Are all "glycols" equal?

[PhilT]

8 hours ago, SteamyTea said:

kJ.kg^-1K^-1

Ta. It would be so much easier to to use the calorie Cp version of 1 !!!

[sharpener]

14 hours ago, PhilT said:

Fernox Alphi-11 (20% in my system) has Cp of 3.99, so mixed Cp 4.15, so nothing much to worry about.

 

Mfrs data sheet says "The minimum recommended ‘in-use’ concentration of the product is 25% in order to ensure adequate corrosion protection." Whereas for their HP-5c it is only 10% hence the attraction for a large system volume in a mild location. Alphi-11 is slightly more expensive from BES. Both are based on PG so I have no idea in what other ways they differ, from the detailed graphs the Cp and viscosity are very similar - though comparing the graphs is a nightmare as they use different units, and log scales with only one line per decade.

 

As a conjecture the HP-5c is specifically formulated for HPs, whereas Alphi-11 has been around for much longer.

 

On 01/03/2024 at 17:57, TonyT said:

And do you suffer from power cuts?

 

When we have been away in the winter I want to be able to re-start the system even if there has been a power cut.

 

15 hours ago, RobLe said:

A bit of rummaging around the internet and I found this, I think it’s what I’ve seen before, but I’m struggling to get the simple glycol is 2x worse than water from it.  

 

Thanks for digging it out. Table 8.2 would seem to be the best fit

 

 

I would imagine pure glycols fit the description of "viscous organic liquids" but in the dilutions used in HP systems I would expect them to behave more like "light organic" or "aqueous solutions" so a reduction of 2/3 to 1/2, maybe that's where you got it from?

 

[sharpener]

On 01/03/2024 at 23:31, sharpener said:

I will pursue this with Hydratech next week to see if they offer a direct equivalent to the Fernox product (as those are notoriously expensive).

 

Have just talked to Hydratech, very timely enquiry. They are in the process of formulating a fluid for protection to -5C which will be more economical, equivalent to Fernox HP-5C. Should be available in the next few months and keenly priced against the competition. May be also produced in an EG version based on their DTX reduced toxicity product. Clearly one to watch for those in temperate climes.

[GLPinxit]

We've just had some minor work done to move a radiator and I was talking to the plumber about bacteria and antifreeze in heat pump systems. He told me about a client who they'd part-installed a system for and who had him back when the whole system ground to a halt some time later. All of the circulating fluid had turned to a gloopy gel and it took several days of continuous power flushing to free it up. He thought that part of the problem might have been that the [clear] plastic drums had sat around in bright sun for some time before their contents were used.

I have a particular interest as we are in a sheltered and relatively balmy part of the UK (minus 5 twice this winter) and would like to be able to just have enough anti-freeze to give us protection to minus 5ish. I'll probably add Fernox F7 but am a bit hesitant as we're on private drainage and I don't want to kill all of the helpful bacteria that live in our sewage treatment plant by draining the system down 'our' drains!

[Dave Jones]

dont use glycol unless you really have to, decreases the heat transfer performance.

[PhilT]

1 hour ago, Dave Jones said:

dont use glycol unless you really have to, decreases the heat transfer performance.

Hardly at all, it turns out, thanks to this post. For example hp-5c at 20% reduces specific heat capacity by around 2%. Nothing to be concerned about

[PhilT]

38 minutes ago, PhilT said:

Hardly at all, it turns out, thanks to this post. For example hp-5c at 20% reduces specific heat capacity by around 2%. Nothing to be concerned about

My mistake, hp-5c specific heat capacity at 40degC = 4.09, water 4.18, so 20% mixture (4.09*20% + 4.18*80%) = 4.16 so only a 0.5% reduction in heat capacity.

[Dave Jones]

my understanding its not the capacity but the mixing/transfer that is noticeably poorer hence poor practice.

 

Heatgeeks mentioned it on a video.

[StevieB]

I spoke directly with Vaillant tech who informed me that glycol is not needed if you have antifreeze valves - they changed their policy recently. These valves only come into play if you have a very cold day -5C and a power cut for a prolonged period at same time.  I have now argued with my installer and won them over to fill system with softened water (only cos I have w/s fitted on cold rising main) and inhibitor only and fit a/f valves. In most installs, unless prolonged power cut in winter is experienced, a/f valves are just insurance. Save on the loss of efficiency caused by glycol and its alternatives AND cost / dangers associated with disposal. 

[JohnMo]

8 hours ago, StevieB said:

AND cost / dangers associated with disposal. 

Think you may be confusing car glycol with that used in heating systems.  Car poisonious - heat pump heating system food grade.

[PhilT]

8 hours ago, StevieB said:

Save on the loss of efficiency caused by glycol and its alternatives

just to put this into perspective and to inform choices, the reduction in heat transfer rate with, for example, a 20% mixture of hp-5c, is only around -2%

[Kelvin]

7 minutes ago, PhilT said:

just to put this into perspective and to inform choices, the reduction in heat transfer rate with, for example, a 20% mixture of hp-5c, is only around -2%

Exactly it’s nothing really for mostly passive insurance. The anti-freeze valves are fine but you really need them to work when you need them to work. The likelihood of it being cold enough and a prolonged power cut is relatively small so these might well be in place for years before that one time they are needed. 

[LnP]

I was curious about what an anti-freeze valve is, and found this useful explanation in case anybody else was wondering!

 

The decision on the best way to protect the external unit from freezing seems to be quite complicated. One aspect not much mentioned in this thread is reliability. Dosing the system with anti-freeze is inherently safe and if you want to, you can test it by taking a sample and putting it in the freezer. Anti-freeze valves are an active protection measure so have a probability of failure on demand and can't easily be tested. I've had a few temperature sensing cartridges in shower controls fail and I suppose it's similar technology. What do they do in Norway?!

[sharpener]

 

9 hours ago, StevieB said:

These valves only come into play if you have a very cold day -5C and a power cut for a prolonged period at same time. 

 

The Intatec valves upthread are supposed to open at +3C so might open much earlier than you think. OTOH after some years of doiing nothing they might be stuck and not open at all.

 

43 minutes ago, JohnMo said:

Think you may be confusing car glycol with that used in heating systems.  Car poisonious - heat pump heating system food grade.

 

Ethylene glycol (= car antifreeze) is inherently higly toxic but some cos e.g. Hydratech DTX use de-toxifying additives, whatever they are. Propylene glycol is inherently less toxic and is used in Fernox HP-5C and Alphi-11. I don't recall right now what the many others are based on, some product details near top of thread.