Experimental Setup

The CSDHWS works in a single phase thermosyphon mode, consisted of a single glazed flat-plate collector and a horizontal storage tank equipped with a resistor located immediately above the collector, as shown in Fig. 1. The system can be easily accommodated on the rooftop and integrated with existing piping (see Fig. 2). An additional electric showerhead, with continuously adjustable power, provides extra heat input. Therefore, auxiliary energy can be added to the system either in the storage tank or in the electric showerhead, but in the present analysis only the electric showerhead was used. The system is also equipped with a thermostatic mixing valve at the storage tank outlet pipe, which prevents scalding. The compact system is only used for showering purposes. Table 1 shows the technical characteristics of the system. The solar collector was tested according to European flat-plate collector test standards (Muller-Steinhagen, 2002).

Table 1. Technical characteristics of the compact solar hot-water system

Flate-plate Collector

Aperture area

1.36 m2

Absorber area

1.32 m2


Single glass cover



Absorber coating

Black organic paint soluble in water with total absorptance equal to 0,95.

Risers and headers


Insulation thickness

50 mm glass wool (20kg/m3)


Solares LTDA, Brazil

Storage tank


100 l

Insulation thickness

50 mm glass wool (20kg/m3)

Heater Power

1.5 kW (disabled)

Electric Showerhead


0-6.8 kW


Botega, Brazil

Thermostatic Mixing Valve

Mixing Range



OSTACO AG, Switzerland





10 mm polyethylene

Figure 1. Compact solar hot-water system scheme

hundred consumers from a housing unit for low-income families (monthly income from US$250.00 to US$500.00) were interviewed using a questionnaire based on a model suggested by Vine et al. (1986). Ninety families were selected according to the similarity with a standard hot-water consumption profile and sixty of them received a CSDHWS. The groups are named as follows:

(i) Group A — sixty consumers with CSDHWSs.

(ii) Group B — thirty consumers without CSDHWSs.

Fig. 2 shows the systems installed on the rooftops. The buildings were financed by Caixa Economica Federal (Federal Brazilian Savings Bank) under a leasing contract.

Figure 2. Compact solar domestic hot-water systems on the roof of the buildings

The power of the electric showerheads of all ninety consumers was averaged over five minute intervals. The consumers without the CSDWHS were used to characterize the typical energy consumption profile of a group of low-income consumers. The comparison between the two groups was used to estimate the solar fraction provided by the solar systems.