Thermo dynamics for hot water that runs off atmosphere

[jason121]

The thermo dynamic panels only require small amounts of heat to operate, the heat comes from the compressor to warm the water, not the panel.

 

[Gavin A]

The thermo dynamic panels only require small amounts of heat to operate, the heat comes from the compressor to warm the water, not the panel.

the compressor doesn't create heat*, it merely concentrates it from a lower grade to a higher grade of heat. The original heat energy input that allows for the high COP's comes from the panels extracting heat / energy from the air and solar radiation.



*actually I suppose it does to an extent in terms of directly transferring electrical energy to heat, but that's not where the bulk of the heat comes from.

 

[jason121]

not if your using gas it dont

 

[jason121]

Heating and cooling is accomplished by moving a refrigerant through the heat pump's indoor and outdoor coils. Like in a refrigerator, a compressor, condenser, expansion valve and evaporator are used to change states of the refrigerant between a cold liquid and a hot gas.
When the liquid refrigerant at a low temperature passes through the outdoor evaporator heat exchanger coils, ambient heat is used to cause the liquid to boil. This boiling or change of state process amasses energy as latent heat. The vapor is then drawn into a compressor which further boosts the temperature of the vapor.
Passing into the building, the vapor enters the condenser heat exchanger coils where it transfers heat to indoor air, which is drawn across the coils by a fan. As the vapor cools, it condenses back into a liquid, and releases its latent heat to the air passing over the condenser unit.
Exiting the condenser, the cold liquid refrigerant is under high pressure. The refrigerant passes through an expansion valve which reduces the pressure, draws in heat and allows the refrigerant to re-enter the evaporator to begin a new cycle

 

[Gavin A]

not if your using gas it dont

basic laws of thermodynamics say you're wrong.

the additional heat energy on top of the electrical input energy isn't just magicked into existence by the compressor, it has to originate somewhere, and in the case of a closed loop system like this that heat input obviously has to come from the panel absorbing it from the air and sun.

 

[jason121]

The panels wont reach 55 degrees if the outside temp at night is -5. Thats why ASHP can work down to -20,

 

[Gavin A]

The panels wont reach 55 degrees if the outside temp at night is -5. Thats why ASHP can work down to -20,

I'm fairly obviously not saying that the compressor doesn't extract the heat energy and boost it up to the required temperature, but you seem to be denying that the heat energy actually has to originate in the panel, which is obviously wrong.

 

[jason121]

Yes but only a few degrees, stick the panel in the ground or lake it would still work, how do you think fridges work or cold stores, freezes.

 

[Gavin A]

I've now found a datasheet for the larger swimming pool / heating systems at least.

It doesn't give proper COP figures, but does at least give min / max electrical input and heat output figures eg for the 4 panels system, as well as diagrams showing the actual heat output expected from different ambient air temperatures in day and night. I don't know what sunlight levels are assumed in the daytime heat output figures, I'm thinking probably they're based on best case scenario of 1000W/m2 insolation, but it doesn't say.

Absorbed Power 0,9 - 1,8 kW ; Thermal Power 3,6 - 7,3 kW

 

[Gavin A]

Yes but only a few degrees, stick the panel in the ground or lake it would still work, how do you think fridges work or cold stores, freezes.

it's not a matter of degrees as such, it's a matter of total energy input into the system. and yes you could put the panel in a lake if you had one, but this is an alternative for those of us who don't have sufficient lakes or ground for a GSHP / WSHP to be an option.

It has occurred to me that we might be both arguing the same position but using different terminology.

 

[steve k]

The heat is magicked from the compressor, from the heat of compression. Imagine a bicycle pump, why do these get hot in use? kinetic energy to heat enegry.
All the evaporator plate/panal is for is to allow the refrigerant to boil and change state from a liquid to a gas, so that the vapour compression cycle can start again.

The gas does not care weather it is 10 deg C, 50 deg C or -10 deg C as long as it can change state in there.

I will try to simplify Jason's explanation:

When a fridge (which is essentially what these are) is switched off the gas in side them will be in a saturated condition; part liquid, part gas.
When we switch it on here's what happens, the compressor starts and does what it does i.e. compresses the gas in the system, as the gas is compressed it heats up and comes out of the compressor in the hot gas discharge line. It is this hot gas line that wraps around the cylinder full of cold water, as the heat flows from the hot gas to the cold water obviously the gas cools down, and then condenses from a gas into a liquid.
The trouble now is that we have liquid refrigerant that we need to turn back into a gas so that it can be compressed again. Then we can utilize the heat of compression to heat our bloody water up. Are you all with me so far???

To do this we send the liquid refrigerant through an expansion valve that will allow the liquid to expand and lower its pressure (think spraying mister muscle in the kitchen) this happens just before the evaporator (the panel), now that the liquid refrigerant is in small particles, like a mist, it will now boil/evaporate easily back into a gas using any heat around as long as it is above the gases boiling point of -26 deg C.

The process can start again..

It's all clear in my head:sifone:, I hope it will help someone understand it all a bit better.

 

[Gavin A]

ok, the heat is effectively created by the compressor, but the energy isn't.

there is the same energy difference in joules between the incoming and outgoing gasses to the energie unit from the panels as there is between the incoming and outgoing heating fluid to the tank plus part of the electrical input to the compressor.

but that's clear from what I originally wrote anyway, in terms of the compressor concentrating low grade heat energy into higher grade heat energy.

and of course it matters what temperature the incoming gas is at, as this dictates how much energy is available - why else would the efficiency and heat output from heat pumps rise with temperature of the incoming gasses?

the worrying thing to me about this conversation is that both of you install heatpumps, and I don't yet.

 

[Gavin A]

I have installed a few of these systems and these are the facts:

Ambient air temp - 6 deg C
Water entering temp - 8 deg C
200l of water 8 deg to 55 deg = 2 hours
amp draw = 9amps

Now i'm no mathematician, but what does this calculate into?

Steve

200l at a little under 50deg temp rise needs around 11kWh of energy input.

9amps x 230 v = 2kW x 2 hours = 4kWh

COP = 11 / 4 = 2.75

a COP of 2.75 at 6 deg c ambient air temperature is reasonable, but not particularly impressive for a heat pump tbh, though it at least demonstrates that it's considerably better than an immersion heater, and maybe just about on a par with a condensing gas boiler.

So possibly worth it for those on full electric heating.

something has been bugging me about these figures, and I've just worked out what it is.

These are the ratings for the 200l energie unit

electrical input 390 - 550Wpower output 1690 - 2900W
anti legionella heater 1200W

assuming you were using the energie system, it's pretty clear from these figures that you must have had the 1200W immersion switched on when you were heating the system up from cold, as there's no other way you could have got anything like 5.5kW heat output from it, or 2kW electrical input. I'd been thinking the electrical input figures seemed extremely high.

http://www.thermogroupuk.com/thermogroup_pdfs/TDY_ECO_Data_Sheets_v1.0.pdf

 

[steve k]

the worrying thing to me about this conversation is that both of you install heatpumps, and I don't yet.

Why? I am an air conditioning engineer and have been installing "heat pumps" for 25 years>

assuming you were using the energie system

You have assumed incorrectly, perhaps the ones we installed have a larger compressor and a more efficient heat exchanger.

Steve

 

[Gavin A]

Why? I am an air conditioning engineer and have been installing "heat pumps" for 25 years>

have a read through Jason's posts and your recent post then, and the answer should be obvious. You don't seem to be understanding, or at least you're not describing very well where the actual energy input originates in these systems, or allocating any importance to it.

it will now boil/evaporate easily back into a gas using any heat around as long as it is above the gases boiling point of -26 deg C.

yes, this is where the actual additional energy input into the entire system (over the electrical input) comes from, not from the compression / expansion cycle itself. This energy input to the otherwise closed cycle* of the heatpump comes from the panel collecting energy in the form of heat from both the air and the solar radiation, and is directly proportional to the actual heat energy output from the other side of the compressor as is clearly shown in the graph posted.

You have assumed incorrectly, perhaps the ones we installed have a larger compressor and a more efficient heat exchanger.

Steve

fair enough.



*well, not entirely closed as the energy is obviously being extracted at the other side into the hot water tank, which balances out the heat energy input from the panel + the most of electrical energy input.