HVAC engineers

Calculating Flow Rate To calculate the chilled water flow rate of a cooling coil (FCU/AHU), you need two parameters: q & ΔT. Now, what's q? q is the total heat load of a given room or space. It represents the sum total of internal & external heat loads. In other words, the cooling coil needs to remove heat from the space at a rate of "q" in order to bring it to the desired temperature. And who's carrying that q? It's the flowing chilled water, of course. The other parameter, ΔT, is the temperature difference between the supply and return chilled water pipes. ΔT, as discussed earlier, is best used at 7-10 °C. For example, if chilled water supply was at 5°C and the return is at 12°C, then your ΔT is 7°C. The higher the delta T, the less the required water flow. So, the question becomes: How much water flow is needed to carry the total heat load, at a certain temperature rise? How to calculate that flow: q = Q*c*ΔT Q: Flow rate of chilled water (L/s) c: Heat ...

Hydrotest in HVAC Systems (AHU & Chiller Piping) Hydrostatic testing is a critical step in HVAC commissioning to ensure strength, safety, and leak-free operation of chilled water systems before insulation and startup. Why Hydrotest ? Detects leakage in joints, valves & welds Verifies piping strength under pressure Ensures long-term system reliability Key Standard: Test Pressure = 1.5 x Working Pressure (Example: 6 bar → 9 bar) Where It's Applied? Chilled water piping (CHW supply & return) AHU coil connections Headers, risers & valve sections Basic Procedure: 1. Line preparation & flushing 2. Filling with water (air removal is critical) 3. Gradual pressurization 4. Pressure holding (2-24 hrs) 5. Inspection for leakage & pressure drop Common Mistakes to Avoid: Air trapped inside pipeline Sudden pressurization Not isolating AHU/Chiller Using uncalibrated gauges Final Step: Proper documentation & consultant approval A successful hydrotest ensures your HVAC s...

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...