HVAC engineers

Pumping Configurations When it comes to chiller plant design, there's a surprising amount of research and experimentation that went into it. Decades of trial and error took the entire industry, worldwide, in quite a few different directions. The oldest chilled water systems had a pump for every chiller. The purpose of the pump was to overcome pressure loss in the piping and supply the required flow rate to the cooling coils. The general rule of thumb was that chillers are best kept at a constant water flow rate. This simplified control and design and protected chiller evaporators. To allow for load variation, a bypass line would be placed at each fan coil or air handling unit, allowing for flow control at the load level. However, this presented a problem, which is that as the heat load decreased (at night for example), keeping all chillers operational would cause a severely low delta T. Solution: turn a chiller or two off. But having one pump per chiller meant that chiller sequenci...

Primary & Secondary Pumping Systems As we all know, a system with only primary pumping at a constant volume will operate inefficiently for most of its lifetime. The primary-secondary system solves one problem in the older system: high pumping energy consumption. But how does a primary-secondary system save pumping energy? First, the system starts by separating the piping into two sides: production (primary) and distribution (secondary). The primary side contains the chillers and the primary pumps, while the secondary side contains the secondary pumps and the cooling units (FCU/AHU). During times of partial load, which make more than 95 % of operational hours, the cooling coils won't be needing the same flow rate of chilled water because the heat load is less. This is controlled by a 2-way valve which regulates the flow of chilled water through the cooling coils based on the room's temperature. To save costs and eliminate the need for bypass lines around cooling units, the s...

Pressure Gauges Pressure gauges are connected to pipes to physically display the flow pressure - particularly the static pressure. Why do we need to monitor pressure in the first place? Pressure reading before and after equipment can indicate whether the component is running correctly or not. A high pressure drop is usually a result of a clog or a leak somewhere. To select a pressure gauge, two parameters are most important: accuracy and range. The range of a pressure gauge is the maximum pressure reading possible on that gauge. It is a good practice to aim for a range that is 1.5-2 times the system's working pressure, with the maximum allowed pressure somewhere in the range. (relief valve pressure) The accuracy of a pressure gauge is expressed by a +/-percentage of error in the pressure reading. For accuracy, ASME (American Society of Mechanical Engineers) has set standard classes for pressure gauges. Grades B, 1A & 2A. In a typical chilled water system, Grade B gauges do the ...

Understanding "Approach" in Chiller Systems: Causes, Impacts, and ASHRAE-Based Best Practices In chiller system performance, one critical parameter that is often overlooked but highly indicative of system health is the Approach Temperature. What is Approach? Approach refers to the temperature difference between: Evaporator Approach: Leaving chilled water temperature vs. refrigerant evaporating temperature Condenser Approach: Leaving condenser water temperature vs. refrigerant condensing temperature A low approach indicates efficient heat transfer, while a high approach signals performance degradation. ASHRAE Guidance What is a "Good" Approach? Based on industry best practices and references from ASHRAE: Evaporator Approach (Typical Range): 1-3°C (1.8-5.4°F) →Excellent / Clean condition 3-5°C (5.4-9°F)  → Acceptable, monitor trend > 5°C (9°F)  →Indicates fouling or performance issue Condenser Approach (Typical Range): 2-4°C (3.67.2°F) →Good performance 4-6°C (7.2-...

  Psychrometric Properties Complete Guide for HVAC Engineers :- Psychrometric properties define the behavior of air-water vapor mixtures and are essential for HVAC design, thermal comfort, and energy efficiency. Understanding these concepts helps engineers design effective cooling and heating systems. Key Psychrometric Properties DBT (Dry Bulb Temperature):  Actual air temperature measured by a standard thermometer WBT (Wet Bulb Temperature): Indicates evaporative cooling effect. DPT (Dew Point Temperature): Temperature at which condensation starts. Humidity Ratio (w): Moisture content in air. Relative Humidity (RH): Percentage of moisture in air compared to maximum capacity. Psychrometric Chart & Processes A psychrometric chart graphically represents air properties and processes such as: Sensible Heating & Cooling Cooling & Dehumidification Heating & Humidification Adiabatic Mixing. Human Comfort Conditions Comfort depends on temperature, humidity, air velocit...

Cooling towers are one of those systems everyone "knows", until performance drops and nobody can clearly explain why. In reality, a cooling tower is not just a heat rejection device. It's a thermodynamic interface between water, air, and ambient conditions - and its performance defines the entire chiller plant efficiency. WORKING PRINCIPLE (What actually happens) A cooling tower removes heat through evaporative cooling: Warm condenser water is distributed over fill media Air is drawn or forced through the tower A small portion of water evaporates That evaporation removes heat from the remaining water Cooled water returns to the condenser Key point from the field: The tower doesn't cool water to ambient temperature, it cools toward wet-bulb temperature, which is the real performance limit. MAIN TYPES OF COOLING TOWERS Induced Draft (most common) Fan at the top pulls air →better efficiency, stable airflow Forced Draft Fan at air inlet →easier maintenance, but more recir...

How Do We Calculate Required Airflow in a Cleanroom? In cleanroom engineering, airflow calculation is not a single-step process. It's a combination of multiple components that ensure cleanliness, pressurization, and system reliability. Total Airflow = ACH Airflow + Fresh Air + Leakage +Heat Load Air (converted) So how do engineers determine the right airflow? Step 1. Air Changes per Hour (ACH) Method This is the most widely used approach. Airflow = ACH × Room Volume Depending on the cleanroom classification: ISO 5  ⏩240-600 ACH ISO 6 ⏩ 90-180 ACH ISO 7 ⏩ 30-60 ACH ISO 8 ⏩ 10-25 ACH This ensures that the air inside the room is replaced multiple times every hour to maintain cleanliness. Step 2: Calculate Room Volume Room size: 10m x 5m x 3m Volume 150 m³ Step 3: Calculate ACH Airflow Formula: Airflow = Volume × ACH ACH Airflow = 150 x 25 = 3750 CMH Step 4: Add Fresh Air Typically 10-20% or as per standard Assume: 750 CMH Step 5: Safety Margin (5%) 5% of 3750 = 187.5 CMH Step 6: Add L...