ELSEVIER Energy and Buildings 26 ( 1997) 215-221 Active solar space heating of residential buildings in northern Hellas- a case study A. Argiriou *, N. Klitsikas, C.A. Balaras, D.N. Asimakopoulos National Observatory of Athens, Znstitute of Meteorology and Physics of the Atmospheric Environment, Group Energy Conservation, P.O. Box 20048, GR-118 10 Athens, Greece Received 28 October 1996; revised 15 November 1996; accepted 25 November 1996 Abstract - The final energy consumption in Hellenic residential and tertiary sector buildings represents almost one-third of the total energy budget. From this, space and water heating represents 70% of the total. Space heating and electricity generation in Hellas are based on fossil fuels, with a serious environmental impact. Despite the popularity of simple solar domestic hot water systems, active solar space heating remains, for various reasons, marginal. The aim of this paper is to demonstrate the potential of combined active space and domestic hot water solar systems, both technically and economically. An assessment of the reduction of the environmental impact is also included. The results confirm that modern solar technology constitutes a viable option for energy retrofit in the building sector in Hellas. 0 1997 Elsevier Science S.A. Keywords: Active solar heating; Space heating; Energy retrofit - 1. Introduction In all developed countries, energy consumption in the building sector represents a major part of the total energy budget. In the European Union this is approximately 40%. The final energy consumption in Hellenic residential and tertiary sector buildings represents 29.8% of the total energy budget, according to 1992 data [ 11. The average annual increase during the period of 1977-1992, was about 4%. At the same time, the energy consumptionin industry remained almost the same, with a slight decrease, while there was a significant increase of energy consumption in transportation. In 1992, the final energy consumption in the building sector (residential and tertiary) was 4.18 Mtoe (Mega tonne oil equivalent), of which 60% was liquid fuels, 38.7% electric energy, and the remainder natural gas and solid fuels. The energy breakdown in Hellenic residential buildings from 1990, is shown in Fig. 1 [ 1 ] . Space and water heating rep- resents 70% of the total. Spaceheating is primarily covered by central thermal sys- tems that use diesel as a fuel, while hot water is usually produced by electric resistance boilers, although small resi- dential type solar collectors have alsobecome popular. Over the last few years, the useof air conditioners for both space heating and cooling purposes, has increased both in residen- * Corresponding author. 0378.7788/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved PZZSO378-7788(97)00003-O limlwc 60% Fig. 1. Energy consumption breakdown in Hellenic residential buildings. tial and other types of buildings. Electric energy consumption in Hellas, hassignificantly increased, primarily as a result of the use of either air conditioners or other electric heating systems. The national power company is periodically facing tremendous problemsin satisfying the demand for electricity, asa result of the useof air conditioners. Sometimes, the peak demand approaches the maximum generating ca.pacityon the national grid. For example, in January and February, 1996, as a result of an unseasonably cold period throughout the country, the electrical energy consumption incre:ased by 24% and 29%, respectively, over the corresponding period in 1995. Consequently, the power company was forced to import electricity from neighboring countries in order to sat- isfy the demand or it would have had to face a black-out situation. At the same time, the company is in the lprocess of constructing new power plants, in order to increase its gen-