Select the name of the space and exterior wall to which the window belongs before entering data in the Input Line. The combination of Frame and Glazing allows the user to define a wide range of windows.

• Glazing Description: Select from the list of typical glazings or from TREAT Glazing Library.
• Glazing Code is a numeric code that may be entered to specify the glazing without opening the Glazing Library.
• Frame Description contains the specification of the window frame. Clicking on the field displays the default frame entered on Weather/Defaults screen. Double click on the field to bring up the Frame Library. 
• Frame Code is a numeric code that may be entered to specify the frame without opening the Frame Library. Select library at the end of either list to open TREAT respective library.

The Glazing Library and the Frame Library are both accessible above the Feedback Panel.

The list of Typical Glazings or Typical Frames may be customized by editing Glazing Description on Windows tab of Preferences. Preferences are accessible from Project Group menu.

Note:  The NFRC (National Fenestration Rating Counsel) has a standardized testing procedure that is used to create the ratings for U-value and SHGC (Solar Heat Gain Coefficient) that appear on the NFRC label on new windows. The NFRC ratings are for the entire fenestration product (glass and frame combined). Smaller windows have a greater ratio of frame area to glass area than larger windows, which affects the overall rating of the window. For this reason, the NFRC uses standard sizes, residential size and non-residential size, to compare different windows regardless of size.

If you have the NFRC ratings for U-Value and SHGC for a particular window, then you may enter these values in the Custom Window Properties dialog. Be aware that the Glazing and Framing type still play a factor in the calculations and must be entered appropriately. TREAT calculates the U-value and SHCG for the specific sizes of windows in the building model. The SHGC and U-value for a specific window are not the same as the NFRC rated SHGC and U-value unless the window is the same size as the standard “residential” or “non-residential” sizes used to generate the NFRC ratings. To help determine which Frame and Glazing should be selected from the TREAT Frame Library and Glazing Library to model existing or proposed replacement window that has certain NFRC U-value and SHGC, the table below contains U-value (including film resistances) and SHCG for various window assemblies. All windows in the table are NFRC residential size. Slider type is either horizontal slider or vertical slider.

Shading ranges from 0 if there are opaque blinds covering the window to 1 for clear glass with no external or internal shading. By default the shading factor is set to the value that corresponds to the selected glazing with no additional shading. The meaning of the shading factor (SF) is similar to the shading coefficient (SC) found in the ASHRAE Handbook of Fundamentals; however, the numerical values are not the same. The shading coefficient in the ASHRAE Handbook is defined as the ratio of the solar heat gain through a given glazing assembly to that of a reference single-pane, double-strength, clear (DSA) glass. The shading factor used in TREAT is the ratio of the solar heat gain through the given assembly to the solar heat gain through a similar glazing assembly with clear glass of the same thickness. For glazing systems with only clear glass, the shading factor is one. However, for glazing systems with tinted glass or with selective coatings, the shading factor will have a value less than one. The shading factor also allows modeling the effects of curtains, Venetian blinds, and various types of external shading devices.

Example (1):

Window A is a double-pane window with clear glass. It’s SHGC=0.52 and SF=0.52/0.52=1.0. Window B is the same as window A, but with a spectrally selective coating on surface 2 and 3 and SHGC=0.47 (Glazing Code 16). The shading factor for window B is calculated as the ratio of the solar heat gain of window B to the reference window A: SF=0.47/0.52=0.9. If you know the value of SHGC or SC of the window you want to use and the corresponding value for the reference window, you may calculate the shading factor SF as described above and enter the value in TREAT.

Example (2):

Window B from the previous example has a shading screen that provides 65% shading. The screen may be modeled in TREAT by adjusting the shading factor of the window as follows: 0.9 × (1-65/100) =0.316.

Height above Floor:

This input is the height of the window sill above the space floor. The value is used in solar gain calculations if the surface has an overhang.

Quantity:  

This field allows entering multiple windows that belong to the same surface and have the same parameters.

Example:

An eight-story 300′ × 300′ building has floor to ceiling height of 8 feet. It is modeled as a single space with an area of 72,000 square feet and a height of 8 feet. Four exterior walls (one wall per exposure) with the width of 30′ and height of 8 × 8′ = 64′ are entered. Each wall has 80 windows of the same size and construction. Input time will be significantly reduced if you create a single record for the windows on each wall and enter 80 in the quantity field. TREAT will use a default algorithm to locate the windows on the wall and calculate the net wall area and window shading. If the walls have overhangs, then this input simplification will not correctly account for the influence of the overhangs on solar gains. If accurate solar gain calculations are of interest, you need to define walls so that TREAT can place the windows on the wall in one row. In our example, if each window has an overhang, for example a balcony above it, then you may need to enter eight walls with overhang per exposure, with ten windows per wall. Remember that you also need to use Layer-by-layer calculation mode in order to accurately account for the solar gains.

Infiltration

TREAT provides 3.4 distinct panes for modeling infiltration. Heated Area Infiltration and Unheated Space Infiltration inputs are required to proceed. Holes in the building is an optional input.

Heated Area Infiltration:

This screen allows the user to enter combined infiltration of all the heated spaces to exterior and unheated areas. Input may be based on the visual inspection of the building or the blower door test measurements. By default the value is set to Air Changes per Hour based on default building air tightness specified on the Weather/Defaults screen.

Unheated Space Infiltration: 

This screen allows the user to enter infiltration of each unheated space in the project. By default the infiltration is set to 2 ACH for unheated vented spaces and 0.5 ACH to unheated unvented spaces. Modify this value to reflect the actual air leakage. Infiltration input for unheated space is ignored if all the walls in the space are adjacent to “ground”.

Holes in the Building:

This screen allows the user to describe the visible openings in the walls of conditioned spaces. If no input is made on this screen then the value entered on Heated Area Infiltration screen is converted to effective leakage area and allocated to surfaces adjacent to outdoors in proportion with their area. Sealing individual holes can be modeled as an improvement only if the holes are defined on this screen.

Place the mouse over the leakage Input Area to view the overall leakage of the heated space. This leakage is calculated using your input on Infiltration of Heated Area screen.

Example:

A heated building envelope has three exterior walls and one wall adjacent to unheated attic. All walls are of the same size. Based on Heated Area Infiltration input (see separate input screen) estimated leakage is 100 SqIn (automatically calculated by TREAT). If no input is made on this screen, leakage area of each wall is allocated to walls in proportion to their area and is equal to 100/4=25 SqIn. If a 20 inch leakage area is entered for the wall adjacent to unheated space then leakage through exterior wall is (100-20)/4 = 20 SqIn. Leakage through the wall adjacent to unheated space is 20+20 = 40 SqIn.

Note: TREAT automatically accounts for the variations of air density at the elevation of Long Term Weather Site specified on Weather/Defaults screen.