- Email: [email protected]
Cold comfort: A post-completion evaluation of internal temperatures and thermal comfort in 6-Homestar dwellings
Building and Environment 167 (2020) 106466
Contents lists available at ScienceDirect
Building and Environment journal homepage: http://www.elsevier.com/locate/buildenv
Cold comfort: A post-completion evaluation of internal temperatures and thermal comfort in 6-Homestar dwellings Rochelle Ade *, Michael Rehm University of Auckland Business School, Department of Property, Auckland, New Zealand
A R T I C L E I N F O
A B S T R A C T
Keywords: Green building Homestar Over-heating Thermal comfort Temperature Under-heating
A minimum internal temperature of 18 � C is recommended by the World Health Organisation to prevent the poor health outcomes that have been associated with cold and damp homes. Green building councils advise that the use of their green building rating tools will achieve this guideline and provide a warmer, drier internal envi ronment compared to code compliant dwellings, usually through the provision of increased insulation levels from code requirements. This study monitors the internal temperatures of 29 dwellings in the autumn and winter in Auckland, New Zealand. The recorded data is used to determine the amount of time three categories of dwellings (old, new and green certified) spent below the minimum temperature threshold of 18 � C, as well as the predicted thermal comfort of the occupants. Whilst the results confirm that certified green dwellings (6-Homestar) spend the least amount of time below 18 � C, there was no statistical difference in performance between the green certified and new code compliant dwellings. Instead both categories of newer housing stock provided a significantly warmer interior environment when compared to the older housing stock. This study provides unique insights into the actual performance of certified residential green dwellings and determines that policymakers may need to consider incorporating thermal comfort metrics, in addition to minimum temperature thresholds, in standards and rating tools.
1. Introduction It is frequently stated that housing quality affects health, with ‘cold and damp’ homes postulated as a key cause of illness [1–5]. The discourse on this is so prevalent that it has become an accepted truth that is disseminated in the literature with statements like “1600 deaths attributed to cold houses each winter in New Zealand,” [6] and “the asso ciation between living or working in a damp building and health effects such as cough, wheeze, allergies, and asthma is well established” [7]. Green buildings and, in particular, green building rating tools are proposed as a way of rectifying this with the New Zealand Green Building Council (NZGBC) stating that ‘a high-rating Homestar home has a heavily insulated thermal envelope for optimal energy efficiency, so your home will be warm in winter and cool in summer (and cheaper to heat)’ [8]. Green building is defined by ASTM Standard E2114–08 as a building that meets specified building performance requirements while mini mizing disturbance to and improving the functioning of local, regional, and global ecosystems both during and after its construction and
specified service life [9]. Green building rating tools are market-based mechanisms that endorse green buildings that achieve green thresh olds as set by the rating tool [10]. Green building rating tools can be loosely categorised in two ways (i) issue specific rating tools that focus on a single environmental impact, such as energy use (e.g. Passivhaus) or (ii) ‘holistic’ rating tools that address many different environmental impacts at the same time (e.g. Leadership in Energy and Environmental Design (LEED), Green Star, Homestar, etc.) [11]. Popular holistic rating tools like LEED, Green Star and Homestar are promoted/administered by Green Building Councils (GBCs), who endorse that buildings certified using their rating tools will be better than code [11]. For example the NZGBC states the use of its residential green building rating tool (Homestar) will provide “better insulation and better ventilation than is available in an average NZ home, including ones built to current minimum building code” [12]. GBCs also promote buildings certified using their rating tools as ‘healthier’ than non-certified buildings. The United States Green Build ing Council (USGBC) states on the homepage of its website that “LEED
* Corresponding author. E-mail addresses: [email protected] (R. Ade), [email protected] (M. Rehm). https://doi.org/10.1016/j.buildenv.2019.106466 Received 29 July 2019; Received in revised form 29 September 2019; Accepted 9 October 2019 Available online 12 October 2019 0360-1323/© 2019 Elsevier Ltd. All rights reserved.
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Building and Environment 167 (2020) 106466
provides a framework to create healthy, highly efficient and cost-saving green buildings” [13] while the New Zealand Green Building Council (NZGBC) says that “one key aspiration of the Homestar scheme is to ensure that the most vulnerable of our society has access to healthy, quality homes” [12]. In terms of the internal building environment the World Health Organisation (WHO) recommends a healthy temperature range of 18 � C–24 � C be maintained for dwellings [14]. However to date few studies have attempted to review the performance of certified green dwellings against code compliant dwellings, especially in the context of the 18 � C recommended by the [14] for occupant health.
It must be noted that green building rating tools typically do not require a dwelling to attain and maintain minimum temperatures without the use of active heating. Instead they set acceptable thresholds of heating demand energy and measure certification against those thresholds. These heating demand energy thresholds are set to ensure an acceptable level of passive thermal envelope performance is achieved by certified dwellings [19]. This passive performance of thermal envelopes is especially important in the context of fuel poverty. About a quarter of New Zealand (NZ) households are estimated to be in fuel poverty. Average indoor temperatures, especially in older hous ing stock, are cold by international standards and social housing occu pants regularly report they are cold, because they cannot afford to heat their houses. Fuel poverty is thought to be a factor in NZ’s high rate of excess winter mortality (16%, about 1600 deaths a year) and excess winter hospitalisations (8%) [20]. Minimum temperature thresholds, and the heating demand energy required to achieve them, are not the only metrics available to evaluate homes. In the past the WHO has referenced a suite of measures which, when used in conjunction with temperature, constitute thermal comfort, stating “indoor temperature of between 18 and 24� when there is also an air movement of less than 0.2 m/s, a relative humidity of 50% and a mean radiant temperature within 2� C of air temperature” [21]; p1). Indeed his torically the WHO defined a healthy dwelling as one “in which the occupant is comfortable” [22]. GBCs also place strong emphasis on the provision of thermal comfort in dwellings and therefore in addition (or perhaps in preference to) minimum temperature thresholds occupant comfort should be evaluated. However there are currently no re quirements in either the NZBC or Homestar for residential dwellings to meet any thermal comfort standards.
2. Literature review 2.1. Temperature Cold air inflames lungs and inhibits circulation, increasing the risk of respiratory conditions, such as asthma attacks or symptoms, worsening of chronic obstructive pulmonary disease (COPD), and infection. Cold also induces vasoconstriction, which causes stress to the circulatory system that can lead to cardiovascular effects, including ischaemic heart disease (IHD), coronary heart disease, strokes, subarachnoid haemor rhage and death [14]. One of the most frequently utilised thresholds, both in the literature and the popular media, is the WHO guideline that states ‘for countries with temperate or colder climates, 18 � C has been proposed as a safe and well-balanced indoor temperature to protect the health of general populations during cold seasons’ [14]; p xvii). The WHO recently published an evidential review to determine if there was any basis for the temperature threshold of 18 � C, finding that there was only moderate evidence that warming a cold house (perhaps to a minimum indoor temperature of 18 � C) would reduce the risk of respiratory and cardiovascular mortality and morbidity [15]. This finding is corroborated by previous research that determined improvement in health outcomes may not be due to maintaining higher average temperatures, but instead to reduced exposure to very low temperatures [1]. Howden-Chapman’s highly cited study documented significant post-retrofit improvements in self rated health, wheezing and absenteeism from school and work, despite only an increase in mean temperatures from 13.6 � C to 14.2 � C in the houses retrofitted with insulation. Despite a lack of scientific consensus on the health benefits of maintaining a minimum internal temperature of 18 � C, this temperature threshold has been utilised in some green building rating tools (Home star version 2) and government legislation (New Zealand’s Healthy Homes Guarantee Act) as a mechanism to remediate ‘cold and damp’ housing and deliver improved health outcomes. The use of the WHO recommended 18 � C temperature threshold in Homestar version 2 (for space heating demand calculation) is of considerable interest when this is contrasted to New Zealand Building Code (NZBC). Clause H1: Energy Efficiency of this code states that the heating demand energy (which is calculated to demonstrate code compliance) must be capable of maintaining the building at all times within a year at a constant internal temperature of 20 � C. Similar calculation methodologies can be used in both NZBC and Homestar (i.e. the Annual Loss Factor algorithm) and it thus intriguing that Homestar version 2 used the lower threshold of 18 � C when it claims to provide better insulation than is available in an average NZ home, including ones built to current NZBC. This contradiction may have been identified as the current release of Homestar (version 4 – issued in 2017) modified its heating demand calculation to also utilise a 20 � C temper ature threshold. Other green building rating tools use different internal temperature thresholds in their space heating demand calculations. For example Passivhaus uses 20 � C [16], as does the Australian AccuRate star rating [17] while Energy Star recommends a thermostat heating set point of 70 � F which correlates to 21.1 � C [18].
2.2. Thermal comfort Satisfaction with the thermal environment is a complex, subjective response to several interacting and less tangible variables, and currently there is no absolute standard for thermal comfort [23]. In 1962, re searchers defined six factors as those affecting thermal sensation: four physical variables (air temperature, air velocity, relative humidity, mean radiant temperature), and two personal variables (clothing insu lation and activity level, i.e. metabolic rate) [24]. These form the basis of Fanger’s comfort model and became known as the ‘‘Predicted Mean Vote’’ (PMV) index. The PMV was then incorporated into the ‘‘Predicted Percentage of Dissatisfied’’ (PPD) index. Fanger’s PMV-PPD model on thermal comfort is widely accepted and used for the assessment of thermal comfort in mechanically ventilated buildings [25]. ISO 7730 is an international standard that stipulates how to measure thermal com fort using the PMV and PPD from Fanger’s research. Whilst not forming a part of the standard itself ISO 7730 contains an Annex A that states that for light, mainly sedentary activity during the winter heating period 80% of occupants will be satisfied if the following conditions are met (i) operative temperature of between 20 and 24 � C (ii) vertical air tem perature difference of <3 � C (iii) floor surface temperature between 19 and 26 � C (29 � C if actively heated) (iv) mean air velocity of <0.15 m/s (v) radiant temperature asymmetry from cold surfaces of <10 � C and (vi) radiant temperature asymmetry from warm, heated ceilings of <5 � C. However Fanger’s comfort model is primarily utilised by ASHRAE 55 to assess comfort in mechanically ventilated buildings. For naturally ventilated buildings (like single family residential dwellings in NZ) an adaptive comfort standard was developed by Ref. [26] and was included in ASHRAE 55. The reasoning behind the adaptive comfort equations is that behavioural adjustments as well as physiological and psychological adaptation can lead to a wider range of accepted thermal conditions [26]. However the ASHRAE 55 adaptive comfort equations are restric tive, with dwellings deemed to be uncomfortable to all occupants if they sink below a single temperature. More recent research by Ref. [27] studied 42 houses in Sydney and 2
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Building and Environment 167 (2020) 106466
surveyed occupants (intermittently across a two-year monitoring period) to gauge thermal comfort in these dwellings. Based on ‘right- here-right-now’ thermal sensation votes, the neutral residential tem perature was estimated to be about two degrees lower than that predicted by the ASHRAE Standard 55’s adaptive model for office oc cupancies. Despite the lower-than-expected neutrality, comfort zone widths for 80% acceptability were found to be wider than prescribed in the adaptive model for office occupants. These findings support asser tions that people in their homes are more adaptive and tolerant of significantly wider temperature variations. While the outcomes of this research may not be relevant in all climates, or in housing markets where active space conditioning is prevalent, the strong similarities between Australian and NZ housing types in terms of both natural ventilation and climates make this research applicable in both environments. [27] used the results from their study to propose an alternative adaptive model that can be used for the assessment of residential ther mal comfort. TnðresiÞ ¼ 0:26 � TpmaðoutÞ þ 16:75
in the literature measuring and evaluating the autumn/winter temper atures and predicted thermal comfort of three categories of houses in Auckland, NZ utilising the WHO recommended minimum temperature threshold of 18 � C and the de Dear proposed comfort equations. 3. Data and methods This study monitors the internal temperatures of 29 houses in Glen Innes, Auckland (see Fig. 1), a suburb dominated by social housing over the autumn (March, April and May) and winter (June, July, August) of 2019. All of the dwellings are owned by a single social housing provider, are occupied by social housing tenants with subsided rents and can thus be viewed as homogeneous in terms of occupant behaviour and pro pensity to experience fuel poverty. This suburb was specifically selected for the study as it is currently undergoing major redevelopment. This has resulted in the unique situ ation of a large number of old and new housing types being present in the same time. In addition some of the new housing has been certified using a green building rating tool while some new housing has not been rated. The dwellings can therefore be categorised as either:
(1)
This equation is further supported with an 80% acceptability band that wraps around Equation (1). This band can be represented by Equation (2) and Equation (3). Tlower 80% acceptabilty limit ¼ 0:26 � TpmaðoutÞ þ 12:25
(2)
Tupper 80% acceptabilty limit ¼ 0:26 � TpmaðoutÞ þ 21:25
(3)
(i) Old building stock (OLD): i.e. built to the previous version of the New Zealand Building Code (NZBC) (ii) New building stock (NEW): i.e. new houses that completed con struction in 2018 under the new version of the NZBC (iii) 6-Homestar (6HS): i.e. new building stock have completed con struction in 2018 under the new version of the NZBC, that also held a 6 Homestar Built Rating
2.3. Green building rating tools
Data loggers were used to monitor the indoor temperature of the dwellings. One device was installed per dwelling, on an interior wall adjacent to another internal room, in the main living area, at seated head height (1.1 m off the floor) in accordance with previous research in NZ [40]. The data loggers are battery powered, the size of a standard smoke alarm and are able to measure temperature from a range of 40 � C–85 � C, at an accuracy of -þ 0.2 � C, with a reading taken every 30 min. Whilst previous researchers [1,41,42] have utilised data loggers that store information internally, the data loggers for this study were spe cifically chosen for use due to their ability to send information, on a real time basis, over the low powered wider area network connection (LPWAN) to a central server. Data was available to monitor in real time, as well as download at any time as a comma separate value (CSV) file. This meant that there could never be a situation that where a data logger would be collected after a period of time, only to discover that it hadn’t been taking and storing measurements. Additional information was also gathered from the social housing provider on the physical properties of each dwelling as per Table 1. Rvalues for insulation are presented in this table as that is the unit of measurement for both insulation and overall wall constructions in NZ as opposed to U-values in other countries. One notable difference between the different categories of dwellings is that newly constructed dwellings are a mix of apartments, terraced housing (form of attached townhouse) and standalone houses, whilst the OLD dwellings are all standalone (Table 1). This would result in the overall exposed thermal envelope of some of the newly constructed dwellings being smaller than the older dwellings as walls (and floors and ceilings in the case of the apartments) will be adjacent to other occupied spaces. None of the study houses had whole house ventilation or central heating as these types of systems are not common in NZ. Further in formation was gathered on the orientation of the living room wall that contained the most glazing and as demonstrated in Table 1 a mix in orientations exist.
Green building ratings tools have a self-proclaimed mandate to provide warmer, drier and thus healthier buildings for occupants. In addition to green building ratings tool there are also technical standards, such as ISO 21931, ISO 21929 and ISO 15392, that evaluate building sustainability. Whilst not rating tools per se, these ISO standards address similar holistic items to many green building rating tools operated by GBCs such as energy and water use, emissions and air quality. However unlike green building rating tools these standards, whilst discussing temperature and thermal comfort, do not set any thresholds. Historically the literature has focused its attention on commercial green buildings with few studies completed on the post-construction performance of residential dwellings. The most frequently studied green building rating tool is Passivhaus (which as noted earlier is an issue specific rating tool) and focuses either on the actual heating energy demand of certified Passivhauser or the potential for these dwellings to overheat [28–32]. Few studies have been completed that review the internal tempera ture and thermal comfort of certified green homes using a holistic green building rating tool with a recent literature review by Ref. [33] finding a dearth of research in this area. They identified four studies that measured temperature and relative humidity in social housing that had undergone ‘green or energy’ retrofits, but none that utilised holistic green building rating tools. Some studies completed on residential dwellings find that occupant comfort is improved after a major energy efficiency renovation [34–36] with others find the opposite is true [37]. One study highlighted large variations in energy and water consump tion, determined poor indoor air quality and concluded that LEED certified residences were less sustainable over time [38] with another study finding discrepancies between building performance as deter mined at the time of LEED certification and the current level of building performance [39]. It is evident that a significant gap currently exists in the body of knowledge with no research that measures internal temperatures across a range of dwelling categories, contrasting the temperature and pre dicted thermal comfort of certified green dwellings to both new, un certified dwellings as well as older dwellings. This study closes this gap 3
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Building and Environment 167 (2020) 106466
Fig. 1. Study location.
Outdoor weather conditions were captured from the NZ national weather database CliFlo.1 CliFlo is the web system that provides access to NZ’s National Climate Database. CliFlo returns raw data and statis tical summaries in 10 min, hourly and daily frequencies. The Auckland MOTAT (Museum of Transport and Technology) weather station (15 km from the study houses) was identified as the most suitable and complete source of exterior weather information for this study.
heat pump due to the device’s operating costs. 4.2. Thermal comfort Equation 1 through 3 were used to analyse the predicted thermal comfort of each dwelling. The time each dwelling was ‘too hot’ or ‘too cold’ during autumn and winter (in accordance with the 80% comfort bands) was calculated with the results shown in Table 3. As expected the older housing stock is ‘too cold’ a large percentage of the time during the winter. The results also indicate a tendency for the newer housing to be ‘too hot’, even during the cooler months of the year. One 6HS dwelling (house 1) is predicted to be ‘too hot’ an astonishing amount of time in the winter, likely indicating a personal preference of warmth and sub sequent occupant behaviour effect with use of space heating. Also of interest is the fact that the dwellings that spent the most time under 18 � C in winter (House 3 at 95%) is a 6HS dwelling, especially when the is contrasted with the results from Table 3 with predicts that occupants of this dwelling would only be too cold 13% of the time. This raises questions on whether temperature or thermal comfort is the more important measure for defining healthy homes.
4. Results 4.1. Temperature Figs. 2–4 depict box plots of the proportion of time each dwelling category’s living room was below 18 � C, uncomfortably cold and un comfortably hot for the seasons of autumn (March, April and May 2019) and winter (June, July and August 2019). There exists a clear difference between older dwellings and newer homes, with the older dwellings spending more time below 18 � C and being ‘too cold’, however little difference is experienced in time spent 18 � C between the Homestar certified and non-certified new dwellings. Table 2 shows the percentage of time that each dwelling spent below 18 � C in the autumn and winter months of 2019. These results confirm the commonly held belief that older dwellings are colder in the cooler months of the year. However as noted by Ref. [1] adverse health effects may occur during exposure to extreme low temperatures rather than exposure to averagely cool temperatures. In the absence of more specific guidance from the literature, a figure of 10 � C was selected to reflect an ‘extreme low’ temperature in accordance research by Ref. [1]. Four OLD dwellings experience temperatures below 10 � C, however no NEW or 6HS dwellings drop below this threshold. Of interest is the fact that one of the two OLD dwellings that experienced a low of 8.5 � C is the dwelling that has a heat pump in the living room, which could reflect fuel poverty. Essentially the dwelling’s occupants opted not to run the
1
4.3. Analysis Table 4 presents the minimum, maximum and mean percentage of time spent at various sub-optimal indoor conditions within each dwelling category (6HS, NEW and OLD). The categories were paired and their distributions tested for statistical difference using the MannWhitney U test, a non-parametric alternative to the independent sam ple t-test. As expected there is a statistically significant difference be tween the performance of the newer and older housing stock. The newer housing spends significantly less time beneath 18 � C in the autumn and winter with occupants in older houses predicted to be uncomfortably cold. However the z-scores and significance levels indicate that there is no statistically significant difference in performance between the 6Homestar and non-certified new dwellings in any measure. Interestingly while there is a significant difference between the
https://cliflo.niwa.co.nz/. 4
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Building and Environment 167 (2020) 106466
Table 1 Dwelling features. Category
House number
Type
Occupants
Orientation
Double glazing
Window Restrictors
Floor Overall Construction R value (m2K/W)
Wall Overall Construction R value (m2K/W)
Ceiling Overall Construction R value (m2K/W)
Kitchen Range hood
Central Heating/ Cooling
6HS
House 1 House 2
Terrace Apartment (Ground) Apartment (Second) Terrace Terrace Apartment (Second) Duplex Duplex Terrace Apartment (Ground) Standalone
4 1
SW N
Y Y
Y Y
1.6 1.7
2 2.1
3.1 3.4
Y Y
N N
1
SW
Y
Y
na
2.1
3.4
Y
N
2 3 1
NE N E
Y Y Y
Y Y Y
1.6 1.5 na
1.9 1.9 2.1
3.1 2.7 3.4
Y Y Y
N N N
1 6 2 1
NW NW NW NE
Y Y Y Y
Y Y Y Y
1.6 1.8 1.8 1.7
2 2 2 2.1
3.4 3.4 3.4 3.4
Y Y Y Y
N N N N
6
NE
Y
Y
1.5
2.1
3.4
Y
N
Apartment (Ground) Duplex
1
E
Y
Y
1.7
2.1
3.4
Y
N
1
NW
Y
Y
1.6
2
3.4
Y
N
Terrace
2
S
Y
Y
1.3
1.9
2.9
Y
N
Standalone
3
N
Y
Y
1.3
1.9
2.9
Y
N
Standalone
5
NE
Y
Y
1.3
1.9
3
Y
N
Standalone
4
NE
Y
Y
1.3
1.9
3.2
Y
N
Standalone
4
N
Y
Y
1.25
2
3.4
Y
N
Standalone
2
SE
Y
Y
1.38
1.85
2.4
Y
N
Standalone
4
N
Y
Y
1.8
2
3.1
Y
N
Standalone
2
E
N
Y
1.2
1.35
1.7
N
N
Standalone
4
S
N
Y
1.2
1.35
1.7
Y
N
Standalone
1
S
N
Y
1.2
1.6
1.7
N
N
Standalone
2
S
N
Y
1.2
1.35
1.7
N
N
Standalone
4
S
N
Y
1.2
1.35
1.7
N
N
Standalone
4
W
N
Y
1.2
1.35
1.7
N
N
Standalone
2
E
N
Y
1.2
1.35
1.7
Y
N
Standalone
2
E
N
Y
1.2
1.35
1.7
N
N
Standalone
4
E
N
Y
1.2
1.35
1.7
Y
N
House 3 House 4 House 5 House 6
NEW
OLD
House 7 House 8 House 9 House 10 House 11 House 12 House 13 House 14 House 15 House 16 House 17 House 18 House 19 House 20 House 21 House 22 House 23 House 24 House 25 House 26 House 27 House 28 House 29
newer and older housing stock in the autumn in the amount of time spent beneath 18 � C this significance disappears in the winter months will all dwellings spending large amounts of time underneath this threshold temperature. Although four older dwellings experienced short periods of extreme low indoor air temperatures (i.e. below 10 � C) no newly built dwellings did and based on the Mann-Whitney U test the new housing stock is statistically indifferent in this measure. As the solar orientation of each home’s living room varies, an anal ysis was undertaken to determine if orientation influences indoor air temperatures and predicted comfort. A Kruskal-Wallis Test, commonly referred to as a non-parametric one-way ANOVA, was computed using data collected from the dwellings with living room window orientation as the testing factor.
The test results shown in Table 5 indicate that whilst the different orientations preform broadly as expected the orientation does not significantly influence how much time a home spends below 18 � C, or the duration of time the home’s living room is uncomfortably cold. Occupancy, type and the height of the dwelling above ground were also tested in the same manner. Only one metric achieved significance. This was the type of dwelling and only in the autumn season. Further exploration using the Mann-Whitney U test determined that this sig nificant difference occurred between the duplex/terrace housing and the standalone housing. As all the OLD housing is standalone this could be measuring the difference between older and newer housing. When the older housing stock (9 dwellings) was excluded from the analysis (leaving 8 duplex/terrace and 7 standalone dwellings) the significance disappeared. This confirms that the orientation, type, occupancy and 5
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Fig. 2. Box plots showing percentage of time where indoor air temperature is below 18 � C for autumn and winter.
height above ground do not affect the performance of the dwellings in the autumn and winter months.
providing sufficient levels of passive thermal envelope performance. However as noted in the literature review the 18 � C temperature threshold is not confirmed to be linked to health outcomes in the liter ature and prominent researchers such as Howden Chapman have determined that improvement in health outcomes may not be due to maintaining higher average temperatures, but instead to reduced exposure to very low temperatures [1]. When a 10 � C temperature threshold is utilised the OLD dwellings still perform the worst (spending a mean of 1% of their time below 10 � C) but there is no difference in the performance of the NEW and 6HS dwellings. It can therefore be reasoned that for the studied houses that both 6-Homestar and NZBC is providing an acceptable level of performance against this metric. When thermal comfort is evaluated a similar trend appears. The OLD dwellings are significantly less comfortable (cold) than the new housing stock, however there is no difference between the NEW and 6HS dwellings. The increased levels of insulation between the OLD and
5. Discussion The results of this study present two clear findings. The first is, as expected, that the OLD dwellings are significantly colder than newly constructed homes, spending 27.0% of the time in the autumn beneath the WHO minimum temperature threshold of 18 � C for occupant health, whilst the newer housing stock spends much less time beneath this threshold. The same trend continues during the winter with the OLD dwellings spending 71% of the time under 18 � C, contrasted to 64% and 56% respectively for the NEW and 6HS dwellings. Somewhat surpris ingly the newer housing stock spends more than half of its time under 18 � C during the winter, indicating that for social housing tenants, who often suffer fuel poverty, that both NZBC and 6-Homestar may not be 6
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Fig. 3. Box plots showing percentage of time where indoor air temperature is uncomfortably cold for autumn and winter.
NEW/6HS dwellings are likely a key reason for these differences in the seasons. A commonly postulated reason for temperature and comfort differ ences in dwellings is orientation. More of the NEW and 6HS are favourably orientated when compared to the OLD dwellings and will likely being received increased solar gain. Indeed favourable orientation is a key consideration of both new and ‘green’ housing design with the NZGBC stating “You don’t need to install flash new gadgets to get a good Homestar rating: nearly half the points a house can earn relate to energy, health and comfort. That’s because getting the basics right – good orientation for sun, high levels of insulation and controlling moisture – is vital to create a healthy, efficient home” [43]. However the statistical results (Table 5) indicate that orientation does not significantly influence how much time a home spends below 18 � C or the duration of time the home’s living room is uncomfortably cold or hot. The performance gap between expectation and reality is often
attributed to occupant behaviour. However occupant behaviour would not be expected to influence these findings too greatly as there are no complicated active heating, cooling or ventilation systems in any of the studied dwellings. Indeed NZ housing is not commonly provided with central heating or cooling [44] and only one house in this study con tained a device capable of cooling. Therefore occupant behaviour in these dwellings would be limited the opening and closing of windows and doors, and the operation of electric plug in heaters (there are no fireplaces in any dwellings). Whilst occupant behaviour may have some effect on the results (as indicted by house 1), the authors believe that it is the structural differences (type, insulation and orientation) between the dwelling categories that explain the differences between the newer and older dwellings.
7
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Fig. 4. Box plots showing percentage of time where indoor air temperature is uncomfortably hot for autumn and winter.
6. Limitations
desert like temperatures of extreme heat in summer and extreme cold in winter. Homestar requires greater levels of insulation in these climate zones and future research could expand the methodology of this study to other climate zones in NZ. It is not possible to assess the effectiveness of holistic rating tools through a review of indoor temperature and thermal comfort alone, with elements such as energy and water use also holding significant interest in the context of climate change. In addition relative humidity and ventilation rates can also impact the thermal comfort of occupants but are not considered by the thermal comfort equations used in this study. Future research could seek to incorporate these data points, as well as survey occupants on their comfort levels.
The results of this study are naturally limited given the small number of dwellings reviewed in the study (thirteen 6HS, seven NEW and nine OLD), the single subdivision location and the heterogeneity of the building orientations. Whilst information was gathered from the social housing provider on structural building characteristics such as insu lation levels, a more in depth interview process with dwelling occupants has not been undertaken. The authors therefore have no understanding around the personal preferences of the occupants. For example some people like it warm whilst others like it cold and it has not been possible to account for these personal preferences, or other elements of occupant use (like a preference for open windows) in this research. Future research in this space could therefore focus on this more specifically to determine if this is key factor in the results. NZ contains additional climate zones, some of which experience
7. Conclusions A strong discourse exists in New Zealand that ‘cold and damp’ 8
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Table 2 Percentage of time spent below 18 � C, 10 � C and too cold in the autumn and winter months of Auckland, New Zealand.
Table 3 Predicted percentage of time ‘too hot’ or ‘too cold’ in the autumn and winter months of Auckland, NZ per dwelling.
Temperature
6HS
NEW
OLD
House 1 House 2 House 3 House 4 House 5 House 6 House 7 House 8 House 9 House 10 House 11 House 12 House 13 House 14 House 15 House 16 House 17 House 18 House 19 House 20 House 21 House 22 House 23 House 24 House 25 House 26 House 27 House 28 House 29
Temperature
Autumn (March through May 2019)
Winter (June through August 2019)
Autumn (March through May 2019)
Winter (June through August 2019)
% of time below 10 � C
% of time below 18 � C
% of time below 10 � C
% of time below 18 � C
% of time too cold (Tlower
% of time too hot (Tupper
% of time too cold (Tlower
% of time too hot (Tupper
–
–
–
1x
80% acceptability
80% acceptability
80% acceptability
limit
limit
–
–
–
36
range: 12.3 to 16.6� C)
80% acceptability
limit
limit range: 21.3 to 25.6� C)
–
9
–
95
–
–
–
63x
–
2
–
42
–
7
–
–
–
7
–
68
–
6
13
–
–
1
–
46
–
1
–
–
–
–
–
49
–
8
6
–
–
1
–
40
–
8
–
–
–
3
–
51
–
5
–
–
–
47
–
100
–
2
–
–
–
–
–
3x
–
–
–
–
–
–
–
-x
–
–
55x
–
–
8
–
80
–
7
–
13
–
1
–
23
–
4
–
9
–
9
–
65
–
9
8
–
–
1
–
63
–
2
1
–
–
7
–
43
–
9
3
–
–
14
–
77
–
–
1
–
–
12
–
94
–
3
1
2
–
19
–
86
–
–
2
–
–
27
–
78
–
–
6
–
–
25
–
80
–
–
9
–
0.2
43
5
89
2
3
25
1
–
29
1
68
5
2
26
–
–
10
–
54
20
–
63
–
–
27
–
82
8
–
33
–
–
27
2
71
–
1
2
–
–
17
–
36
1
1
18
–
–
37
3
85
7
2
30
–
2
3
4
3
11
5
53
–
range: 13.5 to 18.9� C) 6HS
NEW
OLD
x outliers identified by SPSS.
housing is linked to poor health outcomes. This has led to recent Healthy Homes Guarantee Act. This new legislation explicitly references the WHO ‘healthy’ temperature guidelines and stipulates that all rental homes are to feature a fixed heating appliance capable of maintaining a minimum temperature threshold of 18 � C in the main living room. In addition several government organisations, including the central gov ernment’s social housing provider Housing New Zealand and Panuku,
House 1 House 2 House 3 House 4 House 5 House 6 House 7 House 8 House 9 House 10 House 11 House 12 House 13 House 14 House 15 House 16 House 17 House 18 House 19 House 20 House 21 House 22 House 23 House 24 House 25 House 26 House 27 House 28 House 29
x outliers identified by SPSS.
9
range: 22.5 to 27.9� C)
R. Ade and M. Rehm
Building and Environment 167 (2020) 106466
Table 4 Percentage of time where indoor environment is sub-optimal over the autumn and winter months (Mann-Whitney U test). Percentage of time spent by dwelling category AUTUMN
INDOOR TEMPERATURE
Under 18 � C Under 10 � C
OCCUPANT COMFORT
Too cold Too hot
WINTER
INDOOR TEMPERATURE
Under 18 � C Under 10 � C
OCCUPANT COMFORT
Too cold Too hot
MIN MAX MEAN MIN MAX MEAN MIN MAX MEAN MIN MAX MEAN N MIN MAX MEAN MIN MAX MEAN MIN MAX MEAN MIN MAX MEAN N
Mann-Whitney U test z-scores
6HS
NEW
OLD
– 9 3 – – – – – – – 9 5 13 36 95 56 – – – – 13 3 – – – 9
1 19 9 – – – – – – – 9 2 7 23 94 64 – – – 1 9 3 – 2 0.3 7
10 43 27 – – – – 20 6 – 5 2 9 36 89 71 – 5 1 2 63 28 – 3 0.4 9
6HS & NEW 1.885 .000 .000
6HS & OLD 3.329
NEW & OLD **
.000 4.030
2.922 .000
**
3.168
1.419
1.550
0.711
0.688
1.592
0.582
.000
**
**
2.182
*
1.947
*
1.418
3.103
**
2.762
**
1.134
1.455
0.388
*, ** Mann-Whitney U Test exact 2-tailed p-values at 5% and 1% significance levels respectively.
‘too cold’ between 3% of the time based on the adaptive comfort equations by Ref. [27]. This raises a question of whether occupant comfort should be evaluated rather than specific temperatures thresh olds particularly since the [22] definition of a healthy dwelling is one “in which the occupant is comfortable”. This is particularly important in the context of fuel poverty and the ability of the financially vulnerable to operate space heating (or cooling) devices. Both the 6-Homestar and new, code-compliant dwellings spend significant amounts of time below the 18 � C threshold suggesting that this study’s social housing tenants were not operating space heating devices, potentially because they could not afford to. In such circum stances, fuel impoverished occupants must rely on the inherent abilities of the home to maintain a comfortable indoor environment. If thermal comfort is an adequate measure of occupant health, then both new homes built to code and 6-Homestar-rated dwellings achieve signifi cantly better outcomes over the autumn and winter period in compari son with older dwellings. This study provides a limited, but valuable, contribution to the body of knowledge regarding how green dwellings perform post-completion. With 6-Homestar increasingly adopted as a quality standard in New Zealand, policymakers may wish to reassess whether6-Homestar de livers dwellings that provide thermal comfort quality superior to homes built to the current building code. Policymakers should also consider whether thermal comfort is a more appropriate target than the WHO’s inflexible 18 � C ‘healthy’ temperature threshold.
Table 5 Kruskal-Wallis test results for rated and unrated new dwellings by living room window orientation for the over the Autumn and Winter months. Kruskal-Wallis Test Mean Ranks Autumn
Winter
Orientation
Below 18 � C
Too Cold
Too Hot
Below 18 � C
Too Cold
Too Hot
North (including NW) East (including NE) South (including SE) West (including SW)
11.83
11.00
17.67
11.72
9.33
11.50
15.23
16.18
16.55
10.56
12.75
16.19
19.75
19.00
9.17
15.00
17.00
11.50
14.17
14.67
13.00
22.50
18.50
11.50
Kruskal-Wallis H Asymptotic pvalue
3.177
5.684
4.380
4.930
5.215
6.921
.365
.128
.223
.177
.157
.074
Auckland Council’s property development arm, have adopted 6-Home star certification as a quality mechanism to deliver new dwellings that can both improve occupant health and mitigate climate change. The NZGBC claims that 6-Homestar certification will provide dwellings with better insulation and ventilation than is available in an average NZ home, including ones built to the current building code. This study finds that whilst older vintage dwellings spend significant amounts of time (71% in winter) below the WHO 18 � C guideline, and are predicted to be ‘too cold’ when compared to new housing, there is no statistical difference between the interior temperatures and predicted comfort levels of newly constructed certified and non-certified green dwellings. Somewhat surprisingly the new housing stock spends over 50% of its time beneath with WHO guideline in winter, but is only predicted to be
Funding BRANZ Building Research Levy. Declaration of competing interest Rochelle Ade is a Homestar Assessor and has worked as a Homestar Assessor for the Building Excellence Group. Rochelle Ade also has an interest in Tether.
10
R. Ade and M. Rehm
Building and Environment 167 (2020) 106466
References
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[1] P. Howden-Chapman, A. Matheson, J. Crane, H. Viggers, M. Cunningham, T. Blakely, G. Davie, Effect of insulating existing houses on health inequality: cluster randomised study in the community, Br. Med. J. 334 (7591) (2007) 460, doi:bmj.39070.573032.80 [pii]. [2] J. Milner, P. Wilkinson, [Accepted manuscript] effects of home energy efficiency and heating interventions on cold-related health, Epidemiology (2016) (Cambridge, Mass). [3] N. Preval, M. Keall, L. Telfar-Barnard, A. Grimes, P. Howden-Chapman, Impact of improved insulation and heating on mortality risk of older cohort members with prior cardiovascular or respiratory hospitalisations, e018079-2017-018079, BMJ Open 7 (11) (2017), https://doi.org/10.1136/bmjopen-2017-018079 ([doi]). [4] L. Rangiwhetu, N. Pierse, H. Viggers, P. Howden-Chapman, Cold New Zealand council housing getting an upgrade, Policy Quarterly 14 (2) (2018). [5] L. Telfar-Barnard, J. Bennett, P. Howden-Chapman, D. Jacobs, D. Ormandy, M. Cutler-Welsh, M. Keall, Measuring the effect of housing quality interventions: the case of the New Zealand “rental warrant of fitness”, Int. J. Environ. Res. Public Health 14 (11) (2017) 1352. [6] R. Nichol, 1600 Deaths Attributed to Cold Houses Each Winter in new zealand, 2017. https://www.noted.co.nz/currently/social-issues/1600-deaths-attributedto-cold-houses-each-winter-in-new-zealand/. [7] J. Sundell, On the history of indoor air quality and health, Indoor Air 14 (7) (2004) 51–58, s. [8] NZGBC, Homestar for Home Owners, 2019. Retrieved from, https://www.nzgbc. org.nz/homestar/forhomeowners. [9] Y. Li, X. Chen, X. Wang, Y. Xu, P. Chen, A review of studies on green building assessment methods by comparative analysis, Energy Build. 146 (2017) 152–159. [10] B.K. Nguyen, H. Altan, Comparative review of five sustainable rating systems, Procedia Engineering 21 (2011) 376–386. [11] R. Ade, M. Rehm, The unwritten history of green building rating tools: a personal view from some of the ‘founding fathers’, Build. Res. Inf. (2019) 1–17. [12] NZGBC, Homestar for Retirement, 2018. Retrieved from, https://www.nzgbc.org. nz/Story?Action¼View&Story_id¼339. [13] USGBC, LEED Is Green Building, 2018. Retrieved from, https://www.usgbc.org/h elp/what-leed. [14] World Health Organization, WHO Housing and Health Guidelines, WHO, Geneva, 2018 (CC BY-NC-SA 3.0 IGO). [15] L.T. Barnard, P. Howden-Chapman, M. Clarke, R. Ludolph, World Health Organization, WHO Housing and Health Guidelines: Web Annex B: Report of the Systematic Review on the Effect of Indoor Cold on Health, 2018. [16] P. Rohdin, A. Molin, B. Moshfegh, Experiences from nine passive houses in Sweden–Indoor thermal environment and energy use, Build. Environ. 71 (2014) 176–185. [17] A. Albatayneh, D. Alterman, A. Page, B. Moghtaderi, The significance of temperature based approach over the energy based approaches in the buildings thermal assessment, Environmental and Climate Technologies 19 (1) (2017) 39–50. [18] Energy Star, A Guide to Energy Efficient Heating and Cooling, 2019. Retrieved from, https://www.energystar.gov/ia/partners/publications/pubdocs/Heatin gCoolingGuide%20FINAL_9-4-09.pdf. [19] Y. Schwartz, R. Raslan, Variations in results of building energy simulation tools, and their impact on BREEAM and LEED ratings: a case study, Energy Build. 62 (2013) 350–359. [20] P. Howden-Chapman, How real are the health effects of residential energy efficiency programmes, Elsevier Journal of Social Science & Medicine 133 (2015) 189–190. [21] World Health Organization, Health Impact of Low Indoor Temperatures. Environmental Health (WHO-EURO) World Health Organization, Regional Office for Europe, 1987.
11
Contents lists available at ScienceDirect
Building and Environment journal homepage: http://www.elsevier.com/locate/buildenv
Cold comfort: A post-completion evaluation of internal temperatures and thermal comfort in 6-Homestar dwellings Rochelle Ade *, Michael Rehm University of Auckland Business School, Department of Property, Auckland, New Zealand
A R T I C L E I N F O
A B S T R A C T
Keywords: Green building Homestar Over-heating Thermal comfort Temperature Under-heating
A minimum internal temperature of 18 � C is recommended by the World Health Organisation to prevent the poor health outcomes that have been associated with cold and damp homes. Green building councils advise that the use of their green building rating tools will achieve this guideline and provide a warmer, drier internal envi ronment compared to code compliant dwellings, usually through the provision of increased insulation levels from code requirements. This study monitors the internal temperatures of 29 dwellings in the autumn and winter in Auckland, New Zealand. The recorded data is used to determine the amount of time three categories of dwellings (old, new and green certified) spent below the minimum temperature threshold of 18 � C, as well as the predicted thermal comfort of the occupants. Whilst the results confirm that certified green dwellings (6-Homestar) spend the least amount of time below 18 � C, there was no statistical difference in performance between the green certified and new code compliant dwellings. Instead both categories of newer housing stock provided a significantly warmer interior environment when compared to the older housing stock. This study provides unique insights into the actual performance of certified residential green dwellings and determines that policymakers may need to consider incorporating thermal comfort metrics, in addition to minimum temperature thresholds, in standards and rating tools.
1. Introduction It is frequently stated that housing quality affects health, with ‘cold and damp’ homes postulated as a key cause of illness [1–5]. The discourse on this is so prevalent that it has become an accepted truth that is disseminated in the literature with statements like “1600 deaths attributed to cold houses each winter in New Zealand,” [6] and “the asso ciation between living or working in a damp building and health effects such as cough, wheeze, allergies, and asthma is well established” [7]. Green buildings and, in particular, green building rating tools are proposed as a way of rectifying this with the New Zealand Green Building Council (NZGBC) stating that ‘a high-rating Homestar home has a heavily insulated thermal envelope for optimal energy efficiency, so your home will be warm in winter and cool in summer (and cheaper to heat)’ [8]. Green building is defined by ASTM Standard E2114–08 as a building that meets specified building performance requirements while mini mizing disturbance to and improving the functioning of local, regional, and global ecosystems both during and after its construction and
specified service life [9]. Green building rating tools are market-based mechanisms that endorse green buildings that achieve green thresh olds as set by the rating tool [10]. Green building rating tools can be loosely categorised in two ways (i) issue specific rating tools that focus on a single environmental impact, such as energy use (e.g. Passivhaus) or (ii) ‘holistic’ rating tools that address many different environmental impacts at the same time (e.g. Leadership in Energy and Environmental Design (LEED), Green Star, Homestar, etc.) [11]. Popular holistic rating tools like LEED, Green Star and Homestar are promoted/administered by Green Building Councils (GBCs), who endorse that buildings certified using their rating tools will be better than code [11]. For example the NZGBC states the use of its residential green building rating tool (Homestar) will provide “better insulation and better ventilation than is available in an average NZ home, including ones built to current minimum building code” [12]. GBCs also promote buildings certified using their rating tools as ‘healthier’ than non-certified buildings. The United States Green Build ing Council (USGBC) states on the homepage of its website that “LEED
* Corresponding author. E-mail addresses: [email protected] (R. Ade), [email protected] (M. Rehm). https://doi.org/10.1016/j.buildenv.2019.106466 Received 29 July 2019; Received in revised form 29 September 2019; Accepted 9 October 2019 Available online 12 October 2019 0360-1323/© 2019 Elsevier Ltd. All rights reserved.
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Building and Environment 167 (2020) 106466
provides a framework to create healthy, highly efficient and cost-saving green buildings” [13] while the New Zealand Green Building Council (NZGBC) says that “one key aspiration of the Homestar scheme is to ensure that the most vulnerable of our society has access to healthy, quality homes” [12]. In terms of the internal building environment the World Health Organisation (WHO) recommends a healthy temperature range of 18 � C–24 � C be maintained for dwellings [14]. However to date few studies have attempted to review the performance of certified green dwellings against code compliant dwellings, especially in the context of the 18 � C recommended by the [14] for occupant health.
It must be noted that green building rating tools typically do not require a dwelling to attain and maintain minimum temperatures without the use of active heating. Instead they set acceptable thresholds of heating demand energy and measure certification against those thresholds. These heating demand energy thresholds are set to ensure an acceptable level of passive thermal envelope performance is achieved by certified dwellings [19]. This passive performance of thermal envelopes is especially important in the context of fuel poverty. About a quarter of New Zealand (NZ) households are estimated to be in fuel poverty. Average indoor temperatures, especially in older hous ing stock, are cold by international standards and social housing occu pants regularly report they are cold, because they cannot afford to heat their houses. Fuel poverty is thought to be a factor in NZ’s high rate of excess winter mortality (16%, about 1600 deaths a year) and excess winter hospitalisations (8%) [20]. Minimum temperature thresholds, and the heating demand energy required to achieve them, are not the only metrics available to evaluate homes. In the past the WHO has referenced a suite of measures which, when used in conjunction with temperature, constitute thermal comfort, stating “indoor temperature of between 18 and 24� when there is also an air movement of less than 0.2 m/s, a relative humidity of 50% and a mean radiant temperature within 2� C of air temperature” [21]; p1). Indeed his torically the WHO defined a healthy dwelling as one “in which the occupant is comfortable” [22]. GBCs also place strong emphasis on the provision of thermal comfort in dwellings and therefore in addition (or perhaps in preference to) minimum temperature thresholds occupant comfort should be evaluated. However there are currently no re quirements in either the NZBC or Homestar for residential dwellings to meet any thermal comfort standards.
2. Literature review 2.1. Temperature Cold air inflames lungs and inhibits circulation, increasing the risk of respiratory conditions, such as asthma attacks or symptoms, worsening of chronic obstructive pulmonary disease (COPD), and infection. Cold also induces vasoconstriction, which causes stress to the circulatory system that can lead to cardiovascular effects, including ischaemic heart disease (IHD), coronary heart disease, strokes, subarachnoid haemor rhage and death [14]. One of the most frequently utilised thresholds, both in the literature and the popular media, is the WHO guideline that states ‘for countries with temperate or colder climates, 18 � C has been proposed as a safe and well-balanced indoor temperature to protect the health of general populations during cold seasons’ [14]; p xvii). The WHO recently published an evidential review to determine if there was any basis for the temperature threshold of 18 � C, finding that there was only moderate evidence that warming a cold house (perhaps to a minimum indoor temperature of 18 � C) would reduce the risk of respiratory and cardiovascular mortality and morbidity [15]. This finding is corroborated by previous research that determined improvement in health outcomes may not be due to maintaining higher average temperatures, but instead to reduced exposure to very low temperatures [1]. Howden-Chapman’s highly cited study documented significant post-retrofit improvements in self rated health, wheezing and absenteeism from school and work, despite only an increase in mean temperatures from 13.6 � C to 14.2 � C in the houses retrofitted with insulation. Despite a lack of scientific consensus on the health benefits of maintaining a minimum internal temperature of 18 � C, this temperature threshold has been utilised in some green building rating tools (Home star version 2) and government legislation (New Zealand’s Healthy Homes Guarantee Act) as a mechanism to remediate ‘cold and damp’ housing and deliver improved health outcomes. The use of the WHO recommended 18 � C temperature threshold in Homestar version 2 (for space heating demand calculation) is of considerable interest when this is contrasted to New Zealand Building Code (NZBC). Clause H1: Energy Efficiency of this code states that the heating demand energy (which is calculated to demonstrate code compliance) must be capable of maintaining the building at all times within a year at a constant internal temperature of 20 � C. Similar calculation methodologies can be used in both NZBC and Homestar (i.e. the Annual Loss Factor algorithm) and it thus intriguing that Homestar version 2 used the lower threshold of 18 � C when it claims to provide better insulation than is available in an average NZ home, including ones built to current NZBC. This contradiction may have been identified as the current release of Homestar (version 4 – issued in 2017) modified its heating demand calculation to also utilise a 20 � C temper ature threshold. Other green building rating tools use different internal temperature thresholds in their space heating demand calculations. For example Passivhaus uses 20 � C [16], as does the Australian AccuRate star rating [17] while Energy Star recommends a thermostat heating set point of 70 � F which correlates to 21.1 � C [18].
2.2. Thermal comfort Satisfaction with the thermal environment is a complex, subjective response to several interacting and less tangible variables, and currently there is no absolute standard for thermal comfort [23]. In 1962, re searchers defined six factors as those affecting thermal sensation: four physical variables (air temperature, air velocity, relative humidity, mean radiant temperature), and two personal variables (clothing insu lation and activity level, i.e. metabolic rate) [24]. These form the basis of Fanger’s comfort model and became known as the ‘‘Predicted Mean Vote’’ (PMV) index. The PMV was then incorporated into the ‘‘Predicted Percentage of Dissatisfied’’ (PPD) index. Fanger’s PMV-PPD model on thermal comfort is widely accepted and used for the assessment of thermal comfort in mechanically ventilated buildings [25]. ISO 7730 is an international standard that stipulates how to measure thermal com fort using the PMV and PPD from Fanger’s research. Whilst not forming a part of the standard itself ISO 7730 contains an Annex A that states that for light, mainly sedentary activity during the winter heating period 80% of occupants will be satisfied if the following conditions are met (i) operative temperature of between 20 and 24 � C (ii) vertical air tem perature difference of <3 � C (iii) floor surface temperature between 19 and 26 � C (29 � C if actively heated) (iv) mean air velocity of <0.15 m/s (v) radiant temperature asymmetry from cold surfaces of <10 � C and (vi) radiant temperature asymmetry from warm, heated ceilings of <5 � C. However Fanger’s comfort model is primarily utilised by ASHRAE 55 to assess comfort in mechanically ventilated buildings. For naturally ventilated buildings (like single family residential dwellings in NZ) an adaptive comfort standard was developed by Ref. [26] and was included in ASHRAE 55. The reasoning behind the adaptive comfort equations is that behavioural adjustments as well as physiological and psychological adaptation can lead to a wider range of accepted thermal conditions [26]. However the ASHRAE 55 adaptive comfort equations are restric tive, with dwellings deemed to be uncomfortable to all occupants if they sink below a single temperature. More recent research by Ref. [27] studied 42 houses in Sydney and 2
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Building and Environment 167 (2020) 106466
surveyed occupants (intermittently across a two-year monitoring period) to gauge thermal comfort in these dwellings. Based on ‘right- here-right-now’ thermal sensation votes, the neutral residential tem perature was estimated to be about two degrees lower than that predicted by the ASHRAE Standard 55’s adaptive model for office oc cupancies. Despite the lower-than-expected neutrality, comfort zone widths for 80% acceptability were found to be wider than prescribed in the adaptive model for office occupants. These findings support asser tions that people in their homes are more adaptive and tolerant of significantly wider temperature variations. While the outcomes of this research may not be relevant in all climates, or in housing markets where active space conditioning is prevalent, the strong similarities between Australian and NZ housing types in terms of both natural ventilation and climates make this research applicable in both environments. [27] used the results from their study to propose an alternative adaptive model that can be used for the assessment of residential ther mal comfort. TnðresiÞ ¼ 0:26 � TpmaðoutÞ þ 16:75
in the literature measuring and evaluating the autumn/winter temper atures and predicted thermal comfort of three categories of houses in Auckland, NZ utilising the WHO recommended minimum temperature threshold of 18 � C and the de Dear proposed comfort equations. 3. Data and methods This study monitors the internal temperatures of 29 houses in Glen Innes, Auckland (see Fig. 1), a suburb dominated by social housing over the autumn (March, April and May) and winter (June, July, August) of 2019. All of the dwellings are owned by a single social housing provider, are occupied by social housing tenants with subsided rents and can thus be viewed as homogeneous in terms of occupant behaviour and pro pensity to experience fuel poverty. This suburb was specifically selected for the study as it is currently undergoing major redevelopment. This has resulted in the unique situ ation of a large number of old and new housing types being present in the same time. In addition some of the new housing has been certified using a green building rating tool while some new housing has not been rated. The dwellings can therefore be categorised as either:
(1)
This equation is further supported with an 80% acceptability band that wraps around Equation (1). This band can be represented by Equation (2) and Equation (3). Tlower 80% acceptabilty limit ¼ 0:26 � TpmaðoutÞ þ 12:25
(2)
Tupper 80% acceptabilty limit ¼ 0:26 � TpmaðoutÞ þ 21:25
(3)
(i) Old building stock (OLD): i.e. built to the previous version of the New Zealand Building Code (NZBC) (ii) New building stock (NEW): i.e. new houses that completed con struction in 2018 under the new version of the NZBC (iii) 6-Homestar (6HS): i.e. new building stock have completed con struction in 2018 under the new version of the NZBC, that also held a 6 Homestar Built Rating
2.3. Green building rating tools
Data loggers were used to monitor the indoor temperature of the dwellings. One device was installed per dwelling, on an interior wall adjacent to another internal room, in the main living area, at seated head height (1.1 m off the floor) in accordance with previous research in NZ [40]. The data loggers are battery powered, the size of a standard smoke alarm and are able to measure temperature from a range of 40 � C–85 � C, at an accuracy of -þ 0.2 � C, with a reading taken every 30 min. Whilst previous researchers [1,41,42] have utilised data loggers that store information internally, the data loggers for this study were spe cifically chosen for use due to their ability to send information, on a real time basis, over the low powered wider area network connection (LPWAN) to a central server. Data was available to monitor in real time, as well as download at any time as a comma separate value (CSV) file. This meant that there could never be a situation that where a data logger would be collected after a period of time, only to discover that it hadn’t been taking and storing measurements. Additional information was also gathered from the social housing provider on the physical properties of each dwelling as per Table 1. Rvalues for insulation are presented in this table as that is the unit of measurement for both insulation and overall wall constructions in NZ as opposed to U-values in other countries. One notable difference between the different categories of dwellings is that newly constructed dwellings are a mix of apartments, terraced housing (form of attached townhouse) and standalone houses, whilst the OLD dwellings are all standalone (Table 1). This would result in the overall exposed thermal envelope of some of the newly constructed dwellings being smaller than the older dwellings as walls (and floors and ceilings in the case of the apartments) will be adjacent to other occupied spaces. None of the study houses had whole house ventilation or central heating as these types of systems are not common in NZ. Further in formation was gathered on the orientation of the living room wall that contained the most glazing and as demonstrated in Table 1 a mix in orientations exist.
Green building ratings tools have a self-proclaimed mandate to provide warmer, drier and thus healthier buildings for occupants. In addition to green building ratings tool there are also technical standards, such as ISO 21931, ISO 21929 and ISO 15392, that evaluate building sustainability. Whilst not rating tools per se, these ISO standards address similar holistic items to many green building rating tools operated by GBCs such as energy and water use, emissions and air quality. However unlike green building rating tools these standards, whilst discussing temperature and thermal comfort, do not set any thresholds. Historically the literature has focused its attention on commercial green buildings with few studies completed on the post-construction performance of residential dwellings. The most frequently studied green building rating tool is Passivhaus (which as noted earlier is an issue specific rating tool) and focuses either on the actual heating energy demand of certified Passivhauser or the potential for these dwellings to overheat [28–32]. Few studies have been completed that review the internal tempera ture and thermal comfort of certified green homes using a holistic green building rating tool with a recent literature review by Ref. [33] finding a dearth of research in this area. They identified four studies that measured temperature and relative humidity in social housing that had undergone ‘green or energy’ retrofits, but none that utilised holistic green building rating tools. Some studies completed on residential dwellings find that occupant comfort is improved after a major energy efficiency renovation [34–36] with others find the opposite is true [37]. One study highlighted large variations in energy and water consump tion, determined poor indoor air quality and concluded that LEED certified residences were less sustainable over time [38] with another study finding discrepancies between building performance as deter mined at the time of LEED certification and the current level of building performance [39]. It is evident that a significant gap currently exists in the body of knowledge with no research that measures internal temperatures across a range of dwelling categories, contrasting the temperature and pre dicted thermal comfort of certified green dwellings to both new, un certified dwellings as well as older dwellings. This study closes this gap 3
R. Ade and M. Rehm
Building and Environment 167 (2020) 106466
Fig. 1. Study location.
Outdoor weather conditions were captured from the NZ national weather database CliFlo.1 CliFlo is the web system that provides access to NZ’s National Climate Database. CliFlo returns raw data and statis tical summaries in 10 min, hourly and daily frequencies. The Auckland MOTAT (Museum of Transport and Technology) weather station (15 km from the study houses) was identified as the most suitable and complete source of exterior weather information for this study.
heat pump due to the device’s operating costs. 4.2. Thermal comfort Equation 1 through 3 were used to analyse the predicted thermal comfort of each dwelling. The time each dwelling was ‘too hot’ or ‘too cold’ during autumn and winter (in accordance with the 80% comfort bands) was calculated with the results shown in Table 3. As expected the older housing stock is ‘too cold’ a large percentage of the time during the winter. The results also indicate a tendency for the newer housing to be ‘too hot’, even during the cooler months of the year. One 6HS dwelling (house 1) is predicted to be ‘too hot’ an astonishing amount of time in the winter, likely indicating a personal preference of warmth and sub sequent occupant behaviour effect with use of space heating. Also of interest is the fact that the dwellings that spent the most time under 18 � C in winter (House 3 at 95%) is a 6HS dwelling, especially when the is contrasted with the results from Table 3 with predicts that occupants of this dwelling would only be too cold 13% of the time. This raises questions on whether temperature or thermal comfort is the more important measure for defining healthy homes.
4. Results 4.1. Temperature Figs. 2–4 depict box plots of the proportion of time each dwelling category’s living room was below 18 � C, uncomfortably cold and un comfortably hot for the seasons of autumn (March, April and May 2019) and winter (June, July and August 2019). There exists a clear difference between older dwellings and newer homes, with the older dwellings spending more time below 18 � C and being ‘too cold’, however little difference is experienced in time spent 18 � C between the Homestar certified and non-certified new dwellings. Table 2 shows the percentage of time that each dwelling spent below 18 � C in the autumn and winter months of 2019. These results confirm the commonly held belief that older dwellings are colder in the cooler months of the year. However as noted by Ref. [1] adverse health effects may occur during exposure to extreme low temperatures rather than exposure to averagely cool temperatures. In the absence of more specific guidance from the literature, a figure of 10 � C was selected to reflect an ‘extreme low’ temperature in accordance research by Ref. [1]. Four OLD dwellings experience temperatures below 10 � C, however no NEW or 6HS dwellings drop below this threshold. Of interest is the fact that one of the two OLD dwellings that experienced a low of 8.5 � C is the dwelling that has a heat pump in the living room, which could reflect fuel poverty. Essentially the dwelling’s occupants opted not to run the
1
4.3. Analysis Table 4 presents the minimum, maximum and mean percentage of time spent at various sub-optimal indoor conditions within each dwelling category (6HS, NEW and OLD). The categories were paired and their distributions tested for statistical difference using the MannWhitney U test, a non-parametric alternative to the independent sam ple t-test. As expected there is a statistically significant difference be tween the performance of the newer and older housing stock. The newer housing spends significantly less time beneath 18 � C in the autumn and winter with occupants in older houses predicted to be uncomfortably cold. However the z-scores and significance levels indicate that there is no statistically significant difference in performance between the 6Homestar and non-certified new dwellings in any measure. Interestingly while there is a significant difference between the
https://cliflo.niwa.co.nz/. 4
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Building and Environment 167 (2020) 106466
Table 1 Dwelling features. Category
House number
Type
Occupants
Orientation
Double glazing
Window Restrictors
Floor Overall Construction R value (m2K/W)
Wall Overall Construction R value (m2K/W)
Ceiling Overall Construction R value (m2K/W)
Kitchen Range hood
Central Heating/ Cooling
6HS
House 1 House 2
Terrace Apartment (Ground) Apartment (Second) Terrace Terrace Apartment (Second) Duplex Duplex Terrace Apartment (Ground) Standalone
4 1
SW N
Y Y
Y Y
1.6 1.7
2 2.1
3.1 3.4
Y Y
N N
1
SW
Y
Y
na
2.1
3.4
Y
N
2 3 1
NE N E
Y Y Y
Y Y Y
1.6 1.5 na
1.9 1.9 2.1
3.1 2.7 3.4
Y Y Y
N N N
1 6 2 1
NW NW NW NE
Y Y Y Y
Y Y Y Y
1.6 1.8 1.8 1.7
2 2 2 2.1
3.4 3.4 3.4 3.4
Y Y Y Y
N N N N
6
NE
Y
Y
1.5
2.1
3.4
Y
N
Apartment (Ground) Duplex
1
E
Y
Y
1.7
2.1
3.4
Y
N
1
NW
Y
Y
1.6
2
3.4
Y
N
Terrace
2
S
Y
Y
1.3
1.9
2.9
Y
N
Standalone
3
N
Y
Y
1.3
1.9
2.9
Y
N
Standalone
5
NE
Y
Y
1.3
1.9
3
Y
N
Standalone
4
NE
Y
Y
1.3
1.9
3.2
Y
N
Standalone
4
N
Y
Y
1.25
2
3.4
Y
N
Standalone
2
SE
Y
Y
1.38
1.85
2.4
Y
N
Standalone
4
N
Y
Y
1.8
2
3.1
Y
N
Standalone
2
E
N
Y
1.2
1.35
1.7
N
N
Standalone
4
S
N
Y
1.2
1.35
1.7
Y
N
Standalone
1
S
N
Y
1.2
1.6
1.7
N
N
Standalone
2
S
N
Y
1.2
1.35
1.7
N
N
Standalone
4
S
N
Y
1.2
1.35
1.7
N
N
Standalone
4
W
N
Y
1.2
1.35
1.7
N
N
Standalone
2
E
N
Y
1.2
1.35
1.7
Y
N
Standalone
2
E
N
Y
1.2
1.35
1.7
N
N
Standalone
4
E
N
Y
1.2
1.35
1.7
Y
N
House 3 House 4 House 5 House 6
NEW
OLD
House 7 House 8 House 9 House 10 House 11 House 12 House 13 House 14 House 15 House 16 House 17 House 18 House 19 House 20 House 21 House 22 House 23 House 24 House 25 House 26 House 27 House 28 House 29
newer and older housing stock in the autumn in the amount of time spent beneath 18 � C this significance disappears in the winter months will all dwellings spending large amounts of time underneath this threshold temperature. Although four older dwellings experienced short periods of extreme low indoor air temperatures (i.e. below 10 � C) no newly built dwellings did and based on the Mann-Whitney U test the new housing stock is statistically indifferent in this measure. As the solar orientation of each home’s living room varies, an anal ysis was undertaken to determine if orientation influences indoor air temperatures and predicted comfort. A Kruskal-Wallis Test, commonly referred to as a non-parametric one-way ANOVA, was computed using data collected from the dwellings with living room window orientation as the testing factor.
The test results shown in Table 5 indicate that whilst the different orientations preform broadly as expected the orientation does not significantly influence how much time a home spends below 18 � C, or the duration of time the home’s living room is uncomfortably cold. Occupancy, type and the height of the dwelling above ground were also tested in the same manner. Only one metric achieved significance. This was the type of dwelling and only in the autumn season. Further exploration using the Mann-Whitney U test determined that this sig nificant difference occurred between the duplex/terrace housing and the standalone housing. As all the OLD housing is standalone this could be measuring the difference between older and newer housing. When the older housing stock (9 dwellings) was excluded from the analysis (leaving 8 duplex/terrace and 7 standalone dwellings) the significance disappeared. This confirms that the orientation, type, occupancy and 5
R. Ade and M. Rehm
Building and Environment 167 (2020) 106466
Fig. 2. Box plots showing percentage of time where indoor air temperature is below 18 � C for autumn and winter.
height above ground do not affect the performance of the dwellings in the autumn and winter months.
providing sufficient levels of passive thermal envelope performance. However as noted in the literature review the 18 � C temperature threshold is not confirmed to be linked to health outcomes in the liter ature and prominent researchers such as Howden Chapman have determined that improvement in health outcomes may not be due to maintaining higher average temperatures, but instead to reduced exposure to very low temperatures [1]. When a 10 � C temperature threshold is utilised the OLD dwellings still perform the worst (spending a mean of 1% of their time below 10 � C) but there is no difference in the performance of the NEW and 6HS dwellings. It can therefore be reasoned that for the studied houses that both 6-Homestar and NZBC is providing an acceptable level of performance against this metric. When thermal comfort is evaluated a similar trend appears. The OLD dwellings are significantly less comfortable (cold) than the new housing stock, however there is no difference between the NEW and 6HS dwellings. The increased levels of insulation between the OLD and
5. Discussion The results of this study present two clear findings. The first is, as expected, that the OLD dwellings are significantly colder than newly constructed homes, spending 27.0% of the time in the autumn beneath the WHO minimum temperature threshold of 18 � C for occupant health, whilst the newer housing stock spends much less time beneath this threshold. The same trend continues during the winter with the OLD dwellings spending 71% of the time under 18 � C, contrasted to 64% and 56% respectively for the NEW and 6HS dwellings. Somewhat surpris ingly the newer housing stock spends more than half of its time under 18 � C during the winter, indicating that for social housing tenants, who often suffer fuel poverty, that both NZBC and 6-Homestar may not be 6
R. Ade and M. Rehm
Building and Environment 167 (2020) 106466
Fig. 3. Box plots showing percentage of time where indoor air temperature is uncomfortably cold for autumn and winter.
NEW/6HS dwellings are likely a key reason for these differences in the seasons. A commonly postulated reason for temperature and comfort differ ences in dwellings is orientation. More of the NEW and 6HS are favourably orientated when compared to the OLD dwellings and will likely being received increased solar gain. Indeed favourable orientation is a key consideration of both new and ‘green’ housing design with the NZGBC stating “You don’t need to install flash new gadgets to get a good Homestar rating: nearly half the points a house can earn relate to energy, health and comfort. That’s because getting the basics right – good orientation for sun, high levels of insulation and controlling moisture – is vital to create a healthy, efficient home” [43]. However the statistical results (Table 5) indicate that orientation does not significantly influence how much time a home spends below 18 � C or the duration of time the home’s living room is uncomfortably cold or hot. The performance gap between expectation and reality is often
attributed to occupant behaviour. However occupant behaviour would not be expected to influence these findings too greatly as there are no complicated active heating, cooling or ventilation systems in any of the studied dwellings. Indeed NZ housing is not commonly provided with central heating or cooling [44] and only one house in this study con tained a device capable of cooling. Therefore occupant behaviour in these dwellings would be limited the opening and closing of windows and doors, and the operation of electric plug in heaters (there are no fireplaces in any dwellings). Whilst occupant behaviour may have some effect on the results (as indicted by house 1), the authors believe that it is the structural differences (type, insulation and orientation) between the dwelling categories that explain the differences between the newer and older dwellings.
7
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Building and Environment 167 (2020) 106466
Fig. 4. Box plots showing percentage of time where indoor air temperature is uncomfortably hot for autumn and winter.
6. Limitations
desert like temperatures of extreme heat in summer and extreme cold in winter. Homestar requires greater levels of insulation in these climate zones and future research could expand the methodology of this study to other climate zones in NZ. It is not possible to assess the effectiveness of holistic rating tools through a review of indoor temperature and thermal comfort alone, with elements such as energy and water use also holding significant interest in the context of climate change. In addition relative humidity and ventilation rates can also impact the thermal comfort of occupants but are not considered by the thermal comfort equations used in this study. Future research could seek to incorporate these data points, as well as survey occupants on their comfort levels.
The results of this study are naturally limited given the small number of dwellings reviewed in the study (thirteen 6HS, seven NEW and nine OLD), the single subdivision location and the heterogeneity of the building orientations. Whilst information was gathered from the social housing provider on structural building characteristics such as insu lation levels, a more in depth interview process with dwelling occupants has not been undertaken. The authors therefore have no understanding around the personal preferences of the occupants. For example some people like it warm whilst others like it cold and it has not been possible to account for these personal preferences, or other elements of occupant use (like a preference for open windows) in this research. Future research in this space could therefore focus on this more specifically to determine if this is key factor in the results. NZ contains additional climate zones, some of which experience
7. Conclusions A strong discourse exists in New Zealand that ‘cold and damp’ 8
R. Ade and M. Rehm
Building and Environment 167 (2020) 106466
Table 2 Percentage of time spent below 18 � C, 10 � C and too cold in the autumn and winter months of Auckland, New Zealand.
Table 3 Predicted percentage of time ‘too hot’ or ‘too cold’ in the autumn and winter months of Auckland, NZ per dwelling.
Temperature
6HS
NEW
OLD
House 1 House 2 House 3 House 4 House 5 House 6 House 7 House 8 House 9 House 10 House 11 House 12 House 13 House 14 House 15 House 16 House 17 House 18 House 19 House 20 House 21 House 22 House 23 House 24 House 25 House 26 House 27 House 28 House 29
Temperature
Autumn (March through May 2019)
Winter (June through August 2019)
Autumn (March through May 2019)
Winter (June through August 2019)
% of time below 10 � C
% of time below 18 � C
% of time below 10 � C
% of time below 18 � C
% of time too cold (Tlower
% of time too hot (Tupper
% of time too cold (Tlower
% of time too hot (Tupper
–
–
–
1x
80% acceptability
80% acceptability
80% acceptability
limit
limit
–
–
–
36
range: 12.3 to 16.6� C)
80% acceptability
limit
limit range: 21.3 to 25.6� C)
–
9
–
95
–
–
–
63x
–
2
–
42
–
7
–
–
–
7
–
68
–
6
13
–
–
1
–
46
–
1
–
–
–
–
–
49
–
8
6
–
–
1
–
40
–
8
–
–
–
3
–
51
–
5
–
–
–
47
–
100
–
2
–
–
–
–
–
3x
–
–
–
–
–
–
–
-x
–
–
55x
–
–
8
–
80
–
7
–
13
–
1
–
23
–
4
–
9
–
9
–
65
–
9
8
–
–
1
–
63
–
2
1
–
–
7
–
43
–
9
3
–
–
14
–
77
–
–
1
–
–
12
–
94
–
3
1
2
–
19
–
86
–
–
2
–
–
27
–
78
–
–
6
–
–
25
–
80
–
–
9
–
0.2
43
5
89
2
3
25
1
–
29
1
68
5
2
26
–
–
10
–
54
20
–
63
–
–
27
–
82
8
–
33
–
–
27
2
71
–
1
2
–
–
17
–
36
1
1
18
–
–
37
3
85
7
2
30
–
2
3
4
3
11
5
53
–
range: 13.5 to 18.9� C) 6HS
NEW
OLD
x outliers identified by SPSS.
housing is linked to poor health outcomes. This has led to recent Healthy Homes Guarantee Act. This new legislation explicitly references the WHO ‘healthy’ temperature guidelines and stipulates that all rental homes are to feature a fixed heating appliance capable of maintaining a minimum temperature threshold of 18 � C in the main living room. In addition several government organisations, including the central gov ernment’s social housing provider Housing New Zealand and Panuku,
House 1 House 2 House 3 House 4 House 5 House 6 House 7 House 8 House 9 House 10 House 11 House 12 House 13 House 14 House 15 House 16 House 17 House 18 House 19 House 20 House 21 House 22 House 23 House 24 House 25 House 26 House 27 House 28 House 29
x outliers identified by SPSS.
9
range: 22.5 to 27.9� C)
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Building and Environment 167 (2020) 106466
Table 4 Percentage of time where indoor environment is sub-optimal over the autumn and winter months (Mann-Whitney U test). Percentage of time spent by dwelling category AUTUMN
INDOOR TEMPERATURE
Under 18 � C Under 10 � C
OCCUPANT COMFORT
Too cold Too hot
WINTER
INDOOR TEMPERATURE
Under 18 � C Under 10 � C
OCCUPANT COMFORT
Too cold Too hot
MIN MAX MEAN MIN MAX MEAN MIN MAX MEAN MIN MAX MEAN N MIN MAX MEAN MIN MAX MEAN MIN MAX MEAN MIN MAX MEAN N
Mann-Whitney U test z-scores
6HS
NEW
OLD
– 9 3 – – – – – – – 9 5 13 36 95 56 – – – – 13 3 – – – 9
1 19 9 – – – – – – – 9 2 7 23 94 64 – – – 1 9 3 – 2 0.3 7
10 43 27 – – – – 20 6 – 5 2 9 36 89 71 – 5 1 2 63 28 – 3 0.4 9
6HS & NEW 1.885 .000 .000
6HS & OLD 3.329
NEW & OLD **
.000 4.030
2.922 .000
**
3.168
1.419
1.550
0.711
0.688
1.592
0.582
.000
**
**
2.182
*
1.947
*
1.418
3.103
**
2.762
**
1.134
1.455
0.388
*, ** Mann-Whitney U Test exact 2-tailed p-values at 5% and 1% significance levels respectively.
‘too cold’ between 3% of the time based on the adaptive comfort equations by Ref. [27]. This raises a question of whether occupant comfort should be evaluated rather than specific temperatures thresh olds particularly since the [22] definition of a healthy dwelling is one “in which the occupant is comfortable”. This is particularly important in the context of fuel poverty and the ability of the financially vulnerable to operate space heating (or cooling) devices. Both the 6-Homestar and new, code-compliant dwellings spend significant amounts of time below the 18 � C threshold suggesting that this study’s social housing tenants were not operating space heating devices, potentially because they could not afford to. In such circum stances, fuel impoverished occupants must rely on the inherent abilities of the home to maintain a comfortable indoor environment. If thermal comfort is an adequate measure of occupant health, then both new homes built to code and 6-Homestar-rated dwellings achieve signifi cantly better outcomes over the autumn and winter period in compari son with older dwellings. This study provides a limited, but valuable, contribution to the body of knowledge regarding how green dwellings perform post-completion. With 6-Homestar increasingly adopted as a quality standard in New Zealand, policymakers may wish to reassess whether6-Homestar de livers dwellings that provide thermal comfort quality superior to homes built to the current building code. Policymakers should also consider whether thermal comfort is a more appropriate target than the WHO’s inflexible 18 � C ‘healthy’ temperature threshold.
Table 5 Kruskal-Wallis test results for rated and unrated new dwellings by living room window orientation for the over the Autumn and Winter months. Kruskal-Wallis Test Mean Ranks Autumn
Winter
Orientation
Below 18 � C
Too Cold
Too Hot
Below 18 � C
Too Cold
Too Hot
North (including NW) East (including NE) South (including SE) West (including SW)
11.83
11.00
17.67
11.72
9.33
11.50
15.23
16.18
16.55
10.56
12.75
16.19
19.75
19.00
9.17
15.00
17.00
11.50
14.17
14.67
13.00
22.50
18.50
11.50
Kruskal-Wallis H Asymptotic pvalue
3.177
5.684
4.380
4.930
5.215
6.921
.365
.128
.223
.177
.157
.074
Auckland Council’s property development arm, have adopted 6-Home star certification as a quality mechanism to deliver new dwellings that can both improve occupant health and mitigate climate change. The NZGBC claims that 6-Homestar certification will provide dwellings with better insulation and ventilation than is available in an average NZ home, including ones built to the current building code. This study finds that whilst older vintage dwellings spend significant amounts of time (71% in winter) below the WHO 18 � C guideline, and are predicted to be ‘too cold’ when compared to new housing, there is no statistical difference between the interior temperatures and predicted comfort levels of newly constructed certified and non-certified green dwellings. Somewhat surprisingly the new housing stock spends over 50% of its time beneath with WHO guideline in winter, but is only predicted to be
Funding BRANZ Building Research Levy. Declaration of competing interest Rochelle Ade is a Homestar Assessor and has worked as a Homestar Assessor for the Building Excellence Group. Rochelle Ade also has an interest in Tether.
10
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References
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