M. Kordjamshidi, S. King/Energy and Buildings 41 (2009) 125–132
Overcoming
problems in house energy ratings in temperate climates: A proposed new
rating framework
Maria Kordjamshidi a,*, Steve King b
a Faculty of Engineering, Ilam University, Iran
b Faculty of Built Environment, University of New South Wales, Australia
Keywords:
Energy
Rating
Residential buildings
Energy efficient
Thermal performance
assessment
ABSTRACT
This paper first
demonstrates that an efficient design for a house in conditioned operation mode
differs from that for the same
house in the free-running operation mode, and that this is a primary reason for
the inability of current
energy based rating schemes to adequately assess the performance of passive
design in a temperate climate. We examine the Australian Nationwide House
Energy Rating Scheme as an example of this problem. A new practical framework for a house rating
scheme is then presented. In this proposed framework, the efficiency of a house design is evaluated with
reference to its thermal performance in free-running mode, in addition to its projected energy
loads in conditioned operation mode. The study uses simulation to evaluate the thermal performances of
houses, and employs multiregression analysis to develop the framework. The reliability of
proposed framework as compared to the current
energy based rating scheme is demonstrated. By attributing more value to the
performance of houses in the free-running than the
conditioned operation, it is assumed that policy objectives for reducing energy
demand for space heating and cooling in the residential building sector are
more likely to be achieved.
1. Introduction
Throughout the world, a
variety of House Rating Schemes (HRS) has been developed to evaluate residential building performance. While Roulet et al. [ 1] outline multiple criteria and rating methods employed, energy efficiency has been the main parameter in almost all developed building rating schemes. Building rating schemes have
historically favoured an ‘energy indicator’ for their performance evaluation (usually normalized by the area
or the volume of the dwelling) [2–10], because:
(a)
Energy represents a high
percentage of the running cost of a building and has a major effect on the thermal and visual comfort of the
occupants.
(b)
Notwithstanding the likely
discrepancies between projected theoretical energy loads and variable real-world consumption, an energy rating can give a potential buyer information on the energy bills that are likely to arise.
(c) Where heating
and cooling plants are either a normal, or a mandated part of building construction, energy ratings help to choose appropriate HVAC
equipment; and arguably this allows for competition in the market to refine the rated capacity of the size of plant.
(d) In effect this
means that houses are assumed to use artificial energy for their space heating and cooling, However, an axiom of sustainable
energy use for dwellings has to be that in moderate climates effective passive design can minimize or altogether avoid artificial heating and cooling. Thus, where for instance Australian climates differ from those of Europe and Canada, differences in the programming of HERS were expected [ 11]. Nevertheless, house ratings in Australia, as in other countries, are based on prediction of energy requirements, and have not been modified to give more value to free-running houses; as a consequence, such designs cannot be
properly scored through the current Australian rating scheme [12].
Current building rating schemes also
generally assume that a house with less energy
usage is the most energy efficient house [6]. However, low energy use does not necessarily correlate with energy efficiency [13]; energy minimization is related to the efficiency of appliances as much as it is to the fabric of the building. It has been argued and demonstrated that a simple normalized energy based rating is not sufficient to convey the credibility of an energy efficient design [ 12,14–17 ], and that this issue appears to be more critical when a house is specifically designed to be operated in free-running operation mode [18,19]. Based on such criticisms, authors such as Williamson et al. [20] go so far as to suggest that the Australian Nationwide House Energy Rating Scheme (NatHERS) is a technical and policy failure.
The USA Department of Energy Annual
Energy Outlook 2008 with Projections
to 2030 [21 ] provides further
evidence of the necessity of developing a free-running
rating in combination with current energy
based rating schemes, pointing to the role of air conditioning in increased demand for
higher level of indoor comfort, but also to an identified ‘take back
effect’ – which occurs when people
with more efficient homes actually use more energy than expected, because they are less cautious
about basic efficiency measures
such as thermostat settings [22]. It has been
noted that despite
efforts to improve energy performance, the thermal performance of houses when occupied is
generally not as has been expected or intended [23].
Preliminary investigations in this study [ 19,24] comparing
the performance of ‘typical’ houses,
also confirmed that an effective design
for a house for free-running operation mode differs significantly from that for the house in
a predominant conditioned
operation mode. This alone may be sufficient to explain why in current energy based rating
schemes, an efficient free-running
designed house appears to be discriminated against in comparison to conditioned houses. The preliminary conclusion reached was that a systematic method for the
evaluation of projected thermal performance of a house in
free-running operation mode should necessarily differ from that
in conditioned operation mode.
The project described in this paper
explores methodologies and a framework for assessing a proposed building’s projected
thermal performances, in both its free-running and
conditioned operation modes. For the purposes of this study,
free-running houses were defined narrowly as houses ‘without any mechanical
equipment and
artificial energy load for space heating and cooling’. Aynsley [25], amongst
others, has suggested that this definition is overly restrictive, especially for a warm humid
climate. However, the focus of the present study is only temperate
climates, because this climate type has the most potential for promoting
and using free-running houses.
2.
Methodology
In order to develop a framework for HRS
based on the performances of a house in its different
operation modes, it was required:
·
First, to identify the extent to
which the thermal performances of houses vary in their different operation modes. In common with most related studies, a simulation method was employed.
·
Second, to develop an equivalent
rating method for free-running performance, which we refer to as a House Free-Running Rating Scheme (HFRS).
·
Third, to propose a robust method
to aggregate the two ranking systems of HERS and HFRS, based on simulation of projected performance by the common thermal simulation engine.
2.1. Samples
It is impractical to take into account all different house typologies. Attention was focused on six ‘typical’ detached houses, found by an earlier study to sufficiently encompass the size and planning characteristics of houses most common in the marketplace, in the state of New South Wales, Australia [26]. A general description of the sample houses is given in Table 1.
Table 1
Window,
wall, ceiling, floor areas of typical houses.
House |
Number |
External
wall |
Window |
Ceiling |
Internal |
Floor |
|
of
floors |
area (m2) |
area (m2) |
area (m2) |
wall (m2) |
area (m2) |
1A |
1 |
137 |
32.4 |
138.2 |
96.6 |
138.2 |
1C |
1 |
150 |
24.8 |
155.4 |
88.1 |
155.4 |
1D |
1 |
196.5 |
45.9 |
244.9 |
160.4 |
244.9 |
2A |
2 |
256.7 |
50 |
166 |
156.1 |
292.8 |
2C |
2 |
260 |
56.5 |
136.3 |
182.3 |
315.7 |
2D |
2 |
234 |
40 |
144.4 |
174.4 |
229 |
2.2. Tool
The simulation software used for modeling the houses is
AccuRate. A new version of the earlier NatHERS software,
AccuRate has been
developed as the preferred ‘second generation software’ for the Australian Nationwide House Energy Rating Scheme. The
reliability of this software is validated through
BESTTEST [27].
AccuRate predicts an annual energy requirement of a
simulated house in a standardized conditioned operation mode, and can be
run in ‘non-rating’ configuration to predict hourly indoor
temperatures in the free-running operation mode. An
important factor in the change to the AccuRate software is its capability of
considering
the effect of physiological cooling by natural ventilation, when computing cooling energy requirements [28].
2.3.
Simulations
A total number of 1164 simulations of thermal performance of
houses was carried out, for two moderate climates of
Sydney and Canberra. This paper only reports results for the Sydney climate.
Models were generated from the six ‘typical houses’ and
were different from
each other in terms of 17 variables (Table 2). Each variant model house was simulated for two different operation
modes, conditioned and then free running.
3. Performance evaluation
Evaluation of whether a house is more energy efficient than another house can be complex if the activities in the building, or the climate, or the state of operation of house are not the same. Where the one indicator of efficiency is used, a house designed to
be energy efficient
with high-quality performance in its conditioned operation mode might display poor thermal performance in
its free-running operation mode.
Table 2
House
parameters for simulations.
|
Variable |
Parameter description (building
fabric) |
Parametric
set |
1 |
X01 |
Ceiling insulation (resistance) |
0, 1, 2, 3, 4 |
2 |
X02 |
Wall insulation (resistance) |
0, 1, 1.5, 2,3 |
3 |
X03 |
Floor insulation (resistance) |
0, 1, 1.5, 2 |
4 |
X04 |
Internal wall (U value) |
|
5 |
X05 |
Infiltration (air change per
hour) |
0, 1, 2, 5 |
6 |
X06 |
Window covering (resistance) |
0, 0.03, 0.055, 0.33 |
7 |
X07 |
Openable window (%) |
25 (base), 50%, 75% |
8 |
X08 |
Shading device (eave length) |
0, 450, 600, 1000 mm |
9 |
X09 |
Orientation
(degree) |
0, 45, 90, 135, 180, 225, 270, 315 |
10 |
X10 |
Glazing type (shading
coefficient) |
1, 0.52, 0.70, 0.88, 0.60 |
11 |
X11 |
Roof colour (absorbance) |
30%,50%,85% |
12 |
X12 |
Wall colour (absorbance) |
30%,50%,85% |
13 |
X13 |
Window to wall ratio (N&S)
(%) |
0 (base)a,
15%, 25% |
14 |
X14 |
Window to wall ratio (E&W)
(%) |
0 (base), 15%, 25% |
15 |
X15 |
House
type |
Single storey, double storey |
16 |
X16 |
House
construction |
Heavy weight, light weight |
17 |
X17 |
House
plan |
6 typical plans |
a 0 (base) refers to the percentage of window to wall
ratio in the typical houses which
is different for different models. It does not mean that the ratio of window to wall
is 0.
Appropriate indicators
would be values derived from the parameter that
describes the state of a house, dependent on its dominant state
(conditioned or free running). The thermal quality of a dwelling can be assessed in terms of estimation of its annual
energy requirements in its conditioned operation, or an
‘aggregated annual thermal comfort condition’
in its free-running mode. The first demonstrates the conditioned performance of the
house and is used in current house rating schemes. The
latter demonstrates the actual performance of the house, and addresses
multiple aspects of efficiency in a particular
architectural design [ 14]. The thermal
performance of a house in conditioned mode is
quantified
in terms of annual energy requirement (MJ/m2)needed to maintain the
occupied zones within a determined temperature band. The thermal performance of a free-running house is
quantified in terms of Degree Discomfort Hours (DDH) in
occupied zones, taking some account of acclimatization and for variances in
relative humidity. These metrics are described in brief
below.
When the houses were
modelled in the conditioned mode, heating and cooling thermostat settings of 20–24.5 and 18–24.5 °C
were
applied in the living zone and bed zone respectively. This range coincides with the AccuRate software thermostat settings for
mandated ratings for the Sydney climate.
When the house was
simulated in free-running operation mode, the indicator to evaluate the thermal performance was
Degree
Discomfort Hours, a measure of the extent to which the indoor temperature falls outside comfort boundaries. A spreadsheet algorithm was developed to transform annual hourly
temperatures into DDH. For this purpose the boundaries of
thermal comfort conditions for the Sydney climate were
determined using an adaptive thermal comfort model
[29,30] expressed in Eq. (1) for 90% occupant acceptability, on a monthly basis.
TINS =0.31T+17.8 (1)
where T is the average monthly (outdoor) temperature (°C).
The boundary of comfort temperatures shown in Fig. 1 is
applied for the living zone. The lower boundary of
temperature for the bed zone at sleeping time (12 am–6 am) is pulled down by 5 °C
because it is assumed that occupants can easily use a
blanket. The limit of that band changes on an hourly basis in response to relative
humidity. The effect of humidity was accounted for in
accordance with the ASHRAE standard Effective Temperature lines, and by
employing a simplified equation proposed by Szokolay [31]. Indoor
humidity was considered approximately similar to outdoor
humidity in free-running houses, although in reality
indoor humidity slightly differs from outdoor humidity.
Fig. 1. Thermal neutrality comfort band for free-running
houses in the Sydney climate.
4. A comparison of conditioned and free-running thermal
performance approaches
Thermal performances of the simulated
houses were compared and analyzed, using parametric sensitivity analysis and multivariate regression analysis. The aim of this kind of analysis here has
been to investigate the effects of house envelope
variations on the annual and seasonal behaviour of the typical houses, and also to
investigate possible linkages between the thermal
performances of a house in different operation modes in response to the 17
variations described in Table 2. Multivariate
regression analysis was then applied to investigate the correlation, similarity and
differences between the thermal performance of simulated
houses in conditioned and free-running operation modes; and – in order to
establish the factors that need to be considered by those
attempting to design efficient buildings for different
dominant operation modes – to investigate whether the effect of each
parameter
on the performance of a house is similar or different in both operation modes.
The present study does not explore the interaction effects of
design parameters on the thermal performance. It also
does not include all occupancy scenarios, although this is a main parameter
in evaluating dwelling free-running performance. Both
these exclusions are more fully discussed in a previous paper by the
authors [24].
4.1. Parametric sensitivity analysis
The parametric sensitivity analysis demonstrated that changing house fabric parameters to improve the thermal performance of a conditioned house (i.e. reduce annual energy load in MJ/m2) does not necessarily improve the thermal performance of that house in its free-running operation mode (assessed based on annual DDH). This result was generally consistent throughout, when one of the 14 variables in construction was added or modified. A part of this analysis is reported more fully in [ 19]. For example the addition of insulation to the external walls of all typical houses resulted in an improvement in the conditioned operation mode, but for single storey houses with heavyweight construction the simulations project a deterioration of annual free-running thermal performance. This is illustrated, for one of the single storey houses, in Fig. 2. Even where the effect on the predicted thermal performances in response to change in an envelope variable was in the same direction, the proportionate improvement or degradation was not the same for both operation modes. For example the addition of R2 insulation to the ceiling of typical houses gave an
average improvement of 42.5% on their
predicted conditioned performances;
however the improvement on their annual free-running performance was about
32.9%.
The variables were
compared with respect to how strongly they affect the thermal performance of the typical base houses.
The average relative strength of some of variables is
given in Table 3. The main reason for these
differences was found to relate to the seasonal performance of the house in different
operation modes. For example, in the climates modelled,
the addition of
insulation in the external wall improves the winter performance of a house and degrades its summer performance,
in
both free-running and conditioned operation modes. However the improvement in the winter performance of a conditioned
house is about 9% greater than that for the same house in
the free-running operation. Obviously, in winter, added insulation
helps to maintain indoor comfort conditions for longer and
therefore
reduces the energy requirement for space heating. In comparison it does not make a significant difference in the
winter
performance of the house in free-running mode, because winter DDH refer to the indoor condition which is below the
comfort zone and again, insulated walls tend to maintain
the uncomfortable indoor condition for a longer time. The winter
performance of the house therefore was not significantly
sensitive to the addition of insulation in the external
walls in the free-running operation mode. The degradation observed in
the overall thermal performance of the typical house in
the free-running operation therefore is due to degradation in its summer
performance.
These observations
provide further evidence that detailed
design decisions aiming for an energy efficient
conditioned house should differ
from those aiming for a free-running house. This is also addressed in the multivariate regression analysis.
4.2. Multivariate regression
analysis
The result of this
analysis is reported in detail by the authors in
[24]. The analysis supported the outcome of parametric sensitivity
analysis. Further, it demonstrated the following two key
points:
·
Correlation
coefficients between predicted indicators of annual
thermal performances of simulated
houses suggest that there is a key difference between characteristic thermal
performances of single
storey and double storey houses, sufficient to call into question the likely reliability of any system which
assesses those two types of houses under a single rating framework.
·
Comparing the
significance of the variables, according to their
beta coefficients, confirms that
the contribution of design features or building fabric properties to the improvement
of the thermal performance of a house depends on the
operation mode. In other words, design for a conditioned house is
closely related to its envelope characteristics – those
attributes that protect or isolate the building interior from the environmental
loads, and maintain indoor thermal
comfort conditions with minimum energy consumption to overcome those loads.
However, as has long been implied
by the alternative terminology
‘climate responsive’, the determinants of free-running
performance are more complex.
Fig. 2.
Comparison between the effect of wall insulation resistance in prediction of annual thermal performance of a house (D1) in different operation modes.
Table 3
Percentage
variations in annual thermal performance of the typical houses in free-running and conditioned modes.
Parameters |
Percentage thermal performance variations (Sydney) |
|
|
Free running |
Conditioned |
Ceiling
insulation (none to R4.0) |
36.4% |
46.1% |
Wall
insulation (none to R4.0) |
7.8% |
9.7% |
Floor
insulation (none to R2.0) |
4.7% |
1.6% |
Wall
colour (0.30–0.85 absorbance) |
3.5% |
3.6% |
Roof colour (0.30–0.85
absorbance) |
3.16% |
22.6% |
Orientation |
6% |
5% |
Window
overhang (none to 1 m) |
4.8% |
3.7% |
Glazing
type (SG Clr to SG Refl.) |
4.6% |
2.1% |
Window
covering (open W. to Drape) |
7.4% |
9% |
Openable
window (0.25–0.75) |
6.7% |
8.7% |
Window to
wall ratio (N&S) |
1.1% |
1.3% |
Window to
wall ratio (E&W) |
0.24% |
1.7% |
Internal
wall (plasterboard to brick) |
19.1% |
8.2% |
Infiltration
(0–5 air change per hour) |
14.7% |
17.8% |
.
Therefore, heuristic
design decisions inferred from use of a
rating tool, to improve the thermal performance of a house
intended
to be substantially free running, should differ from those for a house intended to be substantially conditioned. It also thereby
implies that the regulatory framework for rating
free-running houses should be different from that for conditioned houses. Such a
framework is developed in the following.
5. Rating thermal performance of
houses
A house rating system
scores a house by comparing its thermal
performance with other houses, which are given the same
conditions of climate, and typically user behaviour
patterns and house operation. Also typically, rating schemes adopt a rating
scale, such as the star categories of the Australian
Nationwide House Energy
Rating Scheme.
If a single overall
rating is to be the objective, it would seem
necessary to avoid any unfair treatment relating to
house type and house operation mode. Preliminary analysis suggested the
following steps in developing a unified rating scheme:
· separating free-running houses from conditioned houses;
· separating
house types (in this study double storey and single storey
houses);
· determining the score boundaries for each group
separately;
· appropriately aggregating the score bands of a house for
its free‑
running and conditioned
performances, to produce one score.
The choice of
procedure used for determining the boundaries of
any rating scale varies from place to place, depending on
the particular legislation involved in the promotion of energy
efficiency. However, five star categories as used until
recently in the Australian NatHERS have provided sufficient and meaningful
differentiation
between the relative efficiencies of different houses in the same condition and operation mode, and are retained in our
proposed framework. To determine the score bands for the
ratings in this study, discrete efficiency categories were adopted for
free-running (HFRS) and conditioned houses (HERS) separately, in each
of which five ranges of scores are represented by five
stars.
The range of the five
categories was defined by‘norm-referenced
measurement’ [32].‘Grading on a curve’ was then applied,
using the means and standard deviations of the normal distribution of the
performance scores. A necessary requirement for
application of this method is that the data has a normal distribution. Normal
distribution was checked and confirmed for our data.
The star bands
derived (based on the mean value and standard
deviation of the relevant measure related to operation
mode for each of the proposed two design categories) are applicable only for
the data and specified climate in this study, and
therefore not reproduced here. To implement the proposed framework more
widely – say nationally in Australia – a larger sample
would have to be simulated, giving rise to modified band boundaries.
6. The combination of the two rating systems
The aim
of the integrated rating system is that it will
differentiate between the value
of an efficient design for a free-running house and one for
conditioned house depending on the climate, and national policy objectives for building
energy conservation, while not compromising unfairly the value of
any efficiently designed house. A
suitable algorithm can be employed for aggregating the two discrete rating systems,
which gives
more value to either an efficient free-running house or an efficient conditioned house. However, this study is
concerned specifically with promoting efficient free-running houses.
Thus the particular method of aggregation illustrated below
aims to give more value to these houses in a moderate climate
such as Sydney, as a matter of policy in the context of
sustainable development. It is intended to encourage the public to
adopt free-running houses in order to reduce energy consumption
for space heating and cooling.
A 10 star rating
scheme is proposed, using an algorithm to
integrate the five star ratings for the same house under
HERS (MJ/ m2/year in conditioned mode) and HFRS (annual Degree Discomfort
Hours
in free-running operation). The algorithm is most conveniently executed as a ‘lookup table’ illustrated at Fig. 3. The eleven
cells of the table correspond to the initial range of
possible ‘half star’ ratings for
conditioned performance. In each cell of the table:
·
the first column allocates the
probabilistic score for the conditioned performance of a house in a 5 star rating;
·
the second column allocates all
probabilistic scores for the free-running performance of
the house in a 5 star rating;
·
the third column allocates the
final aggregated score in which: o the top score is obtained from adding the conditioned rating
score to the 5 star rating of the house in free-running
performance;
o
the other final
scores allocated in the third column are
produced by taking 1 score away
from the resulting upper final score. This establishes a different value to the
different performances of a house by rewarding the free-running
performance of the house.
In this sort of
aggregation the final score is mostly less than the
score produced from simply adding the scores of both
ratings. For instance, in the first group, by adding the first two grades of free-running (5) and conditioned (5) ratings, the result will be 10, which
is the top star rating in the proposed new rating system.
The addition of the second grades in this group, free running (5) and
conditioned (4.5), gives a sum of 9.5, but a score of 9
stars (10-1=9).
A regression analysis
was then employed to confirm, and give
numerical values to the sensitivity of the final score
(as a dependent variable) in relation to the free-running and conditioned scores (as independent variables). The regression obtained
confirms
the greater dependency of the final score on the free-running performance of a house, as expressed in Eq. (2).
S = 0.40S1 + 0.87S2 (2)
The standardized coefficient for free-running
performance is 0.87 where
that for the conditioned performance is 0.4. In other words, to produce the final score for the thermal performance of
the house, the effect of the free-running score is more than
double the effect of the conditioned score. As a result, in order to
achieve an acceptable score in the proposed new HRS, a designer
would be likely
to give priority to free-running design for improving the thermal
performance of the house. This supports the objective of the rating framework: to encourage the public and
architects to opt for free-running houses. Depending on the appropriate
policy for reducing energy consumption, the method could also be
applied to give more value to conditioned houses, simply by
transforming the method of aggregation of the two ratings.
7. Reliability of the
framework
The proposed
framework was finally tested for its theoretical
sensitivity to improvements in efficient design. A
simulated improvement in response to the composite rating was employed.
For this purpose the following steps were taken:
·
The design quality
of the typical houses was improved by modifying design attributes (the 14 parameters in Table 2) in order to enhance, first the free-running performance,
then the conditioned performance of the houses.
·
The resulting projected annual energy
requirements and DDH were
input in a regression model to determine the correlation between the indicators of free-running and conditioned
performances for these
‘improved’ houses.
·
All simulated
houses were scored on the basis of the proposed
rating scheme to check how their
scores on the HERS changed in relation to the changes in their score on the
free-running component.
Fig. 3.
The regression showed a strong linear correlation
between the annual energy requirements and Degree Discomfort Hours of
houses when their thermal
performances were improved (Fig. 4).
Fig.
4. Correlation between energy requirements and Degree Discomfort Hours.
The correlation was
0.86 for the Sydney climate and 0.76 for the
Canberra
climate.
Fig. 4 also clearly shows the relative impact of the improvements, both as lower absolute values (highlighted in the figure by the superimposed boxes) and as changes in the correlations. Before the improvement the correlations were r2 = 0.69. After improving thermal behaviour by modifying the building fabric, the correlation was r2 = 0.86. This implies that if design quality is improved greatly for either free-running or conditioned operation modes, an
efficient house design can result in good
performances for a house in both
operation modes.
This implication was then checked against
the proposed score bands, to examine the relationship between the scores of houses in
free-running (HFRS) and conditioned ratings (HERS). All
simulated samples were therefore scored on the basis of the proposed rating
framework. The relationship between the scores is shown
in Fig. 5.
Fig. 5. Correlation between the scores of houses in
free-running and conditioned modes, in the Sydney climate for single story (a)
and double storey houses (b).
Fig. 6. Pictorial expression of the proposed framework.
It can be seen that
there is a linear relationship between the
scores of double storey houses in different modes.
However, the relationship
would appear to be polynomial amongst the single storey houses. This is evidence of a significant difference
between the characteristics of single storey and double
storey houses, and confirms our previous conclusion that a rating
system would need to separate these two house types for
evaluation.
A point worth noting
in this approach is that houses with 4 stars
in
free-running mode get at least 3.5 stars in their conditioned performances, but houses with 4 stars in their conditioned
performance
do not necessarily score higher than 3 stars in their free-running performance. In other words, an efficient design for a
free-running house could improve the performance of that
house in the conditioned mode if the HFRS score is not less than 4 stars.
This qualification therefore will be included in the
proposed prototype
framework for HRS.
8. Prerequisites for an efficient design in the proposed HRS
In any rating scheme, a
minimum performance level is generally required for designation of efficiency in an architectural
design. In Australia, this varies according to the State
or Territory and is proposed by authorities in each jurisdiction. For example,
the initial regulatory framework of the Nationwide House
Energy Rating Scheme in Australia established a maximum of 5 stars
computed by the NatHERS software, with 3.5 stars as the
prerequisite for an efficient house design. This is now
to be superseded by
the 10 star system of AccuRate, which requires 5 stars as a prerequisite for an efficient design.
This study proposes an
alternative 10 star rating for HRS, derived by aggregating 5 stars for HERS and 5 stars for HFRS. As
observed
above, a house with 4 stars in free-running mode will achieve 3.5 stars in conditioned operation mode. The combination
of
4 star HFRS and 3 star HERS scores 6.5 stars, which is thus defined as the recommended minimum requirement for energy
efficient
design (Fig. 6).
9. Concluding remarks
The study reported in this paper was initiated in
response to long-standing anecdotal criticisms of the Australian Nationwide
House Energy Rating Scheme. Architects and other
designers have pointed to a
perception that it discriminates against the proper application of
climate responsive design by not giving sufficient value to free-running performance of houses. Notwithstanding
some methodological limitations, by employing
conventional analysis of simulated performance, this study has confirmed that
in moderate temperate climates, effective strategy for
improving energy efficiency design of a house is indeed related to the
preferred house operation mode. The findings strongly
suggest the necessity of developing a new regulatory framework for such
temperate climates.
To create a new house rating framework, an aggregation of two rating systems has been developed. While the use of a simplified
indicator of thermal discomfort (Degree Discomfort Hours) is not
new, the study establishes the validity of its use in
such a combined rating framework, as an independent rating metric for free-running performance, employing a common thermal performance
simulation
software.
The proposed new rating
framework gives weight to the benefits of deliberate design for both conditioned and free-running
performance. For the purposes of this study, its
application has been to favour the contribution of free-running performance, but
this weighting may be varied at will to respond to
different policy priorities in different climates or jurisdictions. It is assumed that if
it
is employed as a basis for House Ratings Schemes, this approach is likely to deliver significant benefits in terms of reduction in
energy demand and increased sustainability.
In deriving the rating
measures for thermal comfort and projected dwelling performance, the authors have adopted the
adaptive comfort approach. That approach is undergoing
further refinement as it is being currently incorporated in ASHRAE
standards, and is expected to lead to further improved
discrimination between free-running
and conditioned performance predictions.
References
[ 1] C.-A. Roulet, F. Flourentzou, H.H. Labben, M.
Santamouris, I. Koronaki, E. Dascalaki,
V. Richalet, ORME: a
multi-criteria rating methodology for buildings, Building and
Environment 37 (6) (2002)
579–586.
[2] M. Santamouris, Energy Retrofit of Office Buildings,
University of Athens, 1995.
[3] R. Zmeureanu, P. Fazio, S. DePani, R. Calla, Development
of an energy rating system for existing houses, Energy and Buildings 29 (2)
(1999) 107–119.
[4] V. Richalet, F.P. Neirac, F. Tellez, J. Marco, J.J.
Bloem, HELP (house energy labelling procedure): methodology and present results, Energy and
Buildings 33 (3) (2001) 229–233.
[5] M. Santamouris, E. Dascalaki, Passive retrofitting of
office buildings to improve their energy performance and indoor environment: the
OFFICE project, Building and
Environment 37 (6) (2002) 575–578.
[6] J. Boland, O. Kravchuk, W. Saman, R. Kilsby, Estimation
of thermal sensitivity of a dwelling to variations in architectural parameters,
Environmental Modelling and Assessment 8 (2003) 101–113.
[7] M. Santamouris, Energy Performance of Residential
Buildings: A Practical Guide for Energy Rating and Efficiency, UK and USA, 2005.
[8] M. Santamouris, G. Mihalakakou, P. Patargias, N.
Gaitani, K. Sfakianaki, M. Papaglastra, C. Pavlou, P. Doukas, E. Primikiri, V.
Geros, Using intelligent clustering techniques to classify the energy performance of school
buildings, Energy and Buildings 39 (1) (2007) 45–51.
[9] J.L. Miguez, J. Porteiro, L.M. Lopez-Gonzalez, J.E.
Vicuna, S. Murillo, J.C. Moran, E. Granada, Review of the energy rating of dwellings in the
European Union as a mechanism for sustainable energy, Renewable and
Sustainable Energy Reviews 10
(1) (2006) 24–45.
[
10]
Z. Chen, D.
Clements-Croome, J. Hong, H. Li, Q. Xu, A multi-criteria lifespan energy
efficiency approach to
intelligent building assessment, Energy and Buildings 38
(5) (2006) 393–409.
[
11]
J.A. Ballinger,
The 5 star design rating system for thermally efficient, comfortable
housing in Australia, Energy and
Buildings 11 (1–3) (1988) 65–72.
[12] V.I. Soebarto, A low-energy house and a low rating: what
is the problem, in: Proceedings of the 34th Conference of the Australia and
New Zealand Architectural
Science Association, Adelaide, South Australia, (2000), pp. 111–118.
[13] T. Olofsson, A. Meier, R. Lamberts, Rating the energy
performance of buildings, The International Journal of Low Energy and Sustainable
Buildings 3 (2004)1–18.
[14] M. Kordjamshidi, S. King, D. Prasad, An alternative
basis for Home Energy Rating Scheme (HERS), in: Proceedings of Passive and Low Energy
Architecture, Environmental
Sustainability: The Challenge of Awareness in Developing Societies,
Lebanon, (2005), pp. 909–914.
[15] M. Kordjamshidi, S. King, D. Prasad, Towards the
development of a home rating scheme for free running buildings, in: Proceeding of
ANZSES, Renewable Energy for a Sustainable Future—A Challenge for a Post Carbon
World, Dunedin, New Zealand, 2005.
[
16]
P.C. Thomas, L.
Thomas, A study of an energy consumption index normalized for
area in house energy rating
schemes, in: Proceedings of the 38th Annual conference of Australian and New Zealand Solar Energy Society:
From Fossils to Photons Renewable Energy Transforming Business,
Brisbane, Australia, (2000), pp.
113–121.
[ 17]
T.J. Williamson,
A critical review of home energy rating in Australia, in: Proceedings
of the 34th Conference of the Australia and New Zealand Architectural Science Association, Adelaide, South Australia, (2000),
pp. 101–109.
[18] M. Kordjamshidi, S. King, D. Prasad, Why are rating schemes always
wrong? Regulatory frameworks for passive design and energy efficiency, in:
Proceedings of Passive and Low Energy Architecture, Geneva, Switzerland, (2006),
pp.153–158.
[19]
M. Kordjamshidi, S. King, D.
Prasad, A comparative analysis of the simulated
thermal performances of dwellings in moderate climate,
in: IBPSA Conference, Adelaide, (2006), pp. 104–109.
[20] T.J. Williamson, S.O. Shea, V. Menadue, Nat HERS and Bad Building
Science, Royal Australian Institute of Architects Housing Conference, Adelaide,
Australia, 2001.
[21] EIA, Energy Demand retrieved 10 December 2007, from http://www.eia.doe.gov/ oiaf/aeo/pdf/trend_2.pdf.
[22] J.R. Stein, A. Meier, Accuracy of home energy rating
systems, Energy 25 (4) (2000) 339–354.
[23]
C.P. Wray, M.A. Piette, M.H.
Sherman, R.M. Levinson, N.E. Matson, D.A. Driscoll, J.A.
McWilliams, T.T. Xu and W.W. Delp, Residential
Commissioning: A Review of Related Literature, Lawrence Berkeley National Laboratory, LBNL_44535,
2000.
[24] M. Kordjamshidi, S. King, R. Zehner, D. Prasad, Modelling efficient
building design: a comparison of conditioned and free-running house rating approaches,
Architectural Science Review 50 (1)
(2007) 52–59.
[25]
R. Aynsley, Letter to editor:
Modelling efficient building design: a comparison of
conditioned
and free-running house rating approaches, Architectural Science Review 50 (2) (2007) 91–93.
[26] SOLARCH, Project Homes: House Energy Rating, New South Wales Industry
Impact Study, University New South Wales, A report
prepared for the NSW Sustainable Energy Development Authority, 2000.
[27] A. Delsante, A Validation of the “AccuRate” Simulation
Engine Using BESTEST, CSIRO, CMIT(C)-2004-152, Canberra, Australia, 2004.
[28]
A. Delsante, Is the new
generation of building energy rating software up to the
Task? A review of AccuRate, in: ABCB Conference:
Building Australia’s Future 2005, Surfer Paradise, Australia, 2005.
[29] ASHRAE, ASNI/ASHRAE Standard 55-2004, Thermal
Environmental Conditions for Human Occupancy, Atlanta, 2004.
[30] R.J. de Dear, G.S. Brager, Thermal comfort in naturally ventilated
buildings: revisions to
ASHRAE Standard 55, Energy and Buildings 34 (6) (2002) 549– 561.
[31]
S.V. Szokolay, Handbook of
Architectural Technology, New York, USA, 1991.
[32]
R.L. Ebel, D.A. Frisbie,
Essentials of Educational Measurement, USA, 1991.