Vfds and Rtus

ABC’s of VFDs and Rooftop UnitsTechnology overview and available incentives

Greg Rushby, Rushby Energy Solutions

saveONenergy Show & SymposiumJune 17, 2014

www.saveonenergy.ca

Outline

Topic

VFD Overview

VFD Applications & Incentives

RTU Overview

RTU Incentives

Summary

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Variable Frequency Drives (VFD)

› VFD

› Adjustable speed drive

› Vary frequency (Hz) and voltage going to the motor

› Motor RPM is reduced at lower Hz

› VFDs save energy when the load varies› HVAC equipment is sized for peak loads

› Peak conditions are ~1% of annual operating hours

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VFDs vs. Other Starters

Type Pros Cons Applications

Across-the-line Simple, low-cost No variable speedoperation

<5 hP

Soft starter Variable speed operation

Inefficient part-load operation

Motors that cycle frequently

Variable Frequency Drive

Efficient, active variable speed control

High cost (relative to other starters)

Systems that operate at part-load frequently

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Variable Flow vs. Variable Speed

› Many systems have variable flow with constant speed motors

› Valves used to vary flow for pump systems

› Dampers or inlet vanes used to vary flow for fan systems

› Inlet valve modulation used to vary compressed air output

› VFDs vary motor speed to vary flow

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Common VFD Applications

Commercial› Air distribution systems (fans)› Hydronic distribution systems (pumps)› DCW booster pumps› Cooling tower fans› Chillers

Industrial› Air compressors› Vacuum pumps› Baghouse fans› Refrigeration compressor

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VFDs on Constant Torque Loads

› Power varies linearly with speed

› Example loads:› Conveyors, mixers, positive displacement

pumps, rotary screw air compressors

Image Source: Natural Resources Canada

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VFDs on Constant Torque Loads

› Power varies with the speed cubed

› Torque varies with the speed squared

› Example loads:› Centrifugal pumps, centrifugal and axial

fans

Image Source: Natural Resources Canada

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VFDs on Pumps and Fans

› The majority of pumps and fans used in HVAC applications are centrifugal

› Centrifugal pumps and fans have a variable pressure / flow relationship

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Typical Centrifugal Pump Curve

Image Source: US DOE – Improving Pump System Performance: a Sourcebook for Industry

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Centrifugal Pump & Fan Affinity Laws

Flow vs. Motor Speed Q1/Q2 = N1/N2

Power vs. Speed bhp1/bhp2 = (N1/N2)3

Q – Volumetric flowN – Pump shaft rotational speed or fan wheel velocity (RPM)BHP – Brake horsepower

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VFDs on Pumps and Fans

› VFD› Adjustable speed drive

› Vary frequency (Hz) and voltage going to the motor

› Motor RPM is reduced at lower Hz

› VFDs save energy when the load varies› HVAC equipment is sized for peak loads

› Peak conditions are ~1% of annual operating hours

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VFD Opportunity - Pumps

Image Source: Eaton

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VFD Opportunity - Fans

Source: 2012 ASHRAE Handbook

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Typical VAV Load Profile

Source: 2012 ASHRAE Handbook

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Typical Cooling Tower Load Profile

Source: Danfoss VLT Application Guide

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saveONenergy RETROFIT VFD Incentives

› Prescriptive Incentives

› Incentive is ~30 to 50% of VFD materials costs

› VFD materials cost rule of thumb = $1,000 + ($75 per hP)

› Demand savings are ~10% at 75% motor loading

Advantages Disadvantages

• Simple application

requirements

• Incentive often ~50% of

materials costs

• Engineered / Custom usually has

higher incentives

• Does not cover motors >100 hP

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› Engineered Incentives

› Engineered Worksheets for VFDs on Pumps/Fans/Air Compressors

› Engineered worksheets calculate savings for pumps / fans with the same flow profile before and after VFD operationAdvantages Disadvantages

• Potential for higher incentive

• No hP limit

• Complex inputs required

• Only one flow profile

• Only for pumps / fans

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› Custom Incentives› Best for projects with different before and after load profiles

› Projects with incentives >$10,000 require M&V

› VFDs measure kW and amps

Advantages Disadvantages

• Potential for higher incentive

• May require M&V

• Savings must be calculated

• May require M&V

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Example Custom VFD Project

Base Case

› Induced Draft Cooling Tower with 20 hP Axial Fan

Efficient Case

› Install VFD and new 20 hP motor ($6,200)

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%Flow % Run Hours Run HoursBase Case Input

Power (kW)

Efficient Case

Input Power

(kW)

Base Case

Annual Energy

Use (kWh)

Efficient Case

Annual Energy

Use (kWh)

Annual Energy

Savings (kWh)

40 5 70 3.978 0.83 278.46 58.12 220.34

50 15 200 3.978 1.62 795.60 324.35 471.25

60 35 450 13.26 2.80 5,967.00 1,261.06 4,705.94

70 20 270 13.26 4.45 3,580.20 1,201.51 2,378.69

80 15 210 13.26 6.64 2,784.60 1,394.96 1,389.64

90 10 140 13.26 9.46 1,856.40 1,324.12 532.28

100 0 0 13.26 12.97 0.00 0.00 0.00

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Results

› Peak Demand Savings = 3.8 kW

› Annual kWh Savings = 9,698

› Incentive = $3,040

› Annual Cost Savings = $1,250

› Payback ~ 2.5 years

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Unitary AC

› AHRI defines Unitary as:› one or more factory-made assemblies ordinarily including an

evaporator or cooling coil(s), compressor(s), and condenser(s) and

may include a heating function

› Unitary AC equipment includes:› Split systems

› Air-source heat pumps

› Single package systems a.k.a. rooftop units

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Rooftop Unit Components

Image Source: Bryant / Carrier

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Economizers

Image Source: Energy Designs Resources

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Rooftop Units

› All-in-one functionality – H, V & AC in a box!

› Relatively inexpensive

› Do not take up interior space

› Very high market share in Ontario

› Distribution may be:› Constant volume or variable volume

› Single zone or multi-zone

› Installed cost approx. $1,200 to $1,800 per ton

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Rooftop Unit Efficiency Ratings

› Efficiency ratings – the higher the better!

› Energy Efficiency Ratio (EER)

› Seasonal Energy Efficiency Ratio (SEER)

› Integrated Energy Efficiency Ratio (IEER)

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EER

›Ratio of cooling rate (in Btu/h) to electrical input power (in

W)

›Determined at:

› Outdoor = 95ºF Dry Bulb

› Return Air = 80ºF Dry Bulb, 67ºF Wet Bulb

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SEER

› Ratio of annual cooling energy (in Btu) to annual

electricity consumption (Wh)

› Only units 5.4 tons and below receive SEER ratings

› SEER is primarily a residential rating

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IEER

› IEER is a part load efficiency rating

› IEER is the weighted average of EER at various loads:

› 100% load; 2% weighting

› 75% load; 61.7% weighting



› Two units can have the same EER and a different IEER

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RTU Efficiency – Standards & Specifications

› ASHRAE

› Energy Star

› CEE

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ASHRAE 90.1

› ASHRAE Standard 90.1:› Energy efficiency standard

› Adopted by building codes (including Ontario)

› Specifies minimum efficiency (EER) for RTUs

› Latest version is 2010

› “ASHRAE 90.1 compliant” units

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Energy Star and CEE

› Energy Star maintains a list of qualified Light Commercial Heating & Cooling products up to 20 tons

› Consortium for Energy Efficiency (CEE) publishes a three tiered specification for Unitary A/C equipment

› Tier 0, Tier 1, Tier 2

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ASHRAE 90.1 vs. CEE Efficiency

Equipment TypeSize Category

(Btu/h)

Size Category

(Tons)

Heating Section

Type

Subcategory or

Rating Condition

ASHRAE 90.1

- 1989

ASHRAE 90.1

- 2010

CEE Tier 0 /

Energy StarCEE Tier 1 CEE Tier 2

Air conditioners,

air cooled

<65,000 <5.4 All Split / package 10/9.7 SEER 13 SEER N/A 14.0 SEER 15.0 SEER

>=65,000 and

<135,000

>=5.4 and

<11.25

Electric resistance

or none

Split system, single

package

8.9 EER 11.2 EER 11.7 EER 11.7 EER 12.2 EER

8.3 IPLV 11.4 IEER 11.8 IEER 13.0 IEER 14.0 IEER

All otherSplit system, single

package

8.9 EER 11 EER 11.5 EER 11.5 EER 12.0 EER


>=135,000 and

< 240,000

>=11.25 and

<20

Electric resistance

or none


package




package


7.0 IPLV 11 IEER 11.6 IEER 12.3 IEER 13.0 IEER

>=240,000 and

< 760,000>=20 and <63.3

Electric resistance

or none


package




package



>= 760,000 >=63.3

Electric resistance

or none


package




package



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RTU Efficiency – Old vs. New

› ASHRAE 90.1–2010 min. EERs ~ 2 higher than ASHRAE 90.1 –1989 min.

EERs

› ~0.2 to 0.3 kW per ton improvement

› CEE Tier 1 min. EERs ~ 0.5 higher than ASHRAE 90.1 – 2010 min. EERs


› CEE Tier 2 min. EERs ~ 1 higher than than ASHRAE 90.1 – 2010 min.

EERs


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RTU Efficiency – Existing Units

› Ensure proper maintenance

› Consider advanced controls› Demand control ventilation› After market controllers

› Replacing an existing unit with a new unit is typically not cost-effective

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RTU Efficiency – Advanced Controls

› Demand control ventilation› Reduce outdoor air intake when areas are sparsely occupied

› Aftermarket controllers› Digi-RTU› Catalyst› Aircosaver› Regen

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RTU Efficiency – Advanced Controls

› Advanced Controls Benefits› Low-cost (relative to new unit)› May be cost-effective (2 - 4 year payback or better)

› Advanced Controls Drawbacks:› May not be suitable for all applications

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RTU Efficiency – New & Replacement Units

› Ensure units are properly sized

› Specify high-efficiency units

› Consider specifying high-efficiency controls

› Commissioning

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saveONenergy RETROFIT RTU Incentives

Track Incentive

Type

Base Case Pros Cons

Prescriptive

Fixed $/unit

or

Fixed $/ton

Code

Minimum

Unit

• Pre-approval not

required for

incentives

<$10,000*

• Lower incentive

• Minimum EER

requirements

Engineered $800/kW Existing Unit

• Higher incentive

• No minimum EER

requirements

• Pre-approval

required

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Example Rooftop Unit Retrofit

New CEE Tier 1 Unit – EER = 11.5 New CEE Tier 2 Unit – EER = 12

Incremental Cost

(over ASHRAE 90.1 unit)

$1,200 $2,400

Prescriptive Incentive Ineligible $1,000

Engineered Incentive $1,200 $1,360

Energy Savings* 804 kWh – vs. existing unit

125 kWh – vs. new 90.1 unit (EER = 11)

919 kWh – vs. existing unit

240 kWh – vs. new 90.1 unit (EER = 11)

Demand Savings* 1.5 kW – vs. existing unit

0.2 kW – vs. new 90.1 unit (EER = 11)

1.7 kW – vs. existing unit

0.5 kW – vs. new 90.1 unit (EER = 11)

Payback Instant 16 years**

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SummaryVFDs› VFDs are a cost-effective way to control flow

RTUs

› Maintain units to maintain efficiency

› Consider advanced controls

› Specify high efficiency equipment for replacement units

saveONenergy incentives are available to help fund your project!

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Thank You

Greg RushbyRushby Energy Solutions [email protected]

www.rushbyenergy.com

Vfds and Rtus

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