Savings from Recommissioning and Beyond

Abstract

ABSTRACT Recommissioning, or periodically resolving the operational shortcomings of building systems such as lighting; heating, ventilation, and air conditioning (HVAC); water heating; and refrigeration has been demonstrated to be one of the most cost effective methods for reducing energy use. However, there are simple control or design strategies beyond recommissioning that can be implemented post-design and save energy. There is often resistance to energy savings strategies that require changes to the status quo. Accordingly, it is important for building managers striving to achieve voluntary or mandatory energy intensity reduction goals to achieve “buy in” throughout all levels of their organization. This includes designers, management, store associates, and maintenance personnel. If any of these key players does not understand or does not support the recommendations, it will not be long before the energy saving measures are disabled or overridden. The building selected for this study is a supermarket located in the southeastern U.S. It occupies 71,000 square feet and is open six days a week, 24 hours per day. The refrigeration system, consisting of five compressor racks (three medium-temperature and two low-temperature) with associated air-cooled condensers, serves refrigerated display cases and walk-in coolers. The primary HVAC system is a constant volume, dual path, packaged rooftop air handler with direct expansion cooling. Heating is provided from either hot gas heat reclaim or electric resistance heating. The refrigerated display case lighting, sales area lighting, HVAC, and refrigeration are controlled by an integrated refrigeration monitoring and control system (RMCS). In addition to the recommissioning, four energy savings measures were studied. These measures are listed below, along with typical objections to implementation. 1. Cycle air handling units (AHUs) after business hours, based on space temperature and humidity setpoint changes. Many designers and supermarket store operators feel that if the sales area AHUs are turned off, then the temperature and humidity levels will vary too much. This could cause additional maintenance problems due to extra display case defrosts and the possibility of accompanying product loss.2. Adjust anti-sweat heater control settings to reduce operating times. Often the anti-sweat heater settings are set so conservatively that the heaters operate at higher levels than needed. Will the new settings cause condensation to form on glass doors and mullions?3. Implement floating head pressure control strategy. Will reduced pressures cause problems with incomplete oil distribution throughout the refrigeration system? Will reduced head pressures cause heat reclaim to be uneconomical?4. Return the domestic hot water recirculation loop to the heat reclaim tank rather than bypassing it and going directly to the primary heating tank. Does this change create additional problems? Are the additional savings worth the effort? To measure and verify the savings generated by these energy savings measures, the supermarket's systems were extensively metered, including the following systems: 1. Sales area AHU 1 fan, compressors, and electric resistance heat2. Sales area AHU 2 fan, compressors, and electric resistance heat3. Sales area AHU 1 electric resistance heat4. Sales area AHU 2 electric resistance heat5. Refrigeration systems A-D (two low- and two medium-temperature compressor racks, including their associated condensers)6. Refrigeration system E (medium-temperature compressor rack with associated condenser)7. Domestic water heater electric resistance heating8. Domestic water heater cold water supply volume9. Main electric utility supply feed All meter readings were collected on site and transmitted to an off-site server that is accessible via the internet. Data for outside air temperature and relative humidity from a local weather site were also recorded. The RMCS was the focus of our efforts. We adjusted mechanical control valves and reprogrammed the RMCS to minimize energy consumption while maintaining the required temperatures in the display cases and walk-in coolers. Electricity consumption and weather data were collected before and after each test. We performed regression analyses on each set of data, using the hourly outside air temperature as the independent variable. The results produced equations that can be used to estimate supermarket power use as a function of outside air temperature. These equations were developed for the baseline, after recommissioning and after implementing each of the four energy savings measures. This article documents our efforts to quantify energy savings attributable to recommissioning and the four energy conservation measures (ECMs) that go beyond recommissioning. At the same time, we verified that the objections accompanying each ECM were refuted with both measureable data and on-site observations.