Author Topic: A lesson about cooling from WeatherCat custom graphs  (Read 220 times)

elagache

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A lesson about cooling from WeatherCat custom graphs
« on: August 11, 2017, 11:57:13 PM »
Dear WeatherCat victims of excessively hot summers,

There are plenty of locations where the summers are so hot that there is no choice to but to rely exclusively on air conditioning.  However, some locations can get cool enough to bring your house back to a comfortable temperature before bedtime (probably the most critical time since we all need the sleep.)  However, how cool does it have to get outside before you can cool the house sufficiently?

I created a very simply synthetic channel that I call the Exterior Cooling Potential:

Code: [Select]
-- Script: Outdoor cooling potential.scpt
-- -------------------------------------------------------------------------------------------------------------------
-- This AppleScript is designed to be loaded into WeatherCat synthetic channel feature to
-- continuously compute the difference between the exterior and interior temperature so monitor
-- when cooling an interior space can be cooled by opening the windows.  When it is hotter outside
-- than inside, it returns zero.
--
-- Requires that the Param1 be set to the external temperature and Param2 set to internal
-- temperature
--
-- DISCLAIMER: This AppleScript and associated supporting materials is not subject to copyright
-- protection and has been put into the Public Domain as a public service.  The author assumes
-- no responsibility whatsoever for use by other parties of its source code, documentation or other
-- materials, and makes no guarantees, expressed or implied, about its quality, reliability, or any other
-- characteristics. Any user assumes all risk and liability by attempting to use these materials in any
-- form whatsoever.
--
-- -------------------------------------------------------------------------------------------------------------------

set ExteriorT to Param1 -- Convert parameters into names that make code easier to read.
set InteriorT to Param2

if (ExteriorT ≥ InteriorT) then -- If it is hotter outside than inside, no way to cool the interior
return (0) -- Return 0 in those cases.
else -- Otherwise return the difference between in the interior and exterior temperature
return (InteriorT - ExteriorT)
end if

I have this parameter graphed like this:



The important part of this graph starts after 7:30 PM or so.  You'll note that the graph starts climbing but eventually levels off and even drops a bit.  What is important about 7:30 PM is that I had started a fan in the room where the Davis thermometer is located.  With that fan running, you can see that the room only cools to about 9˚ F warmer than the outside air.  You can see this on this graph that has both indoor and outdoor temperatures:



In the 7:30 PM and beyond time-frame the room cools down at about the same slope as the exterior temperature, but it remains substantially warmer than the outside air - by about 10˚ F.  We have a whole-house fan and with that I can cool down closer to only 5˚ F more than the outside air, but that's still requiring the outdoors to be substantially cooler than you need to have the house in order to be comfortable.

With this in mind, if comfort is the goal, you need to keep running the air conditioner unless you have a reasonable assurance of exterior temperatures early enough and cool enough to cool your home to your target temperature.  The naive notion of opening as soon as the outside temperature is colder than the inside may not result in a comfortable interior temperature, and as a result, an uncomfortably hot night's sleep.

Cheers, Edouard

Blicj11

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Re: A lesson about cooling from WeatherCat custom graphs
« Reply #1 on: August 12, 2017, 12:32:30 AM »
I appreciate you sharing this Edouard. You gave me an early version of this script about 3 years ago and I have used it ever since. I have programmed WeatherCat to use this to send me an email when it's time to open the windows and another email arrives when it's time to close them.
Blick


elagache

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Example of multiple fans in use (Re: A lesson about cooling)
« Reply #2 on: August 12, 2017, 10:27:22 PM »
Dear Blick and WeatherCat fans of comfortable dwellings,

I appreciate you sharing this Edouard. You gave me an early version of this script about 3 years ago and I have used it ever since. I have programmed WeatherCat to use this to send me an email when it's time to open the windows and another email arrives when it's time to close them.

I'm glad you find it useful, I most certainly do!  I have two more example graphs that show how things can get tricky when you have multiple fans involved.  Last night it was warm enough that we needed to use the whole house fan.  That fan pulls hot air from the ceiling and pushes it into the attic.  This does two useful things: it removes the hot air from the house and accelerates the cooling of the attic.  Last night we ran the whole house fan until about 9 PM.  After that, the room which has the Davis indoor thermometer had only a window fan running.  As you can see on the cooling potential graph, once the whole house fan was turned off, the potential increased by about 1 degree:



I expect that it would have climbed eventually to the 9-10˚ of the previous example.  As result the graph of interior versus exterior temperature does something unexpected:



Just at the very end, the interior temperatures start to climb even if the exterior temperatures are continuing to cool.  Without the whole house fan pulling the hot air from the ceiling, the window fan just wasn't as effective in keeping the room cool.  As a result, with only that fan running, the room actually warmed up even as the outside air continued to cool.  By then the room was cool enough anyway, so it didn't matters. Still, it shows that how you use your cooling fans can result in much more efficient cooling.  So much so that without all your fans operating in tandem, things can actually warm back up.

Cheers, Edouard

xairbusdriver

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Re: A lesson about cooling from WeatherCat custom graphs
« Reply #3 on: August 12, 2017, 11:45:20 PM »
Quote
the room actually warmed up even as the outside air continued to cool
You may need to distribute those 'warm bodies' to rooms as distant from each other as possible. Maybe put one or more outside! Maybe one in a tent and another in a garage?  [lol] [sleep]