Lecture 3: Performance
Properties of Architectural
Systems
In the last lecture we looked at heat flow across the building envelope under specific conditions. This
lead to the idea of “peak sizing” or “peak day design” which is the beginning of building heating
system design. We observed how relatively small changes in the performance of the building
envelope result in rather large changes in the peak demand.
A simple approach to building services sizing based on the peak load leads to oversized heating and
cooling systems that run well below their optimum efficiency. The peak conditions only occur on a
few days in a year with the majority of time building loads being significantly (even less than half)
smaller. Since the calculations used for peak day design apply at any time of the year, it would be
possible to make an individual peak calculation for each hour and sum the results. While this idea is
terribly tedious and impractical for manual calculations, it is easy with computers.
Following up on the discussion of Lecture 1, we began to investigate whole building energy
simulation as described in energy code performance compliance terms looking at MNECB 1997 and
ASHRAE 90.1-1999. The calculation procedures for the energy codes help identify the number of
specific assumptions that are made to accomplish a whole building simulation. A review of basic
starting assumptions, building thermal zoning, the impact of schedules, and the building systems
represented introduced the core areas in simulation and discussed their differences from “real
design”.
Lecture 3 will introduce one very successful whole building simulation tool developed for use at the
programming and preliminary design phases. It will continue with a discussion of the derivation of
performance values for walls, roofs, and windows. The correct inputs for these components is
essential for developing the correct descriptions of annual building performance.
This lecture is much heavier than typical in terms of number of slides, an account of the number of
features in the tools to be identified. Not all slides will require a full 2 minutes to explain, although
some will take considerably longer. It may require more than one hour to present, or can be kept to
one hour with the slide deck used as a reference for personal review after the lecture.
1
Whole Building Energy Simulation
• NRCan Screening Tool for
New Building Design;
• Parametric editor based on
over 100,000 DOE 2.1e runs;
• 28-32 data entry points;
• Follows MNECB Part 8 + CBIP
rules;
• Selection of building
archetypes available;
• Selection of mechanical
systems available.
• http://screen.nrcan.gc.ca/
The next series of slides presents a detailed introduction to Natural Resources
Canada’s (NRCan) Screening Tool for New Building Design. Initially developed to
assist designers benchmark their current practices with regard to their ability to
receive an incentive under an energy efficiency program for commercial buildings,
the tool became recognized in both research and consulting circles for its ability to
get a quick breakdown of building energy performance, and to set the context for
other more detailed investigations or to get design teams moving in the right general
direction, with very little time spent on analysis.
The tool addresses energy conservation only, and applies those measures as
directed by the user to a specific collection of building archetypes. Basic
assumptions for occupancy, plug and equipment loads, and buildings services
systems follow the terms of the Performance Path for the Model National Energy
Code of Canada for Buildings (MNECB) 1997. The tool features a comparison
between the “Proposed Building” as intended by the designers and the MNECB
“Reference Building”, which is the same building as if it were built in accordance
with the prescriptive requirements of the MNECB.
The tool offers an option to store runs on a NRCan web server, but if users do not
want to access that feature the “Proceed without Registering” option allows access
to the complete program. Unlike other web based applications where the web
interface sets up a run on a remote server that takes time, Screening Tool runs are
sufficiently fast that only the final run, or representations of significant variations or
options are of interest. They can be saved to one’s own hard drive in a PDF of the
final report output.
2
This is an image of the first working screen. One can add a facility name for ease of
file location on completion, but this is not a mandatory input.
The principal task of this screen is to identify the province and nearest city of the
project in question. This action identifies the MNECB Administrative Region, which
is one of the variables that set building envelope performance values for the
reference building. The process we are engaging uses a comparison between the
building the design team wishes to develop (the proposed building) and a similar
building in all respects except that the envelope, lighting, equipment loads,
ventilation, heating and cooling all conform to the minimum prescriptive
requirements of MNECB 97. This building is known as the reference building.
Selection of Administrative Region is the first fork in the path to using a compact
dataset necessary for quick results from the look-up tables that provide the final
annual consumption.
In this example the Province and city have defaulted to the first entry in each
respective list. Accordingly, Calgary Alberta gets the call.
There is also an option to run two different building types in the same simulation.
This feature sets up two separate inputs for one building and doubles the work,
similar to conceptually separating the building into two individual buildings and
running each on its own. For clarity of this exercise we will use only a single building
type.
3
With a location selected, the next screen completes the information necessary to establish the
MNECB reference building. The selection of city which provides climate data is complemented by
selection of the principal heating system. The principal heating system establishes the heating fuel
which completes the information required to set the building envelope prescriptive requirements.
Selection of the archetype building establishes the default assumptions for occupancy type,
schedules, lighting power, equipment, and building systems. As the tool uses curve fits for each
energy efficiency parameter it is useful to know the description of the archetype. The closer the
proposed building is to the archetype the more reliable the results will be. By clicking on the blue text
“Building Type” the user will see a basic description of the archetype building.
The “Floor Area” entry is initially defaulted to 10,000 m2. This figure should be adjusted to reflect the
floor area of the archetype or the area of the proposed building at the beginning of the process.
Selection of the primary heating system is made from a predefined list, with the intent to represent
the proposed building system as closely as possible. In addition to establishing the principal heating
source the selected system will offer opportunities for energy efficiency depending on the
combination of building and system types. Again the blue text gives a description of the performance
characteristics of the system selected. In the example above the fossil fuel fired Variable Air Volume
(VAV) central HVAC system has been selected. This is the default system for multi-zone buildings in
the MNECB reference.
An estimate of annual energy costs is calculated based on the utility rates entered at the bottom of
the screen. The default utility rates were those provided by authorities in each province during the
MNECB development period, and reflect fuel costs from the early to mid 1990s. The utility
information can be reset following the rate schedules from local utilities. It is important to set both
demand and consumption rates for accurate results.
4
Here is the pick list of building types available in the tool. For this discussion I have
selected the School archetype. The floor area entered is that found in the archetype
description.
5
By clicking on the blue text in the Building Type input title after having selected
“School” the above description is presented.
6
Similar to the building type pick list, here is the primary heating system list. The
variety of system options varies to some degree with the building type.
7
Again similar to the building type, the blue text gives access to the following system
description for the Variable Air Volume (VAV) system. The description for the Fan
Coil system is also seen in the list. Both systems have central air handlers, but the
VAV delivers primarily cooling and ventilation air from the central source. Heating is
usually made up by coils or radiators in the individual thermal zones.
The Fan Coil delivers heat through coils in each individual zone, and its air handler
only moves ventilation air. The volume of air required to serve heating and cooling
requirements is significantly larger than the air volume required for ventilation.
Accordingly the Fan Coil air handler is significantly smaller. Note that the Fan Coil
used in this model does not permit free cooling, which is an energy efficiency
strategy to reduce the loads on electric chillers when outdoor air temperature and
humidity are in the correct ranges. Free cooling can save energy during the Spring
and Fall when chillers are likely to be operating at part load and less efficiently than
in the summer under full load. Lack of free cooling in the model is an example of
how the DOE-2 building services systems are “pure” where Canadian HVAC
designer often design hybrid systems.
8
Once the building type, floor area and primary heating systems have been selected
the detailed entry of the proposed building features can be started. Clicking
“Continue” on the bottom right corner of the building type and heating system
selection screen will move the user to the next input screen. At the top of the new
data entry screen appears this summary for reference.
9
The first section for input is concerned with the building envelope. One sees two
columns of inputs for comparison. The left hand column contains the details of the
MNECB reference building for which a detailed annual energy consumption will be
automatically calculated. The right hand column contains the proposed building
inputs. The proposed building inputs are initially defaulted to the MNECB reference
conditions but are intended to be modified.
The “Average window-to-wall ratio” (also known as “fenestration-to-wall ratio” or
FWR) dictates the whole window area. It covers all building orientations and
assumes an equal percentage of fenestration on each façade. It is also assumes
that the fenestration is not shaded by the building itself or applied external shading.
Following the MNECB the reference FWR will equal the proposed building up to a
maximum of 40%. The proposed building may show higher percentages of
fenestration but the reference will remain at 40% in those cases.
It is important to know that the entries for Gross Wall Area and Gross Roof Area are
based on the building archetype. If the proposed building has a different floor area
or does not follow the archetype form then these inputs need to be adjusted to
represent the proposed building as designed. This ensures accurate results. It is
good practice to adjust the gross wall and roof areas to reflect the actual design
values in all cases.
The entry for Roof Type follows the MNECB direction of different reference
insulation levels for roofs depending on the roof construction type. A discussion of
this feature appears in three slides.
10
This slide is the help screen opened by clicking on the input title for “Overall
Window USI value”. There are two inputs for window performance after setting the
fenestration-to-wall area ratio, whole window U-value, and Shading Coefficient (SC).
Shading coefficient will be discussed in the next slide.
Designers have easy access to U-values for centre of glass, but not access to
whole window values, which will vary based on insulating glazing unit (IGU)
performance, frame performance and window proportion. For commercial glazing
the IGU now has a much lower thermal transmission than the frame. Aluminum
frames tend to cool the window edge resulting in a band of lower performance all
around the frame. As a result the centre-of-glass U-value can be considerably
degraded by a glazing pattern that includes a lot of framing.
The help file gives some generic constructions and U-values that can be used in the
absence of manufacturer’s information or supplementary calculations.
At the end of this talk a more developed way of generating whole window U-values
via a spreadsheet calculator will be introduced.
11
This slide shows the Screening Tool help file for Shading Coefficient (SC) that is
accessed by clicking on the input title “Window shading coefficient:”. Similar to the
discussion of whole window U-values, the SC is sensitive to IGU construction and
window frame to glazing proportion. As frame area increases, the opaque elements
of the window increase and the shading effect increases.
Shading coefficients are important in the design of cooling systems, but are not as
useful as the related Solar Heat Gain Coefficient (SHGC), which also ties into the
design of heating systems. Over time engineering practice is shifting away from
using shading coefficients in exchange for SHGC. SC can be obtained by dividing
SHGC by 0.87.
The help file gives some generic IGU constructions and SC values that can be used
in the absence of manufacturer’s information or supplementary calculations.
Calculating an approximation of the shading coefficient will also be included in the
spreadsheet tool discussed at the end of this lecture.
12
The MNECB 1997 introduced the idea of “effective insulation value”, where the thermal bridging of
structure was taken into account and a “whole assembly U-value” (or RSI value) was used rather
than a nominal or “insulation only” value. All Screening Tool inputs of RSI value must reflect this
concept to produce meaningful results. MNECB Appendix C describes the calculation approach for
producing whole assembly RSI values. Later in this lecture we will demonstrate the EE4 Assembly
Editor, a utility found in the EE4 software that helps prepare effective RSI values.
For the MNECB 1997 it was decided that where roof insulation was interrupted by a structure a
greater amount of insulation would be required depending on the ability to add insulation and still
maintain roof ventilation. As a result, Attic type roofs, where insulation is regularly interrupted by roof
trusses but the truss space has a large ability for layers of insulation over the truss bottom cord, have
the largest requirement for insulation.
Parallel chord trusses and joists (such as wood-”I”s) are similar but do not offer the same potential for
added insulation. They still require insulation upgrades, but less than for attics.
Finally deck roofs, where the insulation is uninterrupted by structure, have the lowest insulation
requirement. The typical case here would be a flat roof where all the insulation is applied above the
structure, but it would also apply to a sloped flat deck over a timber-framed cathedral ceiling. Some
judgment is required for cases such as metal building roofs where the insulation is interrupted by
purlins and z-girts at wide spacings. The Assembly Editor can calculate these conditions easily.
13
With the envelope inputs complete the input screen scrolls down to the entry area
for mechanical systems. As with the envelope system the reference building values
are shown in the left hand column, with proposed building values in the right hand
column. The section has inputs for: the basic efficiency of building plant (boilers and
furnaces, and chillers); ventilation rates and controls including economizers and
heat recovery on exhaust or relief air; service water heating, and; basic boiler
controls.
The ventilation rate is by default set at the MNECB level, but can be adjusted if
required. Ventilation rates match between the reference and proposed. If a designer
wishes to see the impact of heating and cooling ventilation air, the ventilation rate
can be entered as zero and the end use totals compared to a different run of the
same model with ventilation. The reference building will show no ventilation air if the
proposed building has none.
The heating efficiency and chiller coefficient of performance (COP) are defaulted to
the MNECB levels. Chiller COP is based on the assumed size of the chiller, with
larger buildings getting chillers with higher COPs. For the VAV system there is an
option to specify variable speed fans. This produces and energy efficiency
advantage as variable speed fans are more efficient than single speed fans
because they can follow demand as it changes. The impact of this option shows up
as “Auxiliary” end-use energy in the final summary.
For zonal systems such as the Fan Coil, variable speed fans are not used even
though the option may appear on the screen.
14
This slide presents the pick list menus from the mechanical system input area. Demand control
ventilation (DCV), service water heating fuel, and boiler control strategies all have options.
When selecting DCV options it is important to also declare what percentage of the floor area is
controlled by DCV. Both CO2 and occupancy sensors are permitted. CO2 sensors would need to be
present in each occupied room for that input to be acceptable. CO2 sensors in return plenums were
not accepted under the Commercial Building Incentive Program as the air stream would often be too
diluted to permit them to function.
Service water heating fuel is the next option. The entered efficiency value should be supported by a
manufacturer’s specification. If electricity is selected the efficiency input automatically is set to 100%.
To represent heat pump water heaters, it is possible to enter percentages greater than 100%
following the COP of the heat pump. For example, if a heat pump water heater has a COP of 2.25 the
Screening Tool entry for Service water heating efficiency would be 225%, with electricity being
selected as the SWH fuel type.
The mechanical efficiency input at the bottom of the screen allows the designer to select from a
simple on-off control strategy, a modulating boiler control or controls for condensing boilers. Each
selection is based on its own part-load efficiency curve, and assumes proper distribution has been
worked out to allow the plant efficiency to be achieved. This is particularly an issue for retrofits
installing condensing boilers. If one were to enter a boiler efficiency of 92% intending that to
represent condensing boilers, but not change the control strategy from the default On/Off, the overall
building performance will be reduced.
15
With the mechanical system details input, one scrolls further down to the lighting and process load
input areas.
Lighting is represented by three inputs: the average connected lighting power density (CLPD), and
two zones for different lighting controls complete with a variety of control options blending daylight
harvesting sensors and occupancy sensors.
The input for CLPD is initially presented as the default for the building type, but should be adjusted.
The CLPD was adopted almost directly from ASHRAE 90.1-1989 and reflects the common lighting
system of the time, T12 fluorescent tubes in fixtures with magnetic ballasts. Current design practice
would use half of the MNECB amount or less. The NECB 2011 update CLPD for schools is 10.7
W/m2.
It may be most effective to think about the two separate inputs for lighting control zones as
representing the perimeter, or daylight zones, and the core zones respectively. The percentages
recorded in the input boxes cannot be greater than 100% when added.
An entry for process loads completes the input field. Because the tool is based on a whole building
approach the extra energy required for a discrete facility such as a server farm or call centre would
need to be distributed across the entire building area. In general all electricity use is considered
waste heat to space, so the declaration of the proportion of process energy that is electrical is an
important input.
The process load input can also be used to adjust items like the assumed receptacle load, which is
defaulted and not available. Unfortunately this is only possible to represent increases in loads and
negative inputs representing greater efficiencies cannot be used.
Most often there will not be a process load to consider and once the lighting inputs are finished the
input process is complete. At that time one scrolls down to the bottom right hand corner and clicks on
“Continue” to start the simulation.
16
This slide shows the menu of lighting and occupancy based controls for the
proposed building. As the tool is a parametric editor not a live simulation the impact
of the control strategies is to apply a power adjustment factor to the CLPD over the
percentage of floor area described.
Occupancy sensors give a 30% reduction. Daylighting controls give 10%, 20% and
30% reductions as one moves from on/off to continuous dimming. No combination
of approaches can provide more than a 40% reduction.
17
After a gap of a few seconds the tool reports back with the annual energy
consumption of both the reference and proposed buildings. The top of the report is
a text response advising the simulator as to whether the performance threshold of
25% below MNECB has been achieved. This is followed by a declaration of energy
consumption for reference and proposed, the GJ saved and the percentage of
savings. A statement on energy cost savings is the next feature.
18
From the energy cost savings, following the ASHRAE 90.1 Energy Cost Budget
Method used in LEED, a statement is provided declaring the percentage energy
cost savings and potential LEED points for Atmosphere & Energy credit 1.
A report on CO2 emissions savings completes the section.
19
Following the declarations of percentage improvement on energy consumption and
energy cost, there is a comparison of performance by end-use presented in two
parts. The first part is a visual, with a bar graph comparing the two buildings
normalized to show the reference at 100%.
Using the end use breakdown from the DOE-2.1e BEPS (building energy
performance summary) report, space heating combines both ventilation air heating
and actual heating energy at the building perimeter and in the core.
In this example a high performance variant of the school has been entered as the
proposed building. Improved window performance and envelope insulation plus heat
recovery on ventilation exhaust and relief air have substantially cut the heating
requirement. Reductions to connected lighting power are seen as is a slight
reduction in cooling energy. Service hot water energy has been reduced through
flow restrictions and heating source efficiencies. Fan and pump power has been
reduced by using variable speed drives. The one item that does not change is the
consumption for equipment, which we have noted is a default with no access for
credit.
20
The comparison is continued in table form, based again on the DOE-2.1e BEPS
report. These numbers are used to generate other types of graphs and to combine
with results from other tools to represent the benefit of supply side approaches such
as on-site renewable energy generation. Both fuel mixes and costs are provided for
comparison.
21
At the end of the results report one finds the generalized disclaimer regarding the
purpose of the activity and its relationship to government energy efficiency
programs. Because there are many defaults and undeclared assumptions in the tool
it is possible that the terms of the simulation are not quite what the designer
intended. Lecture 2 showed one case where the assumed thermal zoning in the
Screening Tool was not used and the variation in results was dramatic and
damaging for the designers. As with all computer tools it is essential to understand
the simulation assumptions. Garbage in = garbage out.
With that caveat understood, the reported results have been obtained in a very
short period of time; as little as 3 minutes. A simulator with some experience can
generate many runs and begin to explore the sensitivities of a wide range of energy
efficiency measures. Where the occupancies are straightforward and the proposed
building size close to the archetype size the Screening Tool has come within 3% of
the answer generated by the more detailed EE4 simulation tool.
If the results are positive, and a satisfactory position has been achieved one would
now click on the “Summary” text to generate the final report. Otherwise one clicks
on the “Try Again” text to adjust the energy efficiency measures following the
priorities of the project.
22
This is the beginning of the final report. A small area is available for specific
references to the intentions of the simulation run or any other details that would be
beneficial to see before a detailed inspection of the file. The final output report
repeats the information presented in the results screens, but cleaned up for clarity.
23
This slide shows the extent of the full final summary.
24
Architectural subcomponents
• Performance of the building envelope is broken
into two parts:
– Opaque assemblies, and;
– Transparent / translucent assemblies.
• Envelope sets the context for energy
performance;
– Thermal bridging is a significant issue.
• Correct envelope inputs are essential for
accurate whole building assessment:
– Effective RSI values;
– Whole window U-values.
As seen in the walk through of the NRCan Screening Tool the entries for the
building envelope are very straightforward. The two components of the envelope
system are opaque (walls and roofs) and transparent or translucent (windows). Both
are considered as whole assemblies in the Screening Tool entries, requiring a
calculation of the combined thermal properties of frame and infill in addition to area
weighted combinations of different assemblies.
Doors are weak performers even when insulated. Unless special attention to door
construction is given, thermal bridging will reduce the thermal resistance to the point
where they perform similarly to windows. Accordingly door and window areas can
be added for the FWR, especially if high performance windows are being specified.
Thermal bridging is also a serious issue for wall systems using steel studs. It is
possible for the insulation value of the stud cavity to be reduced by more than 50%
due to the thermal transmission through the stud. Wood studs do not as
dramatically reduce overall performance with thermal bridging, but still degrade
overall performance. Optimum Value Engineering for stud layouts is very valuable in
wood frame construction. This approach uses wider stud spacing and single top
plates with joists aligned directly over studs, dramatically reducing the frame
percentage.
The calculation of whole assembly performance using spreadsheets and computer
tools will be presented over the next series of slides.
25
Effective U-values
• Accurate energy modelling requires accurate
inputs of performance characteristics;
• MNECB 1997 Appendix C introduced a standard
calculation approach for including the effects of
thermal bridging in envelope assemblies;
• EE4 version 1.7 software provides a utility to
generate effective U-values for building
assemblies. The utility is called the EE4
Assembly Editor.
Building science can demonstrate that thermal bridging can seriously alter the
nominal thermal resistance of a building assembly. In residential construction the
use of wood studs mitigated this impact to some degree, but in commercial
construction where the use of steel studs is common, performance degradation is
severe. The degradation of performance leads to higher energy consumption and
heating bills in the best case, and failure of wall systems due to corrosion caused by
condensed water vapour inside an assembly in the worst case.
MNECB 97 introduced the concept of “effective RSI value” to the definition of
envelope assembly properties. Appendix C described the 2 dimensional parallel
path calculation where the thermal resistance of the insulated cavity is blended with
the resistance of the wall assembly taken through the stud. This calculation method
is scalable, as it can be applied to a window frame as easily as a wall section,
however the smaller the scale the more important 3 dimensional heat loss becomes
and the 2D parallel path calculation results are less satisfactory.
While spreadsheet calculators are adequate tools for making the parallel path
calculation the EE4 software has a utility that accesses a generic library of material
values which speeds the process of establishing effective RSI values for various
assemblies. Running a simulation is not required for use of the utility, nor is creating
a new project. The following slides will demonstrate the use of the tool.
26
Framing Percentages for Typical
Wood- and Steel-framed Assemblies
MNECB Appendix C, Table C-1: Area Percentages: Where the actual percentages of the building
assembly area that are underlaid by framing and by insulation are known, these values should be
used. Otherwise, the values in Table C1 shall be used. These values include allowance for typical
mixes of studs, lintels and plates.
Steel Framing1
Framing Wood Framing
Assembly
Spacing Area With
Area Without Area With
Area Without
mm
Framing, %
Framing, %
Framing, %
Framing, %
Roofs, ceilings, floors
< 500
10
90
0.33
99.67
≥ 500
7
93
0.23
99.77
Above-grade walls and
strapping
< 500
19
81
0.63
99.37
≥ 500
11
89
0.37
99.63
Below-grade walls and
strapping
< 500
17
83
0.57
99.43
≥ 500
10
90
0.33
99.67
< 2100
-
-
0.08
99.92
≥ 2100
-
-
0.06
99.94
Sheet steel wall
Note 1: Percentages for steel framing are based on 18-gauge (1.2 mm) steel; however, test results
indicate that, for the range of thicknesses normally used in light steel framing, the actual thickness
has very little effect on the overall thermal transmittance.
This table from MNECB ‘97 Appendix C gives direction for the correct input of frame
percentage values into the Assembly Editor where actual values are not known.
Other necessary inputs for the tool are called directly from the interface.
27
Access to the EE4 Assembly Editor starts with launching the EE4 program on one’s
computer. The program is available free from the CanmetENERGY website under
tools.
http://canmetenergy-canmetenergie.nrcan-rncan.gc.ca/eng/software_tools.html
Once the EE4 program has been downloaded and installed it will most likely be
found on the local hard drive (C drive for Windows based computers). It is important
to know that EE4 runs only on 32 bit Windows OS computers. 64 bit machines will
need to run emulators that permit DOS to run in the background.
Once the program is open, select one of the sample projects from the “Projects” tab
inside the EE4 folder.
28
With one of the sample projects open, select the sample project Assembly Library
from the library tab on the main menu. Working with a sample project will permit
new or edited assemblies to be saved and exported to other files. Selecting the
“Default” option will present all of the libraries of interest, but will not allow new
assemblies to be created and saved, or modified assemblies to be saved.
From the sample project menu select the “Assembly” library.
29
This slide shows the list of assemblies that come pre-assembled in EE4. There is a
wide variety of roof, wall, slab and exposed floor types to edit for a new project. The
basic menu has a descriptive name, assembly type record according to MNECB 97,
RSI value, U-value, and framing material. Concrete or masonry walls where there is
no penetration of the insulation layer are considered to have “no framing”.
Select the first wall assembly for investigation.
30
Hi-lighting and double clicking on a selected assembly calls up the dialogue box shown in this
screen, providing the inputs for editing the assembly.
The top left corner contains inputs for the basic identity of the assembly, including the MNECB type,
solar absorptivity (not a significant input for DOE-2 analysis in our climate), the ASHRAE group for
the assembly, and the surface characteristics. For early phases of a design, one can simply enter a
desired U-value and complete the process with that action. For a compliance submission, whether
that is for building permit purposes or for a whole building assessment program such as LEED the full
assembly needs to be developed.
The box in the top right hand corner is the location for entering the framing percentage information
from Appendix C of the MNECB. These details will be put into play if a layer described in the open
box below calls for framing. As previously mentioned “No framing” implies unit masonry or concrete
bearing walls. Due to the severity of thermal bridging for steel studs the largest portion of this input
addresses steel stud spacing and whether or not the exterior face of the stud has any thermal
protection.
Recall the order of magnitude differences between frame area using wood studs and the frame area
using steel studs from Table C1 three slides earlier. Change the framing from wood stud to steel
stud, adjust the frame percentage, and note the impact on the overall assembly performance.
The open box in the middle of the dialogue contains the list of assembly materials. The material
name and dimension of the layer are presented and the tool calls up the appropriate RSI value
adding it to the list and summing the total. The dialogue box also displays the unit weight and the
heat capacity of the assembly taken from the material properties in the Materials library.
To edit a layer in the assembly one clicks on one of the material layers.
31
Double-clicking on a material layer in the Assembly dialogue box brings up a new dialogue that
allows a material to be selected from the material library, or the thickness of the material to be
specified. Framing can also be called for in this material layer.
The Assembly Editor only permits one layer of framing to be specified, which can cause some
complications where exterior or interior insulation layers also include framing. Depending on the
connection details interior layers can reasonably be ignored. Exterior layers may require a workaround that makes a very conservative estimate of the impact of the secondary layers of framing.
In the work around for exterior secondary framing, a custom assembly is prepared, and using the
mass and specific heat, reinterpreted as a custom material in the materials library. This custom
material is then called from the library and added to the assembly being developed. This approach
overestimates the de-rating of the insulation value, but is transparent and was acceptable for LEED
Ca-NC and Commercial Building Incentive Program submissions.
When developing custom assemblies and work-arounds for variations in framing performance, it is
important to remember the context for the work. Minor variances in thermal resistance values may
not have any appreciable impact on annual building energy performance. If it can be shown that
including the thermal bridging of secondary framing does not significantly change the annual whole
building energy performance it is reasonable to ignore it. The sensitivity of annual energy
consumption to changes in envelope RSI can be tested numerically with the Screening Tool prior to
engaging in detail development.
32
Should one wish to review the available materials for the Assembly Editor, or create
new material entries from manufacturer’s literature or custom assemblies (as
suggested previously), the Material Library can be accessed directly from the main
Library menu. Highlighting the “Material” library brings up a new dialogue box as
seen in the next slide.
33
This slide shows the top of the list in the Materials Library dialogue box. A specific
material is listed along with the thickness of the material and its thermal resistance
per unit thickness. Where 0.00 is given as the material thickness, the actual
dimension of the material is specified in the assembly layer dialogue box (the one
with the framing check box), and the thermal resistance in the Material Library is
given per millimetre.
The values given in the Material Library are generic and follow the material
descriptions given in the ASHRAE Handbook of Fundamentals (Chapters 26 and 33
in the 2009 version). Other similar lists of material properties are found in MNECB
1997 Appendix C, and the Modelling Guide for EE4 version 1.7.
Clicking the “New” or “Edit” buttons on the right side of the dialogue calls up the
actual material description dialogue.
34
This is the input dialogue for creating new or editing existing materials for the
materials library. Each material requires a unique name to start. Following the
dimensioning convention previously discussed, the thickness of the material can be
left at zero to permit more effective use of the library. Dimensions will be called in
the assembly layer dialogue. The next inputs, material density in kilograms per
cubic metre, thermal resistance per millimetre, and specific heat will be found in
material data sheets from manufacturers or possible in the materials properties
chapter of the ASHRAE Handbook of Fundamentals (Chapter 33 in the 2009
version).
This completes the introduction to the EE4 Assembly Editor.
35
Window performance
• The NRCan Screening Tool, and other more
detailed simulation tools require whole window
performance values;
– Thermal performance varies with mullion and rail
patterns and dimensions;
– Frame area and thermal performance values are
important inputs;
• Industry standard tools for producing
performance documentation are issued by US
DOE, Lawrence Berkeley National Labs:
– http://windows.lbl.gov/software/default.htm;
– THERM for opaque assemblies and window frames;
– WINDOW for insulating glazing units.
Typical glazing percentages for commercial buildings are much greater than those for low-rise
residential, and the balance of internal to external loads also differ substantially. Accordingly a
different approach is required for commercial glazing than for low-rise residential glazing.
Regardless of scale, insulating glazing units (IGU’s) now offer much better thermal performance than
conventional frames, and the balance of frame impact versus glazing impact on thermal transmission
needs careful attention. Whole window glazing performance offers some advantages at the
commercial scale where larger glazing areas reduce the frame proportion with respect to the total
glazing area, and therefore reduce the negative impact of frame performance. However, it is often
difficult to create appropriately scaled elevations when using the largest glazing area and designers
usually play with mullion patterns as part of elevation design. It is essential then that designers be
able to characterize whole window performance and balance the ability of low-e films and gas fills
with frame geometries and performance characteristics.
The tools most commonly used for determining heat flow through window frames and IGUs are 2D
and 3D heat flow calculators. These tools can also be used for assessing the detailed performance of
opaque assemblies when there is a special emphasis on moisture management or thermal comfort.
The most up-to-date tools are issued by the Lawrence Berkeley National Lab of the US Department
of Energy. “WINDOW” is used for calculating the properties of IGUs especially with regard to heat
flow through spectrally selective systems, which vary hourly following the angle of incidence for solar
radiation. THERM is used to calculate the properties of opaque assemblies.
In Canada the FRAMEplus Toolkit provided a similar level of calculation for both opaque and
transparent assemblies, but it has not been updated for a number of years. As a result it may not
have the desired glazing options available in the product libraries.
36
Representative Window Values
Whole Window U-value (W/m2*oK)
Representative frame values in vertical
orientation (W/m2*oK)
Glazing
Frame
Cavity
Fill
U-value
Frame Type
(Fixed)
Spacer
Double
Glazing
Triple
Glazing
Single
glazing
Aluminum w/
thermal break
air
5.1
Aluminum w/
TB
Metal
6.42
6.3
Double
glazing
Aluminum w/
thermal break
air
3.6
Insulated
5.91
5.79
Double
glazing, 1
low-e film
Aluminum w/
thermal break
air
3.0
Metal
9.94
9.37
Double
glazing, 1
low-e film
Vinyl
argon
2.0
Insulated
9.26
8.57
Metal
7.21
5.91
Triple
glazing, 2
low-e films
Vinyl
Insulated
5.79
4.26
2x
argon
1.5
Source: NRCan Screening Tool for New Building
Design
Curtain Wall
Structural
Glazing
Source: Excerpted from ASHRAE F-2009
Ch. 15.5 Table 1
In the initial project stages prior to specific material decisions, designers need a way of generally
identifying the performance criteria that will contribute to a successful space. This is where tables
from handbooks and other generic design aids come in handy.
The two tables in this slide are examples of the kinds of starting assumptions one might use for
whole window performance in the NRCan Screening Tool. The table on the left hand side has been
taken from the Screening Tool itself and gives whole window U-values representing a variety of
glazing systems for direct entry into the tool. The table on the right hand side is more detailed,
discussing frame performance that needs to be combined with glazing performance and window
geometry to generate a more project specific performance value for a glazing system.
Aluminum frames, especially curtain wall frames are designed to transfer heat from the back tube of
the frame to the IGU at the spacers. This prevents condensation and potential mould growth where
the thermal performance if the IGU is weakest. The spacer in the IGU works with the frame to
complete the thermal resistance of the whole unit. This is why the frame performance lists show that
the U-value of the entire assembly is improved by using thermally insulating spacers in the IGU
(because it describes thermal transmission not resistance, the lower U-value is the better performer).
Frame material influences frame size and hence frame proportion, and solar heat gain, in addition to
overall U-value. The shading effect of operable sashes cuts incoming solar gain while at the same
time increasing the amount of frame in the whole system providing greater potential for heat loss.
Frames in more thermally resistive materials such as wool mitigate the loss in heat gain by
increasing thermal resistance to heat loss. Insulated fibreglass frames improve upon the low thermal
transmission of wood while at the same time offering slim profiles similar to aluminum that allow
greater solar gains.
Values from the right hand table on frame performance and the next two slides giving glazing
performance are combined in a spreadsheet calculator, shown in the final slide. The result is a
custom window performance value that could represent an actual design value or an average of
design values for the proposed project. Additional frame performance values are given under the
“References-Frames” tab in the “WindowUcalculator” Excel workbook.
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Glazing Unit Thermal Performance
Selected Insulating Glazing Unit performance in a variety of fixed frames: U-value (W/m2*oK)
IGU Type
/
Frame Type
Centre
of glass
Edge of
Glass
Alum.
w/ TB
Curtain Wall:
Alum. w/ TB
Curtain
Wall: SSG
Insulated
Fibreglass
(a) = DG, 12.7 mm air gap
2.73
3.36
3.31
3.45
3.22
2.72
(b) = (a) + low-e = 0.20
1.99
2.83
2.55
2.81
2.58
2.12
(c) = (a) + low-e = 0.05
1.70
2.62
2.30
2.56
2.33
1.88
(d) = TG, 12.7 mm air gap,
low-e = 0.2 on surface 2 & 5
1.42
2.41
2.05
2.27
1.97
1.64
Source: 2009 ASHRAE Handbook – Fundamentals, Chapter 15.8 Table 4
• Performance values vary with overall geometry;
• Entries based on selected test sizes:
– Fixed = 1.5 m height x 1.2 m width;
– Curtain Wall = 2.0 m height x 2.0 m width w/ 1 divider;
– Frame percentage and width influence performance.
This slide provides a sample of glazing types with centre-of-glass, edge-of-glass
and in-frame performance values. The varieties illustrate the impact of increasingly
thermally resistive low-e coatings, in addition to the differences between double and
triple glazed IGUs.
It is important to recognize that these values are based on standard test sizes and
configurations given in the bullets below the table. The centre-of-glass value can be
added directly to the “WindowUcalculator” provided separately with this slide deck.
The calculator can be used to capture the information given in this slide and adjust it
for the window size in a proposed project. The geometry is set to the standard test
size and the centre of glass value is adjusted to give a matching answer to the input
at a whole window basis. The real geometry can then be entered in the calculator
and the modified window performance value added to the simulation program such
as the NRCan Screening Tool.
In the WindowUcalculator the edge-of-glass performance is estimated by a
modifiable factor. This factor can be adjusted by comparing the different percentage
performance decreases according to the individual IGUs being referenced.
Additional IGU performance specifications for U-values and SHGC are provided
under the “References-Glazing” tab in the “WindowUcalculator” Excel workbook.
38
Window SHGC Coefficients
Solar Heat Gain Coefficients for Various Glazing Products
Glazing Set
Double Glazed CLR-CLR
Double Glazed LE-CLR
Double Glazed CLR-LE
•
•
•
•
Glass
Thickness
(mm)
SHGC
CofG @
Normal
Incidence
3
6
Whole Window SHGC @ Normal Incidence
Aluminum Frame
Other Frame
Fixed
Operable
Fixed
Operable
0.76
0.70
0.69
0.67
0.62
0.64
0.64
0.64
0.62
0.57
3
0.65
0.60
0.59
0.58
0.53
6
0.60
0.55
0.55
0.53
0.49
3
0.70
0.64
0.64
0.62
0.57
6
0.65
0.60
0.59
0.58
0.53
Entries based on same test sizes as U-values;
Performance varies with frame geometry;
Colour of glass has a significant impact;
Maximize visible light and minimize heat gain for
commercial buildings.
The Screening Tool also has an entry for Shading Coefficient. This entry will be
generated for custom window assemblies automatically by entering the solar heat
gain coefficient (SHGC) in the WindowUcalculator.
This table shows an interesting comparison between heat rejection IGUs and heat
gain IGUs, the latter being of more interest to Canadian circumstances, although
heat rejection approaches may be better for east and west orientations. One can
see how the SHGC for the LE-CLR (indicating a double glazed IGU with two clear
glass lights and a low-e coating on surface number 2, which is the inside of the
outer pane of glass in the double unit) unit is lower than the CLR-LE unit (with the
same low-e coating on surface 3, being the cavity side of the inner pane of glass in
the unit).
The last bullet is a proposal for a general strategy for glazing in commercial
buildings. This strategy prioritizes daylighting and heat rejection over conventional
passive solar gain. Another priority for commercial glazing is to prevent any direct
beam sunlight from entering the workspace, making glare control the priority over
passive solar gain. This approach requires appropriately designed exterior shading.
39
This slide shows the layout of the “WindowUcalculator” provided for the exercises
that accompany this lecture. From a limited number of inputs one can generate the
full range of performance properties for a custom sized single glazing light. The full
formulas for glazing performance from CSA Standard A440.2 are provided, but the
input for dividers has been eliminated for simplicity of calculation. Dividers increase
edge-of-glass area and therefore increase IGU thermal transmission.
This slide brings this very lengthy presentation to its conclusion. Students are now
encouraged to go online and play with the NRCan Screening Tool, the EE4
Assembly Editor and the WindowUcalculator. Understanding the relationships
between the elements of window performance and the various energy efficiency
options at a whole building level is only possible with a relatively deep exposure to
simulation tools.
The benefit of this exposure is an increased ability to use the performance option in
building and energy codes to deliver designs that improve on the levels of code
performance without being restricted to small window to wall proportions that may
not achieve the design objectives for interior spaces. Recognizing that trade-offs
between building system performance and building construction budgets are
available to support the experiences of the building occupants is a key element to
delivering truly sustainable buildings.
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