Improved Thermal Comfort & Energy Efficiency with low-pressure VAV diffusion design

Improved Thermal Comfort & Energy Efficiency with low-pressure VAV diffusion design

Technical Paper A guide to the design of an effective low pressure VAV air distribution system By Noel de Villiers Pr. Eng. BSc. Eng (Mech)

Traditional Building AC AHU \ FCU matched with a High Pressure Air Distribution System Excessive fan power Potential noise issues Common in many buildings VAV Box design used Energy Efficiency Meter

Current Building Trend EC AHU \ FCU mis-matched with a High Pressure Air Distribution System EC Technology is used to be more energy efficient Not a matched solution Moderate improvements VAV Box design used Energy Efficiency Meter

Future Buildings EC AHU \ FCU matched with an energy efficient Low Pressure Air Distribution System Matched solution for optimal energy efficiency Significantly lower fan power required Up to 68% on a well designed system Capable of precise air delivery to every room VAV Diffuser design used Energy Efficiency Meter

High Pressure System Advantages High pressures and velocities allow the duct size to be reduced Cost effective when a large number of outlets are used Pressure Independent System Disadvantages Excessive fan power required Higher noise levels can require attenuation Lack of flexibility Risk of cold air dumping & hot air stratification Costly for individual room comfort applications

Low Pressure System Advantages Lower fan pressure = reduced energy consumption Lower noise levels Flexibility greatly improved Variable and constant grille on the same duct No risk of cold air dumping or hot air stratification Cost effective for individual room comfort applications Disadvantages Duct sizes need to be larger to allow lower velocities Attention to duct design and pressures needed during design Pressure Dependent System

So what is a VAV Diffuser? Variable Geometry Coanda Mixing Effect

VAV Diffuser Benefits Individual Thermal Comfort Energy Efficiency Simulator Flexibility easy to change zones Ease of Commissioning Confirmation of Airflow Building Tuning Simplified Simpler Complaint Resolution Fewer BMS points (on board controls & sensors)

Good Duct Design Principles Three main diffuser take-off problem areas: T-Junction Flex length Flex Bend at neck of the diffuser

Managing T-junction losses 12 17 5 Pa Difference

Managing T-junction losses 6 6 0 Pa Difference

Managing Flex losses 1 11 Maximum Length Recommended at 1.5m 10 Pa Difference

Managing Flex Bend losses 0 3 3 Pa Difference Use the bracket to ensure a smooth 90 elbow

Traditional VAV Box Design RETURN AIR FILTER COIL FAN WITH VARIABLE FREQUENCY DRIVE 120Pa S AHU VAV BOX VAV BOX T THERMOSTAT T THERMOSTAT MULTIPLE FIXED APERTURE DIFFUSER OUTLETS

Traditional VAV Box Design Volume control upstream of diffusers Air diffusion works well at 100% flow rate B After flow reduction upstream Increased Dumping of Cold air Increased Stratification of Hot air Reduced Induction reduced air change effectiveness A System Flexibility Compromised Individual diffuser control costly Dumping takes place at reduced volumes

Low Pressure VAV Diffusion Design Due to variable geometry dumping does not take place at reduced volumes

Simple VAV Diffuser Duct Design VAV Diffusers will function well with duct pressures at -10% to +20% design levels Pressure sensors needs need to be placed 2/3 down the length of the duct Design ducting with a relative even pressure profile

Advanced VAV Diffuser Duct Design

Intermission Trivia

Designing with Equal Friction Most common method of duct design This method has duct sized for a constant static pressure loss due to friction per unit length This method can be used with VAV Diffusion if; The starting velocity is less than 5 m/s in the duct The duct run is short enough so that the pressure drop from beginning to end fails within -10% to +20% range that the VAV Diffusers can accommodate Good duct principles are used, ie short Flex

Designing with Equal Friction Typically used where short duct runs are required This method yields; Excellent individual thermal comfort Excellent levels of room control Improved energy efficiency saving v s traditional high pressure VAV Box

Designing with Static Regain This method has duct sized to obtain the same pressure throughout the duct run Using static regain method of duct design, the increase in static pressure at each branch offsets the friction loss in the succeeding section of the duct The static pressure should then be the same before each VAV Diffuser and at each branch The design does not need to be perfect, remember the diffusers can manage -10% to +20% pressure drop

Designing with Static Regain Due to lower design velocities, the duct dimensions are typically slightly larger than when using the Equal Friction duct design method The increase in duct cost is offset by; Lower operating cost Less ducting since more than one zone can be on the same duct run Savings in system balancing time

Designing with Static Regain Typically used with long duct runs and\or when optimal energy efficiency is required This method yields; Excellent individual thermal comfort Excellent levels of room control Maximum energy efficiency saving

VAV Box Duct Design Example Equal Friction Design More ducting required More branches required Less comfort control No flexibility

VAV Diffuser Duct Design Example Static Regain Design Less ducting required Simpler ducting design Large ducting at start More individual comfort control Excellent flexibility Port Side Example

Product Walk Through Diffusers Ceiling, Linear, Wall

Product Walk Through Master Room Controllers Wall Thermostats On Board

Product Walk Through Power Module 15 Diffusers to one PSU 1 to 15 Master Diffusers Can be Standalone

Product Walk Through BMS Connectivity 60 Diffusers to one access point (IP Address) BACnet IP BACnet ms\tp LonWorks

Product Walk Through Cables All supplied Plug and Play connection

Product Walk Through Air Flow Sensors Measures neck pressure and calculates airflow Electronic commissioning Precise air flow control to every diffuser No air flow hood measurements required Easy building tuning for the life of the building

Product Walk Through Light Switching Occupancy sensing Switch Diffuser and \ or Lighting off Saves HVAC energy & Lighting bills

Product Walk Through Commissioning Tool MLM Tool8 Application

Office Building Aldi Head Office - Sydney 42 Electronic Linear Wall Diffusers Meeting and Office Rooms VLN15001/2 and Airflow sensors CLN15004/2 BACnet IP BMS Integration

University Building Queensland University of Technology 107 Electronic VAV Wall Diffusers Wall Thermostats with Occupancy Sensors Green Star Building BACnet TCP\IP BMS Integration

Shopping Centre Grand Plaza Stage 2 Queensland Large Shopping Centre, Multiple small shops 94 Electronic VAV Square Diffusers BACnet MS\TP BMS Integration

Country Hospital Echuca, Victoria 400 Electronic VAV Square Diffusers 182 Wall Thermostats Variable AHU, static regain, ERV, 100% fresh Air, no attenuation required Designed around the Rickard Diffusers Presented at NEBB conference BACnet IP BMS Integration Won 2014 AIRAH Innovation Award!

Major Hospital Sunshine Coast University Hospital, QLD 4,000 Electronic VAV Circular Diffusers Airflow Sensors on all Diffusers BACnet IP BMS Integration Advanced simple electronic commissioning - No air flow hood measurements required

Take Home Points EC AHU \ FCU matched with an energy efficient low pressure air distribution system provides optimum energy efficiency Improved individual room comfort & control Simplified Building tuning that can be conducted remotely Flexibility for tenant fitouts changes Precise air flow delivery