|Attaching doors to open refrigerated cases can be done both in new installations and in-store retrofits.|
Sources consulted during the development of the DOE’s guide agreed that proper planning before the commencement of any retrofit activity is one of the keys to a successful case retrofit project.
The first step in planning a retrofit project should be the documentation of existing as-built characteristics. This will be imperative in providing inputs to required design analyses, as well as in cataloging changes to the system during and after the retrofit installation. The contractor supervising the project should review existing drawings in order to gauge the impact on the installed equipment. A survey of the refrigeration system should be taken, including the compressor rack, controls, expansion valves, piping, and condensers, to quantify the existing condition of the equipment and any differences between the as-built layout and the original system designer’s plans. Moreover, the condition of the display cases and refrigeration system should be evaluated. If equipment is approaching the end of its service lifetime or is in poor condition, the contractor may advise complete replacement of the equipment.
In many instances, the chosen vendor for the retrofit kit or display doors and frames will provide a form with step-by-step instructions on the necessary measurements and information that should be provided in order to ensure that the new doors and other parts fit properly with the existing case. This will typically involve documentation of the case makes and models, as well as measurements of critical inside and outside dimensions and features present on the cases.
Case Heat-Load Modeling
The installation of doors on previously open cases will result in a large decrease in the heat load (on the order of 50-80 percent) removed from the cases by the refrigeration system. The magnitude of the refrigeration load is the driving factor in the sizing and configuration of the compressor rack and other refrigeration components and, by extension, determines the energy expenditure of the system. Reduction of the load on the cases themselves is only one factor in energy reduction and proper system performance. The refrigeration system must be adjusted as well, or else the imbalance between the refrigeration load and the capacity steps and other operating parameters of the refrigeration system will lead to inefficient, suboptimal performance. For example, during excessive compressor cycling caused by such a mismatch, much more energy is used starting the compressors than is used operating in the steady state, which greatly increases system energy consumption. Thus, it is imperative that proper modeling of the post-retrofit refrigeration loads be performed in order to facilitate accurate modifications to the rest of the system.
Modeling of the as-designed cases post-retrofit should be carried out by a qualified refrigeration engineer and should, to the extent possible, take into account factors such as shopper traffic and climatic variations throughout the year. The result of this modeling should be an estimate of case load in Btuh per foot for the affected cases, which can be used as the basis for comparison to the available capacity of the refrigeration system.
Store owners may consider using the retrofit project as an opportunity to consider upgrading existing T8 fluorescent lighting fixtures installed in the cases to light-emitting diode (LED) fixtures. These fixtures have the potential to reduce lighting energy consumption by a factor on the order of 70 percent while maintaining the level of product illumination needed for proper merchandising and product display. Moreover, lighting power reduction serves the secondary benefit of reducing the heat load in the case (as the lighting energy is dissipated as heat), which in turn reduces the refrigeration load and thus the refrigeration system energy consumption. LED lighting is available from a wide variety of vendors, and is often specified and supplied with the doors and frames by the door manufacturer or retrofit kit supplier. Since display doors often can be easily specified to include integrated lighting, a case retrofit is an ideal time to consider a lighting upgrade. When considering replacement of the case lighting, operators and system designers should take into account the product being displayed and the placement within the store, amongst other factors, in order to select the proper lighting power and color profile. (The DOE Better Buildings Alliance has released a specification on LED lighting for refrigerated display cases, available at www1.eere.energy.gov/buildings/commercial/bba_display_case_spec.html.)
Additionally, operators could consider the use of case occupancy sensors or other lighting controls in conjunction with LED lighting (these technologies are not compatible with fluorescent lighting), which offer the potential to further reduce energy expenditures on product lighting. DOE suggests that the refrigeration engineer or firm planning the retrofit evaluate the cost and payback period for the use of LED lighting and lighting controls in the given application as part of the planning for the project and present that information to the building owner to facilitate an informed decision.
Fan Power Adjustment
Due to the marked decrease in case heat load, the case fan motor configuration may need to be adjusted to ensure proper airflow. Modeling performed prior to the beginning of the retrofit could include analysis of the required case airflow before and after the addition of doors. In some cases, the lack of need for a functioning air curtain after the installation of the doors may allow for the reduction of fan power to levels needed to maintain even product temperature. If a reduction in fan power is found to be warranted, adjustments to the discharge plenum may be required as well. The refrigeration engineer should consult with the case manufacturer or retrofit kit supplier, should this step be needed, in order to ensure that the correct replacement parts are procured.
Industry experts suggested that one relatively simple method for reducing fan power is to reduce the pitch of the evaporator fan blades used in the cases. A suggested guideline provided to DOE was to aim for the goal of achieving a 350-foot-per-minute discharge air velocity as measured at blade pitch to meet the necessary airflow requirement without requiring excess power from the fan motor, which can reduce fan energy consumption with no further changes required. Necessary calculations should be performed in order to ensure that sufficient airflow is maintained.
Additionally, many building owners use case retrofits as an opportunity to upgrade their evaporator fan motors to high-efficiency motors, including permanent split capacitor (PSC) motors or electronically commutated motors (ECMs), which can reduce fan motor energy consumption on the order of 40 percent and 70 percent, respectively, when compared to shaded-pole motors (SPMs). Additionally, since fan motor energy is dissipated as heat inside the case, reducing the motor energy consumption reduces the refrigeration load and, in turn, the energy consumption of the refrigeration system. The system designer or refrigeration engineer coordinating the retrofit project may wish to evaluate the cost and payback period for the use of ECM fan motors as part of the planning for the project and present that information to the building owner to facilitate an informed decision.
The need for anti-condensate (“anti-sweat”) heaters on the new display doors will depend on the make and model of door used, the case configuration, and the ambient conditions within the store. Many door manufacturers currently sell medium-temperature products that utilize only frame heaters or no heaters at all. However, it is important to prevent condensate formation and the customer safety issues that condensation can cause. Thus the need for anti-sweat heaters should be analyzed based upon the anticipated operating conditions of the case and the anticipated ambient condition fluctuations within the store. For example, stores operating in areas with long durations of high-temperature, high-humidity weather may be more prone to condensation issues. Should anti-condensate heaters be required, consider the use of anti-sweat heater controls to mitigate excess energy use by the heaters.
Modeling of the case and building electrical systems should be performed in anticipation of the case retrofit project, in order to ensure that the power supplies and components remain properly sized for the system after the modifications are made. Analyses should be conducted by a qualified refrigeration engineer and should encompass the entirety of the electrical system serving the cases, fans and lighting, compressor rack, condensers, and other components of the refrigeration system. Particular attention should be paid to existing system components, such as circuit breakers, which may prove to be improperly sized when matched with the electrical loads of the upgraded cases and refrigeration system. System designers should work with the retrofit kit supplier to understand the electrical characteristics of the system, including peak load, fuse dimensions, cable dimensions, and power factor, and should account for those characteristics during the planning of the retrofit.
Open refrigerated display cases remove large amounts of heat from the surrounding store space as cold, dehumidified air escapes the case through infiltration. This results in a net increase in the building heating load during the heating season and a net decrease in the building cooling load during the cooling season. The addition of doors onto these open cases greatly reduces the level of infiltration and thus changes the associated impacts on HVAC loads.
In commercial retail buildings, the HVAC system is generally sized, designed, and/or configured to account for the interaction with the refrigeration equipment. The large change in heat load on the HVAC equipment due to the installation of doors on open cases will require a reassessment of the HVAC system configuration to ensure continued optimal performance. In planning for the retrofit operation, the engineer coordinating the analysis should re-evaluate the performance of the HVAC equipment, taking into account the contribution of the retrofitted cases on the system.
In selecting a retrofit kit and doors, users should take into account a variety of factors, both functional and aesthetic. One major consideration is the type and size of doors and the impact that those doors will have on aisle widths and shopper traffic. Additional factors to be considered include the desired product temperature; door hinge opening angle; door width; and glass types, gas fills, and glazing treatments (such as anti-reflective coatings). These factors should be taken into account during system design, and their impact on the store layout and operation should be analyzed. Sources consulted during the development of this guide also pointed out that operators should ensure that doors are certified to American National Standards Institute (ANSI) 297.1 as well as Underwriters Laboratories (UL) and NSF International (NSF) requirements for their applications.
Merchandise Preservation and Retrofit Coordination
One important factor to consider during the retrofit operation will be provisions to preserve the existing perishable inventory that is currently housed in the cases to be modified. During some retrofit operations, the merchandise may be able to remain in the case during the duration of the retrofit. Thus no steps will need to be taken beyond covering the merchandise. In other instances, this inventory will need to be moved to another case, a walk-in cooler, or another refrigerated space with the capacity and capability to hold and preserve the merchandise throughout the duration of time when the cases are out of operation.
Therefore, when planning the retrofit, the operator should account for the time and staff capacity needed to move the product if necessary, and should also budget for the refrigerated space needed to store the merchandise. Incoming inventory shipment schedules may need to be altered in order to allow room to accommodate the product removed from the cases being retrofitted. Additionally, individual store owners or operators should take into account their specific store operating hours and customer traffic patterns to minimize sales disruptions during the retrofit.
EDITOR’S NOTE: This work was accomplished with the guidance of Brian Holuj, Jason Komen, and Kristen Taddonio of the U.S. Department of Energy, and through the contributions of many Better Building Alliance members and representatives of industry. The U.S. Department of Energy wishes to particularly acknowledge the efforts of the following parties: DC Engineering, Hill PHOENIX, Hussmann Corp., REMIS America LLC and REMIS GmbH, and Zero Zone Inc.
This report should be viewed as a general guide to best practices and factors for consideration by end users who are planning or evaluating a retrofit operation, rather than a comprehensive and exhaustive set of specific steps to perform when retrofitting display cases. A qualified refrigeration engineer or firm should always be contracted to oversee any retrofit project. This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government, nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency, contractor, or subcontractor thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
Publication date: 5/20/2013