[OpenTRV-interest] Integrating some OpenTRV hardware into an unusual heating system

Tue Dec 2 20:27:56 GMT 2014


Thought I'd post here by way of writing up some of what I said at OpenTRV Conf at the weekend, as well as some subsequent thoughts.

I'm planning on implementing a heating control system which is largely FOSS based for my house (the heating for which is currently under manual control only), as an alternative to buying some overpriced commercial system which probably won't work very well with it.

I use a single gas-fuelled combi boiler to heat a mixture of under floor heating zones (7 UFH zones spread across 4 rooms), and radiators (3 located in 3 rooms).

There is no 'buffer tank', and all zones receive water directly from the boiler (i.e. without any of the standard UFH mix-down valve and pump stuff), since the rads are sized to work at the UFH circulation temperature, and the house is pretty-well insulated (1920s semi, which will probably fall just short of compliance with the Passivhaus "Enerphit" retrofit spec when I've finished putting EWI on, and fixed a few more things) - otherwise this scheme would often result in monster triple-convector rads.

Individual UFH zones and also the radiators have their circulation water controlled centrally using UFH manifolds (which look like this - http://goo.gl/J5OZIM - the blue knobs are manual valves which un-screw to reveal the same M30.5 mounted pin-actuator valves that are commonly found when you remove the heads from radiator TRVs).

This scheme is reasonably cost-effective to implement, but would benefit from some more-intelligent-than-usual control systems to minimise boiler cycling and achieve effective temperature control (i.e. without under/over heating).

The features which I would like to implement in rough order of priority are:

. UFH manifold flow control preferably using motorized valves - 10 in all in two locations.

. A minimally functional (preferably Android-accessible) user interface

. To incorporate the temperature readings from the in-floor 1-wire temp sensors into the control algorithms

. On-off central heating control via relay

. A half-decent Android-accessible interface

. More extensive boiler control via Vaillant eBus interface (to replace on/off control) e.g flow-return temp monitoring and zone co-ordination to minimise boiler cycling

. Optimum-on

. Weather compensation and load compensation

. Summer cooling via window actuators or other means (e.g. ground loop, summer-mode MVHR etc.)

. Indoor air quality control (humidity and maybe CO2)

My pre-OpenTRV plan was to use this GPL java code:

http://sourceforge.net/p/diy-zoning/code/HEAD/tree/trunk/ (dz3-master / dz3-shell ) - which already does PID control, zone coordination, some sort of Android UI, and 1-wire temp sensor reading/logging.

... and integrate it into some hacked Honeywell HR20 actuators (for the rad circuits), and thermoelectric ones (for the UFH circuits).  I would prefer all motorized actuators (faster response), but the HR20s are too fat for this (can't fit two side-by-side on my manifolds).

Now that I know that OpenTRV is about, I'd quite like to:

1. Possibly use some of the OpenTRV remotes (although I already have a load of cat5 in-place, so I could just use remote SHT temp/humidity sensors instead).

2. Use something based on the OpenTRV actuators if not too much of a headache - the current prototype OpenTRV valves are sadly also slightly too wide to fit on every port of my manifolds (50mm centres vs. ~55mm centres on the prototype), so if OpenTRV kit is to be used, some sort of case hacking or building will be needed.

3. Use OpenTRV boiler control.

I'd probably still like to use the  DZ3 codebase (at least initially - assuming it works out - I last looked at the code when I had it controlling a single zone in my last home about 10 years ago) - but this may well fit-in with your plans for a centralised control mode for OpenTRV (since a lot of the things on my wish list are also on OpenTRV's lists).

BTW, Thanks for the beer and pizza at the weekend guys!



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