Total de extracción de Conocarpus erecta (Zaragoza) para leña.

Models of baseline buildings are necessary because they provide the references to evaluate how much energy is saved using semi-transparent PV façades in office buildings. Because PV glazing of different PVR has various effects on the overall energy performance, baseline buildings can serve as a ―ruler‖ and help us to further understand the benefit from optimal PVR in certain architectural conditions. With the energy saved using semi-transparent PV façades, the economic evaluation including the PBT (payback time) analysis is also available, based on which the

suitability of optimal PVR/WWR of semi-transparent PV façades is further discussed in Chapter 8.

In China, there is no official academic general reference of baseline building models for building energy studies to serve as comparison cases. However, certain architectural codes and regulations provide us with requirements of energy-efficient buildings. According to the Chinese Design Standard for Energy Efficiency of Public Buildings (GB-50189-2005) (CABR, 2008), the standard of ―energy-efficient building‖ is provided, which can save approximately 50% energy compared to traditional public buildings that are built in the 80s and 90s. Because there are is other available option for reference cases in China, two types of baseline buildings are developed based on the requirements of the Chinese Design Standard for Energy Efficiency of Public Buildings (GB-50189-2005). The two types of baseline buildings are described as follows:

 Baseline building A

General and traditional office buildings that are built in the 80s and 90s. In GB-50189-2005, these buildings are defined as consuming two times more energy than energy-efficient buildings.

 Baseline building B

Energy-efficient office buildings that satisfy the minimum requirements of GB-50189-2005.

GB-50189-2005 provides the requirements of different aspects for different climate zones and conditions of energy-efficient buildings. However, not every requirement is necessary in the Hot-Summer Cold-Winter climate zone and suitable for the comparison cases in this study. We defined three main aspects of requirements as the basis to develop the baseline buildings: (1) envelope properties, (2) operation setting, and (3) operation schedule.

The first aspect is building envelope properties, which affect the heat transfer process of a building. Table 5.5 shows the requirements that are defined for the envelope properties of energy-efficient office buildings based on GB 50189-2005, which is specifically for the Hot-Summer Cold-Winter climate zone. Because the

architectural models in this study are assumed in the intermediate floor, the inner ceiling, inner wall, exterior wall and window are included as such.

Table 5.5 Requirements for the envelope properties of energy-efficient office buildings

Envelope Thermal conductivity (W/m2K)

Roof ≤0.7 Exterior wall ≤1.0 Exterior window U-value (W/m2K) Shading coefficient(SC) (East、South、West) One side window (including transparent façade) WWR≤0.2 ≤4.7 / 0.2＜WWR≤0.3 ≤3.5 ≤0.55 0.3＜WWR≤0.4 ≤3.0 ≤0.50 0.4＜WWR≤0.5 ≤2.8 ≤0.45 0.5＜WWR≤0.7 ≤2.5 ≤0.40 Note: only applicable for Hot Summer Cold Winter climate zone

SHGC can be calculated by SC. SHGC = SC/1.15

The operation setting is given as: room lights were assigned a design value of 11 W/m2 in all instances; COP (coefficient of performance) of air conditioner was set to 4.5, and the ventilation system was set to ensure 1.5 air changes/h; office occupancy was set to 0.25 people/m2, and the electricity consumption of the equipment was assumed to be 20 W/m2. Most settings are coherent to the settings of architectural models for the semi-transparent energy evaluation in 5.3. The operation schedule is shown in Figure 5.3.

Other necessary setups for the models of baseline buildings were provided and discussed in Section 5.3. The main difference between the architectural models for the semi-transparent energy evaluation and the baseline buildings are the properties

of the building envelope (façades). Thus, the energy performance and characteristics of the semi-transparent envelopes can be better revealed.

5.5. Conclusions

In this chapter, calculation models and methods including PV power generation model, thermal model and daylighting calculation method are established and validated by field experiments. The results obtained using the power generation model was compared with measurements obtained during field experiments. It was demonstrated that the power generation model could predict PV electricity output with satisfactory accuracy. Thermal model that is developed for both crystalline silicon and amorphous-silicon PV of different PVR as the temperature of the solar cell layers of semi-transparent PV panels need be calculated using this models. The results calculated from the thermal model were compared with the measurements collected during field experiments, which demonstrates clearly that the calculated results agree well with the measurements. In such cases, it is believed these calculation models and methods can be used for further study of overall energy performance of semi-transparent PV façades with satisfactory accuracy.

Architectural models are developed based on the survey of 60 cases of office buildings in the Wuhan area. Generic office rooms are developed with variation of WWR, room depth, orientation. Based on the solid survey in a large area in Wuhan, it is believed the architectural models are proper and can be used for further study of overall energy performance of semi-transparent PV façades.

Two kinds of baseline buildings (A and B) are developed to help us to further understand the benefit from optimal PVR in certain architectural conditions, which is also based on the requirements of Chinese Design Standard for Energy Efficiency of Public Buildings. These standards have been largely used and proved by a lot real projects in China and it is believed they could serve well in objective comparison study for semi-transparent PV façades.

Chapter 6 Evaluation on energy