heat recovery

Mechanical ventilation systems with heat recovery are considered the most optimal systems for residential ventilation. This research focuses on decentralized ventilation which do not need any ducting. Therefore, this system is very suitable for use in retrofitting. The performance criteria of these units are similar to those of central systems. A recuperative and two regenerative ventilation units were tested in a double climate chamber where temperature, air velocity and contaminant concentration were monitored on a fixed 80 point grid.

The use of heat recovery ventilation systems is becoming more and more common. It is clear that these systems contribute to energy efficiency and good indoor air quality. Still there is room for improvement. Analyses by monitoring and modelling have uncovered drawbacks and flaws, especially for the use and application of HR ventilation in highly energy efficient dwellings. This paper will deal with these issues, turning them into suggestions to improve HR ventilation systems. 

Balanced ventilation units are well known to provide a sufficient amount of fresh air in residential buildings in a controlled way, without relying on ever-changing naturally driven forces. During colder periods, heat recovery ensures a reduction of the ventilation heating load. Outside the colder periods, recovery is reduced or shut off automatically, providing mechanical ventilative cooling. During warmer periods, the recovery is used again to provide a comfortably cool supply of fresh air.

Energy performance of buildings has been continuously and systematically improved in Europe with next step of transition to nearly zero energy buildings (NZEB) in 2019-2021. Well insulated and airtight NZEB provide challenges or opportunities – depending on point of view – for ventilation systems. Heat recovery ventilation may be expected to be major ventilation solution because in Continental and Nordic climates, it is simply impossible to build nearly zero energy buildings without heat recovery.

Energy renovations seek to improve the airtightness of dwellings and thus require ventilation and heat recovery to maintain or improve energy-efficiency, indoor climate, and durability. These ventilation systems often control the indoor air of an apartment as a single climate zone, which neglects the different demands of individual rooms. Renovations result in greater retention of heat and air inside the building envelope, so rooms become especially sensitive to gains from solar radiation, occupancy, moisture loads and pollutants.

A “heat recovery hybrid ventilation system” is the combination of passive stack ventilation and mechanical push-pull ventilation. Two heat storage boxes are connected to the natural EA stack and the underfloor natural OA duct. The alternation is done periodically in a way of that the outdoor air is drawn through one of 2 boxes contains earth tiles and the indoor air is exhausted through the other box.

Nowadays, important efforts are deployed to reduce energy consumption in the field of residential buildings. Concerning new constructions, low-energy consumption buildings such as “passive” houses constitute a suitable solution to decrease the environmental impacts.In this kind of building, air tightness is improved and heating needs are reduced compared to traditional constructions. In order to ensure a good indoor air quality, controlled mechanical ventilation is required.

In this study the performance of a residential demand controlled (DC) extract ventilation system with an air-to-water heat pump was analysed via dynamic simulations. A real life test case was setup to validate results. The ventilation system controls automatically the extract air in functional as well as habitable rooms, ensuring indoor air quality (IAQ). The total extract rate is mixed with outdoor air as heat source of the air-to-water heat pump (2.5 kW at standard reference conditions). Domestic hot water (DHW) as well as space heating (SH) can be alternatively supplied.

Ventilation in low energy refurbished buildings is the cause of a big part of energy losses. In order to reduce this impact, some energy regulations prescribe a solution (such as the Swiss energy Law, prescribing heat recovery) and others prescribe a system global performance (such as the EU delegated regulations No 1254 and 1253 /  2004 determining a global energy performance label of the ventilation system).

Radon gas is a pathological agent confirmed by World Health Organization in terms of increasing the risk of lung cancer generation when it is inhaled by human in high concentration. This gas comes from soils with uranium content (i.e. granite terrain) and penetrates through the building envelope, such, as floors or basement walls. Its accumulation in indoor spaces increases the radon concentration level, constituting a health problem for occupants. This can be handled by rehabilitation actions in buildings that reduce indoor concentration to acceptable levels.