FPHX Thermo Pressure siphon, will this work?

SuperJ

This guy (in the attached video) installs FPHX on the cold water supply to a DHW tank (heat by outdoor wood boiler). He says it heats the whole tank (even when you're not using hot water) using the principal that heated water it expands slightly. I'm not sure how the hot water just doesn't get stuck in the HX?
Seems hard to get much thermosiphon flow without separate hot and cold pipes?
Has anyone done or seen something like this work? Avoiding a pump on the DHW side of the HX would be nice. The other idea is a side arm heat exchanger.

GroundUp

Thermosiphon with a plate is near non-existent, especially on top of the WH like that. I've got a few out there in mobile homes that will creep a little bit because the plate is under the WH, but not enough to matter. I will say though, with a properly sized plate on the cold input like this, you can heat enough water during a shower to have enough for another shower several days later. I do all my OWB installs like this. Are you often gone several days at a time or why the hesitance? How much hot water would you say that you use in a typical day? Sidearms are nice if you're gone a lot and use very little water, but assuming you're home at least once a day to feed the boiler and shower or whatever, you'll never run out with a plate. I prefer a 30 plate 5x12 for those needing some storage or a 20 for those using a lot of water and keeping the tank hot. As an experiment last winter I shut the gas completely off to my 40 gallon WH and used a lot of hot water, bringing my domestic tank temperature up to 168 degrees. I left the next morning and was on vacation for 6 days with my dad filling the boiler for me, zero water usage in the house. upon my return, there was still enough hot water left to shower after 6 days. Another experiment was 2 showers, 3 sinks, a jacuzzi tub, washing machine and dishwasher all pulling at once and still preheating the tank input to ~120 degrees. I've never seen a sidearm that'll keep up with 2 showers much less everything else, but I don't use them either.

Jamie Hall

Thermosiphons -- such as with a side arm heat exchanger to a tank -- work nicely. Water is heated in the heat exchanger, moves out the top outlet, over to the tank, cools in the tank and cooler water is drawn from the bottom of the tank to the heat exchanger. With patience, you can get the whole tank at least warm.

Without circulation to the tank, no. Sorry.

Larry Weingarten

Hello, Here's how it worked in the good old days. I don't see how one could realistically hope for convection to work backwards.
Yours, Larry

Zman

His system works because it is an instantaneous water heater on the inlet of the tank. He heats the water to a temp higher than the set point of the tank and everything work great as long as someone uses water once and a while to top off the tank temp.

I sure would like to see an anti scald valve on the outlet.

He sure doesn't lack confidence. I wouldn't want to try to convince him he is wrong

EYoder

> @GroundUp said:
> Thermosiphon with a plate is near non-existent, especially on top of the WH like that. I've got a few out there in mobile homes that will creep a little bit because the plate is under the WH, but not enough to matter. I will say though, with a properly sized plate on the cold input like this, you can heat enough water during a shower to have enough for another shower several days later. I do all my OWB installs like this. Are you often gone several days at a time or why the hesitance? How much hot water would you say that you use in a typical day? Sidearms are nice if you're gone a lot and use very little water, but assuming you're home at least once a day to feed the boiler and shower or whatever, you'll never run out with a plate. I prefer a 30 plate 5x12 for those needing some storage or a 20 for those using a lot of water and keeping the tank hot. As an experiment last winter I shut the gas completely off to my 40 gallon WH and used a lot of hot water, bringing my domestic tank temperature up to 168 degrees. I left the next morning and was on vacation for 6 days with my dad filling the boiler for me, zero water usage in the house. upon my return, there was still enough hot water left to shower after 6 days. Another experiment was 2 showers, 3 sinks, a jacuzzi tub, washing machine and dishwasher all pulling at once and still preheating the tank input to ~120 degrees. I've never seen a sidearm that'll keep up with 2 showers much less everything else, but I don't use them either.


Agree with groundup,
I've used hundred of flat plates preheating the cold entering the water heater on owb installs. No need for it to thermo-syphon. It works a lot better than most folks can imagine.

hot_rod

Larry Weingarten said:

Hello, Here's how it worked in the good old days. I don't see how one could realistically hope for convection to work backwards.
Yours, Larry

They had bungee cords back then?

Larry Weingarten

Hot Rod, Only in California and only after 1906.

Mark Eatherton

Seismic restraint... :-)

ME

Mark Eatherton

The more I look at this configuration, the less I think it would work. Sure, cold water expands, but once its done, what incentive does the water have to move? None that I can see. The video guys talks a good line, but he doesn't really know what he's talking about. He struggles for words, and the ones he's choosing are close, but not right. "Thermo pressure siphon" is not a standard term. He's just trying to move more FPHXers and brass nipples/unions etc. Per Gil Carlson " In order for there to be a difference, you must MAKE a difference." I see no possibility of thermo siphon contributing to the tanks stratification. Place the HXer below the tank, and sure, hot water rises, cold water settles and you have a convective circulation loop. Fill the potable side of the HXer with ice cold water, heat the other side with the OWB, and you get SOME expansion movement, but once its done, it's done. I don't even think a check valve in the circuit (think Copper Cricket solar system) would provide any major movement. Now on draw, it WILL contribute a fairly significant amount of energy to the load. But once the draw ceases, so does water movement between the FPHXer and the tank.

ME

hot_rod

Sort of like his explanation in this move clip. The money just "becomes" theres, not really stealing.

So the tank just "becomes" warm by adding a plate HX. With lead free copper and brass connections, of course

HomerJSmith

WOW! I can't wait to try it.

April Fools!--Even if it would work as he says, it won't work as he described it. Without a check valve on the cold water inlet, the pressure would push out to the street main. AND...the pressure is the same everywhere. There isn't any pressure variation between the FPHX and water heater.

Funny tho.

hot_rod

HomerJSmith said:

WOW! I can't wait to try it.

April Fools!--Even if it would work as he says, it won't work as he described it. Without a check valve on the cold water inlet, the pressure would push out to the street main. AND...the pressure is the same everywhere. There isn't any pressure variation between the FPHX and water heater.

Funny tho.

Exactly, how does the pressure in the water heater drop as it cools if it is connected to a pressurized supply.
If a check were installed the HX and tank pressure would raise at the same rate. If somehow the tank temperature increases, with a check installed, and no apparent exp tank the relief could pop off.

Those long tube side arm DHWHX sold with many outdoor wood boilers work somewhat as they connect at the top and bottom of the tank.

I suppose if the tank has electric elements in it the HO has no idea that the HX is doing nothing to add heat energy, other that an burst when cold water flows across it.

It would be interesting to see if he has one mocked up in his shop to demonstrate performance

Zman

I am sure it "works" just fine. It just heats the cold water as it flows through the heat exchanger into the tank. The thermo siphon/ flux capacitor thing is just marketing.

Wood boiler salesmen and log home salesmen are the same breed of BS artist.

I had a wood boiler guy insist that you could install an open wood boiler system 25' below the top floor (in a log home). He explained, with the same confidence as this knucklehead, that it was just like holding your finger over the end of a straw full of water. Just like the straw, it held for a few days then air locked the upper floor and flooded the boiler.

ratio

What's the difference between a used car salesman and a computer salesman?

The used car salesman knows he's lying to you.

GroundUp

Zman said:

I am sure it "works" just fine. It just heats the cold water as it flows through the heat exchanger into the tank. The thermo siphon/ flux capacitor thing is just marketing.

Wood boiler salesmen and log home salesmen are the same breed of BS artist.

I had a wood boiler guy insist that you could install an open wood boiler system 25' below the top floor (in a log home). He explained, with the same confidence as this knucklehead, that it was just like holding your finger over the end of a straw full of water. Just like the straw, it held for a few days then air locked the upper floor and flooded the boiler.

Been installing OWB my whole life. As long as you have enough pump to overcome the head and no chance of a vacuum break on top, they do work like that. Very well, in fact. I am definitely no salesman, but I can say with absolute certainty that this works and I've done it several times. Break the vacuum and there's trouble, so anything over 10ft I try to swap to a FPHX and close the loop to the upper floors but as we know, most HO know better than the guy they hired to do the job so it gets done their way. Matter of fact I was back to a guy's place a few weeks ago to swap a pump in one such system that I installed 9 years ago, where he refused to buy a FPHX and insisted on the straw deal. 23ft from the top of his OWB to his highest pipe. Never once was there an issue as you describe, the system has been flawless. Heck, it even purged itself of air after the swap!

As for this clown on the video though, yes. I will agree wholly, as was stated in my last post

HomerJSmith

Hahahaha!

Having a FPHX connected to the cold water supply putting in heat energy to the W/H is the same as an Indirect tank with an internal HX. Only the Indirect water heater is more efficient in transfering and storing heat energy. Hahaha, sorry, I can't contain myself.

Zman

@GroundUp
I am not saying it could never work. I don't think it is great idea. This home likely had the slightest of leaks on the upper floor, just like the finger on the straw.
Nature really dislikes a vacuum.

hot_rod

Yeah, plenty of OWF, open systems run with distribution above the water level.

The bigger problem is lack of adequate pressure on the circulator coaxes them into cavitation. And it worsens as temperature increases. Locals around here keep a spare circ on hand and get a season or two out of them. The OWF salesmen just refuse to learn why that keeps happening But they sell replacement circulators like candy

HomerJSmith

Pleezzz--Don't tell me you're taking this video seriously. It's a gag!

GroundUp

That only tends to happen here if said circ is a Taco, and/or is in the house trying to pull water from the OWB instead of pushing from the OWB. Lot of red ones around here 15+ years old, but the Taco usually get a new cartridge every fall. Sometimes two. Not sure why they hate it so bad. Neighbor guy used to buy 009 cartridges by the case; was burning 2-3 every year. I sold him an NRF-36 four years ago and it's still there today. Noticed it primarily with Central Boiler dealers; seems all of them recommend too small of a pump (always Taco), too small of line, and mount the pump in the house instead of the boiler. Had the local CB guy out to point out the abomination he sold a poor customer of his last fall (007 pumping 430ft round trip through 1" PEX, to heat a 9100 sq ft building and DHW) and he stood there and argued with me about how the 120 degree delta T was fine, he "does it all the time". I swapped to a 26-99 and added a 15-58 mixer to bring the return water up to 140 before re-entering the OWB instead of 55 like that clown left it (which needless to say did not heat the building either). It finally works now, but the poor guy had no idea he was getting screwed and the dealer still thinks he knows what he's doing. It's scary

HomerJSmith

The problem with Taco cartridge circulators is that a dirty system will plug up the cartridge. They have low starting torque and debris in the cartridge prevents rotation of the rotor. I never use a Taco on an old system. Take out the cartridge and rotate the impeller and you can feel it grind against the debris.

I cut a cartridge apart once to see why it failed. It was filled with magnetite (black sand). Replaced it with a Grundfos and never had a problem since. I can clean a Grundfos.

I've never seen pitting or destruction of the impeller on a small circulator because of cavitation, but I suppose it can happen. But, I have seen it on large circulators where the NPSHA was less than the NPSHR.

GroundUp

Quite a few 007s have landed in my dumpster with shredded impellers. Most of which were piped stupid and had an elbow or something immediately before the suction flange, causing cavitiation. Seems at lower temps they last much better but when dealing with 180-190 water they will flash steam in the volute and tear themselves up

Zman

HomerJSmith said:

Pleezzz--Don't tell me you're taking this video seriously. It's a gag!

I am pretty sure he is serious. Got a website and everything https://altheatsupply.com/heat-exchangers.html

I thought I recognized the producer. Pretty sure it is the same guy that did this one.

SuperJ

I was actually researching ways to possibly use my Polaris Tank to hot water for heating and DHW with some sort of HX setup. Was looking into side arm heat exchangers and found another one of his videos first. But found it hard to believe that his FPHX setup would work since it's piped basically like a heat trap. It's entertaining to read the youtube comments on the FPHX video.

Here was the first video I watched, it seems fairly conventional.

Mark Eatherton

Zman

@Mark Eatherton
Coincidentally, I just put one of those in my Subaru. I used mostly old vacuum parts

HomerJSmith

Professor Irwin Corey!