[OpenTRV-dev] (no subject)

[Mike Stirling]

Hi Kevin,

Some more comments in-line:
 
----------------original message-----------------
From: "Kevin Wood" EMAIL ADDRESS HIDDEN 
To: EMAIL ADDRESS HIDDEN 
Date: Tue, 2 Apr 2013 13:43:29 +0100 (BST)
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> Hi All,
> 
> Agreed on all points. To answer a few, I had looked at electronic TRVs but
> had dismissed them as not really doing exactly what I want (why we're
> here!), being a bit expensive to buy as an experiment and not being
> capable of being controlled more intelligently (although it's interesting
> to learn that the FHT8V is!). I figured that, lacking the mechanical
> skills to make a motorised TRV head, using a little energy to save a lot
> would be a reasonable approach for an initial toe-in-the-water, with low
> cost as another advantage. It's something I'm still tempted to try while
> hacking, because I can experiment with controlling a lot of radiators that
> way with very little initial investment, but I agree that a motorised head
> is the solution to focus our serious attention on.

I am currently looking at the Eurotronic Sparmatic Comet as a possible development platform for OpenTRV. These were £15 each until a couple of weeks ago, but the weak pound has pushed them up to £20 from Conrad. They seem to be quite a bit cheaper from Europe. It has no transceiver, but adding an RFM23 was easy and the hardware is AVR based. I have already made good progress on custom firmware, which I will publish at some point during the week. There are in fact a couple of existing 3rd party firmware projects for this, but I am avoiding looking at them for licensing reasons and because they appear to be abandoned anyway.

Hopefully this and the work that Stuart is doing on replacement innards for one of the eQ3 valves should be able to share common code.

> 
> Regarding integrating TRV and PIR, I guess physical location is the main
> issue. I think of where my TRVs are positioned and most of them are
> probably in the worst locations for a PIR! Has anyone looked into hacking
> wireless burglar alarm sensors? These achieve decent battery consumption
> and, as self-contained units, can be placed optimally. I guess they rely
> on an "always on" receiver at the alarm box so might not be ideal for an
> autonomous battery operated TRV but there might be the potential to learn
> something from them nonetheless?

Another approach would be a passive add-on for connection in parallel to the zone inputs on an existing wired alarm system. COTS wireless PIRs might be hard to integrate because they would (hopefully) use a secure protocol over the air, so could be hard to reverse engineer. Nothing stopping us from growing our own, though. There are ways around the always-on rx problem such as having designated timeslots (cf FHT8V) or using wake-on-radio/wake-on-preamble techniques.

> 
> Regarding controlling boilers, I wonder if some of the resistance here is
> perceived "complexity". Installing a TRV head is easy. You don't need to
> be a plumber or electrician, so the resistance to purchase is low. Take it
> out of the box, insert batteries, screw it onto your TRV and off you go.
> As soon as you make a box that has to be hooked up to the boiler, it all
> becomes a bit more of a liability. You call your electrician / plumber,
> they haven't seen one before and so ensues the sucking through teeth.
> That's probably why the mass market has avoided it. To get the best
> benefits, though, I believe some control of the boiler is essential so we
> have a challenge on our hands to try and make something that achieves
> acceptance in this respect. It probably has to look, connect and, on face
> value, behave exactly like a room thermostat / programmer yet be a bit
> more intelligent under the skin!
> 

The receiver for my wireless thermostat (Horstmann) is nothing more than a radio controlled relay. My initial plan for boiler control was just to remove the batteries from the stat and command the receiver directly. Maybe it would be worth investigating popular wireless stats with a view to supporting a range of protocols.

Mike


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