**2. Design Aspects**

#### *2.1. Thermal Solar Cooling System Description*

Solar cooling technology uses the solar hot water system as an energy resource for the sorption cycle. The solar absorption cooling system (SACS) under investigation contains two main parts (see Figure 1): the heat medium production and cold medium production. The heat medium production includes solar thermal collectors, a solar tank, auxiliary boiler, two pumps, and a distribution cycle. The cold medium production integrates an absorption chiller, a cooling tower, and two circulating pumps connected, respectively, to the absorber and evaporator. The energy harvested from the incident solar radiation heats the water in a field of the evacuated tube collector (ETC). Then, the hot water flows into a solar tank and is subsequently transported to the absorption chiller through the auxiliary boiler to produce chilled water, which circulates through a conventional distribution system of individual fan coils to deliver cold air to the building. An auxiliary heater is activated if the hot water temperature is not sufficient to drive the chiller. The cooling water dissipates the heat of the absorber and condenser of the chiller through the cooling tower. Figure 1 shows all of the elements that will be taken into account in the simulation and is described, in detail, in the following subsections.

**Figure 1.** Solar absorption cooling system components.

## 2.1.1. Solar Collector

The evacuated tube collector (ETC) is the most popular solar collector in the world and excels in cloudy and cold conditions. The Apricus ETC-30 solar collector has been selected in this study [29]. The ETC is made up of two concentric glass tubes; the interior acts as a collector and the exterior as a cover. The elimination of air between the tubes reduces energy loss. An advantage of flat absorber vacuum tubes, from architectural integration, is that they can be installed on a horizontal or vertical surface, and the tubes can be rotated so that the absorber is at the appropriate inclination [30]. The collector thermal efficiency η*c* is given in Equation (1):

$$
\eta\_c = \eta + a\_1 \frac{\Delta T}{I\_T} - a\_2 \frac{\left(\Delta T\right)^2}{I\_T} \tag{1}
$$

where: η is the optical efficiency, *a*1 and *a*2 present, respectively, loss coefficient, Δ*T* refers to the difference between the average water temperature through solar collector *Tm* and the ambient temperature *Ta* and *IT* is the total radiation incident on the absorber surface, for modeling the evacuated tube collectors (ETCs) in TRNSYS, needs an external file of incidence angle modifier (IAM) both longitudinal and transversal, which can be gained from manufacturer catalog. The performance specifications of the ETC are listed in Table 1 [29].


**Table 1.** Technical specifications of the Apricus evacuated tube collector (ETC)-30 solar collector [29].

## 2.1.2. Solar Tank

The capacity of the hot storage tank is a decisive step in the solar system design and depends on the type of installation of three factors: the installed area of collectors, the operating temperature, and the time difference between the capture and storage. In installations for solar cooling, some authors have used values of 25 to 100 <sup>L</sup>/m<sup>2</sup> of the collector area [21]. For the calculation of the solar tank, we will assume that the hot water is stratified. The stratified storage tank comprises N nodes, the *i* node energy balance is given in Equation (2) [31]:

$$M\_i \mathbb{C}\_P \frac{dT\_i}{dT} = \dot{m}\_s \mathbb{C}\_P (T\_{i-1} - T\_i) - \dot{m}\_L \mathbb{C}\_P (T\_{i+1} - T\_i) - lLA\_i (T\_i - T\_a) \tag{2}$$

where: *Mi* is the fluid mass at the node *i*, *CP* is the fluid specific heat, . *ms* is the mass flow rate from the heat source side, . *mL* is the mass flow rate of the load side, *U* is the overall losses from the solar tank to the environment, *Ai* is the surface transfer area, *Ti* is the node temperature, and *Ta* is the ambient temperature. An overall heat transfer coe fficient for heat loss between the storage tank and the environment of 1.5 kJ/(h·m2·K) will be assumed, close to that used by Barghouti et al. [31].
