Skip Navigation


Classes are in session at the University of Maine today, Tuesday, Feb. 9, and snow removal will be in progress throughout the day. Members of the UMaine community are reminded to take care walking and driving as crews work to keep campus roadways, parking lots and sidewalks clear. Sidewalks may have some drifting snow this morning.

Classes - The Comfort Appliance

Group photo

Left to right: Rory Dunn, Parker Hovey and Warren Taylor


This project has its origins in technologies that were first discussed during the first energy crisis of the 1970’s. This effort made use of the idea that a phase transformation (such as making water into ice) was an effective way of storing energy. This technology is used in a number of large building such as the State of Illinois building in Chicago in order to make use of off-peak energy to cool a building. make ice all night with cheap electricity, and blow air over the ice during the day in order to cool the building. This is not necessarily an efficient system, but given the inefficiencies of energy usage it is a good strategy both for the building owner (depending on electricity pricing) and for the utility.

Bring into this equation the continuing need for low carbon energy and the emerging importance of wind, both terrestrial and in the future off-shore wind. However nearly all of the alternative energy technologies are unreliable and may produce electricity when it is not needed and be still when unneeded. We cannot heat and cool houses only when the wind is blowing, so a storage mechanisms is needed.

Comfort Appliance

Comfort Appliance

Now shift to the cabin in the wood, the off-the-grid house or the low impact house. Heating with a pellet or wood stove is great, and, depending on how it is done, can be a sustainable alternative. But, if you have lived with a wood stove, you know that the temperature in the house tends to vary, too hot then too cold. If you use the damper the fire burns dirty. Really, the best case for wood is to run it hard and then let it die. This is the same storage need that is seen with heating that is based on “extra” electricity from renewable sources.

Therefore, a tool is needed. Think about a spring in a mechanical system or a capacitor in an electrical system. In this case the system is our heating and electrical grid, we need a way to take the heat and to time shift it. Too much heat as you head to bed, too little in the morning before you get the wood stove going. Cool nights, and heat that needs to be dumped from the air all day long.

To quote “The Graduate”, not “Plastics”, but “Wax”.

Wax materials exist that melt and freeze at room temperature. Efficiently storing the heat during the times when the room is hot becomes an issue of melting the wax. Cooling the room is a matter of solidifying the wax. This becomes the “Comfort Appliance”. A ducted fan system with a heat exchanger filled with wax that melts at room temperature and can store the heat from the wood stove or remove heat from the room using wax solidified overnight. Materials such as notable can be used to remove heat over a very narrow range. Fans and flaps and exterior ducting can provide the mechanism for air flow, moving, for example, outside air across the coils overnight in the summer, and circulating interior air across the coils during the day. This project will design a “Comfort Appliance” for an 800 square foot office, with the capability to store enough heat to keep the room comfortable for 4 hours and to cool the same room for 8 hours. The system should be designed for retrofitting between standard stud walls. Existing literature and designs should be used, including patents (such as US Patent 6319599) and technical papers (B. Zalba et al., Applied Thermal Engineering 23 (2003) 251–283 or C.K. Halford, R.F. Boehm, Energy and Buildings 39 (2007) 298–305). An existing system from a German manufacturer which are designed for small scale applications can also be used as a reference, however the goal here is to provide a system with significant capacity for retrofitting into a structure instead of an air conditioner or to make wood stoves more efficient ( The design will include modeling of the structure, heat transfer across the coils and energy usage for the fans. The second semester will include building a prototype unit and demonstrating the use for a small room. Thermal analysis and wax specification will be provided by an outside expert and wax will be provided for the test system.


  1. Basic schematic of the use of a heat storage device, heat transfer and thermal storage per cubic foot
  2. Literature search of alternatives and relevant data
  3. Model of the use of a system in a small controlled room
  4. Schematic design of a system which can be used for use in a small office with a wood stove and for summer cooling
  5. Detail design of a system which can be built and specifications for the wax and other materials
  6. Fabricated test system
  7. Operational results for a system used in a room

Draft Milestones

  • Project Team Selection Complete: September 1, 2011
  • First Revised Milestones Submitted: September 8, 2011
  • Design Notebook Initial sign-off: September 13, 2011
  • First performance data on existing design: September 22, 2011
  • Initial model outline for the system: September 25, 2011
  • System Schematic: October 2nd, 2011
  • First web page goes live with introductory page and menu on left. Page must include resumes, individual photos and milestones: October 4, 2011, 4 pm.
  • Milestone review: October 25, 2011
  • Draft Midterm Report: November 30th , 2011
  • Midterm Report due as a PDF posted as a completed web page: December 8th, 5 pm
  • Tests System Complete: March 10 – 15, 2012
  • Lab Cleanup & Infrastructure Project Completed: Maine Day, April 25, 2012
  • Open House — Review of Projects, April 26, 2012, Afternoon
  • Final Web Page submitted, for review during final exam period: Monday May 3rd, 2012 Noon

Email Comfort Appliance


Back to Classes