Open Loop Radiators

LJPurvis

Our house is heated by the Boise Warm Springs Water District. Basically, 165 deg F geothermal water comes into our house at a fixed pressure like city water. Unlike most systems, however, all homes on the street "dump" our water in a creek behind the house. Our house and water are heated using this geothermal water (which does contain sulfur). We are building an addition and want to put in new radiators that are a little sleeker than the classic floor cast iron radiators. We are finding many radiators, although made with stainless steel or iron, say they are not for open loops, gravity feed, or steam.
I am curious if the term open loop actually applies to our system. The Boise Warm Springs Water District maintains a fixed pressure coming into the house so we are not pumping, don't use gravity, and it is definitely not steam.
Do the standard suppliers have it right or do they not understand our system and are just reading from their brochures?

Ironman

You still have an open system which would be constantly introducing minerals and oxygen into the system. These are the two greatest enemies of a hydronic system.

If you wanna do something like this, use a properly sized heat exchanger to isolate the house (closed loop) from the geo (open loop). Use a tube and shell HX, not a flat plate, but have isolation valves so the open side can be desclaed regularly.

LJPurvis

Our house, built in 1907, has been using this heating method since it was built. Most of the radiators are original. The way this is managed is the system has a discharge valve. When the house calls for heat the valve is open. When the system no longer calls for heat the valve is closed. The valve sits at the very end of the discharge line. Would this still be considered an "open" system?

Ironman

Absolutely. It's really no different from what's known as a "pump and dump" system. You're just using a valve to control flow instead of a pump.

LJPurvis

Ironman, thank you for the responses. I have read threads on this forum discussing the open vs close loop. I am not too interested in which is better. But I do wonder if people understand the system that we have on Warm Springs in Boise, ID.

From what I have read, an open system is "An open heat system is one in which the potable water that serves the drinking and bathing needs of the house is also used to heat."

If you can imagine a line coming in from the street that maintains 20psi into the house with geothermal water (remember we have a lot of hot springs in Idaho) averaging 175 deg F. That water is then run through my radiators (in parallel) and all of them feed out into a single discharge line that is controlled via a valve that has a bypass manual valve that is always open a tiny amount. The system maintains the 20psi whether the house is heating or not. At no time is open air, house water, etc. attached/mixed/etc. with the heating system. And gravity is not used; it is a controlled pressure from a pump house.

We are building a new addition so I met with the plumber today that specializes in houses on Warm Springs avenue. He says that "No, these are not open systems in the traditional sense. People think they are because they discharge but they operate exactly as if it is a boiler system."

HVACNUT

Like @Ironman said, you really need a coax heat exchanger to separate the geo circuit from the heating circuit (open loop on the geo side, closed loop on the space heat side).
There will be work involved using a circulator(s) pressure reducing valve, extol, etc. Basically everything you'd need to pipe a hydronic boiler. A relay with dry contacts to activate the existing geo valve. You can even do zoning.
It won't be difficult for a competent heating professional.

Ironman

@LJPurvis,
I fully understand what you're describing and it is indeed an open system. A closed system is one where the water stays in the loop and no fresh water is added except minute amounts.

By receiving fresh water and dumping it, what you have is very much an open loop. Whether or not it's potable water doesn't mean it's a closed loop.

Again, it's almost identical to what's know in geothermal as a "pump and dump".

So, what your suppliers are telling you is correct.

Again, if you want your radiators, or any other new components to have a warranty, then use a heat exchanger to isolate the house into a closed loop.

LJPurvis

I do currently use a heat exchanger to heat our hot water. It works great. I have to admit that I have thought of installing a closed loop system for several reasons. However, the reasons do not currently outweigh the current system. I think, maybe, someday.
Thank you for the conversation.

Brewbeer

If the hot water coming to the house doesn't have any oxygen in it, rusting of iron components many not be a significant concern. 100+ year old radiators still functioning would seem to indicate that maybe there isn't enough oxygen in the hot water supply to cause significant corrosion.

Gsmith

Can the hot water supplier give you an analysis of the water they supply (minerals, and dissolved oxygen content). You might be able to compare the water quality with problem issues for the proposed radiators.

Zman

The manufactures will always warn against an open system. Most open systems will eat the ferrous components in the radiators as indicated above.
Water from an open system like yours usually has pretty aggressive chemistry. By the sounds of things, yours is pretty mild.
I would either have the water analyzed or check with your neighbors and see what they have had luck with.

LJPurvis

Zman,
I used to have that information. I'll try to get it again. I do know it is not really high in sulfur as the "rotten egg" smell is very low when we tap into it (which we rarely do). I have also read that the real issue does, in fact, occur when the water is exposed to oxygen it can generate hydrogen sulphide which is highly corrosive.
Long story short, we are staying with our current system for awhile. It's worked since 1907.

Brewbeer

The observation of even a low concentration of rotten egg smell indicates that hydrogen sulfide is present. Hydrogen sulfide will react with oxygen if present to produce sulfur/sulfate, and water. The oxidation reaction is probably pretty rapid at the high temperatures of the incoming water. If I had to guess, I'd say the oxygen content of the hot water supply is too low to cause significant rusting of cast iron components.

LJPurvis

Yeah, this stuff just bubbles out of the ground here. Back in 1892 the Boise Warm Springs Water District decided to take advantage and dug a well, capped it, and is now the oldest continuously operated geothermal system in the U.S. Just like pretty much any place hot water comes bubbling out of the ground it has a sulfur smell. As for the oxygen content, it is very little. The sulfur smell is actually created by a bacterium that feeds on the sulfides. It's byproduct is hydrogen sulfide. The bacteria are anaerobic; they only thrive in oxygen deprived areas. Oxygen kills them. Hot springs that smell of sulfur are heated deep in the ground where there is little to no oxygen. The hot water then rises rapidly to the surface. The well for Boise Warm Springs Water District was dug down and capped. So we have very little oxygen in the water.
By the way, I am learning all of this because of the discussions on this thread. Cool stuff.