Maximum length for HW circulation loop??

[jon26]

Some advice please...

Is there a maximum length for a pumped hot water circulation loop i.e. would you say a 40m run from the cylinders to the last hot water tap is excessive... ensuring the bronze circulator is sized sufficiently?

I presume you can get this length of circuit, and probably longer, in large mansions and other buildings?

Does the circ. need to be insulated aswell?

Cheers

 

[Agile]

Just remind me of the name of your company Tony, so that I know not to use you.

In spite of your previous comment I will still reply, not really for your benefit as you dont want me to tell you, but for the benefit of the many people who read and learn from these forums.

The simple answer is that it can be as long as you like but limited by the size of the pipe and the flow rates required and the heat loss.

The pipe must be well insulated so that the heat loss does not defeat the objective of the exercise to provide almost immediate hot water when a tap is turned on without excessive running costs.

This situation is usually encountered in hotels.

Tony

 

[powell30]

Tony, Can you fit a circulator to an unvented system and if so how would this work? ie already mains pressured but you then have to pump the recirculation side......just can't get my head round if this is possible.....

 

[Agile]

Most pumps are rated for a pressure of several Bar but it should be a bronze pump as the standard ones are meant to corrode!

Although I have been using a standard ( used ) one for the last 14 years on a direct water system!

If I was doing that for myself then I would be using a standard pump based on my experience.

The pump circulates hot water from the top of the cylinder and returns it to a tapping about 300 mm down. Thus all the hot water loop is kept hot ready for immediate use by any outlet on the loop.

Tony

 

[jon26]

Just remind me of the name of your company Tony, so that I know not to use you.

In spite of your previous comment I will still reply, not really for your benefit as you dont want me to tell you, but for the benefit of the many people who read and learn from these forums.

The simple answer is that it can be as long as you like but limited by the size of the pipe and the flow rates required and the heat loss.

The pipe must be well insulated so that the heat loss does not defeat the objective of the exercise to provide almost immediate hot water when a tap is turned on without excessive running costs.

This situation is usually encountered in hotels.

Tony

Thanks Tony, please accept my apologies about what I wrote.. i must have been in a bad mood that day.

Thanks again for your helpful reply.

 

[doitall]

Tony, Can you fit a circulator to an unvented system and if so how would this work? ie already mains pressured but you then have to pump the recirculation side......just can't get my head round if this is possible.....

Most un-vented cylinders, you would connect the secondary return into the cold feed as per the manufacturers instructions.

 

[Agile]

Most un-vented cylinders, you would connect the secondary return into the cold feed as per the manufacturers instructions.

I would never recommend doing that because once half the cylinder capacity has been used up and the bottom half is cold then the effect of the secondary circulation loop is to cool the water at the top of the cylinder.

If that must be used ( because there is no tapping near the top ) then the secondary circulation pump must be inhibited while the cylinder is reheating.

Tony

 

[doitall]

Don't be daft

The temperature of the return will be the same, true it will take longer to heat the cylinder, because you will be heating the whole of the cylinder to the set temperature instead of just the top 1/3rd, in practice you will be doubling the available hot water.

The manufacturers instructions are how you do it in any case.

 

[spacethegas]

hang on i'm still trying to get over Agile thinking a bronze pump is not the correct pump to use for the purpose it is designed for.

my father uses old ch circulating pumps for his fish ponds they don't last long, but they are not designed to do so. + i have an endless supply for him.

 

[Agile]

Don't be daft

Dont be daft!

The temperature of the return will be the same, true it will take longer to heat the cylinder, because you will be heating the whole of the cylinder to the set temperature instead of just the top 1/3rd, in practice you will be doubling the available hot water.

I am being practical, not daft.

If the cyliner is full at 60°C and you use half of the water, the top will be at 60°C and the bottom at the cold supply temperature of say 10°.

If you then use the secondary circulation the 60°C top will be returned to the 10°C bottom and you will end up with an average cylinder temperature of just 35°C.

That problem can be prevented by inhibiting the sec pump during reheat periods. In any case its not needed while hot water is being drawn .

Tony