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  • #46
    Originally posted by J.P.M. View Post

    Actually Max, it's more about about dew point temperatures, how oversized HVAC systems do not lower the dew point temps. as much or as effectively as less oversized systems will, and the difference between dewpoint and skin temp. At a given (probably elevated) body temp., the hypothalamus gland will tell the sweat glands to produce liquid to, in effect, turn the body's surface into an evaporative cooler to reduce or regulate the body's temp. For the most part, and to a 1st approx., but not exactly, for the same activity level, the body will produce as much sweat in an environment that has a 20 deg. C. dewpoint as it will in an environment that has a -5 c. dewpoint. The difference is that in a lower dewpoint environment most, or all of the sweat will evaporate, while in the higher dewpoint environment, it will not. That non-evaporation will not cool the body as effectively and cause sweating to continue as the hypothalamus attempts to maintain homeostasis. This is usually a not too comfortable situation for most folks.

    On the HVAC side, oversized systems, in a counterintuitive way, do not wring as much moisture out of the air as smaller capacity systems, mostly but not entirely because their compressors do not run as long, and so don't have as much moist air going through them. That means the dew point of the air in the conditioned space says high(er) - the air tends to stay more humid - making the temp. difference between the dew point and the skin less, with the dew point temp. and what's called the dry bulb temp, closer together. Since the difference between the dew point and the skin temp. is what drives the rate of sweat evaporation, less sweat will be evaporated, with the ensuing discomfort as described above as a result.

    The ways Psychometrics and physiology interact are quite interesting but one of the less precise fields of engineering endeavor,

    FWIW, the actual condensate load (how much moisture is "knocked out" of the air in the cooling process) can be anywhere from zero to maybe ~ 20% - 30% of the load the air conditioner sees.

    Take what you want of the above. Scrap the rest.
    Very interesting, thank you. I shall admit when it comes to HVAC or heating/cooling in general my 'expertise' is at high school physics course level as I never dealt with this on professional level. I was using relative humidity simply because I had such device at home recently while the last hygrometer capable of measuring dew point I saw > 30 years ago in high school .

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    • #47
      Originally posted by max2k View Post

      Very interesting, thank you. I shall admit when it comes to HVAC or heating/cooling in general my 'expertise' is at high school physics course level as I never dealt with this on professional level. I was using relative humidity simply because I had such device at home recently while the last hygrometer capable of measuring dew point I saw > 30 years ago in high school .
      You can make a fairly accurate psychrometer using a bulb or even spring type, or electronic thermometer, some gauze and a fan. I've got a professional sling psychrometer given to me by one of my mentors. The made one using a 10K thermistor, and it's as accurate as the sling psychrometer after I fine tuned the thermistor with boiling H2O, an ice bath and my body temp.

      Just trying to get it right and fill in a few blanks with info.

      As usual, take what you want. Scrap the rest.

      Seems like (Ontario) Canadian high school physics hasn't gone down the tubes yet. Hope it never does. Got lots of friends in, and respect for, the Great White North EHH ?!? Spent lots of time in TO.

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      • #48
        Ya even running the dehumidifier feels like the room is heating up.

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        • #49
          Originally posted by J.P.M. View Post

          You can make a fairly accurate psychrometer using a bulb or even spring type, or electronic thermometer, some gauze and a fan. I've got a professional sling psychrometer given to me by one of my mentors. The made one using a 10K thermistor, and it's as accurate as the sling psychrometer after I fine tuned the thermistor with boiling H2O, an ice bath and my body temp.

          Just trying to get it right and fill in a few blanks with info.

          As usual, take what you want. Scrap the rest.

          Seems like (Ontario) Canadian high school physics hasn't gone down the tubes yet. Hope it never does. Got lots of friends in, and respect for, the Great White North EHH ?!? Spent lots of time in TO.
          Unfortunately is has gone down those tubes and is actually worse than US even if it's hard to imagine so. Locals say it was much better before, some 30 years ago. Nowadays teachers have union, go on strikes and in general not very concerned with outcome of their work. As one of their late 'reforms' I heard was decision to introduce 'sex' education in early grades up to the point parents went to public protests. Just because their current minister of education is lesbian. I'm not making this up: https://www.lifesitenews.com/news/le...he-world-video Sorry if this confirms your pessimism about direction humanity going in lately. I gave up reading those news while ago and just realized the same person was elected Premier of Ontario in 2013. I just don't know what needs to happen for that place to come to senses .
          Last edited by max2k; 09-13-2017, 01:49 AM.

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          • #50
            Originally posted by max2k View Post

            Unfortunately is has gone down those tubes and is actually worse than US even if it's hard to imagine so. Locals say it was much better before, some 30 years ago. Nowadays teachers have union, go on strikes and in general not very concerned with outcome of their work. As one of their late 'reforms' I heard was decision to introduce 'sex' education in early grades up to the point parents went to public protests. Just because their current minister of education is lesbian. I'm not making this up: https://www.lifesitenews.com/news/le...he-world-video Sorry if this confirms your pessimism about direction humanity going in lately. I gave up reading those news while ago and just realized the same person was elected Premier of Ontario in 2013. I just don't know what needs to happen for that place to come to senses .
            Understood. I hear mostly similar comments from my many Canadian friends, although they're still at a loss to figure out what has/will happen to the U.S.

            Back to business.

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            • #51
              Originally posted by Higher Voltage View Post
              Ya even running the dehumidifier feels like the room is heating up.
              Self contained dehumidifier is just another load, like a toaster. Move the condenser outside and then you have an air conditioner.
              5.7 kW DC enphase M250 + SW285 solar patio cover

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              • #52
                Originally posted by philips View Post

                Self contained dehumidifier is just another load, like a toaster. Move the condenser outside and then you have an air conditioner.
                Pretty much, and not entirely unlike turning a window shaker around and calling it a working heat pump. Either project will produce as claimed.

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