Residential summer comfort: passive solutions and air conditioning
Summer comfort is becoming more and more of a concern for house designers and their residents. New buildings, often designed to limit heat inputs through passive solutions, reduce heating requirements. But the problem of cooling persists. Some ways to remedy this follow.
If the most obvious way to cool down a dwelling is to prevent the heat from entering it, in fact it is a little more complicated. Indeed, many recent constructions do not have an effective protection against heat, because often they have large windows or do not have blinds or shutters. Efforts are nevertheless made on this point and make it possible to implement passive solutions during the design. The orientation of the house, in particular, is an important factor to take into account, especially for the distribution of openings. The design of the glazed surfaces must also be carefully considered, because it is through them that 2/3rd of the heat made in summer comes in, as well as their protection in order to avoid summer overheating, limit winter losses, ensure good ventilation and provide sufficient light to limit artificial lighting. Exterior guards appear to be the most effective: roller shutters, swing shutters, sun shades, blinds or even solar shading *.
In a building with high thermal insulation, limiting internal heat inputs is not simple: they must be evacuated. A simple way to lower the temperature inside the dwelling in summer is night-time over-ventilation. By opening the windows at night, the dynamic modelling shows that with a flow of 3 vol./h summer comfort is perfectly manageable and avoids periods of overheating which are too long **. These systems can be automated.
Think ventilation before air conditioning
If all these measures are not sufficient to provide a good level of summer comfort for the occupants of the dwelling, active systems must be provided. Starting with ventilation, before thinking about air conditioning. The solutions?
- Single flow type (flow modulated as a function of the external and internal moisture content) in temperate regions and of double flow type with energy recovery in colder regions. An old solution, the Provençal well can also lower the internal temperature by a few degrees: a duct buried at two meters deep brings renewal air into the house. It is refreshed by its passage in the ground, cooler than the outside air.
On the regulatory side, if the RT 2012 does not prohibit air conditioning as long as the construction is below a reference level known as Cep (consommation conventionnelle d'énergie primaire) limiting the 5 uses of heating, air conditioning, hot water, lighting and electrical auxiliaries, it penalizes their use for housing in most regions. The energy consumption required for the air conditioning of buildings is now taken into account in the regulatory calculation.
Heat pumps have the wind in their sails
Cold production systems should then be carefully chosen. By combining them with solar protection, good aeration and some common-sense practices, it is possible to limit their power and their duration of use. Examples of suitable systems for home use include heated floor-cooling solutions coupled with reversible air / water or air / air heat pump (PAC) heaters. This system of production of warmth in winter and cooling in summer is particularly virtuous because it uses on average one third of electricity and two thirds of renewable energy (air, water, soil ...) and has great performance coefficients. "Direct expansion" air conditioning systems use the refrigerant directly to evacuate calories to the outside and to transmit them inside the rooms to be air-conditioned. They can power wall-type transmitters or consoles. Alternatively: air-conditioning systems. The external production unit is then associated with emitters of the duct type and implement an air distribution via motorised registers.
According to the market figures published in 2016 by Uniclima (the Union of Thermal, Air and Refrigeration Industries), appliances incorporating a reversible PAC (=Heat Pump) are increasingly popular for new housing. Eurovent Certita Certification attests to the performance of these materials through various certification programmes: air conditioners, chilled water production units and residential air treatment plants.
Call on a professional
The installation of these various materials must of course be entrusted to professionals qualified to work on refrigeration circuits. The "Rage" documents published by the CSTB bring together the professional recommendations for each solution. All these elements make it possible to cope with certain technical difficulties that may arise: condensation risk for heating-cooling floors, condensate evacuation, choice of refrigerant or taking account of acoustics.
Good design will also ensure effective upkeep and maintenance.
Air-conditioning systems and reverse heat pumps with a cooling capacity greater than 12 kW are subject to an inspection obligation carried out at least once every five years at the initiative of the owner or the building's condominium syndicate. In addition, a leak test of the refrigeration circuit must be carried out every year. To reduce the leakage of air conditioners and thus reduce greenhouse gas emissions, it can be included as part of a preventive maintenance contract signed with the installer of the equipment.
* « warm outside, cool indoors – Summer comfort », Ademe, January 2011.
** « T 18 Technical Information », Mutuelle des Architectes Français assurance, February 2013.