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http://www.seipub.org/ijepr/paperInfo.aspx?ID=13230 This case study investigated the costs and savings of in ground concrete insulation systems for a home situated in the cooler Australian climates of Canberra, Hobart and Thredbo. EnergyPlus V7.2 was used to determine the annual heating energy requirements for various combinations of insulation systems and soil thermal conductivity values. The costs savings attributed to the in ground insulation were life cycle over 25 years using low, median and high heating energy cost scenarios. The results indicated that in most scenarios the concrete insulation as stipulated by the Building Code of Australia (BCA) is not the most cost effective solution.
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www.seipub.org/ijepr International Journal of Engineering Practical Research (IJEPR) Volume 2 Issue 4, November 2013
178
Simulation Based Lifecycle Costs of Inground
Insulation for Heated Concrete Slabs Colin Simmer*1, Min Wu2*
*[email protected]; 2*Corresponding author: [email protected]
Abstract
This case study investigated the costs and savings of in
ground concrete insulation systems for a home situated in
the cooler Australian climates of Canberra, Hobart and
Thredbo. EnergyPlus V7.2 was used to determine the annual
heating energy requirements for various combinations of
insulation systems and soil thermal conductivity values. The
costs savings attributed to the in ground insulation were life
cycle over 25 years using low, median and high heating
energy cost scenarios. The results indicated that in most
scenarios the concrete insulation as stipulated by the
Building Code of Australia (BCA) is not the most cost
effective solution.
Keywords
Concrete; Insulation; Life Cycle; EnergyPlus; Heat; Ground;
Canberra; Thredbo; Hobart
Introduction
The Nationwide House Energy Rating Scheme
(NatHERS) and the Building Sustainability Index
(BASIX) schemes are the embodiment of the national
push to increase building energy efficiencies across
Australia. This drive for efficiency has resulted in a
community mindset that frequentlyresults in building
professionals over specifying insulation such as that
used to insulate heated concrete slabs on ground. This
study investigated the cost effectiveness of in ground
insulation for heated concrete slabs for a particular
building in the cooler Australian climates using
EnergyPlus V7.2 building energy simulation software.
The Case Study EnergyPlus Model
The Building Model
The case study building has a rectangular floor plan
30m by 10m and its construction is atypical for
Australia. The building follows passive solar design
principles in that the 30m length North facing wall has
the most glazing (39m2), the south wall as a moderate
amount of glazing (18m2) and the East and West walls
have no glazing. Standard EnergyPlus constructions/
materials were used where possible to model the
building in EnergyPlus V7.2, and some imperial units
and American R values are used in table 1.
TABLE 1BUILDING MODEL CONSTRUCTION
Building
element
EnergyPlus construction/material layers
Note: EnergyPlus construction/material libraries use
imperial units even though the program operates in SI units
External W
alls
3m high
1. Poured Concrete‐ Sand And Gravel or Stone
Aggregate Concrete ‐ 4 in. ‐ 150 lb/ft3
2. Poured Concrete‐ Sand And Gravel or Stone
Aggregate Concrete ‐ 4 in. ‐ 150 lb/ft3
3. Poured Concrete‐ Sand And Gravel or Stone
Aggregate Concrete ‐ 4 in. ‐ 150 lb/ft3
4. Expanded Polystyrene ‐ Molded Beads ‐ 2 in.
5. Wood‐Framed ‐ 4 in. Studs ‐ 24 in. OC ‐ R‐11 Cavity
Insulation
6. Gypsum or Plaster Board ‐ 3/8 in.
hip roof 1. Metal Decking
2. Glass Fiber ‐ Organic Bonded ‐ 2 in.
Notes: Pitch ‐ 22.50, Eaves‐ 600mm wide
Roof 1. Metal Decking
2. Glass Fiber ‐ Organic Bonded ‐ 2 in.
Ceiling
1. Plaster Board ‐ 3/8 in.
2. Wood‐Framed ‐ 4 in. Studs ‐ 24 in.
3. OC ‐ R‐11 Cavity Insulation
4. Glass Fiber ‐ Organic Bonded ‐ 3 in.
5. Glass Fiber ‐ Organic Bonded ‐ 3 in
Floor slab
1. Heavyweight Concrete ‐ 65mm
2. Resistive Electric Heating elements spaced 300mm
apart
3. Heavyweight Concrete ‐ 65mm
Doors
1. 40mm solid wood
Windows
U‐factor:3.0 W/m2K
Solar heat gain coefficient:0.43
Visible transmittance0.44
Model Loads and Environment
Heating loads attributed by people or appliances were
not included in the model due to the low occupancy
density of the building. An infiltration rate of 20 litres
per second was used and an automatic natural
ventilation system was introduced to help cool the
house in summer and warm in winter when the
difference between indoor and outdoor temperatures
was favourable.
The sub program “SLAB” was employed to model the
International Journal of Engineering Practical Research (IJEPR) Volume 2 Issue 4, November 2013 www.seipub.org/ijepr
179
ground heat transfer and the default EnergyPlus soil
properties of density: 1200kg/m3 and specific heat:
1200 J/kg∙K were used. Thermal conductivity which is
greatly influenced by moisture levels is the soil
property which most affects heat transfer and is
difficult to estimate because it can vary across the site,
with depth and time. The range of values used in the
model for soil thermal conductivity (λ) is based on the
recommendations for an “Unknown” soil class found
in the AHSRAE Research Project Report RP‐701. The
recommended general estimates of 0.3, 1.2 and 2.6
W/m∙K for low, median and high values of soil
thermal conductivity were replaced with 0.6, 1.5 and
2.6 W/m∙K because suspected convergence issues with
the SLAB sub‐program caused the program to crash
when the value of λ was less than 0.6 W/m∙K.
The EnergyPlus weather files for Canberra Airport,
ACT Hobart, Tasmania and Thredbo, NSW are based
on data provided by the Australia Greenhouse Office.
Concrete Slab Insulation
Fifteen ground insulation scenarios were modelled ,
combinations of 600mm height vertical insulation and
horizontal insulation placed around the perimeter at
three different widths 1.2, 2.4 and 5.0m with R values
of 0, 1.0 and 2.0(see figure 1).
FIG. 1 INSULATION CONFIGURATIONS
System Costs
Insulation
Rigid extruded polystyrene board (XPS) is the
insulation chosen for the modelling. This is the sort of
insulation typically used in ground for slab insulation;
which complies with all the Building Code of
Australia (BCA) requirements for strength and
durability. The material cost was obtained as a quote
from a leading Canberra supplier and the excavation
and labour costs for insulation installation were
derived from a construction cost guide.
Heating
The EnergyPlus simulations only simulate resistive
electric heating because this simplified the modelling.
The assumption is made that the resulting energy
requirements are equivalent for the hydronic heated
systems. The three different heating/energy systems
investigated were:
1) Slab hydronically heated by a wood fired heat
exchanger with an efficiency of 75% using
home cut wood at an estimated $160/t (low
heating energy cost)
2) Slab hydronically heated by a Natural gas
boiler with an efficiency of 95% using natural
gas costed at $0.02825/MJ (median heating
energy cost)
3) Resistive electric heating with a heating efficiency
of 100% using electricity costed at the peak rate
of $0.2014/kWhr(high heating energy cost)
Note: A figure of 15.7MJ/kg is used for the energy
content of typical for air dried Australian hardwood.
The EnergyPlus simulations
At a room air thermostat set to be 190C each
EnergyPlus simulation gave a result of an annual
energy requirement (in Joules) to heat the building. In
all 135 simulations were run, 45for each of the three
weather files (Canberra, Hobart and Thredbo). The
designation of each EnergyPlus simulation is based on
the particular insulation system and the soil
conductivity used for that run and is designated
byKxxVxHxWx where:‐
Kxx = soil conductivity (e.g. K06 = 0.6 W/m∙K)
Vx= Vertical insulation R‐value (e.g. V1 = R1.0)
Hx = Horizontal insulation R‐value (e.g. H2 = R2.0)
Wx = Width of horizontal insulation (e.g. W12 = 1.2m)
Note: W50 is 5m which covers the entire slab
Life Cycle Cost Analysis (LCCA)
The energy savings of each insulation system over the
corresponding non‐insulated scenario were calculated
for every simulation using a low, median and high
cost heating energy system. The energy savings and
insulation costs were then amortised over 5, 10, 15, 20
and 25 year periods using the following equation:
fv=pv(1+r)n+pmt((1+r)n‐ (1+q)n) / (r‐q)where:
fv=future value
pv=present value (cost of insulation)
pmt=payment (energy cost savings over uninsulated case)
ww
180
r=i
q=i
n=n
Re
Lo
Th
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gro
R1
sho
the
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TA
ww.seipub.org
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interest rate (
inflation (3%
number of p
esults
ow Cost Heat
he life cycle
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ound insula
.0 insulation
own in table
ese results is
TABLE 2 LEAST CO
Hom
Location λ
Canberra 0
Canberra 1
Canberra 2
Thredbo 0
Thredbo 1
Thredbo 2
Hobart 0
Hobart 1
Hobart 2
FIG. 2 INS
ABLE 3LEAST COS
N
Location λ
Canberra 0.6
Canberra 1.5
Canberra 2.6
Thredbo 0.6
Thredbo 1.5
Thredbo 2.6
Hobart 0.6
Hobart 1.5
Hobart 2.6
g/ijepr
(5% per annu
% per annum
periods (years
ting Energy
cost analys
ed that in m
ation is une
n is cost effe
e 2. A graphi
shown in Fi
OST INSULATION
me cut wood hy
λ Least cos
5
0.6 Nil
1.5 Nil
2.6 Nil
0.6 Nil
1.5 Nil
2.6 Nil
0.6 Nil
1.5 Nil
2.6 Nil
SULATION LCC
ST INSULATION SY
Natural gas hyd
Least cos
5 10
6 Nil Nil
5 Nil Nil
6 Nil V1
6 Nil Nil
5 Nil V1
6 Nil V1
6 Nil Nil
5 Nil V1
6 Nil V1
International
um)
)
s)
sis using lo
most situation
conomic an
ective in thr
ical depiction
g. 2.
N SYSTEMS FOR LO
ydronic slab hea
st insulation sys
10 15
Nil Nil
Nil Nil
Nil Nil
Nil Nil
Nil Nil
Nil Nil
Nil Nil
Nil Nil
Nil Nil
CA FOR CANBE
YSTEMS FOR MED
ronic slab heati
st insulation sys
15 20
Nil Nil
V1 V1
V1 V1
Nil V1
V1 V1
V1 V1H1W
Nil Nil
V1 V1
V1 V1
l Journal of En
ow cost heat
ns the use o
nd only vert
ree scenarios
n of a portion
OW COST HEATIN
ating
stem for Year:‐
20 25
Nil Nil
Nil Nil
Nil Nil
Nil Nil
Nil V1
V1 V1
Nil Nil
Nil Nil
Nil V1
ERRA, λ=0.6
DIAN COST HEAT
ng
tem for Year:‐
25
Nil
V1
V1
V1
V1H1W12
W12 V1H1W12
V1
V1
V1H1W12
ngineering Pra
ting
of in
tical
s as
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NG
TING
2
2
2
Me
The
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ver
solu
por
Hig
Hig
mo
por
T
Loc
Can
Can
Can
Thr
Thr
Thr
Ho
Ho
Ho
actical Researc
FIG. 3 INS
edian Cost H
e life cycle c
ergy reveale
rtical R1.0 in
ution as show
rtion of these
gh Cost Heat
gh energy c
ore cost effec
rtion of these
TABLE 4LEAST CO
Elect
cation λ
5
nberra 0.6 Nil
nberra 1.5 Nil
nberra 2.6 V1
redbo 0.6 Nil
redbo 1.5 V1
redbo 2.6 V1
obart 0.6 Nil
obart 1.5 Nil
obart 2.6 V1
FIG. 4 INSU
ch (IJEPR) Vol
SULATION LCC
Heating Energ
cost analysis
ed that in m
nsulation w
wn in table 3
e results is sh
ting Energy
costs make h
ctive as show
e results is sh
OST INSULATION S
tric resistive (pe
Least cost i
10
l Nil
l V1
V1 V
l V1
V1 V
V1H1‐W12 V
l Nil
l V1
V1
ULATION LCC
lume 2 Issue 4
CA FOR HOBA
gy
using medi
most situatio
was the mos
3. A graphica
hown in Fig.
higher level
wn in table
hown in Fig.
SYSTEMS FOR HIG
eak rate) slab he
insulation system
15
V1
V1
V1H1‐W12 V1H
V2
V1H1‐W12 V1H
V2H2‐W12 V2H
V1 V1H
V1 V1H
V1 V1H
CA FOR THRED
4, November 2
RT, λ =1.5
ian cost heat
ons the use
t cost effect
al depiction o
3.
ls of insulat
4. A grapho
4.
GH COST HEATIN
eating
m for Year:‐
20 25
V1 V2
V1 V1H1W
H1W12 V1H1W
V2 V2
H1W12 V2H2W
H2W50 V2H2W
H1W12 V1H1W
H1W12 V1H1W
H1W12 V2H2W
DBO, λ = 2.6
2013
ting
e of
tive
of a
tion
of a
NG
W12
W12
W12
W50
W12
W12
W50
International Journal of Engineering Practical Research (IJEPR) Volume 2 Issue 4, November 2013 www.seipub.org/ijepr
181
Conclusions
The BCA states that Canberra and Hobart designated
as climate zone 7 and as such a minimum of the
equivalent of KxxV1H0W0 insulation is required for
heated concrete slabs. Thredbo in climate zone 8
requires KxxV1H2W50 as a minimum. The results
show that if a reasonable soil thermal conductivity
estimate can be determined for a building site, large
cost savings could be made if the optimum insulation
system could be used. These savings could benefit the
home owner directly in reducing building costs or
they could be used to implement other energy saving
or energy producing technologies which are more cost
effective such as heat recovery units, more efficient
windows or photovoltaic systems.
REFERENCES
ACTEW AGL, ʺACT Natural Gas Residential ActewAGL
NG Regulated Offer,ʺ ed: ACTEW AGL,, 2013.
ACTEW AGL, ʺACT Electricity Residential ActewAGL
Regulated Offer,ʺ 27/6/2013 2013.
Environment Australia, ʺReview of literature on residential
firewood use, wood‐smoke and air toxicsʺ, 2002.
G. Satish, L. S. Shen, and L. F. Goldberg, ʺAssessment of Soil
Thermal Conductivity for Use in Building Design and
Analysis,ʺ American Society of Heating, Refrigeration
and Air‐Conditioning Engineers, Atlanta, USA RP‐701,
1993.
Rawlhouse Publishing Pty Ltd, ʺRawlinsons Australian
Construction Handbook,ʺ ed. Perth: Rawlhouse
Publishing Pty Ltd, 2012.
S. Andolsun, C. H. Culp, J. Haberl, and M. J. Witte,
ʺEnergyPlusvs DOE‐2.1 e: The effect of ground coupling
on cooling/heating energy requirements of slab‐on‐grade
code houses in four climates of the US,ʺ Energy and
Buildings, 2012.
Colin Simmer, Bachelor of Construction Management
(Building), Faculty of Engineering and Built Environment,
University of Newcastle, Callaghan, NSW, Australia, 2013.
Dr. Min Wu, was a Professor (on leave) Chongqing Jiao
Tong University; and is a Senior Lecturer, School of
Architecture and Built Environment, the University of
Newcastle, Australia.