Buffer Tanks - 2 or 4 port connections

[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:

 

[Worcester]

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

Interesting post, a bit lightweight though considering his 'qualifications' and disappointingly from such an expert nothing new there that hasn't already been covered in this thread.

The BIG thing that he misses though is how Log gasification boilers work, and the REQUIREMENT to be able to use all the heat from the fuel load at the maximum efficiency.

Their are also the significant benefits of being able to apply weather compensation to the flow to the rads and still maintain the boiler at its maximum efficiency.

 

[Worcester]

Remember that the heat loss from the pipework will most likely be going into the fabric of the building, so be careful not to count it twice - it's common practice to include the pipe losses as part of the emmitter output in large systems.

Even so it sounds significantly undersized and a recipe for disaster.

With a stack that high, won't the bigger problem be too much draught?

IF you take it on, first part of the contract should include a design revue...

 

[Nostrum]

Cooling of the flue gases with such a large external run would be my concern, condensation etc. Although being an induced draft I'm not entirely sure if I'm honest.

The sizing tends to suggest that the biomass is to cover a base load ( buffers to smooth out and absorb heat main losses) with the gas boilers ready to fire for peak demands, hot water etc. I'd be interested to see the design calculations.

Where did you get the heat load figures from? 8kw for a flat seems high. 37kw to hot water would give a flow rate of approx 13-14ltrs/min. Even running a bath would would only require a demand at that rate of approx 5 mins.

 

[missplumb]

They were in the spec that Wilmot Dixon sent us as part of the tender docs. We gave them 3 options, we put in a ridiculously high price to cover all the penalty fines we would get for not providing enough heat via biomass, or we knock the energy centre down, and build a new one with a suitably sized boiler that will cover all heat load all at our cost and we collect rhi, or we speak to Leeds council and have the terms amended to a deliverable outcome. I think option1 is the only thing they will want to do.

 

[Sparkgap]

Cooling of the flue gases with such a large external run would be my concern, condensation etc. Although being an induced draft I'm not entirely sure if I'm honest.

The sizing tends to suggest that the biomass is to cover a base load ( buffers to smooth out and absorb heat main losses) with the gas boilers ready to fire for peak demands, hot water etc. I'd be interested to see the design calculations.

Where did you get the heat load figures from? 8kw for a flat seems high. 37kw to hot water would give a flow rate of approx 13-14ltrs/min. Even running a bath would would only require a demand at that rate of approx 5 mins.

Looks like an existing block, so probably insulation not all that great. Also what size of flats there are. Just looking at heat demands and HIUs for some new 1-2 bed flats at the moment, which are working out at between 3-5.5kW each for heating.
Hot water loading for HIUs is about 35-40kW depending on make then you take into account the coincidence factor (I'm using DS439) so for 249 flats it comes out as about 0.08.

I agree with Worcester about having weather compensation for the rads and if this was individual condensing combi boilers to each flat it would enable the boiler to work at maximum efficiency. However in this case any compensation would have to be done after the HIU on an individual flat basis, probably not feasible, as you'd still have to keep the mains at full temperature 24/7. Best for the biomass to tick over keeping the buffer/mains satisfied and the backup gas to kick in when needed.

 

[Worcester]

Option 3 is the best 'win/win' solution, however that requires them to admit that the existing installation isn't up to the job, which they are unlikely to do.

The Council won't have its own heating experts and will have appointed a consultant to advise them, it would take a heck of a lot to admit that the consultant was wrong.

Knowing the way councils work, they are likely to choose option 1 and then when (if) you win it, prepare option 2, the problem you'll have is that they'll then want to go to tender for option 2... Councils!!

 

[Sparkgap]

The Council won't have its own heating experts and will have appointed a consultant to advise them, it would take a heck of a lot to admit that the consultant was wrong.

Having worked for three councils, two contractors and done consultancy work as well it now seems that many councils have got rid of the people who actually know how things work and just hive off stuff to some favourite consultancy! The consultants in their turn don't seem to bother designing the jobs and just churn out a load of standard spec clauses and expect the contractor to design and price the job in only a few weeks :83:
My latest job at a school was tendered out by some :asshole: who threw several pages together, missing a load of stuff, didn't bother to do a proper survey of the site to actually find out what needed doing..... you get the picture! And this on a job which needs to be done ASAP and is probably in the region of £300k. Must have money to burn!!!
As I said to the estimating guys, make sure you clearly state the exclusions in our price coz I can see somebody coming a cropper.

 

[Norcs]

There's always option 4.
Knock that great ugly monstrocity off a building down.
Which floor is del boy on?

 

[Norcs]

All councils have money to burn. That's why you pay extortionate council tax.

A worker at my local council office blew the lid on the amount of tar that they dump.

An official on a large salary goes out with some yellow paint and marks the pot holes that he has decided should be filled.
For some reason the tar gang are not allowed to just fill every hole they come across.

The tar gang goes out and fills the holes he has marked and at the end of the day several tons of expensive tar is dumped which was paid for by tax payers.

 

[missplumb]

The original tender design was done by consultants in London and a spec produced for pricing. Wilmot Dixon won the contract on that spec. When the contract was signed, the consultants pulled the design and said WD had to use their own design to which they just rebadged the original with out checking to see if it will do the job, so the responsibility lies with them. Hence the QS sat with his head in his hands when we said it won't work. No one had told him why, the just refused to price the job.