Ventilation and Air Quality Control Systems

🚪🌬️ Dedicated Outdoor Air Systems (DOAS) — what they solve DOAS conditions 100% outdoor air to meet code ventilation, control humidity, and keep pressurization stable. It decouples latent (moisture) from sensible (temperature) loads, so local units focus on comfort while DOAS handles moisture and CO₂. 🧭 Two delivery methods Indirect: DOAS supplies to an AHU/FCU return. Easier retrofit, uses existing duct paths. Direct: DOAS supplies straight to spaces. Best for guaranteed ventilation per zone and for avoiding over- or under-ventilation in VAV turndown. 🔗 Where DOAS pairs well VRF/VRV: Local coils manage sensible; DOAS pre-conditions outdoor air. 4-pipe Fan Coils: DOAS treats latent; FCUs trim temperature. Chilled Beams (active): DOAS provides dry primary air; beams handle sensible. Keep beam CHW above room dew point to prevent condensation. WSHPs: DOAS stabilizes ventilation and humidity; heat pumps handle zone loads. 💧 Moisture control that sticks Pre-cool and dehumidify outdoor air so supply air dew point is low enough to carry the room’s residual latent. This prevents wet coils downstream, avoids reheat waste, and protects finishes. 🔁 Energy recovery = free tonnage Add total energy wheels or plate/heat-pipe exchangers on exhaust to cut OA loads and fan power. Size exhaust to match OA to maintain building pressure. (Where contaminants exist, select ERV media accordingly.) 📐 Practical setpoints Ventilation supply: 12–14 °C dry-bulb with low dew point (e.g., 7–9 °C) for moisture control. Space RH: 40–55% for comfort and mold risk reduction. Keep OA filtration at least MERV-6 before wet coils; higher if outdoor air quality is poor. 🛠️ Controls that make it work OA flow control per zone (direct method) or per AHU/FCU (indirect). Dew-point control of DOAS coils, not just dry-bulb. Supply air temperature reset by outdoor enthalpy. Economizer lockout when humidity would rise. Condensate and freeze protection on coils; proper drain pitch. ⚖️ Selection trade-offs DX DOAS: Simple, roof-friendly, independent of plant. CHW/HW DOAS: Integrates with central plant; can share heat recovery; may upsize chiller if DOAS coil is large. Direct vs Indirect: Direct assures delivery per space; indirect leverages existing trunks but needs careful balancing. 🧪 Commissioning checklist Verify OA design cfm at all turndown states. Trend space dew point and DOAS SA dew point; confirm separation. Prove ERV wheel control (frost, purge, bypass). Test alarms: fan failure, high filter Δp, condensate, low-temp cutout. ⚠️ Common pitfalls Ventilation tied to VAV without floor-level verification → over/under-ventilation. DOAS air not dry enough → condensation at terminals. No energy recovery on high OA fractions → oversized plant. Missing pressurization plan → infiltration and IAQ issues. 🔚 Bottom line Use DOAS to own the latent load and the ventilation math. Local systems then run steadier, ducts get smaller, and IAQ becomes predictable.

Designing and using a Building Automation System (BAS) in an existing facility to create well-balanced, efficient, and healthy buildings requires both a strategic retrofit plan and careful operational use once installed. Here’s a structured approach: 1. Assessment and Benchmarking Existing Systems Review: Gather drawings, control sequences, and recent testing/air balance (TAB) reports. Map which equipment is automated, semi-manual, or outdated. Occupant Comfort & Health Data: Collect thermal comfort complaints, indoor air quality readings (CO₂, VOCs, humidity), and hot/cold zone reports. Energy Baseline: Benchmark energy use (kWh, therms, kBTU/sq.ft) before changes to measure impact later. 2. System Design for Retrofit Open Protocols: Use BACnet/IP, Modbus, or MQTT gateways to integrate legacy HVAC, lighting, and power monitoring systems into a common BAS platform. Zoning & Control Strategies: Add VAV box controllers, airflow measuring stations, and smart dampers where feasible. Layer demand-controlled ventilation (using CO₂ sensors) to balance health with energy efficiency. Sensor Deployment: Temperature, humidity, CO₂, and occupancy sensors distributed per ASHRAE/Well Building standards. Thermal imaging or wireless sensor networks to identify air balance and comfort issues in real time. Healthy Building Features: Integrate MERV-13+ filtration monitoring and filter life sensors. Add UV-C or bipolar ionization controls (where appropriate). Tie in IAQ dashboards for occupant transparency. 3. Control Sequences & Optimization Air Balance & Comfort: Program supply/return fan tracking and static pressure reset to reduce drafts and ensure balanced airflow. Zone-level setpoint adjustment with occupant feedback loops (via apps or kiosks). Energy Efficiency: Implement chilled/hot water reset schedules. Optimize economizer use for free cooling. Integrate with lighting controls and occupancy sensors for holistic energy management. Safety & Resilience: Alarms for high CO₂, humidity excursions, filter pressure drop, or equipment failures. Cellular failover routers for visibility during network outages (cyber-secure). 4. Operational Use Analytics Layer: Add FDD (Fault Detection & Diagnostics) to identify stuck dampers, simultaneous heating/cooling, or drifting sensors. Continuous Commissioning: Periodic re-balancing aided by real-time BAS data and thermal imaging surveys. Dashboards: Tailor interfaces for facilities, executives, and occupants (different levels of detail). Training: Facility staff must be trained in both BAS operation and comfort/IAQ troubleshooting. 5. Measurable Outcomes Balanced Comfort: More consistent temperatures across spaces, reduced hot/cold complaints. Efficiency Gains: Typically 15–30% energy savings post-retrofit. Health Improvements: CO₂ maintained below 800–1000 ppm, humidity controlled within 40–60%, reduced absenteeism and improved occupant satisfaction.

We spend one third of our lives sleeping, and this time is crucial for our health, well-being, and cognitive performance the next day. Thanks to ASHRAE funding, we completed a research project (ASHRAE 1837-RP) that has provided new information on the importance of bedroom air quality and ventilation for sleep quality. A paper summarizing the numerous experiments we performed in two parts of the world (Europe and China) has just been published:https://lnkd.in/d6gSgsec. The most important finding is that existing ventilation practice in bedrooms must be changed, and that rectifying this will have consequences for design and residential ventilation standards in dwellings, student dormitories, and hotels. We recommend that bedroom ventilation should be at a level to keep the CO2 concentration emitted by bedroom occupants at 800 ppm or below. This will require much higher ventilation rates in dwellings (bedrooms) than are currently prescribed in the standards. Increased ventilation does not need to consume much more energy, but the actual challenge is how to retrofit billions of bedrooms that currently have no ventilation at all, except the possibility to open a window. We encourage more research and development in this area. To address this challenge, a research innovation network on sleep was recently initiated by @ISIAQ: https://lnkd.in/dVf2UmKV. Mizuho Akimoto Xiaojun Fan Li Lan Chandra Sekhar Shin-ichi Tanabe @David P. Wyon International Centre for Indoor Environment and Energy DTU Sustain

Dedicated Outdoor Air System (DOAS) Why humidity control? ASHRAE 170 sets minimum requirements for outdoor air delivery, overall supply airflow, and maximum relative humidity for many hospital spaces. The 60% upper limit of relative humidity is intended to prevent the uncontrolled growth of mold spores on surfaces and building materials and to potentially reduce the spread of infectious microorganisms. Occupants typically want indoor temperatures in the low- to mid-70s (Fahrenheit). That means maintaining an indoor dewpoint of about 55F for general patient spaces. In operating rooms and other specialty areas where lower space temperatures are the norm, indoor dewpoint may need to be as low as 46F. Whenever the outdoor dewpoint is above those temperatures, the introduction of outdoor air for ventilation brings unwanted moisture. Removing that moisture is one of the principal functions of a hospital HVAC system. Moisture removal can be a very large fraction of the total load that an HVAC system deals with - 75% or even more, depending on outdoor conditions.

💨 Minimum? Acceptable? Or just quietly outperforming expectations? There’s a certain school of thought that never tires of poking at ASHRAE Standard 62.1 by calling it “minimum,” “acceptable,” or “designed to barely get by.” You know the tone. If it sounds modest, it must be inadequate. And yet… when we evaluate actual health harm measured in DALYs (disability-adjusted life years lost), the picture changes. 📊 Using pollutant harm intensities from recent peer-reviewed studies by Morantes et al. (2024) and Jones et al. (2025), I compared how major IAQ standards perform at a population health level, not just in policy language (note: this is not an exhaustive list). • ASHRAE IAQP (2022): approximately 871 DALYs per 100,000/year • LEED v5 (EQc1 – Indoor Air Quality Performance - Option 2): approximately 719 DALYs per 100,000/year • WELL v2 (WELL v2 - Feature A01): approximately 1,093 DALYs per 100,000/year • RESET (Acceptable): approximately 2,113 DALYs per 100,000/year (excluding formaldehyde and ozone) which is roughly equivalent to typical residential exposure Why does this matter? Because ASHRAE 62.1 scope is clear: ....to minimize adverse health effects by keeping contaminant levels below harmful thresholds.... When implemented through the IAQP pathway, it performs exactly as intended, sometimes better than the more "premium" standards. So before dismissing “minimum standards” as merely “acceptable,” maybe it’s time we ask: 👉 Acceptable to whom and based on what evidence? 📚 References - Links in first comment. • Jones et al. 2025 – Harm budget from Indoor Air Contaminants • Morantes et al. 2024 – DALY Analysis in Residential Buildings • Sherman and Logue 2011 – Equivalence in Ventilation and IAQ • Logue et al. 2012 – Hazardous Air Pollutants in Homes • Zaatari et al. 2016 – using DALY-based modeling to develop optimized ventilation strategies. Max Sherman Benjamin Jones Giobertti Morantes William Bahnfleth #IndoorAirQuality #ASHRAE621 #IAQP #DALYs #HealthBasedDesign #VentilationStandards #LEEDv5 #WELLStandard #RESETStandard #EvidenceBased #HealthyBuildings #BuildingPerformance

Understanding the Role of Air Handling Units (AHUs) in HVAC Systems ❄️🔥 As an HVAC professional, I often come across the critical role that Air Handling Units (AHUs) play in ensuring indoor comfort and air quality. Whether in residential towers, commercial complexes, or industrial facilities, AHUs form the backbone of air distribution and treatment in modern HVAC systems. What is an Air Handling Unit (AHU)? An Air Handling Unit is a centralized device used to regulate and circulate air as part of a heating, ventilation, and air conditioning (HVAC) system. It draws in outside air, conditions it (either heating, cooling, humidifying, or dehumidifying), filters it, and supplies it through the ductwork into various zones within a building. 🌬️🏢 Key Functions of an AHU: • Air Filtration 🧼 – Removes dust, particulates, and allergens. • Temperature Control ❄️🔥 – Heats or cools air using coils. • Humidity Regulation 💧 – Maintains moisture balance. • Ventilation 🌿 – Introduces fresh outdoor air. • Air Distribution 🌀 – Circulates air efficiently through fans. Core Components of an AHU: • Filters 🧽 - Trap dust and airborne contaminants. • Cooling & Heating Coils ♨️❄️ - Use chilled water or refrigerant (cooling) and hot water, steam, or electricity (heating). • Blower/Fan 🌀 - Distributes conditioned air through ductwork. • Dampers ⚙️ - Regulate airflow and manage fresh/return air mix. • Mixing Box - Combines outdoor and return air before treatment. • Drain Pan & P-Trap 🚰 - Collects condensate to prevent overflow. • Humidifier (optional) 💨 - (optional) – Adds moisture in dry climates. • Control Panel 🖥️ - Manages automation, safety, and energy efficiency. • Sound Attenuators 🔇 - Minimize operational noise. Types of AHUs: • Modular AHU 🏗️ – Custom-built for large systems. • Packaged AHU 📦 – Factory-assembled, easy installation. • Rooftop Units (RTUs) 🏢 – Installed outdoors. • Draw-Through / Blow-Through Types – Based on design needs. Installation & Maintenance Best Practices: • Proper load calculations (CFM, BTU) ✅ • Routine inspections & filter replacements 🔍 • Lubrication & belt maintenance 🛠️ • Drain cleaning to prevent leaks 💦 • Sensor calibration & BMS integration ⚡ Why it Matters: A well-maintained AHU ensures comfort, energy efficiency, and healthy indoor air quality. As HVAC professionals, our commitment to system performance directly impacts building health and occupant well-being. If you're managing HVAC operations or looking to optimize your facility’s air handling system, feel free to connect or message me — happy to share insights and solutions. #HVAC ❄️ #AirHandlingUnit 🏢 #MechanicalEngineering ⚙️ #HVACTechnician 🛠️ #BuildingManagement 🧰 #AHU 🌬️ #IndoorAirQuality 🌿 #EnergyEfficiency 💡 #HVACSupervisor 👷♂️ #MechanicalSystems

🛠️ *ENGINEERING CONTROL IN OPERATION THEATER (OT)* 📋 Based on *JCI Guidelines and Best Practices* 🔹 *1. Airflow & Ventilation Standards* *Objective:* Prevent surgical site infections (SSI) by maintaining clean airflow. * *💨 Air Changes per Hour (ACH):* Minimum of *20 ACH, with **4 fresh air changes*. * *🔄 Laminar Flow Systems:* Often installed in orthopedic or transplant OTs to provide *unidirectional airflow*. * *📈 Positive Pressure:* Maintained in OT compared to adjacent areas to prevent contaminated air entry. *🧪 Example:* Orthopedic OT uses *HEPA-filtered laminar airflow (LAF)* with positive pressure >2.5 Pa compared to scrub room. 🔹 *2. Temperature & Humidity Control* *Objective:* Maintain comfort and reduce microbial growth. * *🌡️ Temperature:* 20°C–24°C * *💧 Relative Humidity (RH):* 30%–60% *🧪 Example:* During a major cardiac surgery, the OT is monitored to stay within *21°C and 50% RH* to prevent condensation or microbial buildup. 🔹 *3. HEPA Filtration* *Objective:* Eliminate >99.97% of particles ≥0.3 microns. * Must be installed in the *terminal air outlets*. * Filters should be *validated annually* or when airflow performance drops. *🧪 Example:* HEPA filters in a neuro-OT are checked with *DOP (Dispersed Oil Particulate) test* every year. 🔹 *4. Zoning & Pressure Gradient* *Objective:* Control contamination spread. * *Zones:*  * Dirty zone (utility)  * Clean zone (corridors)  * Sterile zone (OT) * *Pressure Differentials:*  * OT > Scrub Area > Corridor > Utility Room *🧪 Example:* In a multi-theater complex, automatic doors maintain pressure zones to restrict bi-directional airflow. 🔹 *5. Airflow Direction Testing* *Objective:* Confirm correct air path. * *Smoke Test* or *Anemometers* used to verify air moves *outward* from OT. *🧪 Example:* Monthly smoke tests in a transplant OT to confirm air flows from sterile to less sterile areas. 🔹 *6. OT Doors and Interlocks* *Objective:* Reduce air turbulence and contamination. * *Self-closing, air-tight doors* * *Interlocking system*: Two doors cannot open at the same time. *🧪 Example:* In hybrid OTs, interlocked doors connect the imaging suite and maintain sterile airflow separation. 🔹 *7. Surfaces and Construction Materials* *Objective:* Prevent microbial growth and ensure easy cleaning. * *Seamless floors, **non-porous walls, and **coved corners* * Use of *anti-microbial paints* *🧪 Example:* Epoxy floor coating in OTs resists chemical damage and microbial colonization. 🔹 *8. Monitoring & Maintenance Logs* *Objective:* Ensure compliance and readiness for JCI inspection. * Daily HVAC checks * Monthly filter pressure drop logs * Annual HVAC performance validation *🧪 Example:* JCI surveyor checks logbooks of temperature and pressure records during OT rounds. 📘 JCI Emphasis: * *Safe environment of care (SOC) standards* * *Facility management (FMS) tracer methodology* * *Documentation and traceability* of all maintenance

Fresh Air Requirement in HVAC (Ventilation Basics) Fresh air is essential to maintain indoor air quality (IAQ), comfort, and safety in buildings. --- 🔹 Why Fresh Air is Required • Removes CO₂ and pollutants • Controls odor and humidity • Improves occupant health --- 🔹 Fresh Air Standards (ASHRAE 62.1 / NBC) 👥 Person-Based Office • 8–10 L/s/person (17–21 CFM/person) Conference Room • 10–15 L/s/person (21–32 CFM/person) --- 📐 Area-Based Office Area • 0.3 – 0.6 CFM/ft² • 1.5 – 3 L/s·m² Conference Room • 0.5 – 1.0 CFM/ft² • 2.5 – 5 L/s·m² --- 🔹 📊 Example (Combined Calculation) For an office of 100 m² with 10 persons: • Person-based = 100 L/s (≈ 212 CFM) • Area-based = 200 L/s (≈ 424 CFM) 👉 Final Fresh Air = 200 L/s (≈ 424 CFM) (higher value considered) --- 🔹 Methods of Fresh Air Intake • Fresh Air Fan (FAF) • AHU with mixing box • DOAS • ERV / HRV --- 🔹 Key Point ✔ Use both person + area method ✔ Select higher value for design 👉 Proper ventilation = Healthy + Energy Efficient HVAC System --- #HVAC #FreshAir #Ventilation #IAQ #ASHRAE #MEP #HVACDesign #BuildingServices

🔵 Central Heating and Cooling with AHU A central air conditioning system using an Air Handling Unit (AHU) and a chiller/heat pump is an efficient combination for providing heating and cooling in large buildings. This approach enables precise temperature and air quality control in every space and facilitates centralized maintenance. ▪️Cooling Section: - Function: The central chiller produces chilled water, which flows through the AHU’s cooling coils to cool the air. The cooled air is distributed through AHU fans into the ducts to cool the spaces. - Benefits: Uniform cooling distribution, zoning and independent temperature control across different areas, and high energy efficiency. - Design note: Minimize duct losses, select appropriate airflow pressure, and measure temperature and humidity accurately in each zone. ▪️Heating Section: - Function: The AHU includes a heating coil that operates with a hot liquid or steam to heat the air and deliver it to the spaces. - Heating sources vary: - Hot Water Coil (hot water from the boiler) - Steam Coil (central steam) - Heat Pump - Benefits: Precise heating for each zone, ability to mix heating and cooling via the same AHU, and centralized maintenance. - Design note: Choose the heating source based on project needs, and coordinate with safety and indoor air quality systems. ▪️How It Works: - The AHU filters the air through filters, then cools or heats it as it passes through the coils, and finally sends it to the spaces via the fans. - BMS/EMS systems coordinate heating and cooling, set temperatures and humidity, and optimize energy use. - Return air: The air leaving a space returns to the AHU via ducts, re-entering the cycle, with or without mixing with fresh air. ▪️Key Operations Points: - Continuous monitoring of temperature, humidity, and air quality in each zone - Regular maintenance of heating coils, cooling coils, filters, and pumps - Data analysis to improve efficiency and prevent failures - Duct design to minimize pressure losses 💬 What experience do you have with centralized heating and cooling in your projects? Given different heating sources (hot water, steam, heat pumps), which option would you prefer for potential projects and why? 🙌 I look forward to your comments. I’d appreciate your follow Monireh Noohian; let’s learn and grow together. 🤝 Image sourced from Air Conditioning Technologies and Appications by Muhammad Sultan, Zhaoli Zhang, et al. #HVAC #AHU #Chiller #Cooling #Heating #EnergyEfficiency #Engineering #BuildingServices