How good is good enough?

SweatyInToronto

Does it make sense to entirely re-pipe a boiler room for primary-secondary, given the following...

We currently are using 2x300K BTU boilers with outdoor reset. The 2 boiler pumps and single circulator run constantly currently which isn’t ideal. However, we have had this for about 15 years and figure we can keep it going for another 8-10 before needing new boilers. Perhaps longer if lucky. Our DHW is a separate new boiler, not attached.

However we do have issues:

a) There is a fair amount of pump noise/vibration heard in the unit above to boiler room although the baseboards are quiet, except for an occasional ping/ting during season startup

b) If we ever want to drain and refill the system, there is bleeding required, which is difficult to arrange with 20+ different units

c) There is no boiler protection, so water temp must be kept over 140 degrees, which means the units are hot in the shoulder seasons.

So piping or re-piping ideally, like is described in the book “Pumping away”, below with power-purging is appealing, however I’m wondering if it’s worth the effort?


Below is what we have now, approximately. Reworking it according the the above would be essentially re-piping it entirely. That said, we have to do some work to replace shutoff valves anyway and drain the system in the summer.

I'd like to get an air eliminator on the system and ideally be able to power purge, and have boiler protection, and cycle on-off the boiler pumps - with or without the primary-secondary.

Would it make sense to revamp the piping entirely per "Pumping Away" or just work with what we have and attempt to retrofit in the desired features, if the current system is only going to be in use for the next 10 years? I'm not quite sure how to approach this...

Thanks for your suggestions!

Jamie Hall

Would it actually be all that hard? I haven't seen your actual layout -- obviously -- but it seems to me that although you would need another pump -- for the secondary circulation -- that if you are going to repipe anyway to pump away and add purge capabilities, adding the necessary crossover pipe couldn't be that hard?

EdTheHeaterMan

If you add isolation valves as indicated in the green area, you can use this arrangement with the new boiler in 10 years or so. Re-pipe is not a waste of time but a time saver when the new boiler is replaced.

If you add valves to bother sides of the manifold you could isolate individual units without shutting down the whole building.

If you add zone valves to each individual loop you could offer individual thermostat control to each unit.

There will be savings on fuel with each additional upgrade. Get a couple of Hydronics pros in there to evaluate the system.

Yours truly.
Mr,Ed

EBEBRATT-Ed

@SweatyInToronto

Repiping is fine. I am a huge fan of P/S piping.

But your 3 complaints, noise/vibration, bleeding and boiler protection will not be automatically fixed just by going to P/S piping.

Would I repipe it? Yes!!

Your pumping toward the expansion tank which is not the best. You need an air separator and valves to isolate the system.

The secret to this is to lay the piping out correctly.......if you have the room.

Keep the secondary circuit away from the boilers. Do not put the expansion tank air separator secondary pumps etc over the top of the boilers. Create some distance and make the primary branches to the boiler with some length.

This way when the boilers are replaced you shouldn't have to touch the secondary loop and replacement will be much easier. The primary branches can be cut and reworked with no issues.

It won' t be money wasted

SweatyInToronto

Ok thanks for your feedback!

Youngplumber... good point on the saving. It would save something for about half the heating season. One thing I've noticed is that the baseboards don't seem to emit unless the water is at least 120 degrees. They are long, and heavy probably cast iron. So can't go lower than that. But it would save some gas.

Jamie: true the diagram from the book has the return close to the supply, as does my modification of it. But in the room the supply and return are a goodly distance,  perhaps 15 feet. Still it's doable. 

Mr Ed: Should mention there is only one zone in our building. I was going to type that in my diagram below the book's but neglected, sorry. Agree we want to be able to isolate the secondary loop and the boilers as well.  

Hopefully I'm not infringing on copyright by copying from the book!

More to say but late, have a good night.

SweatyInToronto

EdeBratt: with you on the big picture. Thanks for mentioning. There is room thankfully.

And to a point mentioned above, I will get Pros input of course, though I'd like to understand the big picture first and have a rough idea of the main issues involved. Hence the reading of pumping away.

One part of this that I'm not quite grasping is whether the two loops would have different temperature settings. The primary loop would always be 140 minimum but could be higher mid-winter. If there is just one secondary loop what would enable it to be at a lower temp than 140? It would be sucking water from the primary loop which is at 140, no? It could cool down if a secondary pump isn't running, so the average temp is lower. Is that the way we would maintain a lower temp in the secondary loop?

I've seen some diagrams where cooler return water is mixed in with the hot supply and sent to the rads to reduce the temperature, using a a mixing valve. We're already mixing in the hot supply with the cold return to help maintain the primary loop at 140. Not sure if we'd need to do the reverse also...want to keep it simple as possible and still have it produce comfort...

Solid_Fuel_Man

Is this all fin tube? Each unit has one zone valve and one thermostat I assume?

EBEBRATT-Ed

@SweatyInToronto

The flow rates in the primary loop and the secondary loop can be the same or different. The heat input from the boiler and the heat output from the baseboard will try to balance. If both loops pump exactly the same amount of water the system will work like a normal system without primary secondary. There will be no water crossing "over the bridge" If the flow rates are different the water temps in each loop will change to a new balance point. It's in Dan's book primaryy secondary pumping