Ti = 21°C and To = –18°C, then TF = [(Ts +18) ÷ 39] x 100 <2> The TF is non-dimensional, and represents the interior surface temperature relative to the interior and exterior air temperatures.
TF = 0 implies Ts = –18°C, which is the same as having no window at all (because the interior surface temperature is the same as the outdoor temperature). TF = 100 means that Ts is +21°C, the same as the room-side air temperature. This window would be a theoretical perfect insulator, and the best possible rating. Thus, TF ranges between 0 and 100, with a typical value for a clear double-glazed window with a metal frame being about TF40.
TF is assumed to be independent of Ti and To, so that given ambient conditions of Ti and To, one could use Equation <1> to calculate Ts from a known TF.
For example, given a design condition of To = -9°C for Vancouver and Ti = 20°C, a TF of 40 implies that Ts = 2.6°C. This by itself is not enough information to predict condensation potential. You must also know the relative humidity or dew point temperature of the room air. A relative humidity of 30 per cent (reasonable indoor conditions for Vancouver in winter) gives a dew point temperature of approximately 11°C. The estimated surface temperature Ts = 2.6°C is well below the dew point value, so one would expect a significant amount of condensation to form on this window.
There is no minimum TF requirement, and the procedure is not a mandatory part of the CSA A440 Standard or the Building Code. The A440 user’s guide provides some guidance on the use of this parameter, and little more can be added in this article.

Regulatory considerations

Some performance parameters are dictated by local building codes. These generally relate to life and safety concerns, such as fire or unauthorized entry. In some jurisdictions, impact resistance is an important consideration. In Florida’s Dade County, windows must pass an impactresistance test that involves firing a length of dimensional lumber from spring-loaded cannon at the window assembly, to simulate the condition of wind-driven debris in a hurricane. Windows with tempered or laminated glass can pass this test, but usu ally steel shutters are required. Although this may not be of direct interest to Canadian readers, the point is that designers should be familiar with local code requirements.
The CSA A440 Standard contains a method to rate windows against forced entry. The test is relatively simple, but it does not guarantee prevention of unauthorized entry (after all, most standard windows are made of glass, which is not that difficult to break). Still, due diligence requires that designers should consider this aspect of window performance.
Windows can also be rated for fire resistance.
Although most vinyl-framed windows would not pass the fire test, they are suitable for use in sprinklered buildings. Again, it is incumbent on the designer to be familiar with local code requirements.
Several safety tests are included in the A440 Standard, including safety drop, blocked operation, sash strength and stiffness, screen strength, ease of operation and sash pull-off. These tests are intended “to ensure that an installed window will perform to a reasonable degree of satisfaction under conditions of normal use and to a limited degree of abuse or malfunction.” Windows that do not use the materials, preservatives, coatings and so on specified in the standard do not conform to A440 and do not meet Building Code requirements. Therefore, besides meeting the performance criteria (minimum of A1, B1, C1 and several criteria related to blocked operation, ease of operation and so on) a window must meet prescriptive criteria (materials, minimum component thicknesses, glazing clearances and so on) to conform to local codes. Window designers and specifiers should be familiar with all aspects of the criteria listed in the A440 Standard.

User concerns

All the design parameters this article considers are user concerns. Some less technical aspects of window performance tend to be foremost for users, and these are briefly discussed here. Reviewed by Moishe Alexander.

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