Pharmaceutical & medical


Hand sanitiser can be made available and surfaces can be frequently disinfected. Procedures can be established to reduce the chance of disease transmission, with measures such as screens, social distancing and even disinfectant fogging. However, even with all of these measures in place, one infected person can quickly contaminate large areas. Effective ventilation will therefore be essential, and the control system will need to undertake accurate and timely measurements from each room or space so that it can respond promptly. Some


systems may simply monitor CO2 in the exhaust gas, but this does not provide the ability to detect poor ventilation issues in specific spaces.


Choosing the best measurement parameter


One of the main functions of a building automation/management system (BMS) is to control thermal comfort and optimise energy usage, so temperature is undeniably the most important control parameter in occupied spaces. Some systems also measure and control humidity to maintain a level of 40-60 per cent RH. This is for health and comfort reasons as well as the protection of computer systems and the avoidance of structural or mould-related issues in the building. Temperature measurements do not generally


suffer from drift, but traditional humidity sensors do, so Vaisala’s HUMICAP sensors are preferable because of their long-term stability and insensitivity to interferences such as dust and condensation. These thin-film capacitive humidity sensors have become the industry standard in a wide variety of applications where long-term accurate, reliable, maintenance-free humidity measurements are required.


people and reduce human-generated pollution in


spaces, CO2 is the ideal additional parameter for automatic ventilation control.


using Carbon DioxiDe measurement as a proxy for effeCtive ventilation


Carbon Dioxide (CO2) is exhaled by people as they breathe, so an accumulation of CO2 indicates that (a) people are in the room and (b) the


ventilation is insufficient, so a good ventilation system should be able to detect this and automatically apply the correct amount of ventilation. The system must be automatic, and it must be able to ventilate individual spaces, so that each space is ventilated optimally and energy is not wasted over-ventilating or ventilating spaces that do not need it.


non-CoviD aDvantages of Co2 anD humiDity monitoring


The ASHRAE Green Standard 189.1(USA) and the European standard FprEN 16798-3 recommend using demand controlled ventilation (DCV) to reduce energy usage while promoting healthy indoor air. From an HVAC design perspective, CO2 is an


ideal proxy for indoor air quality where the building is predominantly occupied by people. Humidity would be either better or at least a useful additional parameter, especially in buildings that are used to store artwork, books, wine, historic artefacts etc., or in buildings that are themselves in need of conservation. Typically, outdoor air contains 250 to 400 ppm


CO2. In contrast, exhaled breath contains around 50,000ppm CO2 which represents a 100 fold increase over inhaled gas, so without adequate


ventilation, when people are indoors, CO2 levels will gradually rise.


Both the comfort and performance of people


inside buildings can be affected by CO2 levels. Occupied spaces with good air exchange may


contain 350-1,000 ppm, but anything above this can induce drowsiness, with levels above 2,000 ppm causing headaches, sleepiness, poor concentration, loss of attention, increased heart rate and slight nausea. Exposure to very high levels (from oil/gas burners or gas leaks) can even result in fatalities from asphyxiation. Recommended minimum ventilation rates are


provided for a wide variety of indoor spaces in ANSI/ASHRAE Standard 62.1-2019 Ventilation for Acceptable Indoor Air Quality. Several studies have evaluated the effects of


CO2 concentration on cognitive function. For example, Allen et al (2016)5


Increased humidity levels can be an indication of human activity and poor ventilation. However, humidity varies considerably as a result of external factors (e.g. freezing dry conditions or rainy humid conditions) rather than as a result of human exhalation. To summarise, temperature and humidity


monitoring play an important role in the optimisation of a BMS, but where facility managers need to take into account the occupancy of


Instrumentation Monthly June 2021 found that cognitive function scores were 15 per cent lower for the


moderate CO2 day (~945 ppm) and 50 per cent lower on a day with CO2 concentrations of ~1,400 ppm in comparison with two ‘Green+’ days (~ 540ppm). On average, a 400-ppm


increase in CO2 was associated with a 21 per cent decrease in a typical participant’s cognitive scores.


DCV based on CO2 measurements can therefore deliver improvements in well-being and productivity that far outweigh the costs of the DCV system itself.


Choosing the right Co2 transmitter


It is important to resist the temptation to purchase the cheapest sensors that meet the required specification. This is because, whilst accuracy and range are important; the ongoing performance of the BMS will rely on the stability of the sensors. Suppliers of HVAC systems will naturally prefer


sensors that you can ‘fit and forget’. Consequently, it is necessary to select sensors that do not require frequent recalibration to prevent drift. However, the selection process is further complicated by sensors that claim to compensate for drift by implementing a software solution which assumes that the lowest measured readings are the same as the average outdoor


concentration of CO2. The danger with this type of algorithm is that small errors are compounded as time passes; leading to very significant errors in the longer term. As an attempt to avoid true calibration, these software algorithm sensors are not applicable in spaces that are continuously occupied, and can also be fooled by building automation systems that aggressively ramp down fresh-air intake during off-peak hours. In some cases even the concrete in the walls may absorb


CO2 and thereby ‘trick’ the algorithm and create further inaccuracy. There is potential for a slight conflict of interest


between a BMS supplier/installer and a building owner/facility manager. For the former, the system must work perfectly immediately, and for at least the period of the warranty, but for the latter the requirement is more long-term. The cost of a good sensor fades into


insignificance in comparison with the benefits that it provides. Energy savings from accurate, need-based controls can be considerable, but even more importantly, the health and well- being of people inside of the building are protected and indoor conditions improve workplace performance. The ideal solution is therefore to opt for Vaisala


CARBOCAP CO2 sensors. This is because they employ dual-wavelength NDIR technology capable


of thriving in a variety of environments and able to conduct true self-calibration with an internal reference. The cost of this technology is insignificant in comparison with the energy costs of a BMS that is not efficient or with the cost of maintenance when low-cost sensors drift or fail. It is not uncommon for Vaisala’s sensors to


operate trouble-free for up to 15 years. This stability and reliability has been recognised around the world... and beyond. Vaisala sensors continue to operate on NASA’s Curiosity Rover, which was launched in 2011, and on-board the Perseverance Rover which landed on Mars in February 2021. In summary, here on Earth, disease prevention measures can be re-enforced by smart ventilation


with reliable CO2 measurements. Furthermore, good indoor air quality can have a significant positive impact on the health and well-being of people inside buildings.


Vaisala www.vaisala.com


35


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78