One of the activities in which ALVA d.o.o. is engaged is energy-efficient renovations or rehabilitations of old buildings.
Most of the old buildings face high heating costs, and the reason for this is the inadequate structure of the roof or façade system by today’s standards. Due to poor insulation, large heat losses occur in such buildings, which in turn affects the heating costs. Therefore, nowadays we recommend energy-efficient renovation of roof systems. In doing so, we first remove the old roofing and deposit it in locations that are specified for this purpose; this is followed by the installation of a new roofing system, which has significantly better insulation and sealing.
The main advantages of energy-efficient renovations are:
- elimination of thermal bridges in place of concrete girders, which covered a very large surface area and had no thermal insulation,
- replacement of existing glazing with new with significantly lower heat losses (lower U-value [W/m2K]) and
- elimination of all leaks from the roof structure, where warm air leaked directly (especially at the points of glazing between plastic and concrete).
Calculation of energy saving in the case of a renovated roof
The comparison of energy saving of the renovated roof will be clearly shown with the help of the calculation below. First, let’s look at all the necessary factors for the calculation:
- U-factor of the existing roof structure – 0.52W/m2K
- U-factor of the new roof structure – 0.38W/m2K
- U-factor of the existing single-layer glazing – 5.0W/m2K
- U-factor of new roof lights replacing existing glazing – 2.7W/m2K
- temperature deficit – 3,500K/day
For the final calculation, we also need the information of the surface area of the old and new roof. The surface area of the old roof totalled 4,247m2 and the surface of the old glazing totalled 353m2. The surface area of the new roof totalled 4,328m2 and the surface area of the new roof lights totalled 272m2.
Calculation of energy savings due to improvements in one year:
- old: 3,500 * 24 * (4,247 * 0.52 + 353 * 5.0) = 333,768kWh
- new: 3,500 * 24 * (4,328 * 0.38 + 272 * 2.7) = 199,839kWh
Thus, heat loss through the roof structure will be reduced by 40% after renovation, without taking into account the improvement of the roof sealing. Assuming a price of €0.12/kWh, this represents a saving of over €12,000 on heating in a one-year period if the building is heated to a temperature between 18 and 20 degrees Celsius.