i need to know how to design an upstairs hvac system that will cool like being in a walk in cooler.

i have sprayed closed cell foam insulation in the attic, but it still seems to be fairly warm. it is unvented. the existing system does NOT have a txv on it and is 22 yrs old.
  3 answers
  • You said you closed cell foamed insulation in the attic? On the floor or did you seal the attic completely and bring the space into the cooling envelope? As far as age. The system now if not before based on the age is over sized to begin with. If its properly charged and clean it should be doing its job and over cooling the area. If the refrigerant is low, the system will have a tendency to freeze up and prevent proper cooling. In any case you need to do some upgrading. IT does not matter whether or not the system runs with one type of coil or not. There are many variables that must be considered when properly sizing and installing a cooling system for upper levels in a home. Location of the air handler, Number of returns. Placement of supply grills, sizing of system and sizing of the ducts themselves. Cooling like a walk in cooler is simple. Put an over sized system in. Cooling so your comfortable is using the Manual J method along with Manual D duct sizing program. Over sized systems will not remove moisture in the air. With that said, you can cool the air down real fast and real cold, but moisture not removed will make the room feel uncomfortable. Under sizing a system will keep moisture out and make you feel more comfortable at a warmer temp, but not lower the room temp enough when its hot. Ideally the right size system will run the unit long enough to dry out the air, and lower the temp within the room based on designed temps. In NJ area I size my systems to be 70 inside when its 92 out. When it becomes 93 out I do not expect my system to maintain 70 but will expect it to keep 71 and so on. Back to the insulation issues. Foaming attics are a great idea, but this also should be done in conjunction with foaming the basement or crawl space sill areas as well. This makes a very large difference on loads both within the walls, and within the attic. It stops moisture in walls causing mold. This is really important when you lower your room temps in summer time as any moisture moving through the wall cavity by natural convection will cause it to condense where it comes into contact with the wallboard. In any case, Use manual J to design size and Manual D to figure out duct then choose a manufactures system that you like to install that will meet the requirements of the design standards that you figured out using the programs.
  • Micky D Micky D on May 28, 2012
    Have a door put in front of the stairway,your cold air is going downstairs! Cold air seeks the lowest level! Cold air falls, hot air rises!!
  • Christel J Christel J on Aug 23, 2012
    try a ductless unit by mitsubishi with those the air will not get lost or exposed.Because there is no duct work to run.
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