## 4 Active Systems
### Hot Water Production and Swimming Pools Heating
#### 4.2.3 Proposed Passive and Active Systems for Hot Water Production and Swimming Pools Heating
It consists of a complex and extensive set of relationships, due to the involvement of a large amount of thermophysical and geometric parameters regarding the specifications of the employed solar collectors and thermal storage tank models. The ultimate target of the dimensioning procedure is to ensure an annual penetration percentage at least 50% for the thermal energy produced or stored by the solar collectors versus the total annual thermal energy demand for both hot water production and swimming pools heating, ensuring, at the same time, the project's economic feasibility. The operation algorithm of the proposed solar-combi systems is analyzed in the following steps:  
* For the current calculation hourly time step i, the water temperature T\({}_{\text{s}}\) (i-1) in each thermal storage tank from the previous time step i-1 is compared to the outlet temperature T\({}_{\text{out}}\) of the corresponding solar collectors' field. If T\({}_{\text{out}}>\) T\({}_{\text{s}}\)(i-1), then the thermal energy produced by the solar collectors can be stored in the thermal storage tank. In a different case, the provided thermal energy by the solar collectors' field cannot be exploited and is rejected. Practically, there is no working medium's flow in the solar collectors' primary hydraulic loop. * At the same time, any potential thermal power demand Q\({}_{\text{d}}\) must be covered by thermal power stored \(\dot{\text{Q}}_{\text{st}}\) in the thermal storage tank. In case of not enough stored thermal power, the thermal power demand shortage: \(\dot{\text{Q}}_{\text{b}}=\dot{\text{Q}}_{\text{d}}-\dot{\text{Q}}_{\text{st}}\) is undertaken by the biomass heater. Figure 14: Annual time series of (**a**) the swimming pools new heating loads, after the application of the proposed passive measure and (**b**) the total thermal power stored from the solar collectors in the thermal tanks. * Taking into account the above thermal power flows from and to the thermal storage tank (\(\bar{\mathrm{Q}}_{\mathrm{d}},\bar{\mathrm{Q}}_{\mathrm{st}},\bar{\mathrm{Q}}_{ \mathrm{b}}\)) and the heat losses from the tank to the ambient, the new water temperature in the tank, at the end of the current time step, is calculated. The execution of the dimensioning optimization methodology concluded to the configuration of four independent solar collectors' fields, each one of them consisting of 32 collectors and connected to a different thermal storage tank. In total, 128 solar collectors will be installed in all four solar-combi systems. The connectivity of each solar collectors' field is depicted in Figure 15a, formulated by eight parallel groups, with four collectors connected in series in each one of them. The siting of the overall solar collector field is presented in Figure 15b. The inclination angle versus the horizontal level is selected at 45\({}^{\circ}\), which maximizes the thermal energy production for the whole annual period, as calculated by iterative calculations of the thermal power production from one solar collector for different inclination angles. The concluded dimensioning led to the calculation of the annual time series of the thermal power stored from the solar collectors to the thermal tanks, in total, depicted in Figure 14b. The results from the calculation of the final thermal energy needs, the consumed energy resources (oil, electricity and biomass) and the corresponding primary energy (PE) consumption on annual basis are summarized in Table 4, for the coverage of the hot water production (HWP) demand and the swimming pools' heating (SPH) loads both in the existing and the proposed operation. Additionally, the annual primary energy saving (PES) is also presented. Primary energy consumption is calculated versus the consumed energy resources by introducing the following factors defined in the Greek Directive on Buildings' Energy Performance [53]: