Electric Demand

Based on energy performance of electric equipments in the residential sector [7] performed by the Portuguese ministry of economy, two consumption and energy performance groups were defined: the business as usually (BAU) group that represents the appliances used by a typical family that neglects the energy efficiency issues and the BEST group that represents a family that takes care about the efficiency of their electric appliances (all of them are class A), and their responsible use.

Table 2. Yearly electricity demand for different domestic appliances [7].

Device

BAU

(kWh/yr)

Energy

Class

BEST

(kWh/yr)

Energy

Class

Fridge

380

C

140

A

Freezer

625

D

225

A

Dishwasher

396

G

264

A

Laundry

240

G

180

A

Cooking

306

250

PCs

200

95

Audiovisual (ST)

335

220

Lighting

500

160

Total

2982

1534

The most efficient domestic laundry and dishwasher machines currently the market can receive preheated water from outside sources. Since 80-90% of the energy consumption of a washing machine results from heating the water with an electric resistance, there are considerable savings
when using a more efficient, preferably renewable, energy source to heat the water. In this study the washing machines used in the BEST group are replaced by machines fed with hot water from the solar thermal system. This represents savings around 80% (80% less than in Table 2) in the direct electricity needs on the washing machines. A standard laundry washing program requires temperatures around 40aC, for dishwashing, 40-50°C.