White paper: Indoor air quality and carbon dioxide sensors

Transcription

1 White paper: Indoor air quality and carbon dioxide sensors January 30, 2017 Author: Markku Rouvala, Hardware Design manager, New Nordic Engineering. Indoor air quality depends mostly on gases and particles developed from indoor materials and structures. Outdoor air is mostly used as a source for pure air, but can also be a source for bad indoor air quality in certain areas and circumstances. Indoor air quality can be controlled in four main steps. 1) Minimizing indoor emissions, 2) keeping building dry, 3) good ventilation and 4) protection for outdoor contaminants. Ref: Nazaroff, Indoor Air, 2013 Protection from outdoor air pollution Protection from outdoor air pollution is important mostly in areas with much of small particle, PM2.5, particulate pollution, mostly important in large cities and industrial areas. Small particles also occur from diesel engines and road dust, where specifically diesel engine pollution is found to be cancerous. Other outdoor contaminant is ozone, O 3, which is causing increasingly chronic lung/respiratory diseases and asthma. Tropospheric ozone, the ozone layer, is not the problem in this matter, but the lower layer introduced as pollution to people. Ozone is developed mostly from carbon monoxide (CO), Nitrogen Oxides (NO x) and non-natural volatile organic compounds (VOC), as precursors. Exposure to sun light makes the chemical process from VOCs and other compounds to the O 3 possible, so the process is mostly happening outdoors. Protection from outdoor pollution for the small particulate matter, PM2.5, can mostly be done with air conditioning filters etc. For even smaller particles that are below 1um in diameter down to 100nm, the problem is larger, and these particles are larger in quantities. Normal building air filtering does not help in many cases due to the particle sizes. Ozone can be partially filtered with activated carbon filtering. Following up the VOC gas levels, hydrocarbon levels, nitrous oxides and small particle levels indoors can enable building owners to know when better filtration is needed, and when better ventilation would be a good option.

2 Minimizing indoor emissions Minimizing indoor emissions is a complex issue in general. There are hundreds or thousands of organic and inorganic compounds developed from building materials, construction elements, furniture, cleaning media, moist conditions in the ventilation and paints/solvents. Some to mention, formaldehyde is a VOC pollution chemical evaporated from glued woods and engineered wood plywood and MDF. Formaldehyde is mostly an indoor pollution even though also exiting in outdoor atmosphere naturally, but in much lower quantities. Formaldehyde is a recognized carcinogen, when exposed over a limit of 0.1ppm. Total Volatile Organic compound TVOC and VOCs are set regulations in European level and by individual countries in EU and US, and documented and tested by many different systems and organizations like Eurofins, LEED, BREEAM, REACH, Green Star and by others. For example VOC contents in paints is regulated in Decopaint directive in Europe. Most effective and available technique to enhance indoor air quality is the reduce the contaminants at the source, like using less cleaning media and cleaning media that has less or zero level chemicals with VOC evaporative pollutants, using water based paints, using building materials with less or no glues. Cooking media and combustion processes in the heating are also globally main sources of the bad air quality, so reducing gimney heating and enhancing the cooking environment by electric cookers and exhausts would be a single worldwide effective indoor air enhancing method that would increase the global IAQ remarkably. Indoor environmental quality also includes people generated pollutions that can be as hazardous as materials chemicals. Carbon dioxide, CO 2, is naturally generated from people breathing. Many people in the small concise room can increase the CO 2 levels very high, over the levels of comfortable being. CO 2 levels of over 3500ppm have been measured in a school with standard amount of pupils and normal school room (link). It has been shown in many studies that high CO 2 levels, as well as high VOC levels are causing problems with cognitive skills, learning and nudging. While elevated levels of CO 2 in range of ppm can cause headaches, heart rate increase and nausea, very high levels, over 10000ppm can cause serious brain damage and death. According to a study by Harvard University on the impact of green buildings on cognitive function, the results concluded that CO 2, VOCs, and ventilation rate have significant and independent impacts on cognitive function (link, Allen 2015).

3 Case study: sound masking system controlled with CO2 sensor CO 2 can also be used as control for sound masking systems. In Figure 1 a sound masking system from ergoacoustic installed in a museum hall is controlled by New Nordic Engineering ndec CO 2 measurement. CO 2 level controlling the sound masking is expected to be more robust and well averaging compared to microphone controlled systems, since CO 2 level is exactly dependent on the population, while sound levels depend on many other things, like machinery, outdoors noise etc. Figure 1. Controlling sound masking system level with CO2 level makes the sound masking adaptive. Green curve: CO2 level in the hall, blue bars: sound level for the sound masking system. Case study: Indoor air and cognitive skills at schools Elevated CO 2 levels can be present in semi-normal class room conditions, as well as any places with nonventilated space or less than adequately ventilated spaces with many people, like in people transport vehicles, waiting halls, indoor market places, museums, old theaters etc. with no automatic ventilation or malfunctioning air conditioning, or HVAC, systems. CO 2 measurement at each occupied room can give information of elevated levels for people present, and guide for extra manual ventilation. Ventilation need can also give input for building management for repairs and upgrades for HVAC systems. CO 2 level can be used to detect occupancy levels in large spaces regarding to actions needed in hazardous situations like fire alarms.

4 Study with New Nordic Engineering multisensory ndec at a school location in Aarhus and Grenå in Denmark show remarkably high CO 2 levels during normal school hours. Data over six days is shown in Figure 2. Figure 2. Carbon dioxide level at a school in five different rooms over 6 days. Pink: Class 3, Yellow: Class 4, Blue: Class 5, and Orange: Class 6. In Figure 2 CO 2 levels are elevated close to workplace official limits (5000ppm). Studies were used for following nudging and cognitive skills at the schools. In past studies, over 2000ppm CO 2 levels are shown to cause loss of attention, nausea, increased heart rate and other symptoms. During the same period, temperature, humidity and noise at the class room were measured. Temperature, humidity and sound (average dba noise) measurements are shown in Figure 3 - Figure 5. Data shows that CO 2 is the only measurement which can fast and without problems estimate the usage of the room. CO 2 level rises fast immediately when the class starts and slopes down immediately after the class. Also in classes 4 and 6 (in yellow and orange in figures) which are less populated, CO 2 is the only sensor that can without mistakes estimate the population, or the class start and stop. Average noise is a good estimation of the classes when no one is in place between the classes, but over the weekend for example, which is comparable to the time between the classes (pauses or non-used class rooms), sound is not a good estimate, since other disturbances are commonly in place. Temperature and humidity on the other hand follow the class room population slowly, and are more prone to changes in door openings and ventilation changes. Nudging at the schools is analysed by Aarhus Universitet Psykologisk Institut, Niels Holm Jensen, and discussion published online on TV, reference: link.

5 Figure 3 Temperature in the same school rooms (as in Figure 2) over 6 days. Pink: Class 3, Yellow: Class 4, Blue: Class 5, and Orange: Class 6. Figure 4. Relative humidity in the same school rooms (as in Figure 1) over 6 days. Pink: Class 3, Yellow: Class 4, Blue: Class 5, and Orange: Class 6. Figure 5. Noise in the same school rooms (as in Figure 1) over 6 days. Pink: Class 3, Yellow: Class 4, Blue: Class 5, and Orange: Class 6.

6 References: IAQ: Four principles for achieving good indoor air quality, Nazaroff, INDOOR AIR, Sep 2013, VOCs, Ozone, PM2.5: Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments, Joseph G. Allen, et. al, ENVIRONMENTAL HEALTH PERSPECTIVES, Oct 2015, Formaldehyde: 022X Acronyms: PM2.5 particulate matter of 2.5um diameter and less VOC Volatile Organic compound TVOC Total Volatile Organic Compound (containing large amounts of different VOCs for regulation purposes) O3 - Ozone CO2 Carbon dioxide CO Carbon monoxide NOx Nitrous oxides (like nitrogen dioxide NO2 and nitric oxide NO) MDF medium-density fibreboard Eurofins European group of laboratories offering services LEED a green building certification program BREEAM - Building Research Establishment Environmental Assessment Method REACH - Registration, Evaluation, Authorisation and Restriction of Chemicals, EU regulation addressing production and use of chemical substances and their impact on health and environment Green Star Originally Australian building certificate for building systainability HVAC - Heating, ventilation and air conditioning dba sound pressure level in decibels, A-weighted for matching human ear perceiving. CO2: levels-in-the-classroom affect-human-cognition-new-harvard-study-shows- 2748e #.d1ahr3jss ere Background noise: