Building ventilation is needed to control moisture levels, get rid of pollutants and promote a healthy environment for building occupants. It is often a result of gaps in the fabric, window and door opening and more deliberate measures like chimneys and vents.
Extensive research shows that good natural ventilation design prevents airborne contagion, reduces Sick Building Syndrome symptoms and improves occupant productivity.
Air Exchange
The basic requirement of any ventilation system is to replace the internal air with fresh outside filtered air. The rate at which this occurs is usually described in terms of “Air Changes Per Hour” or ACH. The ideal is of course to achieve a constant supply of fresh outside air but this requires large ventilation systems that are usually implemented during construction and are not suitable for retrofitting existing buildings.
The most common way of achieving air exchange is through natural leakage. This can be achieved by simply opening windows or doors. However, this has the disadvantages of causing an uncontrolled temperature distribution within the building and often depends on weather conditions that cannot be controlled.
Another problem with natural ventilation is that the flow of air is not constant and it can take a long time for all the stale air molecules to escape from the room. For this reason it is not possible to measure the actual air exchange rate. The best method of assessing the quality of natural ventilation is through the local mean age of the air and room mean humidity (Etheridge, 1996). These indicators can be calculated using a tracer gas technique. GEZE offers window drives and locking systems that can be integrated into the KNX building bus and used to control natural ventilation in conjunction with other HVAC components.
Temperature Control
Whether a building is natural, mechanical or a hybrid (mixed mode) ventilation system, the rate of air exchange will affect the temperature of the indoor environment. Temperature control is important because it determines the relative humidity of incoming outdoor air and enables pollutant control. It also has an impact on the thermal conditions in a room, the pressure differences over the building envelope, and draught.
Ventilation rates must be based on pollution loads, moisture generation and the use of a space. However, it is also crucial that the ventilation does not degrade indoor air quality or climate or damage the structure of the building. Moisture control is especially important in cold climates where condensation can cause severe damage to building structures.
Insufficient ventilation can result in shorter customer stays, poor employee productivity and unhappy occupants. Excessive ventilation can drive up energy consumption, increase CO2 emissions and reduce overall building energy efficiency. The solution is to make buildings more intelligent, with demand control ventilation (DCV).
DCV systems adjust/reprogram ventilation settings, based on changes in footfall/occupancy and weather forecasts, to optimise energy savings. For example, ClevAir can automatically lower ventilation intensity at times of low occupancy, reducing energy consumption and increasing the lifespan of the equipment. Other systems rely on sensors that check for direct occupant counting using techniques such as ticket sales, security swipes or video recognition.
Humidity Control
Humidity control is an important part of building ventilation. Excessive moisture can cause various problems, including corrosion of building materials, microbial growth, and health issues for occupants. It can also lead to damage to equipment and facilities. Expert ventilation system design can help reduce humidity levels in buildings and keep them comfortable and safe for occupants.
The humidity in a building can depend on its location and the amount of moisture it contains. High relative humidity can encourage the development of microorganisms in building fabric, which can cause mould and rot. It can also affect the thermal comfort of occupants, causing condensation and reducing energy efficiency.
ASHRAE continues to publish space-by-space ventilation rate recommendations. These rates are based on epidemiological research, laboratory and field experiments, irritation, odour perception and preferences, and other factors. They are designed to ensure that fresh air is supplied to clean spaces and contaminated space is discharged. However, it is often difficult to achieve these airflow patterns due to pressure differences within a building envelope and draughts.
Previous field studies and simulations have shown that many high performance homes experience elevated indoor humidity for substantial periods during the year in humid climates. This is mainly caused by lower sensible cooling loads that reduce the energy used to remove moisture from outdoor air. Smart algorithms that time-shift ventilation have been developed to mitigate this problem. They have been shown to significantly reduce the duration and number of hours that indoor humidity exceeds 60% RH in modern DOE Zero-Energy Ready residences while maintaining an annual pollutant exposure equivalent to a continuous fan sized according to ASHRAE 62.2-2013.
Noise Control
A ventilation system is not only responsible for keeping interior air cool and comfortable, but also for removing contaminants like combustible dusts, chemical vapors, smoke, and harmful gases. These systems can be very noisy, and excessive noise levels in a building create a health and safety risk for occupants.
There are two main types of noise transmission within a building: airborne and mechanical. Airborne noise travels through walls or floor and ceiling assemblies and can originate from human activities in adjacent living spaces or mechanical systems such as elevator systems, refrigeration and air conditioning systems, generators, trash compactors and fans.
To reduce the amount of noise transmitted between spaces, acoustic materials can be used from the beginning stages of construction to stop sound waves from passing through. Acoustical products can be applied to walls and ceilings, or they can be incorporated in the design of air distribution equipment (i.e. diffusers and registers). Duct cross-section design (to limit air velocity) and the use of turning vanes in larger elbows can help reduce duct turbulence and associated aerodynamic noise.
In addition, acoustic systems such as resonators or loudspeakers can be integrated with the air distribution system. These systems can be either passive or active and may require sensors, controllers or electricity to operate. Passive acoustic systems are cheaper but may not be suitable for all applications. A sound consultant can recommend the right acoustic solution to meet your specific requirements.