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Environmental and Climate Technologies
2020, vol. 24, no. 2, pp. 348–363
https://doi.org/10.2478/rtuect-2020-0078
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©2020 Matxalen Etxebarria, Xabat Oregi, Olatz Grijalba, Rufino Hernandez.
This is an open access article licensed under the Creative Commons Attribution License (http://creativecommons.org/
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Relationship Between Energy Demand, Indoor
Thermal Behaviour and Temperature-Related Health
Risk Concerning Passive Energy Refurbishment
Interventions
Matxalen ETXEBARRIA1*, Xabat OREGI2, Olatz GRIJALBA3, Rufino J. HERNÁNDEZ4
1–4Department of Architecture. University of the Basque Country (UPV/EHU), Oñati Plaza 2,
20018 Donostia-San Sebastian, Spain
Abstract – The main objective of this article is to demonstrate that passive energy
refurbishment interventions influence comfort conditions of households for both cold and hot
annual periods, while they help to avoid or promote temperature-related health risk
situations. However, improving the thermal efficiency of the building envelope is encouraged
in order to reduce energy demand for heating and cooling instead of considering also their
impact on users’ health. The calculation methodology to quantify improvements, on the other
hand, is draw n from regulation-based standards, which describe the optimal achievable
efficiency levels and energy cost savings. The present study, however, addresses how diverse
thermal performance variables are (climate, thermal comfort range and occupancy rate), and
shows that different thermal assessment standards influence the obtained results. An energy
simulation approach was developed to evaluate different scenarios and compare the results.
In conclusion, the results contribute to an understanding or to a discussion of the suitability
of current energy renovation policies with regard to indoor thermal comfort and
temperature-related health risk situations.
Keywords – Energy demand; energy refurbishment; indoor thermal behaviour; indoor
thermal comfort; indoor thermal health risk
1. INTRODUCTION
The objective of public European policies and recommendations towards building
renovation has varied over decades; from being focused on the conservation and maintenance
of buildings [1], [2] to 20th Century energy efficiency standards [3]–[5], due to building
sector’s high percentage of final energy consumption (32 % in 2017) [6].
Energy efficiency measures, therefore, were and are mainly promoted because of their
capacity to reduce buildings’ carbon and greenhouse gas emissions while saving energy costs
and improving thermal performance [7]–[13].
Alongside such purposes, it is worth mentioning their capacity and positive influence in the
indoor thermal behaviour and comfort quality level [14]–[16]. With respect to indoor thermal
well-being, however, there are divergent international recommendations, standards and
regulations, including those defined by the World Health Organisation [17], [18], the
ASHRAE [19], the ISO 7730 [20]. In addition, diverse scientific research support there are
* Corresponding author.
E-mail address: etxebarria.matxalen@gmail.com
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different comfortable temperature conditions for determining indoor comfort [21]–[25],
protecting human health [26]–[36] and decreasing mortality and morbidity rates [37]–[41].
On the other hand, if construction characteristics of buildings are considered, it has been
demonstrated that the residential building sector is characterized by poor thermal efficiency
in countries with milder climates, which promotes low and unhealthy indoor winter
temperatures [42]–[44].
Improvements in the energy efficiency and the thermal behaviour of the residential building
stock, therefore, need to be considered in order to achieve thermally healthier and more stable
indoor hygrothermal conditions for winter or cold periods [45], [46].
Energy efficiency calculations and policies, however, are commonly based on
regulation-based standards, which establish both the achievable comfort ranges and the
occupancy rates [47]. These standards are useful for the simplification of the calculation
methodology, but they are aimed at achieving higher efficiency levels and energy cost
savings. Theoretical comfort ranges and occupancy rates, though, could be regarded as
variable factors due to their high impact on the energy demand calculation and indoor thermal
behaviour.
2. OBJECTIVE
The objective of this paper, therefore, was focused on demonstrating that passive energy
refurbishment interventions, in addition to reducing energy demand, do influence households’
comfort conditions for both cold and hot annual periods, while they help to avoid or promote
temperature-related health risk situations. The evaluation of the influence regarded diverse
regulation-based and thermally healthy comfort ranges, and different occupancy rates.
3. CALCULATION METHODOLOGY
To this end, a calculation methodology was defined in order to determine the relationship
between heating and cooling energy demand, indoor thermal comfort conditions and
temperature-related health risk situations in a multifamily residential building (Fig. 1).
Based on machine learning models [48], different energy simulation scenarios were
developed and evaluated according to three different analysis variables (climate data, indoor
thermal range and schedule, and occupancy rate) and two construction state conditions
(existing unrefurbished and energy-refurbished). Among the energy-refurbishment criteria,
only passive strategies were assessed. Active, renewable and/or control systems were not
considered.
Building type:
Multifamily Residential Building
Construction state:
existing unrefurbished
vs
energy-refurbished
Analysis variables:
climate data
+
indoor thermal condition
+
occupancy
Results:
energy demand
+
indoor thermal comfort
+
indoor thermal health risk
Fig. 1. Calculation methodology scheme.
The results obtained from the diverse scenarios were distinguished according to annual
energy demand (heating and cooling), indoor thermal comfort level and temperature-related
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health risk situations. Dealing with energy demand (kWh/m2 per year), heating/cooling
systems were activated to reach the established temperature ranges, but for the quantification
of the indoor thermal well-being level and thermal risk results (hours per year), no active
systems were used, that is, the results displayed the passive performance of the building.
4. CASE STUDY
The above-detailed calculation methodology was applied to a multifamily residential
building in the Autonomous Community of the Basque Country, region situated in northern
Spain.
According to the most recent Basque statistical database [49], the average age of the
residential building stock is established in 42.8 years, suggesting almost the half (46 %) was
built before the approval of the first Spanish building regulations and thermal envelope
requirements [50]. Within this context, the research project called First step study for the
elaboration of a long-term Action Plan dealing with the residential building stock of Euskadi†
was developed, which aimed to classify and categorize the current Basque residential building
stock. It concluded that 91.9 % of the total were multifamily residential dwellings, of which
46 % described the H2 type, the one built between 1961 and 1980 (Fig. 2).
H2 type was constructed during the economic development period, period in which the
urgent demand of the society promoted buildings with poor construction quality and deficient
thermal properties, with no concern on the resulting health risk. Consequently, it is worth
mentioning their great improvement potential for both energy demand characteristics and
indoor environmental properties.
Fig. 2. Classification of multifamily residential buildings in the Autonomous Community of the Basque Country built
between 1961 and 1980.
4.1. Construction State: Description of Building Model
4.1.1. Existing Unrefurbished
A multifamily residential building constructed between 1961 and 1980 was, therefore,
selected for this study.
With a total building area of 3290.70 m2 and a net conditioned surface of 2487.73 m2, the
building consists of a non-occupied ground floor and 7 residential floors (with 4 apartments
† Original designation: «Estudio previo para la elaboración de un Plan de Acción a largo plazo en el parque de edificios
de Euskadi». The research has been developed by the research group CAVIAR (UPV/EHU) in collaboration with
researchers from the UPC and the Department of Environment, Territorial Planning and Housing of the Basque
Government.
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of 12 m depth on each floor). All apartments are naturally ventilated and lack mechanical
ventilation. No renewable energy systems were installed.
The building envelope’s construction and thermal characteristics were defined during the
initial stage of the abovementioned research project. The U values (W/m2K) of the existing
building envelope, include a cavity wall façade, 1.25 (W/m2K); a reinforced concrete deck
with ceramic finish, 3.46 (W/m2K); a reinforced concrete first floor slab, 2.51 (W/m2K);
monolithic glazing, 5.77 (W/m2K); and aluminium frame, 4.2 (W/m2K) (see Table 1).
As mentioned, this building typology was built before the first Spanish building regulations,
hence, the U values do not meet the minimum requirements established by the current Spanish
Technical Building Code [51].
TABLE 1. BUILDING ENVELOPE LAYERS AND U VALUES FOR THE BASELINE
AND REFURBISHED MODELS
Envelope
Thickness,
mm
Density,
kg/m
3
Conductivity,
W/(m·k)
U-value,
W/(m
2
·k)
External façade
Baseline existing composition
Double hollow brick partition 80 930 0.375
Air gap 80 – –
Double hollow brick partition 80 930 0.375
Refurbishment layers
Insulation – XPS 100 37.5 0.032
Air gap 50 – –
Ceramic panel 15 2000 1
Current façade 1.25
Refurbished façade 0.248
Roof
Ceramic tile 25 2300 1.3
Concrete floor 200 1740 1.923
Current roof 3.46
Concrete floor in contact with heated spaces
Concrete floor 180 2100 1.4
Current concrete floor in contact with unheated space 2.51
Concrete floor in contact with unheated spaces (first and last floors)
Baseline existing composition
Concrete floor 180 2100 1.4
Refurbishment layers
Insulation – XPS 60 37.5 0.032
Current concrete floor in contact with unheated space 2.51
Refurbished concrete floor in contact with unheated space 0.47
Windows (78 % glazing and 22 % frame)
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Baseline existing composition
Single glazing 6 * 5.7
Aluminium frame with no
thermal bridge break
– * 4.2
Refurbished composition
Double glazing 6 + 12 + 6 * 2.0
PVC frame – * 2.1
Existing window 5.37
Refurbished window 2.1
4.1.2. Energy Refurbished State
The principal energy renovation strategy was focused on the improvement of users’ quality
of life, that is to say, increasing the indoor thermal comfort, while reducing the energy
demand. For this purpose, the considered strategies were based on passive measures, such as
increasing the thermal resistance of the envelope, replacing the windows and reducing the air
leakage.
There were three possible intervention strategies related to the improvement of the thermal
resistance of the façade: external insulation, internal insulation, and air gap insulation.
Considering the best technical and energy efficient practice, however, the selected strategy
was the external insulation. The addition of that new skin, though, could also be evaluated
according to two different techniques, that is, external thermal insulation technique or
ventilated façade technique. Based on a previous study developed by Oregi et al. [52], which
evaluated the energy, environmental and economic performance of several refurbishment
strategies, a ventilated façade technique was selected‡, which included a 10 cm XPS
insulation, an air gap and a ceramic outlayer panel (see Table 1).
Alongside with the solid façade intervention, the replacement of the existing windows, both
the frame and the glazing, was also considered. The measure included a new PVC frame
(2.0 W/(m2k)) and double glazing (2.1 W/(m2k)).
In addition to the improvement of the vertical envelope, the strategy also considered the
horizontal one, that is to say, the concrete floors in contact with unheated spaces (first floor
and upper floor). For that purpose, a 6 cm thermal insulation layer with its flooring finish
layer was added to the existing concrete slab.
As a result, the set of passive intervention measures suggested improved the thermal
properties to the total area of the thermal envelope.
4.2. Analysis Variables
4.2.1. Climate Data
Regarding the varying outdoor environmental conditions and the sheer quantity of such
building typology across the whole territory of the Basque Country, this study used climate
data for two cities, Bilbao and Vitoria-Gasteiz, which represent the two divergent climates in
the region.
‡ Note that the climatic zone, type of building and the construction characteristics of that reference case study were
similar to the one evaluated by this study.
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According to the Köppen-Geiger worldwide climate classification [53], [54] and its
identification within the Iberian Peninsula [55], the Basque Country should be considered as
«warm temperate-Cfc» (C: warm temperate, f: fully humid, c: cool summer), or «Cfb»
(temperate with a dry season and temperate summer), respectively. However, if the current
Spanish Technical Building Code is regarded, it provides different reference climate data for
the provincial capitals of the whole of Spain [56]. In the case of Bilbao, the reference climate
zone is C1, where the minimum and average outdoor dry bulb temperatures are –0.2 °C and
14.7 °C, respectively. Vitoria-Gasteiz, instead, falls with a different category, D1, with a
minimum and an average of –4.0 °C and 12.1 °C, respectively [57].
Based on these classifications, EnergyPlus 8.6 [58] simulation tool was selected for the
operational energy use calculations, where the International Weather for Energy
Calculation [59] climatic files were used for both cities. Alongside, the building models were
developed through the DesignBuilder v.5.5.2.003 interface [60]. It should be mentioned, that
the defined construction models reproduced the selected building typology according to pre-
stablished modelling criteria simplifications, which may influence in the results, including
some little errors or variations in comparison to the real construction ones.
4.2.2. Indoor Thermal Condition
4.2.2.1. Thermal Comfort Range and Schedule
Two different definitions of thermal comfort were stablished and evaluated (see Table 2)
to determine the energy demand.
− Condition CTE (“C”): Spanish Technical Building Code regulation-based indoor
thermal range and schedule [51].
− Condition WHO (“H”): healthy thermal range [17], [18] over 24 h.
TABLE 2. INDOOR THERMAL RANGE AND SCHEDULE PARAMETERS CONSIDERED
FOR THE SIMULATION PROCESS
Indoor thermal comfort condition Temperature range Schedule
CTE 20–25 °C
Heating: 30th Sep. – 31st May
From 07:00 h to 23:00 h
Cooling: 31st May – 30th Sep.
From 15:00 h to 23:00 h
WHO 18–24 °C
Heating: 30th Sep. – 31st May
24 h
Cooling: 31st May – 30th Sep.
24 h
4.2.2.2. Thermal Limits for Health Risk
The following thermal limits describe indoor temperatures associated with negative impacts
on health, so the exposure to such inadequate temperatures may result in an increase in
seasonal mortality and morbidity rates.
− Cold-related temperatures may cause higher risk of cardiovascular events [26], [31],
[33], [35], [36], respiratory diseases, or minor problems such as cold and flu [39].
Temperatures below 18 °C, therefore, show an increasing risk:
− Risk 1: Tª < 16 °C, respiratory infections;
− Risk 2: Tª < 12 °C, blood pressure and viscosity increase, which may cause heart
attacks and strokes;
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− Risk 3: Tª <9 °C, deep body temperature fall.
− Heat-related temperatures are less harmful but involve cardiovascular diseases [26],
[35], [61], clinical syndromes of heat stroke, heat exhaustion, heat syncope and heat
cramps [62], [63], permanent damage to organ systems and risk of early mortality.
Several studies demonstrate that the recommended upper temperature should not
exceed from 22 °C to prevent from Sick Building Syndrome [27], while the WHO sets
it in 24 °C [17], [18]. Other studies [38], [64], however, argue that upper temperature
limits should be relative the outdoor climate. Within such context, recent studies
developed in Spain [41], divide the whole Spanish territory in local climate areas and
establish particular upper limits for each area in order to reduce mortality. Considering
the two reference climates evaluated, therefore, these were the fixed limits:
− Risk 4: Tª < 30 °C for Bilbo_C1 climate, and Tª < 34 °C for Gasteiz_D1 climate.
4.2.3. Occupancy
Together with the thermal comfort range and schedule, the occupancy rate may generally
be derived from building regulations. In this study, however, even if the regulation-based
“Pr2 profile” was the base scenario to set the internal energy performance (see Table 3), two
more occupancy scenarios were evaluated in order to consider also other users’
behaviour [65]:
− Profile 1 (“Pr1”): medium occupancy rate, heating and cooling are just switched on in
the most used rooms. Only the 65 % of the total living area of the household was
considered to be thermally conditioned, and the remaining 35 %, instead,
unconditioned. The internal energy performance parameters for the conditioned area,
though, were the regulation based ones (Table 3);
− Profile 2 (“Pr2”): medium occupancy rate. Current Spanish regulation-based
occupancy rate, schedule and internal energy performance parameters;
− Profile 3 (“Pr3”): highest occupancy rate. The regulation-based occupancy was
considered to be the double, that is, 0.06 people/m2. However, the rest of the internal
energy performance parameters were the ones defined in Table 3.
TABLE 3. PR2 PROFILE OCCUPANCY AND ENERGY PERFORMANCE PARAMETERS CONSIDERED
FOR THE SIMULATION PROCESS
Parameter Unit Value
Occupancy (household)
People/m² 0.03
Schedule
Until 07:00 (100 %), until 15:00 (25 %), until 23:00
(50 %), until 24:00 (100 %)
Occupancy (ground floor,
stairs, under roof)
People/m² 0
Schedule Until 24:00 (100 %)
Ventilation (natural) Renovations per hour (r/h) 0.75
Ventilation (infiltrations) Renovations per hour (r/h) 0.135
Lighting (household)
Lighting level (lux) 200
Power (W/m²) 5
Schedule
Until 07:00 (10 %), until 18:00 (30 %), until 19:00
(50 %), until 23:00 (100 %), until 24:00 (50 %)
Lighting (common areas) Lighting level (lux) 100
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Power (W/m²) 3
Schedule Until 24:00 (On)
Lighting (ground floor) Schedule Off
Equipment (household)
Power (W/m²) 4.4
Schedule
Until 07:00 (10 %), until 18:00 (30 %), until 19:00
(50 %), until 23:00 (100 %), until 24:00 (50 %)
4.3. Machine Learning Models: Energy Simulation Scenarios Outline
Finally, from the above-described variables a total of 24 different analysis scenarios (see
Table 4) were obtained.
TABLE 4. ENERGY SIMULATION SCENARIOS BY CASE STUDY PARAMETERS
Construction state Climate data Indoor thermal condition Occupancy ID
Baseline (B)
Bilbao_C1 (B)
CTE (C)
Profile 1 (Pr1) B_B_C_Pr1
Profile 2 (Pr2) B_B_C_Pr2
Profile 3 (Pr3) B_B_C_Pr3
WHO (H)
Profile 1 (Pr1) B_B_H_Pr1
Profile 2 (Pr2) B_B_H_Pr2
Profile 3 (Pr3) B_B_H_Pr3
Gasteiz_D1 (G)
CTE (C)
Profile 1 (Pr1) B_G_C_Pr1
Profile 2 (Pr2) B_G_C_Pr2
Profile 3 (Pr3) B_G_C_Pr3
WHO (H)
Profile 1 (Pr1) B_G_H_Pr1
Profile 2 (Pr2) B_G_H_Pr2
Profile 3 (Pr3) B_G_H_Pr3
Refurbished (R)
Bilbao_C1 (B)
CTE (C)
Profile 1 (Pr1) R_B_C_Pr1
Profile 2 (Pr2) R_B_C_Pr2
Profile 3 (Pr3) R_B_C_Pr3
WHO (H)
Profile 1 (Pr1) R_B_H_Pr1
Profile 2 (Pr2) R_B_H_Pr2
Profile 3 (Pr3) R_B_H_Pr3
Gasteiz_D1 (G)
CTE (C)
Profile 1 (Pr1) R_G_C_Pr1
Profile 2 (Pr2) R_G_C_Pr2
Profile 3 (Pr3) R_G_C_Pr3
WHO (H)
Profile 1 (Pr1) R_G_H_Pr1
Profile 2 (Pr2) R_G_H_Pr2
Profile 3 (Pr3) R_G_H_Pr3
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5. RESULTS
5.1. Energy Demand Variation
Due to the prevailing climatic conditions and residential use of building, almost all the
annual energy demand (Fig. 3) corresponded to heating for all 12 baseline or unrefurbished
scenarios (see Table 4). As a result, the total energy demand, including the heating demand,
was considerably reduced for all refurbished scenarios, even if cooling demand increased (see
Table 5). Even more, there were some simulation scenarios, such as R_B_C_Pr2,
R_B_C_Pr3, R_B_H_Pr1, R_B_H_Pr2, R_B_H_Pr3 for Bilbao_C1 climate, and R_G_H_Pr3
for Gasteiz_D1 climate, in which the cooling energy demand became higher than the heating
energy demand.
Fig. 3. Annual energy demand (kWh/m2) for all the energy simulation scenarios.
TABLE 5. ANNUAL ENERGY DEMAND VARIATION (%) FOR REFURBISHED SCENARIOS.
VARIATION: NEGATIVE VALUES MEAN A REDUCTION, POSITIVE VALUES AN INCREASE
ID
Annual energy demand variation
CTE comfort condition WHO comfort condition
Total Heating Cooling Total Heating Cooling
R_B_Pr1 –59.18 –75.41 238.73 –45.26 –77.48 177.78
R_B_Pr2 –63.60 –79.77 232.48 –50.15 –81.81 171.36
R_B_Pr3 –63.13 –84.10 214.13 –45.79 –87.90 163.58
R_G_Pr1 –59.43 –70.33 297.52 –49.98 –69.63 227.12
R_G_Pr2 –64.26 –75.05 300.55 –55.16 –74.54 224.42
R_G_Pr3 –64.93 –78.35 269.45 –53.99 –78.72 211.55
With regard to the three analysis variables, the major differences corresponded to the
climate; the total energy demand for the extremer Gasteiz_D1 climate was always higher if
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models under equal analysis variables were compared. However, those differences were
higher if only baseline scenario results were considered.
Likewise, the diagram shows there were variations among the results obtained if the
occupancy rate and the indoor thermal comfort condition variables were taken into
consideration.
According to the occupancy, the “Pr2 profile” displayed both the highest annual energy
demand and the heating demand. The highest cooling demand, instead, was defined by “Pr3”
as a consequence of its higher internal gains. The variation between “Pr1” and “Pr2”, on the
other hand, did not describe a considerable difference due to the reduced (35 %) thermally
conditioned area. Nevertheless, the results obtained were not as impressive as the ones
obtained with regard to the climate variable.
If both indoor thermal comfort conditions are considered, it should be noticed that the
requisites set by the Spanish building code, involved the highest total energy demand for
unrefurbished scenarios, in which CTE thermal range described higher heating demand, but
lower cooling demand in comparison with the results for WHO thermal range. However, the
total annual energy demand once the energy-refurbishment strategies were applied was almost
equal for both indoor thermal conditions, which described an important total decrease, but an
increased cooling demand.
Accordingly, provided that both reference climate data, regulation-based Pr2 profile, CTE
indoor thermal comfort range, and both construction state scenarios are compared, that is to
say, B_B_C_Pr2 vs R_B_C_Pr2, and B_G_C_Pr2 vs R_G_C_Pr2, the results described a
significant total energy demand reduction for both refurbished scenarios, a 63.6 % and a
64.3 %, respectively, which depended not only on the decrease of the heating demand, but
also on the increase of the cooling demand.
5.2. Passive Indoor Temperature Variation
With regard to the annual passive thermal behaviour of the building, it is worth mentioning
that indoor comfortable hours were reduced in all energy refurbished scenarios for both
climates and for the three occupancy rates analysed (See Table 6).
TABLE 6. ANNUAL COMFORT/RISK HOURS’ VARIATION (%) FOR REFURBISHED SCENARIOS.
VARIATION: POSITIVE VALUES MEAN A REDUCTION, NEGATIVE VALUES AN INCREASE
ID
Annual comfort/risk hours’ variation
Comfort condition Risk limits
CTE WHO
Lower limits Upper limit
Risk 1 Risk 2 Risk 3 Risk 4
R_B_Pr1 37.62 21.64 58.52 100.00 100.00 –11 560.00
R_B_Pr2 35.24 17.67 64.56 100.00 100.00 –24 233.33
R_B_Pr3 26.66 0.57 87.04 100.00 0 –10 533.33
R_G_Pr1 20.64 16.12 33.38 60.70 100.00 –3900.00
R_G_Pr2 18.28 15.52 35.07 70.60 100.00 –5200.00
R_G_Pr3 12.94 17.75 40.72 95.18 100.00 –7600.00
The variation shows an important reduction for the CTE thermal condition variable,
especially for Bilbao_C1 climate, where the reductions reached up to 37 %, 35 % and 26 %
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for Pr1, Pr2 and Pr3, respectively. The reason for such results was related to indoor summer
temperatures. They were higher than the ones obtained in the existing unrefurbished building
scenarios, which meant that during the hottest months they easily exceeded the established
comfortable upper temperature limits (Fig. 4, Fig. 5).
Fig. 4. Annual thermal passive behaviour for baseline (purple shades) and refurbished (green shades) scenarios according
to the occupancy variable and Bilbo_C1 climate.
Fig. 5. Annual thermal passive behaviour for baseline (purple shades) and refurbished (green shades) scenarios according
to the occupancy variable and Gasteiz_D1 climate.
With regard to cold-related temperature risk limits, none of the refurbished building
scenarios (considering the three occupancy rates) showed indoor temperatures below 12 °C
for Bilbao_C1 climate, and even in the worst scenario, the unhealthy hours below 16 °C were
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reduced in 58 %. For Gasteiz_D1 climate, instead, where winter outdoor temperatures are
more severe, it could be observed that indoor temperatures were never lower than 9 °C, and
in the worst scenario, the unhealthy hours below 12 °C and 16 °C were reduced in 60 % and
33 %, respectively.
Heat-related temperature risky hours’ results, on the contrary, offer a totally different
reading. If existing buildings were healthy for both climates and the three occupancy rates,
after refurbished the situation worsened considerably, leading to completely unhealthy
indoors during hot seasons for scenarios under Bilbao_C1 climate.
On the other hand, the data referring to temperature-related health risk situations, showed
that the evaluated intervention strategies were quite efficient if both cold-related and
heat-related temperature risk limits were all together considered (Fig. 6). However, the results
described completely different situations if upper and lower limits were analysed on their
own.
Fig. 6. Annual health risk hours for baseline and refurbished buildings according to both reference climates.
6. CONCLUSIONS AND DISCUSSION
The energy refurbishment strategies suggested in this study meet the energy demand
regulations’ requirements, hence, they promote energy efficient solutions and fulfil thermal
envelope improvements. The efficiency and the potential of energy refurbishment measures
is commonly calculated according to regulation-based standards. This research, however, was
aimed at demonstrating that considering diverse thermal variables (climate, indoor thermal
conditions and occupancy rates) final optimal results might be influenced. Moreover, the
work carried out has enabled an integrated evaluation of the impact of energy refurbishment
interventions on energy demand, indoor thermal comfort and temperature-related health risk.
An integrated vision has not been present in existing literature
Thermal well-being conditions describe comfortable and healthy indoors, but in order to
reach such conditions, be efficient, and reduce the energy demand, there is a need to
understand their interaction with the thermal performance of the envelope. As demonstrated,
the Spanish regulation-based comfortable temperature range (20–25 °C) is preservatory
towards unhealthy indoors, yet is almost unattainable for unreburbished H2 type residential
buildings with regard to their energy demand control.
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Energy refurbishment interventions, on the other hand, do have a positive impact on the
energy demand reduction, but lead to a variation of the indoor thermal environment.
As supposed, the evaluated energy refurbishment strategies on the thermal envelope result in
higher indoor temperatures during cold seasons, upgraded comfort levels, less thermally
unhealthy hours, and reduced needs for active systems, which describes a beneficial situation
for fuel poverty and low-income households, for instance. Nevertheless, the suggested
interventions illustrate also an increase in indoor temperatures during hot seasons. Therefore,
it could be said that they describe a conflicting scene, in which the cooling demand is raised,
comfortable conditions are worsen, and health risk situations are increased. However, a more
nuanced analysis of the results shows that in the climates studied, comfort conditions during
winter and transitional seasons improve noticeably, and the worsening of indoor thermal
conditions occurs only in summer months. The evaluated climates, however, are mild and
temperate even during summer periods. As a result, the increased indoor temperatures could
be mitigated thanks to the natural ventilation, which may promote also a reduction in the
cooling demand.
Therefore, the important reduction in health risk associated with low temperatures in
dwellings identified in this study tips the balance definitively towards the positive impact of
refurbishment and, therefore, justifies the intervention in the climatic zones analysed.
Nevertheless, refurbishments in climates with harsher summers or in scenarios considering
global warming demand more rigorous prior study that goes beyond energy demand to
determine if the global impact would be positive or negative.
In conclusion, it could be said, there is still an open research line dealing with energy
refurbishment intervention strategies, indoor thermal comfort and their impact on human
health.
ACKNOWLEDGEMENT
The corresponding author would like to acknowledge the Department of Education, Language Policy and Culture of the
Basque Government for the Predoctoral Training Programme for Non-Doctor Research Personnel from which was beneficent
(PRE_2015_1_002) during the research period. Furthermore, the authors thank the Department of Architecture of the
University of the Basque Country for the financial support given for this research.
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