Balanced Ventilation is Energy Efficient and Healthy

Keywords: PM1, PM2.5, simulation, window use, ventilation system, cooking exhaust

Highlights:

·         F7 (ePM1 55%) filters in balanced ventilation improve indoor air quality in homes.

·         In combination with good cooking extraction, the WHO PM2.5year recommended value is achievable.

·         The degree of airtightness has a limited effect when windows are open.

·         Cooling helps to further improve air quality with regard to particulate matter.

What influence do ventilation systems and users have on the particulate matter concentration in homes and, in particular, what is the effect of improved filtering? To answer this question, simulations were carried out with a ventilation model that included the effect of the type of ventilation system, cooking extraction, air tightness and window use.

Airtight homes with balanced ventilation offer the opportunity to significantly improve the air quality for residents in the homes. This possibility is currently not fully utilized. Most systems use standard G3 filters, while better indoor air quality can be achieved with F7 filters (ePM1 55%)[1].

Even with open bedroom windows in summer and spring and autumn, the WHO annual average recommended value for PM2.5 can be met with F7 filters (ePM1 55%) in combination with a cooking extractor.

Background

When renovating homes, the emphasis is on energy savings in order to achieve the climate and energy objectives. Energy savings, necessary to meet the Energy Performance requirements, are usually also the reason for using balanced ventilation in new-build homes. In other sectors such as offices and schools near busy roads, balanced ventilation in combination with good filters is also used to protect users against particulate matter from the outside air [PvE Healthy offices 2021; PvE fresh schools, 2021]. The fact that balanced ventilation, in addition to meeting energetic requirements, can also be used to improve air quality and thus the health of residents, receives little attention in homes.

In any case, little attention is paid to air quality in homes, despite the fact that an estimated 98% of the Dutch homes do not meet the WHO's 2021 recommended value for PM2.5. A large-scale and long-term monitoring study (TKI Be Aware) established that 15 of the 100 homes examined did not meet the 'old' WHO PM2.5 recommended value of 10 µg/m³ annual average. The annual average concentration in the kitchen/living room was on average 8.2 µg/m³. In September 2021, this recommended value was adjusted by the WHO to 5 µg/m³ annual average. Using this new recommended value, 98% of the homes examined no longer met [TVVL 2021].

Based on the Be Aware monitoring study, simulations were carried out in 2020 with the TRNSYS building model linked to the ventilation calculation model TRNFlow (COMIS). Two important simplifications were made when carrying out these simulations. Firstly, a ventilation model was used in which only the living room/kitchen was considered. In addition, the windows were assumed to be closed. This is certainly not a good assumption outside the heating season.

The research question in this article is therefore: What influence do ventilation systems and users have on the particulate matter concentration in homes and, in particular, what is the effect of improved filtering? To answer this question, simulations were carried out with a ventilation model that included the effect of the type of ventilation system, cooking extraction, air tightness and window use.

Simulations of multi-zone ventilation model including window use

Using a multi-zone ventilation model the annual average particulate matter concentration in a single-family home has been determined. The model consists of 4 zones, see Figure 1. The zones are all connected to the stairwell via a gap of 120 cm² under the interior doors. To prevent drafts from occurring straight through the house from facade to facade at higher wind speeds when windows are open, it is assumed that the interior doors are closed.

Figure 1. Schematic representation of ventilation model with connections between the zones.

The ventilation model calculates the air flows between the zones based on wind effects, thermal effects and the type of ventilation system. A constant air speed of 5 m/s perpendicular to the facade has been assumed for the wind. This speed is the average wind speed in the Netherlands. Two air tightness levels have been assumed, 20 and 80 dm³/s at 10 Pa. The air leaks through seams and cracks are distributed over the home envelope in accordance with the BKN equivalence methodology (2018) and are mainly present in the attic. The wind pressure coefficients for the facade and roof surface have also been adopted in accordance with this methodology. Thermal effects are modeled depending on the season. The daily average indoor and outdoor temperatures used for this are shown in Table 1. Window use over the seasons has been simplified as follows: in winter all windows are assumed to be closed, in spring and autumn the bedroom windows are in the tilt position while sleeping and in the summer these windows are in the tilt position throughout the day.

Table 1. Simulated indoor and outdoor temperatures per season.

The balanced ventilation system is equipped with G3 filters as standard, see Figure 2. For a balanced ventilation unit equipped with such a coarse filter, a PM2.5 capture efficiency of 15% is expected based on ongoing practical measurements. Equipped with an F7 filter (ePM1 55%), see Figure 2, the capture efficiency of the balance ventilation unit increases to approximately 75%. These two values were used in the simulations. In addition, simulations have also been carried out with a PM2.5 capture percentage of 99%. This performance can be achieved when using an electrostatic filter that is placed downstream of the balanced ventilation unit (Khoury et al. 2017).

More details about the simulation of turbulent exchange through open windows, particulate matters sources and deposition, cooking extractor efficiency and the simulation of the ventilation system and the determination of exposure times can be found in Jacobs (2024).

Figure 2. Energy-efficient and healthy, in the balanced ventilation unit an F7 (ePM1 55%) fine dust filter has been placed in the air intake instead of the standard G3 coarse filter, such a filter is still in the exhaust.

Simulation results

Effect of filtering and cooking extraction on concentrations with closed windows

Figures 3and4 show the effect of different types of filters on the annual average particulate matter concentration during presence, without and with cooking extraction, respectively. The windows in the bedrooms are closed. Results with open windows are mentioned in Jacobs [2024]

Without using a cooking extractor, see Figure 3, the highest particulate matter concentrations occur in the living room/kitchen. The simulated concentrations correspond well with the measured concentrations in the Be Aware study during presence. Figure 4 shows that better filtering of the ventilation air only results in a limited reduction in concentration in the living room/kitchen. In the bedroom on the windward side, relatively high concentrations occur, especially in system C, because a lot of unfiltered outside air flows in through the grille and the seams and cracks. In the leeward room, system C scores better in terms of particulate matter than system D with a standard filter (15% capture efficiency), because exfiltration occurs via the grilles and therefore supply via the inner door from the relatively clean stairwell (as a result of deposition in the home).

With a cooking extractor, see Figure 4, the particulate matter concentrations in the bedroom remain unchanged. However, the concentrations in the living room/kitchen decrease sharply. It is striking to see that there is almost no concentration difference between the F7 filter with 75% PM2.5 capture efficiency and a filter with 99% capture efficiency. This is caused by the fact that ventilation is set to low during the rest of the day, except during cooking, and the contribution of infiltration is then relatively large. With ventilation in the middle position (figure not shown), the concentration in the living room with the standard G4 filter (15% PM2.5 capture efficiency) remains virtually the same, but with a filter with 99% capture efficiency it decreases to 2 µg/m³.

Figure 3. Effect of filter efficiency on the PM2.5 concentration per living space during presence, qv10=80 dm³/s, windows closed, ventilation in low setting, without cooking extraction.

Figure 4. Effect of filter efficiency on the PM2.5 concentration per living space during presence, qv10=80 dm³/s, windows closed, ventilation in low setting, with cooking extraction.

Exposure

The average annual particulate matter exposure in the home has been determined by averaging the particulate matter concentrations present in the various rooms during the four seasons. It follows from Figure 5 that in both a home equipped with system C and system D with a standard filter (15% capture efficiency), the exposure is higher than the WHO annual average PM2.5 recommended value of 5 µg/m³. Increasing the ventilation flow rate when present to the medium setting even results in an increase in exposure in this situation. This is because when the amount of ventilation is increased, the effect of deposition decreases relatively speaking.

Replacing the G3 supply filter in system D with an F7 particulate filter leads to exposure below the WHO recommended value. Installing an electrostatic filter with a 99% capture efficiency only results in a limited reduction in exposure, because the bedroom windows are open during part of the year. Figure 6 shows the potential of filtering in combination with mechanical cooling (bedroom windows are no longer opened). This reduces exposure by more than half compared to an F7 filter. And with an electrostatic filter, exposure in the home can even be reduced to below 1 µg/m³.

Figure 5. Exposure to PM2.5 particulate matter for different ventilation systems and filter efficiencies. Bedroom windows tilted in spring, autumn and summer, airtightness qv10=20 dm³/s and with cooking extractor.

Figure 6. Exposure to PM2.5 particulate matter for different ventilation systems and filter efficiencies. Bedroom windows closed (mechanical cooling), air tightness qv10=20 dm³/s and with cooking extractor.

Conclusions and recommendations

This simulation study shows that good cooking extraction in combination with better filtering of the ventilation air in the mechanical supply can significantly reduce exposure to particulate matter in homes, even when windows are open in the bedrooms for a large part of the year. This is mainly due to the much lower exposure in the living room.

The simulation results for homes with supply via grilles and for homes with balanced ventilation with standard filters correspond to practical measurements carried out in TKI Be Aware and do not meet the 2021 WHO recommended value. With balanced ventilation with F7 particulate matter filters (ePM1 55%), the new WHO recommended value is met. Because the simulations assume that windows are open for cooling during part of the year, the use of even better filters only has a limited effect. In homes with active cooling, there is clear added value to using better filters than F7 quality, because then windows can remain closed.

This study is a simulation study with a large number of other assumptions in addition to the previous simplification. Practical measurements are required to validate the results. For this purpose, detailed measurements are planned in homes in 2024, in which particulate matter is measured in multiple zones and information is collected about, among other things, open windows, ventilation flow rates and meteorological data. In addition, the effect of better filtering will be measured in homes with balanced ventilation to validate the model described here.

Literature

AIVC, Inhabitant Behavior with Respect to Ventilation – a Summary Report of IEA Annex VIII, Technical Note AIVC 23, Air Infiltration and Ventilation Centre, March 1988.

Indoor climate technology, PvE Healthy offices 2021 (https://www.binnenklimaattechniek.nl/document/pve-gezonde-kantoor-2021/).

Jacobs P., Kornaat W., Borsboom W., Balanced ventilation – energy efficient and healthy, AIVC conference 2024.

Interview, Almost no home meets the new WHO particulate matter standard, TVVL magazine 06, December 2021.

Khoury E., Wijsman S, Vons V., Combating wood smoke nuisance in homes, TVVL magazine 2017.

Public final report TKI Be Aware - Awareness of indoor air quality in homes: sources and effective energy efficient intervention strategies, TNO report 2020 R10627, April 2020.

RIVM, Compendium for the living environment, Finer fraction of particulate matter (PM2.5) in air, 2009-2022 | Compendium for the Living Environment (clo.nl), accessed on 6/12/2023.

Program of Requirements Frisse schools 2021 (https://www.arbocatalogue-vo.nl/media/1149/programma-van-eisen-frisse-scholen-2021.pdf).

VLA methodology equivalence for energy-saving ventilation solutions in homes, version 1.3, 2018.