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Old 08-17-12, 06:57 PM   #1
AC_Hacker
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Default Hot Day House Temp Logging...

I have long wondered what the daily temp profile looks like in my house over the course of a hot day... well I got my chance this week. Temps have been near 100 most of the week, so I turned off the AC and went to work...

All readings were done with AC turned off, and all windows closed, starting at about 8 am.

  • air temp = temperature measured at the nearest 'official' weather station
  • out F = temp measured on front porch (NE facing)
  • out R = temp measured on rear porch (SW facing)
  • bmt = uninsulated basement temp
  • LR = living room temp (NE side)
  • BkR = 1st floor back room temp (SW side)
  • uBR = 2nd floor bedroom (NE side)

First off, compared to the 'official temp' the house's outside temp is about 7 degrees cooler due to it being in a neighborhood with an abundance of shade trees.

The early morning 'bump' on the 'out F' line is somewhat anomalous because the front porch is inset a bit relative to the front of the house and early morning sun really warms up that little front porch corner area. This does tell me that external window shades there in that little corner will be very effective at countering morning heat build up.

Next thing is that the temp inside the house is about 7 degrees cooler than the outside temperature, due to the still unfinished efforts I have been making at installing much better than required insulation.

After that, clearly the temperatures on the first floor is much more bearable than upstairs, no surprise there. I should add that I did run a living room ceiling fan during this test, and it had no measurable effect on temperature (it even may have raised it a tad), but it had a remarkable effect on comfort.

The basement certainly appears to be coolest & most inviting area on hot days, which in fact is quite true.

Before I did this graph, I was thinking that it would clearly show that there was a large temperature difference between the front yard and back yard, and that differentially controlled fans could exploit that advantage. The temperature chart shows the advantage to be quite small, and also indicates that my efforts would be better rewarded by trying to exploit the coolness down cellar.

So I snapped into action and moved a comfortable chair to sit in, and a handy table to set a cool drink on, and a proper reading light all down cellar... oh, and also have a small fan running on 'low'.

Low initial investment, high comfort return.

Best,

-AC

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Old 08-18-12, 02:11 AM   #2
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This is interesting to compare to my experience, I must be lucky on our hottest days I'm not seeing this much heat gain in the hottest area upstairs and the basement temp is still inviting, just like yours. The bulk of my heat gain comes from the setting sun as I have lots of unshaded glass from when the evening western sun is setting, which unfortunately is the result of non-existent solar siting as it isn't south enough to help much in the winter.
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Old 08-18-12, 10:31 AM   #3
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...I must be lucky on our hottest days I'm not seeing this much heat gain in the hottest area upstairs and the basement temp is still inviting, just like yours...
I think it would be of interest to everyone, if more people (yourself included) were to actually log and post their data from a hot day, with the AC turned off.

I know that actually logging and graphing my data completely refreshed my thinking.

-AC
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Old 08-19-12, 02:26 PM   #4
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I'm interested in the data myself but am really unsure of how to do it. I don't have the equipment and am unsure what I would need and if it involves Arduino, I'm not sure I'd spend the money or want to spend the time to try and program it all. If I can figure it out, I'd gladly post details although we are quickly losing our 80+ days here, once September rolls around we have overnight temperatures that are at the bottom of the 60's and I don't need the air conditioning for my own comfort anymore.

Since 8/7 I've only run the A/C once when it was 55 degrees outside overnight to see what the electrical consumption was(2100 watts for my 2 ton) and if I could do some super-dehumidification. Turns out it's a great way to frost the coil, it didn't freeze up but there was less airflow at the 30 minute mark and I can see the cap tube and some of the copper loop tubes through the overflow of the evaporator and was seeing some light frost and the humidity wasn't dropping so I shut it off. It all works great at 60 degrees though.

So basically I haven't run the A/C in a little over a week, it's 70 downstairs, 73 upstairs the dew point is great inside and outside because we've had overnight lows in the high 50's for about a week now and we've had cloudy skies and rain. My chances to log heat swings with good data aren't the best right now. I could log the winter stuff coming up but I'm not sure I feel like explaining how I survive the winter indoor temperatures that I live in.
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Old 08-20-12, 02:56 AM   #5
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I'm interested in the data myself but am really unsure of how to do it. I don't have the equipment and am unsure what I would need and if it involves Arduino...
You can get perfectly good data the old fashioned way with cheap thermometers.

I went to a store that had cheap glass column thermometers, and I got one for each room and one for outside front and one outside back...

Then I put them all in the same room and let them stabilize for 10 minutes or so, and I carefully adjusted the columns up and down (don't touch the bulb with your finger or it will heat it up), so they all read the same, and I put a drop of super glue on the little metal band that holds the glass column. I call this process "calibrating the thermometers'.

Then I put a thermometer in each room, at the same level... eye level is convenient.

I also put one outside in the front of the house, positioned so that it would not have direct sun on it... ditto in the back yard.

Then read about once per hour and write the time & temperature data down.

Not so tough, really.

-AC
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Old 08-20-12, 06:05 AM   #6
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Ok, in that case I already have four digital thermometers that read very close in both temperature and humidity. I was thinking of a more long term logging solution as a 90 degree shady day will leave the house cooler than an 80 degree day with full sun if the starting temperatures were the same. So it's a bit hard to take data from one day and call it good unless I know it's a record day and we won't have clouds which might take more patience to find the day and then log it hourly for a long period especially when I might either not be home or awake during the period I'd like to log.
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Old 08-20-12, 03:33 PM   #7
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Hourly, or more often, data is nice because it shows the lag between the peak outside temperature and peak inside temperature. It's good to do that once to get the lag.

Using the max/min function on digital thermometers tells you the peak temperatures, inside/outside temperature difference, and the temperature swing. That data is enough to compare windy vs calm, sunny vs cloudy, and the effects of improving air sealing and insulation. When using the max/min method, it is necessary to find a location for the outside thermometer that is always 100% shaded.
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Old 09-18-12, 12:51 PM   #8
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You can get a data logger for about $70. Then you have to get some resistors and thermistors to make a voltage divider. I log inside and outside temperature so that i can calculate dT and work out a rough heat transfer coeficient for the house. Now that i have cavity wall insulation i am hoping to see a difference this winter.
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Old 09-18-12, 08:08 PM   #9
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I use a data logger from this outfit: Data Loggers: HOBOŽ Data Logger Products by Onset. I got the U12 with temperature, humidity, and two external channels. It works very well.

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