In the global scene, the energy is spent by three primary sectors; industry, transportation and buildings. IEA (2011) published the worldwide energy consumption by end-use sectors (IEA, 2011). The results are depicted in Figure 2-2.
Figure 2-2 Energy consumption by end-use sectors at 2009 (IEA, 2011)
From the Figure 2-2, it can be realized that buildings is the most consuming sector among the end-use categories, for both the global and EU-27 scene, with almost twice the percentage of the other sectors. It was estimated that the energy consumption by the building sector is about 451 Mtoe (Million tonnes of equivalent)(IEA, 2011).
The building sector is comprised by two categories; (a) commercial and (b) residential. According to Kavgic et al. (2010), 22% of energy is absorbed by the domestic buildings, with the rest 18%, consumed by commercial sector. A breakdown of residential energy use according to (Lapillone and Wolfgang, 2009), reveals that the conditioning of spaces requires approximately two
thirds of this energy, whilst the remaining third is consumed by cooking, appliances and DHW, as depicted in Figure 2-3.
Figure 2-3 Breakdown of household energy consumption by end-use categories in EU (Lapillone and Wolfgang, 2009)
This trend is particularly noticeable in modern societies, where the evolution of mechanisation coupled with the poorer building envelopes has led to the use of artificial cooling or heating to maintain thermal comfortable conditions (Roaf et al., 2010). Clements-Croome (2000) claimed that buildings cannot provide adaptive opportunities, maintaining a moderate indoor climate. Further to this, Roaf et al. (2010) reported that in warmer regions where cooling was necessary for the summer period, a bad design could contribute to the extended use of mechanical cooling.
2.2.2 STATUS OF THE EUROPEAN HOUSING INVENTORY
In general, European housing inventory presents an opposed performance between Northern and Southern European counterparts, due to the absence of policies obligating the energy performance of buildings. Healy (2003)
pointed out that most of the EU’s energy inefficient stock occurs in Greece,
Cyprus) in the EU has burdened the energy efficiency scene of Southern Europe. Despite the fact that some southern countries have some kind of building regulations (i.e., Greece-HBTIR [OHJ 362/4-7-79], Spain-TBC), no significant results occurred (Healy, 2003; IDAE, 2007). On the contrary, northern countries such as Germany, Sweden, Finland, France, Netherlands and Norway present exemplary levels of energy efficiency in the building sector due to stricter policies and regulations (Lapillone and Wolfgang, 2009).
Currently, the EU is running a strategic plan, implementing all the members to accomplish it by 2020, for a smart, sustainable and inclusive growth. The plan is founded on 5 targets related to R&D/Innovation (Research, Development,
and Innovation), Employment, Education, Poverty and Climate
Change/Energy. In the scope of energy and climate change, the plan aims to reduce the greenhouse gas emissions by 20% compared to 1990 levels or 30% if the conditions are right. The 20% of final energy consumption must be provided by renewable sources and the energy efficiency must be increased by 20% (EC, 2010a).
In the perspective of the building sector, the Energy Performance of Buildings Directive-EPBD (2002/91/EC) was initially published in 2002. As a Directive, it
is characterized as a “powerful instrumentation” for the actions in the
residential and commercial buildings (EC, 2011b).Thereafter, a recast-EPBD was implemented in 2010 (2010/31/EC), strengthening the provision of its precursor. Basically, the Directive set the minimum performance requirements for building construction and renovation. Implementation of the Directive
requires the high performance of new buildings and shifts the existing inventory scene towards energy efficiency.
In general, it is expected that emphasis will be placed on existing dwellings, despite the fact that higher savings can be achieved by new buildings (Boardman, 2007). Typically, new buildings account for only 1-2% of residential stock (Steemers and Yun, 2009). Apart from this, most of the housing inventory was constructed before the implementation of EPBD. As it is stated by Balaras et al. (2007), new dwellings consume 28% less energy than houses built before 1985, while the efficiency in the residential sector has increased by 60% since the oil crisis of 1970s.
2.3 R
ETROFITTING EXISTING HOUSES INM
EDITERRANEAN REGIONIt is widely accepted that new dwellings are governed by higher levels of efficiency due to regulations, better construction and advanced products, fostering the awareness on the existing housing inventory. A debate has arisen in terms of demolition or refurbishment with inherent issues of heritage, environmental impacts, community stability, costs, and life-cycle analysis and it can be concluded that the demolition and construction of new buildings offer a better solution. However, this cannot diminish the need to refurbish large amounts of the housing inventory, for energy conservation and associated
CO2 emission reduction (Burton, 2012).
As aforementioned, the efficient scene is burden by the South (Mediterranean region), skewing the performance of the northern European counterparts (Lapillone and Wolfgang, 2009). Apart from the fact that the vast majority of
dwellings were constructed prior to the implementation of any legislation (most directives were based on North countries), resulting in poor building envelopes, a critical factor to be considered is the climate experienced across the Mediterranean region. Steemers and Yun (2009) highlighted the importance of climate, a factor inherent residential energy use, while Humphreys (1996) has also expressed a similar view on the aspects of living that are influenced by. The inability of buildings to adopt to the external climate, contributes to the energy profligate (Steemers and Yun, 2009).
Mediterranean climate1 is described by mild, rainy winters and warm, dry
summers with high annual solar gains. Regions that experience this particular climate are presented in Figure 2-4.
Figure 2-4 Regions with Mediterranean Climate (SCRLC, 2012)
In the context of thermal loads, the Mediterranean countries are generally characterized by a warm climate, however, they endure winter seasons with
average temperatures of about 6oC (Healy, 2003). Generally, the climate may
1According to Koppen-Geiger, the Mediterranean Climate is indexed as C
sa-dry subtropical climate
not be defined as severe; however three distinct weather periods occur: (1) an under-heating period (winter months), (2) neutral period and (3) an overheating period (summer months). Due to this, the ability of the building to deal with such outdoor conditions will be primarily established by a dynamic design and operation (Joanna et al., 2012).
Another crucial characteristic of the Mediterranean region is the excessive insolation. For instance, in Cyprus low lands the average annual hours of bright sunshine is 75% of the time that the sun is above the horizon. In essence, this corresponds to average time of 11.5 hours per day during the summer period and 5.5 hours per day during the cloudiest months, December and January, of the winter period. Meanwhile, at the highest areas the sunshine is estimated as 11 hours and 4 hours, during the summer and winter period, respectively (MetService, 2012a). Admittedly, the measures and actions must be driven by the adaption of the buildings to the particular climate or even microclimate, without ignoring crucial factors such as the solar gains.
Performing alternation to the building envelope, may compromise positively or negatively on the current indoor conditions. The EPBD stated that the achievement of energy goals must not lead to sacrifices of thermal comfort and indoor air quality (IAQ) (Borgeson and Brager, 2011). It is then mandatory to evaluate thermal comfort prior and after refurbishment to estimate the impacts on thermal conditions, which may result on the employment of mechanical systems. In essence, a perceptual refurbishment will be founded on the trade-offs of energy and thermal comfort.
Through the rest of this section, thermal comfort and energy saving measures will be extensively presented in the perspective of retrofitting dwellings. The last part of this section describes building simulation and its implementation to the dynamic investigation of measures to reduce energy consumption in houses.
2.3.1 THERMAL COMFORT
The conceptual definition of thermal comfort is, “…that condition of mind that
expresses the satisfaction with thermal environment…” (ASHRAE, 2010). The
analysis of the topic is backdated to the early part of the 19th century, when
Heberden claimed that the thermal sensation is not only influenced by the air temperature. However, the first study on thermal comfort was established in 1905, when Haldane (1905) attempted to establish design temperatures in
England. In the mid-20th century people were able to manipulate the indoor
environment to their expectations and according to Shove (2004) it was then when comfort adopted its acknowledged meaning, rather a “shelter” from the severe environmental conditions.
Thereafter, a plethora of studies was published, based on findings from environmental chambers and field studies with different climates, genders, ages, cultures and building types. The majority of the studies were mainly driven by the investigation and establishment of criteria, thresholds and standards to define the range of conditions that people are satisfied by their thermal environment.
There seem to be two lines of thought with regards to the perception of thermal comfort. The first relies on the globally accepted predicted mean vote (PMV), so-called static approach, which is based on a study carried out by Ole Fanger in a climate chamber (Fanger, 1970). The PMV was governed by controlled indoor conditions, neglecting the transient conditions of real life scenarios. On the other hand, a group of people accepted that people are not passive recipients of the environment, but tend to interact with it (Roaf et al., 2010). The principle of adaptive model, dynamic method, was initially defined
by Humphreys and Nicol (1998) as: “if a change occurs that produces
discomfort, people will tend to act to restore their comfort”. The method was
founded by field studies carried out in ‘real’ buildings during ‘real’ environmental conditions, without marginalizing the pragmatic activities and actions of the subjects.
WELL-BEING, PRODUCTIVITY AND HUMAN HEALTH
It is internationally accepted that thermal comfort is defined as a condition of mind. However, academic researchers debate whether thermal comfort is related with well-being, productivity and human health. Although it is an open debate, concrete evidence indicates that the aforementioned aspects of human ‘mortality’ are inherent with thermal comfort.
For instance, Parson (2003) stated that the performance of children in schools was reduced when they were subjected to uncomfortable. In addition, a study carried out by Ramsey et al. (1983) shows that temperature higher or lower than the preferable influenced the safety-related behaviour of workers.
telecommunication centres decreased by 5-7% when the workers are sensing high indoor temperatures. Seppanen et al. (2006) wrote that the performance in offices is reduced by about 9% when occupants are subjected to a
temperature of 30oC. Similarly, Cao and Wei (2005) claimed that low
temperatures tend to cause aggression, while elevated temperatures have the tendency to cause aggression, hysteria and apathy.
Considering performance (or productivity) in a workplace as the output of the system, the well-being of each individual person is substantially contributing to the quality and quantity of the productivity. For instance, Warr (1999) concluded that high levels of performance are coherent with greater well- being. Apart from personal or social-economic factors, Clement-Croome (2000) pointed out that the environment is considered as another determinant factor of well-being. In essence, the previous studies presented that the performance (output) of workers was negatively affected, as a consequence of indoor thermal discomfort which is directly reflected on the well-being of people. To this effect, the provision of thermal comfortable environments are associated with higher levels of performance, as health and well-being are enhanced (Clements-Croome, 2000).
Evidently, well-being and health are important factors on the mortality of people. Since workplaces are conditioned to maintain moderate climates in order to enhance well-being and health, people indisputably have the same expectations of thermal comfort at home. In the case of residential buildings, a range of adaptive opportunities (siesta, open/close window, clothing, etc.) might be undertaken to maintain the indoor thermal environment. The
adaptivity and control of environment, gives more “forgiveness” on the fluctuation of indoor thermal environment (Leaman and Bordass, 1999).
However, due to the “nature” of interactivity with the mechanical systems in
residential buildings, the operation of HVAC systems may be considered another opportunity to maintain moderate climates within spaces. To this effect, in a poor-designed environment, the impact of the adaptive options (not artificial system) might not be substantial, leading on the necessary operation of a mechanical system for the maintenance of an acceptable living environment.
ENERGY AND THERMAL COMFORT
Previous evidence presents the significance of thermal comfort on people. However, as already mentioned, the occupants, in order to provide comfortable conditions, are forced to the mandatory employment of artificial systems. This results on the energy profligate due to poor building envelope, inefficient systems and lack of energy awareness.
As already observed, a trend on mechanical systems was observed due to the modern lifestyle and architectures. The indoor thermal environment is artificially maintained in acceptable levels of comfort resulting in excess energy consumption, particularly in the severe climate periods of winter and summer (Auliciems and Szokolay, 2007). However, the energy, consumed by mechanical systems, is stipulated by the difference of the outdoor environment and the desired indoor thermal conditions (Alders and Kurvers, 2010).
At this point, it is necessary to recall the findings from the review of the energy scene in the European Union. In numbers, 40% of energy is consumed by the building sector, of which 22% is consumed by the residential buildings. By rough estimation, space conditioning accounts for more than 11% of energy consumption in the EU-27 (estimation based purely on the residential sector). By summing up the space conditioning of commercial buildings, the total space conditioning (both residential and non-residential buildings) may be estimated at 20-25% of the total energy consumption in the EU-27. In essence, the thermal comfort or the provision of comfortable conditions is definitely acting as a catalyst in European energy scene and carbon emissions.
From a refurbishment perspective, energy saving measures must be implemented on the building envelope, based on the body’s ability to adapt with the environment (Clements-Croome, 2000).Consequently, the evaluation of thermal comfort must be carried out before and after renovation to ensure that thermal comfort is maintained or optimized, shifting away from the utilization of conventional systems (Nicol and Pagliano, 2007).
EVALUATING THERMAL COMFORT IN RESIDENTIAL BUILDINGS
Through retrofitting, the ‘current’ (as experienced by occupants) internal environment may possibly alternate. As Holmes and Hacker (2007) claimed the energy conservation must not compromise thermal comfort and essentially, it is the trade-offs between energy and thermal comfort that will establish whether the renovation of a building was felicitous. Thereby, the thermal comfort must be quantified in the context of accredited standards.
Currently, ASHRAE-55: 2010, ISO 7730: 2005 and EN 15251: 2012 standards govern the criteria for thermal comfort evaluation on mechanical and natural ventilated buildings. The standards contain categories and criteria for buildings. Reference to Roaf et al. (2010) shows that the standards are almost identical for artificial heating and cooling, founded on the static approach. Error! Reference source not found. presents the building