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Energy Analysis Topics

Energy Analysis Topics. Base Case Supermarkets Base Case Assumptions Simulation Methods Energy Efficiency Measures. 1. Supermarket Base Case. Three sizes Small supermarket: 10,000 SF Non 24-hour operation Large supermarket: 61,000 SF 24-hour operation

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Energy Analysis Topics

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  1. Energy Analysis Topics • Base Case Supermarkets • Base Case Assumptions • Simulation Methods • Energy Efficiency Measures 1

  2. Supermarket Base Case • Three sizes • Small supermarket: 10,000 SF • Non 24-hour operation • Large supermarket: 61,000 SF • 24-hour operation • Average of last 50 Savings By Design stores • Big box food store: 150,000 SF • Non 24-hour operation • Includes large point-of-sale boxes 2

  3. Supermarket Base Case • Three condenser types • Air-cooled • Evap-cooled • Evap-cooled fluid cooler with water-cooled condensers • Two refrigeration system types • Central rack systems • Multiple distributed systems 3

  4. Base Case – Envelop, Lighting • Title-24 compliant building • Roof and wall insulation • Code required lighting power density • Minimum skylights and light level control • Not on small supermarket based on ceiling height • Schedules • Operating hours, occupancy, lighting 4

  5. Base Case – HVAC • System type: • Central air handler(s) on large supermarket • Packaged rooftop units on small, big box • Gas heat, no heat recovery 5

  6. Base Case – Display Fixtures • Line-ups taken from Savings By Design • Fixture assumptions *: • T8 lighting; certain lighted shelves • EC (DC) fan motors • No (or small) liquid-suction heat exchangers • Low-watt glass door heater option * Assumed features that would likely be used to meet the Federal appliance standards (kWh daily energy consumption) for DX remote display cases 6

  7. Base Case – Walk-ins • Federal WI Standard/Title 20 compliant • Insulation levels • Glass door heater wattage • EC fan motors on unit coolers • Loads based on widely used look-up tables • Unit coolers sized at typical 10 F approach 7

  8. Base CaseRefrigeration Assumptions • Partial floating head pressure control • 80°F SCT fixed setpoint (SBD basis) • Fan cycling (air) or two-speed (evap) • Fixed suction pressure control • No mechanical subcooling • 404A/507 refrigerant • Typical uneven parallel or multiple stages • Condenser specific efficiency (SBD basis) 8

  9. Analysis Methods • Primary Base Case models (preceding) • Other “Baseline” reference models for comparative and incremental analysis, or to compare alternative packages • Example: heat recovery incrementally evaluated vs. system combination with floating head pressure • Example: efficient DX combination vs. efficient secondary (glycol) combination 9

  10. Modeling Tool • Whole building hourly simulation • DOE 2.2R • Fixtures loads disaggregated, balance space interactions (fixture, HVAC, building, etc.) • Mass-flow/component based refrigeration system modeling, explicit control strategies • DOE2 modeling of building envelope, HVAC, lighting, skylights, etc. • Energy Plus • For aggregation of final results combinations 10

  11. Adjustments and Calibration • Fixture load breakdowns are estimated • Allowance for pressure drops & heat gains • De-rate condensers and evaporators • Actual applied performance vs. catalog • Effect of non steady-state operation • Results compared with actual operation(?) • Some field study and remote data collection • Need more, especially newer systems 11

  12. Questions? Base Case Assumptions Modeling 12

  13. Refrigeration Efficiency Measures Current High Priority Measures • Floating head pressure • Condenser variable speed control • Condenser specific efficiency • Floating suction pressure • Mechanical subcooling • Evaporator coil specific efficiency • Evaporator coil variable speed control • Display case LED lights • Liquid-suction heat exchangers • Night covers 13

  14. Refrigeration Efficiency Measures Other Medium or Lower Priority Measures • Condenser sizing (approach) • Evaporator sizing (approach) • Compressor staging/capacity control • Electronic expansion valves • Demand defrost • Piping insulation • DHW heat recovery • Glass doors on certain medium temperature fixtures Also see to “supermarket efficiency measure matrix.xls” 14

  15. Floating Head Pressure • Float to 70°F condensing temperature • Variable speed fan control • Or low power condenser, to be evaluated • Variable setpoint logic (ambient-following) • Details: • Design to avoid excessive ambient subcooling • All fans in unison (on air-cooled) 15

  16. Condenser Specific Efficiency • Set minimum specific efficiency values • Very large range of existing efficiencies • Savings By Design base case: • Air-cooled: 53 Btu/W at 10 F TD • Evap-cooled: 140 Btu/W at 100 SCT/70 WBT • Appears easy to justify removing least efficient models 16

  17. Condenser Specific Efficiency • However: • Condensers not rated to standards or certified • Current ratings make big assumptions: • Perfect UATD over full range of TDs and SCT • Power not published and not necessarily measured • Standards and certification: • High cost to industry and time required • Allows accurate comparison and competition • SBD experience indicates we can “start” 17

  18. Floating Suction Pressure • Require control logic to float suction • Adjust setpoint based on case or walk-in temperature requirements • Part of most SBD incentives for five years • Simple but requires labor to optimize • Integration: more complex with electronic circuit controls and/or variable speed evaporator fan control 18

  19. Mechanical Subcooling • Require mechanical subcooling • Require only on low temperature systems • Methods: • From medium temperature suction group • Using economized compressors (scroll, screw) • Cost neutral in most cases • At least with 404A/507 19

  20. Evaporator Coil Specific Efficiency • Set minimum specific efficiency levels (Evaporators, “coils”, unit coolers – same thing) • Very wide range of existing efficiencies • Applications and sizes: • Cooler, freezer • Low profile, medium profile • Indirect (glycol)?, often much higher power 20

  21. Evaporator Coil Specific Efficiency • However: • Coils not rated to standards or certified • Current ratings: • Probably significantly commercialized • Rating standards not adequate if they were used • Standards and certification: • High cost to industry and time required • Allows accurate comparison and competition • Appears feasible to start with basic rqmts 21

  22. Display Case LED Lights • Require LED lights in reach-ins and open display cases • Used in majority of recent SBD incentives for low temp reach-in cases • Economics and availability on open cases (canopy and shelf lights) to be determined 22

  23. Display Case Liquid-Suction HX • Require high performance liquid-suction heat exchangers on display cases • More than traditional small LSHX or soldering two pipes together • Choice of one HX per line-up (better performance) or one per display case (easier) • Large savings on LT • Benefits on MT close-approach and refrigerants with glide • Zero cost measure including capacity gain 23

  24. Walk-in Variable Speed Fan Control • Require variable speed fan control • Primary (first) temperature control • Integrate with other temperature control methods (electronic suction regulator, liquid solenoid, suction stop) and floating suction • Inherent variable speed with EC motors • Third power fan savings (~50% power at 75% airflow) • Lack of testing on commercial (DX) coils 24

  25. Walk-in Liquid-Suction HX • Require high performance liquid-suction heat exchangers on walk-ins • Same benefits as display cases • Benefits on refrigerants with glide • Better evaporator and cycle performance • Zero cost measure including capacity gain • Applies to DX systems, not indirect 25

  26. Investigate: Defrost Methods • Compare electric vs. hot gas defrost • Best practice electric defrost • Trunk piping, demand defrost (frost sensor) • Gas defrost • Some penalty on head pressure • Some advantage with higher SSTs • Provide energy analysis for evaluation with reduced leakage with electric defrost 26

  27. Investigate: Heat Recovery • Space heat recovery • Display cases remove heat, high annual heating requirement = big savings vs. past designs’ increased refrigerant charge and charge volatility • Many options and designs; not suitable for mandatory design requirements • Consider a small mandatory % of heat recovery with wide application flexibility • OSA/make-up; stock room; main AHU; etc. • Limit of ~15% additional charge 27

  28. Questions and Discussion Are measures missing? Should priorities change? Are there unidentified technical challenges? 28

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