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  1. #79
    Join Date
    Dec 2002
    Location
    St. Louis, MO
    Posts
    53
    Here is how it was explained to this tech.
    A couple things to remember;
    The rate of heat transfer is dependent on the temperature difference.
    Just like suction superheat, adding heat does not change the pressure.

    The increase in superheated refrigerant vapor temperature, in the solar collector provides faster de-superheating in the top of the condensing (vapor is hotter) therefore more of the middle of the condenser can be used to change the state and thereby, increasing subcooling and at least bring the liquid refrigerant temperature closer to ambient.

    We tested, and concluded, it was time we told them to remove our brand names and that adding these solar panels voids our warranty.

  2. #80
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,344
    Quote Originally Posted by hvac21 View Post
    Here is how it was explained to this tech.
    A couple things to remember;
    The rate of heat transfer is dependent on the temperature difference.
    That part is right.

    Just like suction superheat, adding heat does not change the pressure.
    This part is not. There is a slight increase in pressure if suction saturated vapor is heated above saturation (superheated). It is mostly offset by pressure drop in the suction line between the evap and compressor inlet, so it's wash.

    The solar diagram, as posted, states that it superheats discharge gas from the compressor that already has not only suction superheat, but heat of compression. Discharge gas off a compressor runs between 150 - 225 degrees, so I must wonder how much the solar collector heats the gas above that. Provided it does, it can only elevate head pressure in the condensing portion.

    This whole thing falls apart when one considers what happens when a normal residential a/c system is running on a hot day, say 100 degrees. What happens to the heat rejection capacity of the condenser? It decreases. Why? Because the condensing medium (air) is closer to the saturated condensing temp we like to see for DX comfort cooling (105-110) degrees and the condenser can't reject heat fast enough to maintain that level. Additionally, the load on the cooling coil is higher due to elevated heat gain to the building. So there's more heat entering the condenser than during cooler weather. Temperature and pressure are relative. Add more heat to a condenser that can't reject it at the same rate it can with cooler medium flowing over the coil, only one thing can happen. Head pressure goes up.

    Now we're talking about adding heat to a condenser in addition to suction superheat and heat of compression on the premise that it will reject heat faster than if the solar collector didn't exist? I don't buy it. It may create a wider delta between the cooling medium and the discharge vapor than without the collector, but what's the point? One would need to reject that heat plus suction superheat plus heat of compression PLUS the original amount of heat picked up in the evaporator from the indoor air flowing over that coil!

    Nowhere in this discussion or in the solar assisted material has anyone mentioned net refrigerating effect (NRE)! It's pointless to add heat before the condensing loop if you can't get rid of ALL of that heat plus all the rest of the heat required to be rejected, if the end result is reduced NRE. It's just a waste of time and effort.

    What the solar assisted a/c premise may be banking on is when outdoor ambient temps are below 85 degrees (I've seen several references to that number for whatever reason in their material). At that point, adding heat in addition to normal heat to the condenser could act in a similar fashion as blocking off part of the condenser to raise head pressure (to maintain adequate flow through the metering device). Well, you can do that without a solar collector, and with more precision. It's called a variable speed condenser fan motor. Nordyne even picked up on that concept, and the mini-split camp's been doing it for years.

    The solar assist concept, as I understand it, utterly fails at high outdoor ambient temps with the compressor left in the circuit and running.

    The increase in superheated refrigerant vapor temperature, in the solar collector provides faster de-superheating in the top of the condensing (vapor is hotter)...
    This is the biggest load of horse plop that keeps cropping up. It may reject heat faster due to being hotter than the cooling medium, but it won't necessarily reach optimal saturated condensing temp AND get adequately subcooled before it reaches the metering device. There is only so much time a given sample of refrigerant can reject heat in the condenser before it scoots on out of there and is headed back to the metering device. It's called mass flow. If the system has a piston metering device and the solar collector boosts head pressure considerably above where it otherwise should be, refrigerant will be screaming through the condenser piping and won't have much contact time with the tubing and fins. It also means higher evap pressure, since a piston does not control suction superheat at all.



    therefore more of the middle of the condenser can be used to change the state and thereby, increasing subcooling and at least bring the liquid refrigerant temperature closer to ambient.
    More horse plop. Any modern condenser of respectable SEER rating desuperheats and condenses refrigerant in the upper portions of the coil. The lower sections are subcooling circuits.


    We tested, and concluded, it was time we told them to remove our brand names and that adding these solar panels voids our warranty.
    Good move.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #81
    Join Date
    Dec 2002
    Location
    St. Louis, MO
    Posts
    53
    Shophound, note I said "how it was explained to me". I did not say that I bought it.

  4. #82
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,967
    Quote Originally Posted by hvac21 View Post
    Shophound, note I said "how it was explained to me". I did not say that I bought it.
    I was ready and wanting to buy it. Maybe somebody could make the concept work. Absorption chillers are a bonofide reality, so now someone just needs to figure out how to make solar heat replace flame heat.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  5. #83
    Join Date
    Dec 2009
    Location
    Central Florida
    Posts
    15
    Quote Originally Posted by Shophound View Post
    The solar assist concept, as I understand it, utterly fails at high outdoor ambient temps with the compressor left in the circuit and running.
    Well, that would explain quite a few things. The first two failures were caused by loss of refrigerant from the fittings failing, but the compressor was still working. It wasn't until the fittings were sealed that we progressed into the next phase of failure.

    I looked back at historical temps to the day the compressor first shutdown (but after the system was sealed):

    4 days prior 91.0
    3 days prior 91.0
    2 days prior 91.0
    1 day prior: 91.9
    day of failure: 91.9 (I recall it being very sunny)

    The compressor would eventually start and run after dark, although it started getting louder and louder. I still have it in my garage, any way to tell if high head pressure is what ultimately killed it?


    Quote Originally Posted by hvac21 View Post
    We tested, and concluded, it was time we told them to remove our brand names and that adding these solar panels voids our warranty.
    Aside from the serial number sticker they did. I'm really glad I replaced the unit then, as my warranty would have depended on one person (and actually finding a tech that would touch the thing). Odd though, Sedna's warranty http://sednaaireusa.com/Central%20spec%203.htm seems to mirror the original equipment provider, although I was only given a compressor when mine failed.

    Did anyone else that contacted the manufacturer get a response regarding this thread?

  6. #84
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,344
    Quote Originally Posted by hvac21 View Post
    Shophound, note I said "how it was explained to me". I did not say that I bought it.
    Noted. I did not suspect you were the owner of one, rather someone who had received the same explanation for how this thing is supposed to work that the rest of us have seen via the Sedna website and other sources. The same explanation that is lacking in all aspects to what is being claimed.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  7. #85
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,344
    Quote Originally Posted by tipsrfine View Post
    I was ready and wanting to buy it. Maybe somebody could make the concept work. Absorption chillers are a bonofide reality, so now someone just needs to figure out how to make solar heat replace flame heat.
    Absorption refrigeration is indeed a reality, has been for years. Arkla-Servel mass marketed natural gas fired residential chillers years ago when natural gas was dirt cheap and providers searched for ways to get folks to buy more gas. The end result may have been more gas consumed year round, but the units themselves were unreliable and problematic, unfortunately. My neighbor had one where I grew up and there was always a service tech there working on it. Same story repeated far and wide.

    The Sedna system does not use lithium bromide, which is the basis for absorption refrigeration. Everything you've read what they say, and what I've responded to, deals with a claimed enhancement to conventional, run of the mill, vapor compression refrigeration that we work with every day.

    I've also looked over the attachments you emailed me from Sedna, and I still do not see anything in all of that material that is convincing this thing works as advertised under ALL climatic conditions. The best I can surmise is that in milder weather it keeps head pressure elevated, acting like a low ambient kit in a way. But in milder weather, for comfort cooling, the demand is lower, so why raise head pressure. The only time that's a concern is if you need comfort or space cooling when outdoor air temps are below 70. And that often happens when the sun is low, set, or behind clouds all day.

    Regardless, the Sedna explanation for how their idea is supposed to work has been unsatisfactory from the beginning. If you really want to see some sort of enhancement to vapor compression refrigeration come along that can save energy, hit the books and study vapor compression refrigeration theory yourself. There are things you can do to existing a/c units that can make them perform considerably better than they currently do, and don't require a solar collector to get the job done.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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