Paradise ponders: temperature moderation edition...

Paradise ponders: temperature moderation edition...  My office is located on the second floor of my barn.  It's well-insulated, and last year I installed a heat pump that both heats and cools it.  That heat pump works great, but there are a couple of less-than-perfect things about it.  First, when the weather is very cold (under about 20°F), it stops heating.  The only other source of heat in the office is a little woodstove – which works very nicely indeed, but of course only while I'm there to feed it.  So when I walk into my office after a very cold night, it might well be below freezing in there.  Secondly, in the summertime if I turn off the heat pump when I leave in the afternoon, by the next morning my office is very hot indeed.  So I've been leaving the heat pump running all night, spending the extra money to make it comfortable for me in the mornings.

The engineer in me says “There has to be a better way!”  A couple years ago I thought of one, and actually started to implement it.  This better way depends on the fact that my barn's first floor is heated, and never goes below 64°F.  It's a very nice heating system, using in-floor circulating hot water.  The first floor isn't air conditioned, but it is very well insulated and rarely goes above about 77°F.

So I came up with the idea of circulating air from the first floor through my office in two circumstances.  First, when the temperature in my office goes below about 60°F, and the first floor is warmer than that.   Secondly, when the temperature in my office goes above about 70°F and the first floor is cooler than that.  Last year I installed the fan required to do this, and started with the ducting for the fan's output.  My next big project is to finish that work: the fan ducting, the return and its ducting, and a controller.  The controller will be the fun part, of course. :)

Why not simply use a thermostat?  The challenge there is the thermostat would base its decision solely on the temperature in my office, but I need something different: to take the temperature at the ceiling of the first floor into consideration.  Of course I'm going to tackle that with a Raspberry Pi (diagram of proposed system above right)!  The parts are on order and should be here soon.  I'm going to put a temperature sensor in my office, near my desk, and a second on the ceiling of the first floor.  I'll use a solid state relay to turn the fan on and off.  The Raspberry Pi will implement the fan control algorithm exactly as I described above, and in addition it will act as a monitor for both the first floor temperature and my office temperature.  Once I have that all running, I'll be able to restrict my use of the heat pump to when I'm actually in the office (saving a few bucks a month), and I won't have to worry about the office temperature descending into the deep-freezer realm...

Paradise ponders: powered by UPS edition...

Paradise ponders: powered by UPS edition...  My “install the UPS” project yesterday went about as well as it could.  There were no major challenges, and no extra trips to Home Depot were required.  The new L5-30R receptacle (at right) is about the only visible part of the project, other than the UPS itself.  As I'd hoped, at the current draw my actual equipment has, the UPS is fairly quiet.  I located it in the storage area of my barn, outside the insulated walls of my office, so from inside the office I can't hear it at all.  I put my 'scope on the power produced by the UPS, and it's a beautiful, noise-free sine wave.  Put my freq counter on it, and it's running at 60.0002 Hz: more than close enough for anything I need!  That's actually probably better than the power company, especially when you take the noise on the main lines into account.

I did run into one disappointing thing.  The “Multilink” software that comes with the UPS is a restricted license with very limited capabilities.  It has an embarrassingly bad user interface, and there's no obvious way for me to write software that can interact with it, or monitor it. This is not what I had been expecting out of a datacenter-class piece of kit.

Multilink communicates with the UPS over a serial port.  That got me to wondering whether the serial protocol was documented.  A little googling and I discovered that (a) no, it's not documented and in fact is explicitly proprietary, and (b) of course some other datacenter operations folks have reverse-engineered it (the same protocol is used on many UPSs, including the monsters used in datacenters).  This fellow made a start on documenting it, and includes some interesting information about how he did it.  Here's another guy who actually wrote a Linux device driver for it!  It looks like it won't be too hard for me to integrate some monitoring for this...