About Savings Calculator

About Savings Calculator

This calculator for energy, CO2 and cost savings has been developed based on data from the REECL Programme initial findings of the prevailing condition of the building stock in Bulgaria and most common types of home improvement measures that have been implemented within the framework of the REECL Facility over 2005 and 2010 in compliance with the REECL eligibility criteria and local legislation.

In addition, the calculation model draws on specific data for Bulgaria provided in CO2 emissions baseline documents and the EN 832 simplified calculation algorithm for determining of energy performance of buildings.
This calculator is based on a calculation model structuring the building stock in a simplified manner assuming that it has been built to the prevailing building standards of the time of construction. Heat losses/gains due to prevailing winds, infiltration, air heat recovery, solar gains, and other internal gains/losses after the implementation of the home improvement project have been assumed to deviate slightly from before, hence having a minor impact on savings.

Different climatic conditions in Bulgaria have been summed up in one aggregate climatic zone, based on appropriate weights given to different zones in accordance with sub-projects geographical distribution. The calculated degree days factor for the aggregate climatic zone is 2739 degree days [Kd/a] based on the following split by zones:

Climatic Zone Degree days [Kd/a] Weight
Zone 1 2400 10%
Zone 2 2800 7%
Zone 3 2600 2%
Zone 4 2700 5%
Zone 5 2300 3%
Zone 6 2400 10%
Zone 7 2900 60%
Zone 8 2300 2%
Zone 9 2100 1%

The average U-value of the existing building stock has been determined by aggregating two residential building age groups, which represent over 95% of the dwellings benefiting from the REECL Facility. The parameters of these two groups differ due to changes in respective building regulations and standard applicable at the time of construction. For buildings erected before 1977 the prevailing U-values for walls are 1.8 W/m²K, for roofs – 1.4 W/m²K and for floors 1.4 W/m²K while for buildings built between 1977 and 1994 the respective prevailing U-values are 1.4 W/m²K, 1.2 W/m²K and 1.3 W/m²K.

The REECL Programme has assumed that insulation projects will improve the U-value of the building envelope by 1 W/m²K. It should be noted that this value is only roughly established and is estimated without extensive data investigation. For an exact determination of saving potentials through thermal insulation a detailed building typology would be necessary.

Based on studies done by local window manufacturers, the average age of existing glazing is over thirty years with most typical thermal characteristics in terms of U-value in the range of 3.5 to 4.5 W/m²K. The REECL Programme has assumed 4 W/m²K as a typical U-value of existing glazing that is being replaced with more efficient one under the REECL program, hence the average glazing project achieving improvement of U-value by 2 W/m²K.
Insulation and glazing home improvement projects are assumed to be implemented in dwellings that use electricity for resistance heating and hot water.

Gas boiler, biomass boiler, solar water heating, and photovoltaic projects are assumed to be undertaken as fuel-switching improvements from electricity from the grid to cheaper fuels such as gas, biomass or/and solar energy.
The benefits of improved building envelope on cooling demand has not been considered and factored into the energy and CO2 calculations.

Efficient residential heat pump system seasonal COP is estimated to be equal to 2.7 for the Bulgaria climatic conditions.

The overall efficiency of a resistance electric heating system in Bulgaria is taken at 32%, while a typical residential gas-fired or biomass fired heating system is assumed to operate at 60% load of its installed capacity and seasonal efficiency of 80% and 64% respectively.

According to the Joint Research Centre of the European Commission, the yearly sum of global irradiance incident on optimally-inclined south-oriented photovoltaic modules/solar panels for Bulgaria ranges between 1300-1700 kWh/m2. However, it is estimated that in a typical Bulgarian home one square meter of solar collector surface of a solar water heating system usually generates on the average around 600 kWh per year while the yearly sum of solar electricity generated by 1 kWp PV system is around 1100 kWh/kWp.

For balanced ventilation systems with heat recovery, the amount of recovered energy varies according to the time of operation, outside conditions, heat exchanger heat recovery rate and its fan electric consumption. It is assumed that in a typical Bulgarian home, situated in an aggregated climatic zone with 2739 degree days, occupancy levels of 1 to 3 occupants, supplied with 40-120 m3/h of fresh air at 8 – 12 hours a day evenly distributed throughout the year, an adequate balanced ventilation system will be fitted with a heat exchanger with capacity between 1 – 3 kW, driven by an electric fan with rated capacity between 30 – 100W, and heat recovery rate at nominal conditions and air-flow > 50%. It is estimated that such a balanced ventilation system with heat recovery will recuperate on the average around 500 kWh per year per 1 kW of installed heat exchanger capacity.

All energy saving achieved are savings in terms of kWh electricity equivalents.
According to Appendix 3 of Ordinance 18 dated 12 November 2004 issued by the Ministry of Energy and Energy Resources and the Ministry for Regional Development and
Planning, the use of 1 kWh of energy from different sources in Bulgaria generates a carbon footprint as follows: biomass – 25 gCO2 and natural gas – 247 gCO2.
The electricity carbon emission factor as per the latest approved baseline for Bulgaria is 683 gCO2/kWh. The cost estimates for implementation of energy efficiency home improvements and energy prices used in the calculation model are correct at the time of publishing this calculator but may change over time.