Structural Design of the mCCHP-RES System - Design for Micro-Combined Cooling, Heating and Power Systems - page 149

HDD is useful to calculate the annual heat necessary for a building and the fuel
necessary for heating. Thus, the heating energy demand (kWh) = overall heat loss
coef cient (kW/ o C)

· HDD ( ° C day) · 24 (h/day). The 24 is included to convert

from days to hours.
Cooling degree-days are de ned in the same manner. It is used to evaluate the

annual energy consumption for cooling. For an actively cooled building the base
temperature is the outdoor temperature at which the cooling plant need not run, and
is again related to the casual heat gains to the space (which now add to the cooling
load). In this case cooling degree-days are related to temperature differences above
this base.
The cooling systems are designed to maintain an indoor temperature of 22 ° C

only when the outdoor temperature is below 29 C. When the outdoor temperature

exceeds this limit, the indoor temperature will start to slide at a constant difference
of 7

°

C below the outdoor temperature.
Correlation between indoor and outdoor temperature and the Heating degree-
days and Cooling degree-days, respectively, is shown in Fig. 6 .
Illustrative exercise on the climate data collection, for the city of Galati,
Romania, is shown in Table 2 .

°

3.4.2 Local Energy Sources and Resources

Primary energy sources (meaning energy is created directly from the actual
resource) can be classi ed in two groups: nonrenewable or renewable. Nonre-

newable energy sources are energy extracted from the ground, either in the form of
gas, liquid, or solid. They cannot be replenished, or made again, in a short period of
time. Oil, natural gas, and coal are called fossil fuels because they have been formed
from the organic remains of prehistoric plants and animals.
Renewable energy sources are the energy that comes from a source that is
constantly renewed, and can be replenished naturally in a short period of time.
Examples include solar, wind, biomass, and hydropower. In 2020 at EU level, 20 %
of total electricity used will come from renewable resources. Secondary energy
sources are derived from primary sources. Secondary sources of energy are used to
store, move, and deliver energy in an easily usable form. Examples include elec-
tricity and hydrogen. More than 85 % of the world s current energy needs are met

through fossil fuels whose price is rising due to resource depletion.
Energy sustainability is about

'

finding the balance between a growing economy,
the need for environmental protection, and the social responsibilities in order to
provide an improved quality of life for current and future generations. In short, it is
meeting the needs of the present without compromising the needs of the future.
Energy sustainability can inspire technical innovation with an environmentally
conscious mindset. Renewable resources such as sunlight, wind, and biomass
provide a source of sustainable energy. This includes biofuels like ethanol, which is
created from crops like corn or sugarcane.