Search the forum,

Discuss Buffer Tanks - 2 or 4 port connections in the Plumbing Jobs | The Job-board area at PlumbersForums.net

Status
Not open for further replies.
Yes providing the boiler is sized correctly.

That should go without saying and would apply to any system :biggrin5:

I'm wondering, there must be the need for the buffer/boiler set point to be higher than the heating flow temp in order for the mixing set to work properly and allow enough time for the boiler to fire.
 
I don't see how the system without the mixing valve would work properly as you couldn't have the boiler running and the system being serviced by the buffer. If you have the mixer valve, that provides the mechanical separation between the system and buffer, until the boiler has reached its operating temp.
I think I'll stick to simple boiler - buffer - heatload.
 
Once the heating pump is running the boiler and buffer are effectively working in cascade. The buffer temp and boiler output should presumably equalise although I can't quite get my head around how as the only input to the buffer is the return temp. Surely the buffer would theoretically become exhausted at some point? Or will the fixed flow rate from the boiler pump mean that the only flow through the buffer is excess to what the boiler pump can provide?

If that's the case then the buffer really isn't used much during operation in most circumstances (providing good design)

This would make sense as the buffer only becomes active to satisfy the boilers run time requirements and to provide heat when the boiler is starting up, or to make up any shortfall in boiler output for short periods of time.
 
Last edited:
Which will actually work in the way I was suggesting at the beginning of the thread. It just uses basic principles to achieve it as opposed to any controlled intervention.

Quite a clever set up if I'm correct, if I'm not then I've just wasted half my day thinking up a load of tosh. Where's Worcester for his opinion?


If you could control the flow to buffer depending on flow rate as opposed to temperature, it would make more sense.
 
Last edited:
Worcester's been having a day with family :)

I think we're there, and having gone round in circles as we've gotten our heads around it a combination of MissPlumb's and Nostrum's responses answer it.

i.e assuming the heating circuits use a mixing valve (room stat, external temp sensor, weather comp) and are managed by the boilers inbuilt systems, then the buffer provides instant heat the boiler then fires up only working at the level need to maintain heat demand, it also monitors the buffer, so if there is also a hot water demand or if the buffer tank is cooling - part of the heating return has to go that way if flow is coming from it, the boiler will ramp up and then after heating demand ceases, it will continue to heat the buffer up until it's replenished.

Needs a good boiler controller, so won't work properly with some of the simpler boilers out there.

ETA show basically the same configuration, so it works when the boiler has a comprehensive control system - this schematic presumes using the inbuilt eta controls.

If you're NOT using the built in controls and / or the boiler has simplistic management, or a cheap buffer that doesn't stratify well/properly, then I can see possible problems with plumbing it the 2 port way: increased cycling, buffer tanks not heated properly, poor performance of the heating sytem (client perception).

So what do Windhager / HDG recommend? - I know that Okofen reckon that they don't need a buffer on smaller systems perhaps for similar reasons.

So:
Using Froling/ETA built in heating controls, using indoor and outdoor stats, mixing valves on the heating circuits and their weather comp system, the boilers should run more efficiently. Reducing the flow through the buffer also helps to maintain good stratification.
If you're not using their control systems then a 4 port buffer is a 'safer' configuration as far as ensuring heat is always available, though may trigger greater full power cycling as opposed to modulation; subject to: programming the correct buffer tank control, by using multiple stats - as a minimum top and bottom stats, and now looking at the hysteresis programming of those stats. Once again the "simpler" boilers may not be able to handle those types of inputs and modulate properly.

I think we've finally answered my original question!

For the simpler heat pumps we have developed our own buffer controllers specifically to address this using two stats and hysteresis management. - The controller is less than ÂŁ100, needed a bit of lateral thinking to find it though :) ETA-PE-K-buffer.jpg

So next up is how do you configure the buffer tank control on / off points, what temperatures, what hysteresis?
 
My thoughts would be that the buffer set point would have to be at least 10 degrees higher than the design flow temp and the hysterisis would be maybe 5 degrees below set point to prevent any short cycling on the buffer reheat.

Realistically though it will depend on a lot if you want to be spot on, buffer size, boiler output, heating load.

Here's another thought, I'm contemplating using a buffer with hot water coil in one of the upcoming jobs so that we can use the space of the existing oil boiler and cylinder to house the buffer internally, rather than externally and have to export heat through underground pipe work constantly which will increase losses.

In the 2 port configuration, with heating on in depths of winter and customer runs a bath or has a long shower. Buffer temp will drop fairly quickly, heating pump will be on so flow to buffer will be reversed, how's the buffer going to remain charged?
 
In the 2 port configuration, with heating on in depths of winter and customer runs a bath or has a long shower. Buffer temp will drop fairly quickly, heating pump will be on so flow to buffer will be reversed, how's the buffer going to remain charged?

Same as with any 'small' buffer that could suffer depletion, in the 2 port case you would effectively have heating priority as opposed to in the 4 port case the possibility of reduced temperature in buffer, hence reduced flow temp to both buffer and dhw.

Could always use one of the strap on DHW heat exchanger units - both Froling and ETA offer them, flows up to 40l/min. "Virtual Combi". There again as soon as the Buiffer tank is being deleted the boiler output should raise to match demand up to it's maximum. Should work fine IF using the built in controllers.
 
But how's the boiler able to up any flow to the buffer if the heating pump is on?

The hydraulics don't allow flow to heating and buffer simultaneously from what I can see. You'd have to turn off the heating pump.
 
Just looked at the schematic for this set up and it seems they use an additional buffer sensor half way down the tank, maybe this tells the controller to stop heating if it reaches a trigger point?
 
Unless heat load = boiler output, there will be some spare capacity to heat the buffer. Hence you'll need to design boiler output in this case to cope full heat load plus an acceptable buffer recovery - actually that's no different from normal.

Practice says boiler size = heat load + 200W per person for DHW, if you had a property demanding full heat load, you'll still have a problem heating the DHW cylinder - it'll take a whiie. Plus boilers come in discreet sizes, not actual heat load size, so there should always be some spare capacity.

As you suggest it could also be charging to the middle sensor to ensure capacity for DHW.
 
Last edited:
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.
 
The buffer works when the boiler isn't even awake.

Demand established :-

Buffer satisfies load whilst boiler gets to 55c and flue up to 100c

Boiler hits :- 55c and flue 100c 3 port and pump wind in ..... Buffer still providing load satisfaction

Boiler hot and 3 port swings in:-

Buffer almost depleted but boiler coming on line.

Load side pumps pull from easiest route which is boiler now that the 3 way is playing ball.
 
Won't the boiler and buffer be asking for two separate temperatures though? If the return temperature is coming back in excess of what the boiler is looking for, 20 degrees differential for example, the boiler will modulate to try and match the load?
so unless the buffer is happy to run at 60 also (which is lower than the desired temp at mixer) I can't see how sufficient flow will enter the buffer to raise the temp?

Surely in the example I gave above, you could end up with a buffer at 60 providing no additional input to the heating circuit until the heating mixer pump turns off, at that point the buffer could be loaded by the boiler?

Thats fine for heating, but hot water production is relying on the buffer.

It's a shame they don't explain the controller in a little more detail, maybe most people aren't interested but I'd prefer to know the capabilities of the product in full detail rather than just pipe it up off a schematic as told. It's my companies reputation at stake at the end of the day.
 
Last edited:
The buffer works when the boiler isn't even awake.

Demand established :-

Buffer satisfies load whilst boiler gets to 55c and flue up to 100c

Boiler hits :- 55c and flue 100c 3 port and pump wind in ..... Buffer still providing load satisfaction

Boiler hot and 3 port swings in:-

Buffer almost depleted but boiler coming on line.

Load side pumps pull from easiest route which is boiler now that the 3 way is playing ball.

Yep we've gathered how the set up works on start up, but I'd like to know how the controller can maintain the buffer temp whilst under load.
 
It doesn't, the buffer is only there for peak load demand, once the boiler is up to temp it takes over the best demand and the buffer sits doing not allot as the least circuit of resistance is not through thousand of litres of water in the buffer. As Ermi said, once the demand has gone and heating mixers are diverting back to the boiler, then the buffer is re charged ready for the next peak demand.
 
This is why we don't use the 2 port method. Always have heat and boiler only fires on demand from the buffer
 
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
 
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.
 
Last edited:
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
 
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.
 
Last edited:
Yes but that has a mixing valve which allows the boiler to fire and run whilst drawing from the buffer
 
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 :)
 
Last edited:
Windhager controls have optimum start but they're in my opinion not very user friendly!
 
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
 
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.
 
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
 
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.
 
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.
 
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!
 
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.
 
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 .
 
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.
 
Status
Not open for further replies.

Reply to Buffer Tanks - 2 or 4 port connections in the Plumbing Jobs | The Job-board area at PlumbersForums.net

Creating content since 2001. Untold Media.

OFFICIAL SPONSORS

OFFICIAL SPONSORS

Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock