ASM Engineering Services Pvt. Ltd.

26/03/2026

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19/03/2026

How Variable Refrigerant Flow became the most consequential advance in building comfort since the birth of mechanical HVAC — and why its greatest era is still ahead.

19/03/2026

By Mukesh Deuba
Indoor pools are one of the most technically demanding spaces in building design yet many facilities struggle with humidity, air quality, condensation, and energy costs simply because the fundamentals were overlooked at the design stage.
After going through the Dectron Natatorium Design Guide, I put together this reference covering the 11 most critical design topics every engineer, contractor, and facility owner should know from humidity control and ev***ration calculations to condensation prevention and energy recovery.
Whether you are designing your first natatorium or your fiftieth, these principles apply every time.

18/03/2026

By: Yãshôdhà Bhûjêl
Do you still rely on thumb rules for heat load calculation???
In HVAC design, precision is not optional but it’s essential.Yet, many projects still begin with shortcuts like “1 ton per 500 sq. ft.”

🔹The problem with thumb rules?
•They ignore orientation, geographical position, occupancy, insulation, equipment load, and climate conditions.
•They often lead to oversized systems (higher cost, wasted energy, poor humidity control) or undersized systems (discomfort, frequent breakdowns).
• Modern buildings—hospitals, data centers, offices simply cannot be designed responsibly with guesswork.

🔹What Proper Heat Load Calculation Involves?
Heat load calculation is the scientific process of determining the exact cooling or heating capacity a building needs. It considers:
•External loads: solar gain, conduction through walls/roofs, infiltration of outdoor air
•Internal loads: occupants (sensible + latent heat), lighting, equipment
•Ventilation loads: fresh air requirements add both sensible and latent heat
•Climate & orientation: the same building may need 5.4 tons in Houston but only 3.5 tons in Chicago.

🔹 Standard Methods:
• ASHRAE Handbook of Fundamentals
•Manual J (Residential) and Manual N (Commercial)
• Software tools like Carrier HAP, Trane TRACE, EnergyPlus
These methods ensure compliance, efficiency, and sustainability.

Heat load calculation is not guesswork,it’s engineering.Thumb rules may seem convenient, but they compromise efficiency, sustainability, and comfort.Accurate calculation ensures the right system size, lower energy bills, and longer equipment life.

17/03/2026

By Gaurab Gautam
The terms adiabatic cooling and ev***rative cooling are often used interchangeably in HVAC discussions. However, these are two fundamentally different thermodynamic processes.
Adiabatic Cooling
Adiabatic cooling is defined as a cooling process that occurs without heat transfer across the system boundary.
Thermodynamically:
dQ=0
From the First Law of Thermodynamics:
dQ=dU+ dW
Since:
dQ=0
the equation becomes:
dU=−dW
Where:
U = internal energy
Q = heat transfer
W = work done by the system
In this process, cooling occurs because the system performs work on its surroundings, resulting in a reduction of its internal energy.
From a molecular perspective, when a gas expands, the molecules move farther apart. Part of their kinetic energy (KE) is converted into potential energy (PE) associated with molecular separation. As the average kinetic energy decreases, the temperature of the gas drops, even though no heat is transferred to or from the surroundings.
Examples of adiabatic cooling include:
· Gas expansion through nozzles or turbines
· Rapid expansion of gases in atmospheric processes
Ev***rative Cooling
Ev***rative cooling is a heat and mass transfer process driven by the ev***ration of water into air.
Liquid water → Water v***r
The energy required for this phase change is the latent heat of v***rization, which is absorbed from the surrounding air.
The heat removed from the air can be approximated as:
Q=mevap*hfg​
Where:
mevap = ev***ration rate (kg/s)
hfg = latent heat of v***rization (kJ/kg)
During this process:
1. Dry-bulb temperature decreases
2. Humidity ratio increases
3. Latent heat of the air-water system increases
Ev***rative cooling is commonly used in systems such as:
· Cooling towers
· Ev***rative air coolers
· Spray-assisted condensers and dry coolers
Simply
Adiabatic cooling: Temperature decreases due to work/expansion, with no heat transfer across the system boundary.
Ev***rative cooling: Temperature decreases due to latent heat absorption during water ev***ration, involving both heat and mass transfer.

In HVAC psychometrics, ev***rative cooling is often approximated as a constant enthalpy process, which sometimes leads people to loosely call it “adiabatic.” Strictly speaking, however, it is not a purely adiabatic thermodynamic process.

16/03/2026

By: Aditya Adhikari
💨 Stop ventilating empty rooms.
Most buildings run ventilation at 100% — whether there are 2 people inside or 200.
That's not smart. That's just expensive.
Demand Control Ventilation (DCV) changes the game:
→ CO₂ & occupancy sensors detect who's actually in the space → The system adjusts fresh air supply in real time → You're not conditioning air for people who aren't there
The results?
✅ 20–30% energy savings on ventilation loads
✅ Better indoor air quality — air responds to actual need
✅ Longer equipment life from reduced runtime
✅ Greener buildings, lower carbon footprint
It's not complicated. It's just smarter engineering.
Fresh air when you need it. Not when you don't.
Optimize indoor air quality while reducing energy consumption.
1. How DCV Works - Sensors
CO₂ Sensors, Occupancy Sensors, VOC Sensors
2. How DCV Works - Variable Airflow Adjustment
Low occupancy: Reduces ventilation to save energy
High occupancy or poor air quality: Increases airflow for comfort and safety
3. How DCV Works - Integration with HVAC
•Adjusts dampers, fans, and air-handling units automatically
Here's the framework:
Start with the space, not the equipment. → Define occupancy load, heat gains, and contaminant sources before selecting any hardware.
Size for worst-case, control for average. → Oversized systems running at full speed waste energy. Variable air volume (VAV) with CO₂/occupancy sensors lets the system breathe with the building.
Pressure relationships are everything. → Positive pressure in clean zones, negative in dirty ones. Get this wrong and you're fighting contamination forever.
Commission before you hand over keys. → A system that looks right on paper but isn't balanced is just expensive sheet metal.
The goal isn't maximum airflow — it's the right airflow, at the right time, in the right place.
Demand control ventilation isn't a product. It's a mindset.

16/03/2026

By Binaya Shrestha
𝗔𝗶𝗿 𝗖𝘂𝗿𝘁𝗮𝗶𝗻𝘀 𝗶𝗻 𝗛𝗩𝗔𝗖 𝗦𝘆𝘀𝘁𝗲𝗺𝘀
An air curtain is a device installed above a doorway that blows a high-velocity stream of air across the opening, creating an invisible air barrier between indoor and outdoor environments.
𝗪𝗵𝘆 𝗶𝘀 𝗶𝘁 𝘂𝘀𝗲𝗱?
• Reduces hot or cold air infiltration
• Improves HVAC energy efficiency
• Prevents dust, insects, and pollutants from entering
• Maintains indoor comfort while doors remain open
𝗛𝗼𝘄 𝗱𝗼𝗲𝘀 𝗶𝘁 𝘄𝗼𝗿𝗸?
A fan draws air and discharges it downward at high velocity, forming a continuous air stream that separates two spaces without a physical door.
𝗖𝗼𝗺𝗺𝗼𝗻 𝗮𝗽𝗽𝗹𝗶𝗰𝗮𝘁𝗶𝗼𝗻𝘀:
Supermarkets, commercial building entrances, hospitals, warehouses, restaurants, and cold storage facilities.
Air curtains are a simple yet effective solution for improving energy efficiency and maintaining indoor air quality in buildings.

07/03/2026

07/03/2026

By Aditya Adhikari
Choosing the Right Ventilation System 🌬️
Selecting a ventilation system isn’t just about equipment—it’s about comfort, safety, and efficiency. Here’s a simple approach:
1️⃣ Know the Building – Type, occupancy, and air quality needs.
2️⃣ Check Codes – Follow local standards for airflow and safety.
3️⃣ Assess Space – Make sure ducts, fans, and units fit.
4️⃣ Calculate Airflow – Determine required ventilation rates.
5️⃣ Pick the System – Natural, mechanical, or hybrid.
6️⃣ Energy & Comfort – Choose efficient, quiet, and easy-to-maintain solutions.
7️⃣ Coordinate On Site – Work with other trades to avoid clashes.
Right ventilation = healthier spaces + smooth operations! 💡🏗️

07/03/2026

By Mukesh Deuba
ASHRAE 62.2-2025: Comprehensive Overview & Practical Guidance (For Residential IAQ & Ventilation)

As homes become more energy-efficient and airtight, ANSI/ASHRAE Standard 62.2-2025 is the go-to benchmark for ensuring acceptable indoor air quality (IAQ) through mechanical ventilation, local exhaust, and source control. This edition (incorporating 16 addenda from the 2022 version) raises the bar for health-focused design.

Core Purpose & Scope:
1. Apply to single-family homes, townhouses, and low-rise multifamily dwellings (non-transient occupants).
2. Minimum requirements for dwelling-unit ventilation, local mechanical exhaust, and source control to dilute contaminants from occupants, materials, and activities.
3. Not maximum higher rates are encouraged for better IAQ, especially during pollution episodes or health concerns.

Key Updates in 2025 Edition
From official ASHRAE sources:

1. Filtration upgrade: Systems with mechanical supply now require MERV 11 filters (up from MERV 6) better capture of fine particles (1-3 microns), allergens, and pollutants.
2. New optional IAQ Procedure: Performance-based compliance path for innovative designs (modeling, measurements, or alternatives to prescriptive rates).
3. Local exhaust expansion: Now explicitly required in toilet rooms (in addition to kitchens and bathrooms).
4. Ozone limits: Air-cleaning devices (e.g., electronic cleaners) must not generate excessive ozone.
5. Duct sizing change: Uses equivalent diameter (instead of hydraulic) for prescriptive tables -simplifies calculations.
6. Ground cover requirement: Exposed earth in crawlspaces must be covered to limit soil gas entry (radon, moisture).
7. Shorter separation distance exception: Reduced minimum between air intakes and exhausts under specific conditions.
8. Infectious aerosol guidance: New informative Appendix E (references ASHRAE 241) - boost ventilation, upgrade to MERV 13, if possible, maintain 40–60% humidity, use portable HEPA cleaners during outbreaks.

Whole-Building Ventilation Rate Calculation
Formula (I-P units): Qfan = 0.03 × Afloor + 7.5 × (Nbr + 1) [cfm]
Afloor = conditioned floor area (ft²)
Nbr = number of bedrooms

ASHRAE 62.2 Infiltration Credit

1. Ventilation Equation:
Qfan=Qtot-Qinf(balanced systems).
2. Infiltration Rate (Qinf):
Qinf=0.052x Q50 x wsf x (H/Hr)z
Q50: blower door leakage at 50 Pa
wsf: weather/shielding factor
H: ceiling height, Hr=8.2 ft
z: exponent (≈0.65–0.75)

System Type:
1. Balanced (HRV/ERV): full credit (Φ = 1).
2. Unbalanced (exhaust/supply): reduced credit.
Requirement: Blower door test mandatory; no default assumptions.

Local Exhaust Requirements:
1. Kitchen: 100 cfm intermittent or 5 ACH continuous (ducted outdoors).
2. Bathroom/Toilet: 50 cfm intermittent or 20 cfm continuous (each room, ducted outdoors).

07/03/2026

By: Gaurab Gautam

Types of HVAC Ducts – Based on Shape, Pressure & Velocity
Duct Selection impacts energy efficiency, pressure loss, noise level, and overall system performance.
Based on Shape
1. Rectangular
Commonly used in buildings, industries, residential projects, and plant applications.
Advantages
· Can be used in a small space
· Easy to fabricate, bend, and join
· Suitable for low pressure system
· Applicable for higher airflow requirements
Limitations
· Chances of leakage from joints
· Higher noise as compared to Spiral/Oval ducts
· Heavier than Spiral/Oval ducts requires more structural support
· Higher friction loss

2. Spiral Duct
Commonly used in kitchen, offices, factories and offshore.
Advantages
· Light weight with minimum material
· Suitable for medium to high-pressure systems
· Low friction loss
Disadvantages
· More costly than rectangular duct

3. Oval Ducts
Commonly used in Energy Efficient buildings, Hotels/Exhibition Halls
Advantages
· Better airflow performance than rectangular ducts
· Lower friction loss
· Medium pressure applications
· Space-efficient alternative to round ducts

4. Square Duct
Less common, typically used in specialized layouts where symmetry is required.
Based on Pressure Classification
1. Low Pressure System
· Up to 2-inch wg
· Used in residential and light commercial buildings
2. Medium Pressure System
· 2-to-6-inch wg
· Used in commercial buildings and industrial facilities

3. High Pressure System
· Above 6-inch wg
· Used in large industrial plants and long duct runs
Based on Velocity
1. Low Velocity
· Up to ~1000 FPM
· Residential & comfort cooling

2. Medium Velocity
· 1000–2000 FPM
· Commercial buildings

3. High Velocity
· >2000 FPM
· Industrial & long duct systems