(expletive deleted)ing Weather

[-rick-]

I keep seeing people say that they prefer dry cold of -20/-30 to humid cold around 0. Don't think I've ever experienced dry cold and given I dislike cold I'm in no hurry to try but it's an interesting thought.

[jayc89]

When it dropped to -15 back in 2010 (ish, can't remember exactly which year it was, might have been '11), I genuinely didn't think it felt much colder than negative single figures we typically get each year. No idea what humidity it was but I'm guessing it must have been pretty dry as I can remember a lot of snow, but not much ice needing scraped off the car windscreen. 

[ProDave]

Once it stays below 0 even in the day, there is little humidity in the air and I rarely see the ASHP need to defrost.

 

I think our record was -18 one year, and a friend with a Cool Energy ASHP (that I had wired for him earlier that year) phoned me to say it was not working.  Looking up the error code given it was "outside temperature too low"  so I guess not all of them work in real cold.  Something worth checking.

 

It is no particular hardship at these temperatures, but that is the benefit of a well insulated house, I am not worrying if I can afford to have the heating on like many do.  It only becomes a nuisance when you want to go out, and the daily ritual of shoveling last nights snow away.  At least i am getting some exercise.  If I was not doing that and it was less cold, I would probably be chopping firewood instead.

[saveasteading]

39 minutes ago, ProDave said:

error code given it was "outside temperature too low" 

That's a worry...not that minus 20 is common.

But does it also struggle when approaching that temperature?

 

Do the manufacturers quote their minimum working temperature?

 

Another thought is that a poorly located fan might not be disposing of the cooled air properly, and so the surrounding area gets colder than the  ambient? Much less efficient and eventually gives up?

I've spoken to a few plumbers on this general subject and they didn't appear to understand. Also  I've seen a  fan unit tucked into a window recess  'for tidiness' and jammed with leaves behind, despite supposedly having been serviced.

[JohnMo]

12 minutes ago, saveasteading said:

But does it also struggle when approaching that temperature?

Yes. Mine (R32) at -10 is only good for 55 Deg flow temp, instead of the normal 60 and at -15 only good for 45.  So realistically the latest crop of installs (Octopus etc) with design flow temps of 50/55 at -3, could have a cold few days, or a high immersion bill.

[saveasteading]

49 minutes ago, JohnMo said:

Mine (R32)

Is that the refrigerant type? So applies to all makes that use it?

 

I have the opportunity to optimise. I'm wondering if locating away from the building a bit, might improve the dispersal of the cooled exhaust, and thus bring in warmer air.

Against that we must consider heat losses along the extended route.

Perhaps on a plinth as a compromise?

[JohnMo]

1 hour ago, saveasteading said:

Is that the refrigerant type?

Yes - there are various grades of refrigerant. R290 (another grade) is good down to -15 with a flow temp of 75 degs, then drops to 55 at -25. They stop at or about that point.

[SteamyTea]

58 minutes ago, saveasteading said:

So applies to all makes that use it

PV/T=C

Where P = pressure, V = Volume, T = Temperature and C is a constant (for an ideal gas).

 

A heat pump is a bit more complicated as it also involves the refrigerant usually changing phase, which changes the amount of energy that can be absorbed for a given volume or mass.

When a heat pump modulates, generally the pressure on one side of the pump is varied, though the volume pumped (rather than the overall volume of gas stored) can also change.

To keep C constant, the temperature varies, that can be the air or water temperature supplying the energy, or the delivery temperature exiting the heat pump.

The best way to think of what is happening is to think of a heat pump as having two side, the cold side (absorbs energy) and the hot side (delivers energy).  At the 'end' of each is either a pump, or an expansion chamber (though there are by-pass pipes/valves as well).

So while a heat pump can have just about any gas in it, refrigerant gases are used as they work in the ideal temperature range.  You could use helium and get down to close to 4K, and up to many hundreds of K, but that is expensive, and not that reliable.

Water can be another refrigerant gas, but the temperature ranges it uses are a bit limiting, and it tends to corrode most materials it touches (why it is known as the universal solvent).

It really comes down to how the manufacturer has set up the heat pump as to what temperature ranges it can be used at, and within those ranges, there will be a most efficient temperature to operate it at, with performance changing as it moves away for that ideal.

[SteamyTea]

Ha ha.

Good job I have not turned my heating on.

 

 

[Johnnyt]

Good Job I have my heating on.

 

[Onoff]

Yesterday morning about 04.30hrs driving across the North Downs towards Sevenoaks:

 

[SteamyTea]

12 minutes ago, Johnnyt said:

I have never known it anywhere near that cold down here, but then we do stick out a long way into the Atlantic.

[JohnMo]

Winter tyres (well 4 season tyres) installed this afternoon, can now drive to house, instead of stopping at the bottom a snow covered hill driveway. Van didn't even wheel spin with the new tyres.  Old tyres van came to a wheel spinning stop at the bottom of the drive, when I tried earlier.

 

Currently -6 heading towards -9/10

[SteamyTea]

37 minutes ago, Onoff said:

Yesterday morning about 04.30hrs driving across the North Downs towards Sevenoaks:

Was taken to Whitstable to see the sea when it was frozen, think it was in 1973.

[Onoff]

1 hour ago, SteamyTea said:

taken to Whitstable

 

& other euphemisms...

[SteamyTea]

7 hours ago, Onoff said:

euphemisms

The Manacles.

 

 

[ProDave]

-9 last night here.   The sun is about to pop up from behind the forrest.

[saveasteading]

1 minute ago, ProDave said:

-9 last night here

Altnaharra, not too far from you was coldest last night. On other occasions the warmest place in UK.

 

[JohnMo]

We currently have -9 and -10 at one point over night.

[ProDave]

6 minutes ago, saveasteading said:

Altnaharra, not too far from you was coldest last night. On other occasions the warmest place in UK.

 

Yes, -17.5 last night     https://meteostat.net/en/station/03044?t=2025-01-05/2025-01-10

 

I think Braemar still holds the record for lowest ever?

[SteamyTea]

Currently, at home.

11/01/2025 09:11:51,5.25