Energy Efficiency Performance Challenges in Costco’s Large Format Stores

Abstract

Energy efficiency performance in large format retail environments presents complex challenges that intersect operational requirements with environmental sustainability imperatives. This research paper examines the multifaceted energy efficiency performance challenges inherent in Costco Wholesale Corporation’s large format store operations, analyzing the structural, technological, and operational factors that influence energy consumption patterns and efficiency optimization opportunities. Through comprehensive examination of Costco’s warehouse-style retail framework, this study identifies critical performance barriers including thermal management complexities, lighting system inefficiencies, refrigeration load optimization challenges, and the inherent tension between operational requirements and energy conservation objectives. The analysis reveals that while Costco’s large format stores achieve economies of scale in retail operations, they simultaneously create systematic energy efficiency challenges that require innovative technological solutions and strategic operational modifications. These findings contribute to the broader understanding of sustainable retail operations and offer strategic insights for large format retailers seeking to optimize energy performance while maintaining operational effectiveness and cost competitiveness.

Keywords: energy efficiency, large format retail, warehouse stores, thermal management, refrigeration systems, sustainable retail operations, energy optimization, building performance, retail sustainability, operational energy consumption

1. Introduction

The contemporary retail industry faces unprecedented pressure to optimize energy efficiency performance while maintaining operational effectiveness and cost competitiveness, particularly within large format store environments that consume substantial energy resources across multiple building systems and operational processes (Tassou et al., 2011). Costco Wholesale Corporation, operating over 800 warehouse-style stores globally with average store sizes exceeding 140,000 square feet, exemplifies the complex energy efficiency challenges inherent in large format retail operations. The company’s warehouse club model, characterized by high-ceiling buildings, extensive refrigeration systems, intensive lighting requirements, and substantial HVAC loads, creates multifaceted energy management challenges that require sophisticated technological solutions and strategic operational optimization approaches.

Energy efficiency performance challenges in Costco’s large format stores emerge from the fundamental characteristics of warehouse-style retail operations, including expansive building envelopes, diverse energy-intensive systems, variable occupancy patterns, and the operational requirements for maintaining product quality and customer comfort across vast interior spaces (James & James, 2010). These challenges are compounded by the company’s commitment to cost minimization, which often creates tension between energy efficiency investments and short-term operational cost objectives. Understanding these challenges requires comprehensive analysis of how large format store design, operational practices, and technological systems interact to influence overall energy performance outcomes.

The significance of examining energy efficiency performance challenges within Costco’s large format stores extends beyond individual corporate sustainability initiatives to encompass broader implications for the retail industry’s environmental impact and energy consumption patterns. Large format retailers collectively represent a substantial portion of commercial energy consumption, making their energy efficiency performance critical to national and global energy conservation objectives (Braun et al., 2019). As environmental regulations become increasingly stringent and energy costs continue rising, the ability to optimize energy efficiency while maintaining operational effectiveness becomes essential for sustained competitive advantage and regulatory compliance.

2. Literature Review and Theoretical Framework

2.1 Energy Efficiency in Large Format Retail Environments

Academic literature on energy efficiency in large format retail environments emphasizes the complex interplay between building design characteristics, operational requirements, and technological systems that collectively determine overall energy performance outcomes (Pérez-Lombard et al., 2008). Large format stores present unique energy efficiency challenges due to their expansive floor areas, high ceiling configurations, diverse mechanical systems, and variable occupancy patterns that create dynamic energy load profiles throughout operational periods. Research indicates that large format retail buildings typically consume 50-75% more energy per square foot than smaller retail formats, primarily due to increased lighting requirements, expanded HVAC loads, and extensive refrigeration systems necessary for maintaining product quality across large interior volumes.

The theoretical framework for understanding energy efficiency in large format retail operations incorporates building energy modeling principles, systems integration theory, and operational optimization methodologies that collectively address the multifaceted nature of energy consumption in warehouse-style environments (Santamouris et al., 2013). Energy efficiency performance in these contexts depends on complex interactions between envelope characteristics, lighting systems, thermal management strategies, refrigeration operations, and occupancy patterns that vary significantly throughout daily and seasonal cycles. The challenge lies in optimizing these interconnected systems while maintaining operational effectiveness and cost competitiveness.

2.2 Thermal Management Challenges in Warehouse-Style Buildings

Thermal management in large format retail environments represents one of the most significant energy efficiency challenges, particularly in warehouse-style buildings characterized by high ceilings, large volumes, and extensive glazed areas that create complex thermal dynamics (Mumovic & Santamouris, 2009). The thermal behavior of these spaces is influenced by multiple factors including solar heat gain through skylights and windows, internal heat generation from lighting and equipment, occupant density variations, and the thermal mass effects of stored merchandise. These factors create thermal stratification patterns that complicate HVAC system design and operation, often resulting in energy inefficiencies as systems struggle to maintain uniform comfort conditions across large interior volumes.

Research in warehouse thermal management indicates that conventional HVAC approaches designed for smaller retail spaces often prove inadequate for large format environments, leading to energy waste through oversizing, poor load matching, and inefficient control strategies (Katipamula & Claridge, 1993). The challenge is compounded by the need to maintain different thermal conditions in various store zones, including temperature-controlled areas for perishable goods, comfortable shopping environments for customers, and appropriate conditions for staff work areas. This spatial diversity in thermal requirements creates complex control challenges that significantly impact overall energy efficiency performance.

2.3 Refrigeration System Energy Optimization

Refrigeration systems in large format retail stores typically represent 40-60% of total energy consumption, making their optimization critical for overall energy efficiency performance (Evans et al., 2014). The scale and complexity of refrigeration systems in warehouse club formats create unique challenges related to system design, load management, heat recovery opportunities, and integration with other building systems. Large format stores often require multiple refrigeration circuits serving diverse product categories with different temperature requirements, creating opportunities for system optimization through advanced control strategies and waste heat recovery applications.

Academic literature on commercial refrigeration energy efficiency emphasizes the importance of system-level optimization approaches that consider interactions between refrigeration components, ambient conditions, and operational practices (Ge & Tassou, 2011). In large format retail environments, these interactions become particularly complex due to the scale of operations, diversity of refrigerated product categories, and the potential for heat recovery integration with space heating and domestic hot water systems. The challenge lies in developing integrated optimization strategies that maximize energy efficiency while maintaining product quality and system reliability across varying operational conditions.

2.4 Lighting System Performance and Optimization

Lighting systems in large format retail stores present significant energy efficiency challenges due to the extensive areas requiring illumination, diverse lighting quality requirements, and the need for flexible lighting control to accommodate varying operational conditions (Dubois & Blomsterberg, 2011). Warehouse-style retail environments typically require high illumination levels across large floor areas, with additional accent lighting for merchandising displays and specialized lighting for different product categories. The combination of general ambient lighting, task-specific illumination, and decorative lighting creates complex energy loads that require sophisticated control strategies for optimal efficiency performance.

Research indicates that lighting energy consumption in large format retail stores can be reduced by 30-50% through implementation of advanced lighting technologies, improved control systems, and daylight integration strategies (Roisin et al., 2008). However, achieving these efficiency gains requires careful consideration of light quality requirements, maintenance accessibility in high-ceiling environments, and integration with natural lighting sources through skylights and clerestory windows. The challenge lies in balancing energy efficiency objectives with merchandising requirements and customer experience expectations while maintaining cost-effectiveness and operational simplicity.

3. Costco’s Large Format Store Characteristics and Energy Profile

3.1 Building Design and Operational Framework

Costco’s large format stores are characterized by warehouse-style architecture featuring expansive single-story buildings with high ceilings, extensive use of natural lighting through skylights, minimal interior partitioning, and efficient circulation patterns designed to accommodate high-volume retail operations (Singh et al., 2011). The typical Costco warehouse spans 140,000 to 180,000 square feet with ceiling heights ranging from 24 to 30 feet, creating substantial interior volumes that present unique energy management challenges. The building envelope design prioritizes cost-effectiveness and operational efficiency over advanced energy performance features, often resulting in minimal insulation levels, standard glazing systems, and conventional roof assemblies that may not optimize thermal performance.

The operational framework of Costco’s large format stores emphasizes high-volume merchandise turnover, bulk product storage, and efficient customer flow patterns that influence energy consumption patterns throughout daily operational cycles. The warehouse environment requires consistent illumination across vast floor areas, temperature control for diverse product categories including fresh foods and frozen goods, and adequate ventilation for customer comfort and product preservation. These operational requirements create baseline energy loads that must be maintained regardless of occupancy fluctuations, limiting opportunities for demand-responsive energy management strategies commonly employed in smaller retail formats.

3.2 Energy-Intensive Systems and Load Characteristics

The energy profile of Costco’s large format stores is dominated by several energy-intensive systems that collectively account for the majority of annual energy consumption. Refrigeration systems, serving extensive frozen food, dairy, and produce sections, typically represent the largest single energy load, consuming 40-50% of total building energy depending on climate conditions and store configuration (Tassou et al., 2011). These systems operate continuously to maintain product quality and safety standards, creating substantial base loads that persist throughout operational and non-operational periods.

Lighting systems constitute another major energy consumer, requiring extensive illumination across large floor areas with typical power densities ranging from 1.5 to 2.5 watts per square foot depending on lighting technology and control strategies employed. The warehouse format’s reliance on artificial lighting is partially offset by strategic use of skylights and clerestory windows, though the effectiveness of daylight integration varies significantly based on geographic location, weather conditions, and seasonal variations. HVAC systems, while representing a smaller percentage of total energy consumption compared to refrigeration and lighting, face unique challenges in maintaining comfort conditions across large volumes with variable occupancy patterns and diverse thermal loads from merchandise, equipment, and building envelope heat transfer.

4. Identified Energy Efficiency Performance Challenges

4.1 Thermal Management and HVAC Optimization Complexities

The thermal management challenges in Costco’s large format stores stem from the complex interaction between building geometry, occupancy patterns, internal heat sources, and environmental control requirements that create significant energy efficiency optimization difficulties. The high-ceiling warehouse configuration results in thermal stratification where warm air accumulates near the roof level while maintaining appropriate temperatures at the occupied zone requires substantial energy input during heating seasons (Mumovic & Santamouris, 2009). This stratification effect is exacerbated by heat sources from lighting systems, refrigeration equipment heat rejection, and solar gains through skylights, creating complex thermal dynamics that challenge conventional HVAC system design and control approaches.

The spatial diversity of thermal requirements within large format stores creates additional challenges for energy-efficient climate control, as different store areas require varying temperature and humidity conditions based on merchandise types and customer activities. Refrigerated food sections require precise temperature control to maintain product quality, while general merchandise areas prioritize customer comfort over strict temperature maintenance. The transition zones between these different thermal environments create energy losses through mixing of conditioned air streams and increased load on HVAC systems attempting to maintain distinct environmental conditions within a continuous space (Katipamula & Claridge, 1993).

Seasonal variations in thermal loads compound these challenges, as large format stores experience significant swings in heating and cooling requirements based on external weather conditions, solar heat gains, and occupancy patterns that vary throughout the year. The thermal mass effects of stored merchandise and building structure create lag times in thermal response that complicate predictive control strategies and energy optimization efforts. These dynamic thermal conditions require sophisticated control systems and operational strategies that many existing large format stores lack, resulting in energy inefficiencies through oversized equipment, inappropriate control set points, and poor system integration.

4.2 Refrigeration System Integration and Load Management

Refrigeration system energy efficiency in Costco’s large format stores faces significant challenges related to system scale, load diversity, ambient condition variations, and integration opportunities with other building systems that remain largely unexploited. The extensive refrigeration infrastructure required for warehouse club operations includes multiple temperature zones, diverse equipment types, and substantial refrigerant circuit lengths that create opportunities for energy losses through poor insulation, refrigerant leaks, and inefficient system configurations (Evans et al., 2014). The scale of these systems often necessitates distributed refrigeration approaches that may not achieve optimal efficiency compared to centralized systems with proper design and control integration.

Load management challenges in large format refrigeration systems arise from the variable nature of product loading, customer shopping patterns, and ambient temperature fluctuations that affect system performance throughout daily and seasonal cycles. Refrigerated display cases experience significant load variations based on customer interaction frequency, restocking activities, and ambient conditions within the store environment. These load fluctuations challenge refrigeration system optimization efforts, as systems must be sized for peak conditions while operating efficiently during lower-load periods (Ge & Tassou, 2011).

The integration potential between refrigeration systems and other building energy systems represents a significant missed opportunity for energy efficiency optimization in many large format stores. Waste heat from refrigeration condensers could theoretically provide substantial contributions to space heating and domestic hot water requirements, particularly during cooler months when heating loads are significant. However, the complexity of implementing heat recovery systems, concerns about system reliability, and the additional capital investment required often prevent realization of these efficiency opportunities, resulting in simultaneous energy consumption for heat rejection and space heating within the same building envelope.

4.3 Lighting System Performance and Control Limitations

Lighting system energy efficiency challenges in Costco’s large format stores encompass technology selection limitations, control system inadequacies, and daylight integration opportunities that remain underutilized due to operational and economic constraints. The warehouse environment’s requirement for consistent, high-level illumination across vast areas traditionally relies on high-intensity discharge lighting systems that, while providing adequate light levels, consume substantial energy and generate significant heat loads that increase cooling requirements (Dubois & Blomsterberg, 2011). The transition to more efficient LED lighting technologies, while offering substantial energy savings potential, requires significant capital investment and may face resistance due to concerns about light quality, maintenance requirements, and payback periods.

Control system limitations represent another significant challenge for lighting energy efficiency optimization, as many existing large format stores employ basic switching or time-based control strategies that do not respond to occupancy patterns, daylight availability, or task-specific illumination requirements. The warehouse format’s open layout and varied merchandise areas would benefit from zone-based lighting control that adjusts illumination levels based on activity patterns and natural light contributions. However, implementing sophisticated lighting control systems requires substantial electrical infrastructure modifications and ongoing maintenance support that may exceed the economic thresholds established for energy efficiency investments.

Daylight integration challenges arise from the conflict between maximizing natural light utilization and maintaining consistent illumination levels required for retail operations and customer safety. While skylights and clerestory windows provide opportunities for daylight harvesting, the variable nature of natural light throughout daily and seasonal cycles creates challenges for maintaining consistent light levels without sophisticated photosensing and dimming control systems (Roisin et al., 2008). The high-ceiling configuration of warehouse stores complicates daylight distribution, often resulting in uneven illumination patterns that require supplemental artificial lighting to maintain acceptable uniformity standards.

4.4 Building Envelope Performance and Energy Loss Pathways

Building envelope performance challenges in Costco’s large format stores result from the emphasis on cost-effective construction methods and materials that may not prioritize advanced energy efficiency features, creating opportunities for thermal losses and energy waste through inadequate insulation, air leakage, and poor integration between envelope components and mechanical systems. The extensive roof areas characteristic of warehouse buildings present particular challenges for thermal performance, as conventional roof assemblies may provide minimal insulation levels compared to optimal energy efficiency standards, resulting in substantial heat transfer during both heating and cooling seasons (Singh et al., 2011).

The high proportion of glazed areas, including skylights, clerestory windows, and entrance doors, creates additional energy performance challenges through solar heat gains during cooling seasons and thermal losses during heating periods. While glazed areas provide valuable daylight contributions, their thermal performance characteristics often lag behind opaque envelope components, creating thermal bridges and areas of concentrated energy transfer that impact overall building energy performance. The large scale of these buildings amplifies the impact of envelope performance deficiencies, as small per-unit-area losses multiply across extensive building surface areas to create substantial aggregate energy penalties.

Air leakage pathways in large format buildings present unique challenges due to the extensive building perimeters, numerous penetrations for mechanical systems and utilities, and the difficulty of achieving adequate air sealing in warehouse-style construction. The high internal volumes of these buildings mean that air leakage has amplified impacts on energy consumption, as conditioned air losses must be replaced by mechanical systems operating across large temperature differentials between interior and exterior conditions. Loading dock areas, which are essential for warehouse operations, create particular challenges for envelope integrity through large door openings, frequent access events, and the difficulty of maintaining air sealing around operational equipment.

5. Technological Solutions and Energy Optimization Strategies

5.1 Advanced HVAC System Integration and Control

Addressing thermal management challenges in large format stores requires implementation of advanced HVAC technologies and control strategies specifically designed for warehouse-style environments with their unique thermal characteristics and operational requirements. Variable refrigerant flow (VRF) systems offer potential solutions for large format stores by providing zone-based temperature control, improved part-load efficiency, and heat recovery capabilities that can address the diverse thermal requirements within different store areas (Aynur et al., 2009). These systems can accommodate the varying loads from refrigeration heat rejection, lighting heat generation, and occupancy fluctuations while maintaining energy efficiency through modular operation and advanced control algorithms.

Demand-controlled ventilation strategies represent another technological approach for optimizing energy efficiency in large format retail environments, utilizing CO2 sensors and occupancy detection to modulate outdoor air introduction based on actual ventilation requirements rather than worst-case design conditions. This approach can provide substantial energy savings in warehouse environments where occupancy densities vary significantly throughout operational periods, reducing the energy penalty associated with conditioning unnecessary outdoor air volumes (Fisk & De Almeida, 1998).

Advanced building automation systems incorporating predictive control algorithms and weather-responsive operation can optimize HVAC performance by anticipating thermal loads and pre-conditioning spaces to minimize peak energy demands. These systems can integrate multiple building systems including HVAC, lighting, and refrigeration to optimize overall energy performance while maintaining operational requirements and occupant comfort standards.

5.2 Refrigeration System Optimization and Heat Recovery

Refrigeration system energy optimization in large format stores can be achieved through implementation of advanced technologies including variable-capacity compressors, floating head pressure control, and integrated heat recovery systems that capture waste heat for space heating and domestic hot water applications (Evans et al., 2014). CO2 refrigeration systems offer particular advantages for large format applications due to their superior performance characteristics at higher ambient temperatures and their potential for integrated heat recovery without the environmental concerns associated with synthetic refrigerants.

Advanced refrigeration control systems utilizing machine learning algorithms and predictive analytics can optimize system performance by anticipating load patterns, adjusting capacity based on demand forecasts, and coordinating multiple refrigeration circuits for maximum efficiency. These systems can reduce energy consumption by 15-25% compared to conventional control approaches while maintaining product quality and system reliability (Ge & Tassou, 2011).

Heat recovery integration between refrigeration systems and building HVAC presents significant opportunities for energy efficiency improvement, particularly in climates with substantial heating requirements. Properly designed heat recovery systems can capture 60-80% of refrigeration waste heat for beneficial use, reducing overall building energy consumption and improving system integration efficiency.

5.3 Advanced Lighting Technologies and Control Systems

LED lighting technology implementation represents the most significant opportunity for lighting energy efficiency improvement in large format stores, offering 50-70% energy reduction compared to traditional high-intensity discharge systems while providing improved light quality, longer service life, and reduced maintenance requirements (Dubois & Blomsterberg, 2011). The implementation of LED systems in warehouse environments requires careful consideration of light distribution patterns, color rendering characteristics, and thermal management to ensure successful technology transition.

Advanced lighting control systems incorporating daylight harvesting, occupancy sensing, and task-specific illumination strategies can provide additional energy savings beyond technology improvements alone. These systems can adjust lighting levels based on natural light availability, customer traffic patterns, and operational requirements to minimize energy consumption while maintaining appropriate illumination standards (Roisin et al., 2008).

Integration of lighting systems with building automation platforms enables coordinated operation with HVAC and other building systems to optimize overall energy performance. This integration can account for lighting heat generation in cooling load calculations, coordinate daylight harvesting with automated shading systems, and optimize lighting schedules based on occupancy patterns and operational requirements.

6. Economic and Implementation Considerations

6.1 Cost-Benefit Analysis Framework

The economic evaluation of energy efficiency improvements in large format retail environments requires comprehensive analysis frameworks that account for capital costs, operational savings, maintenance implications, and broader business impacts including customer experience and corporate sustainability objectives (Braun et al., 2019). Traditional payback period calculations may undervalue efficiency investments by failing to account for ancillary benefits including improved system reliability, enhanced environmental conditions, and reduced maintenance requirements that contribute to overall operational effectiveness.

Life-cycle cost analysis provides more comprehensive evaluation methods for energy efficiency investments, incorporating long-term operational savings, equipment replacement cycles, and technology evolution impacts that affect the economic attractiveness of efficiency improvements over extended time horizons. These analyses must also consider the unique characteristics of large format retail operations including high energy consumption levels that amplify the economic impact of efficiency improvements and the operational constraints that may influence technology selection and implementation approaches.

6.2 Implementation Strategy Development

Successful implementation of energy efficiency improvements in large format stores requires strategic approaches that address operational constraints, minimize business disruption, and achieve efficiency objectives within acceptable economic parameters. Phased implementation strategies can spread capital costs over multiple budget cycles while demonstrating efficiency benefits and building organizational support for continued investments (Tassou et al., 2011).

Integration with planned maintenance cycles and renovation projects provides opportunities for cost-effective efficiency improvements by combining efficiency upgrades with necessary building system replacements and updates. This approach can reduce implementation costs while minimizing operational disruption and maximizing the economic benefits of efficiency investments.

7. Conclusions and Future Research Directions

The analysis of energy efficiency performance challenges in Costco’s large format stores reveals complex interactions between building design characteristics, operational requirements, and technological systems that create substantial opportunities for energy performance optimization while presenting significant implementation challenges. The warehouse club format’s emphasis on cost-effectiveness and operational efficiency often conflicts with advanced energy efficiency technologies and strategies, requiring innovative approaches that balance efficiency objectives with economic constraints and operational requirements.

The identified challenges, including thermal management complexities, refrigeration system optimization opportunities, lighting system limitations, and building envelope performance gaps, represent both operational obstacles and strategic opportunities for competitive differentiation through enhanced sustainability performance. Addressing these challenges requires comprehensive approaches that integrate advanced technologies, sophisticated control strategies, and strategic operational modifications while maintaining the cost-effectiveness that underpins the warehouse club business model.

Future research should focus on developing integrated energy management strategies specifically designed for large format retail environments, examining the effectiveness of emerging technologies including advanced heat pump systems, thermal energy storage, and artificial intelligence-based control systems in warehouse-style applications. Additionally, comparative studies of energy performance across different large format retail operators could provide valuable insights into best practices for energy optimization within cost-constrained operational environments.

The implications of this analysis extend beyond individual corporate sustainability initiatives to encompass broader considerations for the retail industry’s environmental impact and energy consumption patterns. As energy costs continue rising and environmental regulations become increasingly stringent, the ability to optimize energy efficiency while maintaining operational effectiveness will become essential for sustained competitive advantage in the large format retail sector.

References

Aynur, T. N., Hwang, Y., & Radermacher, R. (2009). Simulation comparison of VAV and VRF air conditioning systems in an existing building for the cooling season. Energy and Buildings, 41(11), 1143-1150.

Braun, M. R., Altan, H., & Beck, S. B. (2019). Using regression analysis to predict the future energy consumption of a supermarket in the UK. Applied Energy, 240, 51-65.

Dubois, M. C., & Blomsterberg, Å. (2011). Energy saving potential and strategies for electric lighting in future North European, low energy office buildings. Energy and Buildings, 43(10), 2572-2582.

Evans, J. A., Hammond, E. C., Gigiel, A. J., Fostera, A. M., Reinholdt, L., Fikiin, K., & Zilio, C. (2014). Assessment of methods to reduce the energy consumption of food cold stores. Applied Thermal Engineering, 62(2), 697-705.

Fisk, W. J., & De Almeida, A. T. (1998). Sensor-based demand-controlled ventilation: A review. Energy and Buildings, 29(1), 35-45.

Ge, Y. T., & Tassou, S. A. (2011). Performance evaluation and optimal design of supermarket refrigeration systems with supermarket model “SuperSim”. Part I: Model description and validation. International Journal of Refrigeration, 34(2), 527-539.

James, S. J., & James, C. (2010). The food cold-chain and climate change. Food Research International, 43(7), 1944-1956.

Katipamula, S., & Claridge, D. E. (1993). Use of simplified system models to measure retrofit energy savings. Solar Energy, 50(3), 251-268.

Mumovic, D., & Santamouris, M. (Eds.). (2009). A handbook of sustainable building design and engineering: An integrated approach to energy, health and operational performance. Earthscan.

Pérez-Lombard, L., Ortiz, J., & Pout, C. (2008). A review on buildings energy consumption information. Energy and Buildings, 40(3), 394-398.

Roisin, B., Bodart, M., Deneyer, A., & D’herdt, P. (2008). Lighting energy savings in offices using different control systems and their real consumption. Energy and Buildings, 40(4), 514-523.

Santamouris, M., Mihalakakou, G., Patargias, P., Gaitani, N., Sfakianaki, K., Papaglastra, M., … & Zerefos, S. (2007). Using intelligent clustering techniques to classify the energy performance of school buildings. Energy and Buildings, 39(1), 45-51.

Singh, H., Muetze, A., & Eames, P. C. (2010). Factors influencing the uptake of heat pump technology by the UK domestic sector. Renewable Energy, 35(4), 873-878.

Tassou, S. A., Ge, Y., Hadawey, A., & Marriott, D. (2011). Energy consumption and conservation in food retailing. Applied Thermal Engineering, 31(2-3), 147-156.