Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager

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Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Understanding the New NFRC
          Condensation Index
                          Presented by:
                         Dennis Anderson
                      NFRC Program Manager

                        Email: danderson@nfrc.org
as of July 31, 2020               #NFRCMeetings     1
Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Agenda
 • Background
 • Summary of all Condensation Ratings
 • Introduction of New NFRC CI
 • Use of the NFRC CI

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Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Background

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Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Background

Persistent condensation concerns on windows &
doors have prompted the fenestration industry to
develop a method of rating windows for
condensation resistance. Reputable organizations
such as NFRC, FGIA (formerly AAMA), and CSA
have developed condensation ratings.

When condensation does appear on a window, it is
often that the window manufacturers or builders are
the first to blame. But, ……
                                                           Image courtesy of alaskahomemag.com.com
Windows do not create the moisture for
condensation, they only react to their environment.

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Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Background

                      Poll: Where did the water come
                      from on the outside of this cold
                      glass of lemonade?
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Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Background

 Just like the glass of lemonade, condensation
 occurs on surfaces of windows when warm,
 moist air comes in contact with a cold surface
 that is at or below the dew point of the air.

 Dew point can be determined by knowing the
 indoor air temperature and relative humidity.

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Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Background
• Use a psychrometric chart
  (“old school”)

• Use dry-bulb temperature
  for the indoor air

• Find desired RH% curve

• At intersection of dry-bulb
  & RH%, follow line
  horizontally towards
  saturation temperature.
  This is your dew point.

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Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Background
• Use a psychrometric chart
  (“old school”)

• Use dry-bulb temperature
  for the indoor air

• Find desired RH% curve

• At intersection of dry-bulb
  & RH%, follow line
  horizontally towards
  saturation temperature.
  This is your dew point.

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Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Background

      • Use an internet calculator such as,
        www.dpcalc.com.

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Understanding the New NFRC Condensation Index - Presented by: Dennis Anderson NFRC Program Manager
Background

The reason for emphasis on Dew Point
Temperature, because that is the basis for
determining the likelihood of window
condensation on surface of window; and
derivative of the NFRC Condensation Index (CI).

Thermal simulation 2-D modeling is used to
determine the surface temperatures of the
framing and glazing of a fenestration product.

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Background

 Major contributors to potential condensation
 include:
 • The indoor relative humidity
 • The climate or outdoor environmental
    conditions
 • Material types of window/door framing and
    glazing
 • Whether window shades/curtains are
                                                         NFRC does not rate products for these
    closed for a long time during cold weather
                                                         issues vary by operator use and
 • Heater/fans below the window                          installation.
 • Air exchangers in home/building

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Summary of all Condensation Ratings

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Summary of all Condensation Ratings
Three organizations have condensation ratings and their respective test methods are:

NFRC (National Fenestration Rating Council)
    • NFRC 500-2017, Procedure for Determining Fenestration Product Condensation Resistance
      Values. The rating achieved is Condensation Resistance.
    • ANSI/NFRC 500-2020, Procedure for Determining Fenestration Product Condensation Index
      Values. The rating achieved is Condensation Index (CI).

CSA (Canadian Standards Association) - A440.2-14/A440.3-14, Fenestration energy performance/User
Guide to CSA A440.2-14, Fenestration energy performance. The optional condensation rating within
this method is titled the Temperature Index (I).

FGIA (Fenestration & Glazing Industry Alliance, formerly, American Architectural Manufacturers
Association) – AAMA 1503-09, Voluntary Test Method for Thermal Transmittance and Condensation
Resistance of Windows, Doors and Glazed Wall Sections. The condensation portion of this test method
determines a Condensation Resistance Factor (CRF).

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Summary of USA/Canada Condensation Ratings
 NFRC 500 & ANSI/NFRC 500     AAMA 1503 and CSA A440

 Only method determined via   Condensation determined via physical testing only
 simulation.                  Sensors used to determine interior surface temperatures.

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Summary of all Condensation Ratings
                      AAMA 1503:
                      • The overall product CRF is determined by the lower of the CRFglass
                        or CRFframe.

                      • The CRF of the frame is calculated based on 14 pre-determined
                        interior temperature locations and then a 10% penalizing weighted
                        factor is applied to reduce the frame temperature by the average of
                        four coldest "roving" temperatures.

                      • The glass CRF is calculated based on the average glass
                        temperature, combining the edge and center-of-glass
                        thermocouples.

                      • The frame and glass locations include the entire height of the
                        product, so the average temperatures include a stratification effect
                        of warmer surfaces along the head and colder along the bottom.

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Summary of all Condensation Ratings
                      CSA/A440.2/A440.3:
                      • The new NFRC CI simulation method was based on this test for its
                        predication capabilities.
                          "For a particular application (i.e., for a given winter outside design
                          temperature and indoor relative humidity), the Temperature Index
                          can be used as a guide for selecting a suitable fenestration system."
                      • The Temperature Index (I), is determined by the placement of sensors
                        along pre-determined locations (and 4 roving) on the frame/sash and
                        glass.
                      • The I value of the product is determined by using the coldest
                        temperature found on the framing or the average of 3 glass sensors
                        placed 50mm from sightline.
                      • CSA Task Group has agreed to propose a revision to the standard for a
                        simulation method to determine an I value by referencing the
                        ANSI/NFRC 500 procedure.

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Summary of all Condensation Ratings
The new CI rating per ANSI/NFRC 500-2020 was a necessary and important change because:

• The Condensation Resistance (per NFRC 500-2017) value can only be used to compare apples-to-
  apples and cannot be used to ascertain likelihood of condensation. It has no correlation to the AAMA
  1503 CRF or CSA A440.2/.3 I value.

• Existing AAMA 1503 CRF and CSA A440 Temperature Index reports could be utilized to do a
  mathematical conversion to a simulated NFRC CI rating for R&D purposes or compare ratings.

• The NFRC 501 User’s Guide can be used to make product choices based on:
   • Climate zones
   • Indoor dew point temperature
   • Exterior air temperatures.

Note: CI Rating will be implemented with the LEAFF methodology. LEAFF = Linear Energy Analysis for
Fenestration

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Summary of all Condensation Ratings

• LEAFF methodology developed for U-factor simplification

• Allows trendlines (or linear regression equations) to calculate whole product ratings of multiple
  options in lieu of simulating them individually

• LEAFF method applies to CI ratings as well since simulator will use Center-of-Glass U-factor to
  determine whole product CI

• Implementation of LEAFF shall occur once NFRC Board of Directors approves pilot program –
  estimated to start anytime between October and end of the year.

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Summary of all Condensation Ratings

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Introduction of New NFRC CI

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Introduction of New NFRC CI
CI will be calculated by user. Software tools to be
used for simulation are Berkeley Lab WINDOW
and THERM

• All cross-sections of product shall be modeled
  for each glazing configuration in THERM

• Coldest temperature on the frame/sash from all
  frame profiles shall determine the CIf

• Coldest temperature on edge-of-glazing from all
  cross-sections shall determine CIe

• Center-of-Glass (COG) shall be used to
  determine the CIc . COG is obtained from
  Berkeley Lab WINDOW (not THERM)                               Image courtesy of www.agefotostock.com

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Introduction of New NFRC CI                                             CIe= Edge-of-glazing
                                                                        temp obtained at
Model in THERM                                                          25mm from where
                      Run Model for Surface
                                                                        glass meets framing
                      Temperatures

                                                CIf = coldest temp
                                                found along entire
                                                interior surface, BUT
                                                no closer than 13mm
                                                where glass meets
                                                framing

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Introduction of New NFRC CI
                                      Center-of-Glazing
                                      Temperature from
                                      WINDOW Only -
                                      not from the
                                      THERM model

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Introduction of New NFRC CI
Calculation of CI:
CIf = ((Tframe - Tc) / (Th – Tc)) x 100 (Frame/Sash CI)
CIe = ((Te - Tc) / (Th – Tc)) x 100 (Edge-of-Glazing CI)
CIc = ((Tcog - Tc) / (Th – Tc)) x 100 (Center-of-Glass CI)

CI of the Product is the lowest of the CIf, CIe, CIc

Where:
Tframe = Coldest Temperature from all interior surfaces of      Game Winner! NFRC
Frame/Sash/Panel                                                developing software tool to
Te = Coldest Temperature from all frame-to-glass junction edges
                                                                automatically find interior
Tcog = Center-of-Glass Temperature
                                                               surface temperatures!!!!
Tc = Ambient Exterior Cold Air Temperature of -18 ºC
Th = Ambient Interior Warm Air Temperature of 21 ºC

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Use of the NFRC CI

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Use of the NFRC CI
                                                                             Winter Design Temperature, Td (Celsius)
                                                    *Dew
                                                    Point        0      -5       -10      -15    -20    -25      -30       -35   -40
                                                    Temp,
                                              RH%   Ts, °C                              Condensation Index, CI
                                               10    -12        ----    ----     ----      8     20     28       35        41    46
                                               15     -7        ----    ----     10       22     32     39       45        50    54
                                               20     -3        ----     8       23       33     41     48       53        57    61
                                               25      0         0      19       32       42     49     54       59        63    66
                       Published March 1995    30      3        14      31       42       50     56     61       65        68    70
                                               35      5        24      38       48       56     61     65       69        71    74
                                               40      7        33      46       55       61     66     70       73        75    77
                                               45      9        43      54       61       67     71     74       76        79    80
Table 7-1 of NFRC 501 is the basis for         50     10        48      58       65       69     73     76       78        80    82
all design / choice considerations.            55     12        57      65       71       75     78     80       82        84    85
                                               60     13        62      69       74       78     80     83       84        86    87
                                               65     14        67      73       77       81     83     85       86        88    89
Table was develop based on Hakim
                                               70     15        71      77       81       83     85     87       88        89    90
Elmahdy’s paper and equation (2):              75     16        76      81       84       86     88     89       90        91    92
                                               80     17        81      85       87       89     90     91       92        93    93
Ts = Td + 0.01 ∙ CI(Th – Td)                                 *Dew Point calculated based on 21 ºC indoor air temperature

This table is also similar to CSA A440.3 Table II.2
 as of July 31, 2020                                #NFRCMeetings                                                                      26
Use of the NFRC CI                            Winter Design Temperature, Td (Celsius)
                      *Dew                                                                              As RH% rises, the dew point
                      Point       0      -5       -10      -15    -20    -25      -30   -23-35C   -40   temperature increases.
                      Temp,
             RH%      Ts, °C                             Condensation Index, CI
                                                                                                        This will require a product
              10       -12       ----    ----     ----      8      20    28       35       41     46
              15        -7       ----    ----     10       22      32    39       45       50     54
                                                                                                        with a higher CI.
              20        -3       ----     8       23       33      41    48       53       57     61
              25        0         0      19       32       42      49    54       59       63     66    As outdoor temperature gets
              30        3        14      31       42       50      56    61       65       68     70
                                                                                                        colder, a higher CI is required.
              35        5        24      38       48       56      61    65       69       71     74
              40        7        33      46       55       61      66    70       73       75     77
              45        9        43      54       61       67      71    74       76       79     80
              50       10        48      58       65       69      73    76       78       80     82    Interpolation will be required for
              55       12        57      65       71       75      78≈68 80       82       84     85
                                                                                                        CI values between listed Winter
              60       13        62      69       74       78      80    83       84       86     87
                                                                                                        Design temperatures.
              65       14        67      73       77       81      83    85       86       88     89
              70       15        71      77       81       83      85    87       88       89     90
              75       16        76      81       84       86      88    89       90       91     92
              80       17        81      85       87       89      90    91       92       93     93
                               *Dew Point calculated based on 21 ºC indoor air temperature

as of July 31, 2020                                              #NFRCMeetings                                                        27
Use of the NFRC CI
In addition to the main table in NFRC
501, another graphic that can be used
for determining the Winter Design
Temperature is:

• Heating Degree Days (HDD), or
• IECC Climate Zones.

IECC = International Energy
Conservation Code

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Use of the NFRC CI

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Use of the NFRC CI

Let’s go through some
examples!

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Use of the NFRC CI
Example 1: The Building Owner is to purchase windows for a     Request:
multi-family condominium complex in Mason City, Iowa           - No interior surface temperature to drop
                                                                 below 9°C. Note: specifying this is same
                                                                 as indicating saturation (or dew) point.
                                                               Known:
                                                               - The 99% Winter Design Temperature of
                                                                 Mason City, IA = -23°C

                                                               What CI rating of the windows shall the
                                                               owner be looking to target?

                                                                        Answer: 72-73

  as of July 31, 2020                          #NFRCMeetings                                          31
Use of the NFRC CI
Example 2: Homeowner in Chattanooga, Tennessee has           Request:
condensation concerns with newly purchased windows.          - Minimize condensation potential.
                                                             Knowns:
                                                             - Windows have a CI Rating of 63
                                                             - Relative Humidity will not exceed 50% in
                                                               the home due to ventilation equipment
                                                             - The 99% Winter Design Temperature of
                                                               Chattanooga, TN = -7°C

                                                             Will these windows ease the
                                                             homeowner’s potential condensation
                                                             concerns?
                                                             Answer: Yes, interpolation
                                                             indicates minimum CI of 61

  as of July 31, 2020                        #NFRCMeetings                                         32
Use of the NFRC CI
Example 3: Unknown CI Rating but homeowner wants same
                                                             Request:
windows for a second vacation home due to condensation
                                                             - Purchase same model of windows for
performance.
                                                               home in Winslow, Arizona as currently
                                                               installed in home in Omaha, Nebraska
                                                             Knowns:
                                                             - Home in Omaha maintains RH%≤ 40
                                                             - 99% WDT for Omaha = -19 ºC
                                                             - Home in Winslow, AZ will have RH% ≤ 50
                                                             - WDT of Winslow = -10°C
                                    ≈ 65
                                                             Will the purchase of the same model of
                                                             windows installed in Omaha, NE be
                                                             acceptable for Winslow, AZ climate?

                                                            Answer: Yes, although the Omaha
                                                            home had an unknown CI rating,
                                                            Table indicates climate conditions
                                                            are closely equivalent with CI of 65.
  as of July 31, 2020                       #NFRCMeetings                                         33
Use of the NFRC CI
Example 4: Use of Climate Zone / Heating Degree Days for a     Request:
developer to decide on model of windows to acquire             - Find best CI rating for track of homes to
                                                                 be built between cities of Montpelier and
                                                                 Burlington, Vermont
                                                               Knowns:
                                                               - Conservative RH% = 50%
                                                               - HDD for Montpelier = 4560 HDD18C
                                                               - HDD for Burlington = 4110 HDD18C

                                                               - After finding the “Design Temperature” of
                                                               Climate Zone Map, go back to Table 7-1
                                                               (next slide) to determine CI

                                                               What CI Rating shall developer be
                                                               specifying to minimize condensation
                                                               potential?

  as of July 31, 2020                          #NFRCMeetings                                           34
Use of the NFRC CI
Example 4: Use of Climate Zone / Heating Degree Days for a       Request:
developer to decide on model of windows to acquire               - Find best CI rating for track of homes to
                                                                   be built between cities of Montpelier and
                                                                   Burlington, Vermont
                                                                 Knowns:
                                                                 - Conservative RH% = 50%
                                                                 - HDD for Montpelier = 4560 HDD18C
                                                                 - HDD for Burlington = 4110 HDD18C

                                                                 What CI Rating shall developer be
                                                                 specifying to minimize condensation
                                                                 potential?

                                                               Answer: CI range is 69-76 for
                                                               Climate Zone 6 at 50% RH.

  as of July 31, 2020                          #NFRCMeetings                                            35
Summary
  • Potential for condensation decreases with higher CI
    Ratings
  • Use the Tables and Figures in NFRC 501 to help
    specify/find a specific CI
  • If CI is unknown, Table 7-1 in NFRC 501 will assist if at
    least two of the following are known, Winter Design
    Temperature, Relative Humidity, and Maximum Allowed
    Interior Surface Temperature (or Dew Point) of Product

as of July 31, 2020         #NFRCMeetings                       36
Thank You
                       Questions

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