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

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Presentation on theme: "11 Energy Analysis Topics Base Case Supermarkets Base Case Assumptions Simulation Methods Energy Efficiency Measures."— Presentation transcript:

1 11 Energy Analysis Topics Base Case Supermarkets Base Case Assumptions Simulation Methods Energy Efficiency Measures

2 22 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

3 33 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

4 44 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

5 55 Base Case – HVAC System type: –Central air handler(s) on large supermarket –Packaged rooftop units on small, big box –Gas heat, no heat recovery

6 66 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

7 77 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

8 88 Base Case Refrigeration 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)

9 99 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

10 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

11 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

12 12 Questions? Base Case Assumptions Modeling

13 13 Refrigeration Efficiency Measures Current High Priority Measures 1.Floating head pressure 2.Condenser variable speed control 3.Condenser specific efficiency 4.Floating suction pressure 5.Mechanical subcooling 6.Evaporator coil specific efficiency 7.Evaporator coil variable speed control 8.Display case LED lights 9.Liquid-suction heat exchangers 10.Night covers

14 14 Refrigeration Efficiency Measures Other Medium or Lower Priority Measures 1.Condenser sizing (approach) 2.Evaporator sizing (approach) 3.Compressor staging/capacity control 4.Electronic expansion valves 5.Demand defrost 6.Piping insulation 7.DHW heat recovery 8.Glass doors on certain medium temperature fixtures Also see to “supermarket efficiency measure matrix.xls”

15 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)

16 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

17 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”

18 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

19 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

20 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

21 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

22 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

23 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

24 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

25 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

26 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

27 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

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


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