Mixer valves for thermal store?

[Tim S]

Hi,

After much dewiberating, I decided to build my own heatbank and today ordered a copper cylinder with extra tappings and lots of hopefully sensibly placed sensor taps, plus a solar coil, for future proofing.

I'm sorted in principle for heat exchanger (thanks to John Stumbles' wiki article), flow switch and pumps (Wilo Smart modulating is quite cheap and featureful). I'm including 3 immersion heater bosses for 9kW of electrical backup in case of boiler failure (or initially no boiler!).

But I'm confused by mixers. I need 3 high flow 22mm 3-port mixer/blender valves with an adjustable temperature range of about 30-70C (or several ranges - one for tap water, one for rads[1], one for UFH).

I'd like them not to be mentally expensive.

Many valves seem to be aimed at blending tap water down to non-burn levels and the flow may be questionable as well as the temperature range.

The other class are often sold as solar valves.

Is there anywhere else I can look or are solar suppliers likely to be the best bet?

Ta

Tim

[PeterK]

DPS use Reliance Heatguard UHF valves as the heat exchanger mixer

PeterK

[Doctor Drivel]

One for rads? Take the rads F&R at centre or bottom of cylinder. Have TRVs all around and a Wilo Smart pump. UFH below rads and solar coil at the bottom.

Navitron. Reliance for blending valves.

at their instructions the DHW pumps acts as a shunt pump as well - mixing the temperature of the water right down the cylinder. It is always on with no flow switch to switch the DHW pump in and out. So an added cost of running a pump maybe 24/7. What would that cost per year?

It is an electric heat bank using a pressurised thermal store cylinder. It uses an external DHW plate heat exchanger and thus outside of G3. The makers say in the instructions it is within G3, it is not, from what I saw. Nu-Heat do one similar and specify no G3 is required.

There is no T&P valve just a normal pressure discharge valve. I would have a second valve fitted near the cylinder just in case. They specify a tundish when one is not legally required, however, good to put one in, as drips will not ice up in winter and block the discharge pipe with a potential explosion.

[Tim S]

Doctor Drivel coughed up some electrons that declared:

Yep - my cylinder is designed to run at upto 80c. With the kids around, that's a tad hotter than I'd like the rads to run. But I can adjust a mixer to achieve a practical balance between heat output and lack of 1st degree burns :)

Interesting. I'll do some calculations on that. I was going to add an intelligent timed run on the DHW plate pump later on to keep the plate hot at certain times of the day for faster host water.

[Tim S]

PeterK coughed up some electrons that declared:

Ta - I'll look these up.

[Doctor Drivel]

Have a 150kW plate heat exchanger and it can be run at 70C.

[Tim S]

Doctor Drivel coughed up some electrons that declared:

I'm going for approx 100kW (that's expensive enough).

But the key point is extra 10C is extra energy stored. Not that it matters much now, but it might later.

[Tim S]

PeterK coughed up some electrons that declared:

Hi

Looks like the Reliance UFH blending valve is the one I'm after for most of this:

Input range (Hot): upto 85C (Cold): 5-75C Output range: 35-60C

0.6bar drop at 30 l/min (seems reasonable)

Cheers

Tim

[Tim S]

Doctor Drivel coughed up some electrons that declared:

Did you mean plateX on the rads?

It will be direct from the cylinder.

Having just looked at this:

seems that perhaps 75C is a standard running temperature for radiators. Certainly, I'd get the heat out output I'm after with fairly short 700mm high double panel rads (useful as I have a few tight spots and can't get long rads in).

Save 100 quid on a mixer and drop the store temperature slightly.

Anyone disagree that running rads at 75C is a good idea?

Cheers

Tim

[Tim S]

Tim S coughed up some electrons that declared:

Just to add:

900 High Type 22 DF Double - Ultraheatline Radiators Type 22 DF Double Panel Double Convector Radiator 900 x 400 4293 BTU&viewlist=723

seem to have some pretty impressive output powers (all quoted at DeltaT=60 according to bloke on phone). That 400mm wide unit equates to about 1.2kW output power.

[dennis]

> It seems that perhaps 75C is a standard running temperature for radiators.

You want them as low a temp as you can. If you have the space for bigger rads, run them lower. Remember that if the weather is really cold you can always turn the mixer up

10C or more.

[Tim S]

dennis@home coughed up some electrons that declared:

Ideally. I'll try to oversize them, but I'm rather tight for space in a couple of places.

True.

[Tim S]

Tim S coughed up some electrons that declared:

Further adding to that, I think, the correct answer for now is to run the rads direct off the tank. I have the ability to regulate the tank temperature, and technically lower = better boiler performance and is easily adjustable at various times of the year (that could be automated too).

If I ever (big if) add solar and it becomes desireable to run the tank mentally hot for extra energy storage (depending on the output temperature of solar tubes - which I think can be quite high) - then I can always add a mixer to this circuit - I'll leave space to do so.

At least I'll have actual running data to base my decision on then.

Cheers

Tim

[Tim S]

Tim S coughed up some electrons that declared:

On that subject - the tank drawings I gave to Newark Copper Cylinders include 6 extra evenly spaced (on the vertical) dry 10mm sensor pockets. Me and my nephew had some considerable success this week in getting an AVR 8 bit microcontroller to talk to a Dallas 1-wire temperature chip (that looks like a little transistor and needs only 2 wires to connect it, is accurate and fairly cheap).

We take no credit because all we did was run up some example code someone else did and tweak it.

But my longer term goal is to immediately rig this cylinder up with basic relay interlocking controls to govern it in a basic and safe mode of operation.

Then, later, by adding a extra few relays here and there, some of the above sensors and a microcontroller or two (and maybe a proper linux PC) I hope to be able to control it in a much more useful and efficient way (like set back during summer, boiler hold off if solar is likely to be available etc).

The basic relay controls remain as a failsafe (never trust a bloody computer).

The Heatmiser roomstats I'm getting also have an RS485 bus which allows remote interrogation and control, so the scope for total heating automation and remote control exists :)

Cheers

Tim

[YAPH]

Sounds like the Reliance UFH valve Toolstation do for about £60

[YAPH]

---8

[PCPaul]

Absolutely definitely.

It sounds very similar to what I'll be doing if/when I buy this place. And I have an Arduino or two sat around looking for something useful to do as well ;-)

[Tim S]

YAPH coughed up some electrons that declared:

Sure :)

It'll be a few months before even the basics work. And a year+ before I try and get clever.

But I am trying one or two non conventional things - so I'll speak of them if they actually work.

BTW John - relevant to your DIY Heatbank Wiki: Farnell now do a flow switch with inbuilt triac designed to switch mains at upto 3A:

you reckon a trip point (flow switch sensitivity) of 1 litre/min is OK for taps?

Cheers

Tim

[Doctor Drivel]

No DHW!

> It seems that perhaps 75C is a standard running temperature for radiators.

Size them to run at 60C.

[Doctor Drivel]

>>> It seems that perhaps 75C is a standard running temperature for >> radiators.

No need for a CH rads mixer.