Todd M. Rossi, Ph.D.

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Estimating Efficiency and Establishing Baselines
for Verifying the Energy Saving Benefits
Associated with Servicing Air Conditioners

• Todd M. Rossi, Ph.D.
• Field Diagnostic Services, Inc.

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Presentation

• Estimating efficiency economically on a large
  scale
• Benchmark for comparison
• Selling service based on energy savings payback

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Important Technology

• A/C consumes much energy
• Efficiency sensitive to service
• First technology relating service effectiveness
  to energy savings deployed on large scale

You cant fix what you cant measure
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Define Efficiency
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Electric Heated Evaporator
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DX Evaporator - Air side
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Refrigerant Side Measurement
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Compressor Performance Data
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Estimating Efficiency
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Required Measurements
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Instrument
palm comp
AMB
RWB
LT
ST
LP/DP CT
SP ET
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Practical Measurements

• Commonly used in the field for diagnostics
• Field personnel comfortable with concepts and
  required instruments
• Special apparatus speeds up measurement process

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Data Collection Tool
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Efficiency Benchmark for Service

• Same unit serviced to achieve
• benchmark
• ideal
• as new
• No design changes

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A/C Units Respond to their Environment

• Characterized by
• AMB - Outdoor Drybulb Temperature
• RWB - Evaporator Entering Air Wetbulb
• Assumptions
• Air cooled, DX Equipment
• Water condensing on Evaporator

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Characterizing Performance

• Evaporating Temperature
• ET(AMB,RWB)
• Suction Line Superheat
• SH(AMB,RWB)
• Standard Charging Chart - Fixed Orifice
• Condensing Temperature Over Ambient
• COA(AMB,RWB)
• Liquid Line Subcooling
• SC(AMB,RWB)

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Getting the Benchmark

• Measure the driving conditions (AMB, RWB)
• Evaluate expected ET, SH, COA, SC for current AMB
  and RWB
• Ideally these are the values measured when the
  unit was new and installed properly under the
  current conditions.

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Estimating Benchmark Efficiency

• Feed expected values (no faults, current
  conditions) of ET, COA, SH, SC into the same COP
  calculation as the measured values.

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Efficiency Index

• Efficiency of the unit as it is currently
  operating relative to how it could be performing
  if serviced to like new under the same
  operating conditions

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Example - Dirty Condenser
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Advantages of EI

• Same compressor model used to calculate actual
  and expected performance - reduces sensitivity to
  model errors
• Intrinsic value - does not scale with size of unit

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Field Measurement - EI
based on a sampling of 506 units
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Creating Customer Value

• Get from EI to by considering
• Nominal capacity (tons)
• SEER/EER rating
• Utility rates (e.g /kwh)
• Annual runtime hours
• Estimate /year wasted because of degraded
  equipment performance

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Service Decisions

• /year in wasted energy
• Compare to cost of service to enhance performance
• Making service decisions (e.g. when to clean
  coils) based on energy savings payback.
• Other criteria also exist in making service
  decisions

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Service Strategically

• Assess all units in portfolio
• Prioritize units with most compelling service
  needs (e.g. energy payback)
• Target service for maximum effect
• Verify expected performance

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Prioritize Sites
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Energy Savings Example

• Case study
• Big box retail store
• 14 RTUs, 11 with two stages (25 cycles)

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Results All stages all units

• Before Tune-up 318 kW 46,917 hours of cooling
• After Tune-up 268 kW 37,738 hours of cooling
• Savings 50 kW (15.8) 9,179 hours (19.6)

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Payback

• Total costs of service US 4,300
• Estimated energy savings in one year US
  21,000

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How the add up

• Give a tech a tool
• He applies it to 1000 tons
• 100x10 ton units, 200x5 ton units
• Units run between 300 and 2500 hours/year
• 1 kW/ton - 12 EER
• 10 cents/kwh

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How the add up

• That tech is responsible for roughly 100,000 in
  energy spent annually.
• 10 improvement because of strategic application
  of the same resource based on better information
• 10,000 saved each year
• How much would you pay for this information?

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Benefits

• Quick measurements
• It doesnt have to cost much more or require high
  skill
• Measure and Document Efficiency
• Target Service Strategically
• Verify Effectiveness