[OpenTRV-interest] Question from Steve R

Simon Hobson linux at thehobsons.co.uk
Sun Nov 22 16:38:39 GMT 2015

Marko Cosic <marko at coheat.co.uk> wrote:

> What is the purpose of the thermal store in your application?

Lets just say I have "some dislike" of combi boilers, and from a landlords POV they are an even bigger PITA.

My brother in his house renovation put a 350l store in but he has thermal solar (evac tubes) on the roof, a wood burner, a mix of UFH and rads, and a gas boiler for backup heat if needed. Lets say, I was impressed with the way it works, even ignoring the aspects that make it ideal for the mix of heat sources.

I have a flat I rent out, and the old combi was always an issue. The biggest one being that *when* the boiler breaks down it leaves the tenant with no heating or hot water.
Anyway, I fitted a thermal store so that there is a backup for hot water - and heating since the heat demand is so low. It also matches the boiler much better since the heat load in the flat when the weather is around freezing is about 2kW, and the minimum range value for the boiler fitted is a tad under 10kW. Since I fitted the store the boiler hasn't broken down once - I'm not now using the complicated (and unreliable) combi bits on it. And the tenant is very happy with it.
The CH circuit has a modulating pump, all rads have TRVs, and it's almost silent in operation.
I wrote up the project at http://www.navitron.org.uk/forum/index.php/topic,12550.0.html

As an aside, I measured the standing losses and compared with the combi in the house next door (both were empty at the same time. Fairly crude methodology, just left the store on the immersion heater, left it a day to settle, then read the meter a couple of time a few days apart. For the combi, I did much the same, but reading the gas meter.
The store had standing losses of about 80W, but the combi in it's default mode had standing losses of about 160W equivalent - it's default is to fire up from time to time to keep the HE warm for less slow delivery of hot water.

Damon Hart-Davis <dhd at exnet.com> wrote:

> ... an OpenTRV unit should be able to function stand-alone as a smart TRV that turns a rad off for you when you’re not around (and can have a couple of simple programs set).


> If you add an OpenTRV boiler controller which simply listens to calls for heat from the OpenTRV valves instead of using a single house thermostat the aim is to get savings to 50%

Even better

> The target price for a single OpenTRV valve, and no more should be needed to get started, is £10 retail.  A typical whole house target price including boiler control is £100—£150 ...

And it keeps getting better.
That's going to seriously annoy some of the current automation vendors selling expensive closed systems. Good :-)

I look forward to being able to order, unfortunately I'm not in a position to experiment with what's currently available.

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