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Author Topic: Gravity HW heat dump using pump and injector tee.  (Read 8882 times)
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« on: July 28, 2007, 05:31:31 PM »

Hi all,

Anyone got any opinions about using a gravity HW circuit as a solar heat dump utilising an additional loop with a pump and an injector tee?

As I still haven't mastered posting of any of my drawings, here's something similar that Barry Caldwell posted last September - hope you don't mind, Barry. 

Courtesy bcaldwell - Navitron Forum 2006

1 Swing valve, 1" with 28mm compression
2 non-return, built into pump isolation valve, 1"
3 Injector Tee, 28mm equal Tee with 28-15 MF reducer and 15mm internal
4 Normally open zone valve with 22mm compression
5 Swept Tee, 28mm brass

(The posting is here:

My proposal would differ in the following ways:

1. No radiators on this circuit - just gravity from boiler to cylinder - the radiators are on a separate pumped circuit from a four pipe oil boiler - it's an old set-up, the type that can only have either HW or HW+CH.
2. Twin coil solar cylinder with boiler to upper coil (!)

3. Short 'pump loop' at the top end of the flow (hot) pipe in the airing cupboard rather than across the return pipe as above.
4. I initially thought of putting a two port valve between the two loop branches shutting off the gravity flow when pump activated - but I am not confidant that a motorised valve won't disrupt the flow too much - looking at their respective KV values they cause quite a pressure drop, some much worse than others.

So - how about a 15mm loop as above but on the hot flow side, tee'd off the vertical 28mm flow, then a pump, then an injector tee at the upper elbow of the flow just before it enters the cylinder coil (I really wish I could post a drawing!) to circulate the water through the coil and back down to the boiler (which would be off).

Would this work when there is no thermosiphon flow from the boiler (switched off) and I would be trying to force warm water downwards to the boiler 3+ metres below or would the water just take the easy way and run round and round the small pump loop in spite of the injector tee?

In that case, and space is short hence the above plan, would a 1" flap valve in the same position as in Barry's drawing (with the pump loop connected either side), allow sufficient flow when thermosiphoning in normal HW mode?

Hope some of that is understandable! 

I would prefer the injector tee without a check valve partly because the horizontal just before entering the coil is very short - barely 150mm - so accomodating 22mm vent pipe tee, 90o 28mm elbow, 180mm long check valve incl. fittings and a 28 x 15 x 28 tee for the pump loop would require much juggling of plumbing in a contricted space.

What do you reckon?



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Posts: 1509

« Reply #1 on: July 28, 2007, 07:15:25 PM »

Hi Mick,

Rather than sod about with separate pumps, NRV's, motorised valves, injector tee's and extra pipework etc etc, I think the simplest way to use your WBS as a heat dump (using a pump) would be to install a charging unit, have a good look around this website, you may find it a education

One of the primary functions of the charging unit is to ensure that the return temp to the boiler is kept hot enough to prevent corrosion of the stoves boiler due to condensation.  In the event of a power cut the pump is automatically bypassed to allow for thermosiphon.  Everything needed is housed within the unit, just plug and play  Grin

Hope this helps.

« Last Edit: July 28, 2007, 08:16:54 PM by lightfoot » Logged

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