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Idea for a solar "wall"  RSS feed

 
Creighton Samuiels
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I've been thinking about improving the solar gain of my somewhat conventional house lately, so that I can spend less on propane next winter. This past season killed my finances. So I have a large single story 'ranch' style house, with existing 'passive solar' features that are not obvious, but upon inspection were well thought out. For example, the house's front porch is nearly due south, and has an overhang that is just right to prevent sun from entering the living room during the summer, but by theend of fall sunshine is no longer blocked at all. However, the bedroom windows do not benefit from this overhang; so the house is also sited just north of a huge maple tree that shades the entire house with it's leaves in summer, but does little to reduce that sunshine after the leaves have fallen. On the east end of the house, I intend to build out the south corner with a freestanding block wall 7 courses high (4' 8") by 40 feet long extending almost due east from the south corner of the house. Then mount corrogated, perforated steel paneling to the south face of that wall in such a way as to create an enclosed air gap between the block wall and the sheet metal. Paint the steel with some flat black outdoor paint, and perhaps mildly insulate the north side of the wall. Sealing up the east end and calking the seams so that the only air flow is through the holes in the face of the steel. Using a small blower set to run only when the temp under the steel facade hits 90+ degrees, and discharges the dry, preheated winter air into my (otherwise damp) basement space. The goal is to have preheated make-up air for my woodstove and gas furnace, as well as slightly pressurize the house whenever there is enough heat to at least maintain equilibrium, thereby reducing my heat load from air infultration. Additionally, if I were to ever aquire some solar panels, they would be mounted directly overtop the sheetmetal facade. To compensate for the lack of tilt angle, I was considering cutting plywood sheets into 2 foot wide panels, and using spray glue to permanently attach mylar 'space blankets' to one side, and then placing those mirror boards on the grass in from of the solar wall. In this way, I can have the stability and astetics of a vertical wall, and the net solar surface of the hypotenuse of the triangle formed by the solar wall and the mirror board. And mirrors are much cheaper than solar panels! In the summer, I'd just have to disconnect the fan power & cap the vent in my basement so that it can't contribute to infultration in the heating season.

Alternatively, and this would be much cheaper, would be to make a port on the east side of my house that would allow me to connect a 4" HDPE corrogated pipe to my basement in a similar manner, and I could run the pipe as far across my lawn in the fall as I like. I could either run a cable through the pipe itself to supply power to an air intake box, with the blower & thermostatic controls in the box, or mount a single solar panel to the box for the same purpose. This method would be much easier & cheaper to build, but is likely to be vetoed by my wife for it's "redneck"-ness. In the spring, I'd simply disconnect the pipe from it's port in the wall, cap the port, and roll up the pipe so that I could put the pipe and intake box in storage while the grass grows; and once the grass stops growing in the fall, get the gear back out and plug it back up. I have enough yard that it likely wouldn't even get in the way, much less concern the neighbors, but my wife still isn't likely to approve even if it would mean that we could afford to be warmer.
 
Brian Knight
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Location: Asheville NC
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Creighton, youre ideas sound great. It reminded me of an article I read this morning about one of the first passive solar designs from the 70s. http://www.greenbuildingadvisor.com/blogs/dept/building-science/classic-1970s-home-goes-solar-heated-net-zero-energy

Iam skeptical that the investments and devices would outperform simply adding more windows but perhaps Iam misunderstanding or that's not an option.

I couldnt find it, but one of the moderators (Burra?) posted a nice Youtube video using the HDPE pipe for a heater. With both ideas, be careful about using grid energy for circulation as they usually burn more energy than they create.
 
Creighton Samuiels
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Adding more windows would be quite cost prohibitive. As for the power to run the blower fan, I was planning on one small solar panel sized just right for 50 to 100 cubic feet per minute in full sun. I figure that if I size the solar panel as close to the needs of the fan itself, a partially cloudy day will result in a lower flow rate in close to the same amount as the reduced solar heat gain on the collector wall.
 
Angelika Maier
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Passive solar is great but insulation does much more to reduce your power bills.
Insulate walls, ceiling, windows, floor. If you still have single glazed windows it might be possible to put a second pane in. Uninsulated aluminum frames are
the worst ( I tell this from experience). Sew padded curtains (I know it is a pain).
The biggest difference in our house was that we changed somewhat the floor plan in a way that the entrance door does not go directly into the lounge room anymore. It is such a big difference if you don't heat against an outside door. If all insulation is done then think of passive solar.
The second biggest difference were changing the aluminum sliding windows to double glazed wooden framed ones. We still have some single glazed windows but they are not all that bad it was really the frame.
Big open plan house layouts are not great for your power bill either.
It is always better to add some photos.
 
Brian Knight
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Angelika is right of course. Sounds like youre on the right track Creighton but have to agree that there could be lower hanging fruit to make your home more comfortable and energy efficient. Air sealing in the appropriate locations and adding loose fill insulation in the ventilated attic, if thats what you have, would probably result in greater savings and comfort if you havent addressed those concerns already.
 
Creighton Samuiels
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While adding insulation and sealing would likely be "lower hanging fruit", I deliberately allow convection drafting through my house in winter. I don't wan't air to stagnate, as I live in a particularly damp climate. The static shock that some people get in winter is particuarly rare in Kentucky, I haven't experienced it in years. I want air flow for health reasons as well. The goal is to preheat the incoming air with solar energy, so the make-up air being drawn in by convection flow (or the woodstove, or furnace exhaust, etc) won't be cold.
 
Topher Belknap
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Location: Midcoast Maine (zone 5b)
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1) As others have said, insulation and air sealing is usually a better place to start.
2) Air sealing (especially if you plan to run your house at positive pressure) is important, as you don't want to be pumping warm moist air into your walls where it will condense, and encourage rot.
2) Interior storm windows work much better than loose insulated drapes or curtains.
3) 4' by 40' is a huge solar collecting area. That is going to require a lot air flow (50-100 CFM is nowhere near enough).
4) Positive pressure is not a solution for infiltration. It just becomes exfiltration.
5) You are going to want the woodstove when the sun isn't shining, so the solar heater won't be in service.
6) Consider an aspirated solar wall design.
7) BBQ paint is the cheap version of what you want. Low emissivity specialty paint for solar collectors is the good stuff.

Thank You Kindly,
Topher
 
wayne fajkus
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your wall sounds like a trombe wall, less the glass. if you had a vent on top and bottom, both going into the house, it would not need fans based on the principle that hot air rises. cold air would enter the bottom, heat up, then rise to the top and out your vent, into the home. You can also add two more vents (outside on top and bottom). Between the 4 vents you can get creative. In summer you could open the exterior top vent and the interior bottom vent. Air would be drawn up and out, creating a draft, or a small fan effect if you had another vent (window) open on the other side of house. You can get creative (and spend a lot of time) figuring what happens with each vent opened/closed.

Glass would be optimum. I've been able to get 8 sections of sliding glass doors for free over time by keeping my eyes and ears open. They are great for solar projects. My local habitat for humanity sells them for $35 which is pretty inexpensive for what you get- thick tempered glass in a sturdy aluminum frame.
 
Sean Rauch
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Location: Winnipeg, Manitoba
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Few comments in red

Topher Belknap wrote:
1) As others have said, insulation and air sealing is usually a better place to start.
Yes coupled with the addition of an HRV would also help keep things efficient, comfortable, and healthy
2) Air sealing (especially if you plan to run your house at positive pressure) is important, as you don't want to be pumping warm moist air into your walls where it will condense, and encourage rot.
If your less permeable barrier is to the inside of the wall this should be a non issue. Walls should breath to the outside.
4) Positive pressure is not a solution for infiltration. It just becomes exfiltration.
Indeed, why would you want your building to to do either?
5) You are going to want the woodstove when the sun isn't shining, so the solar heater won't be in service.
Yes, I've battled with this problem myself... How can I get solar gain at night? The only solution I know of is thermal mass (anti Knight flame suit on...)

Thank You Kindly,
Topher
 
Topher Belknap
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Sean Rauch wrote:Few comments in red

Topher Belknap wrote: and replied in green
2) Air sealing (especially if you plan to run your house at positive pressure) is important, as you don't want to be pumping warm moist air into your walls where it will condense, and encourage rot.
If your less permeable barrier is to the inside of the wall this should be a non issue. Walls should breath to the outside.
A low-permeability barrier is all well and good, in the appropriate climates. But a) It doesn't do anything to reduce infiltration through holes, which are the vast majority of the air sealing failures. b) It is usually not something homeowners of existing homes have a lot of control over. (or perhaps more accurately, want to take control of) c) Drying to the outside is no substitute for not letting moisture into the walls in the first place, d) Is not a good idea in certain climates.


Thank You Kindly,
Topher
 
Sean Rauch
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Location: Winnipeg, Manitoba
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Topher Belknap wrote:
Sean Rauch wrote:Few comments in red

Topher Belknap wrote: and replied in green
2) Air sealing (especially if you plan to run your house at positive pressure) is important, as you don't want to be pumping warm moist air into your walls where it will condense, and encourage rot.
If your less permeable barrier is to the inside of the wall this should be a non issue. Walls should breath to the outside.
A low-permeability barrier is all well and good, in the appropriate climates. But a) It doesn't do anything to reduce infiltration through holes, which are the vast majority of the air sealing failures. b) It is usually not something homeowners of existing homes have a lot of control over. (or perhaps more accurately, want to take control of) c) Drying to the outside is no substitute for not letting moisture into the walls in the first place, d) Is not a good idea in certain climates.


Thank You Kindly,
Topher


Sealing a wall either from both sides equally or more to the outside is a bad idea all round. Summer humidity should be fine because you won't have a dew point for the moisture to become liquid inside the wall system you want a certain amount of "acclimatization" between your wall and the outside conditions. Where things go sideways is when you have a less permeable surface on the exterior that can get cold enough for interior humidity to condense against during the winter. Winter is where you get humidity condensing and rotting out the inside of your wall system.

Sealing up holes should have zero effect on this one way or another.

If the owner's issue is not enough insulation overall then they will want to address insulation for the entire envelope, however that looks. If there is enough insulation and its just air leakage through services, windows, doors etc then seal up the holes, its a no brainier. Purposely having air move unrestricted into the wall system from inside the house is your worst case scenario.
 
Topher Belknap
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Location: Midcoast Maine (zone 5b)
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Sean Rauch wrote:Summer humidity should be fine because you won't have a dew point for the moisture to become liquid inside the wall system


That depends rather severely on one's climate. All it takes for summer humidity to condense in a wall system is for the temperature of some surface in that wall system to be below the dewpoint of the outside air, and for access to be given.

Winter is where you get humidity condensing and rotting out the inside of your wall system.


That is certainly the case in heating climates.

Sealing up holes should have zero effect on this one way or another.


Where does the moisture in the air that is coming into the walls from holes go? How does the wall know whether the moist air came through a hole or through the permeability of some surface making up the wall?

Purposely having air move unrestricted into the wall system from inside the house is your worst case scenario.


Yes, exactly. Since the discussion here is about putting positive pressure in the house, the amount of air moving unrestricted into the wall system has just been increased. This is my concern.

Thank You Kindly,
Topher
 
Creighton Samuiels
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I don't think some of you quite understand what I'm trying to do. I don't have a well sealed home, as it's about average for a house build for it's era (1970's), and I don't particularly want a well sealed home. Well sealed homes in my (very damp) climate tend to have mold issues. This hous has plenty of gaps that slight positive pressure isn't going to be pushing through wall structures, and the heated winter air would be VERY dry, also a goal. Delayed heat gain can be accomplished by putting baby food jars of candle wax inside the plenum air spaces of the solar wall, allowing the draft of the nighttime woodstove fire to draw make-up air past the jars of melted wax for as long as that heat lasts. The powered venting would be solar powered as well, and therefore only occur during daytime hours, helping to maintain temps and prevent my propane central forced air furnace from turning on. But if it did turn on, it would provide heated make-up air for that combustion as well.
 
Topher Belknap
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Location: Midcoast Maine (zone 5b)
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Creighton Samuiels wrote:I don't think some of you quite understand what I'm trying to do. I don't have a well sealed home, as it's about average for a house build for it's era (1970's), and I don't particularly want a well sealed home. Well sealed homes in my (very damp) climate tend to have mold issues.


I think I do understand what you are trying to do. I just have ideas about the way that I think you ought to do it. A well sealed, properly ventilated house, is by design less likely to experience mold issues. With one you are trusting to passive moisture and air movement, and with the other you are controlling both. It is true that many well sealed houses neglect proper ventilation, and thus have mold issues; that is a failure of execution.

This house has plenty of gaps that slight positive pressure isn't going to be pushing through wall structures


That is an interesting assertion. After having done many hundreds of blower door tests, I no longer feel confident making statements like that.

and the heated winter air would be VERY dry, also a goal.


If the air is VERY dry, where did all the water go?
I am not a medical professional, but I worry about extremely low humidity from a health perspective.

Delayed heat gain can be accomplished by putting baby food jars of candle wax inside the plenum air spaces of the solar wall, allowing the draft of the nighttime woodstove fire to draw make-up air past the jars of melted wax for as long as that heat lasts.


Store heat inside the building, not in the collector, would be my recommendation. I don't think baby jars worth of wax, are going to be enough heat storage.

prevent my propane central forced air furnace from turning on.


I maintain that you are going to need that propane furnace much more with all those leaks in your house. I see 20-50% of heat loss of houses attributable to air leakage, it might be similar in your region. How many complete air changes do you need per hour?

Thank You Kindly,
Topher
 
Creighton Samuiels
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Topher Belknap wrote:
Creighton Samuiels wrote:I don't think some of you quite understand what I'm trying to do. I don't have a well sealed home, as it's about average for a house build for it's era (1970's), and I don't particularly want a well sealed home. Well sealed homes in my (very damp) climate tend to have mold issues.


I think I do understand what you are trying to do. I just have ideas about the way that I think you ought to do it. A well sealed, properly ventilated house, is by design less likely to experience mold issues. With one you are trusting to passive moisture and air movement, and with the other you are controlling both. It is true that many well sealed houses neglect proper ventilation, and thus have mold issues; that is a failure of execution.


I can agree with that. I guess I'm really trying to control the ventilation issue first. Are you saying that I shouldn't err on the side of a heated positive pressure? If I had some way of detecting such a mild negative pressure as caused by the exhaust from the woodstove or furnace, I'd probably do that. Perhaps just not have a blower at all, but just a passive design?


and the heated winter air would be VERY dry, also a goal.


If the air is VERY dry, where did all the water go?
I am not a medical professional, but I worry about extremely low humidity from a health perspective.


Winter air is dryer, because it's temp is below the dew point and the moisture condenses out. Then my solar wall heats that air above 90 degrees, and blows it into my (otherwise usually damp) basement space. The incoming air is dry, the air in the house generally is not; I'm mixing them up to get a dryer winter balance. Indoor humidity would never be 'extremely' low based upon the volume of incoming dry air versus the generally humid space it's entering. When I lived in Oceanside California, it *never* got as humid as I am shooting for, and I'm trying for dryer air for health reasons; my wife is prone to pnumonia. Currently I use dehumidifiers, but they are expensive and consume large amounts of power. I pull a gallon of water a day from them in the dead of winter here. Seriously, if you've never lived in Kentucky, you really can't imagine what it's like. There really isn't a dry season.


Delayed heat gain can be accomplished by putting baby food jars of candle wax inside the plenum air spaces of the solar wall, allowing the draft of the nighttime woodstove fire to draw make-up air past the jars of melted wax for as long as that heat lasts.


Store heat inside the building, not in the collector, would be my recommendation. I don't think baby jars worth of wax, are going to be enough heat storage.

Maybe not. I'm not even sure if I'm going to do it this way at all, mostly just brainstorming. However, due to another thread regarding heat storage using phase change materials, I know that candle wax makes an excellent heat battery.



prevent my propane central forced air furnace from turning on.


I maintain that you are going to need that propane furnace much more with all those leaks in your house. I see 20-50% of heat loss of houses attributable to air leakage, it might be similar in your region. How many complete air changes do you need per hour?

Thank You Kindly,
Topher


Mostly I need dryer air more than air exchanges per se, but air exchanges work towards that end during the heating season. I only want the fan to blow when the solar panel is above 90-100 degrees, so the idea that I'm losing heat by pushing a volume of 70 degree air out of the home using 90 degree air doesn't logicly follow, and for some portion of that time that 70 degree air is being pushed out through a combustion chamber, not walls or windows, anyway. I intend to fix the air leaks that can be (economicly) fixed anyway, but there will still be some that cannot be fixed. I'm really trying to address more than one issue at the same time. 1) air infultration due to make-up air vacuum, which occurs at the farthest points from the woodstove, and thus are the hardest to heat generally. 2) humid air, even during the heating season. 3)a desire for solar energy in my home, 4) a desire for heated, fresh air for my wife's health.
 
Topher Belknap
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Location: Midcoast Maine (zone 5b)
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Creighton Samuiels wrote:Are you saying that I shouldn't err on the side of a heated positive pressure? If I had some way of detecting such a mild negative pressure as caused by the exhaust from the woodstove or furnace, I'd probably do that. Perhaps just not have a blower at all, but just a passive design?


Yes, that would be my suggestion until you have better control over air leakage. Just make sure it flows passively when it warms sufficiently. Perhaps even add a small exhaust fan for times when neither of those is running (which would seem most likely to be when the solar heater is working).

Winter air is dryer, because it's temp is below the dew point and the moisture condenses out. Then my solar wall heats that air above 90 degrees, and blows it into my (otherwise usually damp) basement space. The incoming air is dry, the air in the house generally is not; I'm mixing them up to get a dryer winter balance.


My question concerned inside air, sorry that that was unclear. So dry cold air comes in, (heated to 90°F isn't really relevant, as it is immediately cooled back down to 68°F), mixes with 68°F moist inside air, and lowers the humidity. All good. One should also consider how much water just living in the house puts into the air, and try to reduce that, shorter or no showers (baths put much less water into the air), covering pans of boiling water, etc.

I pull a gallon of water a day from them in the dead of winter here. Seriously, if you've never lived in Kentucky, you really can't imagine what it's like. There really isn't a dry season.


Sounds like my house when it was first built, and full of water. People around here would look at you as though you were crazy, for sure.

However, due to another thread regarding heat storage using phase change materials, I know that candle wax makes an excellent heat battery.


Candle wax has a melting point that is too high for optimal heat storage, preferably you want something with a melting point at room temperature. There are some special wax mixtures which do that.

Mostly I need dryer air more than air exchanges per se, but air exchanges work towards that end during the heating season.


You might also want to consider a HRV (Heat Retaining Ventilator), given your location, someone will no doubt try to sell you an ERV (Energy Retaining Ventilator) but that would retain the humidity that you want to get rid of. Crank that sucker up on cold days, and you could reduce the humidity substantially, while retaining 85% or so of the heat.

I only want the fan to blow when the solar panel is above 90-100 degrees, so the idea that I'm losing heat by pushing a volume of 70 degree air out of the home using 90 degree air doesn't logically follow, and for some portion of that time that 70 degree air is being pushed out through a combustion chamber, not walls or windows, anyway. I intend to fix the air leaks that can be (economically) fixed anyway, but there will still be some that cannot be fixed.


The economics in my area average out around $25 per square inch of hole, though that varies wildly between houses. You might take that as a starting point, if it costs you less than $25 to fix 1 square inch worth of holes, then it is worth doing.

Thank You Kindly,
Topher
 
allen lumley
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Topher Belknap : Very well said, though you saved the best for last, and of course that was $25.oo last heating season, with the price going up, and adding up year
by year !

Creighton Samuiels : A very good source to wrap your head around moisture loads and ventilation can be found at www.cchrc.org it comes from the University
of Alaska Fairbanks, We Know Cold, they Know COLD ! Their Arctic, and Remote Wall structure treatments and their air exchange studies definitely break new ground
for anyone working with 10 year old Building Skills !

For the good of the Craft ! Big AL !
 
Creighton Samuiels
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Topher Belknap wrote:
Creighton Samuiels wrote:However, due to another thread regarding heat storage using phase change materials, I know that candle wax makes an excellent heat battery.


Candle wax has a melting point that is too high for optimal heat storage, preferably you want something with a melting point at room temperature. There are some special wax mixtures which do that.

While such special blends do exist, they are expensive and have much lower latent heat per pound. Soy wax is cheap and melts around 110 degrees, which is certainly in range for my project during sunny days. Beeswax melts around 145 degrees, which would still be in range while the mirror reflector was in use, and has excellent latent heat per pound. Both waxes are far cheaper by weight than the special mixes for amibient temps, which I would still consider for putting into jars and stacking into new walls under drywall, for thermal "mass", but I wouldn't use it in my solar wall idea. Too expensive.


Mostly I need dryer air more than air exchanges per se, but air exchanges work towards that end during the heating season.


You might also want to consider a HRV (Heat Retaining Ventilator), given your location, someone will no doubt try to sell you an ERV (Energy Retaining Ventilator) but that would retain the humidity that you want to get rid of. Crank that sucker up on cold days, and you could reduce the humidity substantially, while retaining 85% or so of the heat.



I'll look into that one. Thanks.
 
C. Letellier
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Mostly solar has been covered.  But I really want to reemphasize the importance of mass in making a passive or mostly passive system work.  MASS, MASS, MASS.


As for the wax discussion I will point something out there that completely blew me out of the water when I learned it.  Look up the specific heat capacity of wax undergoing phase change from liquid to solid or vice versa and compare it to water simply sitting there.  Notice that water has nearly twice the specific heat capacity per unit volume.  Now you have upper and lower ranges of waters specific heat you don't use in a normal passive solar system which about chops usable heat storage in half.  Water though still about equals wax for storage capacity and it is a whole lot cheaper and there is no fire hazard associated with it.

PS you will need more than baby food jars unless there are truly huge numbers of them to store enough heat.
 
Creighton Samuiels
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Yes, the heat capacity of liquid water is truly amazing, per pound; yet stone is much heavier by volume.  It also has other qualities that make it unwise.  Water contained near heat above 212 degrees has a habit of building a catastrophic degree of steam pressure in a short time, potentially resulting in a "boom, squish".  The squish being the human beings nearby trying to keep warm.  In the absence of oxygen, wax doesn't have the ability for an explosive phase change (from liquid to gas) in our typical working temp ranges.  Water would either have to be unconstrained, introducing the possibility of scalding water burns, or pumped using an open cycle to a remote hot water storage location.  And the phase change waxes also have the majority of their heat storage within a very small range, thus keeping the mass close to it's ideal temp for some time after the fire is extinguished.  Lacking that feature, liquid water doesn't have much advantages over basic masonary mass for heat storage.
 
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