Heat in the home

[jois]

I think that by the time I have designed and built something that will be worth doing, it might be ready for March to catch the equivalent spring heat. I take on the advice of all of my consultants, and so it all hinges on whether I can obtain a radiator free of charge. One of my neighbours is going to replace their elderly ones soon, so I may develop the idea further.

In the mean time, I have a better idea. Or at least I think it's a better idea, so I'd be grateful if those of you who know more will scrutinize it fully. Here goes:

Imagine filling 100 litres of tap water, (currently around 15 degrees C), into plastic containers and putting these into an empty freezer and freezing them to -15 degrees C. Then, once frozen, taking out the ice and discarding it in the garden and repeating this with 100 litres of 15 degrees C water again.

If I did this, the freezer could be used like a ground source heat pump - but with a very different initial cost outlay. Is this viable?

Any constructive advice/criticism/calculations gladly accepted

Very intriguing!

My initial thought is that it will work from a point of view of heat generated (although not so much heat), but economically not.

Unless you've a diesel generator running on free, waste plant oil to power the freezer. In which case you'd hook it up to a small electric heater.

100 litres of water weighs 100kg. The specific heat capacity of water is 4184J/kg/1 degree C this equates to 418400J/degree C. In other words, a large number of heat would be produced - which might be significant for a small and well insulated house

I have been told that a ground-source heat pump produces 4W of heat for every 1W of electric used to power the pump. If that is true, and I can get any 'issues' sorted out, that's what I'm looking at. Of the 1W used for pumping, any inefficiency would result in further heat in the house.

You measure heat in therms, saying 4w of heat doesn't have any meaning, what you can say is the device uses 4 w and produces X therms, where as this one uses 1 w and produces y therms

[rjb]

Therms should be confined to the ark. These are old non SI units.
1 therm = 29.3 kwhrs. Everyone knows what a kilowatt is. A kettle is rated at about 3 kw.
My gas bill is for kWh used not therms. My smart meter IHD displays usage in kws.

[Nearholmer]

Having dredged my brain a bit, I think I can add more regarding the "extract heat from water by freezing it" idea.

As I said yesterday, a key question is the Coefficient of Performance that the heat pump is able to deliver (whether it be a GSHP, fridge, deep freezer, aircon unit, or whatever), and that is crucially dependant upon the difference between source temperature and output temperature required.

A GSHP operating optimally, pulling energy from cool (c10 - 15 degrees) ground and depositing it at say 40 degrees, can attain a CoP of between 3 and 4, so for every unit of energy used to drive the system, 3 to 4 units are extracted from the ground. Brilliant!

If the GSHP is required to do more work, to cross a greater temperature gradient, say to raise the output temperature to 60 degrees its CoP drops sharply, which is why a well-designed heating system run from a GSHP uses fairly low temperature, fairly big radiators (sometimes the entire floors of rooms are used as radiators).

The bad news is that a 'fridge bringing food down from ambient to about 2 degrees has a CoP of somewhere a bit either side of 2, and a deep freezer dragging things down to far lower temperatures might have a CoP of only 1. BUT, the cited CoP for cooling plant tells us something different from the cited CoP for heating plant, so the CoP for a freezer viewed as a heater will be different from the CoP of a freezer viewed as a cooler, IIRC from long ago learning, we need to add 1 to the CoP cited as a cooler to get to the equivalent viewing it as a heater.

Anyway, it looks to me as if the best bet here for Heath Robinson arrangements is to cool the water in a fridge, rather than freeze it in a freezer, but I will keep pondering and will correct the foregoing if I realise any mistakes.

[jois]

Therms should be confined to the ark. These are old non SI units.
1 therm = 29.3 kwhrs. Everyone knows what a kilowatt is. A kettle is rated at about 3 kw.
My gas bill is for kWh used not therms. My smart meter IHD displays usage in kws.

Well BTU if you want to be up to date, a 100,000 of which equal one therm, so it's still an accurate measurement you've just move the decimal point about.

One or the other of which is used to calculate heat output, not KW
The Ws used to generate a BTU is dependent on the efficiency of the device, it's may be approx 2.9 KW but it isn't exactly so, which is why it's not used to compare devices of different efficiencies and that appears to be what he is doing here

The statement produces 4w of heat is still with out meaning no matter what your gas bill says

[mjr]

You measure heat in therms, saying 4w of heat doesn't have any meaning, [...]

OK boomer. Modern people measure heat in joules, and 1 J/second = 1 W so it's a pretty easy conversion if told the power delivered in watts or watt-hours.

Edit to add: BTU is still an imperial fossil. Move on, unless you're the sort of person who actually enjoys "26 inch" tyres meaning any of at least five sizes (559, 571, 584, 590 or 597mm BSD).

The Ws used to generate a BTU is dependent on the efficiency of the device, it's may be approx 2.9 KW but it isn't exactly so, which is why it's not used to compare devices of different efficiencies and that appears to be what he is doing here

Watts delivered (not used) is indeed now sometimes used to compare heater outputs. Efficiency differences don't prevent this if it's the delivered power being compared, similar to how people can compare the power "at rail" of locomotives without caring about the efficiency or how much power they're taking from the wires or fuel. It's much better than when people used to use power usage in watts as an indication of light output: that broke down as soon as lights weren't all the same technology.

[jois]

You measure heat in therms, saying 4w of heat doesn't have any meaning, [...]

OK boomer. Modern people measure heat in joules, and 1 J/second = 1 W so it's a pretty easy conversion if told the power delivered in watts or watt-hours.

Edit to add: BTU is still an imperial fossil. Move on, unless you're the sort of person who actually enjoys "26 inch" tyres meaning any of at least five sizes (559, 571, 584, 590 or 597mm BSD).

The Ws used to generate a BTU is dependent on the efficiency of the device, it's may be approx 2.9 KW but it isn't exactly so, which is why it's not used to compare devices of different efficiencies and that appears to be what he is doing here

Watts delivered (not used) is indeed now sometimes used to compare heater outputs. Efficiency differences don't prevent this if it's the delivered power being compared, similar to how people can compare the power "at rail" of locomotives without caring about the efficiency or how much power they're taking from the wires or fuel. It's much better than when people used to use power usage in watts as an indication of light output: that broke down as soon as lights weren't all the same technology.

No I can assure you modern heating engineers measure it in BTU old guys like me are still in therms, non of them measure it in joules

NB you do know that joules is an imperial unit ?

[853]

Having dredged my brain a bit, I think I can add more regarding the "extract heat from water by freezing it" idea.

As I said yesterday, a key question is the Coefficient of Performance that the heat pump is able to deliver (whether it be a GSHP, fridge, deep freezer, aircon unit, or whatever), and that is crucially dependant upon the difference between source temperature and output temperature required.

A GSHP operating optimally, pulling energy from cool (c10 - 15 degrees) ground and depositing it at say 40 degrees, can attain a CoP of between 3 and 4, so for every unit of energy used to drive the system, 3 to 4 units are extracted from the ground. Brilliant!

If the GSHP is required to do more work, to cross a greater temperature gradient, say to raise the output temperature to 60 degrees its CoP drops sharply, which is why a well-designed heating system run from a GSHP uses fairly low temperature, fairly big radiators (sometimes the entire floors of rooms are used as radiators).

The bad news is that a 'fridge bringing food down from ambient to about 2 degrees has a CoP of somewhere a bit either side of 2, and a deep freezer dragging things down to far lower temperatures might have a CoP of only 1. BUT, the cited CoP for cooling plant tells us something different from the cited CoP for heating plant, so the CoP for a freezer viewed as a heater will be different from the CoP of a freezer viewed as a cooler, IIRC from long ago learning, we need to add 1 to the CoP cited as a cooler to get to the equivalent viewing it as a heater.

Anyway, it looks to me as if the best bet here for Heath Robinson arrangements is to cool the water in a fridge, rather than freeze it in a freezer, but I will keep pondering and will correct the foregoing if I realise any mistakes.

Thanks for your excellent answer; I will look more into it, with a regard to trying a fridge rather than a freezer by the looks of it

A GSHP operating optimally, pulling energy from cool (c10 - 15 degrees) ground and depositing it at say 40 degrees, can attain a CoP of between 3 and 4, so for every unit of energy used to drive the system, 3 to 4 units are extracted from the ground. Brilliant!

This is what I was trying to say earlier: 1 unit of energy to produce up to 4 units of heat

[Nearholmer]

1 unit of energy to produce up to 4 units of heat

It isn’t producing heat, it’s moving it from one place (the ground) to another (indoors), it pumps it from one place to the other.

But, I guess you know that - I’m just being picky to avoid confusion.

[ANTONISH]

qu[ote=jois post_id=1728037 time=1664896304 user_id=58323]


NB you do know that joules is an imperial unit ?

[/quote]

The joule (J) is an SI unit.

[Mick F]

23degC here in the living room. No heating.
16degC outside and raining.

I am so warm, I've removed my dressing gown, and was still too warm, so went outside for a couple of minutes in the rain to cool off.

[Nearholmer]

The joule (J) is an SI unit

It is now, but it has been around as a unit since the 1880s (first proposed to an international standards body by the BA, having been suggested by its German-born, naturalised British president of the time, so an international unit of international origin) , but I can't find any suggestion that it was ever adopted into the Imperial system, it may have been, but I can't find any suggestion.

I collect old (1870s to 1950s) electrical and mechanical engineering text books, which contain a serious hodge-podge of units, partly because some of them date from before the formal definition and agreement of units*, and on a quick scan I can't find any use of the Joule, they use several different units of energy according to the application, which makes following energy through from say coal to electricity a bit of a pain. I would wager that physics, as opposed to engineering, text books did use the Joule from an early date, but I don't have any of those in which to check. One thing to watch out for, though, is use of units that hadn't been formally adopted into particular local schemes; Centrigrade was widely used as the unit of temperature by engineers in Britain from at least c1900, for instance, but I dont think it was ever adopted as an Imperial unit.

*I have one within which the unit of electrical resistance is the Siemen, which is particularly confusing.

[Biospace]

Once again jois is correct, no matter how many confident posts from whichever thread insist he's just here to annoy people with mis- or even dis-information, or be called a conspiracy theorist. I was duly humbled when posting a pic of how to heat a room with a candle under a terracotta pot, only for jois to describe how it works better, for him.

I vaguely remember our Physics teacher talking about the Manc brewer's son who played with electricity for fun when not running the family business having his name used in the 1800s as a scientific unit.

After a little research this is confirmed - the Joule was in common use even before it was adopted officially in 1889, on the personal recommendation of Wilhelm Siemens.

https://detailedpedia.com/wiki-Joule

[Nearholmer]

But, where does that say that the Joule was an Imperial unit? I don’t think it does. It is undoubtedly a unit suggest by a naturalised-Brit, and proposed by a British body, but that isn’t the same thing as it having been adopted into the Imperial system. As I said above, it might have been, but I can’t unearth any evidence of that.

[Biospace]

But, where does that say that the Joule was an Imperial unit? I don’t think it does. It is undoubtedly a unit suggest by a naturalised-Brit, and proposed by a British body, but that isn’t the same thing as it having been adopted into the Imperial system. As I said above, it might have been, but I can’t unearth any evidence of that.

Me neither. There were so many organisations and systems around, consolidated as Physics developed. I was reading 'Imperial' as meaning non-SI, which clearly is not technically correct.

Who remembers ergs? And why is a gill a different measurement in Lancashire and Scotland than elsewhere?

I may be wrong but believe that therms (100,000 Btu) are still in use.

Gas suppliers started to use kWh rather than MJ to indicate the illusory price advantage of gas over electricity by virtue of the ‘Second Law of Thermodynamics’.

As engineers know: 1 kWh = 3.6 MJ = 3600 kJ and a steam table calorie = 4.1868 J.

The joule and the watt are SI derived units; the watt hour and calorie are not. Energy suppliers’ bills should use megajoules. A thermochemical calorie = 4.184 J

https://www.imeche.org/news/news-articl ... d-si-units

[Nearholmer]

All of which has made me question what the "Imperial System" actually is, and which units are defined within it.

So far as I can work out, and I may have got it wrong, it formally includes only those units defined in a succession of Weights and Measures Acts, so that a lot of units that we tend to think of as "Imperial" possibly aren't, they're simply units that it was customary to use within Britain and its sphere of influence.

The Weights and Measures Act 1889 includes this:

"The Board of Trade shall from time to time cause such new denominations of standards for the measurement of electricity, temperature, pressure, or gravities as appear to them to be required for use for trade to be made and duly verified, and those new denominations of standards when approved by Her Majesty in Council shall, whether derived from imperial or from other standards, be Board of Trade standards, in like manner as if they were mentioned in the Second Schedule to the principal Act."

I know that several of the units agreed at the International Electrical Congress in 1889 were adopted under this mechanism, so probably can properly be called "Imperial", but whether the Joule was among them I can't discover. The electrical units at that time were all derived in the cgs system, and I think referenced to standards held in Paris, although nobody could nail the Ohm down, because they couldn't create a reprodcible standard for it, so things were still a bit wobbly round the edges.