Simulation Results and Conclusions

6.2Simulation Results and Conclusions

The end energy use for cooling and ventilation is calculated according to EN 15241 and EN 15243 for the comfort temperature according to the adaptive model in EN 15251. There is no energy demand for passive cooling, and the energy demand for the mechanical ventilation during the time of occupancy is 2.9 kWh/m²a for all locations.

Figure 5 shows that the energy demand for different cooling concepts does not differ considerably in Northern climates (Stockholm and Hamburg). The energy demand for mechanical night ventilation increases slightly from Mid-European climates (Stuttgart and Milano) to South-European climates (Rome and Palermo) since this concept reaches its capacity limit and cannot provide thermal comfort in hot summer climates. The energy demand for water based cooling increases significantly from Mid- to South-European climates since the compression chiller has to provide additional cooling. In hot summer climates, the energy demand for active cooling by fan coils is insignificantly higher than for water-based radiant cooling; however, these quick responding cooling concepts do not allow for peak-load shifting.

Figure 5 Useful cooling energy demand: The cooling energy demand increases from North to South. The static comfort model [ISO 7730] result in a higher cooling energy demand than the adaptive comfort model [EN 15251].

Figure 5 End energy demand for five cooling concepts in six locations: The cooling concepts do not necessarily meet the comfort requirements.

Figure 5 indicates clearly the limits of each concept with regard to thermal comfort:

1. 
   Passive cooling and night ventilation concepts cannot provide thermal comfort for typical office buildings in all European climates.
   
2. 
   Water based low-energy cooling can successfully be applied to office buildings in all climate zones and may be operated with additional active cooling.
   
3. 
   A fan coil provides thermal comfort more or less independent from the prevailing weather conditions. Therefore, fan coils might be an acceptable solution for buildings in hot summer regions. In contrast to a VRF system or individual room air-conditioners, the central compression chiller for cold-water supply allows for some load management.
   

Figure 5 Thermal comfort for five cooling concepts in six locations: Passive cooling, air- and water-based low-energy cooling (with compression chiller when needed to meet the cooling load), and active cooling with compression chiller..

Figure 5 does not consider whether a specific cooling concept can provide thermal comfort or not. Furthermore, Figure 5 does not consider the energy demand needed to provide thermal comfort. Figure 5 combines these results and classifies the cooling concepts with regard to both aspects. As some concepts are comparable in terms of energy efficiency and achievement of thermal comfort, the investment costs for these cooling concepts are used as third decision parameter.

Table 5 Application of cooling concepts to European climates: results of a simulation study with a typical office building in different European climate. Cooling concepts are rated according to the thermal comfort achieved during occupancy, the cooling energy used, and the energy efficiency of the system. The specific investment costs are considered as an additional criterion. Legend: (++) preferential concept, (+) good concept, (+/++°) good but comparatively expensive concept, (-) unfavorable concept, (x) not applicable concept to the climate, (ACH) air change rate per hour.

1. 
   In North-European climates, high solar heat gains due to the long-standing sunshine can efficiently dissipated by the cool ambient air. In some situation, mechanical night ventilation is recommended to enhance the night ventilation.
   
2. 
   In Mid-European climates, water-based low-energy cooling makes use of the cool ground in summer. If an additional active cooling is needed, thermo-active building systems (TABS) with a high thermal inertia allow for peak-load shifting.
   
3. 
   In South-European climates, high cooling loads ask for cooling concepts with high cooling capacities. As the temperature difference between ambient heat sinks and the comfort temperature are too low, active cooling is needed to provide thermal comfort.
   

Figure 5 Cooling concepts in six locations: Passive cooling, mechanical night ventilation, water-based low-energy cooling with bore-hole heat exchanger as heat sink (and optional compression chiller when needed to meet the cooling load), and active cooling with compression chiller and cooling tower as heat sink.