To achieve thermal comfort and energy  performance requirements, the above mentioned variables shall be identified and measured. In  case of conservation requirements, these variables cannot be quantified but  they shall be qualified. Hence, critical discussion of this topic shall be done  with respect to all of the previous variables in addition to the context issues that include climate conditions, governmental laws, and society awareness.
This discussion aims at creating appropriate guidelines  that can maintain the cultural heritage building in its context and to adapt the climate change requirements at the same time.
Due to  the importance of this topic, ICOMOS Burra Charter stipulated the concept which  called “Balance of Energy and Culture”. This concept expresses the physical  qualities of comfort of behaviour. It aims at making the historic buildings as a place for dynamic living \citep{troi2014energy}.
Following section discuss that topic considering case of EU comparing to case of Egypt.

Research  Problems of the PhD topic

The world’s global dependency on energy has been increasing at an alarming rate. Since 1971 to 2014, world energy consumption increased by 92% (according to International Energy Agency (IEA)). In 2009, the United Nations Environment Program (UNEP) referred that building sector contributes of more than 30% of the global greenhouse gas emissions and 40% of total world energy consumption \citep{martinez2016energy}\citep{M_Nassief_2014}. Cooling and heating buildings are the most consumers of building energy, meanwhile air conditioning consumes 44% of a building’s energy consumption \citep{Sharmin_2014}.
In Europe, building sector is responsible for consuming 40% of the total energy consumption and 10% of the total CO2 emissions. Whereas new buildings form only about 1% of the housing stock annually, so it is believed that more than 80% of the existing buildings will still exist in 2020. Therefore, the existing housing stock must be renovated in terms of energy efficiency to reduce the building energy consumption. That’s why the European Union decided to solicit enhancement of the energy performance of the old building stock, as a high priority in its research agenda \citep{Serghides_2015}.
In 2012, the energy consumption in Europe was estimated by  1.1 GTOE (Gigatons of Oil Equivalent); \citep{Delmastro_2015}, almost 40% of that consumption is allocated in the residential sector and it is also responsible of up to 40 % of the total CO2 emissions \citep{Kme_kov__2015}.  The following figure (11) shows that 40% of the existing residential buildings in EU have been  constructed before the 1960. Thus, dealing with energy efficiency in  these buildings requires great attention to the cultural heritage values.