Steam converted to gravity HW?

SWEI

We're in the process of cleaning out an old gravity system in preparation for installation of a new mod/con and controls. The usual 3" mains leaving and returning to the basement above where the old boiler (entombed in 1992) used to live. What's odd here is that each of the 3" mains makes a loop around the crawlspace, returning to the boiler. Radiator supply and return lines are tied into the same section of main, in what looks to me like piping from a counterflow steam system. The radiator trim is all hot water, and old. I'd guess 1915, when a second story was added to the original 1880-something house.

I'm having trouble seeing how gravity hot water circulation would actually work in this configuration -- especially now that the mains are uninsulated. Re-piping all the supply lines for 18 radiators would not be easy, and (at this point) converting back to steam is not a viable option.

Harvey Ramer

They did put in some counter flow gravity systems back in the day. They usually used a different type of tee for the take off and returns.

Jamie Hall

Harvey Ramer said:

They did put in some counter flow gravity systems back in the day. They usually used a different type of tee for the take off and returns.

And your tip-off is the placement of those T's -- the feeds are all at 45 degrees up, while the returns are level to the side!

Harvey Ramer

Must have been a frugal gentleman that installed that system.

Zman

How is the heat distribution with the system as is?
The scary thing is that as you reduce the temps to make the mod cons do their thing, the gravity forces will be less.
Can you experiment a bit with it, as is before you commit yourself to the design?

Mark Eatherton

I can't say that I've ever seen an "ENTOMBED" boiler. Must have been covered with Mansville snow. I can see in my minds eye how it would work, and you could probably "enhance" it's operation by putting insulation on the upper half of the pipe. It had to have worked, or they'd have already ripped it out.

You could use a buffer tank with 4 ports, two on the side and one on top, and another on the bottom. Essentially a buffer tank/LLH/control reference point. The modcon goes in and out of the side tappings, with hot high and cold low. Then the heating system supply would be piped off the top and the system return pipe goes back to the bottom of the tank. No circulator on the load side, just good ld dependable gravity.

Basically, it goes back to being a gravity system and becomes proportional to the load, like it was designed to be.

I can see a bull head manifold on the near boiler piping, but I'd be interested in seeing how they piped the gravity system into a forced system. Tough and delicate split for the S&R. An isometric of the near boiler piping would be interesting as well, or more pictures. Or you can just explain it to us.

That radiator is a bread/food warming oven. As long as the heat is on, it works great!

The boiler either looks hot, or it's been run hard in the past and the refractory is breaking up. Either way, not a good scenario. I'm betting the heat exchanger has never been cleaned, and the clinkers are reflecting a LOT of radiant energy downward. Not a good use of gas.

Nice find.

ME

Paul48

M E......You're thinking stratification......right?

Steamhead

That's a one-pipe gravity system. Sometimes they used special tees but it looks like this one took advantage of stratification in the main.

You want to use a VERY small circulator on this. As ME says, it was designed to run on gravity and needs to stay that way. Not sure you could find a buffer tank, let alone a boiler, with big enough tappings for gravity, so your circ just needs to move the water thru the tank or boiler and the system will do the rest.

How much radiation is on this system?

SWEI

Thanks, all.

I have not done a radiation survey, but we did a complete MJ8 heat loss calc and came up with 134k at design conditions. The Raypak had a 514k gross output and was pumped with a Taco 1611. Amazing. Somehow they did have heat, but plenty of complaints. Make-up water (through a softener) into a cast iron fill valve, system leaking somewhere (we're still searching for that) and loaded with black & brown crud. Found a pipe in the upstairs maid's quarters that almost certainly used to feed the gravity tank. It had a leaking Hoffman 75 on it that was encrusted with minerals and rust on the pipe below.

I look at those mains as a kind of giant, extended header. I was actually thinking about a small circ -- just enough to create the appropriate flow in the mains -- that might actually allow the system to stratify. Thanks for confirming that.

We'll be installing proportional zone valves (Belimo CCV's) as usual. The FT mod/con and the mains should have enough mass as long as we don't overpump it.

Love the idea of insulating the tops of the pipes.

SWEI

I think I'm going to want eccentric reducers, at least on the return side. Anyone stock those? I can special order the Anvil Fig. 368 from anyone, but if there's stock on hand someplace...

Mark Eatherton

Paul, yes stratification is what makes it work. I've worked on numerous 1 pipe counterflow gravity hot water systems, and never had the opportunity to look at the distribution piping with an infrared camera due to pipe (ACM) insulation, but I'd bet it is well defined.

I also can't even begin to explain the hydraulic friction of two opposing low velocity flows in one large pipe, but it obviously is a factor, but these systems continue to work, flawlessly in most cases, until someone comes in and breaks up the party with velocity... You can enhance the flow with a pump, but once gravity takes over, I'd take the pump out of the picture.

Kurt, I wouldn't worry too much about finding the perfect concentric fittings. I see where you are going, and in an ideal world, you would be correct.

Now that you mention water QC issues, I'd recommend you cut some pipe and see what's hiding on the other side of the pipe. There may be a BUNCH of barnacles inside the mains, in which case I'd recommend a complete repipe with PEX, and non electric TRV's at each radiator, coupled with a VS DP pump and a mod con and you'd have the ultimate modulating radiant system. Gravity and barnacles should never be in the same sentence... They don't play well together

ME

Mark Eatherton

Regards leak sleuthing, if you turn the make up off, and you can read the residual pressure at the boiler, it will tell you at what level the lowest leak exists. Residual PSI divided by .433 = vertical feet of standing water. Might be tough to do depending upon how big the leak is, but it would at least get you on the same level as the leak. May have to resort to ultrasonic leak detection to get on top of it. Also, you have unions on the basement branch piping. I'd look in there and see whats lurking. Maybe use a small snake camera and take a gander in the main as well.

ME

SWEI

We should be cutting pipe later this week, and I will pay close attention to the condition of the internal walls.

A full re-pipe would be a significant challenge in this 2-story historic building -- quite likely enough to convince them to ditch the radiators altogether, as their plumber recently suggested they do.

SWEI

Two of the three zones are holding air.

The third (and largest) got to 25 PSI and then fell to zero. We could not get anything to register on the gauge after that. Tried filling the zone with water and after 500+ gallons have not found a single spot of water in the crawlspace -- or the walls -- or anyplace else on the property. We can easily vent rads on the first floor to the point of getting water. No water out of anything on the second floor, or out of the old gravity tank pipe. Found a pipe on the roof near there and hoped that might be the old overflow vent that someone had never capped, but no such luck. We believe that is probably an abandoned plumbing vent.

Leak should be above the top of the first floor rads, but have yet to see (or hear) any evidence of anything water-ish.

Jamie Hall

500 gallons? Eek. It's got to be in there somewhere! There isn't a weird cross connection to a plumbing stack anywhere, is there?

FranklinD

My mothers house has a connection to the soil stack on the third floor. It was no fun to locate. In her case, a pipe ran from the supply side of the highest radiator (on the third floor), to the expansion tank with sight glass that was buried in a wall so that only the glass was showing... Then from the top of that tank, a pipe that ran up through the roof (the overflow/vent). I've seen pictures of that in Dan's books.

However....there is a tee in the wall/ceiling somewhere, and another pipe runs across inside the slanted ceilings to the other side of the room, where it tee's into the soil stack.

Maybe some similar setup there, overlooked at some point? It almost sounds like you can fill it up a certain amount, but once you hit a certain altitude it is reaching over the top of a loop and beginning to syphon itself into a drain, at which point the pressure drops...

Boy, I don't know. That's fascinating. I wish I could see it in person.

SWEI

I was worried about something like that. We were looking for a sewer clean-out today, and uncovered several nearby, but nothing we could positively ID as coming from this building. Over the course of the past century and a half there have been at least four different wastewater systems in the area, so pipes can run pretty much any which way.

Harvey Ramer

Do you have the option of getting the water hot, keep filling it, and then get busy with your thermal imager?

Gordy

Fascinating I can see it working. I like ME's description as to being proportional to the load as the delta t narrows flow slows with in the mains. I hope you can salvage this system Kurt a nice meld between old, and new technology in the making.

Paul48

Someone gets the lovely task of listening at the stink pipe.

hot_rod

Maybe get some of that bright colored dye that the sewer districts use, inject it into the system and find the closest sewer manhole and watch for the dye.

That is a lot of water, and weight to not show up somewhere.

Mark Eatherton

Kurt, is there any water cooled refrigeration equipment on site, like a small walk in? Been fiddle faddled by that fickle finger of fate more times than I care to recall. "Oh look, there's a water line right here we can tap into..." My own father once tied a swamp cooler into a heating circuit. "Well, it looked like a water line..." It happens, and it will also give you a variable depending upon the load being imparted by the TXV. Most single pass water cooled equipment has been outlawed in Denver due to water waste, but there are some units out there still in operation.

ME

SWEI

No commercial refrigeration there -- it's a real estate office. I'm betting on an overflow pipe from the old tank and have a call in to their service plumber to find out which way the sewer actually drains (3 streets adjoining, all of which have sewer mains in them.)

SWEI

I was able to access the area behind the knee wall where the old expansion tank pipe is. No tank back there and no connection to the drains or vents -- just a 1" pipe coming off a tee from the radiator in their 2nd floor bathroom. We'll fix that when we replace the leaking radiator valve in the bathroom.

Leak or cross-connection has to be above the first floor but below the vent tappings on the 2nd floor radiators. More sleuthing...

SWEI

Harvey Ramer said:

Do you have the option of getting the water hot, keep filling it, and then get busy with your thermal imager?

At this point, not 'till after we get the new boiler installed.

Mark Eatherton

You may have to resort to helium. They use it to detect leaks in vacuum systems, and I've heard that in a concrete floor situations, their find rate is 100% on the mark. They say it's not cheap, but either is replacing the whole system due to fresh water induction...

ME

SWEI

Update:

The boiler shared its chimney flue with a gas fired water heater. Last week, we pulled in two PP flex vents and installed a small condensing tankless water heater. After pouring ~250 gallons of 135°F water into that zone, I was able to find the leak -- buried in the slab in front of the bathroom in the south addition.

Mark Eatherton

BINGA!! You are their HERO

SWEI

As soon as we located it, the owner commented that those grey discolorations in the floor covering have been there for years. The bathroom developed a leak in its water supply about six months ago and the plumbers were never able to locate the cause. They dug around the outside of the building and routed a new 1/2" PEX line through the outside wall, up and over the ceiling of an adjoining room (not in the attic, but exposed on the ceiling) and down into the bathroom. No hot water there for months.

The addition has a floor mounted radiator in one room and a ceiling mounted radiator in the other. There is also a gas fired wall furnace located almost directly underneath the ceiling radiator. An employee reported that they used to find water on the floor back there, which they always assumed had leaked out of the soda machine. The ceiling radiator stopped working some years ago -- the slab leak (a pinhole at the time) would have prevented water from rising high enough to fill it. When we first pressurized that zone, it built up about 40 PSI of air and then let go. I'm betting that blew out a rust plug.

We've decided not to cut the slab, but will locate and plug the lines feeding the addition. Next spring, we can open the walls and properly repipe the addition, including new hot and cold water to the bath and a working ceiling radiator in place of the inefficient wall furnace.

SWEI

Fired up the boiler on this job yesterday afternoon, starting with a fixed 114°F setpoint and the Taco VR1816F on minimum speed. Less than 90 minutes and all but one radiator was nicely warm. Hung and wired a temporary outdoor air sensor, piped a temporary condensate drain, took a guess at the ODR settings, sped the pump up just a touch and set up call blocking to minimize short cycling at the low end of the curve.

This morning, it's 68°F inside and every radiator (including the outlier way up in the former maid's quarters) is warm. Next week we will install controls, add brick vents to two chimney flues for proper combustion air, and insulate a lot of pipe, but the place is cozy.