Efficient Ventilation, what system is the best for Nearly Zero Energy Buildings?

The popularization of Nearly Zero Energy Buildings and the trend for the market to adapt to their conditions largely stems from mandatory regulations. Since 2018, all public buildings in Spain must comply with the nZEB construction regulations - which in English means nearly Zero Energy Building - and starting in 2020, all private construction projects will also have to adhere to these conditions. This has led to a better understanding of the need for air renewal and the achievement of efficient ventilation. Moreover, much of the success of a low or nearly non-polluting building depends on its ventilation system.

The regulations for Nearly Zero Energy Buildings are practically the same at the European level since the guidelines are community-based. Specifically, Spain is among the countries with the least experience in this matter, which means that mandatory compliance will drive improvements in this type of construction. Furthermore, it presents significant challenges and opportunities for nearly zero energy architecture.

However, in Spain, the regulations have already been adapted to many of these points, such as the comprehensive review that the Technical Building Code underwent to introduce changes in the Basic Document HS3, which specifies the necessary health standards. This includes the requirement for efficient ventilation systems in all buildings constructed within national territory. At the very least, they must have a hybrid ventilation system.

The minimum allowed by the regulation permits the use of hybrid ventilation systems, which mainly mechanically extract stale air, while the intake is usually done through grilles or natural means. This hybrid ventilation adapts to the environment and is modified according to actual needs, alternating between mechanical or natural systems.

Energy efficiency, in any case, must go a step further and requires more advanced systems, especially to comply with the Nearly Zero Energy Building regulations. Above all, because current newly constructed buildings are built with highly airtight materials and tightness is prioritized. Everything points towards energy efficiency, and it is essential to adapt in various ways.

With high airtightness and thermal insulation, efficient ventilation is needed since air does not penetrate through joints, walls, and windows. Mechanical ventilation systems will primarily handle the following aspects in the building:

1. Control the intake and exhaust of air. They will renew the air based on needs, both in extraction and intake if it is a double flow system.
2. Eliminate excess humidity, in addition to smoke and other air contaminants that accumulate in the environment.
3. Regulate temperatures if they have a heat recovery unit that could introduce warm air in winter and also cool it in summer. All of this without using traditional air conditioning systems.

Additionally, when talking about efficient ventilation, we must keep in mind that the mechanical system must guarantee very low consumption, but it must also be capable of improving indoor temperatures.

Mechanical ventilation systems for Nearly Zero Energy Buildings

As mentioned, hybrid ventilation is the minimum option currently required in the Technical Building Code specifications. This option can work very well in old buildings requiring an energy renovation, as it is possible to utilize the old shunt - the internal ducts used before mechanical ventilation became popular - for air renewal.

In modern buildings, the efficient ventilation that works best is provided by mechanical systems. In this case, solutions are understood as those where air renewal occurs entirely mechanically, without opening windows or using other natural means. Air can be renewed with systems that either introduce or extract it, although the most advanced method is the one in which both intake and extraction are done mechanically.

To comply with the DB HS3 regulations and, above all, with Nearly Zero Energy Buildings, totally mechanical efficient ventilation is the ideal solution. In this case, the fans never stop operating, although they adapt to specific situations at any given time. They are automatic devices; there is no need for manual control as with traditional air conditioning. However, it is possible to program them for certain comfort levels.

We can differentiate between three types of mechanical ventilation systems:

1. Mechanical supply ventilation. In this type of solution, air intake occurs through fans that push air from the outside. All air distribution occurs through ducts, and it is possible to filter the air collected from outside. The air exiting the interior is expelled through ventilation grilles or infiltrations leading outside.
2. Mechanical exhaust ventilation. This operates in the opposite manner to the supply system. In this case, the fans connect with the humid areas of the rooms, such as bathrooms and kitchens. Through a network of ducts, the air that has lost quality is expelled outside. Meanwhile, exterior air is introduced through ventilation grilles, naturally, and usually into dry areas such as bedrooms and living rooms.
3. Mechanical ventilation with supply and exhaust. This is known as a double flow mechanical ventilation system, and we can say it is the most advanced way to renew indoor air, besides being the most economical and having the best energy efficiency. In this case, there are two duct circuits. The first extracts the air that has lost quality and expels it outside the homes. On the other hand, there is another network of ducts capable of introducing outside air. Additionally, the double flow system can measure the real needs of each room and even acclimatize the homes. It is the most advanced system in energy efficiency within the ventilation sector.

While double flow systems are the best solution for efficient ventilation, all mechanical systems offer a significant improvement in energy efficiency within buildings, making them essential in Nearly Zero Energy Buildings.

Moderate consumption thanks to efficient ventilation

The improvements in energy efficiency offered by efficient ventilation are numerous. Simple flow mechanical extraction systems can include adjustable supply grilles, passive or active, and extraction can be performed with variable flow. This provides greater comfort and avoids the use of traditional air conditioning systems, resulting in substantial energy savings.

In double flow systems, energy efficiency reaches much higher savings levels since it is possible to install an energy recovery unit. In this case, the extraction of air is used to temper the incoming air. It is possible to heat the air in winter even when exterior temperatures reach 0ºC. Moreover, they operate in summer just as they do in winter, thus avoiding the use of air conditioning or heating systems.

What system is the best? Every mechanical solution is efficient ventilation, but currently, double flow systems with heat recovery are gaining much ground and are becoming popular as the best option for energy efficiency. Thanks to heat recovery, they are capable of avoiding the high consumption of traditional air conditioning. Additionally, with them, we gain health with very high air quality, which also enjoys sufficient sound insulation.

Therefore, Nearly Zero Energy Buildings must find an alternative that allows for minimal energy costs. For this, some of their characteristics must be the following:

• High airtightness and thermal insulation. With the right materials and construction that prioritizes tightness, sufficient protection against the elements can be achieved.
• Better utilization of solar light. The building's orientation must be based on harnessing solar light and the characteristics of the land.
• Alternative energies and low consumption appliances. Some form of renewable energy source and the use of low consumption systems are needed, be it in appliances or lighting.
• Mechanical ventilation systems that achieve energy efficiency.

The last point is essential to reach the necessary levels of Nearly Zero Energy Buildings. Thanks to efficient ventilation, we can do without air conditioning in many situations. For example, in passive houses like Passivhaus - which have no consumption - energy expenditure is only allowed for the mechanical ventilation system with heat recovery.