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Thread: Options for new HVAC system with low Amp draw

  1. #21
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    Quote Originally Posted by Timrf79 View Post
    Essentially there are 3 breaker panels in my house, there is a disconnect that can isolate one of the panels from the grid.
    In this case this one panel is only solar/battery fed.

    During system stress test we:
    - disconnected the grid
    - started and run AC, two ovens, several hair dryers, PC, internet, stove, space heater (maybe a few other things)) until the system breaker finally tripped
    - hence the solar system can easy run the one connected AC

    Limitation is 40A per breaker
    OK... now go back and try that test again...
    (Remember... ONLY solar power... NO utility power)

    With ALL the other loads noted above drawing power FIRST...
    Then start the AC... LAST...

    Then come back here and tell us what happened...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *The value of comfort, over the long term; leave economic choices behind!
    Choose your contractor wisely!

  2. #22
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    Thread Starter
    Quote Originally Posted by ga-hvac-tech View Post
    Breakers for AC units are 'slow-blow'... in the sense that they allow inrush current for a short time.

    As noted earlier... there is a LOT more to this, than meets the eye!

    Personal thought...
    Wisdom... is knowing when to let a PRO handle something...
    Agreed, essentially I am trying to find out which systems could work so I know to which dealer to go to in order to get a quote.
    It seems the concept on running an HVAC system with two feeds (one for cooling, controls and blower, and another feed for heat-strips) is not something common.
    And initial questions to HVAC folks i talked to resulted in that there is no way a system can run with the limitation of 40A breakers....
    Given the expansion of solar homes and the desire to run HVAC off grid, i find this hard to believe that there are no systems for that.

  3. #23
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    Thread Starter
    Quote Originally Posted by ga-hvac-tech View Post
    OK... now go back and try that test again...
    (Remember... ONLY solar power... NO utility power)

    With ALL the other loads noted above drawing power FIRST...
    Then start the AC... LAST...

    Then come back here and tell us what happened...
    Two issues:
    - the HVAC system is currently not working due to defect blower motor
    - Why would I ever run two ovens, several hair dryers, space heaters and AC? (The stress test was not a real life scenario)

  4. #24
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    Keep searching... you will find it.

    I understand what you are trying to do...

    Problem is:
    The rules of this forum... do not allow us to go into that level of technical detail.
    It is both a matter of liability (forum being liable)...
    AND...
    Down the road... someone that should NEVER even change a light switch...
    Will read the thread... get a wild idea... and do something stupid...
    Resulting in property loss, potential injury, or worse.

    The forum does not want to be responsible for that...
    And I agree to be responsible for that would be an irresponsible policy.

    Best to you on this...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *The value of comfort, over the long term; leave economic choices behind!
    Choose your contractor wisely!

  5. #25
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    Quote Originally Posted by Timrf79 View Post
    Two issues:
    - the HVAC system is currently not working due to defect blower motor
    - Why would I ever run two ovens, several hair dryers, space heaters and AC? (The stress test was not a real life scenario)


    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *The value of comfort, over the long term; leave economic choices behind!
    Choose your contractor wisely!

  6. #26
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    Thread Starter
    Quote Originally Posted by ga-hvac-tech View Post
    Keep searching... you will find it.

    I understand what you are trying to do...

    Problem is:
    The rules of this forum... do not allow us to go into that level of technical detail.
    It is both a matter of liability (forum being liable)...
    AND...
    Down the road... someone that should NEVER even change a light switch...
    Will read the thread... get a wild idea... and do something stupid...
    Resulting in property loss, potential injury, or worse.

    The forum does not want to be responsible for that...
    And I agree to be responsible for that would be an irresponsible policy.

    Best to you on this...
    Wait...
    people are not to say something like:
    "Look for trane model series suncloud, or Daiken model series Blue Sky"?

  7. #27
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    "look for a Bosch Bova" THERE!
    “A dying culture invariably exhibits personal rudeness. Bad manners. Lack of consideration for others in minor matters. A loss of politeness, of gentle manners, is more significant than is a riot.”
    ― Robert A. Heinlein

  8. #28
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    Quote Originally Posted by Timrf79 View Post
    Agreed, essentially I am trying to find out which systems could work so I know to which dealer to go to in order to get a quote.
    It seems the concept on running an HVAC system with two feeds (one for cooling, controls and blower, and another feed for heat-strips) is not something common.
    And initial questions to HVAC folks i talked to resulted in that there is no way a system can run with the limitation of 40A breakers....
    Given the expansion of solar homes and the desire to run HVAC off grid, i find this hard to believe that there are no systems for that.
    You're right, the common HVAC system does not utilize two different electrical feeds. The systems that do are the ones with electrical heat strips in them. "Most" electrical heat strips draw significantly more amperage than all of the other components in the system combined, therefore the need for two separate breakers. If they fused the whole system with a breaker that could handle everything, the smaller amp draw components wouldn't be protected from overloads and would easily burn up in case of a malfunction. Look at it like your main breaker panel. There are many different sized breakers in the panel to handle/protect the different types of items connected to them providing enough power plus a safety factor, but still a low enough rating so that if something goes wrong or shorts out the breaker will trip and hopefully protect the item connected from a total melt down and the potential for burning your home down.

    Maybe I missed it somewhere in this conversation, but is the electric heat strips the only form of heat you have when it comes to your HVAC system heating your home in the cold weather? Or, is the AC you refer to actually a heat pump that can produce heat (without the electric strips) in the cold weather?

    If you only have electric heat strips and not a heat pump then you have a problem as it stands unless you replace the existing heat strips with ones that draw less amperage. The starting point would be to find out what the KW rating of the existing heat strip is. "Sometimes" they can be replaced with a smaller KW unit that could still heat the home, IF the original install was oversized for whatever reason. This decision would require a heat load calculation to determine the minimum sized heat strip you need to keep the home comfortable during the coldest expected day.

    If you have a heat pump system then the electric heat strips are used as what's called "emergency heat" and are also used for when the heat pump goes into defrost to keep the HVAC system from blowing cold air. If this is what you have you can "usually" disable the emergency heat option and "usually" disable the use of the heat strips in defrost mode. That ability or option would be something you'd need to discuss with your HVAC service technician that knows your system.

    Most all electric home with solar rely on a interconnect/metered system that uses the grid for the large demands that the solar can't supply at length and when that isn't the case sells back it's excess solar power to the grid. They basically use the grid as their battery storage for when the need is there for more than they can provide.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  9. #29
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    Quote Originally Posted by Timrf79 View Post
    Agreed, essentially I am trying to find out which systems could work so I know to which dealer to go to in order to get a quote.
    It seems the concept on running an HVAC system with two feeds (one for cooling, controls and blower, and another feed for heat-strips) is not something common.
    And initial questions to HVAC folks i talked to resulted in that there is no way a system can run with the limitation of 40A breakers....
    Given the expansion of solar homes and the desire to run HVAC off grid, i find this hard to believe that there are no systems for that.
    Find it hard to believe!

  10. #30
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    I'm not an engineer, an electrician, or even an installer, but I THINK you are only supposed to load a breaker up to 80% of its rating. Which means you really only have 32 amps to work with. Hopefully others will chime in to correct or confirm.


    Quote Originally Posted by Timrf79 View Post
    My situation:
    House 2 story, total ~4,500 sq ft.
    Installed solar system that produces plenty of power
    Limit for items running on solar during grid outage 40AMP breaker
    Two systems (one per floor)
    Houston, TX area

    Looking for a HVAC system that could run on solar only (during power outages), to heat and cool house (if possible).
    Alternatively a system that can cool on solar through one feed and heating on grid only (no 40A limit) through a second feed.
    I do a triple evac with nitro to remove non condensables.

  11. #31
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    Quote Originally Posted by BBeerme View Post
    I'm not an engineer, an electrician, or even an installer, but I THINK you are only supposed to load a breaker up to 80% of its rating. Which means you really only have 32 amps to work with. Hopefully others will chime in to correct or confirm.
    Correct. The conductor can only be loaded for a prolonged period of time to 80% however inrush current is not factored into the conductor sizing for hvac (seperate article 440 of the nec for wiring)
    This reminds me of a generator job I did for a customer several years ago. He had a geothermal heat pump with 20kw of electric strip heat. I added an isolation relay that would only allow 10kw of the 20kw be activated when the utility power was out and the generator was running. Easy to do.

    Sent from my SM-N960U using Tapatalk
    ...

  12. #32
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    Quote Originally Posted by Timrf79 View Post
    Agreed, essentially I am trying to find out which systems could work so I know to which dealer to go to in order to get a quote.
    It seems the concept on running an HVAC system with two feeds (one for cooling, controls and blower, and another feed for heat-strips) is not something common.
    And initial questions to HVAC folks i talked to resulted in that there is no way a system can run with the limitation of 40A breakers....
    Given the expansion of solar homes and the desire to run HVAC off grid, i find this hard to believe that there are no systems for that.
    Hopefully your doing this research BEFORE you have committed to this new house off grid.

    We get calls for this maybe twice a year. People buy these houses off grid and then figure out why it was for sale. Or that it'll cost 50k to bring in grid.

    Get yourself like 4 tesla solar batteries and a backup generator with a transfer switch that can transfer from solar to generator to charge your batteries.

    Again, probably 70k plus and now your powering via sun and propane.

    And noise.

    I'd stick with grid personally.

    Sent from my SM-G998U using Tapatalk
    "This Story Is True, Only The Facts Were Changed"

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    "Is This Your Opinion Or Experience?"

  13. Likes kangaroogod, ga-hvac-tech liked this post.
  14. #33
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    Personally... I plan to go the Generac route... including the 19KW battery...

    However I will stay connected to the grid!

    There is a feature in the Generac software... that allows one to arrange priority of power.
    One can also plug a generator into the system... even a non-Generac generator.

    The grid is a good thing... it will always be there...
    One never knows when there will be a week of clouds/rain...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *The value of comfort, over the long term; leave economic choices behind!
    Choose your contractor wisely!

  15. #34
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    Quote Originally Posted by ga-hvac-tech View Post
    Personally... I plan to go the Generac route... including the 19KW battery...

    However I will stay connected to the grid!

    There is a feature in the Generac software... that allows one to arrange priority of power.
    One can also plug a generator into the system... even a non-Generac generator.

    The grid is a good thing... it will always be there...
    One never knows when there will be a week of clouds/rain...
    I have a 15kw system. True up is November. Paid 4k. Its already back up to 2k. I live at the lake, lake has fog, fog is great insulator from sun, grid is expensive when I have no solar. 45 panels on my roof.
    "This Story Is True, Only The Facts Were Changed"

    "It's Not Black vs White, Left vs Right, Mask vs No Mask! Its Us vs Them! Stop Letting Them Divide Us And Take Our Control!"

    "Is This Your Opinion Or Experience?"

  16. #35
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    Quote Originally Posted by jacob-k View Post
    I have a 15kw system. True up is November. Paid 4k. Its already back up to 2k. I live at the lake, lake has fog, fog is great insulator from sun, grid is expensive when I have no solar. 45 panels on my roof.

    My local elec utility will only allow 10KW of panels connected to the grid... I may set up a 2nd panel later on and power some things off grid.

    My calculations suggest my grid power bill will be something like 100-200 KW a month during off AC season... and probably 400-500 KW in the hot part of the summer.
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *The value of comfort, over the long term; leave economic choices behind!
    Choose your contractor wisely!

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