The UNESCO world heritage “Decorated Farmhouses of Hälsingland” represent a well-preserved Swedish regional timber building tradition from the 18th and 19th centuries, featuring wall paintings of high cultural and artistic value. The houses have remained unheated and naturally ventilated over centuries, and have relatively leaky building envelopes. Recent indoor climate measurements and observations, however, have identified occasional condensation on indoor surfaces during unfavourable weather changes in wintertime. Such condensation poses a risk of degrading the wall paintings and other valuable objects, although low winter temperatures prevent mold growth. To mitigate condensation risk, sorption dehumidifiers – working also at temperatures below 0 °C – were installed in one of the UNESCO farmhouses during a winter season. The dehumidifiers were programmed to limit the indoor air relative humidity (RH) at maximum 80 %, and their dried air was distributed to all rooms via a flexible ductwork. Additionally, climate loggers and passive tracer gas technique were employed to measure temperature, RH, and air change rate in all rooms. By comparing with measured indoor climate in other similar farmhouses in the region, the results indicate that the dehumidifiers chiefly managed to limit RH at 80 %, thus preventing condensation in all rooms, despite a relatively high mean air change rate of around 0.8 ACH. However, locally and temporarily, enhanced RH peaks occurred, possibly due to unfavourable transient wind and/or stack conditions. The study also provides some practical installation guidance.

Most legislations concerning ventilation are based on perceived air quality criteria, but ventilation is also important for the health of the occupants. From a comfort and health perspective, the ventilation rate and an efficient air distribution are both important for achieving a healthy and comfortable indoor environment. Yet, most legislative requirements focus on the ventilation rate. It is recommended that legislation also address the air distribution with the same zeal. Ensuring the efficient distribution of fresh air to the occupied zones. Because there are clear links between ventilation and health, it is extremely worrying that the “energy efficiency first” principle advocated in the Energy Performance of Buildings Directive (EPBD) has led to decreasing ventilation requirements in the European Union legislations, at the same time as the objective is to aggressively tighten the envelopes of the building stock.

Ventilation of buildings is important for occupants' health. Few studies have been conducted on associations between home ventilation and occupant's health in China. During 2013-2016, we measured air change rate in 98 homes by both mass balance of occupant generated CO2 method and PFT method in Tianjin and Cangzhou, China. Questionnaires were used to survey the health data for children. We found that air change rates measured by CO2 method in whole day were higher than those measured by PFT method and those measured during night. Lower air change rates measured by CO2 method during night were significantly associated with perceived unpleasant odor (p=0.04). Lower levels of air change rate measured by CO2 method during night were risk factors for croup (AOR: 7.30(1.25, 42.60)). Air change rate measured in a certain period especially at night may be more representative in analysis of the association with occupants' health. 

A controlled indoor environment is crucial to the preservation of valuable historical artefacts in museums, but is influenced by many factors such as building properties, exhibit design, number of visitors, outdoor conditions etc. This study aims to monitor the local air exchange rates (AERs) and internal air flows in the Viking Ship Museum, Oslo, Norway during different outdoor conditions and is part of a project to create a new museum for the ships. Homogeneous emission tracer techniques (with tracer A) were used to monitor the local mean age of air (from which the local AER can be estimated). The internal air flows from a building zone were monitored by loading that zone with another tracer (B). The building outline is in the shape of a cross with four wings emanating from a central tower and thus naturally creates five zones to investigate. Three measurement periods were conducted with outdoor conditions ranging from winter to late summer. During winter conditions the average hourly air exchange rate (ACH) for the museum is fairly low (0.05 h-1), but during summer conditions it rises fourfold (0.2 h-1). During the summer, windows and doors may be kept open and the number of visitors peaks. The internal flows are very large, as indicated by very similar patterns of the sampler loads for both A and B tracers in relation to the twenty sampling positions. 

Most legislations concerning ventilation are based on comfort criteria, but ventilation is also important for the health of the occupants. The comfort criteria can be viewed as a pragmatic tool to achieve an adequate ventilation for precautionary health measures. From a comfort and health perspective, the ventilation rate and an efficient air distribution are both important for achieving a healthy and comfortable indoor environment. Yet, most legislative requirements concern the ventilation rate. This is not enough, and it is recommended that legislation also address the air distribution. In particular, the efficient distribution of fresh air to the occupied zones or the concentrations of pollutants in the occupied zones. Because there are clear links between ventilation and health, it is extremely worrying that the “energy efficiency first” principle advocated in the Energy Performance of Buildings Directive (EPBD) has led to decreasing ventilation requirements in the European Union legislations, at the same time as the objective is to aggressively tighten the envelopes of the building stock. A second consequence of EPBD is probably that many naturally ventilated buildings will be retrofitted with mechanical ventilation systems. It is not clear that this would be the more sustainable solution in the long run.

Field calibrations of NO₂, NO, and PM₁₀ from AQMesh Air Quality Monitors (AQMs) were conducted during a summer and an autumn period in a busy street in a midsize Swedish city. All the three linear calibration procedures studied (postscaled, bisquare, and orthogonal data) significantly reduced the ranges and magnitudes of the performance indicators to yield more reliable results than the raw data. The improvements were sufficient to satisfy the European Union (EU) Data Quality Objective (DQO) for indicative measurements as compared to reference data only for NO₂ (above 50 µg m^-3) and NO (above 30 µg m^-3) during the autumn calibration period. The relatively simple bisquare procedure had the best performance overall. The bisquare procedure improved the root mean square error by the same amount as other studies using complex multivariate calibration methods. Low concentrations of pollutants were measured, far below the EU Environmental Quality Standard thresholds and even satisfying the future goals for the Environmental Quality Objectives. Cleaning the raw data by removing data points in the reference data that were below the reference station limit of detections (and the synchronous data points in the AQM prescaled data) was found to improve the performances of the calibration procedures appreciably. Many NO₂ and almost all PM₁₀ data points in this study fell below the AQM limit of detection. These low concentrations will probably be a common problem in many field studies, at least in areas with relatively low air pollution. However, the relative errors were sufficiently low for these data points that they could be interpreted as accurately representing low concentrations and did not need to be removed from the datasets. For the NO₂ measurements, a slight periodic error correlated with sunlight and increased ambient temperature was noted. NO measurements correlated strongly with increased traffic.

Estimates of air exchange rates (AER) in buildings are important when ventilation systems areevaluated. Many methods may be used, but here the focus lies on the PFT and CO2- methods.Traditionally, perfluorocarbon tracers (PFT) together with passive sampling has been used.However, the rise of low cost CO2- sensors has opened a relatively inexpensive route toestimating AER using the CO2 emitted by the occupants as tracer gas. The two methods havetheir different strengths and weaknesses, but are typically separated by measuring in differenttime periods. Longer periods for PFT and shorter periods for CO2.The aim here is to simultaneously measure and compare the two estimates of AER in a wellventilatedapartment during the same (short) time period. The homogeneous emission tracertechnique is used for PFT, i.e. the tracer is homogeneously emitted in all rooms of theapartment. CO2 uses the tracer emission of the occupants and usually focus on measuring thenight AER in the bedroom, but placing CO2 sensors in other positions the general AER of theapartment may be estimated. In this study the estimates of AER in the bedroom and for thewhole apartment are compared for three different bedroom door states: totally open; 1 cmopen; and closed.The PFT estimates of AER vary less with the state of the bedroom door, whereas the CO2estimates are lower (than PFT) when the door is open and progressively higher (than PFT)when the door is more closed.

As a part of an ongoing study, we report measurements of air infiltration during winter conditions into two Decorated Farmhouses of Hälsingland designated as UNESCO World Heritage Sites. In winter these two-storied farmhouses are rarely heated, except for special occasions. In this measurement one farmhouse  was  unheated,  whereas  one  room  was  heated  for  a  brief  period  in  the  other  one.  The observed local mean ages of air measured with tracer gas techniques generally increase with height, both  locally  within  each  room  and  between  floors.  The  average  temperature  and  humidity  also increases from the first to the second floor. The indoor temperature follows the outdoor temperature with a time lag. The differences in water content between inside and outside air correlate with changes of the indoor relative humidity. The correlation is stronger for humidity increase than for humidity decrease, possibly due to moisture absorption by interior text.

A method to determine the rate of local transport into the indoor air of a substance originating from the construction frame of a building has been devised and tested. In particular we demonstrate that a tracer located outside the air and vapour barrier in the construction frame of an office building can be detected in varying concentrations in the office indoor air. The tracer may either diffuse directly or follow with outside air leaking through the barrier. Cor-recting for the local air change rate yields an apparent emission rate as an estimate of the rate of local transport from the construction frame to the indoor air. Our interpretation is that high-er apparent emission rates predominantly reflect higher local air leakage rates through the air and vapor barrier. This information could be useful for interpreting office worker complaints and for decisions on renovation options. The tracer techniques used in the study are also more generally applicable to convert measured concentrations of indoor substances into apparent emission rates. Emission rates are more indicative of the location of pollution sources and may therefore be useful in other investigations of polluted buildings.

The focus of this study is to assess the airflows in a school building built in 1963 in Gävle, Sweden, which is subject to energy conservation measures (ECMs) in a forthcoming renovation. Today, the school building is mainly ventilated by several mechanical ventilation systems, which are controlled by a constant air volume (CAV) strategy. Schedules and presence sensors impose a high operation mode during the day and a low operation mode at night, on weekends and on holidays. The homogeneous tracer gas emission method with passive sampling is used to measure the average local mean age of air (τ) during different operation modes. Temperature, relative humidity and CO₂ concentration are simultaneously measured. The calculated relative uncertainty for the average local mean age of air in every measured point is approx. ±20 %. The results during low operation mode show an average value of τ of approx. 8.51 h [corresponding to 0.12 air changes per hour (ACH)], where τ in various zones ranges between 2.55 and 16.37 h (indicating 0.06–0.39 ACH), which is related to the unintentional airflow in the school. The results during mixed operation mode show an average value of τ of approx. 4.60 h (0.22 ACH), where τ in various zones ranges between 2.00 and 8.98 h (0.11–0.50 ACH), which is related to both unintentional and intentional airflows in the school. Corridors, basement and attic rooms and entrances have lower τ compared to classrooms, offices and other rooms. High maximums of the CO₂ concentration in some rooms indicate an imbalance in the mechanical ventilation systems. During a regular school week of mixed operation, which includes both high and low operation modes, it is found that mainly the low operation modes show up in the results. The dynamics of the highly varying airflows in the building cannot be identified using the passive sampling technique.