ASHP - how noisy are they in reality

[LnP]

1 hour ago, JohnMo said:

Also sorry for hijack

 

That arguement is sound BUT, if the wind turbine or whole wind farm is being physically switched off and the wind farm being paid to do so (as happens quite regularly), then renewable to hydrogen makes perfect sense. It's excess electricity being stored instead of having been switched off. Hydro storage is part of that mix also.

 

The BEV makes sense also, but if wind power is being switched off even when the BEV is charging, hydro storage is being pump up the hill, hydrogen makes sense. 

At the moment, curtailment is usually because the grid doesn't have sufficient capacity. We should spend the money on increasing the capacity of the the grid so it can handle all the wind and solar, rather than expensive energy storage just because the grid can't handle it. Eventually though we will need storage to balance supply and demand. How to manage intermittency and curtailment was studied by the Royal Society and reported here, and indeed they found a potential use for hydrogen, i.e. renewable electricity via an electrolyser to hydrogen, stored in a salt cavern and back to electricity by a fuel cell or ICE and generator. It's expensive both in terms of capital cost and the round trip efficiency of 41%, i.e. you only get 41 kWh of electricity back for every 100 kWh of renewable electricity you put in.

 

Back to my original point though, advocates of hydrogen who don't understand the thermodynamics will assume that we can improve on the 41% as we get better with electrolyser and fuel cell technology. I'm afraid lobbyists and parties with vested interests looking for subsidies, exploit this and persuade politicians that the economics will improve. We can't and they won't. These are second law losses and you can't beat the thermodynamics. Some people correctly argue that interconnectors, which were not included in the RS study, could be a better solution - you connect to renewable sources where the wind and sun blow and shine at different times. Interconnectors avoid second law losses.

 

It all about the difference between the two types of energy, heat and work!

[SteamyTea]

7 hours ago, LnP said:

One is the rate of the other.

So not the same thing.

 

[MikeSharp01]

19 hours ago, LnP said:

Work can be converted completely into heat; but heat cannot be converted completely into work, the best you can theoretically achieve is a Carnot heat engine.

Fossil fuels provide heat energy and electricity provides work energy.

So a resistive heater, EG your immersion heater, puts 100% (well very nearly - some energy is always converted into a less useful form) of the electricity consumed into your water but you cannot go the other way? I suppose a question might be "Is that because the 2nd law says so or that we just don't have a technology that does it." after all the Kelvin-Plank statement mentions, IIRC, that any device operating a 'cycle' cannot achieve this perhaps leaving open an opportunity for a device not using a cycle to achieve this.

[SteamyTea]

33 minutes ago, MikeSharp01 said:

I suppose a question might be "Is that because the 2nd law says so or that we just don't have a technology that does it."

It is entropy.

 

If you think of the current, best model, of the universe, it starts with a point that is at high temperature.  As the universe expands, that energy gets dispersed over time.

That is work being done, energy (heat) is moved over time.

To get back to the original state (the big crunch) would need all the universe to be collected and compressed to one point.  PV/T (pressure x volume / temperature)

The kicker is that to do that, energy would have to be used (moving a mass a distance takes energy).  That energy needs to come from somewhere.  What happens is a closed system is that part of the original energy is used to collect all the particles and move them to one point.  This causes some parts of the system to have a lower mean temperature, and one part to have a higher mean temperature, as this goes on, the cold parts will react absolute zero (0K) and no movement will happen (zero kinetic energy).

Because there is a temperature difference, some of the energy (heat) from the hot part will move to the cold part, which then starts to move again.

As temperature is the mean, free path, molecular speed (a thermometer is a speed camera from molecules), those slightly warmed particles will move again.  But as it is based on a mean temperature, some will be very hot, some very cold, it is that ratio of hot to cold that does the work (power), but it takes time.

So you can think of it as a box of 1000 1 kg rocks that needs to be moved 1 metre.  You can do it all in one go, or move the rocks individually.  The energy needed is the same 1 kJ, but energy is needed to move them, 1 kJ.

Now as you know, moving a tonne of rocks is hard work and will make you sweat, so that is where the extra energy comes from.

 

There are some peculiarities in the mathematics that involve forces, and as you remember, F = MA, force (newton) is mass (kg) x acceleration (m.s^-2).

So the only way to get all the power back and convert it to energy, is to do it in zero time.  And that cannot happen (excluding some ideas from the quantum realm).

 

So it is not a case of technology, just a case of it is hard to get the hot particles and move them to the hotter part.

Maxwell created his daemons as a thought experiment, but that is all it is, not a real machine.

Edited April 6 by SteamyTea

[saveasteading]

32 minutes ago, MikeSharp01 said:

you cannot go the other way? 

The waste of heat being pumped out of chill stores is shocking. 

There has to be a way of heating nearby spaces.

I asked a client's contractor if they could heat the offices in the same building. He said no, but I'm not convinced.....simply take the hot waste pipes through radiators or past a fan?

 

[JohnMo]

7 hours ago, LnP said:

grid doesn't have sufficient capacity. We should spend the money on increasing the capacity of the the grid so it can handle all the wind and solar

Slightly issue - you can have all the capacity you want, but if industry and general public aren't using all that capacity available, you will still get curtailment at the generation end. You can put in high voltage DC interlinks to move the renewable energy further away and expand the market. You don't need to understand any thermodynamics for that.

 

7 hours ago, LnP said:

you only get 41 kWh of electricity back for every 100 kWh of renewable electricity you put in

That is then reflected in the price you sell it for. And there is a big market for it. Again no need to understand thermodynamics, it just a marketable product for a given price.

[JohnMo]

9 minutes ago, saveasteading said:

There has to be a way of heating nearby spaces.

I asked a client's contractor if they could heat the offices in the same building. He said no

Not sure they are correct,

 

You can do de-superheat on the chillers to get continuous high temp heat source.

 

A heat pump on chilling mode, is blowing heat out the condenser fan (heat taken out of the cold space). Pretty sure that heat could be used, even another heat pump, in front taking some warmed air, would get a decent CoP all year round.

[saveasteading]

1 minute ago, JohnMo said:

Not sure they are correct,

 

I think few installers understand the science. They just fit equipment. My clients always organised this direct and I couldn't get close to the manufacturers....but I don't feel they were much interested either.

 

So in a new food factory or warehouse,  we or our client's contractor  would put air source into an office and warehouse at one end, and meanwhile hot air is chucked out at the other.   

 

[LnP]

1 hour ago, MikeSharp01 said:

but you cannot go the other way? I suppose a question might be "Is that because the 2nd law says so or that we just don't have a technology that does it." 

You can't beat the second law. Once you've converted the electricity (work energy) into heat energy, any device you design to get back to work energy can never get you back all the energy as work. Some energy will always be rejected as heat. The best you can theoretically do is a Carnot heat engine which has an efficiency of (T_h - T_c )/T_h - hot and cold temperatures in Kelvin. And there's no actual such thing as a Carnot engine.

39 minutes ago, saveasteading said:

The waste of heat being pumped out of chill stores is shocking. 

There has to be a way of heating nearby spaces.

I asked a client's contractor if they could heat the offices in the same building. He said no, but I'm not convinced.....simply take the hot waste pipes through radiators or past a fan?

 

Yes, great if you can find a use for the rejected heat.

33 minutes ago, JohnMo said:

You don't need to understand any thermodynamics for that.

Again no need to understand thermodynamics

I've got a fantastic energy project I think you might be interested in investing in ....

[saveasteading]

48 minutes ago, LnP said:

, great if you can find a use for the rejected heat.

In these cases it was easy in winter....heat an office or factory.

In summer, no..?. The best I can think of is a reversed ground source heater. Storing heat for much later.but there are lots of snags in this.

 

As a further diversion.    Most cold stores are too high. Clients want the better £/m3 that height gives them, then don't use it.

[JohnMo]

1 hour ago, LnP said:

I've got a fantastic energy project I think you might be interested in investing in ....

No thanks, I'll stick with converting my excess PV electricity into either heat or cold for the house. Way better value, than anything a commercial project could offer.