Sysyem config - 2 Heating zone valves and megaflow

[Pete_win]

Hi all, ive just ordered a full evohome system inc. 12 hr92s and hotwater kit, and have a few questions:

1) the existing setup has 2 zone valves for heating and one for hot water. From a bit of reading online it looks like some people suggest to manually override the two heating zone valves so they are always open (because the evohome controller wouldn't know which valve to open when a hr92 calls for heat). Then there is no need for any wiring for these zone valves! Does this sound sensible? The downside is that if hot water system is calling for heat then some water may get pumped around the two heating loops (but perhaps this is negligible if all hr92s are 'closed'). Are there other pros/cons to this approach?

2) alternatively, i could wire up the two heating zone valves so they open when the bdr91 tells them. Then I'd need to be clever about how the zone valves tell the boiler to fire i.e. the boiler live should only be switched on if both heating zone valves are open.(with reference to fig 9 in the evohome installation manual: grey wire goes from mains live to first zone valve - as per fig 9 - but then orange wire from first zone valve acts as the grey wire for the second zone valve. Then the Orange wire from the second zone valve goes to the boiler live.). I hope this text description makes sense. Benefit of this approach would be absolutely no wasted heat for 5 months of the summer when no heating but plenty of hot water needed!

3) we have megaflow hotwater. Wiring the evohome to control this doesnt look a problem but fitting the ecohome hot water sensor might be - there doesnt seem to be a spare dry pocket. Is it best to cut away a section of insulation (including the steel sheet jacket) to mount a strapon sensor? Any other suggestions?

Many thanks for your collective help!

[Pete_win]

System is now installed and seems to be working really well so far. In case anyone else has similar issues, here's what i did:

1) i didn't manually override the 2 heating zone valves. Instead i pretty much did what i proposed in my OP bullet point (2):
- bdr91 switches on power to both heating zone valves so they open at the same time.
- The end switches of these two heating zone valves are then wired in series so that the boiler only goes live when both heating zone valves have succesfully opened. (Wire mains live to grey wire of first zone valve. Then orange from first zone valve goes to grey of second zone valve. Then orange of second zone valve goes to boiler)

3) I spoke to heatrae sadia tech support line (i think this is actually run by biasi). They basically said that the megaflow cylinders all come with 25+ year warranty. And anything involving cutting off the insulation or steel cladding jacket would invalidate the warranty. So ive settled for fixing the wireless temp sensor to the hot water outlet pipe. However, in reality the hot water temperature is controlled by the internal megafow sensor (because this is set to a lower setpoint than the evohome setpoint, and it is mounted near the bottom of the cylinder where the colder water is)

Hope the above is useful to someome else in future, but note that i am in no way an expert. If ive done anything wrong/ misleading/inadvisable please let me know, happy to amend what ive written!

[omdaddi]

Thanks, nice to know I am not alone... I have three heating circuits, which happily enough when I updated the boiler a few years ago the plumber put in three BDR91s (in a row, 2cm apart). The BDR91s control the valve on each heating circuit. It took some fun and games before I worked out (RTM...) that my assumption that the controller just "needed to know" which BDR91 belonged to which zone was wrong. Eventually I put them all in binding mode and then they were all bound to the controller when setting up "Boiler Control". I expected them all to come on every time any room asks for heat, but weirdly they don't. But the ones coming on don't always match where the heat is required, although in the end the heat always arrives (e.g. circuit one is demanding heat now, and the BDR for circuit 1 and 3 are on, but circuit 2 is off). Thinking this was the nearness I have separated them by 30cm. I do wonder about binding them all to one BDR91, but since the heat always comes and I don't like the thought of pumping hot water around a loop with no demand, I will leave it as it is. The BDR91s have power all day now because I changed the timer controls to ON for those circuits. evoHome is in charge.

Anyhow... I just purchased a hot water tank kit from Evohome shop (I don't qualify for the support forum because I got my controller elsewhere) to fit to my Megaflow tank. Mine is a CL210 and has an immersion heater half way up with a pocket for a thermostat. I intend to remove the thermostat and isolate it, then stick the remote sensor in to the pocket. I can refit the immersion heater thermostat if I want, though have only needed it once in 20 years, and that was when the boiler was replaced.

I have talked through what to do with a friend who is a commercial heating engineer (not domestic), but wanted a sanity check, so if anyone sees this a metaphorical thumbs up would be appreciated.

1. Isolate heating system from mains.
2. Tap L and N from the junction box where all the other BDR91 come from and take to the L and N in the new BDR91. BDR91 will now be ready to rock and roll.
3. Wire the A and B sockets in the BDR91 in SERIES with the ORANGE (or grey) wire to the inlet valve to the megaflow.
4. Tweak UP the Megaflow stat to higher than the set point on the evoHome (I have not taken the cover off the control point on the megaflow, it is in an unbelievably awkward position, it will be possible but I am not going near it until the power is off. I only want to do it once).
5. Remove and isolate immersion thermostat, freeing up a void half way up the tank.
6. Push remote probe in to the void, seal lead in with something sensible, I have a vast array of rubber grommets, one should be right.
7. Connect probe to hot water unit, pair it all up with the controller...
8. Power on.

As I see this, the megaflow will always think the water is too cold, so will be powering the valve. The BDR91 will then have full control over the valve.

I have not touched anything on the megaflow, so I think the warranty will be fine.

Does this make sense??

[Richard]

OK, lets cover some basics...

The evohome Installation Guide (https://heatingcontrols.honeywellhome.c ... lation.pdf) Page 43 Figure 4 shows a perfect evohome system when using HR92's and how the software on the evohome Controller has been designed to operate.

You will see there are no motorised zone valves on the space heating side, because there simply isn't the need for them. Anyone calling us up pre-sales to ask how HR92's should be implemented will be told the evohome multi zone system was designed for HR92's on all radiators. Why? Because heating systems are piped in parallel. This means when a valve on the flow or return is shut, the water will not flow around the circuit. Therefore, if you put HR92's on the flow or return of a radiator and turn them off, then no water will flow around the heating circuit just like a JCB's backhoe won't move unless the levers are operated. Leaving zone valves there when they are not supposed to be will just lead to failure of the valves in time and the system not operating.

As for the Megaflo, I have never had any issues getting the evohome Hot Water Kits to fit with these? You should be able to get the CS92A probe against the tank amongst the old control group? As worst, remove the standard control thermostat probe from its pocket and replace it with the CS92A? Part G3 only covers the High Limit Thermostat and the T&P valve on an unvented cylinder, so as long as these are not touched from a legal standing you are safe and legal...

[WRS]

OK, lets cover some basics...

The evohome Installation Guide (https://heatingcontrols.honeywellhome.c ... lation.pdf) Page 43 Figure 4 shows a perfect evohome system when using HR92's and how the software on the evohome Controller has been designed to operate.

You will see there are no motorised zone valves on the space heating side, because there simply isn't the need for them. Anyone calling us up pre-sales to ask how HR92's should be implemented will be told the evohome multi zone system was designed for HR92's on all radiators. Why? Because heating systems are piped in parallel. This means when a valve on the flow or return is shut, the water will not flow around the circuit. Therefore, if you put HR92's on the flow or return of a radiator and turn them off, then no water will flow around the heating circuit just like a JCB's backhoe won't move unless the levers are operated. Leaving zone valves there when they are not supposed to be will just lead to failure of the valves in time and the system not operating.

As for the Megaflo, I have never had any issues getting the evohome Hot Water Kits to fit with these? You should be able to get the CS92A probe against the tank amongst the old control group? As worst, remove the standard control thermostat probe from its pocket and replace it with the CS92A? Part G3 only covers the High Limit Thermostat and the T&P valve on an unvented cylinder, so as long as these are not touched from a legal standing you are safe and legal...

That has helped me sort out my concerns re fitting evohome to a system with two heating zones.
As the two valves are already present, should I just over-ride them to their open positions, and disconnect their power? Then control the boiler pump as per your quoted post and either link out the existing room stats or set them higher than any of the HR92s are set. This should mean that water would only flow through radiators with their HR92s calling for heat.

Finally, does the evohome central controller function as a room thermostat? If so, why, as each room has in effect got its own room thermostat in the form of its HR92.

Thanks,

William

[Richard]

That has helped me sort out my concerns re fitting evohome to a system with two heating zones.
As the two valves are already present, should I just over-ride them to their open positions, and disconnect their power? Then control the boiler pump as per your quoted post and either link out the existing room stats or set them higher than any of the HR92s are set. This should mean that water would only flow through radiators with their HR92s calling for heat.

Finally, does the evohome central controller function as a room thermostat? If so, why, as each room has in effect got its own room thermostat in the form of its HR92.

Thanks,

William

Yes, evohome Controller can be used as a zone thermostat, but I don't personally recommend this.

As for the zone valves, you can leave these in the manually open position and electrically disconnect them.

Personally, I would disconnect any other heating thermostats or programmers as any failures in this equipment would cause issues with evohome (as evohome does not know these products exist).

[WRS]

Yes, evohome Controller can be used as a zone thermostat, but I don't personally recommend this.

As for the zone valves, you can leave these in the manually open position and electrically disconnect them.

Personally, I would disconnect any other heating thermostats or programmers as any failures in this equipment would cause issues with evohome (as evohome does not know these products exist).[/quote]


Thanks.

William