Simulation

After creating the base model, the setup for heating load is defined by setting the percentage of all internal gain to zero to consider the worst-case heating load. The synthetic weather is selected with a clearness number of 0 % to calculate without any solar radiation, and with a fixed temperature of -19.9 ℃, which is the DVUT of 2 days time constant in Borlänge based on building inertia. Hence minimum and maximum dry bulb temperatures within the location are no longer used [26]. By running the simulation, the report of the result generated for the worst heating demand.

Energy simulation was performed to find annual energy consumption. For this purpose, the setup for energy was defined by setting the percentage of all internal gain that should be active during the calculation to 60 %, which is relevant in energy calculation. Synthetic weather is not available as an option; instead, annual climate data for Borlänge is required [26].

The cost for DH and electricity input in IDA ICE under the energy meter detail. The prices referred to Borlänge energy [42] divided per power consumption categories and it was approximate according to Appendix 4.

By running the simulation, the report of the result is generated for annual energy consumption (refer to Appendix 5).

Efficiency measures (VIP)

The heat losses in the buildings are divided into losses through building envelope, infiltration, and ventilation. The simulated results are analyzed for the NH base model. It is found that the significant losses in building envelope related to the walls and windows, and thermal bridge with minor effect for the roof part refer to Figure 3.7.

The reason is that the roof has a good U-value which is 0.17 W/(m² K) (refer to Table 3.3), and with area counts for 17 % of the building envelope, comparing to the walls with a higher U-value of 0.53 W/(m² K) and contributed to 51 % of building envelope.

Although the window area shared 13 % of the building envelope and a 25 % ratio to the wall but it was considered the weakest element in the building envelope due to its high thermal transmittance with a U-value of 2.7 W/(m² K).

The thermal bridge contributed to 30 % of the envelope losses, and together with the wall, it shared approximately 60 % of the total heat losses in the building envelope (refer to Figure 3.7). Hence adding external wall insulation is a relevant efficiency measure reducing heat losses through the wall and thermal bridge simultaneously.

Figure 3.7 Heat losses through Building Envelope.

The selected insulation is VIP due to its highly efficient thermal properties; however, a cost study was performed using the LCCA method to compare the VIP with conventional insulation (Extruded polystyrene).

VIP has been selected for wall insulation due to its high effective thermal conductivity range between 0.004 W/(m K) to 0.008 W/(m K), which can be achieved with lower thickness in comparison to other conventional insulation [27]. There are different ranges of VIP thickness in the market; most studies consider 2 cm, protected by additional layers on both sides. In this study, VIP with 2 cm thickness added as external insulation to the wall, covered with 1 cm with polystyrene from each side to protect the VIP from damage due to moisture or fungi. The recommended thermal conductivity for VIP with fumed silica is 0.007 W/(m K) to 0.008 W/(m K) [28]. In this study, 0.007 W/(m K) was considered to cover any losses in the thermal bridge.

In order to evaluate the result of implementing VIP as a relevant measure, the default existing wall in IDA ICE has been modified by adding external insulation. According to Figure 3.8 the additional VIP insulation to the existing walls improves the U-value from 0.53 W/(m² K) to 0.18 W/(m² K). Furthermore, it improved the infiltration from 6 to 0.5 ACH and thermal bridge from poor to typical.

On the other hand, implementing extruded polystyrene (XPS) will result in an additional 12 cm to achieve the same U-value resulted with VIP which is 0.18 W/(m² K). For XPS, considering a standard 5 cm thickness, with conductivity 0.036 W/(m² K) improve the U-value from 0.53 W/(m² K) to 0.3 W/(m² K) (refer to Figure 3.9).

According to [2], when only part of the building envelope is renovated, it should match with the recommended thermal transmittance, which is 0.18 W/(m² K) for the external wall.

Therefore, using 5 cm of XPS resulted in 0.3 W/(m² K) would be considered only for LCCA purpose. The actual renovation with XPS should be with a 12 cm minimum.

Figure 3.8 External wall with VIP.

Figure 3.9 External wall with XPS.

Life cycle cost assessment was used to evaluate which insulation has an efficient cost reduction according to Section 4.1.1 for this study.

Efficiency measures (ventilated façade)

The base model study showed that heat losses through infiltration and ventilation contributed to the maximum share, and according to Figure 3.10 it is 34 %. Due to that reducing the effect of ventilation is a relevant efficiency measure.

Figure 3.10 Zone heat losses.

While changing the ventilation system to heat recovery could be a solution, it is not the optimized solution [6]. The building will consume additional electricity load with a heat recovery system due to the extra fan for supply air. Moreover, adding a supply duct in the existing structure might be difficult and impossible due to ceiling height limitations and other existing services.

One way to reduce the impact of ventilation heat loss is to preheat the fresh air coming from outside by implementing ventilated façade either wall or window.

Ventilated façade is double skin with a cavity between the glazing panes integrated with the macro PI controller where the air inside is preheated either by the solar or heat losses from inside, as seen Figure 3.11. The air temperature in the cavity depends on both indoor and outdoor temperature. The cold fresh air penetrates from the bottom of the window through the valve, and then the fresh air is heated in the cavity. When the air reaches a specific temperature, the valve on the top will open and the preheated fresh air will enter the building.

This opening valve usually controlled by temperature, and when the air temperature exceeds 26 ℃ in the cavity, the fresh air will be provided from the ambient outside, not from the cavity.

Figure 3.11 Three positions for the ventilated window (from horn group supplier) [27].

In IDA ICE, the simulation was performed in two ways; the first approach using the double façade object, an option in the detailed window feature (refers to Figure 3.12). And the second approach recommended by EQUA support is modeling the ventilated façade as a separate zone added to the existing windows as seen in Figure 3.14. In both scenarios, the ventilated facade was allocated in the southwest direction of the building to maximize the solar heat transmitted to the cavity. The other facades remain unchanged.

Figure 3.12 Double skin façade in IDA ICE (ventilated window).