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
Email: danderson@nfrc.org
as of July 31, 2020 #NFRCMeetings 1
Agenda • Background • Summary of all Condensation Ratings • Introduction of New NFRC CI • Use of the NFRC CI as of July 31, 2020 #NFRCMeetings 2
Background as of July 31, 2020 #NFRCMeetings 3
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.
as of July 31, 2020 #NFRCMeetings 4
Background
Poll: Where did the water come
from on the outside of this cold
glass of lemonade?
as of July 31, 2020 #NFRCMeetings 5
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. as of July 31, 2020 #NFRCMeetings 6
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. as of July 31, 2020 #NFRCMeetings 7
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. as of July 31, 2020 #NFRCMeetings 8
Background
• Use an internet calculator such as,
www.dpcalc.com.
as of July 31, 2020 #NFRCMeetings 9
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. as of July 31, 2020 #NFRCMeetings 10
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
as of July 31, 2020 #NFRCMeetings 11Summary of all Condensation Ratings as of July 31, 2020 #NFRCMeetings 12
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).
as of July 31, 2020 #NFRCMeetings 13Summary 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. as of July 31, 2020 #NFRCMeetings 14
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.
as of July 31, 2020 #NFRCMeetings 15Summary 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.
as of July 31, 2020 #NFRCMeetings 16Summary 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 as of July 31, 2020 #NFRCMeetings 17
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. as of July 31, 2020 #NFRCMeetings 18
Summary of all Condensation Ratings as of July 31, 2020 #NFRCMeetings 19
Introduction of New NFRC CI as of July 31, 2020 #NFRCMeetings 20
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 as of July 31, 2020 #NFRCMeetings 21
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
as of July 31, 2020 #NFRCMeetings 22Introduction of New NFRC CI
Center-of-Glazing
Temperature from
WINDOW Only -
not from the
THERM model
as of July 31, 2020 #NFRCMeetings 23Introduction 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
as of July 31, 2020 #NFRCMeetings 24Use of the NFRC CI as of July 31, 2020 #NFRCMeetings 25
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 26Use 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 27Use 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 as of July 31, 2020 #NFRCMeetings 28
Use of the NFRC CI as of July 31, 2020 #NFRCMeetings 29
Use of the NFRC CI Let’s go through some examples! as of July 31, 2020 #NFRCMeetings 30
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 31Use 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 32Use 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 33Use 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 34Use 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 35Summary
• 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 36Thank You
Questions
as of July 31, 2020 #NFRCMeetings 37You can also read
