HVAC CONTROLS
AS A TOOL IN
ENERGY MANAGEMENT
The Map
1.
Overview on topic selection
2.
Traditional HVAC control methodology
3.
Adapted HVAC control methodology
4.
Areas of focus in HVAC energy saving initiatives
5.
Case Study: Cavendish Square
6.
Case Study: Menlyn Park Shopping Centre
7.
Case Study: Gateway Theatre of Shopping
8.
Summary of savings
Overview on topic selection
 HVAC is responsible for up to 60% of energy consumption in a
building
 Deviate away from “standard” energy management ideas
 Exposure limited in press
 Out of sight – but not out of mind
 Focused on concept of control methodology
Traditional HVAC control
methodology
 Traditional chilled water systems designed to supply chilled water at
a pre-determined temperature
 Chilled water at 6Deg C, off coil at 15 Deg C
 Additional heat load causes chilled water system to work harder to
meet pre-determined settings, using more energy
 Reduction in heat load causes chillers to unload and continue to run
at low load
Adapted HVAC control
methodology
 Exact reverse of the traditional methodology
 Chilled water supply temperatures and common secondary chilled water
Delta T allowed to drift
 Multiple control reference points
 Spacial temperature main driver
 Maximum energy savings made under Part-Load conditions
 Removing equipment from sequence is the intelligence
 Unloading is not a linear relationship to cooling (A chiller running at 50%
load utilizes 75% energy)
Adapted methodology (Cont)
 Impact is measured over time to
test trends with push to upper
control limits
 The use of Variable Speed Drives
(VSD’s) on pumps and fans. A
20% drop in speed equates to a
50% drop in energy consumed
 All HVAC equipment has to be
operating optimally
Areas of focus in HVAC energy
saving initiatives
Control Methodology and Strategy
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Chiller sequencing
Chiller load control
Chilled water supply temperature control
Secondary chilled water pump control by VSD
Chilled water Delta T control
Supply air temperature control
Supply air static pressure control by VSD
Economy cycle damper control
Cooling tower condenser water temperature control
Chiller sequencing and load
control
 Sequenced morning startup allows half hour intervals. This ensures
full loading in sequence as well as maximum demand management
 Chillers run at peak operating load conditions with minimum loading
of 78%
 Utilized multiple reference points including chilled water supply
temperature
 Chillers with less than 78% loading are taken out of sequence or
changed out with different size chiller
Chilled water supply temperature
control, Secondary chilled water
pump control by VSD and Chilled
water Delta T control
 Concept here is to measure the secondary chilled water return
temperature and vary the speed of the secondary chilled water
pump to maintain an approximate 6 Deg C Delta T across the
common chilled water supply and common chilled water return
 Allows chilled water supply temperature to drift
Supply air temperature
control, Supply air static
pressure control by VSD and
Economy cycle damper control
 Uses the space temperature as a reference to reset chilled water supply
temperature
 Chilled water supply temperature can drift higher when external air
temperatures are low
 Free cooling through economy cycle
 VSD vs. PRD
Cooling tower condenser water
temperature control by VSD
 Utilizes return condenser water temperature as reference
 Cooling tower fans controlled by VSD’s to increase air flow at
cooling tower dependant on return condenser water temperature
 Preference is given to multiple cooling towers running at lower
speeds
Case Study: Cavendish Square
Building Overview
This shopping centre is located in Claremont, Cape Town
The GLA is 43,654m2
It consists of three levels of retail & four levels of parking
HVAC equipment consists of the following:
 8 x Water cooled chillers
 6 Cooling towers
 Primary chilled water pumps
 Secondary chilled water pumps
 Condenser water pumps
 Air handling units
 Return air fans
 Parking ventilation fans
 Extract & Fresh air fans
Case Study: Cavendish Square
Scope of Intervention
• Improve HVAC performance to allow chilled water temperature to drift
to reduce chiller load by 400KW in summer and 620KW in winter
•Install Variable Speed Drives to Secondary Chilled Water Pumps
•Install Variable Speed Drives on Cooling Tower Fans
•Automate Fresh Air Dampers with ext air temperature as reference
•Introduce Precooling
Case Study: Cavendish Square
Average Monthly Savings (KW)
616,200 kWh
Annual Savings (KW)
7,394,400 kWh
Annual Savings (R)
R2,246,418.00
Project Cost (R)
R398,788.00
Payback Period
Funded by ESKOM DSM
Case Study: Menlyn Park
Shopping Centre
• Building Overview
This shopping centre is located in Menlyn, Pretoria and has a GLA of 118000
M2 and consists of three levels of retail and four levels of parking
HVAC equipment consists of the following:
• 6 x Water cooled chillers
• 7 Cooling towers
• Primary chilled water pumps
• Secondary chilled water pumps
• Condenser water pumps
• Air handling units
• Return air fans
• Parking ventilation fans
• Extract & Fresh air fans
Case Study: Menlyn Park
Shopping Centre
Scope of Intervention
 Allow chilled water temperature drift to reduce chiller load by 340 KW in
summer and 540KW in winter
 Convert Constant Volume Supply Air Fans to Variable Volume
 Install Variable Speed Drives to control Cooling Towers
 Install Variable Speed Drives to control Air Handling Units
 Install Variable Speed Drives to control Return Air Fans
 Introduce Pre-Cooling
Case Study: Menlyn Park
Shopping Centre
Average Monthly Savings (KW)
875,992 kWh
Annual Savings (KW)
10,511,904 kWh
Annual Savings (R)
R3,820,726.00
Project Cost (R)
R5,624,206.00
Payback Period
1.47 Years
Case Study: Gateway Theatre of
Shopping
Building Overview
This shopping centre is located north of Durban with a GLA
of approximately 150,000m2 it consists of three levels of
retail and four levels of parking.
HVAC equipment consists of the following:
 8 x Water cooled chillers
 8 Cooling towers
 Primary chilled water pumps
 Secondary chilled water pumps
 Condenser water pumps
 Air handling units
 Return air fans
 Parking ventilation fans
 Extract & Fresh air fans
Case Study: Gateway Theatre of
Shopping
Scope of Intervention
 Allow chilled water
temperature drift to reduce
chiller load by 200 KW in
summer and 320KW in
winter
Equipment & Software
Requirement
 8 x 30KW and 2 x 132 KW VSD’s
 Chiller sequencing software
 Install Variable Speed
Drives to control Cooling
Towers
 Chiller load management software
 Install Variable Speed
Drives to control Secondary
Chilled Water Pumps
 Secondary chilled water Delta T
temperature control software
 Introduce Pre-Cooling
 Chilled water temperature reset
software
Case Study: Gateway Theatre of
Shopping
Average Monthly Savings (KW)
1,656,263 kWh
Annual Savings (KW)
19,875,156 kWh
Annual Savings (R)
R5,827,395.00
Project Cost (R)
R853,321.00
Payback Period
Less than two months
Summary of Savings
BUILDING
ANNUAL SAVING
(kWh)
ANNUAL SAVING (R)
CAVENDISH SQUARE
7,394,400 kWh
R2,246,418.00
MENLYN PARK
SHOPPING CENTRE
10,511,904 kWh
R3,820,726.00
GATEWAY THEATRE
OF SHOPPING
19,875,156 kWh
R5,827,395.00
TOTAL
37,781,460 kWh
R11,894,539.00