Off Grid no power design suggestions. Wondering about low temp using vacuum steam from storage.

farmwi

Considering if by using a vacuum steam system that a storage tank could supply heat from a basement to an upstairs without power. Whether this could be done in part by using supported pex for flat slope from supply of HEX in storage tank and at a baseboard sloped.

After reading, not sure whether a single or two pipe runs would be best.

Supply heat to the storage would be solar with wood/pellet boost as needed.

Have searched, is there any such steam power condensate return pump?
Has anyone experimented using a solar collector to steam generate to a lower HEX condenser in a storage tank, but would like a steam powered condensate return pump to the solar collectors.

Low low power input in the heating season. No power or thermister level power would be ideal.

Other no power systems, hot water thermosiphon? Best no power solutions for lower heat?

I couldn't locate a search term for vacuum steam boiler(storage tank).

Larry Weingarten

Hi, I'd be looking at low temperature solutions. I have a gravity driven radiant system in the walls of my off grid home. It uses no electricity. I've been able to keep the house at 70F with 80F water. Of course, the first thing to do is go to nutty-crazy extremes to make the shell of the house efficient. That way, keeping it warm will be much simpler.

Yours, Larry

Jamie Hall

It sounds as though you are thinking in terms of using steam to transfer your heat from a solar storage tank -- probably in the basement -- upstairs.

Problem. Steam systems, as the term is usually understood, operate at a pressure very slightly above the local atmospheric pressure. The phase change from liquid water to water vapour (steam) occurs, therefore, at slightly above 212 F at sea level (lower at high altitude). The corresponding phase change, in the radiation, also occurs at about the same temperature and pressure. The condensate then returns -- by gravity in almost all systems -- back to the heat source to be reheated (at 212 F) and evaporated. And so on.

Now it is perfectly possible to operate the system at a much lower temperature --such as might be feasibly found in a solar hot water storage tank, for instance, but only is you can operate it at a correspondingly low pressure -- a vacuum. For instance, to create water vapour with a tank temperature of 140 F, you would need an absolute pressure of about 3 psi -- 12 psi of vacuum; about 24 inches of vacuum. This would have to be held throughout the system. This isn't impossible, of course --heat pumps and the like achieve much deeper vacuums. There are two problems: first is creating the vacuum in the first place, The second, slightly less obvious, is maintaining that vacuum -- no air would be permitted in the system, which means no leaks. Again, this is quite possible -- heat pumps do it routinely. However, this is not conventional plumbing. This is refrigeration quality work -- brazed or flare fittings, the whole thing.

Alternatively, perhaps your concept is to generate steam in the solar collectors -- not very efficient, but it works -- and condense that steam in your storage tank or in other radiation in the structure. You would have to pump the water back up to the collector, of course. Is this to what you are referring when you reference a "steam powered pump"? The very first application of steam for power was for pumping (Newcomen and Watt), as it happens, so a steam powered pump is hardly novel. I don't think any such machine exists on the market today for the pressures at which you would reasonably operate, but there is no good reason why a good machinist couldn't design and construct one. However, I have a nasty suspicion -- I haven't run the numbers -- that the net steam output from such a system would be negative. That is, it would take more steam to power the pump than you would get from the water you pumped.

Your best bet for zero external power, other than the sun, would be to have the solar collectors at a lower elevation than the storage tank, and the radiation in the structure at a higher elevation. Then you could run the whole thing by thermal siphoning.

A far more practical approach, if I may say so, is to design the structure from the beginning for direct passive solar heat. This is entirely feasible -- I have designed and built a number of houses on this principle, which have been quite satisfactory, even in northern New England. You should be wary, however, as while this isn't rocket science there are a number of individuals who claim to be able to do this -- and can't.

hot_rod

My goal would be to heat the home with the lowest possible temperature, as Larry’s home does

Swt below 100 degrees is quite possible with solar most any place in the US winter. An easy load for solid fuel backup

mattmia2

Of course photovoltaic and batteries are now at a point where you could store enough energy to run a boiler and solar controls and a circulator for several very dark days.

retiredguy

Designing a steam system as you mentioned above is theoretically possible but to get it to heat a home would be a fools errand. Yes, it could be done but not in an off grid setting. Producing steam at a low temperature can be accomplished by reducing the system's pressure to below 0 psig. For example, looking at a "steam temperature pressure table", steam can be produced at 32 degrees F if you could reduce the pressure to 29 in HG ( 0.451 Psia.) or at 140.3 degrees F at a vacuum of 24" HG ( 2.91 Psia). To do this in an off grid home would be near impossible and definitely not cost effective. And as for storing steam to be used at a later date, forget it. It is not feasible in your setting. A better solution would be to do as @mattmia2, @Jamie Hall, @ larry Weingarten, or @ hot rod have suggested.

You could also install a gravity hot water heating system filled with an anti-freeze solution for freeze protection using a wood/coal fired boiler, or using propane as a fuel source, and powering the gas valve with a thermopile type device. If you can "think it", it can probably be done but will it be safe and will it be cost effective.

Build the home, super insulate it, and add the gravity type system of your choice. It just can't be steam. Choose a medium to heat, water or air, that does not change it's state, unless you are talking about "eutectic solutions" and that is for another discussion.

farmwi

Larry Weingarten said:

Hi, I'd be looking at low temperature solutions. I have a gravity driven radiant system in the walls of my off grid home. It uses no electricity. I've been able to keep the house at 70F with 80F water. Of course, the first thing to do is go to nutty-crazy extremes to make the shell of the house efficient. That way, keeping it warm will be much simpler.

Yours, Larry

This is impressive. Do you have a post with a description of your load and supply or design layout?

farmwi

mattmia2 said:

Of course photovoltaic and batteries are now at a point where you could store enough energy to run a boiler and solar controls and a circulator for several very dark days.

This is true. I have looked into it as it seemed a first way to go. These systems are designed often around base need in the winter. I would like to shut off the power at night, right when I would need it most. I checked my high efficiency boiler and a pump at 250 watts. Adding that to a mediocre inverter use depending on size 100watt = 350 watt, that for 16 hrs would be 5kw. For prebuilt batteries might be $500 per kw, replace every 10 years. Panels during the winter make very little in 4 hours of cloudy days, further exacerbating the collection of power. So more panels. After a couple of mos of reading all the minutia, my goal switched to no power when I didn't have to use it, so spend more thought and design on heat system as well as other items. My goal for night usage was a switch to DC to eliminate the inverter losses. So far, I have not seen a DC high efficiency driven boiler system. I'm still looking.

farmwi

retiredguy said:

You could also install a gravity hot water heating system filled with an anti-freeze solution for freeze protection using a wood/coal fired boiler, or using propane as a fuel source, and powering the gas valve with a thermopile type device. If you can "think it", it can probably be done but will it be safe and will it be cost effective.

Build the home, super insulate it, and add the gravity type system of your choice. It just can't be steam. Choose a medium to heat, water or air, that does not change it's state, unless you are talking about "eutectic solutions" and that is for another discussion.

After reading the generous well informed replies, I will be looking for the design criteria for a low grade heat system such as @Larry Weingarten mentioned. It's hard for me to imagine thermosiphoning forces at that low of a temperature, the piping sizes needed. Reading about radiant heating in the walls at that low of a temp, minimizes the need for protection, and improves the head, rather than a low slope in a radiant floor. Now considering how to find low cost radiant heaters etc.

mattmia2

farmwi said:

mattmia2 said:

Of course photovoltaic and batteries are now at a point where you could store enough energy to run a boiler and solar controls and a circulator for several very dark days.

This is true. I have looked into it as it seemed a first way to go. These systems are designed often around base need in the winter. I would like to shut off the power at night, right when I would need it most. I checked my high efficiency boiler and a pump at 250 watts. Adding that to a mediocre inverter use depending on size 100watt = 350 watt, that for 16 hrs would be 5kw. For prebuilt batteries might be $500 per kw, replace every 10 years. Panels during the winter make very little in 4 hours of cloudy days, further exacerbating the collection of power. So more panels. After a couple of mos of reading all the minutia, my goal switched to no power when I didn't have to use it, so spend more thought and design on heat system as well as other items. My goal for night usage was a switch to DC to eliminate the inverter losses. So far, I have not seen a DC high efficiency driven boiler system. I'm still looking.

I was thinking something more like running a circulator for a wood boiler or a storage tank or some combination. An ECM circulator is more like 50w. It wouldn't be an out of the box solution, but you could run the controls off of DC and even switch the inverter to the circulator so you only get its losses when the circulator(s) is running.

Jamie Hall

If one is willing to invest the time (mostly) and money (not really that much) into really working out this sort of thing, and if one doesn't mind coming up with a decidedly unique and non-standard system, there is no reason at all why -- even in the far north -- one can't come up with a very satisfactory completely off grid system. It is actually a good deal more difficult to come up with satisfactory food storage and food preparation schemes than it is to come up with heating (and even, if one goes south rather than north, cooling) schemes.

The passive (strictly speaking, semi-passive) solar houses I have done have focused on three areas. First, arrange for the maximum possible direct solar gain to the living areas. This means among other things big, south facing glass in the areas which are wanted warm, such as a living dining area or a kitchen. When the sun is shining, 10 square feet (measured perpendicular to the line of sight to the sun) of glass with have a power gain to the space of about 3,000 BTUh. Allowing for errors in orientation and the fact that the sun doesn't always shine, one can pretty well count on 1,000 BTU gain per square foot of glass per day. The second key factor is heat storage so that the gain which you make when the sun is shining doesn't overheat the space (a real problem) but is available when the sun isn't shining. This is really a matter of the more the merrier! Water is nice -- great heat capacity -- but has difficulties. Truly massive masonry, however, both in floors and walls, can do wonders and can be, handled well, architecturally very advantageous. The third factor is to minimise the heat loss of the structure. I can hear you moan "but all that glass". True, glass -- even triple glazed -- isn't the best insulator in the world, but one can do much to make sure that the glass area is basically the only heat loss of note. To some extent this is site specific -- one house I did was on a south facing slope, so the north wall (R20 on the OUTSIDE of the masonry) was buried about 5 feet for most of the length, and completely buried for about 10 feet. That house also had a grassed and gardened roof -- 18 inches of soil, waterproof membrane, R30 foam, precast concrete roof planks -- but going for R20 to R30 on the outside of the walls is quite reasonable.

Then, of course, one wants to control outside air exchange (this is where it gets semi-passive). This means sealing the basic structure as completely as possible, and one really has to get the specifications right -- and then be very hard-nosed with one's builders. In some situations -- again, site specific -- it may be possible to use heat recovery ventilators and gravity convection to manage the air exchange. In others it may be necessary to have some ductwork related to the HRV and a fan and thus is, strictly, semi-passive rather than passive.

Once you've done that, let's suppose a basic 1200 square foot house (30 feet by 40 feet, south wall 10 feet high, 40 feet long, triple glazed). You can achieve a heat loss on a 0 degree day of about 15000 BTUh. You have a heat gain of 1,200,000 BTU per day. If you can store that you have three days heat storage.

If you do need a fan for the HRV, power it with photovoltaics and batteries somewhere out of sight.

What's not to like?

Actually, there is one thing from my experience with these things: they overheat, so that glazing -- and windows elsewhere, such as bedrooms -- have to be openable. Big deal...

jumper

Least expensive heat storage is very hot water. Photovoltaic or wind generated electricity can do that. To use low temperature heating system with very hot water you need to blend recirculated with very hot. Advantage of this strategy is that you can get away with one tank. I prefer to use multiple tanks and take advantage of very hot water for radiant heating. Intention is to be comfortable at low air temperature.

Larry Weingarten

Hi @farmwi , Following are some links that might help as an introduction to my form of crazy
https://www.waterheaterrescue.com/funstuff/hummingbird-home.html
http://greenremodelforum.com/grf/?page_id=1416&msclkid=824dd45cafda11ec9b1ccfac8863c118
https://www.nytimes.com/2007/07/05/garden/05cheap.html

Yours, Larry

farmwi

@Jamie Hall Thank You for the thoughtful reply. A layout is under way. South facing, glass not calculated. Cement is high priced. Water in the basement is more likely. 'Passive' isn't a goal, but is a more likely consequence. I suspect that dense pack blown insulation outside of a timber frame will allow for the windows. I'll post an image after redrawing it again. One idea I'm entertaining, is insulated shutters that have a reflective inner surface to enhance the sunlight. I'm also interested in Vacuum Insulated Glass, but haven't found a design method. I'm also interested in Vacuum insulated panels that I would like to install before dense packing around them to protect them. @Jumper, while I was thinking one stratified tank, two or more tanks is quite reasonable, and would be more effective in collecting heat usefully. I'll use whatever space is helpful in the basement.
Have vacuum equipment for refrigeration already, for any tools that come up. Vacuum anything isn't really fast, though.
Any creative ideas for passive radiators for low grade heat, are welcome.
Thank you for your time and thoughts.

hot_rod

Guardian up in Michigan was working on VIGs years ago. I don't know that they ever made it to market?
https://www.greenbuildingadvisor.com/article/vacuum-insulated-windows

Black painted 55 gallon steel drums were a passive storage "thing" back in the day. Along with rock beds with ducts running through them. For the rodents to stay warm

retiredguy

Here is a few more ideas that became popular back in the 1970's when solar heating was just becoming a big deal. Everyone had a new idea such as window solar collectors made with anything you could paint black and install in a box, south facing walls of glass with passive collection devices such as cans of rocks, as @ hot rod mentioned, eutectic solutions of all sorts, super insulated walls and window covers. There were magazines that showed all this stuff; I did not save any of mine. There were solar systems made from almost any material to gather, store, and produce either warm air or warm water for use when needed.

Two companies I found may give you ideas; www.phasechange.com, located in Asheboro, NC 27203 and www.greenbuildingadvisor.com located in Newtown CT 06470 or do a search for any idea you may have. I have no financial interest in any of these companies. Just trying to remember things from the past that may give you ideas.

Solid_Fuel_Man

You really need one of 3 things. 

1. Elevation for thermo siphon

2. Active controls, ie solar powered DC pumps/motors erc. 

3. Virtually no moving parts with a near passive design as @Jamie Hall stated. 

I would take a page out of all 3 if your site allows. 

With today's market, and it sounds like you have done good research on this solar and Li-ion batteries have become quite viable for an active part of the design. 

Of the off grid homes I've been involved with (cabins, hunting camps, and homes) I have always taken the approach to use as much DC directly as possible. I wire the place with typical Romex and switches and use automotive/RV LED lighting. The RV market is an excellent source for sourcing 12vDC stuff. The "van life" trend lends itself well to incorporate that type of tech into a home. 

I like to keep the inverter as small as possible on only have AC to the must have stuff in the kitchen etc. 

I too would focus strictly on gravity thermo siphon with as much vertically oriented piping as practical. Also making the best use of south glazing and very meticulously placed insulation. Keeping as much thermal mass inside the envelope as possible. 

I'm not particularly a fan of water and phase change due to the limitations of heat transport, but those are solvable. I'm more of a boots and straps approach of large thermal storage, either in liquid( water) form or solid form(concrete/masonry).

leonz

Gravity hot water was done and done very well with coal heating over a century ago as it used no electricity with a riser pipe to the radiators and an open to air expansion tank in the attic and was either top fed-the simplest as no bleeding was necessary or bottom fed-all the radiators needed to be bled when the system was drained or initially filled.

A gravity hot water heating system only requires 170 Degree Fahrenheit water temperature to create the temperature needed to cause the water to start rising to the attic or top floor living space.

An A frame home with well insulated walls and attic would be perfect with this as you would have a basement for the boiler a first floor and second floor living space and an insulated attic for the open to air expansion tank and the vent pipe could be routed back to the basement laundry sink or floor drain.

The thermal mass of hot water radiators made from steel or cast iron would store a lot of heat and release it very slowly.

A top fed gravity hot water system could be used easily as the attic would be insulated and the hot water riser pipe would Tee off to the radiators below the attic where they would be heated first and then the hot water in these radiators would drop to the radiators below them to heat them and then back to the drop pipe that returns the cooler water to the basement and the boiler sump header tapping.

It would be simple enough to have a hot water tank or tanks in the basement at the far ends of the basement for the cooler return water that would be fed into the boiler sump header tapping to create huge amounts of thermal mass and slow even heat for the home.