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

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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. Presentation. Estimating efficiency economically on a large scale Benchmark for comparison

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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.

presentation
Presentation
  • Estimating efficiency economically on a large scale
  • Benchmark for comparison
  • Selling service based on energy savings payback
important technology
Important Technology
  • A/C consumes much energy
  • Efficiency sensitive to service
  • First technology relating service effectiveness to energy savings deployed on large scale

“You can’t fix what you can’t measure”

instrument
Instrument

palm

comp

AMB

RWB

LT

ST

LP/DP

CT

SP

ET

practical measurements
Practical Measurements
  • Commonly used in the field for diagnostics
  • Field personnel comfortable with concepts and required instruments
  • Special apparatus speeds up measurement process
efficiency benchmark for service
Efficiency Benchmark for Service
  • Same unit serviced to achieve:
    • “benchmark”
    • “ideal”
    • “as new”
  • No design changes
a c units respond to their environment
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
characterizing performance
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)
getting the benchmark
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.
estimating benchmark efficiency
Estimating Benchmark Efficiency
  • Feed expected values (no faults, current conditions) of ET, COA, SH, SC into the same COP calculation as the measured values.
efficiency index
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”
advantages of ei
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
field measurement ei
Field Measurement - EI

* based on a sampling of 506 units

creating customer value
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
service decisions
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
service strategically
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
energy savings example
Energy Savings Example

Case study:

  • Big box retail store
  • 14 RTU’s, 11 with two stages (25 cycles)
results all stages all units
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%)
payback
Payback
  • Total costs of service: US$ 4,300
  • Estimated energy savings in one year: US$ 21,000
how the add up
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
how the add up1
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?
benefits
Benefits
  • Quick measurements
    • It doesn’t have to cost much more or require high skill
  • Measure and Document Efficiency
  • Target Service Strategically
  • Verify Effectiveness
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