Bypass when using Grundfos Alpha2 pump

[smokebox]

Mysteryman

I quite agree - simple but safe, including equipment protection!

I have actually just 3-4 days ago installed the weather compensation VR430 etc and am full of hope you are right. The 'unload rads' I have are "inside the zones" and rightly or wrongly I worry about boiler flow immediately after zone closure & flame switch off. There are bound to be some very hot, potentially damaging hot spots - indeed it was bangs and explosions at this point that started me focussing on these issues.

My scheme is quite simple and cheap, as suggested by Grundfos. The only flaw is the needless bypassing during ordinary function. My settings as quoted for the flow volume give about 10% bypass of full load flow (worst case scenario I think). Depends a bit exactly where the autoadapt has put itself in its operation region, and relates to the flow resistance of the flow setter and pump output pressure.

In truth the boiler can do brisk shut downs (if starting to cycle on attempted fire up) even with these fancy controls. This is not so bad as the original situation where an old fashioned timer/thermostat programmer could abruptly shut the zone on full power for its "rest period" early in a heating phase algorithm, before it had reached target. I think it was quite a spphisticated Programmer even with limited learning capability nonetheless - Landis & Gyr REV20 some 12 yrs old.

Nobody has commented on my solenoid controlled valve for bypass idea. It would open on closure of all zones, otherwise closed. Good bypass in flame switch off pump overun, no 'condensing wasteful' bypass during zone(s) open. It would have to "activate" quickly to be effective or an ordinary 2 port zone valve might have done.

 

[Agile]

Over complication is not a good idea with heating design.

No one else has ever wanted to do that because they all use a normal pump which raises its pressure as load flow reduces and so creates a pressure high enough to proportionally open the ABV.

I dont know where you get this idea of hotspots! All that is needed is to have adequate flow through the boiler at all times when firing and for several seconds afterwards.

In your case it sounds as if the flow stopped abruptly causing boiling in the HE.

If I had not heard it I might expect there was a lime buildup in the HE. That does not need time to build up. I have seen it in a just installed boiler when incorrect procedures were used in the commissioning. It was so bad that flakes of scale then blocked the boiler flow switch.

Tony

 

[smokebox]

Over complication is not a good idea with heating design.

No one else has ever wanted to do that because they all use a normal pump which raises its pressure as load flow reduces and so creates a pressure high enough to proportionally open the ABV.

I dont know where you get this idea of hotspots! All that is needed is to have adequate flow through the boiler at all times when firing and for several seconds afterwards.

In your case it sounds as if the flow stopped abruptly causing boiling in the HE.

If I had not heard it I might expect there was a lime buildup in the HE. That does not need time to build up. I have seen it in a just installed boiler when incorrect procedures were used in the commissioning. It was so bad that flakes of scale then blocked the boiler flow switch.

Tony

We are in a virtually lime free area with good mountain peaty acid water! The boiler was brand new. It is not a blockage problem., of any sort. Dolt though I may be I had considered that.
Then please explain about kettling and my very loud bangs and damaged heat exchanger!
I could of course go backwards in time to a fixed speed pump, or even gravity circulation and huge bore pipes. But really I at least am moving with the times.
Incidentally the main idea I had (like Grundfos's) was to save electricity, more than noisy TRVs which have never been too bad (Pegler Terriers). Indeed legislation will be enforcing this economy shortly as Lord Hailsham has mentioned!

 

[smokebox]

to Agile
The Vaillant senior area technician had an interesting way of testing the Heat Exchanger. He had a feeler gauge (about 1mm I think) which he ran round and round the spiral of thin walled tubing. Where it got stuck he knew there must have been distortion and /or pipe swelling.

I thought you just possibly might not have known that, fearfully learned though you be. I personally like new interesting information.

Other than that is there any problem in principle with my solenoid suggestion, apart from it being new and "complicated" in your view? Obviously your approach with a fine big high pressure pump is one way dealing with the matter, but without even a nod at efficiency in gas or electricity consumption, and good luck to you and your customers.

Smokebox

 

[gaswizzard]

to Agile
The Vaillant senior area technician had an interesting way of testing the Heat Exchanger. He had a feeler gauge (about 1mm I think) which he ran round and round the spiral of thin walled tubing. Where it got stuck he knew there must have been distortion and /or pipe swelling.

Did the vaillant engineer find any 'binding' within the spiral of the Hex? , other ways of deciphering whether Hex is distorted other than the use of a feeler gauge.

Other than that is there any problem in principle with my solenoid suggestion, apart from it being new and "complicated" in your view? .

Not new & not complicated but as said other ways to skin a cat.

Maybe a typo error regards return water temp @ 15c? , assuming return water temperature can never fall below room tempreature i'm a little confused.

 

[D_Hailsham]

My scheme is quite simple and cheap, as suggested by Grundfos. The only flaw is the needless bypassing during ordinary function.

You said you are concerned about the high return temps this could give an the consequential lack of condensing. There could be a way round this.

You said, on page 1, that the calculated heat loss is 11kW and you have 24kW of rads. You also said that the heat loss was for a 20°C differential, which is a bit on the low side as most calculators assume a room temp of 21°C and outside temp of -1°C. But I'll assume you meant a 20°C differential. You also said the temperature had gone down to -5°C last winter and you like warm rooms, say 22°C; that's a 27°C differential. So you would need a 14.85kW boiler (11 x 27 ÷ 20) say 15kW just for the heating.

You then said you have 24kW of rads. The output of a radiator is not constant, but varies with flow, return and room temperatures. The quoted output is measured at 75°C, 65°C and 20°C. For the boiler to condense, the return temp has to be below 55°C, so if the flow temp is 75°C the differential is now 20°C. If the room temperature is 22°C the radiator output will be approx 19kW, which is the output required for a 34 degree differential between room and outside (-12°C when its 22°C inside!).

You could probably run your boiler with a flow temp of 70 and return temp of 50, which gives rad outputs of 16kW. The rads would have to be balanced to have a 20°C differential between flow and return.

How have you managed to get the VRC430 to work with two CH and one HW zone? Presumably you have used a VR65 as well. But that only allows for one CH and one HW.

 

[smokebox]

to Agile
The Vaillant senior area technician had an interesting way of testing the Heat Exchanger. He had a feeler gauge (about 1mm I think) which he ran round and round the spiral of thin walled tubing. Where it got stuck he knew there must have been distortion and /or pipe swelling.

Did the vaillant engineer find any 'binding' within the spiral of the Hex? , other ways of deciphering whether Hex is distorted other than the use of a feeler gauge.

Other than that is there any problem in principle with my solenoid suggestion, apart from it being new and "complicated" in your view? .

Not new & not complicated but as said other ways to skin a cat.

Maybe a typo error regards return water temp @ 15c? , assuming return water temperature can never fall below room tempreature i'm a little confused.

So its been done before - solenoid idea ? do you know if it works satisfactorarily?

What's this story about 15*C return temps - apparently below room temp - unusual but by no means impossible! Wouldnn't last long if heating was put on. But I can't see relevance or where it comes from!

Yes he did find pinching of the feeler gauge enough to tell him something was amiss, though he thought the exchanger still viable, But at risk for earlier failure than might be expected.
I don't know if he had any other techniques for testing but this seemed quick and effective. I was quite impressed, but I am not a heating engineer as Agile likes to remind me!

 

[Agile]

You dont seem to be telling us the whole story!

You now say a Vaillant staff engineer has been examining your boiler and found the heat exchanger has been distorted!

This would apparently have resulted from overheating after the demand has ceased as you dont have any pump over run because you choose to use a non compatible smart pump.

I would normally expect a manufacturer to condemn the boiler as at risk following damage to the main HE and to refuse to give any warrantee cover on it because you have unilaterally decided to operate it outside the manufacturer's parameters!

Tony

 

[smokebox]

My scheme is quite simple and cheap, as suggested by Grundfos. The only flaw is the needless bypassing during ordinary function.

You said you are concerned about the high return temps this could give an the consequential lack of condensing. There could be a way round this.

You said, on page 1, that the calculated heat loss is 11kW and you have 24kW of rads. You also said that the heat loss was for a 20°C differential, which is a bit on the low side as most calculators assume a room temp of 21°C and outside temp of -1°C. But I'll assume you meant a 20°C differential. You also said the temperature had gone down to -5°C last winter and you like warm rooms, say 22°C; that's a 27°C differential. So you would need a 14.85kW boiler (11 x 27 ÷ 20) say 15kW just for the heating.

You then said you have 24kW of rads. The output of a radiator is not constant, but varies with flow, return and room temperatures. The quoted output is measured at 75°C, 65°C and 20°C. For the boiler to condense, the return temp has to be below 55°C, so if the flow temp is 75°C the differential is now 20°C. If the room temperature is 22°C the radiator output will be approx 19kW, which is the output required for a 34 degree differential between room and outside (-12°C when its 22°C inside!).

You could probably run your boiler with a flow temp of 70 and return temp of 50, which gives rad outputs of 16kW. The rads would have to be balanced to have a 20°C differential between flow and return.

How have you managed to get the VRC430 to work with two CH and one HW zone? Presumably you have used a VR65 as well. But that only allows for one CH and one HW.

My lord
I have been thinking!

First, you are right .There is additional gear - in fact a VR61 and VR81 (in upstairs zone).
The VR61 is near the boiler and zone valves . As opposed to the VR65 it allows separate control of 2 CH zones, and a single DHW zone. I am using simple 2 port zones for all. Actually there are 2 quite big cylinders, and 2 separate DHW zone valves I am planning to simply yoke the valve motors in electrical parallel to begin with, until I have worked out a crafty method of separating their control, 'cos one gets used much more and in a different pattern from the other. In order to have more accurately adjustable cylinder target temps, I am using the Vaillant VR10 NTC on the biggest cylinder at he moment as a 'proper' sensor, which gives finer more flexible control than simple tank stats which would however be useable. A special and not frequently used connection for this sensor to the boiler board is being procured for me (a Vaillant part that only the higher cognoscenti know about!)It plugs the sensor into the block of white square pin connections labelled X2 on the manual drawings. [ NOT the edge connector used for the external sensor but very close to it]

Turning now to your temperature settings for Radiator flows I need a bit of reassurance. My understanding of radiator output power is based on fairly standard figures of 75C flow and 65C return thus giving a notional mean of 60C. The next assumption is the room temp of 20C hence the Delta 50 banded about. ie difference between rad mean and room temp. The so called 75,65,20 system for quoting output rates. these are rarely perfectly accurate, as there is no such real thing as a mean radiator plate temperature, but it is a start.
If the room is colder we will have a larger delta T and higher outputs. likewise outputs differ if radiator means are changed, as they always are by eg TRVs or boiler flow temp, pump flow etc. This relationship is not linear and I have a delta T table of correction factors that Agile will know all about. I rarely use it!
I hope I have this correct?

You are right I calculated Radiator output wrongly and in the old fashioned way on a basis of 50*C difference between mean rad and rooms at 20*C, and the heat loss on a differential between inside and outside of 20 rather than more modern 21*C Based on expected -1*C temps rather than 0*C outside. - global warming??!
The rads are very large fortunately Absolutely no insulation in 1913! and now exceptionally good. A lot of them are renewed, but I kept them oversized on purpose.

I reasoned I could run the radiators cooler, and obtain better and lower average return temps. While reasonable condensing will occur at 50 or even 55*C returns , benefits are actually considerably enhanced at even lower return temps. Later I may try to post relevant efficiency graphs for return temps in gas and oil boilers, but will need to work out how.

Since absolute maximum efficiency is my underlying aim I am a bit reluctant to set boiler flow even half a degree more than necessary! (boiler efficiency is also enhanced the cooler the flow can be set)

When I look at what I have just written I see I am in principle restating your observations and calculations, though I may be a bit more ambitious to get my boiler flow temps lower than you, and I believe that with my gross rad oversizing and careful balancing this will be possible. I am getting surer and surer I will probably need a bigger but still modulating circulation pump. I don't think the installer took the very high boiler flow resistance and length of pipe runs into account. I don't think he did at all, or even knew how to make such calculations, but this could be a vile calumny!

Bye the bye, another big efficiency saving I hope will be moving the boiler from a small 'outhouse' into the Kitchen and inside the heating "insulation envelope". This has also got rid of 9 22mm or 28mm hot pipes running uninsulated through a simple cold bare tiled roof space 23 feet long facing North on one flank! I haven't worked it out but that move alone is possibly saving 2kW! The plumber thought it a waste of time but I insisted. Curiously on gas flu temps and co2 content etc the boiler had a pretty good efficiency of 73% not too bad for late 1950s!

Do you think it will be feasible to run boiler floe beloe 70*C?

Also could you comment on my solenoid valve bypass scheme?!!

Smokebox

 

[Dan Robinson]

Its not much of an idea really... How do you control it. Opening a valve when the system shuts down is easy enough, but what regulates it? What closes it when the need is no more?


Perhaps a MIMO zone valve on a timer with a flow regulator such as the one you linked to (altho0ugh they are very susceptible to system debris BTW).

Like I said opening is easy, closing at the right time - I dunno.

As has been said before. You are over thinking a problem. Way way way over thinking.

 

[smokebox]

You dont seem to be telling us the whole story!

You now say a Vaillant staff engineer has been examining your boiler and found the heat exchanger has been distorted!

This would apparently have resulted from overheating after the demand has ceased as you dont have any pump over run because you choose to use a non compatible smart pump.

I would normally expect a manufacturer to condemn the boiler as at risk following damage to the main HE and to refuse to give any warrantee cover on it because you have unilaterally decided to operate it outside the manufacturer's parameters!

Tony

Agile
I never said anything about Vaillant technicians as it has not been relevant to my initial discussion of bypassing. He did not know the correct 'domestic' answer. Incidentally he thought my plan (proposed only at that time as suggested by Grundfos was sensible, and clearly understood the problem approaching concerning enforced use of more efficient pumps of this type. He could see that an auto bypass was illogical though enforced by regulations already, and on reflection he considered that across the nation they were leading to a lot of waste gas which concerned me and made him think a bit. I gather a million are already installed almost all wastefully bypassed. He admitted Vaillant were not on top of the matter in the advice dept and were deciding what to do.

For your information, though you know a great deal more than I about heating installations, the Alpha2 pump works perfectly on overrun. What are you talking about?
He was a very senior, helpful man with high intelligence.

They have not given me a warranty - you are right, but he did not think it had to be condemned thank goodness. The Plumber will be placing a new HE in front of me with all relevant parts before I pay his bill!! I decided not to accept his offer of a twelve year free guarantee in lieu as I doubt his firm will exist that long!

I always find your contributions exciting and provocative - please keep it going! you've certainly got it in for smart pumps haven't you. Get yourself into this century as soon as you can!

smokebox

 

[smokebox]

Its not much of an idea really... How do you control it. Opening a valve when the system shuts down is easy enough, but what regulates it? What closes it when the need is no more?


Perhaps a MIMO zone valve on a timer with a flow regulator such as the one you linked to (altho0ugh they are very susceptible to system debris BTW).

Like I said opening is easy, closing at the right time - I dunno.

As has been said before. You are over thinking a problem. Way way way over thinking.

I cannot understand why you reckon saving gas is overthinking. Even the MIMO as you call it is not ideal. but better than a randomly set auto bypass!
I reckon the solenoid can be easily opened and or closed by a fairly simple piece of logical wiring and a relay, though have not sat down to it yet.

smokebox
I will plan a circuit with your poke!

 

[smokebox]

Its not much of an idea really... How do you control it. Opening a valve when the system shuts down is easy enough, but what regulates it? What closes it when the need is no more?


Perhaps a MIMO zone valve on a timer with a flow regulator such as the one you linked to (altho0ugh they are very susceptible to system debris BTW).

Like I said opening is easy, closing at the right time - I dunno.

As has been said before. You are over thinking a problem. Way way way over thinking.

I cannot understand why you reckon saving gas is overthinking. Even the MIMO as you call it is not ideal. but better than a randomly set auto bypass!
I reckon the solenoid can be easily opened and or closed by a fairly simple piece of logical wiring and a relay, though have not sat down to it yet.

smokebox
I will plan a circuit with your poke!

It doesn't need 'regulating' It is open when the zones are shut, and closed when any zone is open.

 

[Agile]

For your information, though you know a great deal more than I about heating installations, the Alpha2 pump works perfectly on overrun. What are you talking about?

They have not given me a warranty - you are right, but he did not think it had to be condemned thank goodness. The Plumber will be placing a new HE in front of me with all relevant parts before I pay his bill!! I decided not to accept his offer of a twelve year free guarantee in lieu as I doubt his firm will exist that long!

smokebox

I realise the smart pump runs on the over run. But it is not providing an over run flow as required by the boiler because it does not increase the pressure in order to open the auto by pass.

Unfortunately I did not explain that in a simple form.

Smart pumps are fine for the application they are designed for. I fit them when appropriate.

Recent permanent magnet pump motors however are much more efficient and are easily modulated.

You have now brought in a new revelation of not paying your nupty installer until he brings you a new ( expensive ) spare HE. As the problem seems from the evidence to have been as a result of your insistence on having an incompatible smart pump then I dont see that your installer is to blame.

Based on just what you have told us he does not seem to be terribly clever at system design. But that should not make him to blame for system failures as a result of following your specific requirements.

But I could criticise him for not refusing to fit unsuitable components. I always take the view that no installer should fit anything that he does not fully understand. But if everyone did that then very little would ever get installed.

The customer always thinks that he is right !

Tony

 

[Dan Robinson]

I see you point.

But it has to open and close at the right time.

A MIMO valve consumes nothing between cycles.

However yo will need a relay to switch when the system is off and on.

I am not familiar with the Vaillant controllers (on account of me rating Vaillant as highly as I do Gonorrhoea and the Clap). However, these will all be working on a BUS rather than simple switching, which brings me back to your over thinking the problem.

I still fail to see why you are ignoring a LLH, which allows you to use a smart pump with no bypass and a shunt pump to keep the boiler happy (can't remember if your boiler has an internal pump or not). Insulate the nuts off the entire system pipe work and you're away.