Monoblock freeze protection valve
Akos
| Posted in General Questions on
My Google-fu is failing me and I can’t find a North American equivalent of:
https://www.caleffi.com/en-int/antifreeze-valve-108-caleffi-108601
I could try and order from overseas but would still have to deal with G thread.
There has to be something locally available that will work.
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I have found a few freeze protection devices (Speakman $$$, Zurn) but nothing specifically targeted to monobloc heat pump lines. I have a heat pump waiting for hookup and I really need to make a decision here.
Glycol, anti freeze valves, backup power on the circulator pump, backup power on a heat trace wire. What to do?! I designed the system to accommodate glycol but it costs twice what you are paying in the US and I can't get a matching inhibitor for when it needs boosting years from now.
It looks like this valve just bleeds off a bit of pressure when it operates? I'm not sure how much that really helps if you're worried about the kind of hard freeze that can split fittings and the like.
I'm going to assume this is for a ground source heat pump's underground coil, that will have a water-based fluid in it (with or without glycol). I'm also going to assume the heat pump is smart enough to avoid cooling that loop down cold enough so that the heat pump itself is creating the freezing conditions (i.e. outdoor weather controls the freezing issue). You could presumably bury this beneath the frost line to avoid freezing. You could use a sufficient amount of propylene glycol (less toxic than ethylene glycol) in the water to prevent freezing down to whatever low temperature point is reasonable to expect in your area. Adding glycol is probably your best option.
I've done plenty of closed loop systems on datacenters where ethylene glycol / water mixes are used between the indoor cooling equipment and outdoor "drycoolers" (which are basically big radiators). I've never had a freezing problem with those systems. We do tend to run those systems 24x7 all year long, so they are "warm" even in the winter, but the glycol mixture will prevent freezing even if the system shuts down (horrors!!) for any reason.
If you really need a bleed valve, I would think a regular overpressure relief valve would work, such as is common on water well systems. On my commerical systems at work, we have to have expansion tanks on the loop somewhere, and those tanks have to be ASTM rated -- which means more costly than "regular" tanks. The expansion tanks are sized for the volume of the system and the expected temperature swings that will be seen over an entire year, to ensure the system operates within limits. We have overpressure bleed valves -- indoors -- to bleed off pressure if anything goes wrong. Those overpressure valves don't usually sense temperature though, they operate only on pressure, usually around 50ish PSI or so, but you can get other ranges.
For the other poster: commerical companies exist that will take a sample of your glycol/water mix and send you appropriate corrosion inhibitors to add back in. This is a common annual maintenance checklist item for many commerical systems. Usually you mail off the sample, and they send back a blend of whatever is missing. You have to tell them what type of piping you have, and what the system volume is, then they send you back additives mixed up just for your system. Put those back into your system, usually using a special mixing tank/funnel setup installed on the system for this purpose, and you're good to go. Easy.
Bill
Bill,
This is for an air to water monoblock heat pump. The way these work is when the fluid gets near freezing temp it starts to open up and drip water. Since the system has an auto fill valve which will keep adding water, this will move cold (but above freezing) tap water through the monoblock to prevent it from freezing up. As long as there is a constant feed of water and somewhere for the valve to dump the water, it "should" work.
My thinking is our power is pretty reliable, so first level of freeze protection is the circulator in the unit. The 2nd level would be heat rope on the liquid lines (the unit has heat tape internally on the HX). The freeze valve would be the final backup.
I know glycol would be simpler but I have a lot of old cast iron rads so a pretty big volume to fill. The cost of that much glycol is not insignificant, plus I don't really care for the maintaince of the glycol. Also any leaks would be much harder to clean.
Putting an in-line plate HX for a small glycol loop won't work as I'm already near the limits of the supply temps, that 5F or so drop would really hurt. Never mind the drop in COP.
Note that you don't have to hit any specific standardized glycol/water mix like "40/60". Just look up in the tables how far down in temparture you want things to be safe, then put in that amount of glycol. That gets you a custom mix for whatever amount of freeze protection you desire (or actually need), instead of trying to hit some round number that might use more glycol in the mixture than is actually needed for your specific application.
Maintenance is easy. You don't really "need" to do anything at all, in the case of a closed system. It's really only the corrosion inhibitors that get used up over time, and that's all you put in with maintenance mixes. You can do that annually (standard on big commerical systems), or every 5 years or so, which should be fine on a smaller system. You could skip that step entirely, and not be any worse off than you would be with a system filled with water only.
Glycol leaks do leave a film, so not much you can do there, but it's not terribly difficult to clean up if needed.
I'm with DC on this -- a controlled leak to limit freeze risk isn't, IMHO, a reliable way to go here. Think about how much expense you'll have if something in the system freezes and splits, and you know that spot that breaks will be hardest thing to get to, and the replacement part will probably be out of stock when you put in the order....
Bill
Akos, this is what the SANCO2 system specifies. Are you doing a Monobloc heat pump install with freeze protection instead of glycol?
https://pacesupply.com/Product/sanecofpvktsmtw
Thanks Tim, I'll try to source those.
The one I did find locally is this:
https://www.zurn.com/media-library/web_documents/pdfs/specsheets/bf-zwfr-pdf
It looks like a toy though compared to the Sanco ones.
They look like they would serve the same function, but much smaller. 1/4NPT vs 3/4NPT. Not that you need a high flow rate though. I always thought these were to drain the exterior portion of the system more so than backfill with interior water.
A 20% fill of glycol gets you burst protection down to 10*F. It can still get thick, but will not burst.
IMO, if Sanco finds it safe to use freeze protection, I think it would be fine. I think freeze protection valves are more common in Europe where A2W heat pumps are used more anyway.
Are you doing this on your personal house? I have my A2W heat pump showing up in a week or two, excited to get started on that project soon.
Edit: Might be worth a read. UK based where these heat pumps are much more common.
https://renewableheatinghub.co.uk/do-air-source-heat-pumps-really-need-glycol
A little more digging - Bosch advises against glycol in their heat pumps, and Mitsubishi advises using anti freeze valves. Basically, in areas where these A2W pumps are common, so are freeze protection valves.
Thanks for posting the link Tim_O
Basically what I was thinking with my approach, glad to see I'm not alone. Yes this is for my home. Since I like to tinker with things, I also rather not try to reclaim glycol when I inevitable replumb sections.
A pair of anti-freeze valves seems like simple insurance and it makes sense in terms of how it operates. The Caleffi link has a nice video to show how it supposed to work at about the 2min mark.
An additional backup could be a tiny circulation pump on battery backup. It would take a trickle of flow through the heat pump to keep it above freezing, and it would be almost negligible heat theft from the house.
Let us know what you decide to use for freeze protection valves. I may go the same route for mine.
A small computer UPS would work for this, but I'd recommend getting one that is "pure sinewave output". I've had issues with the "modified sinewave" UPSes (which includes most of the small and cheap ones) not running small motors properly.
Better yet would be a small circulation pump made to run on DC, maybe something for an RV. That way you could wire some batteries in directly (use gel cells here, something like the Powersonic batteries commonly used for alarm systems), and a relay to fire the pump up if the power fails. A simple battery tender could be used to keep the batteries charged. This avoids running a UPS all the time, so it would be more efficient long term.
Bill
Exactly, a small 12V circulation pump and a simple deep cycle battery would be enough for a multi day outage. Pump doesn't need to run all the time, just when water temp dips below say 35F.
That is not a bad idea. I already need to run a booster pump as the primary loop is long and a bit too restrictive, I can put that on a UPS. With an ECM pump, I should get a reasonable runtime on a decent UPS.
Akos, if you get an "extended run" UPS, you can put enough batteries on it to get whatever amount of runtime you need. Most of these use 12 or 24 volt systems (for smaller units), which is easy to setup with additional batteries.
I would avoid the normal "deep cycle" batteries here with liquid electrolyte due to concerns over off gassing over the charge/discharge cycle. You want gel cells here, which are sealed recombinant cells, i.e. they don't offgas. I usually use Powersonic batteries for this as they're readily available and reliable. With gel cells like these, you can safely use them indoors without concern. Good batteries for this would likely be 17 or 35 amp hour batteries. This would give you around 5 or 11 hours of runtime, respectively, assuming a UPS with a 24 volt battery string, and a pump using 50 watts continuously.
Bill
Good point, Bill. Don't put a lead acid inside without ventilation. Lots of cars put the battery in the trunk now, and use AGM for that reason.
On HeatingHelp.com there is a Caleffi rep who posts regularly, I'd ask there.
My opinion: it seems like a dicey way to protect an expensive piece of equipment.
Thanks DC.
If you want to keep something outside that is filled with water from freezing, there are three options: drain it, fill it with antifreeze, and apply energy to keep it from freezing.
The discussion above of ways to apply energy just has me shaking my head. UPS and circulators? What's wrong with a battery and a heat tape? For the same amount of energy you get the same amount of protection.
Now, let's talk about risks. With antifreeze, the risk is that you don't have a strong enough solution of antifreeze. I guess there's also a cost that the heat capacity of the fluid drops somewhat. With draining, there's the risk that draining doesn't happen, as well as the risk that the equipment starts back up without being properly refilled and purged.
With applying energy, the risk is that you run out of energy before you run out of cold.
I'll take antifreeze and sleep at night.
The energy difference is that the circulator is moving/stealing heat from the house and buffer tank where heat tape is directly heating. I get what you are saying, but I also trust that Bosch and Mitsubishi have worked it out.
Canadian west coast market. The antifreeze brands sold locally are generic, ie the inhibitor quality is unknown, and I can't purchase the matching inhibitor for replenishment later. If anybody has a tip on this I'd love to hear it.
Does SupplyHouse.com ship to Canada? I've taken to buying glycol mix from them in five gallon buckets.
No. And we have nothing even remotely like it.
The issue in my case with heat tape is it only heats the pipes to the unit. I would hope that this would be enough to keep the expensive bits inside the heat pump from freezing but not certain. Something that is constantly moving water through the unit is guaranteed to work thus the UPS on the pump plus the freeze valves.
I'm in the city with very reliable grid and infinite supply of tap water even in case of outage. I definitely would go for glycol if this was out in the country somewhere on well water.
Instead of continuous make up water, why not let the outdoor pipes empty out?
I think it will be very hard to get all the water out of a plate HX. If any is left in there an it freezes, you are talking about a very expensive repair. With continuous flow, there is no chance of anything freezing.
If you do, you have to have some way of keeping it from starting up when the power comes back on, running it with no water will damage it.