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Saving energy is one of the main priorities in the building sector. In countries with temperate climates, heating represents an important share of the total energy use of buildings. It is well known that central heating systems operate most of the time at partial capacity during the heating season. Moreover, the elements of the central heating system are usually over dimensioned. In this paper, the outdoor dry bulb design temperatures for heating are analysed across Hungary. Using outdoor dry bulb temperature data from the last 50 years, cumulative frequency graphs were built and new design values are proposed at 99% and 99.5% confidence levels. For two typical residential buildings, a single family house and a block of flats, the consequences of the higher outdoor design temperature were analysed from the point of view of investment costs, seasonal boiler efficiency and intermittent operation. The investment cost decreased by approximately 10% for the large buildings, the seasonal efficiency of traditional boilers increased by approximately 0.6%, the seasonal efficiency of condensing boilers decreased by approximately 1.2%, and the energy savings from intermittent operation decreased by 2–6%. [ABSTRACT FROM AUTHOR]

In all European countries the energy and building related legislature stand for energy refurbishment of existing building stock. Depending on the economical situation of countries there are different national programs that help owners to invest in energy related refurbishments of their houses or flats. The financial support is given only in case of a certain payback time, which should be obtained by the proposed project. The payback time for heating related investments in Hungary is calculated based on the theoretical degree day curve, which can lead to inaccurate results. Thus in this paper a long-term analysis of heating degree day, done for Debrecen (the second largest city of Hungary), is presented. We focused our analysis on residential buildings. It was found that the degree day has important variations during the analysed decades, which can lead to deviations of energy consumption up to 15–18%. Furthermore, taking into account the heat island effects in Debrecen, it was proven that differences of about 22% can be obtained between real degree day values in different zones of the city. The interrelation between specific heat gains and balance point temperature, respectively the effects of glazed area of the facades on the balance point temperature was discussed. It was found that for buildings with similar thermal characteristics of the envelope and the same values of specific heat gains, the balance point temperature can be even double for a detached house compared with a block of flats. [ABSTRACT FROM AUTHOR]