The Science
Summary​
Monkeytronics is a Wellington based social enterprise, on a mission to solve challenging social and environmental issues using simple, high quality technology. Our approach is informed by research and science. We have been working closely with He Kainga Oranga, a world leader in healthy homes research and also with the New Zealand Ministry of Education and the Community Energy Network. Solving the problem of cold, damp, leaky homes must be a collaboration.
Each Airsmart monitor has been designed from the ground up as a scientific instrument. It's purpose in life is data sampling, collection and transmission for a range of physical and chemical quantities to determine whether the environment in which we live and work; and the air that we breathe is healthy. In order to achieve this we insist on using high quality, fully calibrated sensor elements from accredited manufacturers. We work with Sensirion, Texas Instruments, Bosch, TDK Lambda and many more. All of these companies manufacture goods to stringent international automotive quality standards, which includes rigorous testing and independent calibration.
Product Matrix​
We have developed a number of different prodcuts to measure different things and cope with different deployment scenarios. If you find your device from the list below, it will show you which meansurement sections are applicable. For use in homes, the most applicable devices are highlighted in the following table.
| Product | Temp | Hum | CO2 | Lux | dB | VOC | NOx | PM | HCHO |
|---|---|---|---|---|---|---|---|---|---|
| Airsmart CO2 | O | O | O | ||||||
| Airsmart Edu | O | O | O | O | O | ||||
| Airsmart HT | O | O | |||||||
| Airsmart PM | O | O | O | O | |||||
| Airsmart NOX | O | O | O | O | O | ||||
| Airsmart HCHO | O | O | O |
Specifications​
| Measurement | Operating Range | Units | Accuracy |
|---|---|---|---|
| Relative Humidity | 0 - 100 % | % | 3.0 % |
| Temperature | 0 - 80 °C | °C | 0.3 °C |
| Carbon Dioxide | 400 - 10,000 ppm | ppm | 3.0% + 30 ppm |
| Luminous Intensity | 0 - 10,000 Lux | Lux | 5.0 % |
| Sound Levels | 129 dB SPL | dBA | 1 dB |
| Reverberation | 0 - 10,000 ms | ms | tbd |
| VOC | Index 0 - 500 | Ideal = 100 | N/A |
| Nitrous Oxides (NOx) | Index | Ideal = 1 | N/A |
| Formaldehyde (HCHO) | 0 - 1000 ppb | ppb | ±20 ppb / ±20% m.v. |
| Particulates (PM 1.0, PM 2.5, PM 10) | 0 - 1000 μg/m³ | μg/m³ | 10% |
Temperature​
Why is Temperature Important?​
It's not surprising that a warm indoor environment can benefit personal health and comfort. In fact, extensive research conducted in New Zealand over the past 15 years by He Kainga Oranga has shown the link between low indoor temperatures and increased rates of respiratory and cardiovascular illnesses, particularly in the most at risk groups such as young children and the elderly. In New Zealand, there is also a marked inequity in the socioeconomic and ethnic distribution of those affected.
EXPERT ADVICE
It may be surprising but research has shown that temperature alone is the key determinant of what makes a home healthy.
So what can we do about this? Well, in New Zealand, we are fortunate enough to have incredible groups such as the Community Energy Network and a nationwide network of inspiring partner organisations. These groups offer practical advice and life-saving home upgrades across New Zealand for families that need it most. Monkeytronics Airsmart monitors gives us the power to measure temperature in New Zealand homes. Monkeytronics is proud to play a small but important part in the fight against cold and damp New Zealand homes.
OBVIOUS FACT
"If you can't measure it you can't improve it." - Peter Drucker
So let's measure it and use that data to improve.
How We Measure Temperature​
Monkeytronics uses a tiny solid state temperature sensor. The sensor element contains a tiny bipolar junction transistor. The silcon bandgap is used to directly measure the temperature. It's quite a common approach, and with careful attention to the calibration process, it is extremely accurate and results in a cost effective and robust sensor that draws virtually no power in operation. At this point, you're either whispering the words "wow, cooool", or your eyelids are starting to close. Whatever! I think it's interesting.
Ideal Temperature​
| Indoor Temperature | Health Effects |
|---|---|
| Above 29°C | Evidence from the modelling of outdoor temperature indicates that health effects are likely above 29 °C |
| Below 21°C | An indoor temperature of at least 21 °C is recommended for vulnerable groups including older people, children and those with chronic illnesses, particularly cardiorespiratory disease. |
| Below 18°C | 18 °C is the WHO recommended minimum to provide a safe and well-balanced indoor temperature to protect the health of general populations during cold seasons. |
| Below 16°C | Temperatures under 16 °C have been shown to have cardiovascular effects. |
| Below 12°C | Temperatures under 12 °C have been shown to have immediate reductions in children’s lung function. |
Relative Humidity​
What exactly is relative humidity?​
Relative humidity is a fiddly thing to define. It is the amount of moisture in the air relative to the maximum amount that the air can possibly hold before condensing into liquid water. The thing is, this maximum amount that the air can hold changes depending on the temperature. If you imagine you are in a house when it is heating up, the air temperature rises, and with it, the air is capable of holding more moisture. Therfore, the relative humidity falls. The actual humidity is still the same, because the water vapour in the air doesn't magically vanish. It's just that warmer air is capable of suspending more water vapour than colder air. You can think of it like how you can dissolve more sugar in boiling water than cold water. The warmer water has more energy with which to capture the sugar in the solution. Same goes for water vapour in air!
EXPERT ADVICE
Heating your home will reduce the relative humidity in the air. Heating also draws water out of the bones of the building.
Now to define the dew point, let's consider the same house again. It's night time - it's really cold outside and the heating is off. As the temperature inside falls, the air gradually looses it's ability to hold the moisture in the air. At a certain temperature, the moisture will start to condense back into water. This is the dew point. It's important to remember that the temperature inside your home will vary. Your windows are going to be the coldest surface, followed maybe by an exterior wall in a room you don't use very often. This is why water condenses on these surfaces and forms droplets that eventually join together and run down the window and walls. The long term affect of water condenseing on your walls and other internal surfaces of your home is that the moisture soaks into the bones of the building, and is extremely difficult to remove. This is damaging to the building itself (since bora worm and other wood munching beasties only survive in moist wood), but also for your family.
Why is Relative Humidity Important?​
In a nutshell, mould grows well in moist conditions. And some types of mould are incredibly bad for your health - Black Mould. In New Zealand, the relative humidity is pretty much always around 60 - 70 %. It's just the climate we live in. And that is pretty high. Because of this we need to be extra careful to avoid the build up of moisture in our homes. Moisture builds up from pretty much everything we do - from breathing while we are sleeping to drying clothes indoors. Other major causes are showers and cooking without using the fan. The best ways to combat humidity in the home are
- Ventilation - for instance open the windows first thin in the morning and let some fresh air blast through.
- Heating - as we covered above, warm air hold more moisture and lowers the relative humidity. This prevents the moisture from condensing and soaking into the fanric of your home.
EXPERT ADVICE
It's a really good idea to blast some fresh air through your home in the morning. Opening your windows for just 15 minutes will get rid of stale air and make your home fresher.
How We Measure Relative Humidity​
Materials science time again! Our sensor measures humidity using a sort of capacitor. Your average capacitor is sort of like a battery which holds electrical charge in short term storage for you, until you need it. As it turns out the charge capacity of the surfaces on the capacitor changes with the atmosphere's relative humidity. One of the main benefits of this measurement method is that it is solid state - it has no moving parts. The whole process is based on the physical and electrical properties of the materials.
Ideal Relative humidity​
When the relateive humidity gets too low (below 40%), it can be very uncomfortable leading to issues like dry skin, lips and eyes, itchiness and a sore throat. It can actually increase the transmissibility of air borne viruses. Low humidity also affects the building - it can cause parts of your home to contract and warp and wall paper (if you're trapped in the 1980s) will shrink and peel. Realistically, this is almost never an issue in countries like New Zealand except through over-zealous use of air conditioners. So don't do that!
On the flip side, high humidity is bad for your health for the reasons given above. Respiratory symptoms can worsen in humid spaces and for those with existing conditions, humidity control is particularly important. High humidity also damages your home's structural integrity and can result in nasty odours.
| Below 40% | 40% - 60% | Above 60% | |
|---|---|---|---|
| Allergies | O | O | |
| Asthmna | O | O | |
| Respiratory Illness | O | ||
| Viruses | O | ||
| Bacteria | O | O | |
| Dust Mites | O |
The ideal range is between 40% and 60%. In our New Zealand climate, this is a tall order but if we ventilate our homes by opening windows and using fans; and heat our homes, we can make our living spaces safer for our families.
Carbon Dioxide​
Carbon Dioxide is the stuff that animals breathe out and plants breathe in. This simple fact applies to every living thing on the planet. Since the industrial revolution, the equilibrium has been upset as more and more coal and recently other fossil fuels are being mined and extracted, with the effect of adding loads more carbon into the ecosystem. When this is burned, it ends up in the air as carbon dioxide. But you all knew that stuff anyway!
Figure x : Global Carbon Dioxide Concentration Over Time
Why is CO2 Concentration Important?​
Imagine a room full of kids at school. They've all got a copy of a big old book about string theory. The teacher is reading aloud. So everybody is having a good time.
If it's a bit chilly outside, maybe they've closed the windows to keep the heat in. After a few hours, the concentration of carbon dioxide in the classroom may rise up to say 2000 parts per million (2000 ppm). This is common place. It plays out in schools all across New Zealand, every winter. The problem is that when CO2 gets above about 1500 ppm, some of the kids may start experiencing headaches, dizziness, restlessness, difficulty breathing, tiredness and an increased heart rate. And while it affects different people to different degrees, some of them can get really cranky. Studies have shown that an increase in carbon concentration of 1000 ppm can reduce student attendance by up to 0.9% in average annual daily attendance, which is an increase of 20% in student absence. It has also been shown that it can significantly affect concentration and cognitive function. A Harvard study monitored students' performance in a wide range of cognitive areas, and found a decrease in performance by anywhere from 20% to 70%. In the context of our kids' performance in school and exams, this could easily make the difference between an A grade and a C grade.
Figure x : Harvard Study (1400ppm, 800ppm & 500ppm)
But it's not only at school. Studies have shown that teenagers' bedrooms were an area of the home which experienced the highest carbon dioxide concentrations, reguarly above the 1500 ppm guideline.
What About Ventilation and Covid?​
In the current context, carbon dioxide is also being used as a proxy to measure ventilation to reduce the spread of infectious diseases like Covid 19. There is a logical correlation between the amount of exhaled breathe in a room and the carbon dioxide concentration. It cannot directly measure the presence of coronavirus, but it can tell you when a space is inadequately ventilated. This is particularly important in classrooms and other shared spaces such as workplaces, hostipality and events.
How We Measure CO2​
Monkeytronics measures CO2 using a Sensirion SCD30. This device is accurate to within 30ppm and has a T-63 response time of 20 seconds. Each individual unit is factory calibrated and linearised for accuracy. The SCD30 uses NDIR sensor technology, with dual channels for best stability. The principle in use is that carbon dioxide absorbs particular frequencies of infrared light that will pass straight through other gases such an oxygen and nitrogen. The freqency of light that a molecule can absorb is a property of the molecule because of unique energy bandgaps between electron orbits present in the molecule. If we use a laser to generate light at exactly that frequency, we can use a simple light sensor to measure the amount of light that is absorbed and hence the concentration of carbon dioxide.
Ideal CO2 Concentration​
| CO2 Concentration | Effects |
|---|---|
| Below 450 ppm | Normal background concentration in outdoor ambient air |
| 450 - 1000 ppm | Concentrations typical of occupied indoor spaces with good air exchange |
| 1000 - 2000 ppm | Complaints of drowsiness and poor air |
| 2000 - 5000 ppm | Headaches, sleepiness and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present |
| Above 5000 ppm | Extremely high levels with serious health effects |
Sound Levels​
Why are Sound Levels Important?​
Good acoustics are an essential element in an effective teaching space. It's important that the ambient noise level is low enough that the teacher can make themselves heard clearly all the way to the back of the class. Another vital aspect of acoustics is reverb. Reverb is the effect of sound bouncing off the walls repeatedly, which reduces the intelligibility of speech. Let's say you pop a balloon. It will make a very loud, almost instantaneous popping noise,realeasing a sudden spike of acoustic energy. In a room with lots of reverb, the sound will bounce around for ages, gradually loosing energy, after the initial pop! The length of time it takes the sound to drop by 60 dB is called the Reverberation Time (RT or T60).
FUN FACT
The T60 definition (-60dB) seems like quite an arbitraty number. It turns out that 60dB is the normal dynamic range for orchestral music - which may explain how it was arrived upon.
How We Measure Sound Levels​
The Monkeytronics monitor measures ambient noise levels directly as sound pressure levels. Because we are interested in how sound is percieved by the human ear (which is attuned to certain frequencies more than others), we do a real time spectral filtering operation on the measured sound signal to give us the human ear response. We use an A-weighting approximation, which is a good compromise between computational intensity and accuracy.
Figure x : Sound Pressure Weighting Filters
The Monkeytronics monitor is also capable of calculating the reverberation time using our own algorithm. In general the reverberation time (T60) mesurement is measured under quite strict experimental conditions and uses a specialised piece of kit to generate a loud short-duration noise pulse. The resulting sound presssure level is then observed as it decays by 60 dB. We have two problems with this. First, it omits one of the most important elements of noise damping in the room (the twenty plus students and their bags and coats etc), and secondly and perhaps more crucially, we don't have any of the specialised kit so we have no means of observing a 60dB decay.
FUN FACT
Measurements made at St. Paul’s Cathedral in London, England indicated that with the cathedral empty, the reverberation time at 500 Hz was 11 s. When the cathedral was full, the reverberation time was 7.8 s.
We've developed a custom algorithm to continuously observe the (A-weighted) sound pressure in the room, and zone in on the 20dB decay (T20). We then apply some complex mathematics to extrapolate this to a 60 dB decay (multiply by 3 - honestly, it's a valid approach).
Ideal Acoustic Conditions​
Ambient Sound Level​
| dB Sound Pressure Level | What It Feels Like? |
|---|---|
| 40 dB | Soft whisper 2 meters away |
| 50 dB | Quiet speech |
| 60 dB | Conversation 1 meter away |
| 70 dB | Loud classroom chatter |
| 80 dB | Hectic classroom racket / Noisy cafeteria |
| 90 dB | Construction Site with a jack hammer |
| 100 dB | A Night Club |
Reverberation​
| RT60 Reading | What It Feels Like? |
|---|---|
| Less than 0.5 seconds | Acoustically 'dead'. This is ideal for a recording studio where you want no reverb at all. |
| 0.5 - 1.0 seconds | Perfect for classrooms: articulation is very clear but unfortunately music will sound terrible. |
| 1.0 - 1.5 seconds | Ideal for speaking: articulation of speech is clear. Music doesn’t sound full, rich, or warm at this level. |
| 1.5 - 2.5 seconds | A good compromise if the room is to be used for both speaking and music. |
| 3.5 seconds | Better for music, but some loss of articulation. Would likely be difficult to understand speech. |
| 8.0 - 11.0 seconds | Large medieval cathedrals will have a very long RT60! This is by design as the long reverberation time is well suited to organ music or the unaccompanied voice (for example, Gregorian chants). |
Lighting​
Why are Lighting Levels Important?​
Lighting and Visual Comfort in an essential element in classrooms and has been shown to contribute to improved learning performance. In classrooms, daylight is the ideal main source of lighting supplemented by electric lighting when insufficient. This gives rise to complex design requirements in terms of the size, orientation and number of windows, the surface reflectance of the walls, ceilings and floors, and the placement and power of electric lighting in the classroom.
FUN FACT
A study carried out in Holland in 2013 showed that by careful control of lighting in the classroom based on the activities undertaken, students in the experimental group showed an increase in concentration performance of around 15% and a reduction in errors made of around 30% against the control group.
How We Measure Lighting Levels​
We measure lighting levels using an ambnient light sensor (ALS), which has been designed to have a similar spectral response to that of the human eye. For the purposes of optimising the experience of a student, the light sensor is mounted facing forwards into the class, at 1.2 m - 1.8 m above ground level. The Monkeytronics monitor uses a transparent glass front panel, with a light transmissivity of 96%, and a rectangular field of view of 45° left to right, and top to bottom.
Figure x : Human Eye Response of Light Sensor
The following recommended ideal light levels are indicated in a range because different tasks, even in the same space, require different amounts of light. In general, low contrast and detailed taskd require more light.
Ideal Lighting Levels​
| Minumum Lighting Levels (Lux) | What the space is used for |
|---|---|
| 50 - 100 Lux | Corridors, stairs & storage areas |
| 200 - 300 Lux | Canteen, cafeteria and workout gymnasium |
| 300 - 500 Lux | Exhibit spaces, sports areas and general classrooms |
| 500 - 700 Lux | Science classrooms where experiments are conducted |
| 700 - 1200 Lux | Workshops and more serious scienctific laboratories |
Formaldehyde​
Why is Formaldehyde Important?​
Formadehyde is a naturally occuring volatile compound with the chemical formula HCHO, created in a number of natural processes, such as the oxidation of hydrocarbons and the decomposition of plant matter. It has a distinct strong smell. In the indoor environment, formaldehydes are released by resins, glues, paints, insulating materials, chipboard, plywood and some fabrics.
Exposure to low levels of formaldehyde may irritate your eyes, nose, throat, airways, or skin. Some people are more sensitive than others, so an exposure that causes no problems for some may make other people sick or uncomfortable. People who may be more sensitive to the effects of formaldehyde are the very young, the very old, and people with asthma and other breathing problems.
WARNING
The OSHA regulations require any product that is capable of releasing formadehyde at a level of 500 parts per billion or above to include a hazard statement "May Cause Cancer".
How We Measure Formaldehyde​
We use the Sensirion SFA30 for Formaldehyde measurement. This uses an electrochemical cell in which an enzyme reacts with the formaldehyde and produces an electrical signal proportional to he gas concentration. The SFA30 HCHO sensor has a low cross-sensitivity to ethanol and is optimized to operate in the low parts-per-billion (ppb) range to accurately detect low HCHO concentrations around the WHO reference value for indoor exposure.
Like all Sensirion sensors, it is factory-calibrated for accuracy.
Ideal Range​
In 2010, the World Health Organization (WHO) established an indoor air quality guideline for short- and long-term exposures to formaldehyde (FA) of 0.1 mg/m3 (800 ppb) for all 30-min periods at lifelong exposure. This guideline was supported by studies from 2010 to 2013.
The OSHA guidelines for the workplace put an absolute upper limit on Formaldehyde concentration at 500 ppb. The Monkeytronics Formaldehyde Monitor uses these limits for the warning and alert thresholds.
Particulate Matter​
Why are Particulates Important?​
Particulate Matter or Particle Pollution is the mixture of air-borne particles and liquid droplets composed of acids (such as nitrates and sulfates), ammonium, water, black (or "elemental") carbon, organic chemicals, metals, and soil (crustal) material. It can be considered in 2 categories:
- "Coarse particles" (PM10-2.5) such as those found near roadways and dusty industries range in diameter from 2.5 to 10 micrometers (or microns). The existing "coarse" particle standard (known as PM10) includes all particles less than 10 microns in size.
- "Fine particles" (or PM2.5) such as those found in smoke and haze have diameters less than 2.5 microns.
Health studies have shown a significant association between exposure to particle pollution and health risks, including cardiovascular effects such as cardiac arrhythmias and heart attacks, and respiratory effects such as asthma and bronchitis.
Exposure to particle pollution can result in increased hospital admissions, emergency room visits, absences from school or work, and restricted activity days, especially for those with pre-existing heart or lung disease, older people, and children.
The size of the particulate matter is important. Smaller particles (PM1.0 and PM2.5) can penetrate deeper into the lungs and pose a greater risk to a persons lungs and heart. Coarse particles are of less concern, although they can irritate a persons eyes, nose and throat.
How We Measure Particulates​
We use a Senisrion SPS30 Particulate Matter Sensor. This PM sensor uses a laser scattering principle, which works by using a laser to radiate suspended particles in the air. Then scattered light refelected from the particles is collected using a photodiode and photoelectric converter. Lastly the equivalent particle diameter and the number of particles with different diameter per unit volume can be calculated inside a microprocessor by using MIE Scattering Theory. If this sounds hard, it's because it is.
Ideal Particulate Matter Levels​
| Particle Size | Safe Level (μg/m3) | Warning Level (μg/m3) | Danger Level (μg/m3) |
|---|---|---|---|
| PM1.0 | Below 8 μg/m3 | 8 - 24 μg/m3 | Above 24 μg/m3 |
| PM2.5 | Below 10 μg/m3 | 10 - 30 μg/m3 | Above 30 nμg/m3 |
| PM10 | Below 20 μg/m3 | 20 - 50 μg/m3 | Above 50 μg/m3 |