4.1. The Design and Construction
To find a partner for the design and construction of the day-care centre, the local municipality conducted two procurement processes:
In total, four tenders were submitted for the first design procurement. The designer was selected with a total price of 89,000 € [
43]. The design process lasted from 8 August 2016 to 4 May 2017. The architectural solution was prepared based on the client’s initial task. The building also had a creative room for about 40 people, with the necessary facilities. The creative room enabled us to organize circular work and joint activities of children and their parents. The aim of the architectural solution was to create a unique public building that enriches the garden city, which would be sensitive to the local nature and the built context. The building’s architectural solution was based on a single storey building with as playful and logistically diverse mobility facilities as possible. The cost of the building was estimated based on the final design solution because lifecycle cost changes (LCC) were not part of the design process. After the design, the budget of the building exceeded 3 million euros (twice as much as initially planned). This price was too high for the municipality. The competition was considered as failed after the second step, when all the offers exceeded the expected cost limit set in the competition conditions. Therefore, a second procurement was needed.
A second competition was announced following integrated delivery (design + construction cost). In both procurement cases, the final evaluation was done based on the lowest cost to construct the buildings. In total, two tenders were submitted to the second procurement—for design and construction procurement (integrated delivery). The best price was 1,582,007 € (construction price 1,478,511 € + subscriber reserve (7%) 103,496 €) [
44]. The total price with VAT (20%) was 1,898,408 €. The design process lasted from 28 July 2017 to 28 September 2018. The building was publicly opened on 12 October 2018. The total construction cost of the building was 1,478,511 € (1390 €/net m
2). The building was constructed with prefabricated wooden elements. It is noteworthy that the construction time on site was less than five months.
According to the new solution, the building was designed from wood (instead of concrete that was the main construction material for the first solution). Cheerful and child-friendly design solutions were used in the interior and exterior design. Each group of children had its own entrance. The design of the building was thoroughly thought out and offers choices for children and staff, promotes a variety of activities, and is very functional. In the middle of a pine forest in the yard, there are amusement playgrounds for children that take into account their age-specific characteristics. Each group has its own shelter, patio, and play area in the yard with exciting activities for every child.
Integrated project delivery procurement and a prefabricated wooden building helped to keep the budget within limits. Kantola and Saari [
45] conducted a workshop for gathering information and developing the layouts for procurement methods and found that the design must be included in the same contract as the construction work so that the bidders are able to use their expertise to make innovations and improve the whole segment of nZEB construction. In the studied case, this idea was proved in practice. Integrated project delivery (design and construction together) procurement reduced the construction cost of the new building by half. No energy performance optimization covers such a large cost difference.
4.3. Calculations of Lifecycle Costs
The changes in lifecycle costs (LCC) caused by the implementation of the nZEB solutions were calculated (see
Table 6). The analysis includes detailed energy performance-related costs of the actual solution components compared with the reference solution (minimum requirements, BC solutions). The energy performance solutions are derived by increasing/decreasing the insulation value of the building envelope (external walls, roof, and ground floor) in successive steps. These follow the actual building energy performance solution (as in the planning phase) and a proposal for an energy efficiency requirement to be implemented in the future.
The indoor climate and energy simulations and cost calculations for assessing the cost-effectiveness of technical solutions are based on the selected sample building. In the initial energy simulations, the impact of different improvement measures on the energy consumption of the original building was calculated. The annual energy use in the case of different combinations of structural solutions was calculated by subtracting the sum of the gained energy savings thanks to the used solutions from the delivered energy of the BC. Next, the EPI for different combinations was calculated from this result taking into account the conversion factors for energy carriers.
Figure 3 shows the results of the cost-effectiveness calculations for the studied building with different combinations of structural solutions and the EPI with different heat sources. The energy saved over a long term as a result of more efficient insulation solutions lowers the annual costs of the used energy.
The uncertainty of the interest rate and of the escalation of the energy price is high; however, ultimately this has the same effect on the studied and reference building cases. Since the aim of the study was to compare different scenarios, the energy and investment costs of energy saving measures were considered.
The results for different combinations vary to a large degree. An economically optimal solution is assumed to be achieved if the ΔNPV is the lowest. The results of the economic calculation show that higher energy savings gained by combining different insulation measures did not always increase the cost-effectiveness; this was also shown by Pikas et al. [
11] and Sankelo et al. [
16]. The reason for the drop is the ratio between the cost and the gained energy savings. As more efficient measures are more expensive, investment costs and interest charges will be higher.
In the case of a GSHP (
Figure 3a), the cost-even range of the EPI without local production of renewable energy compared to the BC is between 115 and 128 kWh/(m
2·a). The low energy building level is reached, but the nZEB level is not reached. In the case of an effective DH, the cost-even range of the EPI without local production of renewable energy compared to the BC is between 125 and 147 kWh/(m
2·a). The low energy building level can be reached with extra investments compared with the BC, yet the nZEB level would not be reached. In the case of the effective DH (
Figure 3b), the cost-even range of the EPI without local production of renewable energy compared with the BC is between 106 and 124 kWh/(m
2·a). The low energy building level can be reached with no extra investments compared with the BC; to reach the nZEB level, extra investments are needed.
Combinations of insulation measures with different heat sources result in significant divergence of the EPI. The choice of the heat source is not always free, being location dependent. The difference between the EPI values must be compensated for by insulation measures or by local energy production. In the case of non-residential buildings, the installation of PV is more cost-optimal than investment in insulation measures [
47]. D’Agostino and Parker [
48] also showed that a common point in representative climates across Europe is the importance of integrating renewables and energy efficiency measures to reach cost-effective nZEB.
As the architecture of the analysed day-care centre was compact and well orientated, these parameters were not optimized. The window-to-wall ratio (WWR) of the studied building was 30%, which is within the optimal range in a cold climate as shown by Thalfeldt [
49] (optimal WWR = 24−38% depending on orientation).
Based on the definition of a nearly zero-energy building given in the Directive on Energy Performance of Buildings, local production of renewable energy is required to reach the nZEB level.
Figure 4 shows the trendlines of cost-effectiveness calculations of the PV system in the case of the selected building with different combinations of PV systems: PV on a horizontal surface (roof), PV on horizontal surfaces with a battery system, and PV on vertical surfaces. As the installation of PV is a cost-effective measure, in some cases it is necessary to install more PVs to equalize the contractual measures.
Our study showed application of PVs to be the most cost-effective measure to decrease the primary energy use. Congedo et al. [
50] also demonstrated that increasing the number of PVs leads to a reduction of both primary energy usage and global cost. To reach the nZEB level, only the amount of PV electricity that is used in the building can be considered. On a yearly basis, the PV generation used on site could be between 29% [
51] and 75% [
38] of the annual PV electricity production. In the current single-storey case study building, the area for PVs was not a limiting factor. When there is not enough area for PVs, the solution would be to add batteries to extend the lifetime of assets and allow more flexible usage. A combination of PVs with batteries is not a common solution in the nZEB practice. In future studies cost-optimality analysis with different factors such as free area for PVs, orientation, load matching [
52], and a PV system with storage batteries etc. has to be done.
The possible influence on the EPI depends on the combination of the solutions of the BC. The same applies to cost-effectiveness. The results show the influence of insulation measures in the case of the BC if the lowest EPI is reached with the lowest insulation measures in combination with the best building service and technical systems (ventilation with a heat recovery system, very efficient heat source, LED lighting, low plug loads, etc.). The results show that in all cases, installation of PV panels can be considered more cost effective than insulation measures (
Table 7).
Additionally, the cost of a one-step improvement in energy performance was calculated. The different insulation measures were combined to reach different starting EPI levels. The combinations and the selected EPI levels are presented in
Table 8.
The cost of a one-step improvement in insulation measures was calculated considering the change of the ΔNPV and the change of the EPI. The cost of the EPI unit at different EPI levels is presented in
Figure 5. The results show that the most expensive is to improve the roof insulation and the most effective is to improve windows, which means that the gained energy savings compensate more for the investment in the case of windows than in the case of roof insulation.