Energy Performance of Buildings: A Comparison of Standard Assessment Methods - Nearly Zero Energy Building Refurbishment - page 177

European building stock: the uniformity of results seems to be affected by
uncertainties since the standards (such as EN ISO 13790 and UNI/TS 11300) leave
many possibilities for the definition of input data and assessment methodologies.
This is a critical aspect if an asset calculation method is expected to give a general
indicator, useful to compare energy performance of different buildings.

3 Calculation Method (EN ISO 13790 and UNI/TS 11300)

The UNI EN ISO 13790 standard (Energy performance of buildings—Calculation
of energy use for spaces—heating and cooling) provides a series of calculation
methods for the design and evaluation of thermal and energy performances of
buildings and can be used for the following purposes:

1. evaluating compliance with regulations and laws;
2. comparing the energy performance of various design alternatives for a building;
3. energy certification of buildings and
4. assessing the effect of possible refurbishment measures on existing buildings.

There are two basic types of methods:
• quasi-steady-state methods, calculating the heat balance over one month or the
whole season, taking into account dynamic effects by the simplified determi-
nation of a gain utilization factor;
• dynamic methods, calculating the heat balance over 1 h and taking into account
the heat stored and released from the mass of the building in a detailed way.

The mandatory method has to be defined at national level.
In Italy, the assessment method adopted by UNI/TS 11300 is a quasi-steady-
state balance on a monthly basis, and the length of the heating season is provided
by the Italian law according to the climatic zone. As prescribed by the European
standard, for each calculation step, the building energy need for space heating, Q H,
nd , in conditions of continuous heating, is calculated by
Q H ; nd ¼ Q H ; ht h H ; gn Q H ; gn

ð 1 Þ

where

• Q H,nd is the building energy need for continuous heating, assumed to be greater
than or equal to 0 [MJ];
• Q H,ht is the total heat transfer for the heating mode [MJ];
• Q H,gn gives the total heat gains for the heating mode [MJ];
• g H,gn is the dimensionless gain utilization factor
and the total heat transfer, Q H,ht , is given by:

Q ht ¼ Q tr þ Q ve ð 2 Þ