Custom hydronic heating controller

[opiesche]

Hi all,

I've recently installed DIY hydronic floor heating in the ground level of my house (http://ecorenovator.org/forum/renova...tallation.html), although it's not yet in operation, and am now working on the controller stage of this. Vlad suggested I put that part in a separate thread, so here it is

Generally, it's a standard PEX-under-hardwood installation. I plan on using a standard water heater and hydronic circulation pump with water somewhere around 85F. In order to figure out what pump and heater I need, and generally get a better idea of the thermal characteristics of my house, I've custom built a temperature logger.

It consists of a Raspberry Pi with two DS18B20 temperature sensors, and a few custom python scripts. One sensor is outdoors, the other indoors. The python scripts sample temperatures every 5 minutes, log them with a timestamp, and generate plots of the data:




I'm currently working on also getting heat loss information out of the data. Since I know the total volume of air in the house, and the temperature delta between samples, it's fairly simple to calculate heat loss in BTU/h.



Once I've collected a couple weeks worth of data, I should be able to use it to figure out exactly how many BTU per square foot I'll have to output, which should help me predict a needed water temperature and flow rate (leading to a choice in water heater and circulator).

I the near future, the Raspberry Pi will get a couple more interior sensors in different locations, and also turn on and off the circulation pump via a relay based on a variety of parameters. When I know the lag of the system, I should be able to predict very well when to turn on and off the pump based on interior-exterior temperature differential (which seems to be directly proportional to heat loss), to keep interior temperatures comfortable.

The Pi is web accessible through a USB WiFi adapter, and I plan on making the whole thing configurable through a web interface, so I can change parameters on the fly and get live plots of temperatures and the performance of the system. Over time, the software could even learn and adapt its parameters automatically, to end up at the most stable configuration for interior temps, as well as deal with unexpected spikes (such as opening the front door to take out the trash) without going into overdrive and also keeping efficiency of the system in mind.

I'm also putting the whole process on my blog as I go along.
Adventures in home improvement

Any suggestions as to what features would be good to have in a controller software like this? I'd like to hear some thoughts

Thanks,
Olaf