The heatpump, with more energy out than in (FACT)

[ATT]

Ya, I'm saying that the extra heat absorbed in the phase change never enters the equation of compression/decompression.

That's not quite correct. The latent heat was introduced in turning the refrigerant from liquid to gas. The gas enters the compressor gets compressed and the energy needed to compress the gas is added (a small fraction of total energy carried by the fluid). With the gas (and the energy it contains) compressed into a small space the energy is now dense enough to be considered sensible heat.

@angryScientist
I appreciate the detailed explanation, you appear to have an excellent grasp of the refrigeration cycle.

At this point, I think the next thing we are wanting to know would be: Is the published heat-output from a heat-pump the actual BTU quantity delivered into the space?

I would imagine that it is, otherwise how could one accurately size a system for a load?

In the commercial world, if it wasn't, it could be grounds for a lawsuit from the Architect, General contractor, HVAC sub and owner, wouldn't you think?

What's your experience with equipment ratings such as this?

Tony
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[ATT]

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@Nabo00o

I found the spec for an HP with a COP of 3.2 to use as an example, but others with a higher COP could be used, this is just the one that I happened on first.

--------------------------------------------
GE Zoneline Deluxe Series AZ39H15DAB
14,600 BTU Packaged Terminal Heat Pump Air Conditioner with 310 Max CFM, Freeze Sentinel and Heat Sentinel.

Capacity
CFM Indoor Fan High:.......................310
CFM Indoor Fan Low:........................260
Cooling E.E.R. (BTUH / Watt):............10.0/10.0
Dehumidification (pts./hr.):................4.5
Heating - Reverse Cycle - BTUH:........13,400/13,200
Sensible Heat Ratio at 230 Volts:........67%


Power / Ratings
Power Factor:....................................91/92
Voltage:............................................230V/208V
Cooling - Amperes; F.L. - Cooling:..........7.0/7.5
Cooling - Amperes; L.R.:.......................38.0
Cooling - Watts:.................................1,460/1,430
Heating - Reverse Cycle - COP:.............3.2/3.2
Heating - Reverse Cycle - Heater Amps:..5.8/6.3
Heating - Reverse Cycle - Heater Watts:.1,230/1,210
--------------------------------------------


Rated Capacity:
BTU/h (heat)....= 13,400 BTU
Watts (heat)....= (230v x 5.8A) 1334W

1-Watt............= 3.41  BTU per Watt
1/(3.41)...........= 0.293 Watt per BTU

13,400 x 0.2930 = 3926.2W (@ 100% eff conversion)

COP = 3926/1334 = 2.94 (we'll say 3.0)

What this tells us is that at 100% efficiency, we can convert 13,400 BTUs to 3926 Watts with an input of 1334 Watts...now we have to consider losses.

There are several conversion methods to choose from, I decided to try a Rankine Cycle prime-mover for the generator, just to see how it would stack-up.

Rankine-Cycle generators are used in industry to recoup energy that would otherwise be lost due to waste-heat, so they usually use a heat-transfer medium like water or water and ethylene glycol rather than air, as used by the heat-pump described above.

To use water rather than air to transfer the heat off the condenser, we have to replace the original air-over condenser coil with a tube-in-shell condenser. These are available off-the-shelf and will aid us in transfering the heat we need to the ORC boiler-coil.

You might be wondering why we can't just blow hot-air over a can of freon to boil it off, we could, but the losses would be tremendous and the use of water allows for efficient heat-storage, as well as some measure of control for predictable (and constant) expander performance.

One thing, the industrial versions of ORC (Organic Rankine Cycle) generators are geared for 'industrial' size projects and typically run around $50K and up.

http://www.ormat.com

A while back, I found a complete paper on an ORC system in a size compatible with smaller heat-pumps, complete with parts list, specs and test results (University of Leige, 2007):

http://www.labothap.ulg.ac.be/cmsms/Staff/QuoilinS/TFE_SQ010607.pdf

It uses off the shelf components, has good monitoring instrumentation and can be built in a home-shop.

In matching the heat-pump to the ORC, we have to keep two things in mind:
-The ORC has to have the capacity to power the heat-pump.
-The heat-pump has to have the BTUs to power the ORC.

Since I chose this heat-pump randomly, it's not quite a match for the ORC described in the PDF, but it's 'close'.

This is where using the tube-in-shell condenser gives us some lattitude, we can 'store-ahead' to lead the potential heat requirements of the ORC.

If we used this set of components (and they were matched), we'd have this result:

(13,400 x 0.2930) = 3926.2W x .37 = 1452.6W

The efficiency of this particular ORC is 37%

The example heat-pump we're using requires 1334W to run.

Discounting the ORC pump and any unknown cumulative losses, we have a net-gain of 118.6W

That's with a HP COP of 3.0, using a nominal 1-ton HP.

No rigorous matching of HP to ORC was done simply because there are better COPs out there and this is just a thought-exercise to see if there is any viability in pursuing this idea.

On the face of it, it looks like there may be.

Tony
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[ATT]

As was mentioned earlier by another poster in this thread, ground-source heat-pumps are probably the way to go for this application.

A good example: WaterFurnace Enviosion GSHP COP of 5.6

This preclude jumping through all the hoops I mentioned in my last post, no need for tube-in-shell exchangers and all that, just get a GSHP water heater.

I'll run-down the data on this heat-pump when I get a minute.

Tony

[Nabo00o]

Thank you Tony, this was very valuable information indeed!
Another aspect of the process which I think is very important for the efficiency is that instead of creating low volume but concentrated heat and cold, the heat pump should create high volume but low intensity heat, this will mean that the efficiency of the heat pump can be much larger.

The only thing we need then is a way to compress the heat in a concentrated and high temperature that can power the generator.
Also, remember that it is not only the btu's which are important, but also the btu's which it normally would take from the environment, this will also be used to power the cool side of the generator. So theoretically the COP should be the double of normal operation if both the cool and the hot side can be used at the same time, at least that is what I've read.

@ Angryscientist
I understand that you know this subject quite well, but when the total heat which a heat pump can supply is given, and it exceeds the electric power necessary to power it by a ratio which is the rated COP, how then can that be wrong, or something close to miss-information?
Remember, the fact that it extracts energy from another heat source is a plus in this system, so don't use that as an efficiency argument. Else I really want to know how this truly works, if it is just a stupid idea or not.
If it can work it could work really great, especially with the new experimental super-efficiency heat pumps.

Naboo

[ATT]

A few more direct-conversion of heat to electricity methods:

DARPA statement - 77% is Carnot-Limit
www.darpa.mil/dso/archives/dtec/index.htm

Thermoacoustic - approx 30%:
www.sciencedaily.com/releases/2007/06/070603225026.htm
en.wikipedia.org/wiki/Thermoacoustic_hot_air_engine
www.olemiss.edu/depts/ncpa/BasRes/ThermoIndex.htm

Thermoacoustic - possible 60%:
www.popularmechanics.com/science/earth/4243793.html

Convection (CECC) unknown% alledgedly sidesteps Carnot Limit
www.globalwarmingsolutions.co.uk/convective_energy_conversion_cycle.htm

Thermoelectric - 6-10%
www.technologyreview.com/Energy/21125/

Thermophotovoltaic - unknown%
www.macrovu.com/image/PVT/NASA/RPC/uc%3DThermoVoltaic.v3.pdf

Thermoorganic - unknown%
berkeley.edu/news/media/releases/2007/02/15_heatelectricity.shtml

Thermo-alkali-metal - unknown% alledgedly sidesteps Carnot Limit
findarticles.com/p/articles/mi_qa3864/is_200009/ai_n8926045/

Peltier-Seebeck Thermoelectric - 5-10%
http://en.wikipedia.org/wiki/Thermoelectric_cooling

Thermionics - unknown%
http://www.scienceblog.com/community/older/2001/B/200112962.html

And the list goes on...

Tony