Did you compare with Heat Genius? That was cheaper last time I checked.

Hi Gravelld, yes I did compare. It is not as granular as Evohome which controls every radiator on it's own. Also the rad valves are poor in comparison with Evohome's.

JonG, Interesting. I have spoken with Richard at Evohome Shop and will probably buy from him. He is not the cheapest, but his support is really good. So tell us about worst limitations and worst bugs please.

Shall I tell of my experiences? Tell me please.

One important point that took me a long time to discover is that Evohome needs a boiler bypass, even with a 3 position valve in a Honeywell Y configuration.

Which elements of the system are you planning to use topher and in what configuration and I will see if I can shed any light.

OK, no worries.

First off depending on your motive there is a CBA to do because the savings may not justify the expense, especially if air tightness, insulation or both can be improved. If the EH is to give you more functionality and control, especially in your instance when it sounds as if toggling zones to limit the demand on the boiler is needed then fair enough.

Zoning only works if you can fully segregate areas (think closed doors), otherwise you end up with homogenous heat transfer and heat moving from a hot area to a cooler one which then means that the higher target zone may never satisfy.

Quite a few do leave some key areas like hallways/landings open circuit to keep a core of heat in the building and reduce the system cost and complexity, this also negates the issue with the bypass which is becomingly an increasingly thorny issue with modulating pumps (but that is probably a separate thread).

It might be worth getting the wifi test kit to ensure that the signal is available from the furthest reaches of the property, any reflective insulation, steels, laminate foils etc may compromise the signal, test the heads when in situ too and be very wary if the signal strength is low.

The battery life in the central controller is pants, so it does need to be on the stand or wall mount, either plugged in or wired in respectively. It can take up to 4 mins for signals to be sent and received between the various items and if the power is dropped it can be sometimes up to an hour to re-establish contact although 15 mins is more usual. This can engender panic, rage, frantic re-binding and general social unrest if you don’t know. If you manually override the signal re-establishes sooner.

Failures do happen straight out of the box, Richard at Evohome will pre-bind and test for the trade, not sure if he offers this to private clients though. There are some rumblings in the trade about the quality of back-up from Honeywell generally.

If you are using the hot water kit the sensor benefits from plenty of thermal paste or a dedicated small diameter sensor pocket and in either case some insulation to plug the orifice once it is in.

The Vaillant I believe, won’t allow you to use either Opentherm or weather compensation with the system which is a shame because it negates some of the efficiency that either of these engender.

The BDR91’s and cylinder sensor transceiver are best located 300mm away from each other and metal lumps like boilers and cylinders if possible.

It is a good system but it’s not a magic bullet and has to be installed and commissioned carefully.

No problem topher hope it goes well.

In terms of balancing it is indeed a dark art, usually conventional wisdom was get the furthest rad away sorted then work your way back. Don't underestimate how much you can close the lockshields, the closer you get to the boiler the more you will have to throttle and you may have the valve barely a quarter or half turn open.

To get started open everything full whack and see which rads get hot first and last and this will give you a feel for the hydraulic layout.

However in a system like EH or even just with TRV's generally the flow and pressure changes so regularly that accuracy is very difficult to achieve. Also dont even think about doing it until there is a decent cold weather demand in the house, because obviously the delta closes as the rooms reach temp.

I am also unclear why HW recommend 12 degrees, a condensing boiler is looking for 20 degrees and it is better to adjust the delta by throttling the pump speed because this reduces energy consumption.

It really will be trial and error and unlikely to be a one off experience!

In terms of the gadget freak thing, I think HW could have included more visible data about what the system and individual components are doing at any one time even if it was hidden in the installer menus, the actual interrogative level is disappointing from that perspective.

Posted By: topherI got more advice on the boiler bypass yesterday which has to be 1.5 meters minimum in length, so as to dissipate a bit of heat if needed. I have to have one because the EH controller can shut all the valves, but keep the heating demand on in case a valve re-opens.

Most boilers need a bypass, as the pump is kept running after the boiler shuts down for a few minutes, otherwise the heat exchange overheats. (The boiler is still filled with hot gases even after the flame goes out.)

We usually find that rads are oversized mainly due to in-acurracy originally and a desire to avoid a cold client. Plus often the heat loss has dropped due to CWI or loft insulation upgrades.

Ringi why would the boiler not hit flow temp? Depending on load, cyclical rate, system design, rad size etc it may have to reach set point to achieve the design room air temp.

Once close to set point the HR92's will open and close according to the TPI algorithm to avoid under/over shoot but this shouldn't affect the set point FT unless the boiler is cycling on the limit stat, which would indicate a flow related issue and even then the HX would have hit set point.

Surely this is why OT and WC make sense because the FT is flexed depending on load or external temp?

The infrared's are OK but I would only rely on it for a reference delta and use masking tape or similar on copper/rads to avoid it bouncing.

If the lowest pump speed is not low enough (and you still have to consider system response times in all of this), it may be better to introduce a flow setting valve to throttle the flow speed if you can fit one, Taconova do a comprehensive range.

However as you say the changes in velocity in the system may frustrate your efforts, it may be that as the popularity of systems like these increase we see a higher incidence of low loss header usage, which hydraulic decouple the boiler from the system and allow it to work at a constant delta irrespective of what the downstream system is doing.

Hi ringi I still dont think it will affect FT though, we have used CM927's and DT92E's for years with boilers and heat pumps and with heat pumps the FT is critical, it does as the quote says above control fluctuating room temperature but if the heat source isn't hitting set point the design of the system is compromised because the MWT in the heat emitter could be too low.

Thanks for my continuing education, all the comments are very useful.

Could I ask a favour please? I am somewhat in the dark with all the abbreviations. The words that go with the following would be great. Some I might guess like CWI = cold water inlet. But that could be wrong.

FT, MWT, OT, WC, HX, CWI,

FT=Flow temp
MWT=Mean water temp (the average temp in the rad taking into account the FT/RT and the delta)
OT=Opentherm a control protocol that modulates the boiler gas valve increasing and decreasing the FT according to load
WC=Weather compensation a control protocol that modulates the boiler gas valve increasing and decreasing the FT according to external temp via a sensor
HX=Heat exchanger

Hi Topher any chance of a drawing showing what you are thinking.

Also is the pump on your boiler internal or external, I am also guessing it already has an ABV that will need to be shut to allow the new bypass to work.

Whatever you do aim to keep it simple, would be my advice.

If you can post a drawing we can have a look at it for you.

Hope you can understand sketch, had to use 200 bpi to get it accepted . . .

I think this is the point I missed. You said . . . . If there is a differential between the flow temp and the cylinder temp one will strip the other and could possibly increase the heat in the exchanger in an extreme example whilst also depleting the cylinder contents. . . .

If the boiler had just heated the HW and the last HR92on the radiator circuits closes, then your point above applies. I could hasted the death of my boiler due to overheat.

So I will go back to the normal connection.

A better solution would be to alter the firmware to keep just one HR92 open white the 4 to 8 minute EH shutdown occurs. Anyone know how to do this?

You said. . . . Another possibility could be to leave a towel warmer or 2 open circuit to accept the flow where it would actually be more useful. . . . . . How do I leave a towel warmer open? I guess I leave the normal TRV in place, but this means the towel rail heats up when any HR92 call s for heat - a bit of a waste?

Thanks,.......Topher.
.

Hi, Thanks the contributions. My understanding is much better now.

Hi topher which study are you basing the 40%/30% on?

If it was the Salford (?) one the 40% was a house going from a boiler stat to time and temperature and trvs, so would depend on what you have already?