Best control strategy for mid-1950s radiant system?

Steamhead

Looked at this the other day- we hardly ever run into radiant. The original portion of the house is what looks like 1/4" or 3/8" Bundy pipe in the ceilings. There are a couple newer addition zones using PEX in the floor.

The boiler is the original National gas unit, with no return water temperature protection whatsoever. It looks to be in fine shape and the combustion test was spot-on. Based on its condition, the owner doesn't want to replace it.

The current control system is just standard room thermostats. No outdoor-reset of any type. High limit on the boiler is set to 140 degrees.

The system seems to be running OK, but I know we can do better. ODR would be a minimum, and what about mixing and circulation strategies?

I'm a bit out of my depth on this one, so thanks in advance for any help.

hot_rod

It's not so common anymore but a 4 way valve on ODR really solves multiple challenges, mixing, boiler protection and reset control. Super simple piping.

Variable speed injection pumping is another, requiring two pumps.

EdTheHeaterMan

I would be afraid of ODR without the valve that Bob mentioned. If it is working fine for all those years, I would hate to mess with its design and cause condensation of flue gas problems with a new lower return water temperature.

hot_rod

A few other options

kcopp

Sounds like a system I worked on a few years back. Its was an old coal, converted to oil converted to gas system. Had a Sarco thermostatic mixing valve in it. Ended up installing a new modulating IBC boiler that had reset.
How about a partial reset w/ a Tekmar 260.?

Steamhead

I like the 4-way valve option. Seems Watts owns Tekmar now, but they still appear to be in this business.

So we'd need a valve, actuator and control. Maybe a Tekmar 018 valve, 741actuator and 360 control? Would one valve work for all zones, or does each zone need its own mix valve?

hot_rod

A one temperature system is what it has been I imagine? So one mix valve if fine

Id assume that boiler can operate with low, or no flow? So a single pump with zone valves 

I think a delta P circ would work well also

The key will be that the boiler gets adequate flow with one zone only calling.

Paul Pollets

Viessmann used to make an HK-1 control which attached to their 4 way mixing valve and ODR. I'm not sure if it's still available to the US market. Their website does not show it. It worked well and was very dependable.
https://www.viessmann.ca/content/dam/public-brands/ca/pdfs/old/HK1/dekamatik-hk1-uni-io.pdf/_jcr_content/renditions/original./dekamatik-hk1-uni-io.pdf

Rich_49

The 4 way valves might be just what you need .
http://apps.tacocomfort.com/temp/tacopdftmp-220318091218.pdf

Steamhead

Thanks, all. Lots to think about. I'll keep you posted.