To quantify the monthly savings (cost reduction in consumption of electricity and natural gas) of the residents of cooperative housing in dwellings with sustainable characteristics when compared to the same costs supported by the inhabitants of traditional cooperative dwellings, a study is presented comparing two cooperative housing settlements in the district of Porto. One is located in the city of Vila Nova de Gaia (41.118040�N, 8.635900�W) and the other in the city of Senhora da Hora (41.182666�N, 8.665556�W). The first settlement was designed and built following sustainable and energy-efficient construction principles in 2008/2009. The second one was built in the early 1990s, according to the usual features at the time for the construction of traditional cooperative housing. The studies performed show the energy efficiency of each dwelling in the two settlements with the quantification of the energy demand (electricity for space heating and natural gas for water heating) and related costs in order to compare the effort borne by the residents.
2.2.4. Description of the Energy Performance of dwellings
To describe the energy performance of dwellings, an energy audit was made for each one, in order to determine its heating and cooling needs, as well as its needs of energy for DHW. The type of dwelling according to the number of rooms (T2 means two bedrooms) and the acclimatized floor area of the dwellings (
Au), shown in
Table 3, were used for calculations, as well as the area of surrounding walls, pavements, roofs and glazing, along with their thermic transmittance or efficiency shown in
Table 1 and
Table 2. These items are used to calculate the average annual needs for heating, cooling and DHW, per square meter of acclimatized area, shown in
Figure 1, for the average dwelling.
Table 3.
Description of type of dwelling and acclimatized area—Madalena vs. Azenha de Cima.
Table 3.
Description of type of dwelling and acclimatized area—Madalena vs. Azenha de Cima.
Building | Au—acclimatized floor area | T2 (Units) | T3 (Units) | T4 (Units) |
---|
Madalena (sustainable) | 3222 | 17 | 22 | 0 |
Azenha de Cima (traditional) | 2583 | 20 | 12 | 4 |
Figure 1.
Average annual needs for heating (Nic), cooling (Nvc) and DHW (Nac)—Madalena vs. Azenha de Cima.
Figure 1.
Average annual needs for heating (Nic), cooling (Nvc) and DHW (Nac)—Madalena vs. Azenha de Cima.
The items presented in
Figure 1, have the following meaning [
6,
7,
8]:
Nic: Average annual heating needs of electricity to keep the house at 20 °C during the winter season (kWh/m2·year), per dwelling, for the total dwellings of the building;
Nvc: Average annual cooling needs of electricity to keep the house at 25 °C during the summer (kWh/m2·year), per dwelling, for the total dwellings of the building;
Nac: Average annual DHW energy needs to ensure a daily consumption of 40 liters of hot water per inhabitant in the dwelling, in kWh/m2.year (T1 = 2 inhabitants, T2 = 3 inhabitants, T3 = 4 inhabitants, T4 = 5 inhabitants), per dwelling, for the total dwellings of the building.
From
Figure 1 it is possible to conclude that a sustainable construction is prepared to spend 56% less electricity in space heating and 86% less natural gas in DHW, per square meter. Considering that the average of a dwelling in Madalena is 82.6 m² and the average areas of a dwelling in Azenha de Cima is 71.8 m², the annual heating needs and DHW needs for the average dwelling of each building are presented in
Table 4.
Table 4.
Annual energy needs for the average dwelling—Madalena vs. Azenha de Cima.
Table 4.
Annual energy needs for the average dwelling—Madalena vs. Azenha de Cima.
Building | Average floor area (m²) | Annual heating needs (kWh/year) | Annual cooling needs (kWh/year) | Annual DHW needs (kWh/year) |
---|
Madalena (sustainable) | 82.6 | 2,903 | 412 | 1,090 |
Azenha de Cima (traditional) | 71.8 | 5,684 | 520 | 7,023 |
These results show that a non-sustainable dwelling can spend, for heating, twice as much energy as a sustainable one, and is very probable to spend, for the standard comfort, almost seven times more energy in DWH.
The values of Nic, Nvc and Nac mentioned in
Figure 1 are quantified using calculation methods included in the Portuguese thermal regulations [
7]. The following tables also show for each dwelling the values of annual energy needs as well as their maximum allowable values. Relation between Ntc and Nt is used to determine CO
2 emissions and the Efficiency Energy Rating (EER) Label [
6].
Energy rating, as normalized by Portuguese Law [
6,
7,
8], relates the value of annual primary energy consumption with the maximum allowable annual primary energy consumption, as follows:
0.00 < Ntc/Nt ≤ 0.25: “A +” Class; 0.25 < Ntc/Nt ≤ 0.50: “A” Class; 0.50 < Ntc/Nt ≤ 0.75: “B” Class; 0.75 < Ntc/Nt ≤ 1.00: “B-” Class; 1.00 < Ntc/Nt ≤ 1.50: “C” Class; 1.50 < Ntc/Nt ≤ 2.00: “D” Class; 2.00 < Ntc/Nt ≤ 2.50:“E” Class; 2.50 < Ntc/Nt ≤ 3.00: “F” Class; Ntc/Nt > 3,00: “G” Class;
In which:
Ntc: Annual primary energy consumption, in kilogram(s) of oil equivalent (kgoe);
Nt: Maximum allowable values of annual primary energy consumption (kgoe).
Considering the same regulations, the EER of the 39 dwellings of Madalena is “A” and the EER of the all 36 dwellings of Azenha de Cima is “C”. The “A” label of Madalena means that the needs of primary energy for this building are less than 50% than the maximum needs of primary energy allowed. On the other hand, the “C” class in Azenha de Cima means that the needs of primary energy for this traditional building are higher up to 50% more than the maximum needs of primary energy allowed by new regulations.
In order to compare the annual emissions of CO
2 of the average dwelling of each building, it is presented its value in
Figure 2. It is possible to see that the estimated emissions for the building efficiency are almost three times higher in Azenha de Cima than in Madalena.
Figure 2.
Average CO2 annual emissions—Madalena vs. Azenha de Cima.
Figure 2.
Average CO2 annual emissions—Madalena vs. Azenha de Cima.
According to calculations of global heating, cooling and DHW needs for each building, it is possible to present their values for each building.
These results, calculated for Madalena building (sustainable), with 39 dwellings, and for Azenha de Cima building (traditional), with 36 dwellings, are very clear about the importance of thermal insulation, efficient heaters and of use of solar collectors, as shown in
Table 5.
Table 5.
Global annual energy needs—Madalena vs. Azenha de Cima.
Table 5.
Global annual energy needs—Madalena vs. Azenha de Cima.
Building | Heating needs in winter kWh/year | Cooling needs in summer kWh/year | DHW needs kWh/year |
---|
Madalena (sustainable) | 113,253 | 16,078 | 42,530 |
Azenha de Cima (traditional) | 202,139 | 18,548 | 250,790 |
According to
Table 5, efficient thermal insulation is responsible for 46% less energy in heating during winter season; efficient gas heaters and solar collectors are the cause of Madalena building spending 83% less energy in DHW.
2.2.5. Energy Costs for Heating, Cooling and DHW
Based on numerical data from
Figure 1, the annual costs (in euro) for the demands of each type of energy were calculated for the Madalena average dwelling and for the Azenha de Cima average dwelling, as shown in
Table 6. These costs were obtained taking into consideration the annual heating, cooling and DHW needs and the cost of domestic gas and electricity at the time of the case study—September 2011 (€0.12/kWh of electricity and €0.06/kWh of natural gas).
Table 6.
Average expectable energy costs per dwelling—Madalena vs. Azenha de Cima.
Table 6.
Average expectable energy costs per dwelling—Madalena vs. Azenha de Cima.
Building | Average floor area (m²) | Annual cost for heating (euro) | Annual cost for cooling (euro) | Annual cost for DWH (euro) |
---|
Madalena (sustainable) | 82.6 | 348.36 | 49.44 | 65.40 |
Azenha de Cima (traditional) | 71.8 | 682.08 | 62.40 | 421.38 |
The estimated annual costs for heating, cooling and water heating obtained for the average dwelling allow, by summing them, to determine its total expense on energy. Therefore, it follows that the expected average annual expenditure on energy for heating, cooling and heating domestic hot water, is, per dwelling, of €463.20 for the building of Madalena and €1,165.86 for Azenha de Cima.
These costs were calculated for the purpose of maintaining a level of comfort for the residents, with their house heated permanently at 20 °C during winter season, cooled permanently at 25 °C during summer and to ensure a daily consumption of 40 liters of hot water per inhabitant in the dwelling.
But, in opposition to the optimum levels of indoor comfort, involving the costs above mentioned, it is possible to determine the cost actually spent in energy for heating and for DHW, determined by a monitoring procedure, as shown in
Section 2.4.