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  1. #1
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    Default conditioning only parts of a home

    I've been hearing commercials for these mini HVAC systems that are designed to do smaller individual areas of a home. In the adds they talk about the benefit of not wasting energy on conditioning parts of the home that you are not using.

    Is is possible or can you imagine any problems arising from only conditioning specific parts withing a building envelope?

    Perhaps stuff like temp or humidity differences between individual rooms causing condensation or other types of air/moisture movement issues through parts of the home.

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  2. #2
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    Default Re: conditioning only parts of a home

    Not sure how that would be any different to a window air conditioner. Just cools one room.

    Heating may be another matter. Unheated rooms can get musty.

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  3. #3
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    Default Re: conditioning only parts of a home

    We use a lot of electric heat here, mostly baseboard heaters, with a thermostat in each room. It works well as a general rule, but our climate is not too extreme. A room with the heat turned off will still get a bit of heat from adjacent rooms. Keep it dry and it's no problem.

    Where this goes haywire is when people try to sleep in an unheated bedroom. Warm moist air comes in through the doorway, and the respiration from them breathing adds up to condensation problems, dripping windows, mouldy closets, etc. I have seen humidity as high as 75% in a cold house, where the tenants were complaining that the house was sick.

    Another thing to consider is that if you want that room to be warm sometimes, you need to heat the furniture and the carpets as well as the space, and that draws more heat than you would normally need to maintain a steady temp.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  4. #4
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    Default Re: conditioning only parts of a home

    Ductless systems are a good solution for additions and attic spaces converted to bonus rooms or bedrooms.

    http://www.coolairusa.org/wp-content...nditioning.jpg

    Joe Funderburk, CBO, CMI
    Alpha & Omega Home Inspections, LLC
    Serving SC & NC

  5. #5
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    Default Re: conditioning only parts of a home

    Obviously by your picture John you are way to young to remember the days of individual room heating or AC. You lucky SOB
    I don't have an issue with it. In extreme circumstances though it could pose problems.
    As a little kid we had individual coal and wood stoves in each room. Then we moved up to individual gas heaters in each room. Then a central oil fired system. Then ...
    Ah, the good old days hauling coal and wood up from the basement.

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  6. #6
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    Default Re: conditioning only parts of a home

    Quote Originally Posted by John Dirks Jr View Post

    Is is possible or can you imagine any problems arising from only conditioning specific parts withing a building envelope?

    Perhaps stuff like temp or humidity differences between individual rooms causing condensation or other types of air/moisture movement issues through parts of the home.

    In a word, Yes. If you get a 20 degree drop in temperature between areas, you can get condensation as the dew point drops. This can cause mold / mildew issues.


  7. #7
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    Default Re: conditioning only parts of a home

    We installed them exclusively for HVAC in a communications room. In many cases there would be a 20 or 30 degree between one side of the door and the other side in unconditioned space. Never saw any mold. But then, the air was always circulating and the unit wasn't cycling. They stand up well, 24/7 usage, much better than standard wall AC units. I remember only one failure in 10 years in about 30-40 units. The only thing that I would emphasize is---do not use a condensate pump. Gravity only. In a trial, the pump failed after one year---that's when we went to gravity only.


  8. #8
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    Default Re: conditioning only parts of a home

    Quote Originally Posted by Rich Goeken View Post
    We installed them exclusively for HVAC in a communications room. In many cases there would be a 20 or 30 degree between one side of the door and the other side in unconditioned space. Never saw any mold. But then, the air was always circulating and the unit wasn't cycling. They stand up well, 24/7 usage, much better than standard wall AC units. I remember only one failure in 10 years in about 30-40 units. The only thing that I would emphasize is---do not use a condensate pump. Gravity only. In a trial, the pump failed after one year---that's when we went to gravity only.
    Forgot to add... the condenser will require a heater to keep from freezing if you plan to run them in cold weather.


  9. #9
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    Default Re: conditioning only parts of a home

    Quote Originally Posted by John Dirks Jr View Post
    I've been hearing commercials for these mini HVAC systems that are designed to do smaller individual areas of a home. In the adds they talk about the benefit of not wasting energy on conditioning parts of the home that you are not using.

    Is is possible or can you imagine any problems arising from only conditioning specific parts withing a building envelope?

    Perhaps stuff like temp or humidity differences between individual rooms causing condensation or other types of air/moisture movement issues through parts of the home.

    Advertising has a way of twisting the truth to make it look like you can do something with a product that in reality should not be done. Ever seen the commercial where the cars are driving out to sea? Or where someone appears to be cutting a steel pipe in half with a kitchen carving knife? Its just hype used by marketing companies to generate interest in, and curiosity about, the product they are pushing. Reality however has a way of working a bit differently than is sometimes represented in the advertising world.

    It is true that in some climates you could just turn a mini-split zone off in a room you are not using and still not cause a mold issue. In a hot and humid climate however that could be a very bad idea. This would indeed have a high probability of creating a moisture and mold problem if done habitually.

    You could however set the thermostats in unused rooms in a humid climate to allow the temperature to dwell off the comfort point setting. As long as the system is set to permit cycling at least occasionally in the unused zone it would be enough to greatly reduced chances of creating a moisture/mold problem.

    But do they really say that you can just turn the system off or do they say something like "We donít have to 'comfort' rooms we are not using"? Taking a room off of the comfort point setting to save some energy is not the same thing as turning it off altogether in that room.

    I have not seen all of the documentation for the mini-split systems but I would bet that this is discussed in there somewhere. Otherwise its just a class action law suit waiting to happen in a hot humid climate. The manufacturers should be smart enough to avoid that even if their marketing gurus are being somewhat misleading in their ads.


  10. #10
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    Default Re: conditioning only parts of a home

    From what I've learned on the subject, the minisplit systems are typically designed to allow maintenance of humidity as well as temperature within set parameters.


  11. #11
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    Default Re: conditioning only parts of a home

    "Some disadvantages of the mini-split heat pump include its high initial cost and sizing requirements. The mini-split will generally have a higher initial cost as compared to central air distribution systems. It is also critical that the unit be sized correctly for the space to be conditioned. Oversized units can result in short-cycling. Incorrectly placed units may result in poor temperature and humidity control, which can be uncomfortable for the customer as well as waste energy."


  12. #12
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    Default Re: conditioning only parts of a home

    Mini-splits apparently are the wave of the future. I am seeing them as the primary HVAC on million $ homes, sometimes 5 or 6 or 7 systems. As a home inspector, I hate them. Has anybody actually figured out those crazy chinese remote controls? I just keep pushing buttons until something happens. (or doesn't).

    END GLOBAL WHINING

  13. #13
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    Default Re: conditioning only parts of a home

    Quote Originally Posted by Dave Calkins View Post
    In a word, Yes. If you get a 20 degree drop in temperature between areas, you can get condensation as the dew point drops. This can cause mold / mildew issues.
    I was wondering when someone would hit on dew points! Now you're getting into the science of moisture and some nitty gritty discussion.

    Eric Barker, ACI
    Lake Barrington, IL

  14. #14
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    Default Re: conditioning only parts of a home

    "Because it takes heat to vaporize water, removing humidity from air also removes heat from the air. The more humidity there is in air, the more heat the air contains. Condensing water on an evaporator coil uses system cooling capacity and reduces the amount of cooling capacity available for changing the air temperature. As the relative humidity of the return air increases, the temperature drop across the evaporator coil decreases."

    "Comfort is the feeling of physical contentment with the environment. The study of human comfort involves understanding how the area around a person affects the feeling of comfort and how the body adapts to changes in its environment. The surrounding temperature, relative humidity, and air movement are all influencing factors. In the winter, cooler temperatures can be offset by higher relative humidity and less air movement. In the summer, higher temperatures can be offset by lower relative humidity and increased air movement."

    "As the air velocity through an air conditioning coil increases, the amount of dehumidification decreases. Conversely, as the velocity of the air slows through a coil, greater dehumidification will occur. You can use slight changes in fan speed to help control an area's humidity."

    "Systems that are grossly oversized in cooling...can, in severe cases, contribute to mold and mildew formation in the structure."

    "Heat pumps have higher airflows per ton than other heating systems and their air supply temperature is lower than other heating systems. This often results in customers complaining that heat pumps are cold and drafty. In order to prevent this problem, the supply registers should have deep curved louvers so that the air is directed across the ceiling and not down into the room. By directing the air away from room occupants, they are not as likely to feel a cold draft. Most register manufacturers have a specific designed series of registers for heat pumps."


  15. #15
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    Default Re: conditioning only parts of a home

    Quote Originally Posted by Frank Adame View Post
    "Because it takes heat to vaporize water, removing humidity from air also removes heat from the air. The more humidity there is in air, the more heat the air contains. Condensing water on an evaporator coil uses system cooling capacity and reduces the amount of cooling capacity available for changing the air temperature. As the relative humidity of the return air increases, the temperature drop across the evaporator coil decreases."

    "Comfort is the feeling of physical contentment with the environment. The study of human comfort involves understanding how the area around a person affects the feeling of comfort and how the body adapts to changes in its environment. The surrounding temperature, relative humidity, and air movement are all influencing factors. In the winter, cooler temperatures can be offset by higher relative humidity and less air movement. In the summer, higher temperatures can be offset by lower relative humidity and increased air movement."


    "As the air velocity through an air conditioning coil increases, the amount of dehumidification decreases. Conversely, as the velocity of the air slows through a coil, greater dehumidification will occur. You can use slight changes in fan speed to help control an area's humidity."

    "Systems that are grossly oversized in cooling...can, in severe cases, contribute to mold and mildew formation in the structure."

    "Heat pumps have higher airflows per ton than other heating systems and their air supply temperature is lower than other heating systems. This often results in customers complaining that heat pumps are cold and drafty. In order to prevent this problem, the supply registers should have deep curved louvers so that the air is directed across the ceiling and not down into the room. By directing the air away from room occupants, they are not as likely to feel a cold draft. Most register manufacturers have a specific designed series of registers for heat pumps."
    Frank, as you have quotes-------are you quoting someone or something from somewhere else? Comments, references?


  16. #16
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    Default Re: conditioning only parts of a home

    Rich, AHRI Fundamentals of HVAC/R, Stanfield and Skaves.


  17. #17
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    Default Re: conditioning only parts of a home

    Quote Originally Posted by Benjamin Thompson View Post
    Mini-splits apparently are the wave of the future. I am seeing them as the primary HVAC on million $ homes, sometimes 5 or 6 or 7 systems. As a home inspector, I hate them. Has anybody actually figured out those crazy chinese remote controls? I just keep pushing buttons until something happens. (or doesn't).
    I had one last fall, realtor, young guy, was just hanging around, so I gave him a project. He ran it thru its paces, but I think it took a while.

    I like the concept but the retrofitting with all those refrigerant lines running up the walls, not pretty.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  18. #18
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    Default Re: conditioning only parts of a home

    Quote Originally Posted by John Kogel View Post
    I had one last fall, realtor, young guy, was just hanging around, so I gave him a project. He ran it thru its paces, but I think it took a while.

    I like the concept but the retrofitting with all those refrigerant lines running up the walls, not pretty.
    Hide them in a drain pipe, back open, ground to roof.


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