Ian's Thermal System

[IamIan]

I am a turtle (slow progress) .. because I'm a tinkerer who gets more out of the tinkering itself than the functional finished product .. and because I have soo many tikering projects to compete for my time .. and because I have a day job that eats 2k-3k hours a year.

Soo , I've been tinkering with allot of the pieces of this project for many years .. but it's starting to come together enough that I thought I might start to write up the overall combined system here.

DIY Solar thermal collection from less than ideal orientation but sunnier side of house .. and a DIY compost heating pile .. and maybe someday add a DIY geothermal loop.

Make use of DIY heatpump system for higher COP and higher dT.

DIY thermal storage.

DIY PV collection (with small battery backup) to reduce use of grid electricity.

[IamIan]

Compost pile heating.

A fairly good book is "The Compost Powered Water Heater" .. not perfect , but a good place to start.

There is roughly the same wh of energy weather the material is burned or composted .. A well made compost pile has a potential for a small thermodynamic efficiency benefit because burning usually leaves allot of heat energy in exhaust gasses going out a hot chimney .. a compost pile can have much less heat 'going up the chimney' .. colder temperature exhaust gases .. but if the compost pile is outside and uninsulated , than allot of the pile's wh of heat it produces / converts .. will get used / lost just to heat the pile itself from those colder outside ambient conditions (lower net efficiency) .. and if you insulate it , you add cost , complexity , etc.

It does vary .. leaves vs paper , type of wood , etc .. but a basic average for common composted hydrocarbons is around ~5kwh per kg .. although not all compost kg are those wh containing hydrocarbons .. for example water content is needed for the biology of the compost pile to function , but the kg of water does not bring with it kg of hydrocarbon wh fuel chemical energy.

Compost pile is vastly slower than burning (stove or such) .. slower to get up to temperature .. hours to days instead of minutes .. and slower to process the same kg of fuel .. the easiest hydrocarbons break down over days to weeks instead of minutes to hours .. the most resistant hydrocarbons break down over months to years instead of minutes to hours.

Condition Complexity .. A stove burn style is fairly simple (in comparison) operating conditions .. fuel that isn't too wet (the drier the better can't be too dry) .. enough oxygen for combustion (if damper turned down it goes slower but doesn't stop entirely) .. start slow (kindling) and build up to a hot fire .. Composting can be either .. less complex , when years are available to process the kg of fuel , or for very large piles .. it will basically happen all by itself (actually difficult to prevent) if given a big enough material in a pile and enough time .. the smaller the pile and the faster one wants the kg to be used the more complex / details kreep in .. what is the moisture content (not too wet, not to dry) , what is the the O2 ratio content , trace nutrients (available nitrogen , etc) , operating temperature (not to hot , not to cold) , etc , etc.

I have leaves , junk mail , etc .. every year .. and if needed (free to me) where I work has a hundreds of tons of wood waste they dispose of every year .. about a dozen or so people take some home for their wood stoves , fire pits , etc.

Both have a start up cost .. cost to buy and install a wood or pellet stove .. or a cost to buy and install compost pile heating .. it is easier legally to do the compost pile heater .. Here in RI (legally) I would have to pay a licensed pro to install a fire place / wood stove / pellet stove / etc .. and the stove itself has to have been EPA approved .. soo, no DIY home made , or some of the old versions .. etc .. but compost piles do not have such restrictions .. DIY is encouraged .. it can't smoke or catch fire .. but both of those is a failure case to be avoided in design anyway.

The time investment for a compost heater is more concentrated .. subjective if that's good or bad .. you spend ~98% of your invested time at the ends .. beginning and end .. A wood stove / pellet stove / etc .. unless you your entire winter heating fuel in some type of automated fuel delivery to stove heating system , you spend __ of your time every day feeding the stove .. the compost pile heater concentrates all that time .. setup time and then end tear down time , but (ideally) doesn't require your time day to day , week to week , etc.

Space investment .. The wood / pellet stove itself as a reaction space is compact .. but the chimney also uses space .. __ tons of pellets ... or __ cords of wood also eats space .. total combined space is roughly about the same either way .. compost pile or stove .. but .. the orientation and type of the space is a different mix between them.

[IamIan]

1st experiments were just off the shelf compost tumbler style composting.
Didn't work well for me.

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Smallest Compost heater experiment was small
~4 Gallons in a old ~5 Gallon water bottle , in my basement.

pic attached

It didn't make enough heat to create a noticable dT from ambient .. but did compost some of the material over a ~6 Months potential heating season.

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Then I tried 6 different mixes , each ~40 Gallons in it's own ~55Gallon Drum.
Also in my basement .. exhaust gases vented out through old (not in use) natural gas water heater chimney flue.

pic attached.

video
https://youtu.be/dRHOkPpzCaM

Better results , but not good enough.
logged data graph attached.


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This 2020 winter I started the 3rd test / experiment outside in back yard ~600Gallon total.

It's been doing better so far than the 2nd test .. but , there are still some improvements I have planned for a 4th version in the fall/winter of 2021.

Pic attached

Video
https://youtu.be/fpaYgWquZCI

[IamIan]

The DIY heat pump approach I've been experimenting with is converting a used mass produced window air conditioning air to air style heat pump unit.

The mass produced effect means they are inexpensive , and even good condition used ones are available for even less $ (craigs list and such).

The power use scale is good for my current direction .. It takes about ~5kw of heat to heat my house (~800SqFt living ~600SqFt Basement work shop) on those cold single digit F winter nights .. A Heat pump with a COP of about ~3 means it should be able to do that for about ~1.7kw of electrical input .. of course that's isn't the common outside temp .. Soo the vast majority of the time 95%+ far less than they will be needed .. and future planed insulation upgrades will also further reduce the amount of kw needed.

My 1st experiments have been with the smaller ~500w (5-6k BTU) versions.

There are lots of videos and such out on the web of people doing similar for gaming CPUs , Brewing (Wine / Beer) , pet enclosures (aquarium , reptile).

Although the air / air style system works .. and I could blow the cold air where I want to take heat .. and the hot air where I want to give heat .. after only a little testing I decided I wanted to modify it to run as a liquid / liquid style system instead of air/air.

Air/Air is easier , and has the benefit of not needing to worry about frozen water breaking something .. but frost can build up and stop it from working effectively.

Water/water has some attractive benefits .. because of the higher specific heat and material density of liquids like water .. more wh of heat can be moved for a given dT .. that is good because the larger the dT the more it tries to leach out into places I don't want it .. ie. heat loss through a insulated pipe , container , etc is a function of size and dT .. to move the same watts of heat with air requires either larger volume containers (larger size = more loss) , and/or higher temperatures of that air (higher dT= more loss).

After carefully bending the coils out.

I 1st tried the dunk coils (evaporator / condenser) into water bath .. 55 gallon drum .. and it worked .. cold water sinks .. hot water rises .. soo, there was considerable temperature gradient .. which was good for cold side , but bad for hot side.

pic attached.

Then I scaled the dunk bath down to the size of the coil .. ~5Galon and ~8 Gallon. This reduced the temperature gradient effect .. progress .. from there I could then pump the heated / cooled water where I wanted it to go.

pic attached

To further improve the heat transfer from coil to working fluid I blocked off the bottom and sides soo that the water had to flow through the exchanger .. a little better.

pic attached

To further improve the heat transfer from the coil to the working fluid I made a form to go on each side , which will force the water to flow back and forth through the coil (snake like) .. Still tinkering with it .. not 100% done yet.

pic attached.

video
https://youtu.be/HLPhRFaLJXY

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I'm still a little on the fence about the number of heat pumps .. But I am leaning toward 2 systems.

One for the inside storage to outside dT harvesting / expelling.
One for the inside storage to living space dT harvesting / expelling.

Something like the attached diagram.

The thermal storage can be regular water (even free rain water) .. the working fluid might be best to be distilled water or such so as to not clog up the heat pump coils .. where it could do bellow freezing (like outside run in winter) , will either need a 'drain back' design .. avoids need for glycol and such .. or , no need to drain back I use Glycol (or such) .. The inside runs will not ever go below freezing , soo that shouldn't be a issue anywhere else.

[IamIan]

When the house is closed up for a long time the inside air gets 'stale' .. link after months in the winter.

But just opening a window to get 'fresh air' might work .. it also let out allot of heat.

When all that is needed is the fresh air .. it is ideal to keep as much of the heat as possible.

OEM made heat recovery ventilation (HRV) units do this .. you get fresh air in .. because heat naturally flows from to cold the colder outside air will get warmed up some by the hotter inside air going out.

Never 100% efficient .. but something is better than nothing.

Of course off the shelf OEM units are expensive .. so this is a DIY version I made out of a piece of fluted (corrugated) polycarbonate sheet.

When ~67F inside and ~42F outside ~96% of heat retained.
When ~69F inside and ~17F outside ~79% of heat retained.

Fabrication Video
https://youtu.be/_kJB9LPhZDs

Results / Performance:
https://youtu.be/fCgf1lCK4qQ

[IamIan]

Thermal Storage

One of the ironies (to me) .. is that I spend energy in the summer to get rid of heat .. and I spend more energy in the winter to get heat .. If only I could only spend the energy needed to move it to when I need it.

Entropy is a rough .. storing energy as a object of a different temperature is difficult to do for any long period of time .. conventional insulation on water heaters and such do ok in the range of storing for a few hours .. but to get even a few days takes extremely high insulation R values .. never mind trying to store a large % of heat energy for weeks or months.

There are a few 'loop holes' .. if the energy is not stored as heat energy .. there are other types of energy storage that do a much better job of low loss over time.

Energy stored in chemical bonds can more easily be stored for long periods of time numerous years .. wood , coal , hydrogen , etc .. but the down side is the very low round trip efficiency .. a large % of the original heat energy is lost by the time you have converted it back to heat.

Energy could be stored in batteries .. some modern types like LiFePO4 and LTO can have very low .. like under 5% self discharge per year .. and they can have high cycle efficiency ~95% or greater .. but the $/kwh is very expensive to do whole house light heating from them for months at a time.

The reversible desecants are a nice option in that sense .. they give off heat when they absorb water , and they absorb heat when they give off water .. they have very high cycle efficiency , and as long as kept dry they can hold that 'potential' energy for years .. there down side is the cost .. $ , weight , and space needed for a given wh amount of energy storage.

Gravity can be nice .. that weight up high on the hill retains all it's gravitational potential energy for as many years as it's up there .. and no exotic materials .. but .. the density some in again .. the amount of space and weight needed to store significant (to heat a home with) amounts of energy is rather large and prohibitive.

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Where I work gets water soluble wood glue by the 55 gallon drum .. Then when it's empty , they throw away the 55 Gallon water tight drum.

I wouldn't use them for potable (drinking water) .. and I probably wouldn't even use them fro 'grey' water to shower with , without allot of cleaning ... but for thermal storage .. the quality of the water doesn't really matter.

Large amounts of heat for a long period of time will still not be very effective / easy with storing energy as heat .. but at least with something like water .. it's specific heat and density mean a higher amount of wh can be stored in a decent size ... about ~46,000 BTUs can be stored in a single ~55Gallon Drum with 100dT like from 40F to 140F .. that can be used in 1 hour @ 46,000 BTU/hr .. or over 10 hours at ~4,600 BTU / hr.

Soo , I'm leaning this way due to the fairly low cost of tinkering with them.

Because of the insulation losses , this is expected to be a few hours to at most a few days of thermal buffer storage .. not seasonable storage .. not 100% of my heating or cooling needs.

Sense the drums are free to me .. and the water fill them is free to me .. I might splurge and get better insulation .. I'm considering maybe going with something like an ~R70 , 3" thick sandwich shell .. 1" R6 foam + 1" R66 Panasonic Vacuum insulated panel + 1" R6 Foam.

The VIP won't be the cheapest option for insulation .. but .. I do like the crazy high R value from such little space .. all said and done to get a similar R value from normal foam board wouldn't end up being much cheaper anyway.

https://www.digikey.com/en/products/...4DcCGBjEBdAvkA

https://b2b-api.panasonic.eu/file_st...leversion/3247

But , can't puncture or cut them .. they are the size they are .. or maybe I'll try it with just R6 Foam board first , see how it does before splurging.

[IamIan]

My annual electric consumption has been around ~7Mwh .. of which about ~3Mwh is non-HVAC.

I bought 10 used Sunpower 250w solar panels for $891 delivered ~$0.356/watt .. all 10 panels seem to be working fine .. there is of course more risk buying used .. but .. as they say Reduce / Reuse / Recycle .. and it's way cheaper per watt to buy them used.

If I average 4 solar hours per day over the course of a year that ~2.5kw can potentially harvest about ~3.6Mwh per year .. Soo roughly about what my non-HVAC loads are throughout the year.

I haven't decided yet .. but I am leaning toward putting them in parallel with a DC-MPPT on each panel .. AC coupling with micro inverters is also an option , but not my 1st choice.

I like the idea for maximum space use efficiency to combine these PV panels inside my solar thermal collector .. for a combined PVT harvesting system .. the down side is that the higher temperatures will result in lower PV electric yield and faster PV degradation rates.

Spec sheet attached.

[IamIan]

HVAC is by far my largest annual energy use.

I first tried an old used evacuated tube solar thermal collector .. SEIDO1-16AS .. 2142mm x 1940mm x 187mm
pics attached

I had liquid sealing issues .. tubes with lost vacuum ... and soo much of that wall potential surface area not being used .. etc .. might ll be because it was old , maybe a new one wouldn't have had issues .. Soo, I will be replacing that with a custom solar thermal collector to make use of that entire winter sunny wall surface area.

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For the glazing of that solar thermal wall (among other projects) I bought some 4 wall 3 air gap 6mm thick x 1050mm x 2440mm 840g .. clear polycarbonate sheets .. because I was part of a 100 sheet bulk order .. I got them cheaper than usual off the shelf purchase .. $26.34 per sheet (aka $0.96 per sqft) with delivery and tax .. compared to off the shelf like at lowes or such regular 2 wall 6mm would have been around ~$20 per square foot.

pics attached.

[IamIan]

For electrical storage .. mainly to run the HVAC system:

Low self Discharge
Low calendar aging
High cycle life
High cycle efficiency
Ideally used or older cells (reduce / reuse/ recycle)
It's a stationary system so weight isn't as important as it would be in a mobile system.

I currently plan to use , used LTO and/or LiFePO4.

Both of which have good round trip cycle wh efficiency ~95% .. both have very low yearly self discharge less than ~5% .. both have very high useful life to both cycles and calendar aging effects .. and both are among the safest flavors in the Li family.

If I am able to eventually move my whole ~7Mwh a year of HVAC loads to a ~3COP heat pump system that would need ~2.3Mwh per year / 365 = ~6.4kwh per average 24 hr day .. of course more in winter , less in spring/fall .. winter time is my peak .. my record worst day so far was ~38kwh @ ~3COP = I would need about ~12.7kwh

I already have ~7.7kwh of used Toshiba SCiB LTO cells .. I've already tested them .. I may or may not add more on later .. we'll see .. but I think it will be at least a good 'entry' level battery back up system.

I also already have ~11kwh of LiFePO4 A123 20Ah pouch cells .. I've already tested .. 5-7kwh of that plan to go into an upgrade add on to my PHEV .. which will leave 4-6kwh of them I could also add to the house battery system .. if I do , that would bring the house up to 11.7 - 13.7kwh .. that would bring the combined system up near my worst case HVAC loads for an entire day from electrical battery power alone.

If I had to .. I could tap into the 8-10kwh that will also be in my upgraded PHEV battery .. which would bring it up to ~21.7kwh .. or worst case , If I was desperate , run the PHEV ICE as a gasoline generator , ~10Gallon tank of gasoline could provide between 73-107 kwh more electricity (depending on operating details) before needing to go ~2miles and get more gasoline.

I am not planning to go 100% off grid right away .. Soo , unless the grid is down (black out) , I really only need a small enough buffer battery to run the HVAC system while the sun comes in and out of clouds and such , and for a few hours at night .. 100% off grid would require some significant upgrades .. which I might or might not do in the future .. this system will be modular enough that such upgrades will be possible without too much trouble.

[jeff5may]

Chemical energy storage is somewhat less dense than the source. Megajoules per kilogram is the metric. As expected, burning liquified petroleum gas is pretty dense, around 50. Liion batteries come in around 0.8 on the same scale. But you have to have a source to store. And the 2LOT complicates things further, you cannot break even. Rube Goldberg would be proud.

PV solar is so less dense, they had to invent metrics for comparison. The going rate is 25 equivalent watts per square meter. This is with 10% pv panels. Moral of the story is that if you're jimmy carter, you can power a tiny town for the low price of (he doesn't have to tell you) money. In effect, you're replacing a continuous duty burner of a certain size with a PV energy concentrating storage system capable of less service at higher expense. YOLO, it's just money...

The best way to use your dehumidifier scale phase change contraption is to integrate it into your window HRV. Put each heat exchanger at the downwind end and reflect the heat outdoors or indoors, depending on the season. 300 CFM per ton of refrigeration, or 10 watts per CFM of heat transfer, is the standard target indoors. This setup beats the above solar concentrating system described above by a factor of COP times ten. All day and all night, without batteries. Off grid? No problem. Just run it off the power inverter.

If this post sounds scattered, it is fashioned to reflect this thread. If it were me, I would probably post up 4 or 5 separate topics and keep each topic more focused. A combined system is only as strong as its weakest component.