Hello I'm after advice on the installation of a secondary hot water system . The system will be suppling five bathroom s, a kitchen , cloakroom and utility room in a barn conversion. I usually install on a small domestic level so this is a bit bigger than the norm.
The hot water and heating system is being installed my a renewables company . They propose to install a 500 litre unvented cylinder and accumulator .
I'm just doing the first fix for the bathrooms and the rest of the plumbing in the property . This system will definitely need a secondary hot return system.
My query is with the pipe sizing.
I'm proposing to install 35 MM hot flow from the cylinder up to the first two bathrooms ( individual hot bathroom supply's 22 MM ) , then reduce down to 28 MM for the remaining three bathrooms .
The secondary return will be in 28 MM from the cylinder and reduce down as required by the last bathroom.
I intend to install locksheild valves on the returns at the outlets for balancing and fully insulate all pipe work.
Am I right with 35mm hot pipe work or will 28 MM be enough?
Hello Knee pads,
As has been mentioned already by another Member it is VITAL that the Hot water supply and Secondary return is really well insulated - I would state to a `Professional standard` - or any significant Heat loss will fairly quickly dissipate all of the Hot water in the Cylinder - even from a 500 litre one.
I also agree with a Members suggestion that You should be going back to the Renewables Company to have them specify the design / pipe sizing for the Hot water supply and Secondary return.
It is very easy for this type of thing to go wrong and it would usually only be found out after the job was nearly finished / all of the Bathrooms - Kitchen - Utility etc. already installed !
Having said that here are a couple of comments on what You wrote:
You don`t need anything like a 28mm return - the return pipe is only to keep the Hot Water circulating around the 35mm supply pipe so that it is available reasonably quickly to each Hot water outlet in the property.
However You MUST make sure that you Tee off the 35mm / 28mm in such a way that the Hot water is not being drawn form the return pipe.
A 22mm or even a 15mm return pipe depending on how the pipework will be run - will allow the Hot water from the Cylinder to circulate around the property so that it is available quickly at each outlet - but of course you must make sure that there is no `dead heading` when the various secondary returns meet each other / tee in.
You will be trying to circulate the Hot water slowly - as even when correctly insulated while it is circulating it will still be losing some heat.
I am sure that you know there should also be a Programmer or Timeswitch controlling the Pump to allow time setting of the Hot water Secondary circulation - depending on the proposed Hot water usage times.
I have often seen properties where the Hot water demand / Secondary circulation was causing the Cylinder to have to be heated almost constantly - however perhaps the owners of the 5 Bathroom property that you described will not be worried about something like that.
I would urge You to definitely get the Renewables Company to specify what they want you to install - on a job such as you describe it should never be `Fit it and hope`.
I don`t mean anything patronising by that comment - when Plumbing is `upsized` from the normal Domestic Home to supply anything like 5 Bathrooms - Kitchen - Utility & Cloakroom the correct calculations are definitely required.
When calculating pipe sizes for multiple Bathrooms there are `probable usage` factors that are supposed to be used - basically guessing the likelihood of how many Bathrooms / Hot & Cold outlets would be being used at the same time.
However calculating on a `probable use` basis can really backfire if the Householders / Family do use each Bathroom at the same time every day !
And calculating pipe sizes has to take into consideration the `Resistance Factors` of the pipe lengths and fittings which as you know can have a considerable effect on the Flow rate available - especially in a 5 Bathroom property.
To calculate the Resistance in the `Main pipe runs` and the branches to the outlets you would need to know what pipe size and the length of the pipe runs plus the amount of fittings / elbows - then as in calculating Gas pipe sizes you would work out the `Equivalent Length`- length of pipe plus the resistance factor of each elbow / tee [from a Table of resistance factors].
After calculating all of the pipe runs resistance factors you need to calculate the pressure / flow rate within the Main pipe runs and be able to establish if the volume is sufficient to be able to supply all of the branches / outlets simultaneously.
This is FAR from an easy task and should NOT be falling on your shoulders !
I hope that reading this as well as other Members comments will urge You to seek specifications for the Hot - Cold and Secondary return pipe sizes from the Renewables Company.
Chris