Looking for a component

[Nostrum]

Hi all,

I stumbled across this site looking for a part for a controller I am building and, as I don’t know a great deal, I thought this would be the perfect place to find out!

The long and short of it is: I’m trying to build a cascade controller for a pair of boilers we have recently installed. I’ve sourced parts for the cascade side of things using 0-10v controllers which are powered by 24ac and all DIN mounted. I plan to install this into a sealed adaptable box so they don’t get fiddled with.

The boilers are called upon based on demand, and are switched on/off using a potential free contact on the boiler.

The final piece to the puzzle and what I need your help for, is to be able to alternate the lead and lag boilers so that both operate for a similar amount of hours, rather than one being worn out whilst the other collects dust!

So, I was hoping I could find a timed switching relay (amateur term). Ideally I’d like to be able to switch based on run hours, so only timed when energised or similar?

Does anybody know of a dinrail mounted relay, or even a term I could use to find such a thing?

I would really appreciate your help and thanks in advance!

Sam

 

[Minder]

One suitable device would maybe a SmartRelay, they have a real time clock option. There are a few manufacturers, some just re-labeled.
They are a miniature version of an industrial PLC.
M.

 

[shrtrnd]

I'm going to render an opinion. Hopefully others will supply the information you want if you don't like mine.
I've worked in a lot of plants that operate boilers, and it's no small task servicing them. If you alternate boilers, you're going to shorten their service life, because downtime will allow mineral salts to prematurely coat the pipes, when constant water flow helps reduce that. My opinion is to run one boiler. When it starts experiencing problems, switch to your second, back-up boiler for it's run-life while you service the first one for return to service when the second boiler has problems.
Hopefully somebody else here has information you would rather hear.
... and it's not stumbling that got you to this site, it's fate.

 

[Wiginometry]

I'm going to render an opinion. Hopefully others will supply the information you want if you don't like mine.
I've worked in a lot of plants that operate boilers, and it's no small task servicing them. If you alternate boilers, you're going to shorten their service life, because downtime will allow mineral salts to prematurely coat the pipes, when constant water flow helps reduce that. My opinion is to run one boiler. When it starts experiencing problems, switch to your second, back-up boiler for it's run-life while you service the first one for return to service when the second boiler has problems.
Hopefully somebody else here has information you would rather hear.
... and it's not stumbling that got you to this site, it's fate.

Definitely fate! But Shrtrnd is right it's best to run one till it experiences problems to help minimize salt/mineral build ups

Unless your plan is that when they switch over you're going to be doing monthly/quarterly cleaning/maintenance on them but honestly that may be more work than it's worth

 

[shrtrnd]

I just know from experience that running two boilers intermittently might seem like 'equal utilization', but what actually happens is that they both become restricted (less efficient) as time passes. When one requires service, you're left with a less than efficient boiler that you hope will do the job until the one that requires service is overhauled. Praying that the less efficient one in use holds-up, until the one being cleaned can be returned to service.
I see Nostrum's point, as it's common practice to alternate motor utilization in a system to extend the operating life of the system in use. Idle water in a boiler, contributing to mineral build-up within the pipes, can result in problems not seen with motor usage.
Wiginometry makes a good point, if Nostrum's application entails a scheduled preventative maintenance plan. I just haven't seen one like that where I've worked. They run the boiler until they see an unacceptable reduction in output efficiency, then switch to the second boiler while the inefficient one is serviced. I don't know the physical size of Nostrum's boilers, but the ones I've worked the controls on were huge, and it can take weeks to ream-out the pipes of mineral accumulation restricting water flow.
If my opinion is not of use Nostrum, let us know. There are some pretty smart guys here who can suggest the electronic system you originally proposed.