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Heating and cooling: Radiators on a central manifold?

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  1.  
    Our renovation which includes an ASHP is now ready for radiator positioning so we can work out the supply pipework location's.

    Are Trunk and feed layouts now outdated? Should I be best running everything back to a central manifold? It would mean more pipework but potentially less joints.

    Does this then make it easier for balancing etc?

    If we do that, can all of the radiators be fed from 10mm potentially? Where can I get some kind of calculation or diagram made? The traditional S plan would be easy to do in 22mm and 15 to the radiators. Probably a separate circuit for upstairs and one for downstairs

    Any thoughts please?
    • CommentAuthorArtiglio
    • CommentTimeNov 30th 2024
     
    I used manifolds and 10mm pipe runs for 8 flats, ( 4 in a conversion, 4 in a new build) the conversion was an 1870 terrace with some rooms having 11’ ceiling heights.
    Using plastic pipe there are no joints under the floor other than to the manifold and copper tails, doddle running the pipes and any holes in joists are only 12mm. But these are heated with gas combi boilers, all work fine with 60 degree flow temps but invariably i’ll find tenants have it much higher. The flats in the block built in 2004 will quite happily run at 50 degrees, but it’s a waste of breath telling tenants that, 60 degrees seems to be a temperature at which people see rads as being sufficiently hot.
    Only problems i’ve had is when i’d neglected to top up inhibitor in 2 flats and flakes of scale had collected in the manifold and blocked a pipe run. But that was simple if time consuming to sort out and won’t happen again.
  3.  
    That's great to hear, as I've oversized the radiators for 40C flow temperature, I do want to check that it will manage. I think if I used a manifold, the longest run to a radiator would be about 13m including drop. Not sure how I could calculate if that would be too long or too noisy in 10mm plastic or 15mm?

    This radiator has a heat output of 3kW at delta 50C
  4.  
    I have the heat loss or heat output per radiator and I know the Delta t for each rad (5c ideal). Does anyone know how I can then calculate the speed or flow in the pipe either at 10mm or 15mm?

    I have read it needs to be a certain size to ensure deposits aren't left or excess wear on the pipe. The is also the sound.

    If anyone knows how to calculate this effectively given pipe runs and temperature I'd be most grateful for my own learning curve?

    If I can run everything in 10mm drops or runs without issue it will make the plumbing and chases a lot easier
    • CommentAuthorrevor
    • CommentTimeNov 30th 2024
     
    I think manifold would be a good idea you can balance all rads from same place. You could have a stat on each circuit.I would start from working out the heat requirement of the rooms then decide on size of rad for a given flow rate and presumably 40 C. I have only done manifolds for underfloor heating with water from a thermal store. The store I have is at 55 c and the manifold water is at 40c the manifold will mix flow water with return water. The kit I bought had flow and return manifolds with flow meters on the flow and actuators on the return linked to thermostats. The flow rates were calculated by the supplier (Robbens) I see no reason why you could not do something like this. You could get a supplier of parts to do you a quote based on your requirements, you need to buy the bits so why not get someone like Robbens or others to quote based on your drawings they can take in your insulation levels and windows etc in the calc.
  6.  
    I have the heat loss calcs per room both by myself and the MCS company who will be supplying the heat pump.

    I was thinking a simple manifold, don't need flow rates really do I? I could use the danfoss ras-b trv that have self balancing valves.

    My query is more to do with will 10 or 15 work without creating noise or issues?
    • CommentAuthorphiledge
    • CommentTimeNov 30th 2024
     
    40 deg c sounds hot for an ASHP flow temp if you want to get the best COP out of it. Personally I'd be sizing rads on a 25/30 degree flow temp. The HP manufacturer should have tables showing the COP at varying flow temps

    Remember that anyone specifying flow temps for you isn't going to be paying your bills!
  8.  
    I've oversized the rads even higher than the recommendation so I'm sure I'll be able to run a lot lower and we're also not interested in achieving 21c in every room when it is -2c outside so we should be okay in that respect
    • CommentAuthorrevor
    • CommentTimeDec 1st 2024
     
    Posted By: VictorianecoMy query is more to do with will 10 or 15 work without creating noise or issues?


    To determine if you will have noise you need to know the flow rates. There are tables of pipe dia, flow rates, heat carried with limits where you can expect noise. At moment cannot lay my hand on my heating guide but that is to do with conventional boilers but some of the info would be transferable I guess. A friend recently had her heating upgraded with 2 heat pumps. They ran a pipe through her kitchen fixed to the wall within ducting and she is complaining that bit is noisy. So you are wise to look into this aspect.
    •  
      CommentAuthordjh
    • CommentTimeDec 1st 2024
     
    Posted By: Victorianecowe're also not interested in achieving 21c in every room when it is -2c outside
    Bear in mind that you might want to do that when you're ill and older! i.e. requirements change depending on circumstances. But you don't have to meet extremes using the normal heating system. You can always add additional heaters if necessary.
  11.  
    Yeah that's my take on it. For the coldest period I could supplement with the log burner or a few rads.

    Or dare I say it, an extra jumper or thermals ?
  12.  
    The MCS supplier has suggested running everything from a manifold and use 16mm pipe

    I can' really find decent suppliers of 16mm pipe that would include 90deg fittings such as hep20 brand

    Should I just go with Hep20 as they have a wide range of fittings readily available? I'd rather not have any 16mm compression fittings hidden in floor boards or walls (Can anyone recommend a 16mm push fit supplier/brand?)
    •  
      CommentAuthordjh
    • CommentTimeDec 3rd 2024
     
    Posted By: VictorianecoI have the heat loss or heat output per radiator and I know the Delta t for each rad (5c ideal). Does anyone know how I can then calculate the speed or flow in the pipe either at 10mm or 15mm?
    The energy carried away is flow rate (l/s) * specific heat capacity of the transfer medium (water or glycol as appropriate) * deltaT at the heat pump (normally designed for 5).

    So flow-rate (l/s) = heat-output / (4200 * 5)

    To convert the flow rate to speed, divide it by the internal cross-sectional area of the pipe. i.e pi * r² Note that r is in cm, not mm, and the speed is in cm/sec. More simple sums if you want different units.
  14.  
    So would I be looking at the flow rates of the pump or per radiator? How would pipe length effect this also?
    • CommentAuthortony
    • CommentTimeDec 3rd 2024
     
    the longer the pipes the harder it is to shift water.flows can be balanced using the lockshield valve, best done by equalising the return temperature
  16.  
    The largest length of pipe from manifold to radiator would be ~12lm

    If I were to use traditional trunk and branch style the longest length would be about 8lm
  17.  
    Posted By: VictorianecoThe largest length of pipe from manifold to radiator would be ~12lm

    If I were to use traditional trunk and branch style the longest length would be about 8lm

    Don't forget that fittings (Tees etc.) add resistance which can be calculated as equivalent pipe length (tables on the internet) so your 8 lm would increase accordingly but the manifold would also add equivalent pipe length so it's not as simple as it would first seem, unless you have already accounted for fittings in the 12 lm and 8 lm.

    Oh and I've not seen any plumbers accounting for flow rates and fittings resistance when installing domestic CH. they just put in a (oversized) pump and screw down the lockshield valves as needed.
    • CommentAuthorrevor
    • CommentTimeDec 4th 2024
     
    Posted By: VictorianecoI can' really find decent suppliers of 16mm pipe that would include 90deg fittings such as hep20 brand


    16 mm is a continental size widely used here now my u/f pipe is 16mm profitherm which you can use in your application. It bends easily so it minimises fittings and retains shape, you need compression fittings of that size though.

    Don't think you will find this in the general plumbers merchants if your MCS installer has recommended 16mm ask him/her where they source it from.

    There is also another system available seemingly becoming popular which is Alpex needs a special compression tools to make the joints. This can also be bent and retain shape system is popular because it avoids hot work on building site sometimes a H&S fire prevention requirement. See link explore rest of site also.

    https://www.underfloorheating.co.uk/product-category/plumbing/pipe/plumbing-and-heating-pipe/
  19.  
    Posted By: revorThere is also another system available seemingly becoming popular which is Alpex needs a special compression tools to make the joints.

    Alpex is the de facto standard here for any pipe work that is not on show. It can be had plain or pre-insulated (red or blue). Whilst a tool is needed for the joints it is quicker than soldering up copper. Very easy to use.
  20.  
    They sell the pipe and advised you need a hydraulic pressing tool. I didn't ask anything after that as I really don't want to have joints other than Hep20

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