1. GENERAL CONDITIONS PRIORITIZATION TO ENSURE BUILDING ADEQUATE I.A.Q.
• Efficient inactivation/dilution of indoor/outdoor origin biopathogenic aerosols;
• Maximum indoor personal protection against chemical or radioactive contamination of external origin (locally endemic, accidental or conflicting character).
• Maintaining carbon dioxide concentration within acceptable limits.
• Maximum energy efficiency;
• Reducing the building’s carbon dioxide footprint by adapting modern low CO2 concentration direct air capture (DAC) technologies.
2. PARAMETERS THAT DEFINE THE CONCEPT OF INTERIOR AIR QUALITY IN BUILDINGS:
According to the EPA definition, the IAQ refers to ALL the building’s indoor air components that affect the health and comfort of the people within. Understanding and controlling common building pollutants helps reducing the risk of health issues for their occupants. The negative health issues caused by indoor air pollutants may be experienced shortly after exposure or possibly years later. The values for exposure limits for the various pollutants mentioned in this article have been adopted and used in energy estimates, and are part of the compliance
criteria of the U.S. Department of Labor (USDL), Occupational Safety and Health Administration (OSHA) documents, as follows::
• CO2 – Concentrations & symptoms:
- 1000 to 2500 ppm Usual confort limits.
- 5,000 ppm (0.5%) Permitted exposure limit (PEL – OSHA)and Threshold Limit (ACGIH – TLV) for 8 hours exposure.No symptoms.
- 10,000 ppm (1.0%) Usually asymptomatic, possible drowsiness.
- 15,000 ppm (1.5%) Mild respiratory stimulation for some people.
- 30,000 ppm (3.0%) Moderate respiratory stimulation, increased heart rate and blood pressure, ACGIH TLV-Short Term.
- 40,000 ppm (4.0%) Immediate danger to life or health (IDLH).
• Radon and radioactive elements that by spontaneous fission produce Radon; Half-lives according to EPA:
• ⍺ radiation, consisting of a pair of neutrons and a pair of protons, with a body mass of 4, although they have minimal penetrability, produce maximum molecular and cellular distruction, compared to ß radiation, also corpuscular, but with a mass of 1836 times smaller than the ⍺, and γ radiation, of a purely electromagnetic nature. EPA recommends homes be fixed if the radon level is 4 pCi/L (picocurries per liter) or more. Because there is no known safe level of exposure to radon, EPA also recommends that Americans consider fixing their home for radon levels between 2 pCi/L and 4 pCi/L.
• NO2 and SO2 are usually released by the combustion processes in the vehicles’ thermal engines or in the general use heating equipment:
EPA: established NO2 1 hour exposure level at 100 ppb. EPA also maintained the average annual standard NO2 level at 53 ppb. The The standard 1-hour exposure level will protect public health by limiting people’s exposure to short-term peak NO2 (usually occurs near the main roads).
OSHA: The official permitted exposure limit in the air (PEL) of SO is an average of 5 ppm during an 8 hour work shift.
NIOSH: Permissible Exposure Limit (REL) SO2 is 2 ppm average for a 10 hour working shift și 5 ppm, for no more than 15 minutes working time.
• Pathogenic bioaerosols resulted either from outdoor sources or from the respiratory indoor people’s emissions:
There are few international regulations on acceptable limits for indoor or outdoor air microbial, viral or fungal airborne aerosols contamination. The main reason is airborne pathogens have various contaminating power levels, known to epidemiologists as “Minimum Pathogenic Number” (MPN). In general, MPN ranges from a few units to millions. as recently seen with the new Covid-19 variants.
At least here in Romania, there is the Order of the Ministry of Health no. 961/2016.
*Total number of germs /m3. air should not exceed 500-1500 depending on the degree of activity in the room “, values obviously towards the lower limit, as the occupancy rate of the space is higher.
Although it is not clearly stated, specialists in the field recommend that for spaces with an occupancy rate of more than 1 person per 4 m2 . or with sensitive people, not to exceed 800 germs /m3. air.
In the hospitals’ operating rooms (during work), in the newborns and infants rooms, a maximum of 300 germs/m3 of air are allowed, with the absence of hemolytic species.
3. TECHNICAL ANALYSIS FOR EPIDEMIC DESEASE FREE, ENERGY EFFICIENT IAQ.
4. AHU STRUCTURE EQUIPPED WITH UVGI SOURCES FOR AIR DISINFECTION AND HEAT EXCHANGER PROTECTION.
5. INDOOR AIR CIRCULATION PATTERN TO ENSURE BEST AEROSOLS GRAVITATIONAL MITIGATION.
Indoor favorable and unfavorable directions of air movement. Downward circulation will significantly contribute to the gravitational sedimentation of pathogenic particles, ensuring the best protection against contamination.
6. STAND ALONE AIR DISINFECTION FIXTURES – OLD TIMES.
7. STAND ALONE VENTILATED, CARCASSED-RAY-FREE, ULTRA SILENT AIR DISINFECTION FIXTURES – NOWADAYS.
8. PUBLIC TRANSPORTATION VEHICLES.
Public transport vehicles, both surface or underground, pose an extreme danger of airborne contamination.
In many European countries, adaptations have been made, with UVGI sources being introduced into air conditioning systems:
Since the last year, German city of Hale’s local administration, has been equipping all his local public transportation buses with such air disinfection equipment.
9. HVAC PLANT TO ENSURE THE INDOOR CO2 ACCEPTABLE AIR CONCENTRATION BY DILUTION WITH OUTDOOR AIR.
Air flow calculation to ensure classroom CO2 steady level at 2200 ppm.
General data:
- Classroom surface 60 m2
- Classroom height 3 m.
- Classroom volume 180 m3
- Average no. pupils in a classroom 25
- Total no. of classrooms 10
- Outdoor air CO2 concentration 430 ppm.
Dilution data results:
- Classroom dilution outdoor air flow 400 m3/hour
- Total school outdoor air flow 4000 m3/hour
- Season Winter.
- Outdoor temperature -7 0C.
- Outdoor relative humidity 30 %.
The following picture materialize the energy balance of this system:
10.DIRECT AIR CAPTURE (DAC) OF CO2 BY REVERSIBLE CHEMICAL ABSORPTION WITH HODROXIDES.
The process appeared and was widely used to ensure a proper IAQ in enclosed spaces, where it was not possible to communicate with the outdoor for dilution ventilation (submarines, space applications, etc.), or where the insulation conditions of the room were particularly strict, in order to avoid contamination with
extremely harmful elements (anti-atomic, anti-chemical, anti-biological shelters, high-risk bio-laboratories, etc.).
From energy point of view, the most widely used reversible chemical absorption process, the Ca(OH)2, has the following characteristics:
From stoichiometric and reaction energy calculations, the following theoretical data corresponding to the above mentioned nominal capacity, result for the above
mentioned chemical absorption process:
As a result, the active energy for the outdoor air thermal compensation of 445 KWh/day is no longer necessary, but, instead, the process recovered thermal
energy is usable to cover the thermal load to heat the building, for indoor air humidification, or for DHW preparation (115 KWh/day). Comparatively, on the whole, there is a local difference of 561 kWh/day between the two processes, in favor of the chemical absorption process. At the current stage of evolution of ecological solutions for energy production, photovoltaic, wind, geothermal, direct solar heat, one of the essential problems is the energy storage.
The combination of direct CO2 chemical capture, with ecological energy sources, leads to the closure of an energy cycle in which calcium oxide plays the essential role of extremely cheap and efficient energy accumulator. According to the existing practical experience, this chemical capture has a slightlymore complicated functional structure, using NaOH as an intermediate absorber, which has a higher affinity for CO2. :
Absorption: 2NaOH + CO2 → Na2 CO3 + H2O ∆H0 = -109.4 kJ/mol.
Causticizing: Na2CO3 + Ca(OH)2 → 2NaOH + CaCO3 ∆H0 = -5.3 kJ/mol.
Calcination: CaCO3 → CaO + CO2 ∆H0 = +179.2 kJ/mol.
Hydration: CaO + H2O → Ca(OH)2 ∆H0 = -64.5 kJ/mol.
The functional diagram of such an industrial system is presented in the following figure.
Of course, for HVAC systems, special equipment design is necessary.
11.CO2 DIRECT AIR CAPTURE – TECHNOLOGICAL PERSPECTIVES:
Extremely intense efforts are being made worldwide to develop efficient technologies for CO2 DAC. For the highest possible energy and financial efficiency, the mentioned efforts are concentrated towards CO2 industrial sources, combustion processes, where the concentrations are high, the respective solutions being impossible to be adapted to the IAQ management in buildings.
Exceptions are the achievements of MIT – Massachusetts Institute of Technology, where a team led by Prof. Sahag Voskian developed Quinone & carbon nanotubes membranes with electrostatically determined affinity for CO2 (Electric Swing).
Most important, the MIT solution is declared to be effective even at 400 ppm. CO2 air concentrations, which will surely give it an important place in building HVAC
systems. The system is currently undergoing functional testing at a large aluminum plant in Sweden.
The manufacturer (Verdox) estimates the commercial availability in 1-2 years.
REFERENCIES:
(1)Direct Capture of CO2 from Ambient Air
Eloy S. Sanz-Pérez,†,‡ Christopher R. Murdock,† Stephanie A. Didas,† and Christopher W. Jones*,†
†School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332-0100,
United States
‡Department of Chemical and Environmental Technology, ESCET, Rey Juan Carlos University, C/Tulipán s/n, 28933 Móstoles,
Madrid, Spain
(2) Stolaroff, J. K.; Keith, D. W.; Lowry, G. V. Carbon Dioxide
Capture from Atmospheric Air Using Sodium Hydroxide Spray.
Environ. Sci. Technol. 2008, 42, 2728−2735.
(3)TechXplore Engineers develop a new way to remove carbon dioxide from air 25 October 2019, by David Chandler
(4) Faradaic electro-swing reactive adsorption for CO2 capture†
Sahag Voskian and T. Alan Hatton Energy Environ. Sci.,2019, 12, 3530
(5)ISO 15714-2019 – on effective doses for various biopathogenic aerosols.
(6)ISO 15858-2016 – on personnel safety in UV-C exposure.
(7)ASHRAE Position Document on Filtration and Air Cleaning Approved by ASHRAE Board of Directors January 29, 2015
Reaffirmed by Technology Council January 13, 2018 Expires January 23, 2021
(8)ASHRAE HANDBOOK OF FUNDAMENTALS – chapter 62
(9) EPA – Reference Guide for Indoor Air Quality in Schools _ US EPA
(10) WHO GUIDELINES FOR IAQ
(11) Scientific Reports | (2021) 11:6260 – UV‑C irradiation is highly effective in inactivating SARS‑CoV‑2 replication. Mara Biasin1,
Andrea Bianco2, Giovanni Pareschi2, Adalberto Cavalleri3, Claudia Cavatorta3 and others
(12) ASHRAE EPIDEMIC TASK FORCE FILTRATION & DISINFECTION | Updated 10-21-2021 ashrae-filtration_disinfection-c19-
guidance
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