Correction: HVAC Controller Setup

"HVAC Controllers" section of the Configuration Guide was missing a slide - thanks to KF for pointing that out.

Fixed.

Books: too obvious to think about

Usually, the Internet is the best source of information - at least, quickest accessible.

But it has a drawback - you won't find the information you're not specifically looking for. Maybe only as a collateral, but even in this case you have to know that it is relevant to the problem you're resolving - and this may not necessarily be obvious.

A while ago, I was trying to figure out whether it is safe to drill a 1 1/2" hole in a load bearing support beam. The consequences of a wrong decision would be catastrophic - the second floor will come crashing down, and no insurance would help. So I started looking for the solution, but, surprisingly, different sources were giving different advices.

It so happened that I visited a bookstore at the same time. By accident, I was passing by the section with all sorts of DIY books in it. Just out of curiosity, I decided to take a look.

Well, now I'm writing this article. Thanks to many of those books, now I know how to do wiring, framing, drywalling, texturing and painting, investigating installing windows and doors, flooring, all kinds of woodworking, will take a look at tiling when the time comes.

It's not that they are the source of ultimate wisdom. It's that there are things in every business that you simply have to know in order to do things - and those books give you the necessary headstart so you can looks ahead standing on the shoulders of giants. Or at least those who passed this road before you.

Another advice - don't rush buying those books - you'll spend a fortune. Each book is anywhere from $20 to $80. Make friends with your local library instead.

SketchUp Sketches: DZ Testbed

This is a contraption that can be used to test the zoning controller functionality and operation. As the moment of writing (the image above is live, so is the link) it is just a rough draft (yeah, and it's 2:30AM), but I hope you get the idea. Plug heat sources (electric bulbs will do) into big holes. Plug temperature sensors into small holes. Connect the servos to DZ output. Connect fans to DZ output. Switch it on and watch it go crazy.

Four servos may represent up to four zones.
Four fans may represent up to four HVAC units.
Dimmers may be used to simulate variable heat load.
The divider between two middle fans is missing intentionally.
All sizes in the model (fans, servos, planes) are true and correct.

Link to the model page

Short Take: Hysteresis in RTH7500

Frequently asked question with a very vague answer - what is the hysteresis (a.k.a. dead band) of my thermostat?

For Honeywell RTH7500, the measured (therefore not exact) typical value is about 1°C (about 1.8°F) - for the sensor located in the room behind the wall where the thermostat is.

Worst observed value is 2.5°C (about 6.3°F) - for the sensor located on the first floor (the thermostat is at the second) - this is not actually a property of the thermostat, but rather an indication of how badly the airflow was designed.

Another question - can hysteresis be controlled in RTH7500? The answer is: probably not.

If it can, there's no way to do it that is described in the documentation that is sold with the thermostat (yes, I found the manual, feel free to ask me what those numbers mean).