HVAC 101: Chillers andVFDs and BACnet – Oh My!HVAC 101: Chillers andVFDs and BACnet – Oh My!Tim SkellSr. HVAC Application Engineer, ABB

Learning Objectives:1. Examine the functionality of major HVAC

equipment such as chillers, AHUs, coolingtowers and VFDs.

2. Clarify how to use BACnet to create anintelligent building.

3. Demonstrate how VFDs play an essentialrole in energy savings, comfort and control.

4. Understand the value of propercommissioning, coordination, andcontinuous improvement.

Building Overview• Geographic Location: Wisconsin• Size: 147,000 sqft• Multipurpose building

– 1/3 office space– 2/3 factory floor space

• Electronic assembly

Goals of the HVAC Renovation• More reliable system• Reduced operating costs• Lower energy consumption• A “greener” building

– LEED Silver

• More intelligence• Flexibility for R&D

Building Overview

Typical Office AHU

Typical VAV

Highlights of this AHU• Outside air economizing• DP sensing across air filters• VFD on supply fan - maintaining duct pressure• Duct pressure resets based on max VAV• Safeties wired back to VFD

– Duct High Static– Freeze– Smoke

• Discharge air temp reset• VFD on exhaust fan for maintaining building static• Demand controlled ventilation – monitor CO2• Humidification/Dehumidification• BACnet points

Shipping/Receiving AHU

Differences of this AHU• Added staged IR heating for winter• Single zone – no VAV• No demand controlled ventilation• No humidity control

Chilled Water System

Highlights of CHW system• Thermal (ice) storage

– Make ice during off-peak hours– Use ice during peak hours

• Redundant pumps & VFDs• BACnet points

Condenser Water

CW Highlights• Heat recovery chiller

– 90° F setpoint• CW can be routed to hot water system

– No need for boilers to run• Heat exchanger isolates cooling tower

water from hot water system• Redundant pumps• BACnet points

Cooling Tower

Highlights of CT• VFD’s internal PID controls fan speed• Redundant Pumps• Bypass valve• Auto drain• Higher temp setpoint due to VAV reheat• BACnet points

Hot Water system

HW Highlights• Boilers talk to each other (Cascade)• CW is used to limit boiler operation• VFDs on BPs and HWPs• Redundant pumps and boilers

Test Cell

Non HVAC Integration over SerialCommunications – Power Meter

Instantaneous kW Instantaneous Power Factor

What does it look like?

Mechanical Room Continued

Mechanical Room Continued

Cooling Tower & Ice Storage

Recap of a HVAC System with Central Plant• Chiller

– Creates chilled water to cool the air– Heat is a side product – condenser water

• Cooling Tower– Cools the condenser water via evaporation

• Boiler– Creates hot water used to warm the air

• Air Handling Unit– Uses HW or CW to condition the air before

supplying it to the space

The “who,” “what,” “where,” “when,”“why,” and “how” of VFDs

• What are VFDs?– AKA adjustable frequency drives, inverters,

freq drives, pulse with modulated drive, thingon the wall I hope I never have to worry about

– Electronics that control the voltage andfrequency supplied to a motor, providing theability to control the speed

© ABB Group

AC DC AC

Rectifier Inverter

460 V, 60 Hz 640 V, DC 307 V, 40 Hz

VFDs Continued

VFDs Continued• Why are VFDs used?

– Control Flow• HVAC systems are designed to handle the hottest (and

coldest) days of the year– VFDs help the system “back off” on the typical days

• Significant energy savings are achieved by slowingdown a pump/motor

• Soft starting and slower speeds result in less “wear ‘ntear” on equipment

• Enhanced motor protection– Current limiting, ground fault detection, phase loss

protection, brown out protection

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 10 20 30 40 50 60

Frequency (Hz)

%Fl

ow,%

Torq

ue,%

Pow

er

Torque requirement variesas the square of speed

Power requirement varies asthe cube of speed

Flow varies linearlywith speed

10% reduction in speedequals over 25% energysavings

How do VFDs save energy

VFD Payback

Assumptions:• 12 hours a day• 7 days a week

VFDs – Where are they used• Supply Fans• Return Fans• Exhaust Fans• Hot Water Pumps• Condenser Water Pumps• Chilled Water Pumps• Boiler Pumps• Cooling Tower Fan• Booster Pumps• Anywhere there is a three phase motor

BACnet• Serial Communication Protocol

– RS485 and IP platforms• Open Protocol

– Not locked into a specific vendor– BTL certification– Brand A & Brand B can talk on the same wire

• Leading protocol used in HVAC• Now standard (native) on many HVAC

products

BACnet’s role continued• Most VFDs & significant HVAC equipment

are connected to the BAS– Hardwire for start/stop and general control– Serial communications for monitoring

• Troubleshooting• Trends

Goals of the HVAC Renovation• More intelligence (utilizing BACnet) leads

to:– More reliable system– Reduced operating costs– Lower energy consumption– A “greener” building

• LEED Silver

– Flexibility for R&D

Questions?• HVAC System• VFDs• BACnet