The influence of primary measured parameters and electricity consumption in automatic solid fuels-fired boilers on the seasonal space heating energy efficiency

Abstract

Commission Regulation (EU) 2015/1189 of 28 April 2015 implementing Directive 2009/125/EC of the European Parliament and of the Council with regard to Ecodesign requirements for solid fuel boilers presents the way to determine the seasonal space heating energy efficiency (ηs). These requirements are important to develop environmental-friendly sources for space heating. The value of ηs depends on (inter alia) a negative contribution to the ηs by auxiliary electricity consumption. In the current work, the analysis of sensitivity of electricity consumption measurement on ηs has been presented. The analysis includes also other specific measured parameters like water flow rate, water temperature, fuel consumption and higher heating value. Moreover, the impact of specific heat losses on the efficiency of the boiler is discussed and analyzed. The experimental and analytical investigations of 69 boilers (52 coal-fired and 17 biomass-fired) were carried out in the power range of 12–517 kW (nominal) and thermal efficiency of 83.1–96.3%. It was proved that the available relative uncertainty of electricity consumption gauge (i.e. <5%, guaranteed by suppliers) is acceptable to obtain accurate analysis. The seasonal space heating energy efficiency in automatic solid fuels-fired boilers was experimentally determined for 69 units, and the electricity consumption demand was less than 1% of nominal thermal power. The uncertainty of water temperature measurement has the strongest influence on the ηs uncertainty. The absolute uncertainty of temperature measurement at level of 5 °C caused the increase of ηs relative uncertainty to the level higher than 100%. The presented analysis has significant meaning from the practice of the ηs determination and the strategy of uncertainty budget, as well as measurement equipment calibration.