Heating circulator incorrectly sized?

[D_Hailsham]

All bar the 4 radiators achieve this at the same temperatures as the flow and return at the boiler. I can get an 18 degree differential on these 4 radiators but the incoming flow temp is only 65 to begin with.

There will be a drop in temperature along the pipe due to heat lost from the pipes, but a 14 degree drop is excessive.

It's worth noting that these 4 radiators are the last 4 on the system and furthest away from the boiler and pump and when closing all other radiators down the flow temperature achieves 79 degrees at these radiators

This is really strange. If there is a 14 degree drop when the other rads are on, why no drop when they are off?

Why is the flow set to 80 degrees? At this level the return will never get below 55C, so the boiler will never condense and run efficiently. In this mild weather with outside temperatures around 10 degrees the flow temperature should be below 65C. Try setting the boiler temperature to 70C and balance for a 15-18C difference.

Do you have kW output details of your rads? If not, use the information in the Stelrad Catalogue, page 44. Post the total rad output.

 

[PullerGas]

Aye, I wish I had a quid for every time someone tells me a circulation pump will cure undersized system pipe work. Depending on the radiator sizes of course, but a 16 radiator system & 28mm main F&Rs.......Hmmmmmmm??!!!

24kW max with a 11C differential; 45kW with a 20C differential. This is based on a max velocity of 1 m/sec.

The OP boiler is designed for a 20C differential and set to 24kW output, so I don't see any problem if correctly balanced.

DH if you read your input in this post, you may see your contradiction?

 

[D_Hailsham]

DH if you read your input in this post, you may see your contradiction?

Sorry PG, you've lost me. Please explain what you mean.

 

[fezster]

Have a read of my (extremely long!) thread here:

//www.diynot.com/diy/threads/vaillant-438-with-3-zones-frequent-s53.366928/page-15

But summary is that it's a 24 rad system with a megaflow cylinder, split into 3 zones (11 upstairs, 13 downstairs). The furthest rads were struggling to warm up. Fitting a Grundfos 25/80 has helped immensely. I wouldn't say the system is perfect, as I've noticed over the last couple of years that occasionally it'll hit S53. Not sure under what circumstances, and certainly not as often as it was doing so before upgrading the pump. Differential was targetted at 20 degrees on each rad, but this is approximate only, and cant be achieved precisely on every rad.

Another point worth mentioning. Boiler flow temp has to be set higher than the cylinder stat. In my case, cylinder stat is approximately 65 degrees, so boiler flow temp is set to 75 degrees.

 

[PullerGas]

DH if you read your input in this post, you may see your contradiction?

Sorry PG, you've lost me. Please explain what you mean.

Do you have an engineering background DH?? In M&E perhaps?..........Just a thought.

 

[D_Hailsham]

Do you have an engineering background DH?? In M&E perhaps?..........Just a thought.

Some mechanical, but mainly electrical/electronic. However, I don't see that is relevant.

You said I was being contradictory, but can't see where. Maybe you could point out the contradiction.

 

[PullerGas]

Do you have an engineering background DH?? In M&E perhaps?..........Just a thought.

Some mechanical, but mainly electrical/electronic. However, I don't see that is relevant.

No, perhaps you wouldn't. Just that I've often thought that the 'so called' educated mind takes a very self righteous view of practical problems, whereas a Tradesman will always embrace the experienced mind first. It maybe a mindset thing, who knows??!!
Regardless, have a wonderful Hogmanay & a fruitful 2016.

 

[PullerGas]

Aye, I wish I had a quid for every time someone tells me a circulation pump will cure undersized system pipe work. Depending on the radiator sizes of course, but a 16 radiator system & 28mm main F&Rs.......Hmmmmmmm??!!!

24kW max with a 11C differential; 45kW with a 20C differential. This is based on a max velocity of 1 m/sec.

The OP boiler is designed for a 20C differential and set to 24kW output, so I don't see any problem if correctly balanced.

Here's a wee clue DH; where or whom said the OPs boiler is set at a 24KW output or did I miss something??

 

[bhm1712]

Aye, I wish I had a quid for every time someone tells me a circulation pump will cure undersized system pipe work. Depending on the radiator sizes of course, but a 16 radiator system & 28mm main F&Rs.......Hmmmmmmm??!!!

24kW max with a 11C differential; 45kW with a 20C differential. This is based on a max velocity of 1 m/sec.

The OP boiler is designed for a 20C differential and set to 24kW output, so I don't see any problem if correctly balanced.

Here's a wee clue DH; where or whom said the OPs boiler is set at a 24KW output or did I miss something??

I have said that a couple of times including in my initial post.

 

[PullerGas]

Aye, I wish I had a quid for every time someone tells me a circulation pump will cure undersized system pipe work. Depending on the radiator sizes of course, but a 16 radiator system & 28mm main F&Rs.......Hmmmmmmm??!!!

24kW max with a 11C differential; 45kW with a 20C differential. This is based on a max velocity of 1 m/sec.

The OP boiler is designed for a 20C differential and set to 24kW output, so I don't see any problem if correctly balanced.

Here's a wee clue DH; where or whom said the OPs boiler is set at a 24KW output or did I miss something??

I have said that a couple of times including in my initial post.

Apologies, so you did fella. Has that been checked & is that correct according to the heat loss calcs? Has the system bypass been checked?

 

[D_Hailsham]

Here's a wee clue DH; where or whom said the OPs boiler is set at a 24KW output or did I miss something??

I have said that a couple of times including in my initial post.

Can we get back to the problem now?

OP: Have you found out the actual rad outputs?

 

[Steelmasons]

Why is the flow set to 80 degrees? At this level the return will never get below 55C, so the boiler will never condense.

Why a figure of 55c?
Are you suggesting flue gasses won't condense above 55c with respect to O2/CO2%?

Do you remember back end rot mixing valves along with their intended purpose DH?
I'm sure Google will assist you with this , was it not yourself calling out some of the so called 'professionals' on here?
I have some time on my hands for a few days so maybe we can have a good ole chinwag regarding the industry?

Looking forward to it.

 

[D_Hailsham]

Are you suggesting flue gasses won't condense above 55c with respect to O2/CO2%?

The temperature at which condensing stats to occur depends on the Dew Point of Natural Gas, which varies with the composition of the gas. I've seen values of 57C (Viessmann) but most sources recommend 55C.

Are you suggesting that condensing can be achieved at higher temperatures by adjusting the 02/C02? If so, what improvement would it achieved, remembering that this is only the temperature at which condensing begins

Do you remember back end rot mixing valves along with their intended purpose DH?

Never heard of it, but I can guess what it means: corrosion of the heat exchanger of a non condensing boiler due to too low a return temperature.

 

[Steelmasons]

Are you suggesting that condensing can be achieved at higher temperatures by adjusting the 02/C02? If so, what improvement would it achieve.

You tell me DH considering you're one of the main players on here who tried to ridicule (with not much success .) the very ones who have forgotten more than you will ever know with regard to system design/installation/combustion etc etc etc.
Now if you would like schooling on any of the above just shout , domestic of course as you're not yet ready for commercial.

 

[Steelmasons]

remembering that this is only the temperature at which condensing begins

Really?????