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Energy Efficiency Project Analysis for Supermarkets and Arenas

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Presentation on theme: "Energy Efficiency Project Analysis for Supermarkets and Arenas"— Presentation transcript:

1 Energy Efficiency Project Analysis for Supermarkets and Arenas
Clean Energy Project Analysis Course

2 Objectives Review basics of advanced refrigeration systems & energy efficiency measures for supermarkets and arenas Illustrate key considerations in energy efficiency project analysis for supermarkets and arenas Introduce RETScreen® Energy Efficient Arena & Supermarket Project Model

3 What do energy efficiency measures & advanced refrigeration systems provide?
Refrigeration and cooling in supermarkets and arenas Space, ventilation air, and water heating; dehumidification …but also… Reduced energy consumption Reduced power demand charges Reduced refrigerant leaks Reduced greenhouse gas emission Reduced maintenance costs Improved comfort Ice Rink and Bleachers Photo Credit: Regos Photography/Andrus Architecture Supermarket Interior

4 Supermarkets: Background
Among most energy-intensive commercial buildings 5,000 MWh-eq/year for electricity in large supermarket (>1,000 m2) Over 5,000 large supermarkets in Canada Refrigeration accounts for 50% of energy costs; lighting, 25% $150,000/year for refrigeration in large supermarket Energy costs are ~1% of sales But this is approximately same as store profit margin! Conventionally have very high refrigerant charges Average store has 1,300 kg of refrigerant Long piping runs result in leakage of 10 to 30% of charge per year Synthetic refrigerants are potent greenhouse gases (GHG) Can have over 3,000 times the effect of CO2

5 Arenas: Background Typical arena in Canada:
~ 1,500 MWh-eq/year consumption ~ $100,000/year energy cost Major consumer of energy 2,300 skating rinks in Canada 1,300 curling rinks in Canada Conventionally have high refrigerant charges Average arena has 500 kg of refrigerant Open compressor results in significant leakage Synthetic refrigerants: potent greenhouse gases Can have over 3,000 times the effect of CO2 Energy Consumption for Typical Arena in Canada

6 The building as a system
Supermarkets and arenas are systems with purchased energy inputs… Electricity, natural gas, etc., …that satisfy simultaneous heating and refrigeration loads… …in proximate warm and cold zones.

7 Heating and refrigeration loads
Influenced by… Gains/losses through building envelope Gains/losses in ventilation fresh and exhaust air (sensible + latent) Gains from occupants (sensible + latent) Gains from equipment (e.g. lighting) Gains/losses in mass flows (e.g. hot water down drain, ice making) Gains/losses through floor Solar gains …and heat transfer from heated to cooled areas!

8 Where are improvements possible?
Control according to activity & environmental conditions Reduce heat transfer from warm to cold zones Reduce unwanted gains and losses Process integration: transfer heat from cold to warm zones Use heat rejected by refrigeration systems to satisfy heat loads Improve HVAC&R equipment efficiency Reduce refrigerant charge and leakage Major reduction in greenhouse gases

9 Review of vapour-compression refrigeration cycle

10 Supermarkets and Arenas: Problem: Heat transfer from warm to cool zones
Heat draining from warm zones to cold zones accounts for majority of refrigeration load Majority of heat dumped to outside air by condenser Heating system must make up for some of this rejected heat Heat rejected by refrigeration system generally exceeds heating load Typical Canadian skating rink heating load and heat rejected by refrigeration system, by month

11 Measures for Supermarkets and Arenas: Process Integration makes use of heat rejected by refrigeration system Capture rejected heat in a secondary loop Secondary loop facilitates heat distribution Desuperheater at outlet of compressor Recovers up to 15% of rejected heat– good for hot water Further heat recovery before condenser Heat can be used for space, ventilation air, and water heating Heat pumps raise temperature of heat from secondary loop as necessary Excess heat can be… Stored for later use Heat under ice rink slab Snow pit melting Export to nearby buildings Sidewalk, parking lot, street heating Dump any surplus to outside air

12 Measures for Supermarkets: Minimize refrigerant leaks with secondary loops
Refrigeration loads are distributed around building Long loops of refrigerant-filled piping connect mechanical room to loads and condenser Leaks in piping and joints account for 50% of supermarket’s greenhouse gasses Solution: secondary loops on hot and cold sides Secondary loop with water, glycol mix, brine, CO2, methanol, etc.: not potent GHGs like synthetic refrigerant Small refrigerant load contained in hermetic unit Low temperature loads: use autonomous refrigeration sub-units (with low refrigerant charge) that dump heat to the secondary loop

13 Measures for Arenas: Minimize refrigerant leaks with secondary loops
Open compressors and high refrigerant charges lead to significant greenhouse gas emissions Solution: secondary loops on warm (condenser) side Small refrigerant load contained in hermetic unit Water or glycol mix in loop: no GHG’s

14 Measures for Supermarkets and Arenas: Tailoring HVAC&R equipment to cold climates
Equipment is conventionally designed for warm climates Condensers typically operate at high temperature, regardless of the exterior air temperature Solution: Permitting condenser temperature to drop during cold weather improves efficiency and compressor longevity “Floating head pressure” operation COP can double, (e.g. from 3 to 6) Reduces usefulness of rejected heat Must optimize operating temp.

15 Measures for Supermarkets and Arenas: Mechanical/ambient refrigerant subcooling
Conventionally, output of condenser feeds directly into expansion valve Capacity and efficiency can be improved by cooling liquid exiting condenser to temperatures below condensing temperature (subcooling) Ambient: cold exterior air or rink snow pit Mechanical: second refrigeration system Better than simply removing more heat from condenser – second system operates with higher COP

16 Measures for Supermarkets and Arenas: Thermal storage
Storage of rejected heat Peak demand charges associated with heating can be reduced Short-term: water tanks of 2,000 litres for several hour storage (e.g. night) Seasonal: underground storage with horizontal/vertical heat exchanger Arenas can also store“cold” under slab or in reservoir Reduce peak demand charges by extracting cold from storage during times of peak load Reduce design capacity of refrigeration equipment Increase in COP through use of heat pump to produce heat and cooling simultaneously

17 Ice rink with daylighting
Measures for Supermarkets and Arenas: Efficient lighting and daylighting Artificial lighting augments refrigeration loads Solution: More efficient lighting technologies Solution: Highly reflective ceilings – reduce lighting needs by 30% Can be combined with low-e paints or materials in arenas Solution: Reduced light intensity where permissible Multi-light level intensity lamps Vary number of operating lamps Consider activity and occupancy level Reduce height of fixtures and ceiling, taking ceiling and wall reflectivity into consideration Solution: Natural lighting Pleasing ambience Must avoid solar gains, excessive heat losses or gains through windows Ice rink with daylighting Photo Credit: Skating Club of San Francisco

18 Measures for Arenas: Ceilings that radiate less heat
Infrared radiation from ceiling: up to 30% of the ice sheet refrigeration load Ceiling gets hot from space heating, solar gains and artificial lighting Common materials have high emissivity index (e = 0.80 to 0.95) Solution: use materials with low emissivity Low-e aluminized cloth (e=0.03 to 0.08) Aluminium-based low-e paint or other low-e paints Additional Benefits Reduced condensation Improved acoustics Reduce lighting requirements Reflective, Low-e Ceiling Photo Credit: Marius Lavoie, NRCan

19 Measures for Arenas: Reduce heat losses from stands
Space heating in stands adds to refrigeration load Air temperature in spectator stands may be as high as 15 to 18ºC Typically adds 20% to the refrigeration load Solutions: Heat stands with low temperature (≤32ºC) radiant flooring system Use heat rejected by refrigeration system Slab heating maintains spectator comfort Reduce temperature in stands during unoccupied periods Simulated Temperature

20 Measures for Arenas: Optimize ice temperature
Rinks normally maintain ice temperature around –6ºC Refrigeration load can be reduced by letting ice temperature rise During figure skating: -3 to -4ºC During free skating: -2 to -3ºC During unoccupied periods (e.g. night): -1 to -2ºC Stop secondary fluid pump during unoccupied periods, and restart only when infrared sensor indicates ice temperature has risen to a preset maximum allowable temperature

21 Measures for Arenas: Reduce refrigerant pumping energy
Ice cooled by secondary fluid circulating in concrete slab Piping network transports secondary fluid across ice in one direction and then back to header: a two-pass layout Secondary fluid pump accounts for over 15% of the refrigeration system’s total energy consumption Secondary fluid pump’s heat adds to refrigeration loads Solution: Reduce secondary fluid flow rate according to schedule/occupancy Two-speed pump, two pumps, or variable speed pump Piping network that transports fluid four or more passes through slab allows flow rate to be halved Affects ice uniformity? Piping in slab Photo Credit: Marius Lavoie, NRCan

22 Measures for Arenas: Optimize ice and concrete slab thickness
Heat transfer from secondary fluid to ice surface reduced by thick ice and thick layer of concrete above tubes Lower heat transfer results in higher refrigeration energy consumption In most arenas, ice 25 to 40 mm thick, but can be as high as 75 mm In most arenas, ~25 mm of concrete above embedded tubes Solution: During construction or renovation, ensure concrete slab should be ≤ 25 mm above tubes Keep ice thickness at 25 mm, where permitted In combination with under slab cool storage, reduces capacity requirements Pouring of slab Photo Credit: Marius Lavoie, NRCan

23 Measures for Arenas: Different dehumidification approaches
Dehumidification normally involves stand-alone cooling unit Heat rejected to ice rink and adds to refrigeration load Solution: Reject heat from dehumidifier to condenser-side secondary loop of principal refrigeration system Rejected heat can be used for space heating, etc. Solution: Desiccant dehumidification system

24 Supermarkets: Costs of efficiency measures
Secondary Loop Depending on measures implemented, 0 to 40% higher initial costs than conventional systems A full range of measures cost additional ~$250,000 Supermarkets often require paybacks of 3 years or less Additional costs may be offset by elimination of combustion heating system Standard DX system Secondary loop system

25 Arenas: Costs of efficiency measures
Major rink renovation every 25 years: ~$700,000 $175,000 (single pad) or $200,000 (multipad) for efficiency measures Owners and operators generally want simple payback of 5 to 8 years or less Process integration of heating and refrigeration typically has 3½ year payback in new construction, 5 to 8 years in retrofit Minor Investment Moderate Investment Major Investment Better controls Desuperheater Low-e ceiling Nighttime setbacks Dehumidification Efficient lighting Optimize ice thickness Snow Pit Process integration Power factor correction Cold-climate adaptions Thermal storage

26 Supermarkets: Project considerations
Systems must demonstrate very high reliability A one day refrigeration system failure is extremely costly in terms of lost revenue and produce Incorporate advanced refrigeration innovations in new buildings and during major equipment overhauls Supermarket refrigeration systems overhauled every 8 years on average In existing supermarkets, new systems may need to be installed and brought on-line while supermarket is operating Rejected heat from refrigeration system can supply all heat required for supermarket Elimination of combustion heating system with financially attractive alternative is a convincing argument

27 Arenas: Project considerations
Incorporate advanced refrigeration innovations in new buildings and during major equipment overhauls Arena refrigeration systems overhauled on 25 year basis (30 to 40% of Canadian rinks presently operating beyond projected life span) Many arenas close for 1 to 2 months per year when retrofits can be done Rejected heat from refrigeration system is three times heating energy requirement on annual basis But for short periods in winter heat load may exceed reject heat Reduction in power demand charges can be a significant source of annual cost savings In some provinces, power demand charges account for 40% of electricity invoices

28 Example: Quebec, Canada Repentigny supermarket
Refrigeration systems reject heat to two secondary loops Medium temperature refrigeration system loop provides up to 250 kW of space and air heating Low temperature loop provides up to 220 kW of heat to heat pumps (2nd function: air conditioners) Desuperheater meets hot water needs Medium temperature cold side secondary loop used to subcool low temperature refrigerant by 30ºC at output of condenser Evaporator (cold) side secondary loops Condenser temperature/pressure floats according to building heating requirement and outdoor air temperature Supermarket Entrance Vegetable Display

29 Example: Quebec, Canada Repentigny supermarket (results)
No boiler or backup heating installed! All heating provided by waste heat from refrigeration system Energy consumption reduced by 20% On-going monitoring GHG emission reduction of 75% anticipated Due to reduced natural gas consumption and reduced refrigerant leaks Minimal commissioning: system functioned well from start No problems since April 2004 Supermarket Interior

30 Example: Quebec, Canada Val-des-Monts recreational ice rink
Heat rejected by refrigeration system recovered in secondary loop Radiant floor heating (stands and space heating) reduces refrigeration load Service hot water and resurfacing hot water (with heat pump) Under slab heating Snow pit melting Excess heat to nearby community centre Thermal storage Short term: 2,000 litre water tank for heat Short term: Under pad storage for cold Seasonal: Horizontal loop underground Circulation of secondary coolant in five-pass rather than two-pass configuration Six cascaded 3 hp pumps achieve variable secondary coolant flow rates as required Floating condenser pressure Low emissivity ceiling Efficient lighting (10.5 kW vs 25 kW) Val-des-Monts Recreational Ice Rink Photo Credit: Marius Lavoie, NRCan

31 Example: Quebec, Canada Val-des-Monts recreational ice rink (results)
60% reduction in energy compared with model building code reference rink 50% reduction in power demand compared with average rink Power demand and energy savings of $60,000 annually Greater than 90% reduction in GHG emissions Mainly due to reduced refrigerant leaks achieved with sealed units and secondary loops Refrigerant charge of 36 kg (vs 500 kg in typical system) Refrigerant with no impact on ozone layer Autumn start-up and end-of-season shut down require no special skills (where permitted) Exceptional comfort for spectators

32 RETScreen® Energy Efficient Arena & Supermarket Project Model
Calculates energy savings, life-cycle costs and greenhouse gas emissions reductions For supermarkets & ice rinks Process integration (waste heat recovery) Secondary loops to reduce refrigerant losses Lighting and ceiling improvements Floating condenser pressure Ice and concrete slab thickness Other efficiency measures Also includes: Multiple currencies, unit switch, and user tools

33 Conclusions Cost-effective energy efficiency measures, as well as improvements to refrigeration systems in supermarkets and arenas, can greatly reduce energy consumption and greenhouse gas (GHG) emissions Through process integration, heat rejected by refrigeration system can satisfy most or all of supermarket/arena heating load and, in certain cases, eliminate fossil-fuel combustion heating systems RETScreen® calculates energy savings and greenhouse gas emission reductions for a wide range of energy efficiency measures for supermarkets and ice rinks RETScreen® provides significant preliminary feasibility study cost savings

34 Questions?
Energy Efficiency Project Analysis for Supermarkets and Arenas Module RETScreen® International Clean Energy Project Analysis Course For further information please visit the RETScreen Website at

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