Phase Change Material PCM insulation application

[dbill74]

I am evaluating a proposal to supplement or replace a building's roof insulation with sheets of Phase Change Material (PCM).

I have started researching these PCMs online to a point where I have a rudimentary knowledge of what PCMs are and how they work.

My questions for the community here are:
Does anyone have experience with PCMs in building construction?
In what environment(s) are they most cost effective?
Would they economically viable in a tropical environment where the winter design temperature is 67°F?

Based on what I have learned about PCMs to date I am having a hard time seeing the benefit of PCMs in the environment I mentioned above.
Any comment to confirm or dispute my concerns are welcome, I am keeping on open mind on the subject of PCMs.

EDIT: Mean Daily Range is 14°F.

 

[dbill74]

From the lack of response here, I am left to assume that PCMs are either too new in the construction world or are ineffective in the application for which it is being proposed.

 

[Ziggypump]

Never heard, nor used a PCM. I'm assuming that since this is on the HVAC/R thread that you are most interested in the thermal properties this can have on benefiting the building.

I'd worry about the life cycle of the material. Phase changing would have me worried as it sounds like a chemical change that will break down over time (how long?). Also what is the 10 and 20 year insulation value of this material? LEED has been pushing for the "Life" span U-Value (R-Value if you want) as the insulation mats down after awhile and the U-value after 10 years is less than the new product U-value.

I'd say that if you have a roof U-value of 0.04 and at 10 years the U-value is 0.1, you might want to pass on the material.

Engineers should be designing to the life span U-value and not the new product U-value because as the building ages, the insulation properties degrade, and now the HVAC system can't handle the required load.

 

[tkordyban]

Phase change material is not primarily a replacement for roof insulation. The purpose is to reduce cooling energy costs for a building. It does this by evening out the daily temperature swing between day and night. For example, if the days are hot and the nights are cool, the PCM is exposed to the outdoor air at night to freeze. During the day, the outside vents are closed and the air inside the building is passed over the frozen PCM to keep the interior cooler than the outside air. The building still needs to have conventional insulation to make this work.

If the local climate has only a small temperature swing between day and night, the PCM will not have much benefit. I have read of this being used, at least in trial runs, in places like India where electric power is either very expensive or not reliable. It takes a lot of PCM to cool a building, and, naturally, it does nothing to control humidity. I don't think it has proven to be cost effective over the long run, but that may be just a matter of how and where the PCM is applied.

 

[dbill74]

Thanks for the input guys.
Like you Ziggy, it's a new technology to me; and yes in this application would be intended to benefit a building by reducing cooling costs.
The objective for this application would be to reduce energy use of buildings in a location where, like India, the cost of electricity is expensive.

 

[IRstuff]

"The objective for this application would be to reduce energy use of buildings in a location where, like India, the cost of electricity is expensive."

I'm not sure that makes sense. A phase change material may delay the onset of some sort of thermal change, but you have to "reset" the material, which requires power, unless you can get a perfect temperature cycle, such that phase change temperature is exactly midway between temperature extremes, thus allowing equal phase change and solidification times. More likely, you'd still have to use electricity, but it might bee off-peak, which might still be worthwhile.

In order for the PCM to be viably used, it probably needs to be micro-encapsulated, for a number of reasons, which might still be well beyond the economical means of most of poor countries.

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[Compositepro]

PCM only makes sense in mobile applications or where a low mass system is very important. Otherwise it cannot compete economically with simply adding more insulation or adding more thermal mass to the wall, like concrete.

 

[dbill74]

Thanks guys. You've echoed some of my own concerns about this product. Sounds like we as a community need more information about the product/technology before using it on a regular basis. At least for now it appears not worth the cost.

 

[HVACMech]

I will say this about PCM. They must make some money, somehow... they have an ad in every edition of the ASHRAE Journal... I haven't used it, but I guess someone must be.

 

[lukaiENG]

I have come across a couple of applications recently which I will share -albiet they are different applications to the original question.

One is a liquid cooling system for computer equipment. a refrigerant type liquid* which is pumped through a small heat exchanger mounted to the chip. The liquid partially boils and leaves the heat exchanger in a mixed mode flow. This results in efficient heat transfer to the fluid. The mixed flow fluid is then passed through externally mounted heat rejection which rejects the heat to atmosphere. The whole system is designed to run at a fluid temperature of 130 (ish) degF which means the heat rejection can in most cases be a simple dry cooler.

*strictly speaking it's not classed as a refrigerant but has similar properties

The second application is a desktop exercise. Basically for a particular process system in a particular climate there is a very small amount of hours per year where we can not provide 100% free cooling via an adiabatic air cooled process. For those few hours per day in the peak of summer, I have looked at pumping the make-up water for the adiabatic system through cooling coils to provide the necessary trim. Effectively this would use the thermal mass of the make up water storage tanks to trim the peak cooling load and avoid the need for compressorized cooling completely. A major win.
Where the PCM come into play is looking at how much inertia you need vs how much you get from your storage tanks. in theory using a PCM which changes state around 60-70 degF would mean we could greatly increase the thermal mass of the storage tanks. Of course this would need to be recharged overnight. This is purely a desktop exercise at this point but hopefully it helps to show there are applications for this type of technology if you think a little outside the box.