RENEWABLE ENERGY DESIGN OF TWO HOUSES ENERGETICALLY INDEPENDENT LOCATED AT THETHE PICO S ISLAND (AZORES ISLANDS, PORTUGAL)

Transcription

1 RENEWABLE ENERGY DESIGN OF TWO HOUSES ENERGETICALLY INDEPENDENT LOCATED AT THETHE PICO S ISLAND (AZORES ISLANDS, PORTUGAL) PART 1: FROM THE PROJECT DESCRIPTION TO THE THERMAL CALCULUS DESIGNER: MR. BIGONI ANDREA COMMISSIONERS: MR. GUIDO AND MS. LAURA 1

2 INDEX Design of two houses energetically independent located at the the Pico s island (Azores islands, Portugal)... 1 Part 1: from the project description to the thermal calculus... 1 Project description...4 Azores climate...8 Temperatures... 8 Wind... 8 Solar radiation... 9 surface hydrology Rainfalls Humidity Sustaining house design...11 basic concept basic assumptions Thermal dissipation calculation thermal flux equation walls structure of the walls Floors windows Thermal calculation Setup Overall heat transfer coefficient (U) walls and floors Windows Heat dissipation calculation test phase test phase-results

3 total power dissipated of the walls and floors at 20 C description total power dissipated of the walls and floors at 23 C description test phase further results heat diffusion thermal maps (isotherm and color) applied calculus phase conclusions next phase: heating/cooling system and hot water power supply Bibliography...26 Annex

4 PROJECT DESCRIPTION The aim of this project is to design two houses energetically autonomous located into the Pico s Island (Azores Islands) (figure 1). Energetically independent means that the energy production comes from renewable sources like sun, wind and water without the use of fossil fuels. Into the prescribed area will be made two buildings but, considering the fact that the geometry of the houses is the same (figure 2), the energy design will be referred just to one of them. The sustainable house has a total surface of 150 m 2 and is made of 6 rooms: a patio of 40 m 2, a kitchen/living room of 40 m 2, two bedrooms of 20 m 2 each, two bathrooms of 6 m 2 each and a corridor of 18 m 2 (figure 3). The walls will have a height of 2.6 m. (assumption). The house will be made of a woody floor and roof and the exterior of the house will have rocky walls (volcanic rock) and the patio will be made of a covered area without lateral walls. The front of the house will comprehend a main entrance made of a sliding door with obscurant in the middle (figure 4). However, the back of the building there will be a door in the wall between the corridor and the living room and there will be three sliding windows: one in the kitchen s wall and two at the limits with the corridor (figure 5). Also, the house will be comprehensible of seven windows: in the front of the house, sliding windows with external cover (bedrooms) and the bathrooms, two smaller with internal open. Finally, the limit corridor/living room and the patio will be made of woody pillars. And, at the back of the house will be built a smaller rocky wall with a glassy wall on the top (length 12 m.). 4

5 Figure 1 - Map of the Azores Islands Figure 2 Map of the area and location of the two houses 5

6 Figure 3 Top view Figure 4 Front view 6

7 Figure 5 Back view 7

8 C RENEWABLE ENERGY AZORES PROJECT AZORES ISLANDS: CLIMATE TEMPERATURES The climate of the Azores Islands is characterized by cold winters and hot summers. According to the diagram of figure 6, the average daily temperatures are at about 15 C from January to April and from November to December. Then, from May to August the temperatures raise until 25 C in August. The thermal excursion (thermal difference night/day) does not have a significant variation and it is almost stable around 5 C throughout the year. Exceptions are July, August and September (7 C). 30 temperature Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec Mesi thermal difference (day-night) max daily temperature min nightly temperature Figure 6 - Average monthly temperatures. Source: WeatherReports.com WIND The winds speeds data were provided by the Azores weather service and represent an average of the wind speed calculated over ten years and therefore are considered reliable data. Figure 7 Wind speed. Source: WeatherReports.com 8

9 According to the table of figure 7, the wind speed goes from 29 Km/h (January) to 17.7 Km/h (July). From August the velocity ranges from 19.3 to 27.4 Km/h of December. SOLAR RADIATION The diagram of figure 8 shows the variation of the yearly daylight hours and the data related to the monthly insulation (kwh/m 2 *day). The daylight hour variation has been expressed as percentage of insulation in 24h (insulation %/24h). Therefore, in the y-axis 100% means that in one month the total insulation hours is 24 and 50% is of course 12h. So, from January to July there is an increase in the daylight hours (July=15h) and from August to December there is a decrease towards 10 hours of sunlight. A design consideration is related to the kwh/m 2 that can be used in function of the monthly sunlight hours. During the design phase, the sunlight data will be used to calculate the power that, for example, the photovoltaic system has to provide for the electric energy production. According to the data of figure 8, it is possible to observe that the months from May to August are not only the longest days (15h of sunlight), but also represent those months where it is possible to extract the highest power per m 2 (July=90 kwh/m 2 *day). According to the climate data presented until here, it is obvious to trace a first conclusion related to the fact that the photovoltaic system will show lower performance on winter. Therefore, the design phase will have to consider this aspect and one direct solution could be the sizing of a hybrid system. Figure 8 Solar radiation. Source: WeatherReports.com. 1 Data from (Ricardo Aguiar R. 2008). 9

10 SURFACE HYDROLOGY The table of figure 9 shows data related to: average monthly rainfalls, average daily relative humidity, average nightly relative humidity and average relative humidity (night and day).the average monthly rainfalls are in expressed in mm. and the others in %. RAINFALLS According to the weather data, the rainy months are from January to March and from September to December with 120 mm. In contrast, from April to August the rainfalls are scares with a minimum on July (32 mm.). HUMIDITY According to figure 9, there are no important variations through the year and its value is around 80%. Those data will be considered in the next design phases because they could be useful. Figure 9 Surface Hydrology data Source WeatherReports.com 10

11 SUSTAINING HOUSE DESIGN BASIC CONCEPT What follows are the main design steps to undertake in order to design an energetically independent house. The first step is: preliminary assumptions. The preliminary assumptions are based upon geometric (shape and size) and climatic considerations. Once the assumptions are made, the second step is the energetic design of the main structures of the house (walls, floors and windows) with eco-compatible criteria. This means that the construction of the house will be stick to the use of natural material like wood and non-toxic substances like glass wool. The third step will be the design of the heating and electricity production system (with assumptions included). The part 1 of this design will focuses on the basic assumptions adopted for the thermal dissipation through: walls, floors and windows only. Finally, the results obtained by the thermal calculus will be used to get an estimation of how much heat dissipates the house in one year (kwh/year). Once it has been got the heat dissipation, the next phase will be the design of the energy systems (PV, solar collectors...) that will be able to provide the same amount of heat that the house will dissipates in one year. So, the thermal balance will be maintained. BASIC ASSUMPTIONS In order to calculate the thermal dissipation through walls, floors and windows, it has been chosen the following target temperatures. The target temperatures are those temperatures of the rooms on winter and summer time. Therefore, in order to have an idea of the thermal dissipation the calculus is based on the average of the monthly temperatures and this because the yearly thermal excursion is not so high (5 C). Therefore, if one assumes C on winter, then the temperature to heat up the room is assumed to be 23 C. On the other hand, if one assumes that on summer the outside temperature fluctuates between 15 and 25 C, then the cooling temperature is assumed to be 20 C. It is, of course, clear that the target temperatures are not so different and this can induce one to assume that the best way would be to use an average of the target temperatures instead of the two extreme ones. But is also true that in this phase of the project it is unknown how is the thermal behavior of the building materials in function of little temperature variations. Therefore, it is not clear if the material chosen to build walls, floors and windows will behave as perfect insulators. So, in order to make realistic choices, it is necessary to perform calculus and simulations based on the target temperatures. Another consideration is related to the duration of the target temperatures. This means that it has been decided to keep the rooms at 20 and 23 C respectively, all over the day (24h) and this because of the very small thermal excursion. Final assumptions are related to the windows surfaces and walls height. Considering the fact that the total wall surface is 156 m 2, it has been assumed that the surface of the windows is 40% of 156 m 2 (62.4 m 2 ). Concerning the walls, it has been assumed 2 m. the height of the kitchen/living room walls and 2.6 m. for the rest of the rooms. 11

12 THERMAL DISSIPATION CALCULATION THERMAL FLUX EQUATION In order to calculate the heat dissipation through walls, floors and windows it has been used the equation of the thermal flux: ( ) (1) Where, Ie is the heat loss (kwh/anno), h is the heat transfer coefficient (W/m 2 *K), A can be the walls, windows or floor surface (m 2.), T target is the target temperature (20 C or 25 C) and T outside is the average monthly temperature ( figure 6). The parameter h h is calculated from the equation (1): (2) The heat dissipates through homogenous surfaces in three ways: conduction, convection and radiation. Therefore, the parameter h of the equation (2) is directly proportional to the power dissipated Ie and inverse proportional to the surface A and the thermal difference (T target - T outside ). What is important to mention is the fact that h is typical of each material and the higher is that value, the higher will be the tendency for that material to dissipate heat. Usually, the building materials are diverse, but the materials considered for this project are the followings: 1. Roccia vulcanica (basalto, basalt) 2. Lana di roccia (rock wool) 3. Legno(oak) 4. Polistirene (polistirolo)(polystyrene). The first material considered is basalt. This is a magmatic rock generated by surface crystallization of magma. It has a basic whole rock chemistry and it is higher in MgO (Machado 2008). On the Azores Islands this rock is one of the most abundant as well as Trachytes and Hawaiites The last ones are rock with a different chemistry because they are higher in silica(sio 2 ), sodium (Na 2 O) and potassium (K 2 O) (Machado 2008). For this project, the only thermal properties available were the basalt s ones and therefore the basalt has to be considered here as the volcanic rock. The second material is the glass wool (or rock wool). Usually, the rock wool is preferred as building material because is not carcinogenic. Rock wool is made from the partial melting of basalt at 1600 C and then mixed to calcareous material like Dolomite and Limestone. Rock wool is an insulator high in silica and it is also an acoustic, draining and fireproof material. (AAVV 2012). Another material is oak. Houses that are built with this type of wood show the best insulation and therefore the oak is the best choice to insulate houses. (AAVV 2012). Finally, the polystyrene is a material is derived from the oil synthesis and it is a common insulator use in every house. 12

13 SOLUTIONS WALLS STRUCTURE OF THE WALLS In this project, it has been assumed a thickness of 30 cm. and the solution investigated are the following: 1. Basalt rock wool Basalt 2. Oak rock wool Oak 3. Oak polystyrene rock wool polystyrene Oak. The first and second combination consist in a wall made of: an internal thickness (7.5 cm.) of basalt (or oak), a 15 cm.-cavity of rock wool and an external layer of 7.5 cm. of basalt (or oak).the third combination is always a 30 cm.-wall with the following structure: a woody internal layer of 5 cm. thick, a second layer of polystyrene (5 cm.), a cavity of 10 cm. filled with rock wool a third layer of 5 cm. made of polystyrene and an external one of oak (5 cm.). Figures 10 and 10.1 summarize as described above. NOTE: Figures 10 and In those figures glass wool has been used as an alternative to rock wool during the first thermal calculus. But when it has seen that they have the same thermal performance, it has been used rock wool instead of glass wool. Figure 10 Walls structure 13

14 Figure 10.1 Walls structure. Dimensions FLOORS Concerning the floors, the constructive solutions would be: basalt-rock wool-basalt and oak-rock wool-oak. WINDOWS The solutions adopted for this project are three: double glazed windows, triple glazed windows filled with Ar and vacuum insulated glass. The first type of windows is commonly used in all houses, but concerning the other two, a description is due. The triple glazed windows filled with Ar (figure 11) are made of three glasses separated by a space filled with Argon (Ar). Those empty spaces ensure the isolation because allow for a slow diffusion of the heat and therefore it can reduce the condensation. The triple glazed windows are type of windows that can reduce the energy consumption of the house sensibly (AAVV, 2012a). 14

15 Figure 11 Cross section of triple glazed window filed with Ar The vacuum insulated glass (figure 12) windows have a structure that is more simple and slim than the previous ones. The vacuum insulated glass windows are made of two glasses 4 mm. thick very close each other (0.2 mm.). In the very narrow space in between there is the vacuum. Figure 12.1 shows its structure. These windows have an extensive filed of applications in architecture because they are very light compared to the double and triple glazed windows. Moreover, they show high energetic performances. This is due to the fact that the vacuum guarantees a very slow diffusion of the heat and for this reason they are considered very high insulators. Figure 12 Vaccum insulated glass Figure 12.1 Structure of the vacuum insulated glass 15

16 THERMAL CALCULATION SETUP OVERALL HEAT TRANSFER COEFFICIENT (U) U has the same physical meaning of h (equation 2), but in the case of multilayer structures, the value of h of each material is called overall heat transfer coefficient and this name is part of a standard nomenclature. But before passing over is necessary to explain the basic steps in order to calculate the U value (W/m 2 *K). U is calculated as follows: Where R tot is the total resistivity (m 2 /K*W) and R 1,...,R n are the value of resistivity of each material and they are calculated as follows: Where R is the resistivity (m 2 /K*W), k is the thermal conductivity (W/K*m) and thickness is the thickness of the wall layer, floor or window through which the thermal dissipation has to be calculated. For the thickness of the walls materials see figure k value is given. WALLS AND FLOORS The table of figures 13 and 13.1 summarize the values calculated for he three building solutions applied to walls and floors. Figure 13 Values of k and R ( 1 a and 2 a solution) 16

17 Figure 13.1 Values of k and R ( 3 a solution) The table above shows the values of R tot and U for the three building solutions. The U-values of figure 14 are those ones to be used in the following thermal calculations. Figure 14 Values of Rtot and U for the three solutions.. 1 Definition of volcanic rock in this project WINDOWS The table above shows the values of Rtot and U for the three building solutions tested. Figure 15 Values of Rtot and U of the windows 17

18 HEAT DISSIPATION CALCULATION The calculation of the thermal losses has been divided in two phases: test and applied calculation. The first phase consists of the calculus of the thermal dissipation through the floor and front wall of the kitchen/living room only. The second phase is the calculation of the heat dissipated through walls, floors and windows of all rooms (patio excluded). The test was done in order to visualize the thermal behavior of all the building solutions and, based on those results, to decide what the best insulators are. Next, once it is known what the best insulators are, the related U value will be applied to the thermal equation (1) to calculate the thermal losses through walls, floors and windows of all rooms (applied calculus phase). Finally, it has to be specified that the test phase was a preliminary investigation that has been done in order to inspect the thermal properties of walls and floors materials only. Windows have not calculated because this will be done on the next phase. TEST PHASE In the following table are shown the various combinations related to walls and floors in order to known what the best insulation combination is. Basalt-rock wool-basalt Oak-rock wool-oak Materials Basalt- and Oak-rock wool-oak Basalt and Oak--polystyrene-rock woolpolystyrene-oak Tested combinations 1) Walls and floors 2) Walls and floors 3) Woody walls and rocky floors 4) Woody walls and rocky floors On the table above it has been chosen two different material layers for the woody walls (Oak-rock wool- Oak and Oak-polystyrene-rock wool-polystyrene-oak) and for this reason they are labeled under woody walls and rocky floors and not the combination woody floors and rocky walls. The reason is that the thermal investigation has the aim of inspect the thermal properties of the materials in function of the climate of the Azores islands. It is obvious that all solutions are possible woody floors and rocky walls. 18

19 Wh RENEWABLE ENERGY AZORES PROJECT TEST PHASE-RESULTS TOTAL POWER DISSIPATED OF THE WALLS AND FLOORS AT 20 C 70 total power dissipated C Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec -20 basalt-glass wool-basalt (floor+walls) basalt floor/oak-glass wool-oak walls oak-glass wool-oak (floor+walls) basalt floor/woody walls(3td solution) Figure16 Total monthly power 20 C The diagram of figure 16 shows the total monthly dissipation (Wh) for the kitchen/living room only when it is assumed that the room has to be cooled at 20 C (see assumptions page 11). DESCRIPTION If one wants to keep cool the rooms (20 C), the thermal results of walls and floors show thermal patterns slightly different. Therefore, it can be noted that on summertime (from August to September) the room test will not dissipate heat but will gain heat from the outside and this can be seen from a negative result (-20Wh). So, there is the possibility that on summer the room temperature will increase due to a heat flow that from the outside goes into the room. 19

20 Wh RENEWABLE ENERGY AZORES PROJECT TOTAL POWER DISSIPATED OF THE WALLS AND FLOORS AT 23 C The diagram of figure 17 shows the total dissipation (Wh) of walls and floor of the kitchen/living room in case it has to be heated up at 23 C. 90 total power dissipated C Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec basalt-glass wool-basalt basalt floor/oak-glass wool-oak woody walls oak-glass wool-oak basalt floor/woody walls(3td solution) Figure 17 Total monthly C DESCRIPTION In this case the insulation is perfectly provided throughout the year. Figure 17 shows the thermal pattern of the different material combinations tested in case the room temperature wants to be warmed up to 23 C. Therefore, it can be seen that the fourth combination (basalt floor/woody walls (3td solution)) is the most insulating because this materials allow the wall to dissipate around 60 Wh yearly, compared to the first solution (basalt-glass wool-basalt, 75Wh). So, the fourth combination is the most insulating. 20

21 TEST PHASE FURTHER RESULTS HEAT DIFFUSION THERMAL MAPS (ISOTHERM AND COLOR) In order to investigate about the isolation quality of the suggested combinations, simulations have been performed using THERM 6.3. This is a Finite Element Method software to simulate the thermal behavior of walls and windows. In order to simulate the outside conditions of the Azores islands it has been used the above mentioned thermal properties (figure 14). Therefore, the simulations will take into account the following temperatures: 20 C inside and 25 outside; 23 C inside and 10 C outside. Figures 18 and 19 1st solution. Isotherm maps 21

22 Figures 20 and 21 2nd soluztion. Thermal Color map. 1 pixel resolution 22

23 FIGURES 22 AND 23 3TD SOLUTION. ISOTHERM MAPS The figures 20 and 21 show color thermal maps and not isotherm output in order to improve the readability of the outputs. So, it can be clearly seen that all material combinations represent very good insulators. The reason for that is that the isotherm maps as well as the color thermal maps show a sharp separation between the internal and external temperatures. However, among all four combinations, the best one is the fourth assemblage of materials (figures 16 and 17). So, in order to calculate the heat loss through the rooms, it will be chosen the U-value of the fourth solution. 23

24 kwh RENEWABLE ENERGY AZORES PROJECT APPLIED CALCULUS PHASE One important aspect to be aware of is the geometry of the house. The house does not have a regular square shape but it has an L -shape top view. Therefore, the house has been considered made of two rectangles of different area: the first is represented by the kitchen/living room and the second by the other rooms. In order to calculate the total heat loss yearly it is necessary to know how much the heat loss of the rooms is in one year. So, first it has calculated the heat loss through walls and floor of: kitchen/living room, bedroom (x2), bathroom (x2) and corridor. Second, once it has known the heat dissipation of all rooms, those heat loss values have been summed up in order to get the total power dissipated through walls and floors of all rooms (kwh/month) (Annex, figure 3). After that, it has been summed up the previous value and the heat loss through the windows and this value represents the total power dissipated monthly (kwh/month) (Annex, figure 4). Furthermore, the figure 24 shows a summary of the thermal situation. Finally, the yearly total power dissipated is the sum of the monthly total power dissipated (kwh/year) (figure 25). The last values will be used in the next design phase in order to create the heating and hot water supply system. 350 monthly total power dissipated from the house Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec -100 floor + walls + 20 C floor + walls + 23 C Figure 24 Plot of the total power dissipated monthly for rooms at 20 and 23 C 24

25 Figure 25 Total power dissipated yearly for rooms at 20 and 23 C CONCLUSIONS The first design phase was fundamental because it has determined how much the heat loss is yearly (1.87 MWh/year). Furthermore, the first part of the design phase was important because it has compared the various thermal performances of the materials. However, despite of what it has been said initially (page 3), additional thermal investigations have shown that two possible building solutions could be: - rocky floor with multi layered walls (figures 22 and 23) and vacuum insulated glasses - woody floor (figures 22 and 23) and rocky walls with vacuum insulated glasses. Concerning the windows additional options are possible. The use of vacuum insulated windows can be limited to the bathrooms and triple glazed windows for the kitchen/living room. The other rooms can use double glazed windows. This considerations have been done on the size of the windows because in rooms of a certain area, such as kitchen/living room (40 m 2.), the best solution would be greater windows; for other rooms, like bathrooms (6 m 2.), maybe vacuum insulated glasses could fit into this type of room. NEXT PHASE: HEATING/COOLING SYSTEM AND HOT WATER POWER SUPPLY The next phase will focus on the design of the heating/cooling system and hot water supply. Therefore, it will be designed a system so that the rooms can be kept at the target temperature (20 C and 23 C). In addition, the system has to satisfy the following requirements: Availability of hot water all year the hot water supply has to able to produce hot water for extra rooms also (example: greenhouses and so on) - The cool/hot water has to be present for other uses than the domestic one (example. Car washing) - Preferably the system will be designed as an hybrid system that will combine more than one renewable source Figure 26 shows the schematics of a possible hybrid system for hot water supply. 25

26 Figure 26 PV + solar thermal hybrid system. 26

27 BIBLIOGRAPHY AAVV (2012). "Low Energy House - What is Rock Wool Insulation?". from AAVV (2012). "Wood - from Wikipedia the Online Encyclopedia." from Machado (2008). "Geochemistry of volcanic rocks from Faial Islands (Azores)." Geosciences Online Journal - Revista Electrónica de Ciências da Terra 5(1): Ricardo Aguiar R., S. R. A. a. C. R. (2008). Solar Climate of Azores: results of monitoring at Faial and Terceira islands 1st International congress on Heating, Cooling and buildings - EUROSUN. Lisbon, Portugal. 27

28 ANNEX Figure 1 Test phase Material choice calculations 28

29 Figure 2 Applied calculus. Heat loss through walls 29

30 Figure 3 Applied calculus. Heat loss through walls and floors of all rooms Figure 4 Applied calculus. Heat loss through windows and summrizing table of the total heat loss of the house. 30