East European heating System

[contacteric]

Hi,

I have an interesting project/nightmare in Ukraine on the go and have so many questions. I have been following a few posts and feel confident there will be some ideas out there to help me.

I have a large 25 year old boiler (only used for about ten years) and a wood burner supplying four radiator circuits. I would like to disregard the wood burner for now (I do have some questions about it - later). There may be some further details of the boiler on the way to me. But the company that made it was has gone bust.The system is open and was thermosyphoning. The system has steel pipework from 4" down to 1" Practically all of the pipework is unlagged and the pipework adds to the general heating.

I understand that the type of system was common in communist times but it took me ages to get my head round how it could possibly work or not!

The large volume radiators have no valves on them. They too rely on thermosyphoning, with their flow and return going into the same pipe work.

It sort of worked but some of the ends of circuits were not getting hot enough, for comfort or possibly even for fabric protection.

I put a couple of pumps and a non return valve (all in parrallel) in the flow from the boiler. The non return valve was to allow thermosyphoning in the event of electrical failure which is quite common. The pumps were sized by what I had available and I went for the two in case I required greater volume than just one (they are the same size, make, model).

The alterations have achieved the objective, ie getting a greater volume to the extremeties and no spills or air suked in (I read that this could happen when putting pumps in open thermosyphoning systems).

Please excuse the length of my description and finnaly to my first question.

Without having specs for the boiler, given that was designed for a thermosyphoning system, has 4" connections, has a stat that goes from 30 to 85 DegC, is 25 years old, can I make (or really can you make!) any generalisations about optimum flow rate and temperature for the boiler efficiency? Or can these be calculated or gained through testing?

I appreciate that I have provided little information to go on, there may be more soon.

If I find that there are most efficient flow rates and temperatures to run the boiler at, or if these can be assumed, I am thinking of putting the boilers into their own circuit with a low loss header (or even heat stoer for DHWS) header and feeding the house via a VT circuit c/w it's own pump and a mixing valve.

I am thinking the low loss header may not be nessacery because the boiler was surely designed for the thermosyphoning. Then again, when running in that mode the boiler is controlled by it's own thermostat.

If there is to be a header, I can only guess about sizing it. The whole system is about 1000 lts. Space is not a problem. So my thinking is to size the the header so that the primary circuit is the same volume.

I am sure it will be possible to incorporate DHWS heating into the system (this is currently electrical).

In every case, I am trying to leave as many options open as possible. If the gas goes (as it has) there is still DHWS. If the electricity goes, there is HWS and DHWS.

The above is not the half of it, but enough for now. I would appreciate any comments and/or suggestions would be greatly appreciated.

 

[Agile]

You can fairly safely assume the boiler is designed for a temperature differential of about 11 C.

You can set that by pump power/valve settings.

Its not very critical and will be difficult to achieve when you have four circuits.

You can measure the power input of the boiler at th gas meter, see FAQ for how. The power output will be about 70% of the input.

Tony Glazier

 

[contacteric]

Thank you Tony.

I will try and set it up for 11 Deg C differential.
I hadn't even thought of watching the meter while adjusting the set point check efficiency. I will read the posts.
I got some further detail from the boiler today;
Manufacturer: Steel Works Number 63, Model: KC 25
I feel sure that is 25Kw
Unfortunately the company went bust a couple of years ago.
I thought of ripping everything out and starting again but If I can get the system just a little more efficient we will be in a lower fuel tariff band.
Also, with modern stuff you have to rely on electricity and/or gas supplies. I want to be prepared for if/when they get cut off.
Did you have any thoughts on introducing a primary circuit, enabling me to set up the flow rate and temp for the boiler independent of the radiator circuit?
Thanks again.

 

[Agile]

To run that system without electricity you only need about 10 w for the boiler and 100w for the pump so it can be run from a battery and inverter for an hour or two.

 

[Onetap]

It is a gravity circulation system. The circulating pressure is caused by the different densities of the flow and return columns and so depends on the temperature differential and the height of heat emitters above the boilers.

These systems were usual in Victorian schools. They were used in conjunction with sectional cast iron boilers (Beeston? Coal, later oil, later gas-fired) , which had very wide waterways and so very little hydraulic resistance. They worked well and were self-regulating, to some extent. Gravity circulation is still used for most solid fuel systems in the UK.

If you're fitting a pump, you should ensure the return temperature doesn't drop below 50 degC, except during warm-up. That would cause condensation in the combustion chamber and rapid corrosion.

There's no reason why you shouldn't fit a primary circuit with a low loss header or a buffer vessel (similar to the Dunsley neutraliser arrangement). If the primary circuit is pumped, you'd need to find a pump capable of moving the design flow at the (very low) hydraulic resistance of the primary circuit. Pumps don't like low differential pressures, you may have to add resistance with a regulating valve.

The neutraliser pdf is just provided as an example of how a gravity primary can be linked to pumped &/or gravity secondary circuits. A cylindrical buffer vessel will work in the same way.

 

[dcawkwell]

Only one thing to do with these systems.
Rip out and put something modern in.

 

[Onetap]

Only one thing to do with these systems.
Rip out and put something modern in.

Why?
If it works, then it has much to commend it.
A lot of modern stuff won't work as reliably or as quietly. It certainly won't work as well when the electricity goes off.
No-one installs gravity systems now, by choice, because they need big pipes. If the big pipes are already there, there's not much point in ripping them out.
The problems with Victorian gravity circulation systems usually started when they were butchered or neglected by someone who didn't understand how they worked.

 

[contacteric]

Excuse my delay in thanking you for your posts.

I investigated the design of old Victorian systems to figure out what I had.

Onetap, thanks for your advise about keeping the return at 55 Deg C, that was the reason for my thinking that I should put a buffer in, to avoid the house demand affecting the temperature through the boiler. I did have in mind the system requirements but the pumps installed were what was available and they seem to do the job ok.

I was also assuming that there was a most efficient flow or return temperature that I could run the boiler at to reduce gas consumption. If you go up one tariff here you are very heavily penalized.

Ripping it all out and putting something modern in? Well, Agile thanks for pointing out how little power is actually needed to run a heating system but I have known the power go off here for days at a time with OAT at -10 to -20 Deg C in winter.

Also there is a solid fuel boiler as well. So if the gas goes off for a while I am covered.

Again my apologies for not thanking people sooner, I got wrapped up in some underfloor heating also in the above installation.

The more I look at this system the more I like it. I would like to make it bullet proof though!

Is is possible that I can introduce a mixing valve and not put in a buffer? I don't want the boiler cycling on and off too much.

Also any advice on heat stores? I had thought about going the whole hog and allowing for future ground source and solar panels but the tanks are so expensive, I think I will settle for a big cylinder for HWS (possibly another reason for the header?

Any thoughts, tips, etc, are still most welcome.

 

[Onetap]

I was also assuming that there was a most efficient flow or return temperature that I could run the boiler at to reduce gas consumption. If you go up one tariff here you are very heavily penalized.

A lower return temperature will be more efficient, with the proviso that you cannot allow it to condense the water vapour in the flue gases in a non-condensing boiler, so you're limited to 56 degC minimum return or so. This won't provide adequate heating in very cold weather.

A weather compensating system, which alters the flow temperature according to the outside temperature turns the return temperature to the lowest possible setting whilst still providing adequate heating. I don't know how WC would work with a gravity circulation system since varying the flow temperature would change the flow rate. You could have a similar control system which altered the flow temperature according to the indoor air temperature.

You'd need a mixing system to supply the underfloor heating, you could have a similar mixing valve set to supply the radiators, but these are usually pumped systems. I think it would lend itself to a buffer vessel, as the Dunsley pdf systems, but can't make any detailed suggestions from afar. I suspect a suitable control system and much trial and error will require more work than the pipework.