12 meter header – 18.5 meter pump – Addition to system.

[BBunter]

We currently have an oil boiler producing 50/70 kw linked to a 25mm 5.5m head Grundfos circulation pump serving zone 1 as detailed below (pressurised system).

The boiler is in the basement so there about 4 meters from the bottom of the boiler to the top of the radiator in Zone 1 office.

Zone 1 – Existing Offices – 4 meters above boiler (1[SUP]st[/SUP] Floor)

• 14 radiators 19,000 watts total
• 28mm copper reducing to 22mm half way around run – final reduction to 15mm for some spurs and end rads
• 66 meters in 28mm (including return)
• 50 meters in 22mm (including return)
• 46 meters in 15mm (including return)

We are completing the offices on the third floor and would like to link them into the existing system as the boiler seems to have the capacity.

Zone 2 – New Offices – 12 meters above boiler (3[SUP]rd[/SUP] floor)

• 8 radiators 12,000 watts total
• 34 meters in 28mm (including return)
• 46 meters in 22mm (including return)
• 48 meters in 15mm (including return)

We have a Grundfos 40mm 18.5 meter head (40-185) pump but have some concerns about plumbing in the new offices.

The plan was to t-off at the boiler with a motorised 3 port valve between the two zones

• run 28mm the 17 meters (34m inc return) to the new offices (12 meters up and 5 meters across from the boiler),
• reducing to 22mm around the ring 23 meters. (46m inc return)
• t-ing off at 15mm to the rads 24 meters (48m inc return)

Is the pump likely to be too powerful – exceeding the 1.5m/sec water rate if only 1 of the two zones were active?

Is 28mm sufficient for the run to zone 2?

Are there any problems connecting 28mm to a 40mm pump – would the pump be short of water in some way?

Are we way off the mark?

Mike

 

[jonnyswamp]

Too much info for me to absorb, but use 2 x 2 ports instead of a 3 port valve
As for the rest of the figures, doubt many would take the time to work things out for you for free (myself included)
Ask in the "I'm looking for a plumber" section of this forum, or are you going to do the work yourselves

 

[wattsie1987]

Too much info for me to absorb, but use 2 x 2 ports instead of a 3 port valve
As for the rest of the figures, doubt many would take the time to work things out for you for free (myself included)
Ask in the "I'm looking for a plumber" section of this forum, or are you going to do the work yourselves

As above a 3 port won't pass the load.

 

[ShaunCorbs]

and your design is partly wrong (pipesizing)

 

[BBunter]

Hi Guys,

I appreciate asking for complex calculations to be done for free is more than general advice.
Thanks for the tip on using 2 x 2 ports.

Changing the question slightly then...

What if we left the existing system as is with the current pump etc and T'd off after the boiler and ran the second pump in parallel - with check valves on the returns.

Would there be a danger of the bigger pump on zone 2 starving the smaller pump on zone 1?
I have seen (online) several installations with parallel pumps but the pumps all seem to be the same size.

Mike

 

[Howsie]

You're going to cause problems doing that way without the requisite knowledge I'm afraid. You should get someone in who can work out what you need. You'll need additional thermostats, pump (possibly), expansion vessel, to name but a few.

If you want to have a go yourself, everything you need to know (including the working spreadsheets) are in here: CIBSE - Domestic Heating - Design Guide 2015 (Domestic Building Services Panel)

 

[ShaunCorbs]

You're going to cause problems doing that way without the requisite knowledge I'm afraid. You should get someone in who can work out what you need. You'll need additional thermostats, pump (possibly), expansion vessel, to name but a few.

If you want to have a go yourself, everything you need to know (including the working spreadsheets) are in here: CIBSE - Domestic Heating - Design Guide 2015 (Domestic Building Services Panel)

That's the domestic one how I would think they need the commercial one

 

[Howsie]

LOL - he'll be alright with that based on what he wants to do.

 

[BBunter]

Thanks for the links - will take a look.
On a fundamental theory of operation - as these are circulating pumps does the weight (pressure) of the water coming back balance the head required to pump it up? i.e. the only real consideration is the physical resistance of the circuit and not the height it has to pump the water?

So even though we are pumping 12 meters high we may only need a 6 meter head pump to overcome the physical resistances?

Mike

 

[Howsie]

Thanks for the links - will take a look.
On a fundamental theory of operation - as these are circulating pumps does the weight (pressure) of the water coming back balance the head required to pump it up? i.e. the only real consideration is the physical resistance of the circuit and not the height it has to pump the water?

So even though we are pumping 12 meters high we may only need a 6 meter head pump to overcome the physical resistances?

Mike

No, there's more to it. It's in the book or have a search on the net for pump sizing, pipe sizing, water velocity, etc.

 

[oz-plumber]

No Offence Pal,

but you are clearly out of your depth.

We've all been there and learnt from our experiences.
( pity my learning curve was before the internet and Forums like this )

The original pump you intended to use - Grundfos 40 / 185, would be used on boilers of the size of 200 kW plus - in fact with 18.5m head, getting up near 300 kW.

We did a 165 kW boiler recently and put a Grundfos 40 / 120 on it and had it running on speed 2.

The pump size you would most probably need is a 32 / 10 or a 25 / 10.
Not knowing the full set-up and if I was quoting the job, I would make an allowance for either on of these in my quotation.

Hope this helps

 

[BBunter]

Absolutely no offence taken.

Your reply is exactly the kind of reply I was hoping for.
It is clear I have misunderstood the difference between circulating pumps and non-circulating pumps when looking at the head.