Buffer Tanks - 2 or 4 port connections

[missplumb]

This is why we don't use the 2 port method. Always have heat and boiler only fires on demand from the buffer

 

[Ermintrude]

2 port is a buffer 4 port accumulator which incorporates buffer. I've just fell off a ****ing wall in the dark. Should bay more attention to where I'm walking the dog at 23.17

 

[Nostrum]

As Worcester said you could use the hot water module on the buffer and pipe the boiler direct to the buffer and come out the other side to your heating. You then add the middle sensor to help monitor the buffer charging status. Difference between the two schematics you've shown is the ETA shows a shunt circuit with mixer valve, the Froling does not.
We have always used the 4 port buffer system, we set top of buffer to 80 min with 5 deg hysteresis and bottom off at 70 deg. We find that the systems are never short of heat as the buffer is always already 70% charged and boiler only fires using buffer sensors only.

That's how I would have done so prior to this conversation, but if you are being recommended to pipe it in another way to increase efficiency then you've got to look at why?

For me, efficiency is top of the list, after all, that's what it is being sold on. For you perhaps being non domestic, efficiency is lower on the list because of the non domestic RHI returns.

The domestic RHI covers the majority of the upfront cost but for it to really stack up financially, it needs to be as efficient as possible for the long term.

 

[missplumb]

For non domestic rhi, it's more about making the boilers last the 20 years, when we commission and put the fga on, we still have them running at 92-94% efficient, it's what the rest of the system does with that heat.
Ermi, a 2port would be used as an accumulator and the 4 port would be the buffer as it is inline

 

[Nostrum]

Just spoken to the technical team at ZCF. Very interesting and the boilers controller is smarter than I first thought.

The controller can load the buffer and export at the same time. On the P1 and P4 the modulating pump is purely for buffer loading. The boiler uses the internal water ways as Worcester talked about to divert flue gases through various sections of the boiler to achieve the required return temperature, eliminating the need to a return riser. If the buffer temperature drops, the buffer pump will run and the boiler will charge the buffer to the desired set point and provide output for export until it cannot modulate low enough to continue running. When this happens the boiler will switch off, buffer pump goes off and export will come from buffer only by reversing the flow on that section of pipe. So interestingly, the boiler and buffer don't appear to be able to output simultaneously.

The mixing valve ensures water is only circulated through the export with a minimum temperature as well as a set flow temp. The ESBE controller can also be directly controlled through the boiler controller for weather compensation for blended heating flow but maintain the higher set point for the buffer.

 

[missplumb]

Interesting, mind you ive not looked at the Froling pellet boilers as all we do are chip.

 

[Nostrum]

Same setup for chip

 

[Nostrum]

Even upside down as well!

 

[missplumb]

Yes but that has a mixing valve which allows the boiler to fire and run whilst drawing from the buffer

 

[Worcester]

Yep, we're back to the capabilities of the controllers and boilers. With the changes to the RHI, we're finding that the clients are also looking at the most efficient way to control the heating, and using the built in controllers in both ETA and Froling you'll benefit from weather compensated flows to the heating circuits and hence higher efficiencies from the boilers.

If you're not using the built in controllers, then the next most efficient is to use the 4 port buffer.

Next thing is self learning optimised start - we have that built in to our heating circuit controllers that we use with underfloor heating and heat pumps - typically the Heatmiser controls, they offer both comfort levels (i.e different temperatures at different times of day) as well as optimised start. At the moment I'm not aware that either ETA or froling offer optimised start - YET

 

[Nostrum]

Windhager controls have optimum start but they're in my opinion not very user friendly!

 

[missplumb]

We don't use the built in controllers as most of our systems are district heating pumped from a remote plant room to PEX so temperature control becomes a bit more awkward

 

[Worcester]

Are you mixing the flow as it leaves the buffer to keep the temperature down in the heat distribution mains? I am aware of a few doing that so as to allegedly prolong the life of the heat main.

 

[missplumb]

No, it generally leaves the plantroom at about 80 and according to the rehau rep, the pipe can easily cope with them temps fire the duration. I don't see the point in heating the buffers up and then cooling it before it leaves

 

[Worcester]

The reason for different temperatures is to operate all parts of the system at their most efficient temperatures.

Biomass boilers work well with high output temperatures, and controlled return temps. (say 80/60)

Most heating systems for houses in a retrofit environment should have been designed for condensing boilers, so would be expecting 65 flow /55 return.

You lose more heat through a district main pumping at 80° than at 70° because of the temperature gradient.

Do you therefore mix down at point of use? If not then you'll presumably that means greater cycling of the end user heating system, are the end user control systems updated? - Are the end user heating systems rebalanced and flow / return temperatures of the radiators optimised as part of the installations?

There are loads of extra efficiencies to be had that way. So far all our clients are using significanlty less than predicted when they have comprhensive heating management systems in place.

 

[missplumb]

Where necessary our temps are reduced at point of use but the reason for the higher temps is that the systems we retrofit into are old stone stately houses with over 100 rooms, old column rads, no temperature control and they are tight with they're money. They are not interested in altering the internal plumbing because "it worked before on the oil boilers" and because we are financing the systems anyway they don't want anything disturbed because other than a cheaper fuel bill, they don't get anything out of it.

 

[Nostrum]

Unfortunately there are buildings out there now that have never been heated before as its not required, with a biomass boiler installed burning wood for the fun of it. Like wise although a renewable technology is being used, energy efficiency goes out the window as it has an opposite effect on the repayments. It all makes a mockery out of the whole scheme really.

We went to see a district system in North Devon, no lagging on any of the pipe work, all the pumps and HIUs purposely fitted in outside 'sheds' with no insulation etc

In some respects I'm glad the tariffs have dropped. I'm in it for the long haul and just hope the domestic tariff dropping is enough for the gold rush installers to move on, leaving the rest of the money to fund the customers who make the most of it.

Oddly we are getting more enquiries now for biomass then were we 2 months ago. Fortunately the customers aren't solely interested in it for any return. I just hope it continues like that!

 

[Worcester]

Yep, it's one of those anomalies, if you're metered, you'll consume as much as possible. Even in the domestic market, when we install systems to maximise efficiency, if they aren't using up to the EPC figure, then open the windows and wind the heat up else you'll never get the maximum back, and when the payments are greater than the cost of fuel that's what the clients (some of them not all) will do.

 

[missplumb]

I agree, but there is a big difference in thinking between the domestic customers with sub 50kw boilers and the larger commercial customers we have. Wealth breeds wealth, that's all they think about - how much they can get for least outlay. Domestic customers i guess would be much more receptive to having the most efficient controls and systems fitted as the benefit to them is cheaper bills.
We've been to see installations on farms where they have installed copper pipes in the concrete yard to warm the tractor tyres! !!!! And warm air blowers fitted externally .

 

[Nostrum]

Yep, it's the way of the world. People will find a way to make money out of anything. They should have sewn up the loop holes long ago, somehow. with the amount of money they are giving away they should be doing more inspection to check eligibility. Perhaps they will, I hope they do.

 

[Worcester]

Just for info read here, the press rumors are circulating like wildfire that there will be an announcement at 7am tomorrow morning...
Here we go again- Feed in tariff cuts to come in weeks | Electricians Forums

Got my DECC twitter feed on ...

 

[Nostrum]

The rumours have been kicking around for solar and on shore for a while, hopefully not a repeat of 2011, do you still do much on the solar side?

RHI is guaranteed until 2016 I believe? Although judging by that meeting, there doesn't seem to be much in the way of security for it beyond then.

The difference with solar/wind and renewable heat is that solar is an emerging market still and a lot of money has gone into the R&D of the technology, which has led to a sharp fall in manufacturing costs. Much of the renewable heat market already existed, we've just been late adopters to it all.

As a small company we're very competitive and can often spec a much better system for less than our competitors. Theres not much room for movement, the capital cost won't come down like it has with wind and solar, maybe it could for non Domestic, the latest cuts will soon see. In fact the RHI may have inflated the installation costs at the beginning?

 

[Sparkgap]

We put in a couple of pellet boilers to feed a couple of primary schools about 9 years ago. Absolute disaster! Ripped out one after a couple of years and put oil back, other went about three years later, a year after the manufacturers replaced the boiler with another! :banghead:
One site didn't have a buffer tank to start with, soon had the biomass boiler bods changing their minds and saying it needed one putting in as boiler needs to develop a temperature difference from top to bottom to provide a load. Did that but school eventually got sick and tired of the boiler and wanted it out.
Also did a survey at a new PFI school in Bedford four years ago: both Hovel pellet boilers had broke within 6 months to a year of opening, school didn't bother fixing them and happy to run on backup gas boilers as problems with dust from pellet store was causing problems.

 

[missplumb]

we have taken out quite afew biomass boilers from schools, but when you looked at the system, they were never designed correctly and tbh, the boilers were s~*t, but 10 years ago we didnt know any different. we have replaced some of these boilers with new ones, altered the systems and controls, and had them accredited to Rhi which makes a huge difference to them - and now they are much happier using them.
i just think there wasnt enough technical knowledge in the uk about biomass back then!

 

[Sparkgap]

we have taken out quite afew biomass boilers from schools, but when you looked at the system, they were never designed correctly and tbh, the boilers were s~*t, but 10 years ago we didnt know any different. we have replaced some of these boilers with new ones, altered the systems and controls, and had them accredited to Rhi which makes a huge difference to them - and now they are much happier using them.
i just think there wasnt enough technical knowledge in the uk about biomass back then!

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!

 

[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:

 

[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.