How to combat the risk of overheating in low energy buildings

ES-SO/TOLDO Magazine – 

The European Parliament voted overwhelmingly on Tuesday 4 October 2016 to ratify the Paris climate agreement, a move that means the urgency of meeting the targets is becoming a reality sooner than expected. Buildings in Europe account for approximately 40% of total energy consumption and 36% of CO2 emissions. Currently, around 35% of buildings in the EU are more than 50 years old. By improving the energy efficiency of buildings, total EU energy consumption could be reduced by 6% and CO2 emissions reduced by approximately 5%.

ES-SO strongly supports the Energy Performance of Buildings Directive (EPBD), which since its new role in 2010 has given Member States a powerful means to improve the energy efficiency of their buildings. The EU Commission announced on 30 November 2016 its Clean Energy Winter Package, among which are measures that have an impact on the review of European energy-related directives such as EPBD. ES-SO wants to emphasize a point of attention to strengthen the awareness of Member States on a growing problem that is not sufficiently addressed in the current EPBD.

Overheating, a problem so new and so old
Since 2008, multiple reports have emerged in northern, central and eastern Europe showing that low-energy buildings are sensitive to overheating. The reports refer mainly to new homes. Overheating is an unexpected side effect due to changes in construction methods to achieve energy efficiency in homes: high levels of insulation, airtightness, maximization of free solar gains to reduce heat losses and the energy need for the heating.

 

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Overheating not only has the effect of increased thermal discomfort and energy use, but can also cause serious health problems, especially for more sensitive population groups. Scientific reports emphasize that due to global climate change, the risk of overheating will increase, not only in summer, but also in transition seasons. They also predict that the risk of active cooling in developed countries will explode by as much as 150% by 2050, raising the price of energy and increasing energy problems.

According to reports from the IEA-International Energy Agency, published in 2013, energy consumption for cooling will increase by 150% in 2050 in Europe (increased risk of peak power problems). Thus it is understood that highly insulated windows, dynamic solar control and natural lighting are crucial to transforming into zero energy buildings.

 

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Indoor air quality, thermal comfort and natural light were analyzed in the 2015 BPIE report, which among other things said: » Even today, between 50 and 125 million Europeans suffer from cold in winter (bpie.eu/fuel_poverty .html). However, there is an increasing risk of overheating that also needs to be addressed. "Therefore, thermal comfort should be recognized in building regulations and the use of simple and efficient measures, and shading, solar protective glazing and ventilation cooling should be encouraged."

What the Energy Efficiency in Buildings Directive (EPBD) 2010 says about overheating
«Energy performance must be calculated on the basis of thermal characteristics, but also on other factors that play an increasingly important role, such as passive heating and cooling elements, shading, adequate natural light.
Priority should be given to strategies that improve the thermal performance of buildings during the summer period. To that end, it should focus on measures that prevent overheating, such as shading and sufficient thermal capacity in the building construction, and further development and application of passive cooling techniques; The methodology will be established at least taking into account the following aspects, such as passive solar systems and sun protection.

ES-SO Comments and Recommendations
The European reports cited above clearly demonstrate that the current "considerations" in the EPBD are not sufficiently directed at Member States to take into account the risk of overheating. As new buildings represent only 1-1.5% of the annual building stock, member states will increasingly focus on renovating building stock to make them energy efficient, following the same measures as increasing insulation and the tightness of the building envelope. Therefore, the risk of overheating will also occur in renovated homes.

The risk of overheating in newly constructed and renovated buildings will shift the energy needed for heating into more energy needed for cooling. Reducing the need for cooling will be as important as the need for heating. Therefore, an explicit article on overheating should be included in the EPBD revision.
For the ES-SO a series of revisions must be adopted:

• Universally accepted definition of overheating in homes, and member states should develop in the national building code robust national thresholds to address overheating in new construction and renovations for use by planners, designers, builders and authorities.
• In low energy buildings, the cooling load should be considered as important as the heating load and this for both summer and winter conditions.
• Overheating risk assessment in new and renovated buildings/dwellings will be carried out not only at the overall building level but also at the individual room level for an as-built situation.
• As energy efficiency is the number one priority (the cheapest energy is that which is not used), the building envelope (building shell) must be considered first (before the use of mechanical systems).
• In the transparent part of the building envelope, measures must be included to prevent overheating, among which is dynamic (intelligent) shading of the glazing. Passive measures such as shading must be prioritized before active cooling can be applied.

The EPBD should facilitate and recognize innovation: actual validated energy performance data from energy efficiency measures should be met rather than predetermined (conservative) values.

Windows in low energy buildings will be based on their total energy balance, including dynamic shading
Among the various components of the building, windows are a static element, while climatic conditions vary continuously. Because people now spend almost 90% of their day indoors, they expect to be comfortable indoors all year round.
The evaluation of the energy performance of the transparent part of the building envelope in national cost-optimal calculation methods is simply based on the insulation properties, that is, the thermal transmittance (u-value), while it is also necessary to consider the heat gains (g-value). For this reason, the energy performance of windows is best evaluated using "energy balance", which is an equation that calculates heat losses and heat gains based on climatic conditions.

 

 

Windows are made more energy efficient by using smart shading to manage your energy balance. In the summer season, shading reduces or eliminates thermal discomfort caused by overheating and therefore reduces the need for active cooling by controlling the amount of solar energy entering through the windows. In the heating season, smart shading, operated by occupants and automated controls, enables the collection of free energy sources through the windows. In both seasons, it provides additional insulation to the transparent parts of the building envelope, helping to reduce heat loss in winter and limiting heat gain in summer.

Solar shading will also manage and control the entry of daylight to reduce glare and thus improve visual comfort, thus creating better indoor environments.

Recognition of solar shadow and its CO2 footprint
Shading is a cost-effective energy-saving technology, offering energy savings of up to 60 times its CO2 footprint over its 20-year lifespan. For a 50:50 energy end-use split between space heating and cooling, the potential energy savings that can be accrued from dynamic shading: 22% heating and cooling energy use savings of 59Mtoe/a and a Reduction of carbon emissions from 22% equivalent to a saving of 137.5 MtCO2/a (if energy split 70:30: 19% savings and CO2 reduction).
Innovation must be recognized in the national EPB regulation. ES-SO has established a database of validated solar shading energy performance (iv).

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