Stirlingengineforum.com

I want to create a new compact heat source for household heating by utilizing two technologies: Compost heat recovery (CHR) and Stirling engines as heatpump.
My project is halfway done and I've created a compact compost reactor which is capable of producing heat energy.
The compost heap inside can stay above 50 degrees Celsius for 14 days.
In the next step, I want to build up a small Stirling heatpump to tap heat from the reactor and store it in a water tank.
By doing so, I can validate how much energy I can harvest from this system and prove its effectiveness.

However, I'm not quite good in engineering and manufacturing a Stirling engine.
I don't have a CNC machine and know nothing about machining.
I'm also incapable of welding.
Luckily, I have a delta 3D printer and I can model some basic parts like crank shafts and gears.
A typical aerobic compost heap can only reach up to 70 degrees Celsius so I think my printed parts will be able to survive as long as they are not in the heated areas.

So, here is my question:
Is there any simple and effective Stirling heat pump design that I can build by myself?
I need detailed description like sizes and materials required.

(I've already made three attempts to build simple Stirling engines(not heat pumps) and failed in all cases.)


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I've found this on YouTube
https://www.youtube.com/watch?v=yf9H-KuwA5w
But I can't find a detailed diagram of it.


Gitpharm

-------------Some details about this project-------------------
1.Goal:

The world is in a severe energy/food crisis and I think an alternative energy/fertilizer source would reduce the damage.
I want to develop a system which can simultaneously produce heat and fertilizer.
It will be a very compact build which can be integrated into the heating system of a house.

2.How it works

2a.Aerobic compost reactor:
Aerobic composting can generate a great deal of heat without burning all carbon contents into CO2.
A Technology called Compost Heat Recovery(CHR) is to harvest such heat energy from the compost heap.
It has been practiced in many places by various methods.
Here's an example on YouTube: Warning up a hoophouse with a barrel of wood chip compost.
https://www.youtube.com/watch?v=NlGu5ZHV6WM

If the compost heap is contained in a well ventilated and heat-insulating reactor, the heat loss will be minimized.
A reactor can also significantly shrink the minimal size of a compost.
It usually takes at least one cubic meter of material to start a hot compost pile.
But my prototype reactor, which is only 0.24 cubic meter (1.2m * 0.4m * 0.5m) in volume, successfully reached 60 degrees Celsius and stayed above 50 degrees Celsius for 14 days.
https://drive.google.com/file/d/1knFxcE ... E94io/view
Due to the heat-insulating effect of the Styrofoam made reactor, the reaction will not be stopped by cold weather.
This feature will allow the system to be deployed at cold areas where household heating are needed most.

2b.A hot water tank as buffer/ reservoir:
The heat output of a compost heap follows a rigid pattern:
mesophilic phase --- a short period when compost temperature climbs up
thermophilic phase --- the temperature enters a plateau stage, could last for several days
cooling phase --- the heap starts cooling down in this stage

Therefore, it is impossible to dramatically boost a compost heap's thermal output like a combustion engine.
However, the household heating demand could change at any moment.
In order to fix this problem, a heat reservoir must be included in this system.
https://drive.google.com/file/d/1iQY2Uv ... sp=sharing
The heat will be pumped from the reactor to the reservoir with a small Stirling heat pump.
And then the main heat pump of the house will tap thermal energy from the reservoir when heating is needed.
Notice that there are two reactors in this system, one is in thermophilic phase and another is in mesophilic or cooling phase.
This setting will guarantee constant thermal output from the compost when one of the reactors is harvested and restarted.


3.Comparison between fossil fuel and CHR heating:

Fossil fuel-based heating and fertilizer production:
a.fossil fuel controlled by governments/companies and usually requires long range transportation.
b.The process produce a great deal of pollution
c.Not sustainable

With CHR heating:
a.The raw material is abundant and readily available.(grass clipping, coffee grounds or other food waste)
Manure, which might cause environmental nuisance, is not necessary at all.
b.It will not suffer from any significant supply chain issues.(Where there's people, there will be organic waste)
c.It's actually reducing/processing organic waste and eventually it can reduce the diesel/gasoline consumption for garbage disposal.
d.Sustainable (Return nutrients back to the land instead of vaporizing them in waste incinerators)

That all sounds pretty well thought out. I'd only be careful about taking too much heat from the compost lest it shutdown the reaction and suspend the thermophiles.

(I've already made three attempts to build simple Stirling engines(not heat pumps) and failed in all cases.)

I'm pretty sure the sterling engine is considered a heat pump when driven by an outside motor. Once you do get one working, try driving it externally and see if your surfaces develop a differential temperature gradient.

The main difference is the heat exchange area and efficiency. Whereas when running as an engine you are supplying excess heat with much of it lost to the surroundings, as a heat exchanger you want to transfer every bit of the heat one way or the other. That's my my best guess anyway.

You show a video demonstrating a copper coil in a compost, presumably this will circulate water through the compost?

Is the reservoir going to receive the water circulating through the compost? Basically a warm water tank or do you intend to increase/concentrate the heat by means of an actual Stirling "heat pump".

In other words, I'm not entirely sure of your use of the term "heat pump".

A Stirling engine that pumps hot water is a vary different thing from a Stirling "heat pump".

It appears there is considerable distance between the compost "reactor" and the "reservoir". Which seems could be achieved by just circulating the hot water from the compost to a hot water tank.

Generally a Stirling heat pump (a Stirling engine driven by a motor) does not circulate water. It transfers heat, but only a very short distance, one side of the engine to the other side of the engine.

Also a Stirling heat pump (or "cooler" as in the first video from blade attila), does not run on a heat source. It is driven by an electric motor. That beer can heat pump in the video is being driven by an electric aquarium pump motor.

What I am asking I guess is are the two "heat pumps" associated with the compost going to be plugged in and driven by electricity?

I was wondering also; is the "main heat pump" also a Stirling engine?

If your intention for the Stirling engines is simply to circulate water through the compost and into a water tank that would be rather simple and straightforward. It might even be possible without any kind of engine or pump just using convection (or "thermosiphon").

Tom Booth wrote: ↑Wed Jun 15, 2022 9:08 pm You show a video demonstrating a copper coil in a compost, presumably this will circulate water through the compost?

Sorry for not providing enough data on this build.
It actually does not have any water and pump.
Here's the compost heater in action:
https://youtu.be/ekQqA6DRjRE
The copper coil is just sitting there and hot air will naturally come out of it.

Tom Booth wrote: ↑Wed Jun 15, 2022 9:08 pm Is the reservoir going to receive the water circulating through the compost? Basically a warm water tank or do you intend to increase/concentrate the heat by means of an actual Stirling "heat pump".

No, I'm not planning to use water to circulate through the compost heap.
According to a review article, it's better to harvest heat from the steam rather than the heap.

I want to install a heat pump at the top of the reactor and collect the heat from the steam to a hot water tank(The heat reservoir).
The water in this tank will not flow in to the reactor.

And the "Main Heat pump" is just a regular compressor heat pump which is already installed in many houses.
The heat reservoir tank can deliver its heat to the main heat pump by a water pump circulating its content.

Ok, thanks for the clarifications.

It is a bit puzzling though, in that and another follow-up video, the intent to circulate water through the system to warm the soil is mentioned.

Regardless, the problem at hand is getting the heat from the top of the compost into the water in the storage tank.

There is still the distance issue. And also what is powering the Stirling "heat pump". As mentioned, a Stirling engine runs on heat but a Stirling heat pump is just a Stirling engine turned by an electric motor or some other external mechanical means.

There is a kind of Stirling heat pump, some variations of which are supposed to run exclusively on heat alone and don't require external mechanical input. As far as I know, though, this is only theoretical or experimental.

Those two images from Wikipedia: https://en.m.wikipedia.org/wiki/Vuilleumier_cycle are about the extent of what I've been able to find regarding these self-driving Vuilleumier heat pumps. I recall reading somewhere, though that these are being used very reliably, to cool nuclear missile silos or warheads or some critical military application along those lines.

Apparently there is/was a prototype "free piston" version.


https://www.energy.gov/sites/default/fi ... 4.4.14.pdf

I'm not entirely sure if this "free piston" requires some mechanical drive of some sort to move the displacers.

There is some red and yellow bit at the bottom, the purpose of which is not indicated. Maybe just buffer space, but could be some kind of electromagnetic drive (like a loudspeaker). Displacers take very little power but are not ever somehow self actuating afaik.

Tom Booth wrote: ↑Fri Jun 17, 2022 3:35 am Ok, thanks for the clarifications.

Regardless, the problem at hand is getting the heat from the top of the compost into the water in the storage tank.

There is still the distance issue. And also what is powering the Stirling "heat pump". As mentioned, a Stirling engine runs on heat but a Stirling heat pump is just a Stirling engine turned by an electric motor or some other external mechanical means.

There is a kind of Stirling heat pump, some variations of which are supposed to run exclusively on heat alone and don't require external mechanical input. As far as I know, though, this is only theoretical or experimental.

Thank you for providing these designs. Heat powered heat pumps are actually what I first came up with when I started this project.
However, the compost heat in this compact reactor is not likely to be strong enough to make such system work.
In my system, some amount of electricity will be consumed to drive the Stirling heat pump.
I made some pictures to further describe it:


The goal of this project is NOT to completely substitute natural gas and electricity with compost heat, but to reduce the consumption.
This reactor/heat reservoir system will serve as a support unit for existing heat pump systems.
The compressor heat pump's performance(cop) can be significantly improved by increasing the temperature of its heat source.
The setting looks like this:


What I need is a simple and electric driven Alpha or Beta Stirling engine which can effectively pump heat.
But my tools and skills are quite limited, and thus I need detailed diagrams to craft one for myself.

Sorry I didn't get the pictures properly loaded.
Here's what I want to show on last post.
a.Detailed compost heat recovery system configuration:
https://drive.google.com/file/d/1QJzsmD ... sp=sharing

b.Compost heat recovery system and existing household heat pump
https://drive.google.com/file/d/17tJCgu ... sp=sharing

c.Concept of a alpha Stirling heat pump / engine
https://drive.google.com/file/d/1JhwU1R ... sp=sharing

I don't want to be discouraging, but I honestly don't think a DIY type "tin can" Stirling heat pump would ever be able to do what you have in mind. There are companies that have had similar goals with millions of dollars in R&D, government grants, investors etc. and after millions of dollars spent, maybe have a one-off prototype, NASA type engine charged and pressurized with helium gas or something that apparently does the job.

On the other hand, if a beer can engine and aquarium pump motor can produce a few degrees temperature change, I wouldn't entirely write off the possibility of a home built engine/heat pump of some sort working, I just don't know of any real success stories, though I've continued working on, and experimenting with such things myself to a very limited degree, I certainly can't claim any big success.

I do have some speculative/experimental ideas I hope to try, as soon as I finish setting up my new workshop.

Actually, nearly everything in the Stirling engine field seems to be research/experimental, though the technology is 200 or something years old, until recently, it has been mostly, completely neglected for 200 years, so just about any modern application, other than "toy" model type engines, or pumping water, is considered pioneering research.

Thank you Tom, I'll take your advice seriously.
Though that beer can heat pump footage by Blade of Attila seemed really promising, I think I will try other technology that I can handle.(Peltier plate, etc.)
I wish you good luck on your new project.

gitPharm01 wrote: ↑Mon Jun 20, 2022 7:07 am Thank you Tom, I'll take your advice seriously.
Though that beer can heat pump footage by Blade of Attila seemed really promising, I think I will try other technology that I can handle.(Peltier plate, etc.)
I wish you good luck on your new project.

You want to transfer the heat from a compost to a storage tank and/or concentrate it there?

I don't know how a peltier device would be of any use and the efficiency (maybe 5%) is abysmal by comparison.

My advice, if I were to give any would be not to give up, and continue with your pioneering research. A "tin can" type engine, though, is way too small to fully utilize the heat output from a compost heap.

Something more along the lines of a "sun pulse" type LTD would be more appropriate, or somewhere in between, maybe like this:


https://youtu.be/9jQgAnPrwbM

Not really that difficult to build, possibly, but I wouldn't count on being able to find any ready made plans or diagrams for your specific application, it's just never been done before that I know of.

It also seems to me that whereas congress or whatever is continually making grants and funding available for alternative energy research, the purpose of these big government funded research projects is to absorb the available funding while going nowhere, i.e. protect the established energy monopolies and maintain the status quo.

If I may expand slightly on an earlier comment or two - a "Stirling Heat Pump" is a fairly well-known device, though rarely needed/built by amateurs, I suspect! As noted, it needs something to drive it, which can just as easily be a "Stirling Engine" as anything else.

MikeB wrote: ↑Tue Jun 21, 2022 8:22 am If I may expand slightly on an earlier comment or two - a "Stirling Heat Pump" is a fairly well-known device, though rarely needed/built by amateurs, I suspect! As noted, it needs something to drive it, which can just as easily be a "Stirling Engine" as anything else.

I had explored this idea earlier in this thread: viewtopic.php?f=1&t=5325 but with an emphasis on a Stirling "Cryocooler".

A Cryocooler is also a "heat pump" but the heat is discarded.

The simplest mechanical heat pump I've ever seen, also mentioned in that thread was a kind of Ringbom engine with the "free displacer" functioning as a "cold finger".


I suppose this simple design could be modified to utilize a HOT finger as well as a cold, but I haven't really thought about what that would actually look like.

I suppose, rather than just allowing the hot end of the cold finger to dissipate heat to atmosphere, the heat could be dissipated into a tank of water or directly to a living area or whatever, but again, the design would likely need some modification from what is shown in that patent drawing.

I think my idea in that thread was to simply attach a cold finger directly into a Stirling engine using the engines own pressure differentials, but don't really know if that would work. Certainly, though, a Stirling engine should be able to drive one of these very simple "free displacer" type mechanical heat pumps.

It would basically be the same device but rather than putting the cold finger into an insulated box to make a cooler, it would be allowed to absorb heat unrestricted from ambient (or a compost) which, of course, should greatly increase the heat to be dissipated at the other end, (by a water tank).