improved thermal comfort & energy efficiency with … · improved thermal comfort & energy...
TRANSCRIPT
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
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
Pressure Independent System
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
Flexibility – easy to change zones
Ease of Commissioning
Confirmation of Airflow
Building Tuning Simplified
Simpler Complaint Resolution
Fewer BMS points (on board controls & sensors)
Simulator
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
0 Pa Difference6 6
Managing Flex losses
10 PaDifference
1 11
Maximum Length Recommended at 1.5m
Managing Flex Bend losses
3 Pa Difference0 3
Use the bracket to ensure
a smooth 90° elbow
Traditional VAV Box Design
FILTERCOIL
AHU
T
MULTIPLE FIXED APERTURE DIFFUSER OUTLETS
THERMOSTAT
120Pa
VAV BOX VAV BOX
RETURN
AIR
FAN WITH VARIABLE
FREQUENCY DRIVE
S
T
THERMOSTAT
Traditional VAV Box Design
Volume control upstream of diffusers
Air diffusion works well at 100% flow rate
After flow reduction upstream
Increased Dumping of Cold air
Increased Stratification of Hot air
Reduced Induction – reduced air change effectiveness
System Flexibility Compromised
Individual diffuser control costly
“Dumping takes place
at reduced volumes”
B A
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