Suggestions on a perfect setup

[mousebndr]

The temps that you posted are not what we usually see for hydronic boilers, but OTOH, I don't know anything about your boiler, aside from what's on their site. From what you wrote, it sounds like the pump driving your load(s) comes on at a low temp - maybe 50*C ? So, I''m wondering, by circulating fairly cool water through the boiler, if perhaps it's struggling for a long time to get a good fire going (due to poor combustion environment), and actually never really does get to optimal output. Being able to almost touch the flue would tend to support the idea that the fire is weak. If what I said is correct, is it possible to keep the load pump off until the boiler has a good, hot fire going? (initially just to test the theory) Again, I don't really know anything about your system - sounds like it might be unpressurized, and maybe operates differently. But, based on your boiler's firebox size, the quality of wood you're using, and your outdoor temps, it just seems like your existing boiler should be doing better than what you're reporting. Also, how about your chimney - any big amount of soot or creosote? Just some ideas, but I could also be barking up the wrong red box.

Be interested to hear what the expected normal temps are in a boiler like this with an open system.

When we have the pump thermostat set to say 70 degC then the pump cycles so much that the radiators are ineffective. Often toyed with putting something like the Danfoss on it but could not get any advise from the boiler maker what return temps should be.

 

[mousebndr]

I am sure you are aware of this, but it strikes me reading your post that the need for storage would depend on the size of the boiler with regard to your load. This following diagram was posted in comment #9 on the linked forum for evaluation of storage requirements.

https://www.hearth.com/talk/threads/76064/

This graph has nominal boiler size in kW times burning period in hours for an abscissa scale of kWH.
The ordinate is storage volume in liters.
Heat load of the building divided by minimum boiler output for various sizes are depicted by the sloped straight lines.

An example might be a 30 kW boiler that is fired for 5 hours = 150 kWH;
Building heat load of 25kW and boiler minimum power output of 10 kW = 2.5;
Graph reads 560 liters of storage. If in this example, the building heat load was 10kW, 1600 liters of storage would be required.

In other words, if your building can’t use the boiler output, storage has to be available to absorb the boiler output. Or if your boiler is undersized for the load storage may not be useful. Food for thought. I am sure you are way ahead of me on this, but I thought I would offer in any case. I have fond memories of Oz and the people.

EDIT Added linked

Interesting, this seems to suggest if I have a 50kW boiler, burning for 6 hours, with a heat load of 49kW and minimum heat of 15kW then I need 10,000 L of storage?

This seems to be out if step with the sizes of storage I have read about on various forums.

I must say I am having trouble reconciling storage needs vs demand to get to a point where you fire twice per day.

 

[willworkforwood]

Be interested to hear what the expected normal temps are in a boiler like this with an open system.
When we have the pump thermostat set to say 70 degC then the pump cycles so much that the radiators are ineffective. Often toyed with putting something like the Danfoss on it but could not get any advise from the boiler maker what return temps should be.

If I'm understanding this correctly, you have an amount of emitters such that a water temp of perhaps 55-65*C would give you consistent heat (i.e. without lots of cycling on and off), and maintain your desired room temp throughout the house. If that's correct, then what you have is a classic mismatch with the water temp that a typical boiler likes to produce (80-95*C). Running without storage, I'm very familiar with that issue - we burn very small fires, and do frequent loading, in order to match the boiler output to the heating load. The following info from your boiler website supports that idea: "The Belvedere is the best choice for in-floor slab heating as its high output, spacious firebox and considerable water jacket capacity, enables the initial temperature rise required for in-slab heating." What they're saying is that their boiler will work best with storage (just like every boiler will). They say slab, but water storage works if you don't have slab ;-P. A Garn would be great if you have the $$$, and could get your hands on one. But if that doesn't fly, you might give some consideration to hooking in some non-pressurized storage (which should work well with your existing open system). Due to the skyrocketing price of copper (HX), this stuff isn't cheap. But it would certainly be much less than bringing in a Seaton, storage, and all of the components and controls required to make it go. Then, if your current boiler still can't do the job, you can switch the same storage over to a larger (hopefully gasification) boiler. One of the pros on this site, Tom in Maine, is an expert on non-pressurized storage, and I'm sure he would be able to give you lots of good advice on this if you send him a PM.

 

[mousebndr]

If I'm understanding this correctly, you have an amount of emitters such that a water temp of perhaps 55-65*C would give you consistent heat (i.e. without lots of cycling on and off), and maintain your desired room temp throughout the house. If that's correct, then what you have is a classic mismatch with the water temp that a typical boiler likes to produce (80-95*C). Running without storage, I'm very familiar with that issue - we burn very small fires, and do frequent loading, in order to match the boiler output to the heating load. The following info from your boiler website supports that idea: "The Belvedere is the best choice for in-floor slab heating as its high output, spacious firebox and considerable water jacket capacity, enables the initial temperature rise required for in-slab heating." What they're saying is that their boiler will work best with storage (just like every boiler will). They say slab, but water storage works if you don't have slab ;-P. A Garn would be great if you have the $$$, and could get your hands on one. But if that doesn't fly, you might give some consideration to hooking in some non-pressurized storage (which should work well with your existing open system). Due to the skyrocketing price of copper (HX), this stuff isn't cheap. But it would certainly be much less than bringing in a Seaton, storage, and all of the components and controls required to make it go. Then, if your current boiler still can't do the job, you can switch the same storage over to a larger (hopefully gasification) boiler. One of the pros on this site, Tom in Maine, is an expert on non-pressurized storage, and I'm sure he would be able to give you lots of good advice on this if you send him a PM.

Hmm more that the boiler isn't able to constantly heat at 70 with the radiators (after a while) thus the pump cycles because temps drop bellow 50. I suppose the degrading return temps cause the boiler to drop off sharply.

 

[jimbom]

....
Interesting, this seems to suggest if I have a 50kW boiler, burning for 6 hours, with a heat load of 49kW and minimum heat of 15kW then I need 10,000 L of storage?

This seems to be out if step with the sizes of storage I have read about on various forums.

I must say I am having trouble reconciling storage needs vs demand to get to a point where you fire twice per day.

50kW x 6 hours = 300kWh 49kW / 15 kW = 3.3 Off the chart ~ zero storage.

With design load 49kW and boiler output 50kW, there is no excess energy to go into storage.

Have you recorded heat loop flow, supply temp and return temp at outdoor conditions where it can keep steady state? That would enable a calculation on load at design conditions.