demand controlled ventilation

Industrial kitchens have high HVAC load requirements due to high exhaust rates from hoods. Especially in cold climates to heat the makeup air in winter requires high initial and - more importantly - high operating costs. Heat recovery always looks like an attractive alternative due to the high temperatures of hood exhaust air. However, since hood exhaust is quite dirty, heat recovery sections are clogged very fast. Heat recovery systems are established in six restaurants in Ankara, Turkey.

Ventilation systems assume that the outdoor air quality is better than the indoor air quality at al times as they use outdoor air to dilute pollutants emitted by humans, activities, the building itself and other objects. However, the outdoor air quality is not always as clean as assumed. Traffic, industry and agriculture can pollute the outdoor air making the outdoor air also a source of certain unhealthy pollutants indoors. This challenges the before stated assumption as in this case less ventilation would lower this source of pollution to the indoor environment.

Performance based approached for ventilation started to be used in Belgium in 2008 in the context of EP regulation. Until 2015, demand controlled ventilation (DCV) systems were considered as “innovative” products and were not directly taken into account in the EP calculation method. Their energy performance was then considered through a principle of equivalency. A first performance based approach was developed in this frame.  

Demand controlled ventilation (DCV) seems to be the main way to comply with both energy and internal air quality (IAQ) concerns. Largely spread in non-residential building since more than 2 decades (Fisk, 1998) because of large potential energy savings, its application for the residential sector is nowadays becoming the basis of ventilation systems for dwellings. Indeed, thermal regulations for residential buildings in several countries give targets that are difficult to reach with constant air changes rates.

HVAC systems in newly built or extensively renovated dwellings were all developed with the aim for energy saving with equal or better comfort. However, these systems (floor heating and DCV systems) have certain characteristics which increase the emissions of Volatile Organic Compounds (VOCs) and give VOCs the chance to accumulate to higher concentrations. This interaction is investigated based on dynamic simulations using a temperature and humidity dependent VOC emission model. 

Use of Demand Controlled ventilation (DCV) can potentially save more than 50% of energy use for ventilation purposes compared to constant air volume (CAV) ventilation. Correct and updated calculation of preset minimum (Vmin) and maximum (Vmax) airflow rates are important to maximize energy saving and to ensure good indoor quality. Furthermore, earlier studies have shown that controlling units' ability to actually handle V min is lacking and causes instability in the DCV systems 

In a recently built zero-carbon neighborhood, demand controlled exhaust ventilation systems (DCMEV) and mechanical ventilation systems with heat recovery (MVHR) are compared under operational conditions, with focus on the energy performance of both systems. The analysis is based on automatically gathered monitoring data, complementary in situ measurements and occupants surveys. 

Design of ventilation systems in Belgium is currently based on the Belgian Standard NBN D 50-001:1991. This regulation is more than 25 years old, and is not anymore suited to new technologies developed in the frame of increasing energy performance of buildings and its associated ventilation systems. This standard defines four classic ventilation systems, going from A (natural ventilation) to D (double-flux ventilation eventually with heat recovery). One of its main shortcomings is that it does not consider demand controlled ventilation (DCV) systems.

Demand controlled ventilation (DCV) can improve the energy performance of all kinds of ventilation systems, in residential and non-residential buildings and is already part of the European Lot 6 and Ecodesign regulations and standards. However, the lack of recognition of DCV in SAP (Standard Assessment Procedure) forms a great barrier for the use of this technology in the UK. A methodology was developed to prove the guarantee on good IAQ, with potential saving on heating and auxiliary energy by modulating ventilation rates based on actual demand.

Nowadays, due to the higher energy performance of dwellings, ventilation plays an increasing role in maintaining a good indoor comfort. Therefore new ventilation strategies in combination with demand controlled ventilation are needed to accomplish high energy-efficient ventilation (limiting ventilation losses and auxiliary energy consumption) while providing good indoor air quality, thermal and acoustic comfort.