VR65 with on-off heating and hw

[The831Bunny]

The system will still meet G3 regulations as the boiler now forms the overheat protection.

 

[ALEC1]

vr66 with the 47O is fine...with the mixing valve...

Bunny this is great information, but shoiudn't installers know all this before the public?

 

[ALEC1]

That is extremely helpful, many thanks for taking the time.

I'm contemplating going full WC controls. I'd like to talk to people with the 400 series boiler to see how it benefits and if there's any reduction (or increase) in heating bills. I had a vaillant engineer out today, and he was raving about it (maybe he would!). He said he had it installed in his house. The vaillant cycling blog worries me as it's the high KW 400 series boiler which had problems with the WC controls.

I think, as you say, investing in the VR65 and rewire without the vaillant controls is probably a little pointless.

I would forget that blog, as long as you get the new PCB.

I have a set up with with a 438, 430f vr66 with the esbe mixing valve...client very happy..

 

[The831Bunny]

vr66 with the 47O is fine...with the mixing valve...

Bunny this is great information, but shoiudn't installers know all this before the public?

Sorry Alec, maybe should air in the CC, but in a rare opportunity of some time to post on Vaillant stuff, I'm a stickler in trying to give the right advice!

I'm sure there's a market for 'A Dummies guide to Vaillant boilers and controls' ...

Now where's Mr.V when you want him

 

[ALEC1]

I really think all boiler manufacturers fall into the trap of selling on price to the bottom of the market..and miss the trick of adding value to their products & pounds to their sales..

A few committed installers with dedicated support technical and marketing could do wonders for the manufacturers bottom line...

 

[fezster]

This may have been done elsewhere, but did you REALLY need 38Kw?? Pity about the standard S Plan you have - Sizing a boiler with a HW priority system (VR65) means you only need to size for the largest load, possibly the cylinder, at around 18-20Kw for a Megaflo.

There is an extensive thread here:

//www.diynot.com/forums/plumbi...ones-frequent-s53.366928/page-3#ixzz2pH7KlFGc


Not all of it is relevant any longer, as some of the issues seem to have been solved. A quick summary though:

1) IDHEE whole house calculator shows 34KW loss for my house. It's difficult to get a completely accurate figure as some parts of the house are solid walls and others up to modern insulation.

2) Radiators were deliberately oversized. There are 25 radiators in total, totalling 44KW. All are double panel, with the exception of two. One of those is single panel, the other is double convector.

3) Downstairs zone rads are approx. 26KW, upstairs approx 18KW.


Given the above, I think a large boiler was warranted. Having said that, range rating the boiler to 26KW still allows the house to be heated up quickly. My understanding is, though, that as the outside temperature drops, I may need to increase the KW output to achieve the same result.

The main problem with the 438 is the high output on minimum output (about 6.5Kw) and the start up output (about 26Kw) for 50 seconds REGARDLESS of the setting in D.0. This has been addressed in later release PCBs AFAIK, but is not helped by over zealous installers/customers thinking 'bigger is best'. The best and most efficient boiler is the correctly sized one!!!!

The absolute latest is that I've increased to 30KW, with (hopefully!) the new PCB, which should help the boiler ramp up slower on first fire and then modulate down.

Lastly, don't think a 5M or even a 6M pump will do, it probably won't. Due to the need to shift 27 L/min through the boiler to extract 38Kw than a larger pump than a 'domestic' model is sometimes needed.

Here's what I've calculated. At 30KW, with a 20 degree temp differential:

30000/(4185*20) = 0.36 l/s (1.29 m^3/h) (1290 l/h)

At 1290 l/h flow rate, the head loss at the boiler is 2.6m:

Thanks to D_Hailsham, I know the index circuits on both upstairs and downstairs:

I have assumed: flow = 75°C; return = 55°C. (20°C differential)

The index rad is on the ground floor, but not the one suggested by the OP. It is the top right corner. The loss is 2.12m. The worst rad on the first floor is only 1.09m.

The system is complicated by the fact that the whole thing is driven by this pump:


View media item 62496
It's a Grundfos UPS 26-50R. Ive been unable to find the specs for it. However, the closest recommendation is the 25-55, but I believe the 26-50R is perhaps more powerful. Let's assume not, then the 25-55 pump chart shows available head of 4.8m, at 1.29 m^3/h:

Total head loss for upstairs is 3.69m.
Total head loss for downstairs is 4.72m. (Downstairs is complicated further by the fact that it has a secondary pump, a 15-60. Im not sure how this would factor into the equation).

So going by the facts and figures, it *looks* like the system should be fine at 30KW. In fact, it should be fine at a little more too. But I know for a fact at 34KW, I get an S53, which indicates the pump may be undersized to achieve 34kW, which is the heat loss of the house. Alternatively, it could be the pipework, but I think 7m of 28mm for both upstairs and downstairs should be sufficient, going by what Ive read and others have said on this forum.

 

[Agile]

That's all very good in theory.

But if you can reliably operate at a delta of 20° C then you are very lucky ( or the pump is seriously undersized! ).

Most systems only manage about 15-17 C.

Its not an exact science as its always dynamically changing as the TRVs start closing.

But I don't see much wrong with want you have said.

Not sure why you want to heat all the rooms all the time though. I would have it seriously zoned and heated on a follow me basis.

Tony

 

[Steelmasons]

You won't listen fezster so what is the point?

The 15/60 that has been installed on the ground floor zone is 'robbing' (laymens terms so it is understood) any head/flow available from the 15/50 in order to circulate water through the upstairs zone (when both calling for heat) , it has been said umpteen times the circulators must be installed in series BEFORE any zone valves , either remove the 15/60 and install it downstream of the 15/50 or simply remove both circulators and fit a 25/80......................or leave the circulators in situ and install an additional 15/60 to first floor zone.

 

[fezster]

You won't listen fezster so what is the point?

The 15/60 that has been installed on the ground floor zone is 'robbing' (laymens terms so it is understood) any head/flow available from the 15/50 in order to circulate any water through the upstairs zone (when both calling for heat) , it has been said umpteen times the circulators must be installed in series BEFORE any zone valves , either remove the 15/60 and install it downstream of the 15/50 or simply remove both circulators and fit a 25/80......................or leave the circulators in situ and install an additional 15/60 to first floor zone.

Oh ok - sorry, thats the first time Ive read this. I must have missed it in the original thread. I must admit, that with both zones open, the upstairs was taking a lot longer to heat up. *However* - since increasing to 30KW, both heat up in an acceptable time. I take your point, though, that the pump should have simply been put in series with the primary pump.

If I do ever upgrade the primary pump to a 25-80 (probably a smart pump of some sort), then I will look to have the second pump removed at the same time. My hope is that the single 25-80 will be enough to drive the whole system at 34KW or above.

 

[Steelmasons]

I must admit, that with both zones open, the upstairs was taking a lot longer to heat up. *However* - since increasing to 30KW, both heat up in an acceptable time.

I doubt it would be 'acceptable' in relation to a correctly installed system but possibly what you have had to get used to or should we say put up with.

Obviously increasing boiler output would increase deltaT due to inadequate flow rate.

 

[fezster]

It seems Grundfos no longer sell the UPS 25-80, and instead recommend the MAGNA1 25-80. From reading the literature, it seems the best cost savings on these new smart pumps are when using one of the variable speeds (either proportional pressure or constant pressure). Given the much higher initial cost, it'd be nice to get some cost savings over the life of the pump.

Looking at the pump charts confuses me a little. Let's assume that I want to be able to cope with 38KW, which is 1.634 m^3/h at 20 degrees differential, giving a total head loss of 6.57m.

The MAGNA1 25-80 pump chart shows (look at the green line I've added):

It looks to me that on PP3, the pump only provides max 5.5m head, but at a fixed speed of 3, it provides max 8.5m head. Therefore, would have to be run at the fixed speed ? Is my understanding correct ?

A reason Im doubting myself, is that on the 15 pager thread, user matt1e (who seems very knowledgeable) was kind enough to recommend the DAB evotron 80. This would be a significantly cheaper alternative. But looking at the chart:

It only seems to provide max 5m head at 1.634 m^3/h.

I'm therefore thinking perhaps my interpretation of these charts is incorrect. Any help appreciated.

 

[Norcon]

This whole saga comes down to a £500 quid circulator?

Combine its cost, electricity consumption and then it will help negate the benefits from a so called efficient boiler!

If it was mine I'd either be ripping the boiler out or the pipe work or both!

 

[fezster]

This whole saga comes down to a £500 quid circulator?

Combine its cost, electricity consumption and then it will help negate the benefits from a so called efficient boiler!

If it was mine I'd either be ripping the boiler out or the pipe work or both!

Not sure I agree with that assessment at all. Why would you rip out the boiler ? Replace with what ? Remember, the whole house heat loss is 34KW according to the IDHEE calculator.

At 38KW, the boiler resistance is 4.05m. That doesnt leave much room for much else on a standard 15/60. So a larger circulator is a must if you're to extract the full power from these boilers.

The grundfos 15/60 uses 105W. A bigger circulator uses more power, but then that's the price to pay for heating a large number of radiators. As I understand it, the magna circulators should be able to provide some efficiency here by not running at a constant speed. But this is where my knowledge lacks, and am looking for guidance.

Pipework may well not be optimal, but the house is fully decorated, and all but the first 10m is completely inaccessible, without considerable cost. You may well rip it all out, but I simply cannot afford to.

 

[Norcon]

"At 38KW, the boiler resistance is 4.05m"

 

[Agile]

The practical reality of these smart pumps seems to be that they only give any power saving in the variable mode.

Unfortunately, that does not suit many installations and so they need to be left in their fixed speed setting which does not give any power saving.

Tony