Central heating pump sizing

[Reddwarf4ever]

Your old pump isolating valves are probably 1/4 turn ball valves that you shut with a screwdriver (slot) or a allen key, nothing sticks out, but unfortunately they almost always leak after operation, you can easily buy new ones with gate valves.

It would seem that you can get a Dab Evosta3 with 130mm centres. it might be a 6.5/7M pump but you should ask your supplier if they have one, this will also be adequate IMO, the pump curves for all their models are in the link.

https://evosta.dabpumps.com/wp-content/uploads/2019/03/Evosta-2-3-Installation-and-Operation-Manual_UK.pdf

have ordered the DAB 3 21412 model, not sure which curve is applicable to the pump I ordered.... some websites don’t give the numbering, just the performance data, the site I bought mine from had some contradictory info, confirmed it was 130mm and 6.9m head by phone and has a 5 year guarantee not 3 as shown, hopefully they will change the info on their site...ordered it from https://plumbingsuppliesdirect.co.uk/dab-evosta-replacement-grundfos-circulating-heating-pump/ but the invoice is from STUART PLUMBING & HEATING SUPPLIES, but on their website it’s more expensive and have to pay postage so assume PSD is owned by Stuart plumbing.....must be offering competition to their own company.....marketing strategy the pump seems to have numerous control options, what’s my best setting to start with ? And best setting long term....

P.S. the pump iso valves are gate valves, not quarter turn, with a single square 1/4” approx post, no thread that I can see to hold a handle, can’t understand why they are sold like this, to shut off in an emergency, requires hunting around for an adjustable ( or normal ) spanner.....so much easier with a handle......maybe will replace them when I change the pump

 

[SJB060685]

John what would happen to the watts display if there was a pump problem or restriction in the system?

 

[John.g]

have ordered the DAB 3 21412 model, not sure which curve is applicable to the pump I ordered.* some websites don’t give the numbering, just the performance data, the site I bought mine from had some contradictory info, confirmed it was 130mm and 6.9m head by phone and has a 5 year guarantee not 3 as shown, hopefully they will change the info on their site...ordered it from https://plumbingsuppliesdirect.co.uk/dab-evosta-replacement-grundfos-circulating-heating-pump/ but the invoice is from STUART PLUMBING & HEATING SUPPLIES, but on their website it’s more expensive and have to pay postage so assume PSD is owned by Stuart plumbing.*.must be offering competition to their own company..marketing strategy the pump seems to have numerous control options, what’s my best setting to start with ? And best setting long term.

P.S. the pump iso valves are gate valves, not quarter turn, with a single square 1/4” approx post, no thread that I can see to hold a handle, can’t understand why they are sold like this, to shut off in an emergency, requires hunting around for an adjustable ( or normal ) spanner..so much easier with a handle...maybe will replace them when I change the pump

You have the correct type isol valves as the gland nut can be tightened up if any leak, so no need for renewal.

Would suggest constant pressure, either CP2 or CP3 see below, answer to SJB.

 

[John.g]

John what would happen to the watts display if there was a pump problem or restriction in the system?

Look at the pump curve on pge 25 in attachment which is for a 7M Evosta2, can,t find one for a 7M evosta3.
you will see that on constant pressure CP3 that the pump will maintain 4.8M from 0 flow, if the system demand is 1 m3/hr 16.7 lpm then the pump power is 35w, if a restriction in the system and the flow fell to zero then the power is 16.5w and so on in between. more later

 

[SJB060685]

Look at the pump curve on pge 25 in attachment which is for a 7M Evosta2, can,t find one for a 7M evosta3.

Which chart am I looking at?
Through common sense I imagine if there was a restriction on PP then the pump would modulate down and display a lower wattage?

 

[SJB060685]

Thanks John. As I said the other day, the ins and outs of pumps is new to me, so still trying to figure the charts. I understand what you said above but feel free to share more in case I missed something

 

[Reddwarf4ever]

Thanks John. As I said the other day, the ins and outs of pumps is new to me, so still trying to figure the charts. I understand what you said above but feel free to share more in case I missed something

I am in the same boat as you, things are always so complicated until you understand them, then you wonder why it was so difficult......it’s not rocket science.....so we‘ll get there keep asking questions, it’s the only way to learn.....also when people understand something so well it’s sometimes easy to downplay an answer.....I will persevere, I want to understand this.....trouble is the pump I ordered has lots of options so need to understand that also, just hope the others are patient with me

 

[John.g]

Thanks John. As I said the other day, the ins and outs of pumps is new to me, so still trying to figure the charts. I understand what you said above but feel free to share more in case I missed something

Page 25 shows two graphs the top one is the normal pump curves and I am just assuming that you have choosen the pump to run on setting CP3 and just suppose that your system will circulate 16.67 LPM at this setting of 4.8m. if you look vertically downwards you will see another graph of power vs flow for all the different pump settings, you have choosen CP3 and because the system is circulating at 16.67 LPM then the pump power required is 35W, if the system, say boiler Hx starts getting dirty/fouled then the pump speed will reduce to maintain this constant head of 4.8M and if it got completely blocked the pump will still maintain 4.8m but with no flow and still require 16.5W. If you had a smaller system in that even when spotelessely clean only circulates 8.3 LPM (0.5m3/hr) then you can see that the pump only requires ~ 25.5W at the constant pressure of 4.5M.

If you take my system as a example which circulates ~ 15 LPM (0.9m3/hr) @ 3.5M.......I could set the pump to CP2 which is constant pressure at 3.8M, my system would then circulate 15.7 LPM (0.94 m3/hr) @ 3.8M.
with a power demand of 26W.

I woud suggest CP2 (3.8M)as a reasonable starting point, it can very quickly be changed especially with all the info that will be displayed on this pump.

 

[SJB060685]

I am in the same boat as you, things are always so complicated until you understand them, then you wonder why it was so difficult...it’s not rocket science..so we‘ll get there keep asking questions, it’s the only way to learn..also when people understand something so well it’s sometimes easy to downplay an answer..I will persevere, I want to understand this.***.trouble is the pump I ordered has lots of options so need to understand that also, just hope the others are patient with me

My background is oil fired appliances, thats all we were, burner technicians. The system side of things is not something we did much of, so this last year I've been studying and learning a lot of new things to better my understanding. I have a passion for learning and a desire to at least have a good understanding in all areas of heating systems. John here has taught me a few things that I didn't know before joining this forum and to be honest, when it comes to pumps he's probably one of the best on here.

 

[Reddwarf4ever]

John what would happen to the watts display if there was a pump problem or restriction in the system?

Hi
i can only relate to my experience in the oil industry ( Mobil Coryton refinery ) when the pump discharge was shut back ( or there was another restriction to flow ) on a centrifugal pump the Amps ( power ) would drop off, as the pump would just be stirring the liquid and not doing any real work......not sure if that’s applicable, but IMO should be....