11 energy analysis topics base case supermarkets base case assumptions simulation methods energy...

11

Energy Analysis TopicsEnergy Analysis Topics

• Base Case Supermarkets

• Base Case Assumptions

• Simulation Methods

• Energy Efficiency Measures

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Supermarket Base CaseSupermarket 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

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Supermarket Base CaseSupermarket 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

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Base Case – Envelop, LightingBase 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

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Base Case – HVACBase Case – HVAC

• System type:

– Central air handler(s) on large supermarket

– Packaged rooftop units on small, big box

– Gas heat, no heat recovery

66

Base Case – Display FixturesBase 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

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Base Case – Walk-insBase 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

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Base CaseRefrigeration Assumptions

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)

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Analysis MethodsAnalysis 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

1010

Modeling ToolModeling 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

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Adjustments and CalibrationAdjustments 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

1212

Questions?Questions?

Base Case

Assumptions

Modeling

1313

Refrigeration Efficiency MeasuresRefrigeration 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

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Refrigeration Efficiency MeasuresRefrigeration 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”

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Floating Head PressureFloating 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)

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Condenser Specific EfficiencyCondenser 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

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Condenser Specific EfficiencyCondenser 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”

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Floating Suction PressureFloating 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

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Mechanical SubcoolingMechanical 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

2020

Evaporator Coil Specific EfficiencyEvaporator 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

2121

Evaporator Coil Specific EfficiencyEvaporator 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

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Display Case LED LightsDisplay 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

2323

Display Case Liquid-Suction HXDisplay 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

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Walk-in Variable Speed Fan ControlWalk-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

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Walk-in Liquid-Suction HXWalk-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

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Investigate: Defrost MethodsInvestigate: 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

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Investigate: Heat RecoveryInvestigate: 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

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Questions and DiscussionQuestions and Discussion

Are measures missing?

Should priorities change?

Are there unidentified technical challenges?