MANEJO DE DISPOSITIVOS DENTRO DE UNA PLATAFORMA .1 Eléctricos

Lightweight timber frame buildings, SIPs included, with modern construction method of prefabricated building elements has low level of mass compared to conventional brick and block buildings. Thermal mass related to admittance value as discussed in Appendix A Section A.3.1.2. Due to lack of thermal inertia, it results in rapid swings in the internal temperatures. In order to alleviate discomfort in summertime as well as reduce overheating risk in this lightweight building unit, it is suggested to add more mass into the building envelope. In practice, concrete either blocks or panels, precast or

0

Energy consumption (kWh/m² pa)

Heating load - Base case Heating load - SC glass Overheating - Base case Overheating -SC glass

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cast in-situ is the most practical and most common (The Concrete Centre, 2006).

Thermal mass from medium to high level is provided from walls and floor construction with suitable finishes.

Phase change materials (PCMs), one of new alternative materials, have higher thermal energy storage capacities per unit mass than conventional building materials by storing energy in form of latent heat rather than sensible heat. PCMs outperform concrete, blocks or bricks from the aspect for the same heat storage capacity, the amount of mass required for PCMs is minimal as well as the required production energy (Kendrick and Walliman, 2007). For instance, in comparison with conventional thermal mass products, a 5 mm DuPont™ Energain® panel behaves approximately like 20 - 40 mm of concrete depending on the temperature. Typical heat storage capacity of DuPont™ Energain®

panels 143 Wh/m², 18 - 24 °C (DuPont™Energain®, 2010) .

Thus, PCM is selected as an incentive of increasing mass for SIPs envelope. It is also suggested that the phase change temperature or melting point is close to the desired mean temperature of the room aims to provide effective thermal storage for both cooling and heating applications (Kendrick and Walliman, 2007).

Amongst PCMs, paraffin wax is seen as a particularly promising material for use in building components because of its cheapness and ready availability as well as flexibly adjustable properties (Demirbas, 2006). The study on the effect of fusion temperature on comfort concludes that the best overall performance could be expected with the use of PCM operating around the mid-point of the comfort range as the best compromise between cool morning and hot afternoon (Kendrick and Walliman, 2007). For an optimal range of comfort temperature in residential building, a PCM’s melting point around 22°C is suitable, taking 19°C as low extremity for heating desire and 25°C as high extremity for acceptable summer temperature from this band (25°C), people starts to feel hot.

6.2.2.1 Production selection

The DuPont^™ Energain® product was selected as an example to consider the effectiveness of thermal mass panel on building performance. The thermal mass panel is laminated to aluminium protective foils and the panel core is mixture between copolymer and paraffin wax. The product properties are given in Table 6-4.

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Table 6-4: DuPont^™ Energain® properties (DuPont™Energain®, 2010)

Property Description Dimensions Area: 1x1.198 (mxm) and thickness 5.26 mm Area weight (Mass per unit area) 4.5 kg/m²

Density 810 kg/ m³

Melting point 21.7 °C

Heat storage capacity 515 kJ/m² (18 - 24°C) Thermal conductivity liquid phase 0.18 W/m K

Thermal conductivity solid phase 0.17 W/m K

The required amount of thermal mass depends on how severe overheating occurs in a room thus increasing the area in direct contact with internal air and the storage capacity.

It is suggested that DuPont^™ Energain® panels need to be placed in the warm side of the room and within the structure, located behind the insulation. If there is any cavity within the structure then it needs to be behind the thermal mass panel (Norris, 2011).The effect of Energain® panel on cooling performance is not influenced significantly when it is covered by the plasterboard as the finishing layer. A time lag of around 10 minutes was recorded in monitored buildings in which Energain® boards were installed (Norris, 2011). During heating period, installation of thermal mass helps to mitigate the indoor temperature at around the maintained comfort temperature by heating devices as room temperature is below the melting point of the phase change material. Considering this option with the current building envelop, the installation of DuPont^™ Energain® will be between SIP and the internal plasterboards.

6.2.2.2 Simulate PCM on building envelope

It is suggested that PCM panel was modelled as the air conditioned cavity zone in IES

<VE> software tool (Kendrick and Walliman, 2007). The cavity was maintained at a set-point as related to the melting point of the selected PCM product and the latent heat capacity of PCM was the limited power capacity for the conditioned space. If the cumulated cooling load was higher than the total latent heat capacity of the selected PCM product, the air condition system would be switched off. This means that the air conditioning system in PCM cavity was turned on and off based on the maximum system power thus it allows the temperature of the conditioned space to pass beyond the set-point and rise in a normal manner. In brief, the principle to simulate melting phase was to use the nominal value of latent heat of the PCM material, average its maximum

outputs ov

137 (1) PCM on inner side of the pitched ceiling (2) PCM on inner sides of external walls

(3) PCM on inner sides of the pitched ceiling and external walls 6.2.2.3 Results of cooling performance PCM

By integrating PCM onto the building envelope, overheating risk diminishes in the bedroom and rest spaces except the living space. Figure 6-10 illustrates the overheating risk in the living space with different design solutions of incorporating PCM within the building envelope. It is important to note that for the PCM board to absorb by its full capacity, a careful ventilation design is required. Opening windows providing ventilation to purge out all the heat stored within the PCM board thus enable full capacity of absorb heat the following day. Night time ventilation by the use of mechanical ventilation or opening top hung windows should also be included to enhance the performance of PCM board.

With the scenario when windows are kept shut, the simulation method by air conditioning the air cavity zone still allow the heat absorptance to work in full capacity.

Such scenario helps to test the effectiveness of PCM location and mass level within a space in reducing overheating risk via different orientations. The cooling effectiveness of each design strategy varies with orientation. It works best in the south case and worst in the north case. A remarkable overheating risk was reduced in the south case from 17.1% annual occupied hours down to 4.1% which equates to 325 hours of occupancy with PCM installed on the roof. It is less effective installing the PCM on ceiling than on external wall in all cases, taking account of more PCM to be installed to cover the surface area of external walls than the roof area in living space (See Figure 6-10). The overheating risk reduces but does not disappear when locating more PCM on both external walls and roof areas (i.e. 35.23 m² on the wall against 21.15 m² on the roof, See Table B-16). For all the three design options, there is no overheating risk with zero number of hours that operative temperature in living space exceeds 28°C when windows are open. Simulation results show that overheating risk diminishes in the rest of spaces like bedroom, office, bathroom and the hall.

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Figure 6-10: Overheating risk in the living space when PCM installed on the roof, the external walls or both within the building envelope via 4 main orientations.

Regarding the comfort benchmark for natural ventilated spaces, the presence of PCM board within the building envelope helps the percentage of annual occupied hours around the 5% benchmark for the living space and less than this level for other spaces.

Such performance is valid as when windows kept shut that relies on background ventilation and the assumption of effective ventilation is provide to purge out the absorbed heat in the PCM board. It is impossible to indicate how much ventilation is required then when and how long the windows should be open to make sure the PCM works. It could be achieved just by continuous fresh air supply as background ventilation provided by mechanical ventilation system during occupancy/night time or a supplement of some more air exchanges to removing the heat during a short period of time.