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Thanks to solar energy cooling systems it is possible to cool buildings yet avoid any environmental impact. However, whilst solar energy, that is the source of energy they use, is free, given the same amount of cooling power generated, such systems are far more expensive than air-conditioning systems using traditional compression cooling systems. Therefore, if deciding to install a solar energy cooling system, one should carefully analyse the features of the building to be climatised and adopt all the measures needed to reduce energy requirements. The purpose of the text that follows is to recap the principles, strategies and techniques for reducing summer cooling loads. The advice contained in this document covers both buildings still to be designed, for which it is possible to opt for far more innovative approaches and solutions, and existing ones for which there are, anyway, many intervention strategies. In summer cooling systems, the cooling power of the cooling machine is assessed on the grounds of the summer cooling load , that is the summation of all cooling loads, both internal and external, which go to affect the thermal balance between the closed environment and whatever is to be found outside it (not only the external environment as such but also all the neighbouring environments which are not air-conditioned). In summer the amount of heat to be removed depends on a number of factors some of which, like solar radiation incidence, vary depending on the time of the day. It should, however, be borne in mind that at present there are no Italian regulations for calculation models, and, as a result, Italians often make use of procedures developed in the United States (the Ashrae method), which are taken as standard procedures. The factors having the greatest impact on summer cooling loads are the following ones:
Summer energy balance of a building: the cooling system must "remove" excess heat the building cannot dispose of
When airing a room, the air coming from the outside brings sensible heat, as its temperature is higher than ambient temperature, and latent heat, given its vapour content. Basically, we have the sensible and latent heat resulting of the airing of a room and internal sensible and latent heat. The sum of these corresponds to the amount of heat the cooling system must remove. The summer cooling load of a building and, therefore, the energy requirements of the cooling system, may be reduced by adopting "bioclimatic" strategies.
Reduction of heat loads, by foreseeing in the design stage:
Instance of natural protection from the sun ensured by means of suitable external landscaping Reduction of outside temperature by intervening on the external setting in close proximity to the building by means of:  increase of relative air humidity by means of ponds, fountains and vegetation; shading through planting schemes (trees, pergolas, etc.); reduction of external sun-glare (creation of green areas); choice of light-coloured scheme for exterior walls. Protection from sun
Instance of natural protection from the sun ensured by means of suitable external landscaping -> The impact of solar radiation may be reduced by having recourse to different kinds of shading devices: vertical shading devices (for east or west-facing orientations) or horizontal (for south-facing orientations);
External shading devices prove to be the most effective as they prevent solar radiation from beating on clear surfaces. Solar radiation reduction factors for some kinds of screening devices
The thermal gain due to solar radiation on dark vertical surfaces is shown in the figure here below and quantitatively assessed in the graph showing different temperature profiles.
Thermal mass control The thermal inertia of a building has a major impact on the transfer of heat to the inside ambient. A building characterised by a major thermal mass takes longer to heat and allows for the distribution of the heat entering through clear walls over a longer period. As a matter of fact, the structures accumulate direct radiance from the outside and release it to the inside ambient a few hours later. In buildings having high thermal inertia, therefore, cooling system peaks are lower. Ventilation Natural ventilation also depends on the lay-out of buildings. Rooms with a double orientation with at least two walls facing externally but in opposite directions make for easier ventilation. In summer, ventilation is one of the easiest ways to ensure the thermal comfort of occupants of a building. There are two possible strategies. The first one also has a direct impact on the psychological well-being of the occupants, and consists in moving the air inside the building by stirring it with ceiling fans or the like or by getting the air to circulate, possibly thanks to the help of air from the outside (provided this is not warmer than air inside the building). The second approach, directed at cooling the building, consists in insistently airing the rooms provided the external air is cooler than the air to be found inside the building: this way the structures cool thus prolonging occupant comfort also during the hottest hours of the day. In both instances the goal may be achieved either mechanically or by means of an airflow which is conveyed naturally through the building. This entails having:
If buildings are carefully planned taking into account the building design parameters discussed above, the need for summer air-conditioning is drastically reduced. Although some of the techniques discussed can be efficiently applied to buildings still in the design stage, many interventions aimed at the reduction of the summer cooling load may be implemented also in existing buildings at a reasonable cost.
Natural Techniques and Passive Cooling The planning criteria to be adopted are clearly set out in the "Natural and Low Energy Cooling in Buildings" brochure (see bibliography). Passive Cooling techniques may be subdivided into two major groups:
those contributing to remove summer heat from the air-conditioned ambient by conveying it towards other ambients (water, air, ground, etc.).
We have already introduced the key notions pertaining to the first group, while for the second it would be advisable to remember the following solutions which have already been applied and thoroughly tested in low energy consumption buildings: Evaporative cooling. Adiabatic air humidification causes a decrease in air temperature and an increase in relative humidity. Passive Cooling, which - be it direct or indirect - works for sites characterised by low external relative humidity values, is based on this principle.
Ground cooling. Excess summer heat is directly dissipated towards the ground by conduction via walls in direct contact with the ground or indirectly through exchangers located at variable depths and through which thermal-conductive fluids run (as a rule water or air). Reduction of summer cooling loads in existing buildings Reduction of summer cooling loads in existing buildings In existing buildings it is possible to reduce summer cooling loads, both as peak power as well as energy consumption, by:
In the table below are reported in a synthetic way the possible interventions that can be undertaken. Certain measures imply no costs whereas others involve limited costs that can be repaid in few years. The interventions that are more costly are related to the building envelope (for example the application of external shading devices and the insulation of perimeter walls and roof, etc.). A correct planning of these interventions within standard maintenance practices can reduce significantly the costs. List of possible interventions to reduce summer thermal loads in existing buildings
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Radiant Cooling 
