[retrotecchie]

@wizzo227

Evacuated Tube Thermal Collector.

[wizzo227]

I really like those but have no justification to do that because they'd collect much more heat than I use in spring/summer. Proper design with 2kW evac tube solar thermal collectors as I'd use them needs a 2kW "overflow" in case of surplus heat in summer. I reckon that dumping to the radiator of a mini-800cc engine hung on the outside of the cold side of the house would make that safe, but misses the opportunity of 2kW of high-grade heat. Indonesian mechanical engineers have designed a turbine engine-generator to make electricity from geothermal warm water. A turbine engine to the outdoor surplus heat overflow if necessary or to slow down movement of heat from roof to house water tank would do what I want. There would be greater opportunity for that in a bigger household who use much more hot water than the halfsize kettle which is sufficient for me.

[retrotecchie]

@wizzo227

I used most of my hot water in summer but even in the middle of December they produced just about enough in winter for my more modest needs, supplemented by the calorifer on a wood burning lambda-controlled boiler once or twice a month.

[wizzo227]

Whats the lambda-controlled thing ? Does "calorifer" refer to a brand comparable to "Baxi" of water pipes at the back of the wood burning boiler ? Again my household is too small to justify retrofitting a wood burner.

Were I an architect, I'd try specifying one wood burning boiler between two houses, with one shared chimney up the party wall, series connected radiators and wet plumbing across at least four households, with one gas connection to the group, series connected to wood and solar boilers. Who'd buy a house where the neighbours take it in turns to empty the ash out of the wood burner ?

[retrotecchie]

@wizzo227

Lambda controlled means working on the same principle as fuel injection in a car. Exhaust gasses are analysed to produce the minimum amount of emissions and varying the air supply to keep the 'lambda' value to as close to 1 as possible. This not only increases efficiency to around 90% but ensures you extract the maximum amount of energy from your biomass with the absolute minimum of 'nasties' going up the flue.

A calorifier is a type of heat exchanger. Calorifiers can be gas to liquid, liquid to gas, gas to gas or liquid to liquid. Think of them as a highly insulated cylinder that not only converts heat from one form to another, but also stores it. Often used on boats to produce DHW from the ECS. In my system, recirculated flue gasses were used to heat water.

We also used gas to gas calorifiers for circulated warm air space heating.

[wizzo227]

A very primitive lambda control, if it is me watching the flames, is to use spectroscopic exhaust gas composition estimation to do the same, with the goals being about the same. I never got bored of keeping an eye on that fire from time to time and closing down the air inlet slider when gainful to do so. I expect that the automatic one scores a bit better in all metrics. I don't believe 90% though. Best case possible but one month average ?

Baxi geometry was single pass air&smoke to water heat exchange, alternative route up to the back of the chimney, fully convection driven, with an iron flap to select chimney route. Lasted a lot better than gas boilers too. The chimney necessarily stays hot to pull convection, so it has to lose some energy.

I don't like the sound of recirculated flue gasses. How often do you have to clean the tar off the fan ?

[retrotecchie]

@wizzo227

If you use properly seasoned wood with moisture content less than 20% then tar and creosoting is not an issue. It was run for an hour or two a couple of times a month, just to supplement the solar thermal. The fan system is a DC external motor driving a turbine, similar to a turbocharger on a car, so wouldn't tar up anyway. The whole thing self-powered without needing an external mains supply. Peltier generator, with backup battery, to run the fans and the control system, and a bit of spare capacity left over. In fact, a CHP system if you prefer.

EGR is a fundamental component of the system, and that ensures the minimum emissions and maximum efficiency. Any volatiles or unburned hydrocarbons are recirculated as part of the lambda control.

[wizzo227]

It occurrs to me, that as soon as you need to quieten the fire to get it to last overnight, you close the air inlet to less than stoiciometric in order to suppress the burn rate, so that necessarily defeats lambda control and may make smoke. Unlike an engine management controller, you don't have the option to inject less fuel - you get whatever tars vapours boil out of the wood plus the reaction of carbon embers in contact with air, and it takes several minutes to slow that down. Until then it blows quite a few nasties up the chimney. So a wood burner set to track lambda=1 is not a setting which I'd choose. Any thoughts ?

[retrotecchie]

@wizzo227

As explained, it was not part of the heating system therefore never left running or slumbered overnight. Burned flat out for an hour or so every couple of weeks, just to raise the calorifier temperature.

[wizzo227]

Your thing sounds better than I've ever used. 20% is pretty well seasoned. I wouldn't sign off on a fireplace design unless it can tolerate pretty much any old muck which could burn in a heap; as bad as cereal packet cardboard and twigs which only got a month to dry after gardening. I'd scavenge locally to decrease supply-miles hence decrease CO2 caused for supply. I'm surprised that yours was was 'like a turbocharger'. I'd have used a radial blower with the 'snail shell' external appearance, as found above combi gas boilers, and using quite a lot more power to combat convection than is available from quite a big DC thermoelectric device. Unless the outlet is very hot indeed, it is lacking the conditions which keep an automotive turbocharger clean, so I'm still very skeptical indeed.

I perceive another problem with what you wrote. "Any volatiles or unburned hydrocarbons are recirculated as part of the lambda control." How do you seperate the ideal deoxygenated air from the smoke and other gas which stays inside recirculation ?, I could see one aiming to recirculate X and vent to chimney (1-X) of whatever is going around the recirculation, but what is vented is necessarily not always clean.

So this has been an interesting thread but I'm not out to beat your claimed performance. I reckon that bigger gains could be obtained not from improvement of one fireplace, but from siting it for shared heating for the whole block.