@tufty

its worth a call to your service engineer and ask exactly what the scale reading is. And a second question is to what temperature below 0degC is your system protected. (-4 might be a ratio of dilution eg 40% which, if it is, should protect to below -20c. But I suggest you get confirmation from your servicing company since they have your money for doing the work.

This is about peace-of-mind for you. Once you know the pipes are protected.

best regards

@sunandair Great, thanks Ill email them now. 🙂

@sunandair : Theyve said that the -4 is the temperature to which your system is currently protected! They said they would recommend it being -15 degrees. They asked if Id like them to quote to come back out and top it up. (I dont know why they didnt tell me this when the engineer was here! Isnt it a simple case of adding some glycol!?). 

Do you think-4 will suffice?

@tufty Sounds to me as though they would like to extract more money from you by degrees. 😉 (Sorry) Toodles.

@toodles Is this a simple case of them just needing to put glycol in? I sit a 5 minute job or am I over simplifying it? I paid them to service the unit, I would have thought the engineer would have just done it there! Its like getting a car serviced and the mechanic not topping the oil up! Or maybe im oversimplifying it?

@tufty

I suppose that this is one of the grey areas, where one would hope that the engineer would at least explain the meaning of the -4, before he or she dashes rapidly into the sunset.

Having anti-freeze in the system, and its degree of protection, is much like having an insurance policy. It is an added expense just in case the worst happens. One only needs the anti-freeze in case a lengthy power cut occurs during freezing weather conditions that are below the protection level provided by the anti-freeze.

So it is down to personal choice and how risk adverse you wish to be.

Thanks @Derek M . As you say - the engineer dashed off without explaining anything to me!! Had he have said "The system is only protected to -4, we would recommend -15" then obviously I would have got him to do it there and then. No doubt their going to charge me another call out fee etc...

Am I right in thinking its a 5 minute job?

"One only needs the anti-freeze in case a lengthy power cut occurs during freezing weather conditions that are below the protection level provided by the anti-freeze." this has relaxed me a little, but even so, Id like it protected to -15. (I live at the bottom of a valley so it does get very cold at night)

Posted by: @tufty

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Thanks @Derek M . As you say - the engineer dashed off without explaining anything to me!! Had he have said "The system is only protected to -4, we would recommend -15" then obviously I would have got him to do it there and then. No doubt their going to charge me another call out fee etc...

Am I right in thinking its a 5 minute job?

"One only needs the anti-freeze in case a lengthy power cut occurs during freezing weather conditions that are below the protection level provided by the anti-freeze." this has relaxed me a little, but even so, Id like it protected to -15. (I live at the bottom of a valley so it does get very cold at night)

I have no idea how long it will take or the likely cost. I have an A2A heat pump which doesn't require anti-freeze.

Posted by: @derek-m

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Posted by: @tufty

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Thanks @Derek M . As you say - the engineer dashed off without explaining anything to me!! Had he have said "The system is only protected to -4, we would recommend -15" then obviously I would have got him to do it there and then. No doubt their going to charge me another call out fee etc...

Am I right in thinking its a 5 minute job?

"One only needs the anti-freeze in case a lengthy power cut occurs during freezing weather conditions that are below the protection level provided by the anti-freeze." this has relaxed me a little, but even so, Id like it protected to -15. (I live at the bottom of a valley so it does get very cold at night)

I have no idea how long it will take or the likely cost. I have an A2A heat pump which doesn't require anti-freeze.

 

@tufty

changing from -4 to -15 freeze protection would mean adding glycol to the system.  That's not a quick or cheap job.  It normally needs the system to be drained and refilled or some sort of pump used to add glycol. Also, the glycol itself is expensive; low hundreds of £ to treat a whole system, obviously less to just top it up.

Ah ok, thanks @Kev M . Ill ask the installers for a quote.

The system is only 4 years old. Perhaps Im expecting too much from it, and these ASHP are expensive to maintain, even moderately newly installed ones. 

Would you say -5 is a dangerously high number? I would rather err on the side of caution. I dont want to risk the whole system being damaged.

Glycol - good for frost protection, not so good for thermal performance. Be mindful that increasing the concentration of glycol to lower the freezing point reduces the Specific Heat of the fluid.

Pure water has a specific heat Specific Heat of 4.2kJ/kg degC

10% glycol for -3.4degC frost protection is 4.07kJ/kg degC

30% glycol for -13.7degC frost protection is 3.76kJ/kg degC

You are reducing your heat pump rated output by around 10% once the loss on specific heat and increase in viscosity (lower pump flow due to increase in total head) is considered. If it has been sized for such a high glycol concentration then that's fine, but maybe not?

If all external piping, valves, heat exchangers are properly insulated, then questionable need for -15degC frost protection. -15degC air temperature might be experienced once every few years, and then only for an hour or so. To cause freezing of fluid inside pipes that are well insulated, an extreme low temperature would need to last for quite a long time coincident with a long power cut that meant the ASHP was not running and had no automatic circulation frost protection. 'Double jeopardy?'

Great, thanks @AllyFish.

Ive just been outside and taken some photos. As you can see, hardly any external pipework (a few inches), intrenally the pipework is in a comparatively warm out-building. Would you say that this is properly insulated?

Comforting what you have said about the double jeopardy. It would have to be a black swan event over prolonged, very cold temperatures together with a prolonged power cut.

I will get a quote from them and make a judgment call.

Worst comes to the worst, what damage could be caused if a black swan event happened? Are we talking major major expense and damage, with a replaced system? I guess so. Just curious what the actual damage could be caused.

Thanks for your help. I was ready to send an angry email to the supplier, but now I know its not a simple case of popping a bit of glycol in there. (Having said that, I would expect a service to include 'recomemndations'.)