Pipe runs for 2 storey extension

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I am building an extension which consists of two storeys. At the moment I have two downstairs rooms that have been plastered and I am about to install a solid timber floor (the downstairs heating pipes sit on top of the floor slab and will be underneath the floor). The original heating system consists of a 22mm feed and return to the pump which is located on the 1st floor. The 1st floor is feed by a circuit which also feeds the ground floor radiators via a series of drops (single radiator per drop for all bar two radiators).
All existing radiators are fed via 15mm pipes and total 11 in number.
The extension sits at the far end of the house and what I have done for the ground floor is to create a circuit which is fed (via tees) from one of the existing 1st floor radiators (this radiator is now redundant and is no longer connected). The ground floor circuit feeds 5 radiators and then goes back up to the 1st floor in the extension to feed a bedroom radiator. This radiator is the last one on the circuit.
The remaining 1st floor radiators (5) in the extension are fed via a series of loops from the same tee that feeds the downstairs circuit.
At the moment I don't have any new radiators connected but I have capped off the pipes to allow me to test for leaks etc. I shut off all existing radiators and managed to get a good hot flow to the furthest new radiator location (the one that is on the 1st floor fed off of the ground floor circuit).
My questions are as follows:
1.With hindsight should I have connected the furthest radiator (1st floor) to the ground floor circuit as the water will flow down from the 1st floor round the ground circuit then up to the last radiator before dropping down again and then back up to the 1st as a return. I do have the opportunity to change this if necessary so that only the ground floor radiators are on the "ground" floor circuit - the bedroom radiator would then be connected as a loop off of the 1st floor circuit.
2.Are there likely to be issues feeding the ground floor circuit off of tees with the other side of the tees servicing the upstairs radiators (I realise that the system will need balancing).
3.Should I be ok with all radiators being serviced by 15mm pipe (as the existing ones are) or am I likely to need to upgrade to 22mm up to the point where the ground floor circuit tees off in 15mm.
4.I need to replace my existing pump as it is on its last legs - I intend to switch from a 6m head to an 8m head to cope with the larger system - are there any potential issues with this.
I realise that I have only provided limited information above and that it would have been best to ask the questions previously but I hope the above makes sense and would appreciate any comments/help.
 
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An 8 metre pump does not necessarily pump a greater VOLUME of water than a 6 meter unit! the 8 meters is the maximum head of water not always a direct correlation with litres/min!

You need to revisit your pipe sizing cos 15mm is going to struggle to deliver the required flow rate to 11radiators !! :eek:
 
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I now pretty sure that I will run a new section of pipe (22mm) to feed the extension radiators. Due to the size of the overall system I am looking at installing a second pump and zone valves for the new rads. My question is, for the new pump can I simply Tee off of the incoming feed adjacent to the existing pump or do I need to run new feed back to the boiler and connect there (again would it be a Tee connection). The feed from the boiler is 28mm most of the way before reducing to 22mm. It is difficult though not impossible to run a new feed back to the boiler for the new pump but I want to avoid this if possible.
Thanks
 
You shouldn't need a second pump.

Can you post a diagram showing how everything is joined together? (Which floor anything is on is not really relevant.) Please show:

Pipe sizes
Type/size of each rad.

The make/size of boiler would also help.
 
Attached are a couple of drawings and my calcs - hope they make sense but please let me know if they don't. I need to re-visit the calcs as I think there are a few minor errors in there at the moment but they are reasonably accurate.
The reason I am looking at a second pump is because the calcs were indicating that a single pump was looking on the industrial size. I was considering a Grundfos Pump Plan but now think I would be best leaving the existing circuit/pump alone i.e. don't change the pump out.
The boiler is a Ravenheat CSI Primary AAA which I know is likely to be on the small size.


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Wow! I wasn't expecting that! :D

Can you confirm that the whole house is equipped with only two sizes of rads. It seems a bit odd to me as most houses have rads ranging from under 500W to about 2kW, depending on size of room and heat loss.

You seem to have assumed an 11C differential, but the boiler is designed for a 20C differential - see Fig 5 on page 7 of manual.

If the differential was 11C the flow rate at max output (22.3kW) would be (22.3 x 3600)/(4.18 x 11) = 1746 litre/hour, which is off the graph! At 20C the flow rate is 960 lph.

Were the rads sized to take into account the lower output when run with a 20C differential? What is the design flow temperature
 
I must confess I did make some assumptions on some of the radiator heat outputs in my calculations as I was unsure of the values (original units that will be retained). So, there are actually 5 types of radiators but the vast majority are 1.8KW types - the others have a lower heat output.
I used the Copper Development Association paper for the calcs where they assume a temperature drop of 11C. Being an amateur I am struggling to understand table 5 but from what you have said, I assume that I would need to re-do my calculations and that I am not likely to need such a large pump as I originally thought - is that correct?
I used an on-line calculator to determine the number of radiators required but am not sure what the design flow temperature was.
 
I would have 28mm fom the pump to the branch and run 22mm off the 28mm for the new extension.

I would also say you have proposed to many radiators on 15mm pipe.

Rough rule of thumb is 3 rads per 15mm run, obviously it depends on rad sizes.

I always try and get each rad on a single 15mm run..if possible.
 
According to your diagram, there are 16 large rads and four small, which is a total of nearly 32kW, but you have only a 22kW boiler! Have you done a heat-loss calculation for the house, including the extension? If so, what was the result?

Incidentally, Rad 10 is show on the diagram as 732W, but in the table (B-10) as 1804W.

I'm not clear what is happening at point H and how it connects to the pump.
 
I used the Copper Development Association paper for the calcs where they assume a temperature drop of 11C.

AIUI, 11C temp differential was what was used with older designs of boiler. Modern condensing boilers are designed for a 20C differential
 

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