Tag Archives for " radiant barrier "

How PCM works to keep your home cooler–and warmer

We are always eager to hear about advances in technology that the average homeowner can use to live healthier lives with less expense or energy.  Lots of new materials are being engineered that use the ambient air or temperature to reduce heating or air conditioning costs.  Phase Change Materials (PCM) are not new, in fact water is one of them!  PCM describes the way that the material absorbs or gives off heat while changing phase (from ice to water or vice-versa) but does not change temperature during the phase change.  Water doesn’t give much advantage in home insulation, however, because the phase change happens at 32 degrees F or 212 degrees F, which are outside of our comfort zone in the home!  However, there are other materials being used that fall in the perfect range for keeping our homes cool or warm.

Phase change material is like a heat battery.  In warmer climates, solar heat starts to warm the roof and wall areas early in the day, but with PCM installed, the heat is absorbed in the material while the material temperature remains constant.  It continues to “melt” inside the pouches as heat is applied, and only increases in temperature after absorbing a lot of heat.  In the evening, PCM gives off the heat back into the attic or wall space, which radiates toward the outside.  In cooler climates, PCM forms a barrier to keep heat from escaping your warm home in the same way.  This is different from traditional insulation such as fiberglass, rockwool or sprayfoam, which all “resist” passage of heat over time, meaning they constantly allow some heat to pass through by conduction, convection, and radiation.  PCM insulation is not meant to replace traditional insulation, but it is a great supplement to it.

There are several companies that manufacture PCM insulation using a soybean/palm oil blends. QE Platinum is a Dallas, Texas-based company, and Phase Change Solutions is based in North Carolina.  The oils are contained in pouched sheets that are flexible.  They can be installed behind drywall (vertically, horizontally or at any angle), above ceiling tiles, or simply laid over existing batt or blown-in insulation in the attic.  The great benefits about this type of insulation are that it is 

• Non-toxic 

• Green, sustainable material

• Moisture, humidity and mold-resistant

• Self-healing (any punctures cause the material to harden and seal in remaining material

• Long-lasting (30-year warranty) and guaranteed energy reduction

• Class A fire rating

• QE Platinum is also a radiant barrier

• Has the same thermal mass as a 12” concrete wall!  QE Platinum absorbs and stores up to 100 BTUs per square foot.

• The company can tailor the melting/solidification range of the PCM to your climate (customized!)

There are two great videos reviewing it.  This reviewer is based in San Diego; he is renovating his older home to get to net zero and is planning to install it in walls and attic.  This reviewer is based in Texas.  Both videos go into the science of PCM and why this product is a game-changer for homeowners and business owners wanting to make their spaces more energy-efficient and comfortable.  We love that it’s non-toxic and easy to install–even for DIYers.  At $2.50-3.50 per square foot, it’s expensive but not ridiculous, and the companies may be able to reduce the cost even more as production increases.  

As great as this material sounds, however, it’s not for every home.  In order for it to be cost-effective, you need to live in an area that has significant daily temperature swings, like 20 to 30 degrees between daily and nightly temperatures.  This allows the PCM to full change phase and be ready for the next day’s cycle.

Another PCM has incredible capacity, but it’s not quite ready for the residential market.  Fraunhofer’s zeolite are small pellets that can be heated, which extracts all their moisture and in the process creates and stores heat.  They can then store that heat for indefinite periods of time.  The amazing things about this zeolite is that due to the huge internal surface area, the pellets store more than 4 times the heat of water (which is has one of the highest heat capacities of any substance), the heat storage is indefinite until water is added, heat losses are very minimal over time, and the zeolite does not change temperature, making it a true PCM.  In the energetic state, zeolites are therefore completely dry; conversely, when water vapor is passed through the pellets, heat is released. The advantage of this is that the energy is not stored in the form of increased heat but in the form of a chemical state. This means that heat is not lost during long-term storage. There is one drawback: Zeolites have poor thermal conductivity, which makes transferring the heat from the heat exchanger to the material and back difficult.  The engineers have finally solved the heat transfer problem by coating the pellets with aluminum.  Amazingly, the aluminum did not impact the ability to adsorb/desorb water, but it enhanced heat transfer. (Thermal Storage for the Energy Transition)  Can you imagine, instead of receiving a heating oil delivery, receiving a delivery of pellets that are already charged with energy, but not hot?  Or using the summer heat in your attic to recharge a bank of pellets for use in the cold winter heating system?  This is incredible technology!

So, homeowners, keep dreaming and scheming to keep energy costs down and comfort levels up.  Science can sometimes satisfy our wish-lists, and when it does, do your research and ask lots of questions to make sure it’s effective and non-toxic.  PCM insulation seems to be a good fit for many smart, green buildings, with no internet connection required.

How to get free ventilation without sacrificing heat (or cool)

Something has piqued my interest for some time: the transfer of heat to make something cooler or warmer than the ambient air without mechanical means.  Living in the hot and humid southeast US, I’m keenly aware that air conditioning is key to my comfort during the summer.  Ventilation is necessary, but ventilation will make my house hot like the outside…or will it?   

I’m going to draw on a 2023 study that showed how to ventilate a building by natural means (no fans) but still cause it to be 7 degrees cooler than the outside, even with an internal heat source.  Whoa!  This is noteworthy.

I’ll give you the simplified version. The study involved placing 2 insulated boxes on the top of a shipping container in a warm, dry climate (Topanga Valley, CA).  The “reference” box had insulation on all 6 sides.  The “test” box had insulation on the four vertical sides and bottom, but for the top had an aluminum plate on which a radiant material was glued.  The only ventilation in each box was 2 PVC pipes.  On the reference box, the ventilation pipes were in the top of the box, while on the test box, they were in the bottom of the box.  Each box contained (4 to 6) 1-liter water bottles for thermal mass, as well as a small heater to simulate lighting, fans and other electrical loads that would be operating in a home.

What happened in these boxes?  The differences of a) removing the insulation from the roof and replacing it with conductive and radiative materials, as well as b) placement of the ventilation pipes, caused a substantial difference in the way the boxes ventilated and their interior temperatures.  Here’s a schematic of the boxes:

In a nutshell, this type of natural ventilation is driven by differences in temperature.  During the day, the reference box did not ventilate because the interior stayed cooler than the exterior.  It only ventilated at night, because with cool desert temperatures at night, the interior was relatively warmer than the exterior.  However, the test box actively ventilated during the day because the cool air in the box sank out through the ventilation pipe on the bottom, and was replaced with warmer air.  However, it stayed cooler than the reference box because the conductive material on the roof (aluminum) drew heat from the inside and the radiative material reflected 93% of solar heat back into space.  Here’s a summary of the benefits of the test box setup:

• There was a net loss of heat during the day and the night, even with an internal heat source. 

• Ventilation during the day occurred 7 times per hour (7 ACH).  

Here’s an architectural concept of what a real house could look like:

Other details:

• The reference box only ventilated at night and the test box only ventilated during the day.  In a real building, however, both ventilation approaches can be combined to produce continuous ventilation, switching between downwelling and upwelling by activating different vents as necessary.
• The thermal mass inside the boxes had the purpose of modulating heat fluctuations.
• The insulation used on the boxes was vacuum panels, which are a very effective insulation, albeit an expensive one for residential housing!  
• Convection shields of metal with a radiative coating were placed over the sides of the boxes to prevent them from absorbing solar heat.  
• The boxes had no penetrations except for the ventilation pipes, which is not a realistic residential scenario with no windows or doors. 
• The boxes were tested in a warm dry climate, without humidity/mold concerns.  In a more humid climate, dehumidification would probably be necessary.  
• Ventilation pipe size and thermal mass would need to be fine-tuned for each home and its occupants. 
• Removing the roof insulation from a modern home is quite unusual; in fact, a previous version of movable roof panel insulation and radiant covering was key in Harold Hays’ Skytherm innovation. 

Wow, this is really quite fascinating.  Imagine having copious ventilation AND keeping your home cool in the summer.  Windows don’t have to be heat loss/gain devices, either: with new insulation materials coming into existence all the time (there’s a new aerogel made from cellulose that’s even more transparent than glass), or the Parans solar lighting system that captures sunlight and sends it indoors via fiber-optic cables, a super-insulated, light-filled home is possible (with the right budget).  The idea of thermal mass is certainly not new, either; that’s the reason stone and earth have been used in warm-climate homes for millenia!  We also wrote about a new insulation material that uses phase-change to absorb heat without transmitting it into your home.  With the invention of new radiant systems like the SkyCool system, buildings are actively rejecting solar heat and removing heat from inside the building, saving from 15-40% of cooling costs.

Even without the high-tech materials, the main takeaway of this concept is to seal up your home and ventilate naturally: to do this in warm climates it’s best to have the ventilation intakes lower in the house, on the “cool” side.  Also, look into a radiant barrier for your attic space; we give some tips in this article.   Finally, always monitor humidity, no matter the temperature.  No one can live in an ice-box and turn a blind eye to humidity and mold!

Will a Radiant Barrier Help My Home’s Air Quality?

Radiant barriers have been a “hot” topic for the last few years: If to install them, where to install them, and how to install them.  Are they worth the work and cost?  It’s time well-spent to do some research before diving in with such a project.

Radiation is one of the three types of heat transfer, along with convection and conduction.  A radiant barrier is a material with a shiny surface that reflects radiant heat back outside the home.  If the barrier gets dusty or is installed incorrectly, however, it does not work well. 

According to Attainablehome.com (a builder’s website devoted to building of modern, sustainable, and high quality homes that is within reach of household incomes), properly installed radiant barriers can reduce heating costs in the hottest months in southern climates, if the home’s air conditioning system is located in the attic. It can also offer a degree of protection to that equipment when the barrier is installed over the equipment, “shielding” it. 

In colder climates, however, radiant barriers are not recommended for several reasons.

• The savings in reflecting heat away from the home in summer is minimal.

• Cold climates can allow moisture to condense behind the barrier, creating mold issues.  Perforated radiant barriers can reduce this problem, though.

What is “properly installed”?  Here is a good video showing installation of a radiant barrier over a garage.  Radiant barriers:

• Need an air gap: don’t install the barrier sandwiched between existing insulation, as it can conduct heat into it.  For instance, do not install radiant barrier foam board (such as LP’s Techshield) and sprayfoam over it. (energyvanguard.com)

• Need to be relatively clean: dust will reduce the effectiveness of the barrier, so installing on the attic floor is not recommended in most cases. 

• Must be the right type for your home/climate. There are:

• Perforated and non-perforated: Perforated barriers allow vapors to escape through the barrier, reducing the chance that moisture or mold will build up behind it.   If you live in a hot, humid climate and have a vented attic, a highly permeable barrier like “Super-Perf” from AtticFoil is recommended to allow moisture to pass through. 

• Made with insulation or board attached to the radiant surface

• Must not block air flow in the attic.  Most vented attics have soffit and ridge vents, so do not block the air flow between these two, or moisture issues may result.

In a 2010 article that still applies today, energy advisor Martin Holladay stated there are 5 factors that determine whether a radiant barrier is a good option for your home (discussed in this video):

• Do you live in a hot climate?  Yes = consider radiant barrier.

• Do you live in a humid climate?  Yes = the radiant barrier must be carefully and correctly installed so that moisture problems are not created.

• Do you have a one-story home?  One story homes tend to have larger roofs to cover the livable square feet, so a radiant barrier in a one-story home will be more effective than a two-story home of comparable square feet.

• Do you have air ducts in your attic?  Yes = consider radiant barrier to shield them.

• Is the air barrier installed correctly?  This is imperative, so the barrier has to be compatible with the insulation in your attic.

In times of low-cost energy, installing a radiant barrier may not be worth it. (energyvanguard.com)  For example, in Houston in 2011 (a hot climate in a year with similar kilowatt-hour (kwh) energy cost to today), a homeowner could save about 180 kwh per year with a radiant barrier installed on their 2000 sf newbuild home, considering that it is installed under the roof decking and the only additional cost was the more expensive barrier under the decking ($200).  This is about $25 per year savings, which would be an 8 year payback if there is no mortgage, or only about 50 cents per month if there is a mortgage (check the article for the explanation!)  It’s not a whole lot, but if energy prices go up (they will at some point), the savings could be more.

According to this video, LP Techshield (an OSB board with aluminum coating on one side) produced an 18 degree reduction in temperature in a doghouse.  Another video using the same product achieved an 8-10 degree reduction in a real house. 

So, how does all of this affect your air quality?  At HypoAir, we are in favor of not adding things that harm you or your home, so adding a radiant barrier to an existing home must be carefully considered.  Here are some steps to check whether it is right for you: 

• If you have an unvented attic, a radiant barrier is likely not to benefit you.  If you have a vented attic, make sure the vents are not blocked and there is sufficient insulation in the walls/floors of the attic facing the conditioned space. 

• Consider the current state of your attic and take temperature and humidity measurements in the attic and in the home as a “baseline”.  

• If possible, you could conduct a small “experiment” in a part of your attic that faces the sun by installing one roll only (best if it shields some ductwork) and seeing how it affects attic and home temperature and humidity.  

• If this test is favorable, continue with installation of the rest of the south- or west-facing sides.  Although I could not find much information about it, radiant heat is not very applicable on the north-or east-facing walls in the northern hemisphere. 

• If humidity increases with the test spot under similar atmospheric conditions, it’s best to terminate the experiment and remove the barrier. 

Radiant barrier material is not very expensive, so if you can install it yourself, it can provide energy savings going forward.   It’s best to take your time and research the pros and cons of installing it in your home and not succumb to pressure from a salesperson, however.  Overall, it should not increase your energy use or humidity levels, so make sure to hold the manufacturer and/or installer to their claims.  We’d love to hear from you on how radiant barrier affects your home’s atmosphere!