Buffer Tanks - 2 or 4 port connections

[ShaunCorbs]

The other issue is staff not wanting to get dirty clearing the ash. One site the caretaker said it wasn't in his job description to clean out the boiler!

im sure something can be made so it dumps the ash into a galv bucket and the site manager (caretakers new job description ) empty's/ spreads on garden

 

[Worcester]

im sure something can be made so it dumps the ash into a galv bucket and the site manager (caretakers new job description ) empty's/ spreads on garden

It can be, where there's a will there's a way. All of the systems of that size that we install have the option of automatic ash removal into multiple ash storage containers.

However if your agin' it no solution will be acceptable..

 

[JonG1]

Just had a read through of the thread, interesting stuff. Has anyone seen the CIBSE pdf on best practice biomass design considerations,I have attached it but not sure if it will work. If not PM me and I will send it direct.

Somewhere I have another which details a crop of low performing systems, which included oversizing, small buffers, PHE, high temps and no WC in district mains etc etc. basically a lot of the themes discussed here.

We are ETA through and through, and have been through various discussions with tech about how best to ste up. The standard Austrian approach is evidently as per their schematics with 2 port buffers, but they are very wary of promoting this approach, because if the system pump isn't sized correctly their contention was that it can overpower or conflict with the return riser and draw too much heat away from the boiler.

The benefit is that the boiler and buffer can as as has been discussed work together to cover a larger load, destratify slower or satisfy the heat demand as the boiler comes to temp but with lower destrat levels.

We have done it once on a log gas boiler and it does work well, 30m of pre-insulated in a pipeline set up, DHW priority, WC for heating so it ramps to full output for the cyl and then drops back to the curve once satisfied.

Not had the balls to do it again tho or on a bigger system, always default to the 4 port!

 

[Nostrum]

Just finished a Froling log boiler as per the 2 pipe method, weather compensation and DHW. As above, works well, heat even when the buffers not loaded.

Strangely, Hargassner suggest a 4 pipe method for pellet, 2 pipe for log. Possibly due to buffer volumes.

 

[Norcs]

A buffer, volumiser, accumulator, thermal store etc should only be fitted as a last resort as they only add to the heat load, add a lot of cost to the install and lose heat for a past time.
If the boiler modulates or good control can be added to avoid cycling then that's the way to go.

 

[Worcester]

Y

A buffer, volumiser, accumulator, thermal store etc should only be fitted as a last resort as they only add to the heat load, add a lot of cost to the install and lose heat for a past time.
If the boiler modulates or good control can be added to avoid cycling then that's the way to go.

So wrong. When used properly they can dranatically improve efficiency.

Agreed boiler modulation and good controls are an important part of the mix. There are lots of reasons why and circumstances when you should include a buffer or similar.

 

[Norcs]

Theres no data out there to suggest they increase efficiency. Quite the opposite most likely.

 

[Nostrum]

Buffers cannot always be designed out. It depends on the heat sources operating characteristics, start up time and efficiency, minimum run time, operating efficiency at full output etc etc

Then you have to look at the system it is installed onto to see if they are compatible, uncontrolled water volumes, flow rates, demand etc


It's a sweeping statements to say they should always be designed out. I would agree that hey aren't always required, but often not having a buffer can create a whole load of efficiency related issues if they aren't available.

It's particularly awkward when retro fitting into an existing system. Designing out often isn't an option without major disruption. Hence why most biomass installs will incorporate a buffer.

In a perfect world we'd be installing new systems where everything is calculated prior to install, in reality, we're having to make some assumptions on existing systems and walk away knowing we're not going to be called back.

 

[Sparkgap]

A buffer, volumiser, accumulator, thermal store etc should only be fitted as a last resort as they only add to the heat load, add a lot of cost to the install and lose heat for a past time.
If the boiler modulates or good control can be added to avoid cycling then that's the way to go.

It might be possible to design out a buffer tank, but in most cases they are required to provide a heat sink due to the slow response of biomass boilers. The first school I put biomass in had a system designed by a 'professional' biomass company and no buffer. Problems galore! Next they put in a buffer to handle when the system was on low demand/shutting down and also to give the boiler something to work against. Four years of grief later we ripped it out!
Incidentally, just been designing a system for some blocks of flats which uses a buffer to handle sudden demands so the size of the boiler plant can be reduced. Installed one several years ago at a site which wasn't on the grid to take surplus energy from a wind turbine and use it to heat up water for the heating system which reduced the amount the oil boiler had to run. Works a treat!
Horses for courses.....

 

[missplumb]

im going to look at a new install district heating system to 3 blocks of flats with 249 flats each with its own HIU, 8kw heating, 37Kw hot water. The plant room has a 201kw herz pellet boiler and 10000 litres of buffer as the lead boiler and then 3x 530kw gas boilers as backup. we are tendering for the service contract for the whole system. looking at the schematics for the plantroom or "energy centre" its all gonna go pete tong .

 

[Worcester]

Buffer and boiler sound way to small ...
Sounds like they should have done it all on gas from the beginning
As anyone done a proper hourly heat demand calculation over a 7 day and monthly profile?

 

[Sparkgap]

Buffer and boiler sound way to small ...
Sounds like they should have done it all on gas from the beginning
As anyone done a proper hourly heat demand calculation over a 7 day and monthly profile?

Course they haven't! That takes time and money!! :tongue3:
Even just for heating they're 200kW light, then take into account a proportion of them running a bath/shower/sink at once when Coronation Street finishes and I reckon it's going to get a bit parky!

 

[missplumb]

It was an absolute joke. The peak heat load worked out they say at nearly 1.6mw, and part of the agreement is that the biomass boiler covers 70% of that. No chance!!!!. Then they reckon the heat loss over the whole system being in mind there is 230 hiu's, all pipework above and below ground is 5" steel, is only 8%.loss.which is to be taken on the chin in our price. We reckon the heat loss will be nearer 40%. And the flue!!!!!, 250mm, no fans other than the draught fan on the boiler, has 4x 90 degree bends, and then runs up the side of the flats for 18 floors.

 

[Norcs]

View from across the pond....
https://blog.heatspring.com/2-pipe-versus-4-pipe-buffer-tank-configurations/

 

[Sparkgap]

It was an absolute joke. The peak heat load worked out they say at nearly 1.6mw, and part of the agreement is that the biomass boiler covers 70% of that. No chance!!!!. Then they reckon the heat loss over the whole system being in mind there is 230 hiu's, all pipework above and below ground is 5" steel, is only 8%.loss.which is to be taken on the chin in our price. We reckon the heat loss will be nearer 40%. And the flue!!!!!, 250mm, no fans other than the draught fan on the boiler, has 4x 90 degree bends, and then runs up the side of the flats for 18 floors.

Some funny figures there. Heat loss from 5" pipe will depend on the type of insulation and temperature difference, but digging out my trusty *** packet I'd guess about 35-40W/m heat loss per pipe assuming 40mm insulation thickness. As for the loadings, heat losses give you 1992kW (8kW x 249). For hot water the coincidence factor for that number of HIUs comes out about 0.08 so for 37kW x 249 gives 737kW. Total 2729kW, which is some way from the 1700-odd kW you mentioned! Or perhaps they're not supposed to have hot water in winter? :vanish: