Ideas for resolving one hydroair zone freezing

marksigfried

I am a homeowner with a Buderis gas boiler that supplies hot water to 6 radiant zones, 4 hydroair handlers, and the hot water tank. All of the zones and air handlers are within conditioned space with the exception of one hydroair zone that supplies one wing of the house over the garage.

The air handler for this one zone that intermittently gives us trouble is in an insulated, but unconditioned attic. The hydroair tubing goes up through an outside wall to this attic, although the outside wall has foam insulation. It then traverses a short section of the sloped roof before entering the attic where the air handler is located. I suspect the traverse through the roof is the section most exposed to the outside cold temperatures.

This one zone freezes up on the frigid cold days of winter and we lose heat to that section of the house. We have added antifreeze to the system, twice over the last 4 years, at a cost of thousands of dollars each time. Most recently, after adding the antifreeze, we got through one heating season with no freezing. Then last winter the system tested to no freezing down to zero, but during a very cold snap, that zone again froze for a few days until the outside temperatures rose. We are currently awaiting our appointment for system maintenance and performance check, including a freezing point depression check to be ready for the winter.

I am getting frustrated with the episodic freezing up of this one zone. I am wondering if there might be a more permanent solution. First, I am tired of adding thousands of dollars worth of antifreeze to the system every two to three years, the antifreeze cost is as much as my energy cost for a whole heating season in my otherwise highly insulated home. Second, we want to have a system with a higher degree of reliability and trouble free performance.

Is there some type of recirculator we could add to this one zone, triggered only by very low outside temperatures, that would keep this zone from freezing? I am also looking for any other thoughts regarding this situation.

pecmsg

There are several ways of solving that but how can it freeze if the glycol has 0°f freeze protection?

What has the installing contractor advised?

marksigfried

pecmsg said:

There are several ways of solving that but how can it freeze if the glycol has 0°f freeze protection?

What has the installing contractor advised?

The temperature was zero for several days when that zone froze, even though the freezing point depression test said that we were ok down to zero.

The contractor advised to keep testing the freezing point depression at the beginning of each heating season, and keep adding antifreeze when needed. Each time they add antifreeze, given the large size of our system, it costs thousands of dollars.

Jamie Hall

Something's wrong with this picture. As @pecmsg says, if the antifreeze protection is adequate, it won't freeze. Simple as that. It's possible to run glycol antifreeze down to -40 F with the proper concentrations.

Also, I find the dollar figure you allude to for antifreeze protection somewhat dubious, unless your system is really huge. I wouldn't want to say how far off it is, 50 gallons of 50/50 mix propylene glycol (good to about -25 F) can be had for less than a grand...

marksigfried

Jamie Hall said:

Something's wrong with this picture. As @pecmsg says, if the antifreeze protection is adequate, it won't freeze. Simple as that. It's possible to run glycol antifreeze down to -40 F with the proper concentrations.

Also, I find the dollar figure you allude to for antifreeze protection somewhat dubious, unless your system is really huge. I wouldn't want to say how far off it is, 50 gallons of 50/50 mix propylene glycol (good to about -25 F) can be had for less than a grand...

The antifreeze reportedly tested down to zero, and the outside temp was right around that temp or barely below that the last time that zone froze.

Our home is about 6000 square feet. We live in one of the most expensive areas of the US and service calls are typically around double the cost seen in other areas. And we live in the nicest part of town, so unfortunately we typically see higher end bills for service calls.

Each time, the cost of the service call for loading up the system with antifreeze was around $2,000, and we paid for this twice over the last several years. I am going to check my records to see if they listed how many gallons were added.

clammy

I typical stay away from attic hydro air install and yes it’s gonna be glycol and hopefully your heating contractor figured that in but if it’s already froze and caused damage well u best be looking for a new heating guy cause he don’t know **** ..you could add a freeze stat to the coil to protect it from freezing and if the lines are in the outside wall ,well maybe a low limit aquastat to ensure that the loop temp doesn’t get below say 50 .in a lot of cases I see there no flow control on the supply or return to the coil so there is usually some great thermal migration even better if you have a indirect w no check also ,it will migrate happily and keep all from freezing until your get that artic blast happens then your done .on a side no one notices until it’s summer why the ac runs constant well there your great hydro air system thermal migration go both ways the opposite is true for the summer to hi temp goes to low .i find the easiest way to solve is to throw lots of money and controls at it like they should have in the first place or maybe do some baseboard or radiant .i do not do new work due to this bs and gc they always want hydro air they want cheap they don’t care and neither do the contractor installing it that’s why they work for gc s if they wouldn’t have that system in there own home but they will put one in yours .go with glycol first do the tds testing and then fill w deminerlized water then add your glycol and inhibitor then test yearly to make sure your ph and glycol are at the right level as not going south ( acidic ) also hopefully the heating pump will be able to deal w the glycol higher specific gravity then water. I can only wish you good luck hydroair 1 stone two birds and usually some one gets holding the turd .the new home owner also hi bills less comfort hydro a builders dream hardly ever done w all the bases covered .personally I have never seen a freeze stat installed on residential hydro ithe no check valve and thermal migration again usually keep them from freezing also work great for oversized ac by also migrating from boiler .the real fix Costs money knowledge and experience the just add glycol just add to tap water and you ll be good at least that’s what they say .do some reading on the subject there not to much on the coil protection except a freeze stat possible 3 way valve and temp sensor circ loop from the coil ,the list goes on and on .i would first find the guy who designed and installed and ask what was his idea for protection and then ask the builder both will say that the first time it ever happened .. Hydro air there’s reason why it’s not done in attics but it always seems the cheapest way so it must be the best duh like I said I just walk when I see them even on commercial jobs unless there are 3 way valve s and controls other wise it’s usually just junk bs some one threw together on a whine usually with out any thinking just despoiting of a check never to return when the issue arises . On a side note where u able to get any relief from the builder or installation contractor peace and good luck clammy

marksigfried

Fortunately we have never had damage to the coil in that air handler. We just had freezing in the plastic tubing that sends the hot water and glycol mix to the air handler.

The attic where the air handler is located is unconditioned but very well insulated, so the temps in the attic are about half way between indoor and outdoor temps.

A “low limit aqua stat” that would keep that zone water temp at a minimum of 50 degrees sounds like exactly the type of solution that would resolve our problem.

Thank you for that suggestion. Much appreciated.

HVACNUT

> @marksigfried said:
>
> Is there some type of recirculator we could add to this one zone, triggered only by very low outside temperatures, that would keep this zone from freezing? I am also looking for any other thoughts regarding this situation.

Yes, kind of. It's called a Freezestat. It can be wired to run the circulator on temp drop or force a heat demand for that zone.

Add one more guy to all the advice from above.

One way, although a bit intrusive, is to isolate the part of the loop that is in the freezing conditions using a plate heat exchanger. Installed in a second floor closet or laundry room, you can have the glycol mix in the secondary loop only.

Also, next time they test, ask to look through the refractometer to see the readings for yourself.

GroundUp

Sounds like either your contractor is an uneducated gouger, or you have a leak somewhere that requires a quantity of makeup water which is diluting your glycol. Or both. If it were mine, I'd probably do away with the glycol and use a delta T circ on that zone to keep a minimal flow rate at all times, avoiding all extra controls

pecmsg

With 0°F freeze protection Glycol gets Thick, it never really freezes until much much colder.
If you have to check and adjust every year there's a leak that needs to be found and repaired.
Just have it rewired for when the stat is set to "Heat" the circ comes on. If the t-stat requires heat it cycles the fan!
Taco Viridian circulator's can operate off of return water temperature, that will give you less on off cycling of the fan and better comfort.

marksigfried

GroundUp said:

Sounds like either your contractor is an uneducated gouger, or you have a leak somewhere that requires a quantity of makeup water which is diluting your glycol. Or both. If it were mine, I'd probably do away with the glycol and use a delta T circ on that zone to keep a minimal flow rate at all times, avoiding all extra controls

A delta T circulator on that zone sounds straightforward and simple, which sounds quite appealing to me. I always like a simple and more reliable solution to a problem.

Also, I have been wondering if there could be a leak somewhere in the system that requires us to add more glycol more often than is typical.

Jamie Hall

I completely agree with the idea of constant circulation on that line -- and a low limit on the circulating liquid temperature.

With regard to freezing and glycol. If the solution tests good to 0, that's exactly what it means. It will start getting remarkably goopy even above that -- say at 10 above or so -- and be very difficult to move. At 0 it will be very difficult to move indeed, and may well defeat the efforts of the usual circulating pumps completely. If your low temperature is close to 0, I'd plan on protecting to no less than -10 and probably lower.

pecmsg

Glycol inhibits heat transfer as such your wasting fuel.The few jobs we add Glycol to is strictly for during power losses. We maintain 10 - 15° Freeze protection that's about -15 - 0°f burst point.

STEVEusaPA

If your dropping 2 grand every year, cant you just spray foam the attic (roof and walls, and make it a conditional space, blowing some heat in there.
If outside is at 0° that unit has to be running a lot (unless your design temp is -40°), enough to keep the newly conditioned attic space in the 50's, then do away with all the glycol.

Zman

You must have a leak or a relief valve that keeps relieving. Can you post a picture of your system?
I would recommend getting rid of your fresh water fill valve and installing one of these.https://www.supplyhouse.com/Axiom-MF200-MF200-PRESSURE-PAL-Hydronic-Mini-System-Feeder-6-Gallon?gclid=Cj0KCQjwgNXtBRC6ARIsAIPP7RtSc43rczGXZdbJtC91LeNNgi1wN2Pqqmm_HtE5BU2W6TX7q4fHFq4aAj23EALw_wcB

You can then keep and eye on your glycol levels and refill the system yourself. Glycol is not that expensive. It can become expensive if you have to dump a bunch of it because it has become diluted.

marksigfried

Jamie Hall said:

I completely agree with the idea of constant circulation on that line -- and a low limit on the circulating liquid temperature.

With regard to freezing and glycol. If the solution tests good to 0, that's exactly what it means. It will start getting remarkably goopy even above that -- say at 10 above or so -- and be very difficult to move. At 0 it will be very difficult to move indeed, and may well defeat the efforts of the usual circulating pumps completely. If your low temperature is close to 0, I'd plan on protecting to no less than -10 and probably lower.

Yes, our low temp is usually in the single digits, last winter we got to zero or just a tad below during the arctic blast. Thanks for the suggestion that the glycol mix should aim for around -10.

And yes, we did have to replace the circulator pump on that zone because it burned out when the fluid was not circulating.

Zman

pecmsg said:

Glycol inhibits heat transfer as such your wasting fuel.The few jobs we add Glycol to is strictly for during power losses. We maintain 10 - 15° Freeze protection that's about -15 - 0°f burst point.

I don't believe this is true. Glycol actually carries more heat per gallon than H2O. It does take a bit more energy to pump but in a simple residential system, it likely just slows the flow rate and increases the delta t a bit. 30% glycol should be plenty.

marksigfried

pecmsg said:

Glycol inhibits heat transfer as such your wasting fuel.The few jobs we add Glycol to is strictly for during power losses. We maintain 10 - 15° Freeze protection that's about -15 - 0°f burst point.

Interesting point. Is it true that glycol inhibits heat transfer and reduces efficiency?

But as far as heating costs, we have been happy with our reasonable winter fuel costs for our large home. Rather, it is the high maintenance costs that have been “burning me up”. Hah!

marksigfried

Here are some pictures of our system.

pecmsg

Zman said:

pecmsg said:

Glycol inhibits heat transfer as such your wasting fuel.The few jobs we add Glycol to is strictly for during power losses. We maintain 10 - 15° Freeze protection that's about -15 - 0°f burst point.

I don't believe this is true. Glycol actually carries more heat per gallon than H2O. It does take a bit more energy to pump but in a simple residential system, it likely just slows the flow rate and increases the delta t a bit. 30% glycol should be plenty.

Depending on the concentration up to 10% loss.

marksigfried

I looked back at my records. The big drum of Fernox Alphi 11 antifreeze was the biggest part of the expense. They also wrote on the service ticket that they checked for leaks and did not find a leak.

marksigfried

Zman said:

You must have a leak or a relief valve that keeps relieving. Can you post a picture of your system?
I would recommend getting rid of your fresh water fill valve and installing one of these.https://www.supplyhouse.com/Axiom-MF200-MF200-PRESSURE-PAL-Hydronic-Mini-System-Feeder-6-Gallon?gclid=Cj0KCQjwgNXtBRC6ARIsAIPP7RtSc43rczGXZdbJtC91LeNNgi1wN2Pqqmm_HtE5BU2W6TX7q4fHFq4aAj23EALw_wcB

You can then keep and eye on your glycol levels and refill the system yourself. Glycol is not that expensive. It can become expensive if you have to dump a bunch of it because it has become diluted.

This also sounds like a really good idea. Would I then put Fernox Alphi 11 into this system, to add glycol when needed? Or some mix of water and glycol?

One great benefit of this would be that I would clearly know if there is a leak somewhere in the system based upon how much fluid is being added from the mini-system feeder.

GroundUp

You would put a mix of ~30% Fernox into the feeder (or whatever concentration is in the system currently). Then you could monitor the amount of makeup being used, but honestly there's no reason for glycol in the entire system just for one cold zone. Glycol requires more maintenance and does slow heat transfer a bit when compared to straight water, I think you'd be money ahead forever with some variation of constant circulation whether a Delta T Viridian or just hard wiring your existing circ to stay on 24/7 during heating season

Zman

@pecmsg
"Depending on the concentration up to 10% loss"

Since energy cannot be created of destroyed, where are you thinking that 10% is going?
I am thinking with that many circs, slowing things down a bit is not a bad idea.

Zman

The tank would have the same mix as system. You can buy an inexpensive refractometer and PH kit and manage the mix yourself.

pecmsg

Zman said:

@pecmsg
"Depending on the concentration up to 10% loss"

Since energy cannot be created of destroyed, where are you thinking that 10% is going?
I am thinking with that many circs, slowing things down a bit is not a bad idea.

Its not lost its the Transfer of heat where the losses are. In the boiler and hot water coil. Think of insulation, it doesn't prevent heat transfer just slows it.

Zman

I respectfully disagree. The energy gets transferred at a slower rate and more pumping energy is required. Unless we are thinking that it gets wasted out the vent, (I have never seen that in combustion analysis) it is staying in the system and conditioned space thus not wasted.

Zman

If the OP is going to add the glycol feeder, it would be a good idea to have them add one of these as well to be able to service the expansion tank without a drain down. https://www.supplyhouse.com/Webstone-41672-1-2-Pro-Pal-Full-Port-Brass-Ball-Valve-w-Hi-Flow-Hose-Drain-600-WOG?gclid=Cj0KCQjwgNXtBRC6ARIsAIPP7RtiwSsSJKIpSe5ydUO5hwDUciU_GJP-kYTZgBQysVaswYZndFrCeBUaAipgEALw_wcB

Where does the boiler relief valve drain to? My first guess is that expansion tank is waterlogged and causing the relief valve to dump occasionally. Just a guess....