Implementation of Thermal Storage in Refrigerator/Freezer Smart Grid Units
The idea of the "smart grid," envisions demand control to reduce the use of less efficient and or more polluting power plants. One area of possible demand management is in residential refrigerator/freezers (R/F). Addressing this possibility was the focused subject of the project, specifically innovating an energy saving system that the R/F units would be under addressable control over an internet interface. On the RIT campus alone there is the opportunity for demand control over a Mega Watt of electrical load.This project is based on remotely monitoring and analyzing the temperature distribution of Refrigerator/Freezer unit using wireless sensors. Specifically this project developed and fabricated wireless temperature instrumentation to be placed in multiple locations in the refrigerator and freezer compartments. This wireless data acquisition system allows minimal thermal leakage; and data storage and display remote to the R/F allows continuous and offsite monitoring.
A "Smarter Power Plug/Strip" was developed to allow direct addressing and control of the power to the R/F compressor. Previous and ongoing research shows R/F may have 4 hour and longer off cycles, staying in temperature ranges for food not to spoil.
Thermal and control performance has demonstrated the viability of the "Smarter Power Plug/Strip" to be suit for demand management of R/F units. Studies of the thermal behavior of the R/F units under demand control are to continue, along with the fabrication of the "Smarter Power Plug/Strip," that has begun. The objective would be to include some RIT R/F units under RIT demand management during the summer quarter, ultimately leading to implementation of the "Smarter Power Plug/Strip" permanently at RIT in Fall 2012.
The opportunity large electrical consumers, such as RIT, have to reduce their carbon footprint is participation in demand management. RIT currently participates in such a program. Developing a program to include the estimated 5000 refrigerator/freezer (R/F) units in RIT housing could allow as much as a megawatt of additional demand control. Several things have to happen for this to be possible; the time/temperature response of R/F units under demand shedding control needs to be well characterized, extension of on/off time by using thermal storage will be investigated and performance of "smart grid" connected power strips, such as Tenrethe, tested for their suitability and reliability as the control interface. Avoiding incremental addition of capacity to meet demand has a significant carbon impact since the last plant on line is likely fossil fueled. This project will facilitate the reduction of carbon dioxide emissions.
The project is designed to enhance the power shedding capabilities on R/F units in RIT dorms. The concepts used in this project will allow the appliances to be placed under grid demand management, limiting the amount of power consumed at a given time interval, typically during peak time. This project will study the temperature variations inside R/F units with and without PCMs and smart grid technology incorporated together. Additional variables for the project include: effects of time on temperature, effect of the transition temperature, mass of the PCM, and the effect of the location of the thermal storage inside the R/F unit. Temperature sensors will be installed using a single wire sensor network to determine the temperature at different locations inside the R/F unit. With an 11 sensor network, at least 22 temperature readings are taken a minute.
This project is feasible and can help RIT reduce its power consumption through demand management. RIT is already a Demand Management participant, meaning the campus sheds electrical demand upon request. By incorporating the thermal storage in R/F units RIT will be able to shed a larger load for a longer period of time. Since RIT has approximately 5,000 R/F units on campus, being able to control the refrigeration cycle will help manage the load, possibly avoiding turning on a fossil fueled/ high carbon emission power plant. This project could play a substantial part in reducing carbon emission not only for RIT, but for the community in general.
This project is unique because there's been little to no research on thermal storage units in refrigerator/ freezers . The project will utilize previous undergraduate research pertaining to applications of R/F units. The sensory equipment from the past research will be used in the project. As stated before, this project has many unique research points and applicable solutions to smart grid management. This project will build on current studies at RIT and at Purdue University1.
The introduction of phase change materials (PCMs) into student housing refrigerators/ freezers will promote sustainability by controlling demand. The PCM will be installed conveniently in the R/F, connection for grid control will be with a smart grid power strip, from Tenrethe. The combination of the PCM and the power strip will allow student housing R/Fs to be shed when requested or required. Basically the power strip will control when each refrigerator's compressor turns on and for how long, the PCM will be used as thermal storage, extending acceptable off time. The advantage of incorporating the PCM is it increases the time required for temperature to change inside the R/F, allowing energy efficiency to be more easily monitored, controlled, and optimized.
The power strip will allow the R/F unit to be brought under demand management, where the power cycles can be monitored and controlled. This concept will help limit power consumption when the grid is at its peak. Grid Demand Management helps control the amount of active power from demand sites. This helps prevent expensive and/or high carbon emission power plants from turning on. With approximately 5,000 campus housing refrigerators, this equates to 1.25 Mega Watts of power under demand control. This study will help determine how much of the 1.25 Mega Watts can be shed for a given period of time and for how long.
The benefits for this project can be summarized by first being a scalable idea, secondly the PCMs can be incorporated into any R/F unit. In addition, this project could extend beyond college campuses, and play a large role in demand management throughout the community. Also, the idea of shedding load through one's refrigerator is a great idea since almost everyone owns one. An aftermarket product could be created for any fridge allowing anyone to incorporate thermal storage, saving energy and money.