Heat pump type system and sizing.

Discussion in 'Shop Talk' started by caballoviejo, Apr 10, 2005.

  1. caballoviejo

    caballoviejo Well-Known Member

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    I live in the South were heat pumps are most economical for cooling and heating. On new construction that I've built, I'm at the stage where I just about have to figure what type of heat pump system I'll need to install. Local expertise is limited to standard housing, standard heatpumps, exchangers, blowers, and ductwork that is is fine for a regular house with attic but dumb for my application. I've built within a metal barn. Square footage is about 1000 to 1100 ft. 800 first floor, 200-300 on upper floor.

    I'm super-insulating with far more insulation (foam for air infiltration, batting for greater R value) than is used in the South. I figure I'll have about and R-40-50 envelope. I have heat gain from 2 insulated windows (with thermal breaks in the window frame) that measure only 36" by 28". Bathrooms are vented to reduce humidity and there is a hood over the cook top to reduce humidity. 6 people residing.

    How do I size the heat pump to get correct run time to produce cooling AND dehumidification?

    1. What types of package (I install and charge) heat pumps are available at this size?

    2.Other than the big, poorly insulated, commone sheet-metal ductwork for attics in standard housing, what type of reduced size easy to install, perhaps high velocity duct work is available?

    I see all sorts of stuff on the internet, including separate heat exchangers for each room, etc. But none is used in this are and nobody has any experience with these.

    Thus, I'll have to insall myself.

    Suggestions?
     
  2. mtman

    mtman Well-Known Member

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    i think a 2 ton would be big enough but you can go to www.acdirect.com they have a sizeing chart
     

  3. agmantoo

    agmantoo agmantoo Supporter

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    I am in the process of installing a 12 seer 2 1/2 ton package heatpump on a 14 x 70 mobile home in zone 7. Had the wall insulation been better I would have gone with a 2 ton. To obtain the best results at the lowest costs I want a heat pump to work nearly 100% of the time on the hottest day in August. The unit I am installing has a 10 kw heat strip for just in case on the coldest day in Jan. I prefer package units since the integrity of the manufacturer's sealed freon system should be superior to a field connection. You should be able to install a unit of this type yourself. The problem you will have is in obtaining one at wholesale. FYI.... There is typically a 30 % markup on the units sold on the internet.
     
  4. mtman

    mtman Well-Known Member

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    buying from a store how much is a 12 seer 21/2 ton i was going to buy a 2 ton 12 seer for 11oo dollors free deleivery
     
  5. agmantoo

    agmantoo agmantoo Supporter

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    picked up by me $999.40 with a 10 year warranty. You need to ask the internet source about the warranty as mine had a disclaimer by the manufacturer that internet sales were NOT warranteed.


     
  6. 2story

    2story Well-Known Member

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    you need to do a load calculation to know what size unit will work for your climate, insulation level, windows ect. go here: http://hvac-talk.com/uploadb/ click on the red bulls eye and run a load calculation.

    Package unit's are nice all in one units, there life span is shorter because they set in the elements. the average split system HP last 15 years.

    You have spent a lot of cash on insulation, you deserve a properly sized system. why not call a pro, insist on a Manual J load calculation, and at least give him a listen, if you install the system yourself so be it, a real pro. can hanlde you unusual building. To size a house by square footage is foolish when you consider the cash involved.
     
  7. caballoviejo

    caballoviejo Well-Known Member

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    Thanks everyone for the replies.

    The insulation has been pretty cheap. I should mention that my "house" is being built INSIDE a metal building that has R-10 insulation installed. I'm spraying foam insulation on all the girts, purlins, and metal beams next to the framing, around the 2 windows and any area that might have air infiltration. Between the metal walls and the framing is a 6" gap that I will fill with commercial blankets of faced 6" fiberglass insulation. Then I can put 4" and 6" batting between the wall studs.

    I don't mind using a professional. I called the HVAC man who replaced the heat pump at my current house last year. When I described my barn "house" he said that since I was super-insulated I should just put in window units. But I've only got two windows approx 3 x 3' to supply outside light to the 1200ft2 living quarters. Othersise, I don't want to pierce the insulated metal shell.

    I guess I need to shop around for someone to come out and look at the set up. This is a small town rural area, however, and you tend to get the job that people are used to doing. The small town is booming and contractors don't need weird work out at some farm 20 minutes from town. I'll see.
     
  8. agmantoo

    agmantoo agmantoo Supporter

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    caballoviejo, I have functioned as the company rep for a number of large construction projects where we were contracting work done. I have never yet seen a HVAC engineer that did not over spec a job. The HVAC installers do not want to ever return due to a system being inadequate. Therefore they will always error on the side of overkill. As a consequence, the user will be penalized with higher utility bills but the "sytem" will always be adequate then some. Since you have a unique building I am certain that whomever specs your job will error to the larger size also. A strong consideration would be to take the cubic footage of the space you plan to condition and just state that you have maximum insulation as per the walls and ceiling and go from there. If you have a really good water well or if you have the area/land space, I suggest you consider a geothermal heatpump for your home. Provided you do the work, a geothermal heatpump should be cost competitive with a typical air to air heatpump regarding the purchase price but the geothermal will operate much cheaper. You would quickly recovery the added costs in saved utility bills. A geothermal heatpump is all located inside the structure and the elements will not impact the life of the unit. Someone stated that a package unit is exposed and will deterioate but so will a split unit. The condenser of an air to air is also outside and I find that replacing the outside portion and refilling with freon is comparable to replacing a package unit so there really is little saving if any.
     
  9. caballoviejo

    caballoviejo Well-Known Member

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    Agmantoo,
    Yes I've very specifically been concerned about oversizing. We often have high humidity and with 6 people breathing, bathing, and boiling cook water getting rid of the moisture we generate is a high priority. I don't want consdensation hidden behind walls, etc., and would rather have a unit the ran longer cycles to remove the moisture instead of short cooling cycles that don't remove enought moisture.

    I've considered geothermal. I've got a backhoe and can dig for and install the ground loops myself. However, our ground temps at 4 ft deep are higher here than up north so cooling advantage of soil over warmer air will be less. This is a cooling climate, we need real heat only for December through February (which would do better with geothermal). Since I'm going to well insulate I'm not sure what the payout time would be on geothermal vs. and air unit. One guy who works for the power company had a ground loop system installed. He had to get out of state guys to come to install it - good luck getting service. Whichever system I get a want to be able to service it myself.

    An additional problem is the type of distribution system from the heat exachanger/air handler that I want. I've no attic but am considering using the smaller high CFM sytems that require small ductwork. I hope to run the ducts in a chase that runs down the ceiling of the hallway shotgun style with short branches to each small bedroom and the bathroom. And maybe a couple of long runs snaked over to the far end of the greatroom/den/kitchen. How and where I position the airhandler is important in this and depends on what type of system to which a high CFM distribution can be mated. I'll relook at package units for geothermal. Do you recommend any particular brands?
     
  10. agmantoo

    agmantoo agmantoo Supporter

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    caballoviejo, I will attempt to get you some more info tonight. I am in the house for lunch and am pressed for time now. What is the temperature of well water in your area? Are you aware that you can get supplemental hot water from the geothermal heatpump in the cooling mode? You will not need outside support for a package geothermal unit, you can be your own! You will know as much about it after the installation as the local guys, maybe even more. You will save a lot more on the utility that you imagine. Are you in zone 8? I am in zone 7. Just think about it, even if your water temp is in the 60's F, how efficient would an AC work if that was the outside temp? And that is what the geothermal unit would function under. It is not difficult to get cooling when you are trying to extract cool from such a low temp. An air to air would be attempting to lower from 100F in August to say 76 F which is difficult dropping 24 F. Under ideal conditions you could be getting $2 to $3's worth of heat or cooling for a $1 of utility. Remember, the unit is extracting heat/cool, not generating.