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  1. #1
    Join Date
    Jun 2011
    Location
    South East
    Posts
    4

    AC design question- heat is not as important

    Thanks in advance for assistance.

    I build houses in GA/SC area and have been for the last 18 years. Back in the day we cooled and heated houses just fine without the variable speed compressors, air handlers. It was just the single speed systems and usually had no issues- issues were related to duct runs or defective equipment.

    What we did not have back then:
    - Impact glass and the sealed window assembly
    - Spray foam roof deck
    - too many choices on what systems
    - 410a

    I recently replaced the systems in my personal house with dual fuel variable speed units. A huge upgrade from the single speed 20 year old systems.
    My house was built in the 70's and I added foam to roof deck, but I have single glazed windows. The systems are ok. I got a great deal so no complaints there, but the bottom line is I don't think it has made that much of a difference in the power bill to warrant the significant cost of the systems.


    That was just a personal experience with todays systems, my question relates to the houses I build.

    The houses are typical open cell foam, batt walls, slabs or crawl with closed cell if crawl. Windows are Marvin impact. Window assembly includes silicone over visqueen at jambs. Flanges are taped over with window wrap and tyvek or 30lb felt over. Wood siding and metal roofs are typical.


    Here's a senario:
    approx 4700sqft
    Bonus room over garage (attached to house via covered roof) approx 500sqft
    second story of house is only 500sqft and contains a bedroom/bath
    Main area is bedrooms/kitchen/master wing
    Ceiling heights vary, but it does have a high vault in family room
    -One of the prices I got back was $ and zoned the bonus with the 2nd floor and the main with the downstairs bedroom and put the master on a 2 ton system. Everything variable speed indoor and out.

    Going to (5) 14 SEER systems with a ducted mini in the 2 second floor areas saves me about $.

    Opinions?

    I know there's a lot more than what I have just said, but I'm trying to keep it as short as possible


    Thanks,

    Chris
    Last edited by beenthere; 02-25-2012 at 07:21 PM. Reason: prices

  2. #2
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Quote Originally Posted by Onebadhabit View Post
    I recently replaced the systems in my personal house with dual fuel variable speed units. A huge upgrade from the single speed 20 year old systems.
    My house was built in the 70's and I added foam to roof deck, but I have single glazed windows. The systems are ok. I got a great deal so no complaints there, but the bottom line is I don't think it has made that much of a difference in the power bill to warrant the significant cost of the systems.

    Perhaps your house leaks air a lot. The extreme example would be if you put in the most energy efficient AC system you could ever find but you install it outdoors and have no walls or ceilings. You are trying to heat all of Georgia no matter the efficiency of the equipment. That's extreme just to help get your mind around it but leaking air can play havoc with the nergy bills, despite having really efficient equipment


    The houses are typical open cell foam, batt walls, slabs or crawl with closed cell if crawl. Windows are Marvin impact. Window assembly includes silicone over visqueen at jambs. Flanges are taped over with window wrap and tyvek or 30lb felt over. Wood siding and metal roofs are typical.


    Here's a senario:
    approx 4700sqft
    Bonus room over garage (attached to house via covered roof) approx 500sqft
    second story of house is only 500sqft and contains a bedroom/bath
    Main area is bedrooms/kitchen/master wing
    Ceiling heights vary, but it does have a high vault in family room
    -One of the prices I got back was $ and zoned the bonus with the 2nd floor and the main with the downstairs bedroom and put the master on a 2 ton system. Everything variable speed indoor and out.

    Going to (5) 14 SEER systems with a ducted mini in the 2 second floor areas saves me about %.

    Opinions?

    I know there's a lot more than what I have just said, but I'm trying to keep it as short as possible


    Thanks,

    Chris
    Zone controls by dampers must be done by very knowledgeable contractors. There's lots out there these days purporting to do zone controls and in fact they do but at the expense of noisy systems that can be very costly and often less comfortable then for what the homeowner paid.

    That all said, the method of zoning is one issue. The method of room use another. For example, if the main house can be done with a single unit and some zone control dampers and you put a mini-spit in the bonus room, then you've achieve multiple zone using a combination of equipment and dampers. This might be appropriate if the bonus room is going to be used little by the owner or maybe not at all for periods of time. Being able to turn off the mini can be a nice advantage. Likewise, the variable output of the mini can also be a nice comfort factor. The second issue is determining the smallest zone using dampers and whether that zone can handle the minimum output of the HP under all conditions. If not, then maybe using dampers isn't the best way to do things.

    Bottom line, there are many variables and one you've already touched on, the cost of each option. I guess as a builder, absent a buyer to specify options, you'll do what is most cost effective for you. In other words, there is no clear right way/wrong way. Regards, SO
    Last edited by beenthere; 02-25-2012 at 07:21 PM. Reason: prices
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  3. #3
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,922
    Quote Originally Posted by skippedover View Post
    Zone controls by dampers must be done by very knowledgeable contractors. There's lots out there these days purporting to do zone controls and in fact they do but at the expense of noisy systems that can be very costly and often less comfortable then for what the homeowner paid.

    That all said, the method of zoning is one issue. The method of room use another. For example, if the main house can be done with a single unit and some zone control dampers and you put a mini-spit in the bonus room, then you've achieve multiple zone using a combination of equipment and dampers. This might be appropriate if the bonus room is going to be used little by the owner or maybe not at all for periods of time. Being able to turn off the mini can be a nice advantage. Likewise, the variable output of the mini can also be a nice comfort factor. The second issue is determining the smallest zone using dampers and whether that zone can handle the minimum output of the HP under all conditions. If not, then maybe using dampers isn't the best way to do things.

    Bottom line, there are many variables and one you've already touched on, the cost of each option. I guess as a builder, absent a buyer to specify options, you'll do what is most cost effective for you. In other words, there is no clear right way/wrong way. Regards, SO


    Zone systems are not putting some fancy dampers in...the contractor really needs to know how to do it right.

  4. #4
    Join Date
    Jun 2011
    Location
    South East
    Posts
    4
    Quote Originally Posted by beshvac View Post


    Zone systems are not putting some fancy dampers in...the contractor really needs to know how to do it right.
    Thank you. While I know there is no right or wrong way to go with system choice. What's your take on the variable speed in/out vs. variable in vs. single speed only.

    Do you feel its worth the additional cost?

  5. #5
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by Onebadhabit View Post
    Thank you. While I know there is no right or wrong way to go with system choice. What's your take on the variable speed in/out vs. variable in vs. single speed only.

    Do you feel its worth the additional cost?
    If VS is sized and installed properly, lots of benefits, but if sold and installed to overcome poor duct work a huge costly and aggravating experience.

  6. #6
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    If I may, I'd like to draw you an analogy.

    If you couldn't purchase a car all assembled but rather had to shop for a mechanic to build you your car, you'd be pretty choosy about which mechanic, right? Well the HVAC system is more like having a car built than buying a car. However, just like buying a car like having one built, there are lots of options. Some, like having an engine or brakes are basic. Others like having a 4-speaker stereo or electric windows or heated driver seat and more dependent on the individual. So it is with the HVAC system. What suits one, won't necessarily suit another.

    A variable speed motor can be a nice enhancement for some, not so for others. Some will put value on soft starts, controlled airflow and lower energy bills. Another just wants the lowest price. Sometimes energy rebates in some states/municipalities come into play.

    As far as sophistication of the HVAC system is concerned, if $$$$ are not a consideration, the I'd recommend a modulating furnace for heating and/or a modulating heat pump for primary heating and all cooling. In that case (modulating) you're getting the most comfort and most operational economy that's available in today's market. It's also the most costly to purchase and proper sizing and installing company training is of the utmost importance.

    So when you ask for OPINIONS, you need to understand that your going to get 100,000 different ones and a lot of confusion will result. I'd recommend you get a contractor that does load analysis on every job, then ask all your questions, get his/her answers based on their knowledge/training/comfort with the equipment and move to the solution that best suits you or your buyer and at the same time you know will be a comfortable system that will be supported by the installer. BTB, this will NOT be the least expensive contractor you can find as guessing at size and duct systems has been and continues to be very much in vogue. The companies that guess are unlikely to be able to even answer your questions, let alone take care of the equipment.

    So if you're going to put the higher efficiency, optional equipment into the home, all you have to do is be able to sell that sizzle to the buyer of the home at your price point. Then you know you've got the right combination of you, the contractor and the buyer. Doesn't get any better than that for a builder, eh?
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

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