System design advice please!

[Andygasman2010]

wrong post

 

[Andygasman2010]

you need to tell the owner at the start that there could be other, undetected faults and you can't guarantee satisfaction, not having a crystal ball. He may get the hump with you if he spends money and doesn't get what he'd expected

Yep covered myself here, told him this is only part of a bigger job required.

 

[Andygasman2010]

I did think about where to take the hot water circuit from Would it be best to take it from another pair of tapping in the LLH? Or take it from the boiler side of the LLH?

 

[spraggo]

I did think about where to take the hot water circuit from Would it be best to take it from another pair of tapping in the LLH? Or take it from the boiler side of the LLH?

Hi, am I missing something here, surely if you fit a ABS across the flow and return approx 1.5m from the boiler and set it to give 1633I/h through the boiler at max heat of 80c then fit balancing valves on the flow to the cylinder and heating circuit is the way forward. As I have already suggested it does seem that the pump is undersized according to the size of the heating system. I would have thought that you ned to calculate the pressure drop due to the friction in the pipework, alowing for the pressure drop across the boiler and then fit a pump, preferably a vario speed one to cope with same, before you alter the pipework.

spraggo

 

[D_Hailsham]

I would have thought that you need to calculate the pressure drop due to the friction in the pipework, allowing for the pressure drop across the boiler

You must come from a commercial background, where the job tends to be done properly; this is the domestic market.

I doubt if 10% of domestic heating installers would know where to start when it comes to calculating the index circuit of a heating system.

 

[ajrobb]

As the pipe layout is down to guesswork, he might have to measure pipe friction.

The boiler manual charts the (large) pressure drop across the boiler against flow, so can he get a good estimate of flow from pressure tappings? Perhaps he could he work one floor at a time (turning off radiators on other floors). Run the existing pump flat out with the ABV closed and measure the pressure drop across radiator feed and return and across the boiler. Tot up the rad sizes on each floor. Either work it out himself or come back with the readings. Try and figure out what size pumping station it needs.

 

[spraggo]

[quote="D_Hailsham";p="1812276I doubt if 10% of domestic heating installers would know where to start when it comes to calculating the index circuit of a heating system.[/quote]


Try this for starters.
http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm

Regards
spraggo

 

[Andygasman2010]

I doubt if 10% of domestic heating installers would know where to start when it comes to calculating the index circuit of a heating system.

I'm affraid i'm one of that 10%! I did learn how to do it all properly several years ago but day-to-day I just don't use it. Even this system is way bigger than what i'm used to! Cheers to the guys on here for the advice on this stuff, particularly Lee who's first post was very helpful.

 

[spraggo]

I'm affraid i'm one of that 10%! I did learn how to do it all properly several years ago but day-to-day I just don't use it. Even this system is way bigger than what i'm used to! Cheers to the guys on here for the advice on this stuff, particularly Lee who's first post was very helpful.

What?!! when he suggests increasing the primaries froim 28mm or even 35mm with only 22mm tappings on the boiler.

 

[D_Hailsham]

Try this for starters.
http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm[/QUOTE]


I think Small Bore Heating Systems and Copper Tubes in Domestic Heating Systems would be adequate for most domestic installations.

Run the existing pump flat out with the ABV closed and measure the pressure drop across radiator feed and return and across the boiler.

As I said before: provided you know the boiler output and the temperature differential across the boiler you can work out the flow rate. It is then a simple matter of using the pump manufacturers published literature to find the head which equates to that flow rate for the pump speed setting. The boiler pressure loss graph will provide the loss at that flow rate. You can then easily calculate the loss in the rest of the circuit.

 

[spraggo]

[quote="D_Hailsham";p="1812365installations.

As I said before: provided you know the boiler output and the temperature differential across the boiler you can work out the flow rate. It is then a simple matter of using the pump manufacturers published literature to find the head which equates to that flow rate for the pump speed setting. The boiler pressure loss graph will provide the loss at that flow rate. You can then easily calculate the loss in the rest of the circuit.[/quote]


Well done D_Hailsham, And don`t forget you can even calculate how many litres the system contains using the same formula.

 

[D_Hailsham]

Don't forget you can even calculate how many litres the system contains using the same formula.

Enlighten me.

 

[bengasman]

...You must come from a commercial background, where the job tends to be done properly; this is the domestic market.

I doubt if 10% of domestic heating installers would know where to start when it comes to calculating the index circuit of a heating system.

Says the expert householder who has never been corgi/gsr registered in his life.

 

[Biggles..]

I'm affraid i'm one of that 10%! I did learn how to do it all properly several years ago but day-to-day I just don't use it. Even this system is way bigger than what i'm used to! Cheers to the guys on here for the advice on this stuff, particularly Lee who's first post was very helpful.

What?!! when he suggests increasing the primaries froim 28mm or even 35mm with only 22mm tappings on the boiler.

And why not.

 

[Gasman77]

Thats because 90% of installers don't need to know it