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Chiller & Boiler Pump Location – Upstream or Downstream? Let’s Settle This Debate

  Chiller & Boiler Pump Location – Upstream or Downstream? Let’s Settle This Debate One of the recurring questions I hear from engineers, operators, and even contractors on site is: 👉 “Should pumps be located upstream or downstream of chillers and boilers?” At first glance, it feels like a simple “rule-of-thumb” answer. But in reality, it’s a nuanced design decision guided by hydronic principles, ASHRAE handbooks, and equipment manufacturer limits. Let’s break it down 👇 🌡️ Chilled Water Systems Low- to Mid-Rise Buildings: Pumps are often placed upstream of the chiller evaporator (on the return side). ✅ Benefits: Pump heat is absorbed by the chiller, positive NPSH margin, and evaporator stays flooded. 🔎 Backed by: Trane Engineers Newsletter & ASHRAE guidance. High-Rise or Pressure-Limited Plants: Pumps are placed downstream of the chiller evaporator (on the supply side). ✅ Benefits: Prevents adding pump head across the chiller tubes (protects pressure rating). ❌ Drawback...
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A "VAV refrigeration system

 A "VAV refrigeration system" is a misnomer for a Variable Air Volume (VAV) HVAC system, which is a type of heating, ventilation, and air conditioning system that controls temperature by modulating the volume of conditioned air delivered to different zones. Unlike a constant-volume system, a VAV system supplies variable airflow at a constant temperature, adjusting the airflow up or down based on the cooling or heating demand in each zone. This makes it more energy-efficient and allows for precise temperature control in different areas of a building simultaneously.

How it works
Constant temperature, variable airflow: The main
air handling unit (AHU) delivers air at a consistent temperature.
VAV terminal boxes: As the air travels through the ductwork, it reaches a VAV box in each zone (room or area).
Thermostats and sensors: A thermostat or sensor
in the zone detects the temperature.
Dampers: If the zone is too warm, the sensor
signals the VAV box to open a damper, increasing the airflow. If the zone is too cool, the damper closes to reduce airflow.
Variable fan speed: A Variable Speed Drive (VSD) on the AHU fan adjusts its speed based on the system's overall demand, further saving energy by not running the fan at full power all the time.
Benefits
Energy efficiency: Reduces fan energy use by only running the fan as fast as needed. It also avoids over-cooling or over-heating unoccupied areas.
Precise temperature control: Each zone can be set temperature.
VAV terminal boxes: As the air travels through the
ductwork, it reaches a VAV box in each zone (room or area).
Thermostats and sensors: A thermostat or sensor
in the zone detects the temperature.
Dampers: If the zone is too warm, the sensor
signals the VAV box to open a damper, increasing the airflow. If the zone is too cool, the damper closes to reduce airflow.
Variable fan speed: A Variable Speed Drive (VSD) on the AHU fan adjusts its speed based on the system's overall demand, further saving energy by not running the fan at full power all the time.
Benefits
Energy efficiency: Reduces fan energy use by only
running the fan as fast as needed. It also avoids over-cooling or over-heating unoccupied areas.
Precise temperature control: Each zone can be set
to a different temperature, providing better thermal comfort than single-zone systems.
Reduced noise: Lower fan speeds in the VAV system result in quieter operation.
Flexibility: Systems can be easily adapted to changes in building layout, notes starduct.vn.
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