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  1. superheat

    reflective barriers

    Reflective barriers are very effective in attics. There can be 100F to 150F difference between the air in the duct and the surfaces in the attic. Radiation is probably the largest form of heat transfer in some systems. I was wondering about R30 insulation in the ceiling joists compared to R4...
  2. superheat

    reflective barriers

    JB There are at least 2 surfaces in the attic, the roof and the ceiling. they will be at different temps and have different radiation. I solved to problem you discuss in a college class. We had to come up with a relationship between shape factor between an infinite plate and a rod based on...
  3. superheat

    thermo problem

    You will not have throttling in a fixed pipe. Throttling is done to control pressure and temp between evap and cond. It requires a compressor to pump the freon before the valve can throttle the flow. Heat pipes rely on latent heat and 2 air streams to boil and condense freon to transfer heat...
  4. superheat

    hermetic vs. scroll compressor

    Liquid handling ability is vastly overrated on scrolls. Liquid will enter the oil in the crankcase in most compressor before entering the "cylinder". Some low temp, aircooled system do not have that luxury. Bearings can be damaged on scroll compressor just like recips due to oil...
  5. superheat

    Sizing air conditioner units?

    The latest version of Manual J has software with it. It covers almost all aspects of commercial and residential sizing calculations. It will answer all of your questions. It is on sale this month too. If you don't have the time to research, you should accept the canned programs.
  6. superheat

    Need HVAC advice

    Sounds like a good idea. I would put a thermostat in the room and a low temp limit on the circulating water. A small compressor would probably have the least temp swings.
  7. superheat

    reflective barriers

    That is the kind of info I have been getting. I am sure it is R19, in an extreme case. I asked one of those manufacturers about the conditions of the test. They did not respond to my e-mail. Radiant barriers work, but without the details it is hard to design with them. If manufactures do...
  8. superheat

    reflective barriers

    I would like some quality info on the effectiveness of reflective barriers. I could calculate the effective R-value of ducts in the attic, but the geometry gets quite involved. I have looked at the ASHREA handbooks, but find it lacking. There is nothing about temp difference. It would seem...
  9. superheat

    100% Outside air application

    Your client will never be happy. The system that does a great job in Detriot will not make a dent in load in Houston. The system that does great in Houston will be short cycle and not last long in Detriot. Not to mention it will cost lots more money.
  10. superheat

    Backpressure on domestic heating/cooling systems

    I too say replace with the right size. Close off dampers until you lose superheat. That means you do not have enough airflow. Get a superheat charge to tell what the superheat is suposed to be. If you are going to install a larger system, You will replace condensing unit, evaporator and line...
  11. superheat

    Combustion Air

    After reading my post and rereading your post: The outside vent would be the same as soffit vents in a house attic. I think that is 1 in. free space per 4000 BTU. Code still says permenant opening. You need to call the inspector on the louvers. You need 2 pipes 17 x 17 with no louvers or...
  12. superheat

    Combustion Air

    Assuming 2 horizontal vent to the outside, you need 1 sq. in of free space per 2000 btu. 144 sq in. will work for 288,000 BTU. The third vent does not qualify because they must be in pairs, one high and one low. If you plan on putting louvers or screens of some sort on those vents, the area...
  13. superheat

    PTACs

    Reduce air flow if the heat in the air is too high. There are motor controlers out that set the fan speed based on supply air temp. I do not think you will find a PTAC off the shelf to do what you want.
  14. superheat

    Perimeter zone in HVAC design

    When you get right down to it most good systems are perimeter systems. Most of the load comes from outside unless there is a lot of mechanical equipment inside. If the perimeter is conditioned the rest of the structure is conditioned. That would be particularly true if there is no clear...
  15. superheat

    External Static Pressure vs. Total Static Pressure

    The info received so far is good, but if you look at the amp draw you will get a good idea about the fan. Higher static means the fan will more less air. The fan moving less air does less work and draws fewer amps. It is a shot in the dark, but if the amp draw is real low compared to FLA...

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