Author Topic: UK Heat Pump/Exchanger Heating.  (Read 2514 times)

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Online paulca

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Re: UK Heat Pump/Exchanger Heating.
« Reply #50 on: March 23, 2019, 04:54:56 am »
For example: if you put 1kW of energy into a heat pump with a COP of 2.5 you'll get 2.5kW worth of heat moved using that 1kW of electricity.

Yes and at 30% efficiency at the generation/distribution end that works out as 75% net "efficiency".  Still less efficient than a gas boiler, though not be much.

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Online james_s

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Re: UK Heat Pump/Exchanger Heating.
« Reply #51 on: March 23, 2019, 05:09:57 am »
There are significant losses in transporting the gas too, although I have no idea what the actual numbers add up to. Natural gas pipelines use large gas turbine powered compressors which burn some of the gas in order to compress the remaining gas into the pipeline. The LM1500 is one such popular engine, developing around 15,000 horsepower so not an insignificant amount of fuel burn.
 

Offline apis

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Re: UK Heat Pump/Exchanger Heating.
« Reply #52 on: March 23, 2019, 05:31:29 am »
The pipelines are the most efficient part of the transportation chain from the source which is typically imported from far away.

LNG isn't as good as it might seem (compared to oil) when it comes to greenhouse gas reductions if you consider the whole production and supply chain because there is a lot of leakage of methane which is a much more potent greenhouse gas than CO2.

(And whenever you burn something you also get air-pollution, more the more inefficient which usually isn't as good at small scale).
« Last Edit: March 23, 2019, 05:34:12 am by apis »
 

Online nctnico

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Re: UK Heat Pump/Exchanger Heating.
« Reply #53 on: March 23, 2019, 05:44:04 am »
For example: if you put 1kW of energy into a heat pump with a COP of 2.5 you'll get 2.5kW worth of heat moved using that 1kW of electricity.
Yes and at 30% efficiency at the generation/distribution end that works out as 75% net "efficiency".  Still less efficient than a gas boiler, though not be much.
I don't think this shifting of numbers adds anything to the discussion. I already wrote that a COP of 2.5 isn't going to beat a  gas boiler by a great margin. The bottom line is that heat pumps can move more energy than they consume. Whether that leads to a reduction of CO2 and costs depends entirely on the situation.
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Online NiHaoMike

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Re: UK Heat Pump/Exchanger Heating.
« Reply #54 on: March 23, 2019, 09:50:55 am »
Yes and at 30% efficiency at the generation/distribution end that works out as 75% net "efficiency".  Still less efficient than a gas boiler, though not be much.
There have been attempts at making gas powered heat pumps, the problem is that the absorption cycle is very inefficient compared to electric heat pumps, plus it uses highly toxic ammonia as the refrigerant. Running an electric heat pump from a generator ends up with similar efficiency and much more flexibility, and then you can recover the waste heat from the engine to get way ahead in overall efficiency for heating. Or use the heat to run a desiccant cycle dehumidifier during the summer.
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Online james_s

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Re: UK Heat Pump/Exchanger Heating.
« Reply #55 on: March 23, 2019, 10:06:42 am »
The idea of running an electric heat pump from a generator never occurred to me. When the goal is to make heat, an internal combustion engine burning natural gas could be quite efficient. A liquid cooled engine would make it easy to extract the heat and move it indoors where you want it, with some of the electricity produced powering a heat pump to get additional heat into the house. Maintenance of a piston engine would likely kill the overall practicality of the project other than for emergency use and small gas turbines while requiring much less maintenance are far more expensive and tend to be inefficient outside of a very narrow band near full throttle.

As far as natural gas being imported, that depends on where you are. Here in the US we produce quite a bit of the gas we consume. Obviously the further you are from the source, the less efficient it will be, that applies to any fuel.
 

Offline coppice

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Re: UK Heat Pump/Exchanger Heating.
« Reply #56 on: March 23, 2019, 10:39:04 am »
Yes and at 30% efficiency at the generation/distribution end that works out as 75% net "efficiency".  Still less efficient than a gas boiler, though not be much.
There have been attempts at making gas powered heat pumps, the problem is that the absorption cycle is very inefficient compared to electric heat pumps, plus it uses highly toxic ammonia as the refrigerant. Running an electric heat pump from a generator ends up with similar efficiency and much more flexibility, and then you can recover the waste heat from the engine to get way ahead in overall efficiency for heating. Or use the heat to run a desiccant cycle dehumidifier during the summer.
There are commercial methane powered heat pumps with claim a COP of 2.5 to 3. These don't use ammonia, but I am not clear what they do use.
 

Online nctnico

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Re: UK Heat Pump/Exchanger Heating.
« Reply #57 on: March 23, 2019, 10:43:47 am »
The idea of running an electric heat pump from a generator never occurred to me. When the goal is to make heat, an internal combustion engine burning natural gas could be quite efficient. A liquid cooled engine would make it easy to extract the heat and move it indoors where you want it, with some of the electricity produced powering a heat pump to get additional heat into the house. Maintenance of a piston engine would likely kill the overall practicality of the project other than for emergency use..
Let me stop you right there. These systems aren't fantasies but already widely used to heat large (apartments) buildings and companies. A gas turbine drives a generator to produce electricity (which feeds back into the grid or for whatever electricity is needed) and the residual heat is used for heating. The economics are very favourable. This also works on a large (city wide) scale. For example: my own home is heated from residual heat from a power plant for over 2 decades already. Cost wise it doesn't make sense for me to get an electric heat pump.
« Last Edit: March 23, 2019, 10:50:08 am by nctnico »
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Offline apis

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Re: UK Heat Pump/Exchanger Heating.
« Reply #58 on: March 23, 2019, 10:44:14 am »
I just mean you have to look at the entire life-cycle if you want to compare environmental impact. In car-fuel terms, a well-to-wheel analysis.
 

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Re: UK Heat Pump/Exchanger Heating.
« Reply #59 on: March 23, 2019, 12:12:19 pm »
There are commercial methane powered heat pumps with claim a COP of 2.5 to 3. These don't use ammonia, but I am not clear what they do use.
I wouldn't be surprised if they're just electric heat pumps combined with generators. Or maybe fuel cells.
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Online IanB

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Re: UK Heat Pump/Exchanger Heating.
« Reply #60 on: March 23, 2019, 12:18:53 pm »
The idea of running an electric heat pump from a generator never occurred to me.

Why go through the extra steps of generating electricity to run a motor to drive a compressor, when the compressor could be driven directly by the gas engine and avoid the whole generator/motor piece?
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Re: UK Heat Pump/Exchanger Heating.
« Reply #61 on: March 23, 2019, 01:14:35 pm »
Why go through the extra steps of generating electricity to run a motor to drive a compressor, when the compressor could be driven directly by the gas engine and avoid the whole generator/motor piece?
Easier said than done to seal the refrigerant inside, there's a reason why hermetic compressors have been the norm for decades.
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Offline wraper

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Re: UK Heat Pump/Exchanger Heating.
« Reply #62 on: March 23, 2019, 01:20:43 pm »
The idea of running an electric heat pump from a generator never occurred to me.

Why go through the extra steps of generating electricity to run a motor to drive a compressor, when the compressor could be driven directly by the gas engine and avoid the whole generator/motor piece?
Refrigerants are extremely leaky. They will happily leak through any seal.
 

Online james_s

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Re: UK Heat Pump/Exchanger Heating.
« Reply #63 on: March 23, 2019, 02:43:24 pm »
Well they do make semi-hermetic compressors that are belt driven, I've seen them used in very large refrigeration systems like AC units for shopping malls and movie theaters or huge walk-in freezers like you'd find in a meat packing plant.

The reason for using electricity is that it is assumed that the electricity would do other things, like power the electric loads in the house including the fan in the air handler.
 

Offline george80

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Re: UK Heat Pump/Exchanger Heating.
« Reply #64 on: March 24, 2019, 02:40:48 am »
Easier said than done to seal the refrigerant inside, there's a reason why hermetic compressors have been the norm for decades.

Refrigerants are extremely leaky. They will happily leak through any seal.

Oh FFS!   :palm: :palm:
Where do people come up with this shit??

What the hell do you think is under the bonnet of every car and has been in at least some for 50 Freaking years?

A belt driven Refrigeration compressor for the AC.
The seals last just fine and by law in about every country are not allowed to leak refrigerant into the atmosphere.

I have set up  car AC systems driven by a small Diesel engine.  Just took the system out the car, extended the High and Low side Pipes with copper which I used normal AC line insulation for and put a thermostat on the evaporator to cut the compressor as the normal cut out for icing  was controlled by the cars computer and another inline for internal temp control. This was also hooked to the engine through a solenoid on the engine so it went to idle when the AC clutch cut out. The signal went through a 10 sec relay to the clutch so the engine had time to come back up to revs before the compressor load dropped back in.  Cutout was instant.

 As I have done with all my vehicles, Instead of R134a I used regular LPG. Works like a charm and is cold as Charity.   ( and I'll wait for the comments on that!  ::)
Instead of charging by weight as normal with refrigerants I charged by pressure ( around half on 134a) but it's easy to " tune" by measuring the outlet temp from the evaporator as would normally be checked anyway. Add in plenty of oil and all is good.

A decent size  vehicle AC has about the same BTU capacity as a mid size domestic split system so they are far from weak.
For heating all that would need to be done would be to put the condenser in the home  and put the evaporator outside. Could use the normal coils just reverse positioning to make packaging easier.
 It would be a waste not to put in a normal reversing valve from a domestic AC which are readily available as spare parts so the unit could heat in winter and cool in summer. 

The advantage of an engine driven AC as a heat pump would be you could direct the cooling air and exhaust through the evaporator coils to bump the efficiency hugely. Instead of that 30% energy as heat being wasted, it could now be utilized going back to the Home or space.  This would be a massive benefit in very cold temps below about 5 oC as it would allow the unit to operate on a much more efficient curve and prevent Icing problems of the evaporator. As the evaporator is not size specific, One could get a larger Condenser off a domestic unit which would allow better heat transfer still though larger surface area and allow the use of a lower powered fan if that was needed at all.  Exhaust gas and sealing and ducting the Inlet side of the air cooled engine so as to set ap a positive pressure exhausting through the condenser would probably be more than enough.

As said, large commercial AC compressors are nearly all belt driven over a certain capacity and are usually reciprocating Piston types in multi cylinder configurations. Been used for years and give many years of service without leakage which is almost always from the pipes and joints when they do occur.

It really would be best if people did know what they were talking about before they proved their ignorance.
 

Online james_s

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Re: UK Heat Pump/Exchanger Heating.
« Reply #65 on: March 24, 2019, 03:24:58 am »
Car AC systems are notoriously leaky, in every car I've ever owned the AC system was dead by the time I got it and I had to replace some seals and recharge it. If it goes 10 years without leaking out the refrigerant charge you're doing pretty well. That's not to say refrigerant is particularly leaky stuff, but it is a gas at atmospheric conditions, is pressurized in the system and there isn't a whole lot of it in a typical car AC system. You typically have at least half a dozen fittings and a seal on the compressor shaft so there are ample opportunities for leaks to form.

Fully hermetic systems on the other hand very rarely leak at all, I've seen it twice, once in a domestic heat pump where the discharge line from the compressor was contacting a bracket and vibration eventually wore a small hole. The other was a refrigerated air dryer on an industrial compressor where the high side over-pressure switch came apart and dumped the charge.
 
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Online nctnico

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Re: UK Heat Pump/Exchanger Heating.
« Reply #66 on: March 24, 2019, 11:42:47 am »
Car AC systems are notoriously leaky, in every car I've ever owned the AC system was dead by the time I got it and I had to replace some seals and recharge it. If it goes 10 years without leaking out the refrigerant charge you're doing pretty well. That's not to say refrigerant is particularly leaky stuff, but it is a gas at atmospheric conditions, is pressurized in the system and there isn't a whole lot of it in a typical car AC system. You typically have at least half a dozen fittings and a seal on the compressor shaft so there are ample opportunities for leaks to form.
Exactly! On every car I have owned so far the AC needed refilling every 4 to 5 years due to lack of refrigerant (which obviously leaked away somehow).
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Offline george80

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Re: UK Heat Pump/Exchanger Heating.
« Reply #67 on: March 24, 2019, 10:31:34 pm »

Exactly! On every car I have owned so far the AC needed refilling every 4 to 5 years due to lack of refrigerant (which obviously leaked away somehow).

Do you even know what point you are trying to argue here?
 

Offline ahbushnell

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Re: UK Heat Pump/Exchanger Heating.
« Reply #68 on: March 25, 2019, 03:29:14 am »

Exactly! On every car I have owned so far the AC needed refilling every 4 to 5 years due to lack of refrigerant (which obviously leaked away somehow).

Do you even know what point you are trying to argue here?
We have determined that AC systems leak. 
 

Offline george80

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Re: UK Heat Pump/Exchanger Heating.
« Reply #69 on: March 25, 2019, 07:30:19 am »
We have determined that AC systems leak.

But not where from.
The claim was made that Refrigerant leaks from and could not be contained by seals.

That is complete and utter BS. 

Car systems I used as an example leak from a number of places and the seals of the compressor are vary rare ones.  They have many joints and are subject to a LOT of vibration. It has been well known for years that AC compressors should be operated regularly but there will be those that neglect such Maintenance and then use that improper operation to claim that something is faulty.

For those looking for an argument, look up the facts and then come argue, don't think because that's the opinion you have it's fact.

Lots of hermetic systems leak and run out of gas too because it's not the compressor type that is the problem, it's the Joints in the pipe and everything else attached.
 

Offline nimish

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Re: UK Heat Pump/Exchanger Heating.
« Reply #70 on: April 05, 2019, 11:09:27 am »
For example: if you put 1kW of energy into a heat pump with a COP of 2.5 you'll get 2.5kW worth of heat moved using that 1kW of electricity.

Yes and at 30% efficiency at the generation/distribution end that works out as 75% net "efficiency".  Still less efficient than a gas boiler, though not be much.

30% efficiency? CCGTs get 60%. Thermal coal plants are dead and dying due to fixed costs + immense pollution. Coupled with renewable power (90+%, effectively) which gets cheaper over time, it's a no-brainer for anyone who isn't already gas connected to switch.

Distribution losses are ~10%.

Heat pumps, for the UK climate, are the right choice. Gas is a dangerous anachronism.
 

Offline grifftech

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Re: UK Heat Pump/Exchanger Heating.
« Reply #71 on: April 06, 2019, 02:10:49 am »
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