Outdoor dry bulb heating design temperatures for Hungary

• New outdoor dry bulb design temperatures were determined for Hungary.
• Investment cost analysis of central heating systems was done for new design temperatures.
• Effects of new design temperatures on the boilers's seasonal efficiency were analysed.
• Effects of new design temperatures on the energy saving by intermittent heating were studied.

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%.