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geothermal vs. airsource

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Comments

  • SWEI
    SWEI Member Posts: 7,356
    They don't have to match

    but there are places (e.g. Las Vegas, Nevada) where GSHP's simply don't work after awhile.  The interactions of soil moisture, groundwater movement, and heat transfer to/from the atmosphere are way beyond my pay grade, but I'd settle for a survey of existing systems to see what has happened after 10+ years of use.  In the systems I have looked at, problems were always attributable to poor design, poor implementation, or inadequate maintenance.
  • archibald tuttle
    archibald tuttle Member Posts: 1,085
    what is a PH chart?

    I may be looking at those  charts but I'm not sure.  I can find a lot of information about specific properties of refrigerants but i'm not sure how to translate those fixed properties into understanding the amount of latent heat they can carry in a certain set of temperature operating conditions.



    thanks,



    brian
  • archibald tuttle
    archibald tuttle Member Posts: 1,085
    but dirt doesn't move as much as water . . .

    and i don't anticipate being near the water table even at 10 feet in this location so it would be more a question of whether the extent of cooling of the ground compared to natural conditions would persist through the summer enough to set up the effect SWEI is talking about.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    PH Chart

    The PH Chart will do exactly that. It allows you to plot the refrigeration cycle for a specific refrigerant and extrapolate numerical values for the amount of BTU"s being either rejected or absorbed from the condenser or evaporator. You can draw either an ideal cycle or you can also calculate a cycle with the compressor included, real life cycle.



    It's a complex chart and I wouldn't expect to fully grasp it in 1 day. It is actually what engineers use to design a system.



    By the way, every different type of refrigerant will have it's own PH chart.



    Harvey



    Here is a link to a you tube video that might help you get started in your research. http://www.youtube.com/watch?v=FS3En9Npvxc
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    And more.

    Once you learn how to read the PH chart, compare R410a to 134a. You will notice that R410a has higher volumetric heat rejection at 120° to 115° than does 134a. However, if you get above that condenser temp, the efficiency really starts dropping off and not far above that you will reach the Critical Point where the refrigerant will not condense, therefore, no heat rejection. 134a on the other hand, has a much higher Critical Point and will be able to reach much higher condenser temps at reasonable efficiencies.



    The resulting facts are that r410a is a more efficient refrigerant for space conditioning as long as you can stay within the specified parameters.



    The way VRV is able to extract heat from cold ambient temps is simple. They simply increase the volume of refrigerant flow so they can get the required heat rejection (btuh) to condition the space.



    You could extract heat from -100°F theoretically but the energy required to move the volume of refrigerant required to do that would far outweigh any benefit derived from the refrigerant cycle. Not to mention you would have to have a compressor that would move the required volume at a 400psi differential.



    A VRV also attains most of it's seasonal efficiencies by taking advantage of ambient conditions that are above (heating) and below (cooling) of what a conventional single speed refrigeration system is designed for. There is a VRV unit that can take advantage of geothermal http://ramermechanical.com/downloads/VRV-WIII.pdf

    It can operate in heating mode with water temps as low as 14°F



    When it comes to a selection between Air Source  and Geo in my area South Central PA, I select air source. From my observations, (taking ALL things into consideration) I have reached the opinion that air source costs the consumer quite a bit less in the long term.  



    There is one thing that would be a tremendous benefit to Geo. That is if they combined air source and ground source. But, it would probably cost to much :-)



    Harvey
  • archibald tuttle
    archibald tuttle Member Posts: 1,085
    ahh or do i mean aha, critical point is critical

    who'd have thunk it.



    actually i kind of understood that and had noticed the distinction in the critical point.  what i didnt' know how to read or maybe i didn't have a table, i was getting specific heats at a certain temp in the specs but no sense whether or how much that changed as the temp. of the system changed.



    thanks very much for that explanation.  i haven't gotten to the you tube yet but i will.
  • Techman
    Techman Member Posts: 2,144
    edited March 2014
    PH charts

    I thought that 410a runs closer to that Critical Point than is desired at higher ambients and that is why 410a is on its way out.!?!?
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    Critical Point

    I hadn't heard about that Techman. I suppose it would get close in some parts of the country. I have personally never witnessed the pressures get that high in my area.



    Harvey
  • Techman
    Techman Member Posts: 2,144
    edited March 2014
    PH chart

    That was at a "Freon" class at Johnstone Supply ,providing memory is intact! Nor have I seen any 410a P/T problems.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    I wouldn't doubt it Techman.

    Refrigerant phase-outs and reengineering drives a huge economy for a lot of different folks associated with the industry. It puts money in our pockets to.



    Harvey
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    I got myself curious.

    I drew a theoretical refrigerant cycle on the attached PH Charts. Both are done with the same operating parameters. 120° condenser temp and 40° evaporator temp.

    The theoretical cycle is calculated using an adiabatic compression process, therefore will result in a higher COP than an actual cycle that considers the effects of the compressor, friction and piping. One would need the compressor discharge temp to calculate the actual COP.



    But for the purpose of refrigerant comparison. I got a COP of 5.28 for 134a and 5.71 for R410a

    Note, that is only sharpie accurate with a low quality diagram.



    Harvey





      
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    Mr. Tuttle

    Don't know where you are at with this but here is a manual that I use a lot during Geo design and troubleshooting.

    It's a good read! Hope it helps.



    Harvey
  • Bergy
    Bergy Member Posts: 11
    Geothermal is great... but

    Jack,



    We sold "pricey" Geothermal systems LONG before tax credits and will continue to do so LONG after the credits expire.



    Bergy