T HE MODEL

A model of an apartment which is located in the 2^nd floor of the GEL is given to the author by GEL students and used for the analysis. All the dimensions are given in the model, which is made in an older version of TRNSYS. The dimensions are taken into Trnsys3d, sketched and imported to TRNBuild so that the detailed long-wave radiation and comfort models can be utilized. Figure 5.4 shows the model in Trnsys3d. The left of Figure 5.5 shows the dimensions as seen from above, with north pointing upwards. It comprises three zones where the large one is considered as a living room and the two smaller ones as bedrooms. The northern bedroom is referred to as room A while the southern room B. One bedroom could possibly be considered a bath room, but this is not taken into account here. South, east, north and roof are exterior surfaces, while the west surface has adiabatic boundary conditions. The floor has a constant temperature boundary condition of 22°C. On the roof of the actual GEL building a large triangular structure, on which PV-modules and thermal collectors are installed, provides approximately full shading for the roof surface of the apartment. To model this shading the solar absorption α of the roof is changed from 0.6 to 0.1.

Wall layers are the same as for the model used in the validation simulations (see Appendix C) with exception from the ceiling, where an insulation layer is added to lower the u-value to 0.34 W/m²K. Windows are given to be of U-value 2.83 W/m²K as in the validation simulations, but this is changed to 0.86 W/m²K considering that the aim is to analyze a modern building. The roof has a U-value of 0.34 W/m²K.

To capture a bit of real condition with possible solar irradiation effects the exterior shading on the eastern façade windows is set to 50%, while on all other windows 100%. Detailed shading and short-waved radiation analysis is not a part of the scope for this work and is thus omitted.

Detailed models of long-wave radiation and thermal comfort are utilized. The right of Figure 5.5 shows the positions used for thermal comfort. All are in a height of 1.5m. In the living room there are two positions used, but throughout the analysis these two did not show any difference in PMV between them. This is because of the shading of the windows of this zone and the homogenous floor temperature of the model. With a partitioned floor surface and no shading some difference would be expected. Also, the thermal comfort models do not consider short-wave radiation.

Figure 5.4: The model as made in the SketchUp plug-in Trnsys3d. 3 zones can be seen: One large living room and two smaller bedrooms to the east.

Internal calculation of convection coefficients is used on internal surfaces.

Infiltration is assumed constant and equal to 0.4 h^-1. Ventilation and internal gains are implemented according to schedules. In small bedroom there is one person present 23:00 – 07:00 on weekdays and 24:00 – 08:00 on weekends. In the larger bedroom 2 persons are present at the same times. For the living room all 3 persons are present 07:00 – 08:00 and 16:00 – 23:00 on weekdays and 08:00 – 11:00 and 17:00 – 24:00 on weekends. The activity of the persons in the living room is labeled “Seating, eating” in the standard ISO7730, while for the bedroom “Seated, at rest” in the same standard. In the living room there are also implemented internal gains from a computer of 140 W and 5 W/m² of artificial lighting heat gain which follows the occupancy schedule. The ventilation is demand controlled and follows the occupancy schedule for the entire model. The rate is set to 26 kg/h/person according to standards plus a constant air exchange rate of 0.15 h^-1 for removal of pollutants from materials. Inlets are assumed in bedrooms, and outlet in living room. A type91 heat exchanger is used to model a constant 90% efficiency heat recovery unit.

Weather imposed is the typical meteorological year (.tm2) for Shanghai.

Figure 5.5: Room dimensions and geopositions used in the detailed thermal comfort model.

White dots in the right figure are the location of the thermal comfort nodes.

Each zone has one active surface on the floor and the model is the same as the one validated in chapter 4 with dx = 15 cm. The floor surface of the living room is quite large and with only one loop the length of that loop would be long and the pressure drop significant. In real life this is normally tackled by splitting it into several, shorter loops. In the type56 model pressure drop is not accounted for, and for these simulations a partitioning of the surfaces in the living room is thus not necessary. This is not considered to have an influence on the results because the total flow and temperature drop would be the approximately the same for one loop as for several, in the simplified simulation model. For very detailed simulations a more realistic layout of the tubes should be considered, but for this model it is non-significant.

The heat curve for the model is shown in Figure 5.6. This is made with a simulation of an ideal heating using the TMY weather model, which do not capture worst case scenarios. Maximum heat load calculation is performed by TRNBuild and with a heating set-point of 22°C and design outdoor temperature of -4°C yields 41 W/m², which is depicted as a circle in the figure. It is thus not a super-insulated building, but as a typical Chinese apartment in which a radiant floor could be installed it is important to analyze.

Figure 5.6: Heat curve of the Chinese model. Design outdoor temperature -4°C.

A summary of maximum heat load calculations is presented in Table 5-1. The heat load presented above can be recognized in the third row. Original windows are poorly insulated and cause a 10 W/m² increase in load compared to the proposed new windows. To see how this model would perform in a climate much colder than Shanghai, like the northern parts of China, a design outdoor temperature of -14°C was simulated. Even with the more insulated window this shows a maximum heating load of 57 W/m²K, which is higher than the maximum heat rate from the floor (see Table 5-2). For the old window model in Shanghai conditions, the radiant floor can barely provide the maximum heat load of 51 W/m²K. The model needs a better insulation level to be operated by a radiant floor and the proposed new window with a u-value of 0.86 W/m²K is therefore used in this analysis. If a radiant floor is to be used in a cold climate, the level of insulation must be even better, and a focus on improving exterior wall insulation is recommended (In the GEL model the u-value for the exterior walls is 0.57 different climates are simulated: Shanghai climate with a design outdoor temperature of -4°C and a colder climate.

Zone air temperature 22°C