7 Case study buildings and their simulation models
7.1 Luhtaa day-care centre
Luhtaa day-care centre, approximately 6 km from central Tampere, is the first passive-grade day- care building in Finland. The decision on building Luhtaa day-care centre was made in 2007, and the project plan was formulated in 2010. The building was inaugurated in early 2012, and now provides day-care and pre-school education for approximately 120 children. Luhtaa day-care centre has a net floor area of 1438 m2. [78] Figure 11 shows a design drawing of the building.
Figure 11. Axonometric drawing of Luhtaa day-care centre. Image from BST-Arkkitehdit Oy [78].
Luhtaa day-care centre is one of Tampere city’s low energy building pilot projects. According to the design-phase simulations, the building was to reach energy class A, and also to fulfil the passive- grade building requirements, with annual primary energy use of 135 kWh/brm2 or less. According to design phase simulations the building consumed 84 kWh/brm2a, and calculated with German energy carrier factors this resulted in primary energy use 156 kWh/brm2a. This was more than the
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targeted passive grade primary energy consumption, so own renewable generation was installed to produce some of the required energy on-site. [78]
Both solar thermal and solar PV technologies were considered in the planning phase, and solar PV was decided to be the more efficient way to improve the building energy performance [78]. The building was equipped with 56 TopSun TS-S390 solar panels, each with a nominal power of 390 Wp. The total area of the panels is 143 m2.The panels face south-west and are placed in a 23° angle to the horizon (see Figure 12). The total nominal power of the system is 21,8 kWp. [79]
Figure 12. Luhtaa day-care centre photographed 9.4.2016. Photo: Paula Sankelo.
Several other methods, both passive and active, were applied in Luhtaa to reach the energy target. The day-care building has a wood frame construction. The total thickness of the walls is 500 mm, with 400 mm of insulation. All building elements, including doors and windows, have a low U- value, and passive methods are applied for solar shading. Temperature efficiency of heat recovery varies between 60% and 80% depending on the air handling unit (AHU). [78]
In the work package 4.1, it was found that the optimal heating solution for Luhtaa would be GSHP, having both lowest costs and lowest primary energy use. The actual heating system in Luhtaa is district heating, with the connection dimensioned at 1,8 m3/h. The heating set-point temperature is 21 °C. Heat is distributed via water-based floor heating on the ground floor, and water-based radiators in the basement and ventilation system. Dimensioning of floor heating and radiator heating capacities are performed in IDA ICE for Tampere design temperature of -29 °C. [5]
The basement houses three centralized air-handling units, all equipped with heat recovery. One of the AHUs is designated for the kitchen only, and provides also cooling for the kitchen. In reality, only the kitchen space is cooled. A cooling setpoint of 25 °C was utilized in the simulation model for this study, and it was found that the simulated indoor temperatures violated the target of 25 °C, which is the target maximum indoor temperature recommended by the national building code [13]. To prevent the violation of the target, the simulated AHUs were all equipped with supply air cooling. [5]
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The building usage profiles for the Luhtaa building model, as well as for the other case-study building models, are based on 1) profiles defined by the The Finnish Association of HVAC Societies (FINVAC), 2) building user interviews and 3) measured data. FINVAC suggests standard building occupancy profiles (available at http://www.finvac.org), and in these models, the standard profiles have been modified somewhat (but not extensively) according to the interviews with the building users. Domestic hot water (DHW) consumption is modelled with the help of measured data. The resulting occupancy profiles for all three case study buildings have been explained in detail in [5], and they are not repeated here. Luhtaa day-care building is assumed unoccupied during weekends and holidays.
Figure 13 shows the 3D visualization of the Luhtaa day-care centre in the original IDA ICE model, without the existing solar PV incorporated into the model. In the 3D view the model is shown in the original form, because it gives a more realistic view of the doors and the windows, and therefore shows a more correct outside appearance of the building. Luhtaa has roof planes facing south-east, south-west and west. By design, it is well suited for solar PV production. A rough estimate of the best suited roof area available for panel installation is 600 m2, and this has been set as the maximum panel area in the optimization runs.
Figure 13. IDA-ICE model showing the building envelope of Luhtaa day-care centre, without the existing solar panels.
Virhe. Viitteen lähdettä ei löytynyt. shows the floor plan for the ground floor. This time the view
is of the modified model, already simplified for the optimization purposes e.g. by combining some building zones together. The simplification process is explained in Chapter 7.4. The detailed zone divisions in the original, un-simplified models are shown in [5], where the original building model is documented in detail.
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Figure 14. Floor plan of Luhtaa modified IDA ICE building model, with simplified zone division, ground level. The building also has a basement space.