Energy and cost analysis triple glazing Energy and cost analysis on

Transcription

EXCEPT
Architecture, Urban Design, Consultancy & Presentations
February 2009 - Tom Bosschaert
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Energy and cost analysis of double and triple glazing
Introduction
In western society buildings can be responsible for more than 30% of the national energy usage and greenhouse gas emissions. In the search for solutions to combat these issues and reach the targets of policy agreements, new building materials and construction methods are introduced frequently, as is the case with triple
glazing. In recent years there are movements to make the use of triple glazing mandatory through building
codes or performance standards in the Netherlands, instead of double glazing. There are many studies done
on triple glazing, but none to compare the actual energy costs and benefits for various comparative products
for the Dutch climate. Therefore Except has initiated a small research project using energy analysis software,
basic cost calculations, LCA data and recommendations from the industry to review the consequences and
characteristics of triple glazing versus double glazing.
What is triple glazing?
Triple glazing can take the form of a variety of products. Commonly, it is similar to a standard
double glazing unit with an extra pane of thin glass inserted in the cavity between the other two
glass planes (fig. 1) using a spacer1. The two chambers that are thereby created inhibit convection and allow for a higher insulation value than with double glazing alone. The chambers can
contain air, or filled with a gas that increases the insulating properties of the unit (for these units
the ‘HR’ abbreviation is used). In Scandinavia the use of triple glazing has seen some following
due to the cold winters. In the Netherlands, due to the more temperate climate, this product
has only recently appeared on the market. A triple glazed unit is not necessarily thicker than
a double glazed one, but it is considerably heavier. This incurs costs for fabrication, storage,
transportation, handling and placement.
The insulation value UGlass is the degree of resistance to convection and conduction energy
loss, the lower the better, expressed in m-2 K-1. Double HR glazing has a value of around 2,
HR+ between 1.6 and 1.1, and HR++ a value lower than 1.1. Triple glazing can be indicated
by ‘HR+++’. The transmission value of glass determines how much radiation can penetrate the
glass, consisting of both a heat and light component, and varies among products.
Experiments with filling the cavity with insulative aero gel have been performed, reaching U
values lower than 0.72, but are not yet widely available. Also, research into creating a vacuum
in the cavities resulting in U values as low as 0.23 is underway, but also not yet available.
Outer Pane
Outer Pane
Outer Pane
Outer Pane
Insulation Insulation
gas
gas
Insulation Insulation
gas
gas
Center Pane
Center Pane
Inner PaneInner Pane
Inner PaneInner Pane
Spacer & Seal
Spacer & Seal
Seal
Frame
Seal
Spacer & Seal
Spacer & Seal
Seal
Frame
Frame
Seal
Frame
fig. 1
Jacob Catsstraat 103b, 3035 PH Rotterdam info@except.nl
http://www.except.nl
EXCEPT
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Experiment
This experiment focuses on the following three questions:
•
•
•
The energetic performance of glass types (does triple glazing reduce required heating energy?)
The environmental impact (are the extra energy and material for fabrication less than its savings?)
Cost (is it financially beneficial to invest in triple glazing?)
The energetic performance is measured using computer analysis software, which also gives us our usage
cost. Using life cycle analysis data a comparison is made concerning the environmental costs of the product
itself, and a quick cost comparison shows the financial benefits and drawbacks between products.
Experiment setup
The experiment is setup for residential usage, and uses as a model a worst case scenario of a small single
freestanding house with one occupied layer. The house is 10x10 meters square with openings on each side.
There are four variants of the house used, to measure the effect of south glazing and a comparative measure
such as better wall insulation. The house has an average Dutch activity schedule and climate, has floor heating and a gas powered high efficiency heating installation.
Variant 1: 10% North glazing, 20% East/West glazing, 30% South glazing, 100mm EPS wall insulation
Variant 2: 10% North glazing, 20% East/West glazing, 90% South glazing, 100mm EPS wall insulation
Variant 3: 10% North glazing, 20% East/West glazing, 30% South glazing, 140mm glasswool insulation
Variant 4: 10% North glazing, 20% East/West glazing, 90% South glazing, 140mm glasswool insulation
Variant 1 and 2 have average building materials for the Netherlands (brick, eps foam, concrete, gypsum),
and variant 3 and 4 have increased wall insulation and 20% less infiltration through gap treatment.
Analysis model 1 & 3 with
30% south glazing
Analysis model 2 & 4 with
90% south glazing
fig. 2
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These houses were then outfitted with various double and triple glass types, and one single plate glass type
as a reference, and were then modeled and analyzed using EnergyPlus, a comprehensive environmental
calculation and analysis algorithm for buildings. This method generates a variety of data, among which total
energy use for gas and electricity, solar gains, and CO2 generation. The advantage of using such an analytical
model is that various other parameters are taken into account, such as airtightness, real-world climate data
on a day-to-day basis, usage characteristics, etc. Reliable and repeatable experiments can be performed in
for regression testing. EnergyPlus does not take into account all possible physical processes that are taking
place, such as temperature gradients over the glass surface, or angle dependence for solar energy transmittance4, which we predict for this experiment not influence the results in a significant way.
0
KWh Gas
25000
Tested Glass Types
extra wall
insulation
Si
ng
le
=
bl
e
Si
ng
le
There are many glazing types available on the market. For this experiment five types of glazing were tested,
20000
90%
all commonly
used products in the building industry, and standardized for EnergyPlus calculations. A single
plate glass type is used as a reference, and for each double and triple glazing unit a high performance variant
is added. “UGlass” is the insulation value, and “Trans.” the transmission value.
Double HR
3mm/13mm
Argon
Triple
6mm/13mm
Air
Triple HR
6mm/13mm
Argon
Uglass = 5.36
Trans. = 0.351
Uglass = 2.45
Trans. = 0.216
30%
90%
30%
Uglass = 1.60
Trans. = 0.688
Uglass = 1.21
Trans. = 0.303
Uglass = 0.78
Trans. = 0.470
R
H
e
bl
R
30%
H
90%
le
Tr
ip
90%
Tr
ip
D
ou
le
Tr
ip
30%
H
R
H
e
bl
90%
R
H
R
H
e
D
ou
bl
le
90%
5000Calculations
Energy
le
R
R
H
30%
Tr
ip
Tr
ip
le
le
Tr
ip
30%
D
ou
H
e
bl
D
ou
Tr
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Tr
ip
D
ou
Characteristics:
10000
R
Double
6mm/13mm
Air
bl
e
Single
90%helder
6mm
30%
le
D
ou
30%
15000
Type:
Glass:
Filling:
90%
The graph in figure 3 below shows the total energy usages of the various glazing types and for the 30% and
90% south glazing houses, as well as the models with increased wall insulation. It’s immediately clear that
there are0 large benefits to using double glazing types and beyond. It’s also clear that the double HR glass
Glass & Housetype
outperforms the normal triple glazed unit.
KWh Gas
25000
=
20000
15000
extra wall
insulation
90%
30%
90%
30%
10000
30%
90%
30%
90%
Double HR
30%
n
tio
H
R
le
30%
la
info@except.nl
Tr
ip
n
tio
R
In &
su
la
ou
bl
e
H
R
KWh Gas
Jacob Catsstraat 103b, 3035 PH Rotterdam 7500
Triple
30%
90%
Triple HR
H
R
Double
e
Single
bl
0
D
ou
fig. 3
30%
90%
90%
bl
e
W HR
al
lI &
ns
u
5000
30%
90%
30%
kWh
/ yr
kg CO2 / yr
Co2 Generation:
20000
H
R
R
R
30%
R
90%
Tr
ip
4 / 10
H
90%
le
Tr
ip
le
bl
e
H
R
H
R
H
D
ou
le
30%
Tr
ip
90%
R
H
D
ou
D
ou
90%
5000
bl
e
bl
e
le
30%
H
H
30%
Tr
ip
Tr
ip
30%
le
le
90%
Tr
ip
30%
bl
e
Tr
ip
le
Tr
ip
EXCEPT
0
D
ou
10000
R
le
30%
90%
KWh Gas
25000
0
extra wall
Glass &
insulation
Housetype
Si
ng
le
=
ng
le
20000
KWh
Gas 90%
25000
e
bl
90%
90%
D
ou
20000
D
ou
30%
15000
extra wall
insulation
bl
e
Si
=
H
e
H
R
H
R
30%
H
90%
Tr
ip
Tr
ip
le
bl
D
ou
90%
le
R
H
le
30%
R
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ou
90%
30%
90%
10000
fig. 4
bl
D
ou
90%
R
H
bl
e
le
30%
Tr
ip
Tr
ip
le
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H
R
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e
30%
Tr
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5000
30%
Tr
ip
90%
90%
bl
30%
D
ou
Tr
ip
30%
15000
le
Tr
ip
10000
R
le
30%
30%
0
90%
30%
90%
5000
30%
Glass & Housetype
30%
90%
30%
90%
90%
KWh Gas
25000
30%
90%
As we can see in figure 4 as well, triple glazing alone is not a guarantee for lower energy usage,
nor autoextra wall
=
insulation
matically a better investment over better wall insulation. It is dependent on the specific type
of triple glazing
used, the0unique conditions of the location, house design and placement, insulation of the other construction
Single
HR
Triple
Triple HR
components
and
the transmissionDouble
characteristics ofDouble
the glass.
20000
R
90%
H
30%
30%
5000
90%
90%
30%
90%
30%
90%
5000
G
15000
30%
30%
90%
30%
10000
90%
90%
2500
Tr
ip
30%
20000
Tr
ip
Jacob Catsstraat 103b, 3035 PH Rotterdam 2500
10.000
10000
info@except.nl
Tr
ip
le
H
Tr
ip
H
e
Gas usage
le
8% - 11.668 €
R
e
Co2 Generation:
15000
Figure 5 shows us that extra wall insulation can be an equal or better improvement to
the energy usage of
30%
the house
5000 than even high performance triple glazing.
euro
90%
90%
12.000
bl
ng
le
H
R
D
Ex ou
b
tr le
a
W HR
al
lI &
ns
ul
at
io
n
bl
e
at
io
n
D
ou
90%
30% 30% South Glazing
H
R
D
Ex ou
tr bl
a e
W H
al R
lI &
ns
ul
D
ou
bl
e
H
R
90% South Glazing
kWh / yr
kg CO2 / yr
bl
0
le
Triple HR
D
ou
Triple
D
ou
Double HR
le
Double
Si
Single
KWh Gas
7500
fig. 5 0
30%
90%
5000
H
R
0
Co2 Generation:
20000
30%
Tr
ip
le
90%
kWh / yr
kg CO2 / yr
le
Tr
ip
tio
30%
H
R
D
Ex ou
tr bl
a e
W H
al R
lI &
ns
ul
a
le
H
90%
D
ou
b
10000
n
R
D
ou
30%
7500
15000
R
D
Ex ou
b
tr le
a
W HR
al
lI &
ns
ul
at
io
n
bl
e
H
KWh Gas
5000
90%
EXCEPT
Triple
Triple HR
kWh / yr
kg CO2 / yr
5 / 10
Co2 Generation:
20000
Solar Gain:
Gas usage
15000
10000
le
H
R
le
Tr
ip
H
e
bl
Tr
ip
R
e
bl
le
D
ou
D
ou
ng
Si
le
H
R
le
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ip
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e
bl
Tr
ip
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bl
D
ou
D
ou
ng
0
fig. 6
le
5000
Si
a e
W HR
al
lI &
ns
ul
at
io
n
The left side of figure 6 shows the gas usage versus CO2 emissions. We can see that they are related, but
that CO2 emissions are not decreasing by as much as the gas usage of the entire house. This is due to other
forms of energy use within the house such as electricity and water. This means that only a limited amount of
CO2 reductions can be affected by triple glazing.
8%
On the right of figure 6 we can see a large difference in solar gains between the
different glazing types due
to the difference in transmission values. Glass with a higher transmission value admits more light and heat
from the sun. In winter this has a direct effect on gas usage, and the effect is in the same order of magnitude
as the gas usage itself. This explains why the double HR glass outperforms the normal triple glazing, despite
the higher insulation value of the triple glass, because the double HR glass allows more solar energy to enter
the house.
The CO2 reductions resulting from using Triple HR glass instead of Double HR are approximately 200 kg
a year. This is a reduction of 5.5%, equivalent to approximately 1/40th of the output of an average car a
year.
6%
3%
=
extra wall
insulation
EXCEPT
20000
90%
30%
15000
90%
6 / 10
30%
10000
30%
Cost Calculation
90%
30%
5000
30%
90%
30%
90%
30%
90%
90%
30%
H
R
90%
Following a simplified version of an existing model5, we compare
the total cost of ownership with the extra
implementation
costs
with
the
benefits
gained
during
the
life
span
of the product. Only the double HR and
0
Single
Double
Double HR
Triple
Triple HR
triple
HR products
are shown,
for a period
of 30 years,
for the house with 90% south glazing (37m2 glass
surface). We are using a value of 45 euro/m2 for double HR and 125 euro/m2 for triple HR glazing6.
5000
n
ti o
la
D
Ex ou
tr bl e
a
W HR
al
lI &
ns
u
Tr
ip
le
la
90%
90%
Cost Difference:
Co2 Generation:
20000
30%
Implementation costs double
HR: Implementation costs Triple
30%HR:
H
R
D
Ex ou
tr bl
a e
W H
al R
lI &
ns
u
90%
30%
kWh / yr
kg CO2 / yr
Solar Gain:
1665 euro
4625 euro
Gas usage
15000
Tr
ip
le
D
ou
bl
e
ti o
n
H
R
D
ou
7500
H
R
bl
e
KWh Gas
2960 euro
10000
2500
5000
90% South Glazing
euro
12.000
R
H
le
R
le
Tr
ip
H
Tr
ip
D
ou
bl
e
Si
ng
le
D
ou
bl
e
R
H
le
Tr
ip
R
le
H
Tr
ip
D
ou
bl
e
D
ou
bl
e
0
Si
ng
le
Energy costs are calculated using a value of 3% and 6% rise in gas prices per year. The base difference in
costs at year 0 is 103 euro7, which follows from the difference in gas usage per year, multiplied by the gas
0
price. Figure 7 shows the cumulative financial gain over a period of 30 years.
30% South Glazing
8% - 11.668 €
8%
10.000
6% - 8.143 €
6%
8.000
6.000
3% - 4.900 €
3%
4.000
2.000
fig. 7
0
5
10
15
20
30 years
25
The total savings in gas usage over 30 years is 3500 m3. With an interest rate of 4% we can calculate the
cost savings back to its current cash value:
Current value of total savings in energy cost with 3% price raise per year after 30 years: 1510,84 €
Return on Investment (ROI) is the time period in which the investment has paid for itself. The ROI for 3%
and 6% rise in gas prices is more than the lifetime of the product, and the ROI for 8% rise in gas prices is
more than 26 years. This is a very low ROI often insufficient for investment by consumers or private parties.
These calculations may be affected in the future by price reductions due to increased production in the Netherlands.
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Life Cycle Analysis
Using Life Cycle Analysis (LCA) data we can investigate what the difference in energy costs is during the entire cycle of a product’s life, including raw resources, fabrication, transportation, maintenance and disposal.
The actual costs are of course dependent on the location of application, re-seller and individual manufacturer,
but using comparable data we can make an estimate of the expected performance.
LCA Calculation8:
Double HR: 547 MJ non-renewable energy
29 kg CO2eq = 151.9 kWh/m2
Triple HR: 837 MJ non-renewable energy
40 kg CO2eq = 232.5 kWh/m2
The difference in energetic life cycle costs for the triple glazed unit is 80.6 kWh per square meter of product, and almost 3000 kWh for the entire house. With an energy saving of more than 1000 kWh per year
compared to the double glazed unit, the extra investment in total life cycle costs is entirely warranted, and
regained within three years. Triple glazing would repay its extra 11 Kg CO2 cost in its material lifecycle in
just months.
Note that this LCA data assumes the products come from the same factory, and are delivered at the same
location. In reality, this will not be the case. Triple glazing is only available from select firms, sometimes even
only in another country. The extra transportation cost, which will be significant, needs to be factored in for
each case separately. If the triple glazing comes from Sweden, and the double from a local source, this extra
transportation cost will likely double or triple the environmental cost.
Conclusions
Please mind that all these results are based on a particular climate and experiment. Triple glass performs
better than double glass, and wins back its life cycle and financial costs over the lifetime of the product if:
•
... The primary energy generation for the house is on gas or a similar fuel according to the standard
used in this experiment. With a zero-energy house, for instance, the characteristics will be much less
beneficial.
•
... Direct solar-gain is used as a form of energy gain, and the transmission value of the triple glass
does not remove too much solar-gain compared to the alternative glass unit.
•
... The triple glazed unit is of high enough quality. There are triple glazed units that perform worse
than (much cheaper) double glazed units.
All these factors are heavily influenced by orientation, ventilation, internal load changes, and other construction materials9.
Drawbacks:
•
Triple glazing is considerably heavier than double glazing. This increases transport and placement
EXCEPT
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costs. It can also become the cause of increased injury in the work place. Lifting glass is already a
health hazard with double glazed units.
•
The return on investment (ROI) is very low due to the high price of triple glazing, and the modest
energy savings.
•
Energy gains for triple glazing will diminish if the insulation of other parts of the building are increased,
or if less glazed surface is used. Only the high performance triple glazing units have energy and cost
benefits, and in the Netherlands it’s already common practice to use very high performance double
glazing with a Uglass of 1.1, better than the double glazed HR glass used in this experiment.
•
Applying triple glazing requires a careful investigation of its particular performance. Transmission values are of high importance, glazing types that inhibit solar gain have higher energy usage characteristics.
•
In many cases more energy and emission reductions can be achieved by other means, such as better
wall insulation and closing of infiltration gaps, than by applying triple glazing. This means that making triple glazing mandatory will force the usage of a solution that may not be as effective as other
solutions, or not beneficial at all, while still incurring costs, hazards and extra life cycle energy investments.
Advantages:
•
Triple glazing has better sound insulation properties than double glazing, and can thus be used as an
extra advantage in areas with sound problems.10
•
Good triple glazing has less problems with condensation issues than double glazing.
Long-term consequences
The question whether a government should prescribe a specific solution, or should focus on the outlining of
required performance goals is relevant here. Requiring the application of a certain specific product type can
increase the performance of the bottom end of the spectrum. However, it can also be in the way of improvements attempted in the other end. In some cases changes in design are a better way to save energy than the
application of any specific product, such as triple glazing. The quality of the offered products also influences
the performance of these prescribed measures, resulting in for instance some double glazed units outperforming triple glazed units, making the resulting policy measure miss its target. The higher costs and risks
of triple glazing will become a major drawback in issues like these. Also, new development like aero-gels and
vacuum cavities allow an even higher insulative properties than current products. Basing a policy prescription
on a technology that is still in midst of development is inadvisable.
With passive-house and zero energy building design becoming more and more common in the industry, the
balance of these measures shift as well. When total energy usage is zero, and which can be achieved with
double Hr glazing alone, it would not be beneficial to apply triple glazing in most circumstances. This would
also unnecessarily drive up the cost of construction, costs that could be better applied elsewhere.
Except has the opinion that stimulation of performance increases should only occur on the basis of performance outlines, and that the mandatory usage of certain products or product groups will often not benefit
the overall targets of the policy measures.
EXCEPT
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References
1) US Patent 4149348, Stanley J. Pyzewski, July 1977
2) Super insulating aerogel glazing - SCHULTZ J. M, Solar Energy Materials and Solar Cells, 2005, vol. 89, no 2-3 (221
p.)
3) Triple vacuum glazing : Heat transfer and basic mechanical design constraints, by Manz, Brunners, Wullschleger,
Solar Energy, 2006, vol. 80, no12, pp. 1632-1642
4) Evaluation of predictive models for the angle-dependent total solar energy transmittance of glazing materials, by
Karlsson Rubin & Roos, Solar energy, 2001, vol. 71, no1, pp. 23-31
5) The Environmental Performance of Public Procurement: Issues of Policy Coherence By Nick Johnstone, Organisation
for Economic Co-operation and Development, OECD 2003
6) Cost for a project with more than 1000m2 glass surface. Price is an average of three market sources, February 2009
7) Caloric value gas: 31,65 MJ/m3 , Gas price 0,72 per m3 euro incl. tax: Eneco 10-Feb-2009, Gasprofile 1, Region 1
8) LCA data from: Energy Manual (Hegger, Fuchs, Stark, Zeumer) - 2008 Birkauser Verlag, p 262
9) THE EFFECT OF GLAZING TYPE AND SIZE ON ANNUAL HEATING AND COOLING DEMAND FOR SWEDISH OFFICES by
Helena Bülow-Hübe, 1998, http://aesl.hanyang.ac.kr/resource/misc/hbh_retcc98.pdf
10) Prediction of sound transmission loss through multilayered panels by using Gaussian distribution of directional
incident energy, by Kang, Hyun-Ju; Ih, Jeong-Guon; Kim, Jae-Seung; Kim, Hyun-Sil, The Journal of the Acoustical
Society of America, Volume 107, Issue 3, March 2000, pp.1413-1420
This document has been created by Tom Bosschaert in cooperation with Except Architecture, Urban Design,
Consultancy & Presentation. More information about Except can be found on: www.except.nl
Contact information: tom@except.nl
Copyright © 2009 Except. The rights to reproduce and distribute this article in any form of reproduction (printing, electronic media or any other form) is reserved. For non-commercial purposes, this article may be freely distributed, in its
entirety without changes, and translated into any language, provided due acknowledgement is made to Except and copies are sent to our contact address. If any information from this document is referenced, full mention needs to be given
to its author and Except. For all other uses, please contact us beforehand. We take great care in preparing and publishing
our research. Nevertheless this and other articles of Except may contain mistakes that we are not liable for. No rights
may be derived from the information contained within this document.
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Energy and cost analysis triple glazing Energy and cost analysis on

Transcription

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