Structural Design of the mCCHP-RES System - Design for Micro-Combined Cooling, Heating and Power Systems - page 178

maintained. In addition to temperature, there are other environmental conditions
that should also be taken into account when planning a thermographic building
survey. External inspections for example, may be in

uenced by radiation emissions

and re ections from adjacent buildings or a cold clear sky, and even more signif-

icantly the heating effect that the Sun may have on surface.
For calculation of the overall heat transfer coef cient (U-value) in building

envelopes with infrared thermography the following conditions must be met [ 14 ]:

The minimum test duration is 72 h if the temperature is stable around the ow

￿

meter, and to be sure that a suf cient heat flow is present.

The minimum difference between temperatures has to be of the order of
10

￿

- 15 ° C.

For at least the 24 h before the beginning of the infrared audit and during its
execution the following relationship must be respected:

￿

ðh i h e Þ [ 3 = U ð 34 Þ

where: U is the value (W/m 2 K) of the element being considered.
However,

D h ¼ ðh i h e Þ

has to be at least 5 ° C.

For at least the 12 h before the beginning of the infrared audit and anyway
during its execution, the analyzed building surfaces should not be exposed to
direct solar radiation.

￿

￿ During the thermographic analysis the exterior and the interior temperature must

not vary by more than

± ° ± °

5 C and 2 C, respectively.

5.1.2 Analytical Estimation Based on the Global Coefficient
of Building ' s Thermal Isolation

For heating, the annual consumption can be calculated with the formula:

024 G

V
g heating HDD

¼ : ð = Þ ð Þ

Q 0 kWh y 35

where:
ʷ heating

ef ciency of the heating device;

heated volume of the building (m 3 );

V

HDD annual heating degree-days;

G global coef s thermal isolation (which represents the

sum of heat losses resulting from direct transmission through the area of
the building

cient of the building '

K between
the interior and the exterior, related to the volume of the building, to
which the heat

' s envelope, for a difference in temperature of 1 °

losses due to refreshing the interior air and to the