The CheapWeather project

tl;dr – I’m finding a way to gather data so I can figure out how to better utilize energy in heating/cooling my home.

Air conditioning is a marvel of our modern age. Using the phase change of a gas to a liquid and back to a gas, between two pressure domains, heat is absorbed in one and discharged in another.  The system is driven by a compressor and an expansion valve.  The gas is compressed, and sent through a coil where it dumps it’s heat to one domain (usually outside), sent through a valve where it can expand (into the lower pressure side, like the evaporator coil in the furnace) and by expansion evaporate from a liquid into a gas and take heat with it.  From the evaporator coil, it’s back to the compressor to repeat the cycle.  This is amazing feat.  But it takes work.  The compressor and fans involved are necessary to move this gas through it’s phase change stages.  This work can be expensive.  And if you throw in any inefficiencies, like equipment that has aged and is no longer operating at peak efficiency, you end up with a very expensive air conditioning bill.

This is my current problem.  I’m always feeling like I’m never getting the cooling I’m paying for.

Why don’t I replace it?  It’s just not an option at this time.  While the system lives and breathes, it won’t get replaced.  Until it’s demise, I need to investigate alternatives that could help.  Turning on the blower fan all the time tends to even out the temperatures throughout the house,  or so I was told by an AC guy.  Attic fans could also help reduce the enormous thermal battery that is my attic (testified to by my friend who put them in his attic and immediately felt a difference).  Keeping the house at a warmer temp and using fans.  These are all strategies that might work.

The key to knowing, is data.

Data is hard to pin down if it’s a subjective feeling.  Feeling like it’s working can differ from person to person and day to day.  In addition, remembering it is even harder and sticking to a schedule to write down each data point is near impossible.  That’s where having a system that can report the temperature throughout the day and record them is critical to making decisions.  I needed a way to record multiple points of data throughout my house.  I needed to know data points over time such as:

  • When my furnace or AC was on
  • What the temperature at the thermostat was when it went on
  • What the temperature in each room was, throughout the day
  • What the temperature outside was, to know the delta between inside and outside temps.
  • A temp sensor for every room, or at least the rooms that count
  • A humidity sensor, only really need one of these within the house
  • An outside station that captures
    • light, to know when the clouds have overcast
    • temp
    • humidity
    • barometric pressure (maybe?  nice to have?)
  • The battery level at each station.

The central server piece of software needed to satisfy these requirements:

  • Would be a simple REST based web application, hosted on my in-house server.
  • Needs to run on free packages available.
  • Needs to be something that could run multiplatform.  Linux on a PC at a minimum, Raspberry Pi being a secondary target, with MacOS and Windows last.
  • Data needed to be stored in a concurrent safe manner, that is if two sensors sent data at the same exact time, they wouldn’t collide, they’d be queued properly and inserted.

Stay tuned, in future posts I’ll get into the sensor design itself including the firmware running it, the design of the server software, the design of the outside sensor node, and the processing of the data that it’s produced so far.

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