Flow rate comparison s or y?

[gassafe]

Went to quote a boiler recently, 18 rad system, and was surprised to see a little 22mm mid pos valve in the airing cupboard. Customer says some rads struggle to heat, its a 28kw system at present.

I am going to quote a 30 cdi sys, would it be beneficial to change to a 28 3 port in airing or changing to a s plan in airing? Would either of these changes increase flow rates? Or am I wasting time?

Does anyone know the max btu through the different sized valves I am basically asking? A 30 cdi kicks out approx 100,000 btu!

 

[chris watkins]

ruff & ready- with a system designed with an 11deg C (old) drop 22mm will give you 13kW. With a 20deg C (new) drop 22mm will give you 23kW. So IMHO 28mm is required (22 & 40kw).
Can I suggest treating yourself to a copy of the Domestic Heating Design Guide a very good book full of all this sort of info. Have you done a whole house heatloss to size the new boiler a professional should not be guessing at the size should they?

 

[kozak1968]

Balancing the system may help or the system boiler pump may struggle with the amount of rads.. Maybe worth fitting an OV boiler with a bigger external pump.

 

[Roger Welton]

According to honeywell

22mm 3 port is good for 13kw, 28mm for 23kw

22mm 2 port 23kw and 28mm 36kw

 

[chris watkins]

According to honeywell

22mm 3 port is good for 13kw, 28mm for 23kw

22mm 2 port 23kw and 28mm 36kw

Am I right Roger that these valve have a resistance to flow of less than that of an equivalent length of pipe?
They always look like they restrict to me with that big ball in the pipeline but I am sure that is what I was told.

 

[gassafe]

ruff & ready- with a system designed with an 11deg C (old) drop 22mm will give you 13kW. With a 20deg C (new) drop 22mm will give you 23kW. So IMHO 28mm is required (22 & 40kw).
Can I suggest treating yourself to a copy of the Domestic Heating Design Guide a very good book full of all this sort of info. Have you done a whole house heatloss to size the new boiler a professional should not be guessing at the size should they?

Have just ordered a domestic heating design guide! Bit of bedtime reading! I hope it has stuff like this in there or I'm blaming you

 

[gassafe]

According to honeywell

22mm 3 port is good for 13kw, 28mm for 23kw

22mm 2 port 23kw and 28mm 36kw

im sure there are alot of systems out there bigger than 13 kw on 22 mid pos!!!!

 

[Roger Welton]

Am I right Roger that these valve have a resistance to flow of less than that of an equivalent length of pipe?
They always look like they restrict to me with that big ball in the pipeline but I am sure that is what I was told.

I'm not sure what the exact pressure loss characteristics are but the values I mentioned were those provided by honeywell on their training day.

But visually they have to be more of a resistance than a strait length of pipe. Even if the Csa is greater they will reduce flow as the laminar flow breaks down and reforms as it passes through the valves.

 

[Roger Welton]

im sure there are alot of systems out there bigger than 13 kw on 22 mid pos!!!!

There are a lot of things out there that shouldn't be!

 

[chris watkins]

Have just ordered a domestic heating design guide! Bit of bedtime reading! I hope it has stuff like this in there or I'm blaming you

Where do you think I get all my info from ? It is now used as the base to teach the apprentices on C&G courses so if you don't like your bed time reading & keep falling asleep you most certainly can't blame me, you will just have to go back to school. LOL.