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