Increasing Pump Head

S

sanj.varah

what do the plumbers out there do to increase the head on pumps? I've got a system boiler and need a bit more head for pumping up to my loft and keeping a decent flow rate. Whats the best way of increasing pump head? I've got it set to max at the moment.
 
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What the b*ggery b*llocks are you talking about?
 
what do the plumbers out there do to increase the head on pumps? I've got a system boiler and need a bit more head for pumping up to my loft and keeping a decent flow rate. Whats the best way of increasing pump head? I've got it set to max at the moment.

Just change the circulator for one with a larger head pressure capability.
 
I've got a system boiler and need a bit more head for pumping up to my loft and keeping a decent flow rate.

The head has nothing to do with the height of the radiator above the pump. It is a way of talking about the pressure loss in the pipes caused by friction etc. Provided the pipes to the loft are the correct size for the heat which will be carried through them, there is a good chance that your pump is perfectly adequate.
 
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the height of my highest rad is approximately 3.2m above my boiler. Allowing for losses from pipe friction, I reckon there is somewhere around 3.5-4m of head loss in my system (to the worst radiator).

The pump in my boiler is rated at 4m head (after the losses within the boiler) at 1100litres/hour flow (High flow rate is something I want). The only way I can get sufficient head is to drop the flow rate which is something i'd rather not do as i'll end up with inefficient radiators.

I would therefore like to increase the head generated by the pump to somewhere around 6m-7m, to maintain flow rate and also decent pressure.

I'm just wondering what the best way to do this is, would it be best to get another pump and just hook it up in series with the first or decouple the boiler pump completely and run an external pump.
 
you don't know how head works, do you? The CH pump does not lift water against gravity. it just circulates it.

is there something wrong with the way your radiators are working? What is it?

Have you got a sealed system, or a feed & expansion tank?i
 
Hang on , Sanji is a fluids engineer!

However, he does not seem to know the difference between a pump and a circulator!

He also seems not to have thought about the need to keep the flow LOW to ensure that an adequate temperature differential is provided across the boiler.

The flow rate needs to be RESTRICTED through the radiators so that each one individually displays the design temperature differential between flow and return.

Tony
 
you don't know how head works, do you? The CH pump does not lift water against gravity. it just circulates it.

is there something wrong with the way your radiators are working? What is it?

Have you got a sealed system, or a feed & expansion tank?i

I have a sealed system.

I am fully aware what head is. If I follow your explanation that would suggest that I can put my boiler in a block of flats with the existing pump and it will pump all the way up to floor 50. that wouldn't work

My central heating pump is circulating against both frictional losses and gravitational (height) losses.

When I did my heating calcs I opted to increase the size of my rads by 50-100% to allow my boiler to condense more = less gas consumption. However the drawback is there is increased pressure loss through the system, resulting in low flow (radiators are very warm at the top and cold at the bottom). This isn't sludge because the rads are new and when the
TRV's click off, the remaining rads get hot all the way down.

I want to get even heat distribution on the rads and also decent flow up to my loft radiator. I think to do this i need another pump. Having trawled the net, i've found my boiler has an external output for another pump so i'm going to look at installing that
 
Hang on , Sanji is a fluids engineer!

However, he does not seem to know the difference between a pump and a circulator!

He also seems not to have thought about the need to keep the flow LOW to ensure that an adequate temperature differential is provided across the boiler.

The flow rate needs to be RESTRICTED through the radiators so that each one individually displays the design temperature differential between flow and return.

Tony

I'm actually a fluid mechanics lecturer! i'm an aerothermal engineer

Is a circulator in this case not just a paddle wheel pump? the fluid which you push out of the discharge goes round the circuit and comes back to the suction (inlet). The fluid returning to the suction will obviously be at lower pressure than the discharge but if there is too much resistance (head/friction etc) then the paddle wheel will not send any water around the system at all - ie a tall block of flats.

I tried the lockshield screwing down with my trusty thermometer gun and tried to get my 20C temperature drop (50 flow to 30c return) I could get this on most rads but the ones far away from the boiler were taking ages to warm up (lockshields open). So I was getting significant temperature drop from my boiler. I went to town with the insulation so I'm guessing the flow was too low.

I will do some more fiddling, the guy from Viessmann was pretty good but he also suggested the same as everyone on here (I should have sufficient head). I did point out that I had circa 40kW (@80C flow, 60C return) of rads hooked up to my boiler but he still said i shouldn't have a problem.

I'm going to work out the pressure loss tomorrow and actually quantify how much head loss i've got. There's also a whole host of parameters to fiddle with on the pump so i'll check them first.
 
Hang on , Sanji is a fluids engineer!

However, he does not seem to know the difference between a pump and a circulator!

He also seems not to have thought about the need to keep the flow LOW to ensure that an adequate temperature differential is provided across the boiler.

The flow rate needs to be RESTRICTED through the radiators so that each one individually displays the design temperature differential between flow and return.

Tony

I'm actually a fluid mechanics lecturer! i'm an aerothermal engineer

You seem to be a tube. If you're an Engineer/Lecturer and can't work that out for yourself, then you need to take yourself out behind the polytechnic, sorry, university bikesheds and give yourself a good kicking.

I regularly rant at the clueless plumbers on here who claim to be Heating Engineers and then we get someone who is (allegedly) lecturing on Fluid Mechanics and thinks the height of the building has some relevance to pump head (wanders off mumbling to look for a Webley).
 
sanj.varah said:
I am fully aware what head is.
In that case you're doing an impression of someone who has not the first idea.

If I follow your explanation that would suggest that I can put my boiler in a block of flats with the existing pump and it will pump all the way up to floor 50. that wouldn't work
In that case don't do it.

When I did my heating calcs I opted to increase the size of my rads by 50-100% to allow my boiler to condense more = less gas consumption. However the drawback is there is increased pressure loss through the system
Nonsense.

I want to get even heat distribution on the rads and also decent flow up to my loft radiator. I think to do this i need another pump. Having trawled the net, i've found my boiler has an external output for another pump so i'm going to look at installing that
In that case why did you come here asking idiotic questions?
 
Sanji, can I try to get you to stop thinking that the height of the building is terribly relevant.

The flow of system water is rather like a large wheel.

Now think about the London Eye. You would be saying that the gravity will require a motor to LIFT the cars right up to the top!

However thats obviously wrong! The cars going up are counterbalaned by the cars going down!

The only power the Eye motor needs is to overcome the frictional resistance of the bearings and the extra lift if Chris is going up while Shylene is going down!

The only difference a larger heating circulator will make is to increase the circulation rate. Even if its four floors there will still be a circulation with a small pump.

If you go and look at circulating pumps in larger buildings you will see that they are still only around 700 W as thats all the power you usually need to provide a flow round a properly pipe sized system.

Tony
 
When I did my heating calcs I opted to increase the size of my rads by 50-100% to allow my boiler to condense more. However the drawback is there is increased pressure loss through the system.
You say that you have 40kW of rads at 80/60/50 and will be running the boiler at 50°C flow, 30°C return. Assuming a room temp of 20C, the output of the rads reduces to 40 x 0.304 = 12.16kW. Is this what you calculated the heat loss from your house to be?

Provided you are using the correct size pipes there should be no significant difference in the pressure loss.

The pump in my boiler is rated at 4m head (after the losses within the boiler) at 1100litres/hour flow (High flow rate is something I want). The only way I can get sufficient head is to drop the flow rate which is something i'd rather not do as i'll end up with inefficient radiators
Why do you want high flow rate?

If you need 12.16kW, the mass flow rate will be 12.16 ÷ (4.2 x 20) =0.14476 kg/sec = 0.521 m³ per hour (521 litres/hour - half what your pump can deliver!)

the height of my highest rad is approximately 3.2m above my boiler. Allowing for losses from pipe friction, I reckon there is somewhere around 3.5-4m of head loss in my system (to the worst radiator).
My last house had a 15/50 Selectric with 7m between boiler and highest rad. If you were right that pump would not even get the water up to the top rad; but it did!

It might be a good idea if you read Copper Tubes in Domestic Heating Systems. This will explain everything and help you calculate the loss in the index circuit, which may not be the one in the loft!
 
have you tried closing the lock shield then cracking it open by 360 degrees ( 1 full turn) this will reduce the return allowing the water to enter the rad quicker than it is leaving. Also is the btu output big enough for your system if you have upgraded the rads to 50-100%
 

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