Thermal rehabilitation of buildings

Transcription

1 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 Thermal rehabilitation of buildings Ioan Sarbu and Calin Sebarchievici Abstract One of main research direction on the construction field is the reduction of the energy consumtion, which suoses materials, technology and concetion of buildings with lower secific energy need on one hand and equiment with high erformances on the other hand. Proer thermal rehabilitation of a building will lead to a significant reduction of heating energy demand offering a higher degree of comfort, and better condition for hygiene. At the same time the environment is less oluted. The energy saving deends on the initial building characteristics and the thermal rehabilitation level on one hand, and on the roer adjustment and control of the heating system on the other hand. In this aer is analyzed the main effects of building thermal rehabilitation, with imlications uon heating energy consumtion and uon comfort of the occuants.thus, it is develoed a comutational model of otimum additional insulation thickness, taking into account the investment cost to imrove thermal resistance of building enveloe and oerational costs as heating energy consumtion. Keywords Buildings, Additional insulation, Thermal bridges, Oerative temerature, Balance oint temerature, Otimum insulation thickness, Energetical analysis. B I. INTRODUCTION UILDINGS are an imortant art of Euroean culture and heritage, and they lay an imortant role in the energy olicy of Euroe. Economical strategy of a sustainable develoment imoses certainly to romote efficiency and a rational energy use in buildings as the major energy consumer in Romania and the other member states of the Euroean Union (EU. Studies have shown that saving energy is the most cost effective method to reduce green house gas emissions (GHG. It has also ointed out that buildings reresent the biggest and most cost effective otential for energy savings. The reduction of 6% energy use is set as a goal for buildings by the year which corresonds to 11% of the reduction of total energy use in EU countries [1]. The buildings sector is the largest user of energy and CO emitter in the EU, and is resonsible for more than 4% of the EU s total final energy use and CO emissions. At resent heat use is resonsible for almost 8% of the energy demand in houses and utility buildings for sace heating and hot water generation, whereas the energy demand for cooling is growing year after year. Ioan Sarbu is currently a Professor and Deartment Head at the Building Services Deartment, Politehnica University of Timisoara, 333 ROMANIA, address: ioan.sarbu@ct.ut.ro Calin Sebarchievici is currently a Assistant Professor at the Building Services Deartment, Politehnica University of Timisoara, 333 ROMANIA, address: calin.sebarchievici@ct.ut.ro Retrofitting is a means of rectifying existing building deficiencies by imroving standard and thermal insulation of buildings and/or the relacement of old sace conditioning systems by energy efficient and environmentally sound heating and cooling systems. In terms of heat engineering, building rehabilitation involves increasing thermal resistance of building enveloe and the condensation henomenon elimination where these henomena manifest, and ensure the thermal comfort requirements, for both winter and summer regime. In this aer are analyzed the main effects of building thermal rehabilitation, which have imlications on heating energy consumtion and on comfort for building occuants, and is develoed a comutational model for otimum insulation thickness. II. EFFECTS OF ADDITIONAL INSULATION Additional insulation of a building directly or indirectly influences its energy balance and has many reercussions on thermal roerties and thermal comfort of the building. The manner and extent to which these influences occur deends largely on thermal insulation osition in the structure of exterior building element and on the joints execution. Direct and indirect effects of additional insulation are shown in Figure 1. Exterior element thermal resistance R of buildings manufactured with refabricated anels is much smaller than that resulting from calculations because of the insulation thermal conductivity influenced by mechanical and thermal factors or moisture during the execution rocess, and unctually ther-mal bridges. Through an additional thermal insulation to the exterior walls thermal resistance increases, until the additional insulation reaches a certain thickness limit, over which this increase is insignificant. Corresonding to these increases in thermal resistance, heat losses through the oaque surface are reduced several times, but it occurs simultaneously with a reduction of heat losses by heat transfer in the two and three dimensional thermal bridges. Based on the resulting temerature field of thermal bridges at joints can be determined one factor, which is used to calculate the additional heat losses occurring in the thermal bridges. This factor is called linear thermal resistance (unidirectional R l, corresonding to 1 m of joint. The effect of exterior thermal insulation is varied for different tyes of joints: very favorable to T joints (exterior wall interior wall, exterior wall intermediate floor, less good in the corners, it has little influence on balconies and deends on to realization of lateral surfaces to the windows erimeter. 43

2 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 For a given exterior building element it can be defined the equivalent thermal resistance R e, numerically equal to the heat flow that crosses a unit area er unit time at a temerature difference of 1 K, taking into account the additional heat losses caused by thermal bridges: N l j = + R A (1 R Re j= 1 in which: R is the thermal resistance for building element, in m K/W; A element area, in m ; l j j tye joints length, in m; R lj linear thermal resistance for j joint tye, in m K/W. For buildings thermal rehabilitation is interesting to follow the ratio variation for the equivalent resistances of exterior elements before and after additional thermal insulation. A. Interrelation between Thermal Bridges and Air Exchange Rate Locking elements are non homogeneous elements, with thermal bridge. Due to two and three dimensional heat transfer in the joints occures more intense heat transfer, having as effect the aearance at interior surface of a much lower temerature than the temerature of the interior surface in element oen field. These low temeratures can determine the aearance of caillary condensation on those surfaces. It considers three tyes of thermal bridges for tyical aartment blocks realized with refabricated anels. Thus, in Figures 4 are resented: a joint between the exterior wall and the floor, which searates a room from a garage; a joint between the exterior wall and the floor, which searates two rooms; a joint between the exterior wall and the flat roof. The indoor air temerature in all rooms is of C and in garage of 15 C. In each case, existing exterior wall thermal resistance is 1.5 m K/W, and after exterior rehabilitation cladding with exanded olystyrene (1 cm becomes.5 m K/W. Also, the corresonding values of thermal resistance for the roof are l j Fig. 1 Effects of additional insulation m K/W and 5 m K/W. Calculations are based on a steady state heat transfer, corresonding for the heating season, outdoor air temerature ranging from 15 o C to +1 o C. In Figure 5 are reresented the variation curves, in relation to outdoor air temerature t e, of minimum temerature t m on the interior surface of condensed building element for the three tyes of thermal bridges, before and after exterior cladding with exanded olystyrene (1 cm for walls and cm for roof. Fig. Joint external wall first floor (a 1-concrete foundation (3 cm; -mineral wool ( cm; 3-mineral wool (8 cm; 4-reinforced concrete (7 cm; 5- reinforced concrete (15 cm; 6-concrete (15 cm; 7- concrete (.5 cm; 8- reinforced concrete (14 cm; 9-rendering (3 cm. Fig. 3 Joint external wall intermediate floor (b 1-steel concrete (1 cm; - con-crete (1 cm; 3-steel concrete (6 cm; 4-slag concrete 15 cm; 5-steel concrete (4 cm; 6-ex-anded olystyrene ( cm; 7- bitumastic sealing (8 cm 44

3 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 Fig. 4 Joint external wall flat roof (c 1-reinforced concrete (9 cm; -mineral wool ( cm; 3-bitumastic sealing (3 cm; 4-steel concrete (1 cm; 5- slag concrete (14 cm; 6-concrete laque (5 cm; air (1 cm; 8- reinforced concrete (14 cm; 9- concrete (5 cm; 1-reinforced concrete (15 cm Also, Figure 6 shows the variation in relation to t e of indoor air relative humidity to avoid the condensation on the building element interior surface in the analyzed situations. Based on the values of the charts resented in Figures 5 and 6 results the variation curves for relative humidity ϕ i of indoor air for avoiding caillary condensation in the two examined cases (Fig. 7. Rehabilitation of thermal rotection leads to reduction of thermal bridges negative influence, with beneficial effect on temerature distribution on the interior surfaces of exterior building elements. With this decreases significantly the ossibility of condensation, resectively the structural damages. Indirectly, it affects the energy consumtion because if the temeratures are higher in joints where the relative humidity of indoor air can be larger, it may be reduced the air exchange rate and with this, the heat losses through saces ventilation. Fig. 5 Variation of minimum interior surface temerature Fig. 6 Allowable maxima of relative humidity of indoor air Fig. 7 Relative humidity of indoor air for avoiding caillary condensation 45

4 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 It is considered that the exterior wall, comrising a thermal bridge is art of one room with geometrical dimensions in Figure 8, all located on the first level (thermal bridge tye a at an intermediate level (thermal bridge tye b or the last level (thermal bridge tye c and avoiding caillary condensation in such saces is achieved by increasing the fresh air exchange rate. The double glazed window surface reresents 8 % from the total surface of exterior wall and its thermal resistance is of.4 m K/W. In the room two ersons are taken into account, so the required fresch air exchange rate is n =.91 h 1. 3,5 1,5x1,8 (t = C i h =,7 m i 4,5 Fig. 8 Geometrical characteristics of room In Figure 9 those air exchange rate values are shown in function of outdoor air temerature which is required to avoid the caillary codensation, for the three tyes of rooms. It is noted that at a given outdoor air temerature (critical temerature, the air exchange rate increases sharly, exceeding the minimum required value. That means is introducing a cold air flow rate into the room more than lanned. In this case, or is not rovided an aroriate thermal comfort for occuants, or additional air flow rate must be heated to indoor air temerature, when the heating energy is no longer considered to coincide with the designed one. Table I shows the values of additional fresh air heating energy Q c to avoid caillary condensation during the heating season and the values of outdoor air critical temerature t e,cr, for the three tyes of analyzed rooms. One of the three tyes of thermal bridges least demanding in terms of caillary condensation is the (b tye, followed by (a and (c tyes. For the latter one results substantial amounts of additional heat to be introduced into the room to avoid caillary condensation. By the thermal rehabilitation is not avoided the additional consumtion of energy, but due the increase of the interior surface temerature of exterior building elements results a reduction of additional air flow rate, resectively is obtaining an increase for critical outdoor air temerature, so a reduction of the time eriod where there exist additional energy consumtion. Fig. 9 Variation of air exchange rate Table I. Additional fresh air heating energy and outdoor air critical temerature TYPE OF ROOM Data (a (b (c Actual Reabilitated Actual Reabilitated Actual Reabilitated [kwh] Q c [%] t e,cr [ o C] B. Variation of Oerative Temerature The subjective sensation of thermal comfort is decisively determined by the following arameters [14]: indoor air temerature (t i ; mean radiant temerature (t mr of bordering surfaces; relative humidity of air (ϕ i ; artial water vaours ressure ( a ; air velocity (v i ; thermal resistance of clothing (R cl or R h, and their influence on the vaorization. In order to evaluate the sensation of thermal comfort we use the thermal sensation scale with seven levels [4]: +3 (hot; + (warm; +1 (slightly warm; (neutral; 1 (slightly cool; (cool; 3 (cold. Numerical rediction of thermal comfort in a room is erformed by using the PMV PPD model. The oerative (comfort temerature t c may be defined as the average of the mean radiative temerature θ mr and indoor 46

5 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 air temerature t i weighted by their resective heat transfer coefficients: t c αrθmr + α t = α + α r in which: α r and α c are the radiative and the convective heat transfer coefficient between body and environment, in W/(m K. In Figure 1 are reresented the values of oerative comfort temerature t c (corresonding to index PMV =, correlated to thermal resistance of clothing (R cl and R h, metabolic rate i M and metabolic heat roduction M. The linearized radiative heat transfer coefficient α r can be calculated by [4]: c c i ( θ 4 mr n = ϕ itsi 73. (5 i= 1 where ϕ i is the angle factor between body and surrounding surface S i with temerature t Si. Considering a room in a block of flats, situated on intermediate level, with geometrical characteristics resented in Figure 8, one can calculated the variation of oerative temerature deending on the outdoor air temerature. The calculus is erformed taking into account a stationary heat transfer regime. Two thermal bridges are analyzed, which aears esecially in buildings from Romania built in 7 s. The first tye (Fig. 3 reresent a joint between the exterior wall and floor which searares two rooms with t i = C. The second tye of thermal bridge (Fig. 11 reresents a joint between the interior walls, which searates also two rooms with similar temeratures (t i = C. Fig. 1 Oerative temerature function of clothing and activity Ar tcl + tc α r = 4εσ (3 AD in which: ε is the average emissivity of clothing or body surface; σ Stefan Boltzmann constant, W/(m K 4 ; A r effective radiation area of body; A D nude body surface area [8]; t cl average clothing temerature. The ratio A r /A D is.7 for a sitting erson and.73 for a standing erson [9]. The convective heat transfer coefficient deends on indoor air velocity:.6 α c = 8.3vi (4 The mean radiative temerature is given by [5]: 3 Fig. 11 Thermal bridge 1-rendering (3cm; -steel concrete (5cm; 3-mineral wool (5cm; 4-steel concrete (15cm; 5-mineral wool (cm; 6-steel concrete (3cm; 7-steel concrete. Thermal resistance of initially structure was.935 m K/W. Considering an additional thermal insulation of 1 cm exanded olystyrene, the thermal resistance increases to.5 m K/W. The double glazed window surface reresents 8% from the total surface of exterior wall and its thermal resistance increases from.33 m K/W to.8 m K/W. In diagrams from Figure 1 are resented the minimum interior surface temerature t Smin at considered joints, deending on outdoor air temerature t e.the effect of thermal bridge is ercetible on.6 m band from the edge. Fig. 1 Minima of interior surface temerature for the two joints 47

6 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 There is a single erson in the room, which works on the comuter (i M =1. met. Considering the clothing termal resistance R cl =.9 clo, results a minimum oerative temerature t c = o C (Fig. 1. If the interior wall temerature is not influenced by thermal bridges and is equal with indoor air temerature (t i = C results the variation curves of mean radiant temerature resented in Figure 13. It can observe that the value decrease with the outdoor temerature. Assuming an air exchange rate n =.8 h 1 results a fresh airflow rate of 3. m 3 /h. This airflow rate should be heated u to the new value of indoor air temerature to assure the required comfort arameters. In Figure 16 is resented the variation of additional daily energy consumtion E s function of t e. Based on this diagram it can be determined the yearly additional energy consumtion (using the secific degree day curve. The variation of energy saving E is resented in Figure 17. Fig. 13 Mean radiant temerature Assuming the values α r = 4.7 W/(m K and α c = 3.1 W/(m K results the oerative temerature variation (Fig. 14. These values are lower than the otimal required value of C. To obtain the otimal value the indoor air should be heated u sulementary. The required values of indoor air temerature are shown in Figure 15. It can be observed that increasing thermal erformance of exterior building elements (walls, windows the oerative temerature increases. Fig. 16 Daily variation of energy consumtion Fig. 14 Variation of oerative temerature Fig. 15 Required temeratures of indoor air Fig. 17 Energy saving In resent in most buildings are not assured the comfort arameters, or there is additional energy consumtion. Thus, considering a building with three levels, with 1 rooms/level, the yearly additional energy consumtion to assure the required oerative temerature is about 5 MWh. Deending on the insulation level it can obtain a reduction with 15 3% of this consumtion, at the same time, the heating energy with 4 6%. C. Variation of Balance Point Temerature The heat to be delivered by heating system deends on the climatic conditions and the internal set oint temerature. The balance oint temerature t ech is the outdoor temerature when heat gains are equal to heat losses: Qa tech = ti (6 K in which: Q a is the heat gains of building; K heat loss coefficient of building. Using the balance oint temerature and the secific degree day curve the length of a heating season could be determined (Fig

7 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 Fig. 18 Determination of day number in heating season Using the geometrical interolation method the degree day curve, for Timisoara, can be aroximated with a function [14]:.3835 t e = x (7 in which x is the number of days with the same average outdoor temerature t e. In this equation if the outdoor temerature is equal to the balance oint temerature the day number in a heating season could be obtained: t = ech te N ( where t e is the outdoor design temerature. After building rehabilitation the heat loss coefficient K will decrease considerable whereas the heat gains remain the same. Thus, the new value of balance oint temerature could be calculated with following relation: ' K tech = ti ( ti tech (9 K' Having the value of the balance oint temerature after thermal rehabilitation the number of days in the new shorter heating season is: K ti te ( ti tech ' N = N K' (1 tech te The variation of balance oint temerature and number of days in the new heating season in function of the rehabilitation level when the original value of balance oint temerature is of 1 C is resented in Figure 19. (t ech -t' ech /t ech [%] (N-N'/N [%] (t ech -t' ech/t ech (N-N'/N (K-K' /K [%] Fig. 19 Day number in a heating season and balance oint temerature The heating energy demand for a building could be written as: N K E = ( ti t e dx η (11 where η is the efficiency of heating system. Taking into account of (9 (11, the ratio of energy consumtion before and after rehabilitation could be determined as follows: ' ' ' '.3835 E K N ( ti te.566n = ( E K N ( ti te.566n In Figure is illustrated the variation of heating load ratio Q /Q and variation of energy consumtion E /E deending on thermal rehabilitation level, for t ech =1 C. Q'/Q; E'/E 1,8,6,4, 1 Q'/Q E'/E,95,9,85,8,75,7,65,6 K'/K Fig. Variation of heat load and energy demand The length of the heating season deends also the thermal roerties of building enveloe. Assuming that before thermal rehabilitation, for a building, the balance oint temerature was 1 C, in Figure 1 the variation of heat demand is resented during the heating season. After thermal rehabilitation the heat demand ratio is the same but as it could be seen the heating season will be shorter taking into account the heat gains (Fig.. Fig. 1 Heat demand variation before rehabilitation Fig. Heat demand variation after rehabilitation 49

8 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 When the heating system is dimensioned the heat gains are neglected so that the system will oerate at artial caacity during the whole heating season. Furthermore, as it could be seen in Figure 3, 6 8% of heating season the heat gains cover more than 5% of the heat demand. Fig. 3 Heat gains ratio from total heat demand When a building is retrofitted from energy oint of view about 3% of the total energy saving is obtained due to the shorter heating season. The new balance oint temerature deends on the rehabilitation level and on the original thermo hysical state of building enveloe. The influence of heat gains will increase significantly after rehabilitation. III. DETERMINATION OF OPTIMUM ADDITIONAL INSULATION THICKNESS A. Investment Cost One of the most tyical rehabilitation methods for exterior walls of block flats, built with industrialized technology is the thermal skin system (Thermohaut. The insulation material is exanded olystyrene. Taking into account the insulation and other necessary material rice, the scaffolding and execution costs, and using the geometrical interolation method [16] the secific investment cost (for 1 m wall surface can be aroximated as: ( δ δ + 48ah = + I 158δ A + ( A (13 in which: δ is the insulation thickness; building erimeter; a number of building corners (ositive and negative; h height of building; A area of exterior walls. B. Oeration Costs The heat to be delivered by heating system deends on climatic conditions and internal set oint temerature. The main goal is the minimization of heat load and energy consumtion. From energy oint of view the achievement of internal set oint temerature without auxiliary heating is favorable. The heat loss coeficient of building K can be determined as: K ( 1+ C U A (14 where: = AoU o + AfU f + lul + AU ρecenv C = (15 in which: A is the area of exterior walls, in m ; U thermal transmittance of exterior walls, in W/(m K; A o area of other exterior oaque surfaces excet walls, in m ; U o thermal transmittance of exterior oaque surfaces excet walls, in W/(m K; A f area of glazed surfaces, in m ; U f thermal transmittance of glazed surfaces, in W/(m K. Imroving the thermal resistance of exterior walls the new value of building heat loss coefficient will be: K λ ' = + C U A δu + λ (16 in which: λ is the heat conductivity of insulation, in W/(m K; δ thickness of insulation layer, in m. Thus, the new thermal balance oint temerature can be written as: ' ( 1+ C ( ti t ech t ech = ti (17 λ + C δu + λ where t ech is the thermal balance oint temerature corresonding to the initial conditions. Taking into account the (7, number of days with auxiliary heating (t e < t ech corresonding to the heating eriod in the new conditions will be: (1 (.37 + C ti tech N = t i te (18 λ + C δ λ U + The energy consumtion in a heating season is given by equation (11, which taking into account the revious equations becomes as:.4u E = η ΣA λ + C t i t δu + λ e.6 ( t t (1 + C i λ + C δu + λ (1 + C ( ( ti tech.113 t + i te.57 (19 λ + C δu + λ The cost of heating energy C t, for a heating season is given by: C t = E e ( where e is the rice of 1 kwh thermal energy. The total cost is given by: F = AI + TrCt (1 where T r is the oerating duration. The otimal insulation layer thickness is obtained when the function value F is minim. ech.6 5

9 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 C. Numerical Alication At examle is considered a block of flats, built with medium size monolythic anels in 7s. The dimensions of building are m. The exterior walls are 3 cm slag concrete with U = 1.5 W/(m K, the flat roof is reinforced concrete with air cavities, where the sloe is rovided with slag in variable thickness, U a = 1.1 W/(m K. The U value of windows is U f =.5 W/(m K. The glazed surfaces and the corresonding average solar gains for heating season are resented in Table II. Table II. Glazed surfaces and solar gains Orientation Glazed surfaces, [m ] Solar gains, [W] NE SE SW NW Building Based on above resented dates the secific solar gains for studied building are Q s = 5. W/m, and the internal gains are Q i = 17.8 W/m. The heat load and the heating energy before rehabilitation are resented in Table III. Floor Table III. Heat load and energy consumtion for existing building Heated area [m ] Heated volume [m 3 ] Heat load [W] Secific heat load [W/m 3 ] Energy consumtion [kwh/year] 1 st floor Gen. floor th floor Building Secific energy consumtion of existing building is kwh/(m year. In Figures 4 and 5 is illustrated the variation of balance oint temerature and heating season length in function of insulation tickness δ and original U value, for a thermal conductivity λ =.45 W/(m K. In Figure 6 is resented the variation of total cost F deending on insulation thickness δ and heating system efficiency η for T r = 1 years, U = 1.5 W/(m K, λ =.45 W/(m K. t [ C] ech U =1,5 W/m K U =1,1 W/m K U =,7 W/m K U =1,3 W/m K U =,9 W/m K U =,5 W/m K Fig. 5 Variation of heating season length with insulation thickness ,,4,6,8,1,1,14,16,18,, δ [m] Fig. 4 Variation of balance oint temerature with insulation thickness Fig. 6 Variation of total cost with insulation thickness Floor Table IV. Heat load and energy consumtion for reabilitated building Heated area [m ] Heated volume [m 3 ] Heat load [W] Secific heat load [W/m 3 ] Energy consumtion [kwh/year] 1 st floor Gen. floor th floor Building The heat load and energy consumtion after rehabilitation with an otimum insulation thickness of 1 cm are resented in Table IV. The heat load of building decreased with 9%, and secific energy consumtion of retrofitted building is kwh/(m year. The total energy saving due to the reduction of heat load and heating eriod is 38%. In Figure 7 the variation of otimum insulation thickness is resented in function of heating system efficiency η for 51

10 INTERNATIONAL JOURNAL OF ENERGY, Issue, Vol. 5, 11 different U value, a oerating duration of 1 years and λ =.45 W/(m K. δ [m],16,14,1,1,8,6,4, U =1,5 W/m K U =1,1 W/m K U =,7 W/m K U =1,3 W/m K U =,9 W/m K U =,5 W/m K 1,9,8,7,6,5 η Fig. 7 Variation of otimum insulation thickness with heating system efficiency IV. CONCLUSIONS In the resent economic and energetical conditions the reduction of energy consumtion in building sector is a roblem of global interest. For this urose it is imerative that the works to imrove the thermal insulation of buildings should be erformed as stated in the actual regulations. Thermal rehabilitation of existing building enveloe is obtained by increasing the thermal rotection of structural comonents. This leads to a reduction of investment costs for rehabilitation/ugrading of heating systems, due to diminuated building heat demand. Thermal rehabilitation of existing buildings determins a considerable reduction of heating energy, offering a higher degree of comfort, and better condition for hygiene. At the same time the environment is less oluted. Based on a comlex economic and energy analysis the otium thickness of additional insulation can be established for each building. REFERENCES [1] F. Allard. and O. Seänen, Euroean actions to imrove energy efficiency of buildings, Rehva Journal, vol. 45, no. 1, 8,. 1-. [] W. Allen, Enveloe design for building, Architectural Press, London, [3] ASHRAE Handbook, HVAC Alications, American Society of Heating, Refrigerating and Air Conditioning Engineers, Atlanta, 7. [4] ASHRAE Handbook, Fundamentals, American Society of Heating, Refrigerating and Air Conditioning Engineers, Atlanta, 9. [5] L. Bánhidi and L. Kajtár, Komfortelmélet, Műegyetemi Kiadó, Budaest,. [6] J.P. Curtis, Otimization of multile thin thermal insulation layers, Proceedings of the 3 th IASME/ WSEAS Int. Conference on Heat Transfer, Thermal Engineering and Environmet, Corfu, Greece, August -, 5, [7] S. Dan, Energy saving with rehabilitation solutions for existing structures, Proceedings of the 4 th WSEAS Int. Conference on Energy Planning, Energy Saving, Environmental Education, Kantaoui, Sousse, Tunisia, May 3-6, 1, [8] D. DuBois. and E.F. DuBois, A formula to estimate aroximate surface area, if height and weight are known, Archives of Internal Medicine, no. 17, 1916, [9] P.O. Fanger, Calculation of thermal comfort: Introduction of a basic comfort equation, ASHRAE Transactions, vol. 73, no., 1967, III.4.1 [1] C.P. Hedlin, Effect of insulation joints on heat loss through flat roofs, ASHRAE Transactions, vol. 91, no. B, 1985, [11] L. Mantzos, Euroean energy and transort trends to 3, Euroean Commission, Directorate General for Energy and Transort, 3. [1] A. McGowan and A.O. Desjarlais, An investigation of common thermal bridges in walls, ASHRAE Transactions, vol. 13, no. 1, 1997, [13] I. Sârbu, Prediction of building energy erformances, Proceedings of the 1 th Conference on Building Services and Ambient Comfort, Timisoara, Romania, Aril 1-11, 3, [14] I. Sârbu, F. Kalmar and M. Cinca, Thermal building equiments Energetical otimization and modernization (in Romanian, Publishing House Polytechnica, Timisoara, 7. [15] I. Sârbu. and O. Bancea, Analysis of thermal and olfactory comfort in closed saces, WSEAS Transaction on Heat and Mass Transfer, vol. 4, no. 3, 9, [16] I. Sârbu, Numerical modellings and otimizations in building services (in Romanian, Publishing House Polytechnica, Timisoara, 1. [17] B. Wilcox, A. Gumerlck, C. Barnaby, R. Mitchell and C. Huizenza, The effects of thermal mass exterior walls on heating and cooling loads in commercial buldings, Thermal Performance of the Exterior Enveloes of Buildings, III, 1985, [18] CEN/TC89/WG4 N 174. Thermal erformances of buildings, [19] Mc 1/1, Calculation methodology of building energy erformance, Bucharest, 6. 5