Newbie

[Steve_rutland]

Hi Gordon, the 2 valves are proper solenoid valves, bit like you find in a washing machine, but bigger. The blending valve is indeed a TMV and I'm looking at a Gledhill GT152 pcb with sensors to possibly control the pump ( lots of these boards around so keeps the cost down ).

 

[Worcester]

Steve, still got my thinking cap on.

Couple of things to watch you'll probably need a Warwick flange Warwick Flange - Search Results | Screwfix.com on the top of the cylinder to stop air being pulled down the expansion pipe (often used for shower pumps) . The store should have a separate feed from the feed and expansion (f&e) cylinder (your 'open topped tank') else you could end up circulating cold water from the f&e round the heat exchanger and so cooling the vented thermal store.

More to come..

 

[Worcester]

Check this out for pump, feed and expansion positioning - treat the thermal store as the boiler i.e. heat source. J.Mac's Pump Tool and the hex as the heating circuit in his diagrams.


If you still have excess energy at the end of the day, you could also consider a larger store like this one http://en.wikipedia.org/wiki/File:Fernwärmespricher_Theiss.JPG

 

[Worcester]

There's also this which, so lang as the combi can take 24° would work, though at a retail price of £354 it's a killer! (trade nearer £200 inc vat) Grant Combisol Solar Water Heating. Combine Your Existing Heating With A Grant Solar Heating Solution | Grant UK

Will use solar heated water, or if not hot enough, will send to combi or blend it down for combi, so uses the maximum possible heat out of the thermal store. So, if the store is > 29° then run the HEX pump (allowing for a Δt across the HEX), water will be heated to whatever it can reach it can then either go direct or blend down if nescessary for the combi - means you don't need the solenoid valves, and it uses whatever heat is in the thermal store even if not up to usable temperature directly so maximises the use of the 'free' heat. So now all you need is a flow switch, stat and pump...


However, since you've already invested in what you've got so far ..... then need to find another way to do that . If you were just starting out it may have been the easier solution.

 

[Steve_rutland]

I've been very fortunate with the kit I've picked up, mostly from EBay over the last 8 months. Everything I've bought new but even so, its come in at a fraction over £300. I spoke to Glow Worm about my boiler before I started, and was told catagorically that it wouldn't accept any preheated water although they couldn't tell me the max it could take ( hmmphh ). Looks like we are using about 8.5kw/day of hot water inc heat loss. Nice to actually use some of what I'm producing and a free long and hot soak feels sooo much better!

 

[Steve_rutland]

Been back on the drawing software to draw up what i actually have in the loft. My first drawing was my plan....it has evolved :thinking:
There is no vent pipe as i'm not actually using any water from the tank and expansion can still easily take place back into the header (did take a while to fill mind you!!). So basically the HW tap is turned on, this activates the flow switch which in turn puts power into the top tank stat. If the water is above 48'c in the tank, then the stat puts power into S1 and also the pump. 85'c water is then circulated around the HEX to heat the incoming mains and this in turn is mixed with more cold water using a TMV to bring the temp down to a more reasonable 45'c to supply the house. If the water in the tank falls below or hasn't reached 48'c then the stat opens S2 instead of S1 and the boiler works as normal. Both solenoid valves (S1 & S2) are normally closed when there is no HW demand.
Have picked up a Gledhill GT152 pcb (pump speed controller) today to see if i can use the pump speed to control the DHW temperature rather than a TMV as at present i've had to partially closed the pump gate valves to restrict the flow of water through the HEX because even on the slowest pump speed, my return water to the tank is too warm. With the valves partially closed, it is cold. Will keep you informed

 

[Worcester]

You could really do with a double check valve on the DHW exit from the Hex to stop potential reverse flow in the event of S1 failing.
You should also consider a potable water expansion vessel on the DHW Hex loop as you do have a closed volume of water (I know it's less than 15 ltrs)

AND (apart from the fact that you should should budget for a new boiler in the near future ..) Although they wont admit it, the way your boiler works it should cope with pre-heated water:

I believe The GlowWorm's thermistor is on outlet of hot and flow switch on inlet.

So it should require no mods to boiler. She's not allowed over 65 and the Thermistor will shut out burner once at 58. So initially to combi will flick in but then it will drop out as the store pre heats. As you've done, heat the store to max of 85c run it across plate so the plates always hot and ready to go - use one of those grunny smart pumps with a remote pocket stat on hot outlet on plate. Bring cold via a double check into plate then tmv down on to DCW inlet on boiler at max of 65c (or 45° as you're already doing though in that case the boiler will probably fire up to continue heating...)

Unfortunately Glowworms don't have the best rep on the market, so when it comes time (probably in the not to distant future ) to replace it, better to consider and Intergas, Atag, Ideal Logic + or a Baxi Duo-tec 2 as I'm pretty sure all of those can take pre-heat.

If you don't want to run the risk of trying the preheat on your existing boiler, rather than shutting off the HEX completely, you could also blend down the heating INPUT to the HEX using an underfloor heating thermostatic blending valve myson do one so you recycle a proportion of the output from the hex back to the input so reduce the temperature of the inflow.

(p.s. for anyone else considering something similar get hold of a Baxi 105E and rip its guts out - almost all the components you need are lurking in there somewhere, including a nice pcb with a variable pump speed controller )

Beware unless you are GSR you must not touch the insides of the boiler.....

 

[Steve_rutland]

I do have 2 mini potable expansion vessels in the system, they are about gratefruit size, one is on the HEX side of S1 and the other is on the heat input side of the flow switch ( fitted to stop any chance of hammer). Will look into the check valves athough if a solenoid failed it would be sprung shut. Would rather play safe though so i'll see what the local merchant has got in

 

[Steve_rutland]

Quick update.......have gone from £106 per month for gas & electric in my pre solar days to £43 per month with the solar and hot water setup. All this and I get around a grand a year! Win win.
Would recommend a solar install to anyone, even with today's lower rates.