Designing A Smart Home With Phase Change Thermal Mass


A phase change thermal mass material that is applied over
wall cavity insulation before the drywall is applied.
This material is rated to store 91 Btu per square foot.
Phase Change Energy Solutions USA
Australia | Europe

  A smart home as some would think might be computer assisted in its day to day operations such as controlling the interior environment to make decisions on how to handle energy matters.  However a smart home can have passive features built into it to help manage its energy and hence not require a computer, one energy management solution has been the use of thermal mass in the form of brick, stone, terracotta or ceramic tile.  However lets suppose that we had a thermal mass that acted in a smart way to store heat energy above 73 degrees F and then release that energy back into the interior air when the air temperature fell below 73 degrees.  Our home then would have its interior temperature remain constant year round.  This would come in handy in the winter time where one made use of passive and active forms of solar heating in a green built energy efficient home design, where the interior environment would not suffer wild temperature swings and the thermal mass would hold heat until later in the night to release it back into the home.  Our home temperature then would gravitate around this 73 F point at all times.  Hence the material would act this way of its own physics and be a passive component that acted on its on in an active way, with no thermostat or any sort of external power applied to have the thermal mass act to maintain a specific level of home temperature.

  Such a thermal mass that could be used to help maintain the home temperature around 73 F would in no wise interfere with anyone wanting to lower the air conditioning temperature below 73 F since this merely means that the thermal mass will have its thermal energy removed and exhausted outside via the air conditioner.  It does however mean that in rooms where the temperature rises in the daytime due to heat gain, this smart kind of thermal mass will help maintain the temperature more within the comfort zone.  If we set our air conditioner at 72 F then our thermal mass will help to maintain this temperature and the air conditioner would run less than ordinary.

  The kind of thermal mass under discussion here is called "phase change thermal mass" some might call it "transitional thermal mass" where its state or phase is changed when thermal energy is applied to it above a certain temperature.  Candle wax is an example of phase change thermal mass, where at room temperature it is in a solid phase or state, however given a little heat it begins to melt and as long as the heat is above a certain temperature it remains in a liquid state.  When the temperature falls below its liquid state, then the mass of wax gives up its thermal energy into the air and returns to its solid phase or state.  Phase change thermal mass for home use comes as a material that is a solid at temperatures below 73 F which transitions to a liquid state above 73 F.

  To calculate the amount of Btu storage that a specific room could be capable of, just calculate the square footage of the room's walls and the ceiling and multiply this by the chosen type of phase change mass selected (M21 ~ M91 etc).  Depending upon the room and the sources of heat in the home, a typical room could store from 10,000 to 40,000 Btu of thermal energy according to your design.



  The concept of the product is that it is made of a vinyl like substance that contains cells in which the phase change material is stored (refer also the the first photo in this article).  This material either comes folded or in rolls, in the same length and width dimensions of insulation and can be stapled into place between studs over top of the insulation.  It can also be applied to ceilings.  It comes in ratings of 21 Btu per square foot to approximately 130 Btu per square foot.  In addition to these properties it comes with its own flame retardant rated to slow down the burning of interior walls by 21 minutes more than without this material, hence in some locations this might be able to reduce one's home owner insurance rates.  This product has a lifetime rated to 80 years and hence is well worth the investment in terms of helping us to better manage and save on energy use.

  There are applications for this material beyond its use in homes, in some places this is used in coolers and large refrigerators as well as in refrigerated delivery trucks.  An interesting home owner application for this material using those versions rated high in Btu storage capacity is to use this in kitchens to help maintain a more comfortable temperature in which case this would be ideal in large restaurant kitchens.  The objective however is to place this in most every wall in our homes and the ceiling with versions rated differently for the walls and ceiling and such rooms as the kitchen and bathroom.  In the laundry room you would want to use the highest rated version of this product to acquire and store large amounts of heat given off by the cloths dryer, which would be the same concept used in the kitchen.

  An interesting idea to use with this material is to use it to store heat within during the day in the summer time, and then when the temperature drops at night outside air can be brought in to cool the interior and take away the stored heat.  Hence reducing the air conditioner load in the day time and at night.  You definitely have to use the air conditioner during the day but this is not always the case at night since the outside air temperature in some regions of the nation drops at night to a more comfortable cool temperature.  However in this scheme we are storing unwanted heat and then using the night time cool air to remove it, and hence we can devise a better energy management scheme this way.  Without this suggested scheme we however still have something better in terms of smart thermal mass to manage the thermal energy in our homes.

  If you have designed a home with solar heating and solar shading, as well as phase change thermal mass,  your will have designed a smart home with built in decision making features.  Solar shading does not come into play until the summer time due to the high angle of the sun, where you can use solar shading to shade the entire south facing wall with its thermal mass, windows and solar heating panels thus reducing the heat gain in this way.  In the winter due to the lower angle of the sun, its light and hence radiant energy shines beneath the solar shading features to enter the windows and solar space heating panels.  Hence when you have added phase change thermal mass you have added something else that makes the design smart.  In this way you have designed a smart home that virtually runs itself, well to some degree.

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Comment by Dannie Jackson on November 4, 2017 at 5:36pm

Jim Baerg  that's a good example of how thermal mass can help make the temperature range more comfortable by controlling wild swings in temperature.  It slows down the interior heat gain and slows the drop in interior temperature.  Smart thermal mass (phase change mass) on the other hand adds a specific cross over temperature point so that you can set your thermostat around that temperature and have an even better control scenario.  Brick does make a good mass to store thermal energy in, you excess energy can be stored there and slowly released as the temperature drops.  It will run cooler and warmer depending on the season.

Comment by Jim Baerg on November 2, 2017 at 12:29pm

I live in a 100 year old brick house with double wythe exterior walls.  A few years ago, I insulated the space between the inner and outer bricks.  We live in a dry climate with 20 to 30 degree temp swings in the summer, so we religiously open and close windows and drapes.  Last summer we had a week of peak temps in the mid 90's and then it went up to 103.  The house never went above 72 degrees the whole time.

Many people have asked us about our air conditioning (none).  I'm convinced that having cool walls on hot days has significant physical comfort benefits beyond what air conditioning could provide.  It's the "mean radiant temp" issue which works in the summer as well as winter.

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