Vaillant 438 with 3 zones, frequent S53

[matt1e]

Hi dave we must have posted at the same time

Grundfos Webcaps seems to have moods

Must do it suggested a magma 25/80 for me
Unless we are entering different data of course

I used 1.633 for flow rate and 6.57 for headloss
I also played around with the other variables and it still suggested a 25/80

Matt

 

[D_Hailsham]

It doesnt look like the 25-55 provides more than 4.25m head at 1.6m^3/s. So the u/s definitely requires either a bigger pump, or a secondary pump. One thing I would say is that my pump is a Grundfos 26-50, which doesnt look to be identical to the 25-55. I'll try and post a picture of the front, as I believe it may be more powerful than the 25-55.

A pump which can only provide a 5m or 5.5m head at zero flow will never do the job!

Am I right in saying a Grundfos 25-80 would suffice, as a single pump for the whole system ? Looking at the pdf, it seems it would be ok (and definitely be a cheaper solution).

It would do the job, but a Magna 25-80 would be a better solution because it is a variable speed pump and would automatically adjust to the varying load as rads and zones open or close.

At 26KW, flow rate is 1114 l/h

You have already said that your heating requirement is about 34-36kW so there's no point talking about 26kW - Unless you've made a mistake using the whole house calculator!

If you need 34kW when it's -1°C outside, 26kW will be enough when it's 4°C outside. At 10°C you will still need 17kW.

 

[D_Hailsham]

I did attempt to do the head loss calculation for upstairs, and have come up with a figure of 0.8m for the index circuit upstairs. This was using a 20 degree temperature differential. Based on this, it would seem my single pump is sufficient for anything less than 30kw output on the 438 (factoring in head loss at the boiler).

So my u/s calc wasn't that far wrong (!)

I was hoping you wouldn't notice that.

To be honest, I was thinking of a complete house with an 11C differential and including the boiler.

 

[matt1e]

As daves post above
You definitely need variable speed Fezster ie the magma/ dab evotron or similar

Matt

 

[fezster]

You have already said that your heating requirement is about 34-36kW so there's no point talking about 26kW - Unless you've made a mistake using the whole house calculator!

If you need 34kW when it's -1°C outside, 26kW will be enough when it's 4°C outside. At 10°C you will still need 17kW.

If Im being honest, it's very difficult to get an accurate answer on the whole house calculator. The property is very old, with bits added on, and varying (and unknown!) insulation levels. Eg. whilst doing some building work last month, we found one of the walls had a cavity (no insulation), whereas we had assumed all exterior walls were solid. Also, some extensions have been added which have modern insulation. All in all, whilst the whole house calculator suggests 34kw+, i know for a fact that at 26kw, the boiler was heating the whole house up pretty adequately during the extremely cold weeks we had in January.

 

[fezster]

To be honest, I was thinking of a complete house with an 11C differential and including the boiler.

Not at all mate, I didnt mean it like that. I was just quite chuffed that my (very rough!!) calculation was somewhat in the right direction. I found doing it, interesting. I dont fully grasp the finer points of the calculation, though, because some of the questions you asked me I did not factor into my calc at all. I'll try and do some more reading on the subject at some point.

 

[D_Hailsham]

I used 1.633 for flow rate and 6.57 for headloss. I also played around with the other variables and it still suggested a 25/80

Just done it again! If Grundfos can't provide consistent results, what chance has the poor plumber!

Untitled

• D_Hailsham
• 13 Jun 2013
• 1

 

[matt1e]

All in all, whilst the whole house calculator suggests 34kw+, i know for a fact that at 26kw, the boiler was heating the whole house up pretty adequately during the extremely cold weeks we had in January.

That may be, but it does not detract from the fact that even rated at 26 kw your pump does not have enough head to over come the system losses
Your downstairs works because you have the second pump in series which increases the head ( why was it installed only serving the downstairs)
You could move the second pump so that it also serves the upstairs but it would be far far better to just install a new correctly sized pump with variable duty

Matt

 

[matt1e]

I used 1.633 for flow rate and 6.57 for headloss. I also played around with the other variables and it still suggested a 25/80

Just done it again! If Grundfos can't provide consistent results, what chance has the poor plumber!

Untitled

• D_Hailsham
• 13 Jun 2013
• 1

Was that using the same figures?
Try using the same figures but pick canned rotor / union / in the more option
I also used max temp 80 degrees working temp 75 and min temp 30
I will have another look when I get in as on mobile at mo

Matt

 

[fezster]

All in all, whilst the whole house calculator suggests 34kw+, i know for a fact that at 26kw, the boiler was heating the whole house up pretty adequately during the extremely cold weeks we had in January.

That may be, but it does not detract from the fact that even rated at 26 kw your pump does not have enough head to over come the system losses

Matt

Could you tell me why ? My post further up suggests my pump would be adequate at 26KW ?

Your downstairs works because you have the second pump in series which increases the head ( why was it installed only serving the downstairs)

At the time, only the downstairs radiators were having trouble heating up (and only the furthest ones). In hindsight, i'd have been better off if he had installed it to serve both.

 

[matt1e]

Scroll down to the evotron 80 this has a Suitable curve

http://uk.dabpumps.com/dep/60145405_Evotron_TS_ENG_DEF.pdf

The inverter software is user friendly very easy to navigate is bms/0-10v compatible and You can pick them up for around the £270 mark

http://www.colglo.co.uk/product.php?product=DABSP60143304

 

[D_Hailsham]

If Im being honest, it's very difficult to get an accurate answer on the whole house calculator. The property is very old, with bits added on, and varying (and unknown!) insulation levels. Eg. whilst doing some building work last month, we found one of the walls had a cavity (no insulation), whereas we had assumed all exterior walls were solid. Also, some extensions have been added which have modern insulation.

Yes. it's much easier if the house is a modern rectangular box.

I know for a fact that at 26kw, the boiler was heating the whole house up pretty adequately during the extremely cold weeks we had in January.

It would have been interesting to know what the flow and return temps were then as well as the rad temps.

I'm still trying to work out what exactly will happen when a 10kW boiler is connected to a circuit with 20kW of rads. If you run at 60C flow and 40C return the rads will then produce only 10kW. But if the flow temp is maintained at 75C the return will be only 35C; a 40C Delta!

 

[matt1e]

All in all, whilst the whole house calculator suggests 34kw+, i know for a fact that at 26kw, the boiler was heating the whole house up pretty adequately during the extremely cold weeks we had in January.

That may be, but it does not detract from the fact that even rated at 26 kw your pump does not have enough head to over come the system losses

Matt

Could you tell me why ? My post further up suggests my pump would be adequate at 26KW ?

Regardless of the setting of your boiler output the flow through it is governed by two things
1 The system curve ( resistance to flow)
2 the pump curve ( flowrate to resistance ratio)
Ie a particular pump will provide a certain flowrate which will decrease as resistance(head) to it increases this is known as. It's operating curve

The headloss has been calculated not measured it is a estimation
And will err on the side of caution and there is good reason as the losses will increase as the system gets older
The pumps you have now when running probably lie just within some of the necessary curve, you will still have enough flow through the majority of the system as not all of the system has the same losses
The boiler has enough flowrate through it to operate at a certain output, the higher the output the more flowrate it reqs
Flowrate is fixed via the system curve and the pump curve
If there is enough then the boiler will be happy at its highest output
If there isn't , as in your case it won't
Your pumps are only providing enough to operate the boiler at a lower output

Matt

 

[D_Hailsham]

Was that using the same figures?
Try using the same figures but pick canned rotor / union / in the more option
I also used max temp 80 degrees working temp 75 and min temp 30
I will have another look when I get in as on mobile at mo

Ah! you were using the 'overview' option. I unticked that and went through all 9 stages.

If I used the overview with your suggested changes it still came up with the Magna 1 32/100 as first choice; the Magna 25/80 was third.

Off Topic
Have you seen that there is now a UPS2 range of pumps which have 3 fixed speed and three proportional pressure settings? It replaces the UPS 15/50 and 15/60 It's a simplified version of the Alpha 2L. which was a simplified version of the Alpha 2.

You can even swop just the head on an existing Selectric 15/50 or 15/60.

 

[matt1e]

http://net.grundfos.com/Appl/WebCAP...ngappl=1&selectedRow=0&detailid=1371128261680

mmm yes I am using overview but it still gives me a magna 25-80
I don't know if the above link will work for you but I am using

flow 1.633
head 6.57
min temp 30
working temp 70
max temp 82
working pressure 1.5
I am using canned rotor only
material cast iron
thread= 1in

are you entering webcaps from the grundfos uk site or the american one?

on your other topic no mate I haven't but its rare I come across pumps of this size, interesting thanks for the heads up though

Matt