Newbie with Nibe Vedex 3000 - seeking optimal burning

[craig73]

I'm quite new to this, having bought a house in the countryside in southern Sweden. The previous owner invested a lot of time in the heating and hot water setup - with solar taking care of about 4 months of the year (hot water) and the rest with a wood burning furnace - a Swedish Nibe Vedex 3000 - which was installed in approx 2005. There is no English manual for this model however it is very similar to the replacement Vedex 3300 for which I have an English manual, so I believe I am operating it correctly.

We've been burning the furnace for about 2 months, for hot water only the first month and turned on the heating system about a month ago. Now with the outside temperature range of -2C to 7C each day, I'm burning it every evening for 3-4 hours (usually it's 1 full load of wood per day - mostly birch).

The system has 3 x 1000L accumulator tanks (it is quite a big house of 270m2 with around 200m2 being heated) with floor heating in about 1/3 of the house and radiators in the rest of the house (which is in 2 stories where the radiators are). Attached is the standard system diagram for this installation, which is what I believe we have installed.

I have a few questions.

1. There are 3 temperature gauges for the accumulator tanks (which are well insulated behind a fiber board wall so i have not inspected them) - and I am unsure if these are the temperatures for each of the tanks or the top/middle/bottom temperatures of the primary tank. Any ideas?

2. The burner normally operates with a flue temp of between 180-230C for the whole burn. By the end of the burn, the top accumulator temperature gauge reaches 90-100C, while the other two reach only around 50C. I burn in the evening (finishing around 11pm) and the 3 gauges reach an equilibrium by the next morning of around 50-60C - by which time we get a couple of warm showers in the morning, and heating is ok through the day. Is this normal or should the three gauges increase and decrease at the same rate? (i'm still unsure what they measure - see question 1!).

3. There is a ceramic grate (in 5 pieces which fit together) for the floor of the boiler (above the flame trough) which are due for replacement (there is quite a large hole in the middle which should not be there). Should replacing these be a top priority for efficient burning?

Thanks for any advice in advance! I quite like the whole exercise with this form of heating, which certainly makes me more conscious of ensuring we don't overheat the house or waste hot water

 

[velvetfoot]

Here's a bump to the top for you, and a few lame attempts from a non stick wood burner. Hopefully somebody that knows something will reply.

0. Here is a link to the manual for others to refer to: http://www.nibe.eu/nibedocuments/10792/231312-1.pdf

1. I tend to think they are for the top/middle/bot. I think the idea is that the three tanks, with a total capacity of about 800 gallons, should act as one unit.

2. It is still not winter yet, even in Sweden. I think when it gets colder out you will appreciate more hot water in that 800 gallons of storage. I feel that you can charge the tanks more. Exactly how you do this might be an art, so you don't have extra heat you can't get rid of. This is where the subject matter experts should chime in, lol.

3. I would say yes. I have read of people who try to extend the life of their nozzles, but it's an iffy thing.

4. Any chance of contacting the original owner?

 

[craig73]

Thanks velvetfoot! Was hoping for a little more action on this thread

I did contact the former owner yesterday, and he confirmed that the temp gauges are top/mid/bottom as you wrote. He also said that the behaviour I experience is correct.

I think you're probably correct about heating to higher temps as the mercury plummets - it does feel a bit like an art and I've figured out that evening boiling suits our lifestyle more or less.

 

[velvetfoot]

For the middle and bottom to be only 50 seems low. You might not have enough "juice" to last the whole day when it gets really cold. But, if that was what the previous owner did, I guess you're golden.

 

[maple1]

The thing to learn will be judging how much wood to load in to get all the tank temps up to where you want them or need them. Trial and error. Although with some scales and math you might get in the ballpark. You likely got little response because nobody had heard of that boiler before. Good luck!

 

[velvetfoot]

Regarding the ceramics:
-Have you looked into replacing the ceramic grate? As in: availability and cost?
-There apparently is a sight glass for the to the fire trough. Maybe if you knew what you were doing the condition of the flame would tell you something, lol.
-I've heard of flue temp more related to whether the boiler needs cleaning (high=needs cleaning). I have no experience about whether flue temperature is related to nozzle (grate) condition. 180-230C (356-446F) doesn't sound that bad to me, but I'm no expert.

 

[jebatty]

My take on your questions and comments:

1) Three temperature gauges: the diagram shows the temperature gauges are one at the top of each tank, thus three gauges, each measuring only the top tank temperature of each tank. Your installation may be different from the diagram. I agree though that the three tanks are intended to act as one. A flow pattern based on resistance may exist to result in heating the one tank first and then the others. Plumbing design is tricky to get even distribution of hot water among separate tanks. Based on the diagram, it appears probable that the first tank is favored both for supply/return CP1 and for system supply/return CP2.

I don't see a reasonable way for one gauge to effectively measure the top tank temperature of each tank, and similarly one gauge for middle and bottom of each of the three tanks. Of course, the three gauges also could be simply measuring top, middle and bottom of only one tank and no measurement on the other tanks.

2) The disparity of the three gauges is consistent both with the gauges measuring only one tank and with the gauges measuring three tanks, if the plumbing is well designed.

3) Flue temperature is within a reasonable range.

4) The top gauge reading of 90-100C (194-212F) is high. I have not seen high temperature greater than 90C in the specs for any wood boiler. Shut down typically is in the 185-195F range. This high temp suggests than one tank is being favored, although with good plumbing design it is possible, although IMO not probable, that the tops of all tanks are the same.

5) The sharp differential in temperature between the top of tank from the middle and bottom is not unusual, so long as the supply to the tank top is not too turbulent. The longer the burn continues, the high temperature line will also move down the tank as the tank charging continues. This is good stratification occurring.

6) After the burn is over, and system draws continue from the tank, there will be warm water returned to the bottom of the tank from the system, and the tank temperature will tend to equalize top to bottom.

7) I think repair/replacement of the ceramic grate is important, both for efficient operation of the boiler and for protection of the boiler burn chamber from the high heat of combustion. The grate absorbs that heat and shields the steel walls of the combustion chamber.

=====
I hope you have a long and useful experience with your wood boiler. My Tarm now is in its 11th season of operation, trouble free. A quality boiler is a solid investment, and it is worth taking good care of the boiler and the balance of the system.

 

[craig73]

Thanks jebatty, maple1 and velvetfoot for the replies!

I believe the burner was installed in 2005, so it has been running 12 years. Seems like it will carry on a few more years with some maintenance (and now I get to know more about it, I'll invest some time).

Yes, it does have a sight glass... which probably needs a good clean because at the moment it's only possible to see that there is a flame when the lights are out in the boiler room! (and not quality of the flame). I'm aiming to optimise step by step and will research this more

I did manage to find replacement ceramics, and they have been delivered today, so I'll install tomorrow.

I had a confirmation from the previous owner that the temp gauges are top/mid/bottom and all 3 tanks act as one. I agree with jebatty that I can't see how they would accurately measure all 3 tanks, and it "feels like" they are measuring the primary tank only. If I heat the top to 90, but don't continue to fire to heat the mid/bottom past 50 to 60-65, the temperature drops real fast. And it takes A LOT of wood to get all temperatures up to a level that will give me a hot shower 24 hours later (seems like 50 is the lowest for a shower where my wife doesn't complain). We're also opening up another room shortly with floor heating (20m2 with high ceilings), so I'd better order more wood to get through the winter

I appreciate all of your insights!

(By the way, we are in southern Sweden where the temperatures are pretty mild - only 1 in 10 winters are truly cold. Up north they tend to use a little more moonshine to keep warm!).

 

[maple1]

You might want to consider some more temperature measuring things, in order to get a good handle on how it is all working together. Usually, a dT of 20°f thru the boiler is a decent figure. And return to bottom of boiler of 140°f is pretty well a given. Which means output to top of tanks of 140+20 = 160f or 71c+/- until you get all the storage water through the tanks once. So I think your temps on charging could be improved, thereby performance. When mine charge, the top rises to 160, then they eventually get to 160f throughout, then the top rises again another 20 to 180-185 or so. Then it stays at that while the rest of the tanks get to that.

So maybe to start measure the ins & outs (supply & return) at the boiler & seeing how that behaves though a burn. It almost sounds like your loading circ CP1 is pumping too slow. But can't be sure. And also if you add more temp things to all the tanks at all the same levels you could be sure they are flowing & charging evenly - which to me would still be an uncertainty at this point.

 

[velvetfoot]

It's been running 12 years, so something's going right! Does the boiler have a gauge for water temperature? Maybe that could provide some info, like if it's operating within temp. specification. Tanks could be pretty well stratified! I would think that as long as the charging pump is removing sufficient excess heat, the slower the better for stratification.

we are in southern Sweden

Are you in the Skane? I read all the Wallander books, lol.