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Energy Analysis Topics

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Presentation on theme: "Energy Analysis Topics"— Presentation transcript:

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 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 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) 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 Energy Plus
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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