A first theoretical comparison between current and future indoor thermal comfort conditions, in Greece, as a result of the greenhouse effect

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1 METEOROLOGICAL APPLICATIOS Meteorol. Appl. : 7 76 (007) Published online in Wiley InterScience ( DOI:.0/met.9 A first theoretical comparison between current and future indoor thermal comfort conditions, in Greece, as a result of the greenhouse effect D. J. ikolakis* University of Athens, Department of Geology and Geoenvironment, Laboratory of Climatology and Atmospheric Environment, Panepistimiopolis, 57 4, Athens, Greece ABSTRACT: In the present study, current and future indoor thermal comfort conditions in Greece are estimated from the monthly mean temperature values of climatological stations. The data concern the period Data from January have been taken to represent the cold season, while those from July represent the warm season. The estimation of the current comfort of indoor climates was assessed by considering lightly clothed sedentary people. For future climate conditions, the estimation was made by considering a possible temperature increase of about C, according to the general circulation models prediction for Greece. The calculations showed that in the cold and the warm seasons, in both current and future conditions, it is recommended that the thermostat should be set at the calculated local comfort temperatures instead of the generally accepted positions of and 5 C for summer and winter respectively with considerable energy saving. However, due to the possible temperature increase even larger amounts of energy will be required for air-conditioning in some parts of Greece during the warm season. Copyright 007 Royal Meteorological Society KEY WORDS greenhouse effect; indoor comfort conditions; air-conditioning; Greece Received 4 April 006; Revised 7 March 007; Accepted March 007. Introduction One of the dominant issues of our time is that of possible climatic change. This interesting issue engages a number of scientists, apart from climatologists (Schneeberger et al., 00), as ecologists, biologists, biochemists, botanists (Roughgarden and Schneider, 999; Chakraborty et al., 000; Briones et al., 004; Ellis et al., 007; Occhipinti-Ambrogi, 007), environmental engineers (Huang et al., 99), foresters (Karjalainen et al., 00), hydrologists and geographers (Matondo et al., 004). Climate change is likely to modify one or more climatic parameters, for example, surface temperature, sensible heat, atmospheric humidity and precipitation. The change of climate parameters will affect the human heat balance and, as a result, an adjustment will be required to restore human thermal comfort conditions. Little work has been done on possible climate change and thermal human comfort because of incomplete bioclimatic indices and the lack of adequate bioclimatic models, even for current bioclimates (Hulme et al., 99). Therefore, the possible change in frequency, duration and intensity of thermal discomfort periods, depending on geographical region, will demand a number of actions * Correspondence to: D. J. ikolakis, University of Athens, Department of Geology and Geoenvironment, Laboratory of Climatology and Atmospheric Environment, Panepistimiopolis, 57 4, Athens, Greece. nikolakis@geol.uoa.gr so that the public s health and comfort is maintained. An important point is that possible climate changes will consequently alter the thermal and humidity comfort conditions, whilst the control of this through either heating or cooling (by air-conditioning) will result in energy use or saving. Previous work has been done on the investigation of these issues, either by developing the criteria for indoor climate management (Auliciems, 99) or by applying these criteria for the area of the south Pacific (McGregor, 994). However, no work has been done regarding the effect that a possible change in thermal conditions may have in the heating and cooling energy demands in Greece. Greece is situated in the northern temperate zone, in the eastern Mediterranean basin (between latitudes 4 and longitudes 9 E 9 E). Greece has a Mediterranean climate, but doesn t present a climatic unity, mostly because of geographical features. The northern parts of the country are influenced by those factors that determine the climate of southeastern Europe, whereas the southern parts, bordered by the Mediterranean Sea, tend towards the marine Mediterranean climate. The country s topography with multifarious, complex and large partitions, both horizontal (a long coastline and many islands) and vertical (polymorphous mountainous formations and isolated cone-shaped mountains with altitudes up to 97 m), results in a mosaic of climates all over the country. This variety, which can rarely be found Copyright 007 Royal Meteorological Society

2 7 D. J. IKOLAKIS over similar areas of the Earth, is within the limits defined by the climates of the northern Balkan countries and of the east Mediterranean basin. With regard to temperature, Greece is situated between the isotherms of 9 C (southern Crete) and C (northern Greece) (astos, 995). Owing to a possible temperature increase as a result of the atmospheric greenhouse effect, relatively cold areas will save energy on air-conditioning as a decrease of cold stress is expected, whilst warm areas will require an increase in air-conditioning due to the expected greater humidity stress. There are, also, intermediate situations (depending on the geographical area), where energy will probably be saved during the cold season but more energy will be demanded during the warm season for air-conditioning. There may even be areas where, on an annual basis, no important change in energy use will occur. Therefore, given that the climatic change will influence indoor climates, this paper reports an investigation of future possible thermal comfort conditions in cold and warm seasons in Greece.. Methodology and materials The method that was followed in the present study is the one described by Auliciems (99). The indoor climate estimation was made by taking in consideration lightly clothed sedentary people. The current and future thermal comfort conditions were assessed according to the following formula (Auliciems, 9): T u = 0.T m () where T u is the indoor comfort temperature and T m is the monthly mean temperature. Although this empirical model is very simple, since in fact the human thermal comfort is influenced by other complex factors, the use of such a simple empirical formula gives a first satisfactory approach to the problem. To estimate current indoor thermal comfort conditions for the cold (January) and warm (July) season, the mean monthly temperatures from climatological stations in Greece were used (Figure ). According to Equation for the mean monthly temperature T m, the comfort temperatures T u were calculated for all the stations as well as the difference (T m T u ). Similarly, the respective differences (T m T ) were calculated. This arises by taking T u = T since C is the generally accepted thermostat position for winter (Hulme et al., 99). Similarly, the comfort temperatures T u for July were calculated (using Equation ), as well as the differences (T m T u ). Also, the respective differences (T m T 5 ) were calculated by taking T u = T 5 since 5 C isthe generally accepted thermostat position for the summer. For the estimation of future indoor thermal comfort conditions, for the same stations, the monthly mean values of January and July were used by considering that: ALBAIA IOIA SEA Figure. Geographical distribution of the climatological stations. This figure is available in colour online at () general circulation models (GCMs) predict a doubling of carbon dioxide until about 00 (Bretherton et al., 990; Mitchell et al., 990) and () the probable temperature increase in Greece, according to the above assumption, will be approximately C in Greece (Houghton et al., 990). Given the variation between the various models results a temperature increase of C was used to calculate future values of comfort temperatures. The current mean monthly temperatures for January and July were increased by this amount. This means that the future T u values are calculated from Equation, using T m + C as T m. For the winter period, the differences between (T m T u ) and (T m T ) are calculated for possible future values of T u, as well as the differences (T m T u ) and (T m T 5 ) for the summer period.. Results and discussion The scope of the present study is to provide a quantitative estimation that the expected temperature increase due to the greenhouse effect will have on energy heating and cooling demands in Greece. Also, the benefit arising from the use of the indoor comfort temperature T u is investigated instead of the generally accepted thermostat position... January Applying the methodology described in the previous section, the predicted present day indoor comfort temperatures T u are calculated for the winter period (January) and in Figure (a) the differences (T m T u ) (T m T ) are shown. Using the T u temperatures there arises a difference ranging from 0 C in southern Greece to 4 C in northern Greece (Figure (a)). This difference, when transformed into a percentage (Figure (b)), shows that from the current temperature values and the comfort temperatures T u results in a gain in heating ranging from 4% Copyright 007 Royal Meteorological Society Meteorol. Appl. : 7 76 (007) DOI:.0/met

3 CURRET AD FUTURE IDOOR THERMAL COMFORT CODITIOS I GREECE 7 (a) ALBAIA IOIA SEA (b) IOIA SEA (c) ALBAIA IOIA SEA (d) ALBAIA IOIA SEA (e) ALBAIA IOIA SEA Figure. Spatial distribution of current differences (T m T u ) (T m T ) (a), current energy gain % (b), future differences (T m T u ) (T m T ) (c), future energy gain % (d) and possible energy gain % using T u, between current and future conditions (e), in January. This figure is available in colour online at in southern Greece to % in northern and mountainous Greece. Observing the differences (T m T u ) for January, it is established that the indoor heating demand during the cold season for current conditions, when using T u ranges from 9 (southern Greece) to C (northern Greece and central mountainous formations), while when using C it ranges from (southern Greece) to 0 C (northern and central mountainous Greece). Figure (a) also shows that it is advisable to use the local T u instead of the thermostat position at C, because of the heat gain varying from 0 (in southern areas) to 4 C (northern and central mountainous areas) or, in terms of percentage (Figure (b)), the gain varies from 6 (southern Greece) to 0% (northern and central mountainous areas). The predicted winter future indoor comfort temperatures T u are calculated in the same way. As a result, in all areas future T u will rise by 0.6 C and the energy demands in the cold season will decrease, this corresponds to a difference between current and future differences (T m T u ) future (T m T u ) current of. C at all the stations. Copyright 007 Royal Meteorological Society Meteorol. Appl. : 7 76 (007) DOI:.0/met

4 74 D. J. IKOLAKIS (a) ALBAIA (b) ALBAIA IOIA SEA IOIA SEA (c) ALBAIA (d) ALBAIA IOIA SEA IOIA SEA (e) ALBAIA IOIA SEA Figure. Spatial distribution of current differences (T m T u ) (T m T 5 ) (a), current energy gain % (b), future differences (T m T u ) (T m T 5 ) (c), future energy gain % (d) and possible cooling demands % using T u, between current and future conditions (e), in July. This figure is available in colour online at The differences between (T m T u )and(t m T )are calculated for possible future values of T u.fromthis, temperature differences varying from 0 C in southern Greece to C in northern and mountainous Greece are obtained (Figure (c)). These differences, when converted to a percentage (Figure (d)), show that if there is temperatures rise by C by the year 00, as is predicted by the climatic change models, for the winter in the future conditions and by using the local T u instead of the thermostat position at C there is a gain in heat, which, when translated to a percentage (Figure (d)) ranges from 0 (southern Greece) to % (northern and central mountainous areas). Therefore, it is obvious that for the winter period the use of the local T u instead of the thermostat position at C is advantageous, both currently and in the possible future climate conditions. The possible temperature rise of C will increase the T u values by 0.6 C and will decrease the respective heat energy demand by. C in all the stations. Translating this into a percentage it is shown that in the possible future conditions energy will be saved in comparison to the current conditions ranging from 9 to 5% (Figure (e)). Copyright 007 Royal Meteorological Society Meteorol. Appl. : 7 76 (007) DOI:.0/met

5 CURRET AD FUTURE IDOOR THERMAL COMFORT CODITIOS I GREECE 75 Figure 4. Indoor design criteria (Auliciems, 9)... July The predicted present day indoor comfort temperatures T u are calculated for the summer period (July) and in Figure (a) the differences (T m T u ) (T m T 5 ) are presented, while in Figure (b) the energy gain percentage in current conditions using the local T u is shown. For northern Greece (the largest part of Greece) in current (and the probable future) conditions no change will occur, since both the monthly mean temperatures and the T u remain at about 5 C. That means that airconditioning (cooling) is not needed at present and will not be needed in the future. For southern and southeastern Greece, and particularly in the region of Attica (Athens), the southeastern Peloponnese and Crete the use of the comfort temperature T u instead of the thermostat position at 5 C will result in an energy saving ranging from 44 to 65%. The predicted future indoor comfort temperatures T u are estimated for the summer, as well as the future differences (T m T u )and(t m T 5 ), and the difference (T m T u ) (T m T 5 ), at all the stations. The results are presented in Figure (c) and (d). It can be deduced that due to the possible temperature increase by C and the use of local T u, cooling energy will be saved ranging from to 4%. Therefore it is recommended to use the T u instead of the thermostat position at 5 C. In south southeastern Greece however, the possible temperature increase by C will raise the demand for air-conditioning (cooling) ranging from 0 to 0% (Figure (e)). Figure 4 shows that for a narrow temperature range around 5 C the comfort temperature T u is equal to the outdoor temperature, T m. In northern Greece in both current and possible future comfort conditions (+ C), T m and consequently T u remain at the level of 5 C. Therefore air-conditioning is not required, either in the present or in the future. 4. Conclusions It is obvious that the above approach to the calculation of the indoor comfort temperatures from the aspect of energy saving during the cold season in both current and possible future climate conditions is rather simplified. It is noted that many other factors, such as a building s insulation and humidity, that were not taken into account, play an important part in this issue. Despite this, however, as a first theoretical and simplified approach to the problem a satisfactory estimation of these values, is given in this paper. For the cold season (represented by January) and the warm season (represented by July) it is recommended to use the local indoor comfort temperature T u instead of the generally accepted thermostat position of C for the winter temperature value and 5 C for that of the summer (Auliciems and Dedear, 96). The use of T u results in an energy gain in heating demand in the range of 6 0% under current conditions and in the range of 0 % in future conditions, taking into account a possible temperature rise by C as a result of global warming. The use of T u and the possible temperature rise will reduce the energy demands during the cold season in comparison to the current conditions by between 9 and 5%. For the warm season the use of T u in current conditions entails an energy gain from less use of airconditioning that ranges from 44 to 65%, while in future conditions the respective energy gain will range from to 4%. The northern areas of Greece, both currently and Copyright 007 Royal Meteorological Society Meteorol. Appl. : 7 76 (007) DOI:.0/met

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