6 storey house. vented cylinder in basement. Bronze pump sizing issue

[justalex81]

I have a 500L vented cylinder in a 6 storey building. It has a secondary hot water return loop that is currently using a grundfos 15-50 pump. I don't think it's the correct size but i'm unsure because of the differences between a sizing a closed loop system (i.e a heating circuit) and an open vented hot water circuit.

If i sized it using the normal methods then i'd need a pump with at least a 15m head on it. Am i on the right track or is there a different way of calculating it for hot water circulation?

Any help is appreciated!

 

[Howsie]

It's different. What symptoms are you experiencing?

 

[justalex81]

low hot water temp on top floor. takes longer for hot water to come through at the outlets.

 

[Howsie]

Turn the pump off and see what that does to the temperature. Let it run for a minute or so.

 

[albatross]

Has it always been like that? Could the top floor have longer draw offs from the main ring?

 

[snowhead]

Has the system been balanced?

 

[ADM360]

sound like the secondary return loop doesn't go to the top floor!! what floor is the cylinder on?

 

[Howsie]

Basement.

 

[justalex81]

there is a cold water tank on the roof and the cylinder is in the basement.

the draw offs are approx same distance from the main ring as on the other floors. water temp is low everywhere but that's because the cylinder is knackered. I'm confident the return loop has been balanced correctly.

I am quoting to rip out the existing boilers and cylinder and replace it all. I don't want to quote for the wrong pump and then i keep getting call backs. The house has been turned into medical consultation rooms so the system only feeds wash hand basins in the toilets and the consultation rooms.

 

[ADM360]

Basement.

Good guess Howsie:clap:

If your only symptom is that the water temp is low, yet you say later that the water temp is low due to a faulty DHW cylinder I don't see the problem!! or am I missing it!!

I far I know the secondary return doesn't have to "pump" the water round at a high rate only keep it circulating to cut down on wasted water at draw offs, I would have though that a 15/50 would be up for the job.

How long dose it take for the warm water take to get the the draw offs?

 

[ADM360]

OK re-read title

 

[justalex81]

top floor takes 15 seconds longer that the other floors. The secondary return loop definitely serves the top floor.

I inderstand that it doesn't need to pump the water at a high rate but would it even circulate to the top floor if the pump head is not enough?

wouldn't it take the path of least resistance and just circulate around the floors it can reach. we are talking about a minimum of 15m from basement to top floor versus the pumps 5m, without taking into account resistance from the pipe work and fittings.

as said the water temp is low everywhere due to the cylinder being a squillion years old and scaled up.

 

[stevetheplumber]

with six floors all above the cylinder i'm surprised its got a pump should fly round on gravity

 

[zzzjim]

Is the building well heated ( or is that job done by un-lagged secondary hot water return loop ! )

 

[justalex81]

heating system is a seperate issue lol

 

[doitmyself]

Pump sizing information starts at page 15.

http://www.wee.no/doc/Gode forslag - pumper og løsninger.pdf

 

[happyflyer]

with six floors all above the cylinder i'm surprised its got a pump should fly round on gravity

Steve its a pity you can't do a double like or even a triple what do people think we did before pumps, just what you said, this is most likely a balancing problem, there is less known about balancing secondary circuits than is about plain heating, Oventrop even do an automatic secondary circuit balancing station so you don't need to balancing, commercially only. Sorry files are too big to post.

 

[happyflyer]

Pump sizing information starts at page 15.

http://www.wee.no/doc/Gode forslag - pumper og løsninger.pdf

Good info in this booklet

 

[SafeGasInstall]

unless your mixer has fail near top floor and mixing the hot and cold ......

also if pressure is good in the house can you not reposition new UHW cylinder on middle of the house and use 15/60 bronze and make sure all secondary run is in 15mm?

 

[justalex81]

It's no longer a house it's a medical consultancy and putting in UHW is not an option. There are currently no blending valves on the basins (there will be after the new tank goes in)

 

[Howsie]

Turn the pump off and see what that does to the temperature. Let it run for a minute or so.

<cough>

 

[chris watkins]

Checked all the circuit (F&R) is insulated ?? Quote for one of the Grundfos Comfort's either the auto-adapt or the one with temp / time control.