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How to calculate COP on air source heat pump.

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Harvey Ramer
Harvey Ramer Member Posts: 2,239
I have often been confused on COP ratings for airsource heat pumps. I know that as the air temp changes, so also does the COP. For example, I am looking at using the SpacePak reverse cycle heatpump, which advertises a COP of up to 4. The average mean temp of south central PA is around 50 deg/F. This bumps the COP back to 2.7.



Would 2.7 be the proper COP number to use when selling the product to a customer?



I wish these manufactures would quit using (up to) numbers and give us some real time data.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Refer to manufacturers information...

    The COP depends upon the OSA temperature, and the required hot water supply temperature. The further apart they are, the lower the COP. The closer together they are, the higher the COP.



    The one company I am familiar with (Daikin) has soft ware that can tell you what to expect as it pertains to seasonal COP's.



    You are looking at a snap shot in time, under worst case scenario conditions, and those are really not indicative of true seasonal operating characteristics.



    It is STRONGLY recommended that with ANY heat pump (air or ground source) that a good ODR program be used to increase the COP of the appliance. Running on a high fixed temperature will cause a low seasonal COP.



    Tracking the COP requires a lot of data logging equipment that can look at what watts are being consumed, and how many watts of energy are being delivered. If you get 3 watts back for each watt you put in, then the COP is expressed as a 3 to 1.



    What this means, in terms of efficiency, is that at that point, the heat pump is 300% efficient in moving heat from where it was to where you need it. (its not creating heat, only moving it, except for compressor wattage, which IS producing heat)



    What is sad though, is the fact that the driving forces (coal/gas/oil fired electrical generation facilities) are only 30 to 40% efficient...



    Thats one of those facts that seems to slip through the cracks when people talk about efficiency...



    Now, if were talking Nukes, its a different story altogether.



    ME

    There was an error rendering this rich post.

  • LarryC
    LarryC Member Posts: 331
    edited February 2012
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    Hijack !

    ME,

    As one who used to operate nukes, the thermal efficiency of nukes are still only around 30 %.



    Check out the ratings of most power plants.  You will see the differences in MWt and MWe.



    Larry



    PS  MWt is thermal output of the reactor.  MWe is the electrical output of the generator. 



    Typical thermal to electrical ratios are about 3:1.
  • scott markle_2
    scott markle_2 Member Posts: 611
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    How to calculate Nuclear COP

    Don't forget that high grade uranium ore is in short supply. We have been "burning" the tragic excesses of " mutually assured destruction" for some time, and this has temporarily eased some of the pressure on the nuclear fuel supply.



    Civilian reactor core design was a rushed program that has left us with a legacy of inefficient reactors that have been scaled up to a point where containment can not be achieved in a worst case cooling failure.



    If we are serious about nukes it's time to move on from the giant PWR and BWR designs of the 60's.



    When you add up the mining and refinement, security, inefficient fission, resources that go into building and decommissioning the plants, and the still unsettled issue of the waste, nukes are probably the most expensive and inefficient way to generate electricity ever conceived.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Wow...

    and here I'd been lead to believe that Nuclear was far better than the fossil fuel plants. I learned something new today Larry. Thanks!



    I took Dan H and a whole bunch of other people on a tour of the Coors Brewery in GOlden COlorado a number of years back. They generate their own electricity with natural gas. Their Chief Operating Engineer told me that their plant was 80% efficient. I believed him too :-)



    To their credit, they utilized almost EVERY Btu that they generated from their steam plant, to the point that no cooling towers were necessary. Heat exchanger after heat exchanger after heat exchanger, extracting heat for different processes along the way.



    The last, lowest temperature application was used for growing the sprouts in the barley, that is used for mashing and making their final product, BEER.



    We found out during the trip, exactly what HELL looks like. They showed us some access ports that we could look into the combustion chamber and see the fire going on.



    Impressive...



    Well, at least the electrical generation systems of today are much more efficient that the solar PV cells of today (10 % is considered GOOD?!?) ;-)



    Other than, obviously waste heat recovery and thermal re-use, what can be done to increase these physical plant efficiencies? Off peak thermal energy storage?



    Thanks for the education.



    ME

    There was an error rendering this rich post.

  • Zman
    Zman Member Posts: 7,573
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    Check my math please

    Xcel energy in Colorado claims to be 30% efficient.Including plant inefficiency and line loss.

     A typical ground source water to water heat pump in this area has a COP of about 3. This would give me an overall efficiency of about 90% using a mix of fuels,primarily coal.

    If I install a Natural gas condensing boiler I should be able to achieve 90% overall efficiency.

    Why would anyone spend the resources to do a heat pump in this area? Am I missing something?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • scott markle_2
    scott markle_2 Member Posts: 611
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    Thermal efficiency

    Mark,



    That tour sounds great.



    Remember that when it comes to converting thermal energy to motive power (turbine etc.) the absolute max. for a theoretical frictionless engine is 73%. http://en.wikipedia.org/wiki/Thermal_efficiency



    Breweries have a wide array of thermal recovery possibilities, but we need to keep track of physical reality when it comes to turning fire into motion.



    I get really bothered when people talk about the relatively low efficiency of automobile engines, at 30% it's implied that there is anther 70% room for improvement. This is the kind of week thinking/deception you see all to often in the alternative energy universe, the reality is that we are probably very close to the practical limitations of internal combustion efficiency. Smaller lighter and less powerful is the only way to go, and that basically applies to our entire way of life in this brave new world.
  • LarryC
    LarryC Member Posts: 331
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    Please no politics or value judgements.

    Scott,



    I do not wish to get into a discussion about the pros and cons about various sources of electricity generation.  As I understand it, EVERY form of power generation has issues.  A look at recent history (last 5000 years) will show that many of today's solutions became tommorrow's problems.  Examples include open pit mining, asbestos, mercury, chlorinated hydrocarbons, fighting forest fires, damming rivers, PCBs, leaded gasoline, acid rain, open sewers, DDT, coal tar, urban areas, zebra mussels in non native environments, belief systems, colonization, gunpowder, steel, electricity, etc.



    I just wanted to correct a posted fact that I knew was incorrect. 



    Another significant energy loss is in the transmission and distribution of the power once it leaves the generation station.  I do not have definite numbers, but my guess is that it is greater than 10% of the power that enters the system.



    Larry
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
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    Google headquarters, Ebay headquarters and

    a couple other companies use the Bloom Box to produce a large amount of their electricity. From what I understand the Bloom Box takes natural gas and converts it to electricity at near 100% efficiency. The way I understand this is the brain child of some NASA scientist. Currently they are $60,000 a pop, but he is predicting in the future you will be able to buy one for $3,000. We'll see.



    Mark, I am also familiar with Daikan and have used there COP calculator. The SpacePak does basically the same thing. They don't have the Hydrobox, you have to run the water supply and return to the outside unit. The pricing is much more attractive then the Altherma. They don't have the computer program in place to calculate the COP.



    So I guess what you are saying there is no practical way to run the numbers without a program?
  • scott markle_2
    scott markle_2 Member Posts: 611
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    hijacked

    Larry,



    Sorry for the Huxley reference.. I guess that's completely off topic.

    Questioning the "efficiency" (or EROEI) of nuclear power is non-political, and it's vaguely on topic.



    I'v been hammering the point about including electrical conversion in the heat pump efficiency numbers for years. I only jumped into the nuke thing because I know Mark supports nuclear and I wanted him to explain how he thought it was exempt from Carnot.



    Mark,



    I'm not dreamy about the PV future, but it is interesting to note that PV is unique in it's ability to derive motive power without fire. 10% solar conversion may seem low, but it's way ahead of biological solar energy systems. If we include electrical generation with HP efficiencies, we should also include the photosynthetic and geological processes that over millennia created the energy bubble our civilization is currently feasting on.

    In other words- it's all sunshine and a 95% mod-con is no better than a 1% blade of grass.
  • LarryC
    LarryC Member Posts: 331
    edited February 2012
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    Read the mega thread.

    Scott,



    Several years ago there was a mega thread that nearly broke the website.  it rambled all over the map on topics and included a discussion about nuclear power and system efficiencies.  Look for a user named Perry and that should lead you it.



    Larry



    Mega thread name:  FULL THREAD. PLEASE DO NOT ADD ANY MORE OR IT WILL CRASH.
  • Zman
    Zman Member Posts: 7,573
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    Check my math please

    Xcel energy in Colorado claims to be 30% efficient.Including plant inefficiency and line loss.



     A typical ground source water to water heat pump in this area has a COP

    of about 3. This would give me an overall efficiency of about 90% using

    a mix of  generator fuels,primarily coal.



    If I install a Natural gas condensing boiler I should be able to achieve 90% overall efficiency.



    Why would anyone spend the resources to do a heat pump in this area? Am I missing something?

















    Reply
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Jardonhu
    Jardonhu Member Posts: 1
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    doubt

    If the manufacture would  not give you some real time data, how will you do?
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
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    natural gas

    is hard to beat. the only way heat pumps typically beat natural gas these days is:



    1. you can skip additional cooling equipment

    2. initial install can be cheaper (minisplits)

    3. people who want to netzero/don't want fossil fuels.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • SWEI
    SWEI Member Posts: 7,356
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    nothing can approach

    100% conversion efficiency from fossil fuel.  But almost any well-designed cogen (or trigen) setups will do 75-80% overall (thermal plus electrical output.)  The electrical efficiency of a good fuel cell is typically about 40-44% - a marked improvement over the 32-34% from a non-recuperated turbine or a recip engine.  Lifecycle costs on fuel cells so far have not panned out, and Bloom remains a big question mark.  They're holding their data very close to the vest and their customers are under NDAs, which I do understand.



    The bottom line is that cogen/trigen (by whatever means) is still our most efficient way to utilize NG.
This discussion has been closed.