JonG,

Do you have a link to the study that Evohome uses to claim the 40% saving? I can't find the formal Salford study.

My existing system has a cylinder thermostat, a Honeywell digital room thermostat that controls the whole house, but has different temperatures for different times. So 17 degrees at night, 19 in the morning and 21 in the evening.

Another time clock controls the cylinder on times, 1 period morning, one noon, and one in the evening.

I have TRVs on most radiators, two rooms have skirting board heat, no TRVs. No external temperature measurement.

With Evohome, I would have control of absolutely everything.

I guessed at 30% saving, to try and be a bit conservative. What do you think? Too high?

JonG,

Thanks for the link. Very interesting.

I think you are right, 30% is too high, but I must get some benefit from only heating the part of the house that is being used, not the whole thing as today.

My Honeywell digital control is old and just puts the temperature up/down at the set time. I dont think it has TPI. However I will get a benefit in comfort from Evohome's TPI and optimum start related to outside temperature.

This Honeywell website http://getconnected.honeywell.com/en/evohome claims the 40% saving and refers to this bit at the bottom of the page. . . . . .

* Source Energy Saving Research Unit, Strathclyde University 2013 & TACMA 2013 - Energy savings quoted were calculated using a 3 bedroom, 2 level home, located in the UK, modelling a family of 4 over a typical week’s activity, comparing an evohome smart zoning system, with recommended settings, to a system comprising of a simple timer, single non-programmable room thermostat and no Thermostatic radiator valves. Individual Energy savings gained are dependent upon existing controls, environment and lifestyle.

So the 40% saving is made by comparing a very basic system with the most sophisticated available. Not surprising really.

You mentioned Opentherm, I had a quick read, and can see the benefit, but my Valiant has modulated flame control and I can hear the boiler operating at a low setting when the demand is slight, and at full power when the demand is high. Is this not similar to the Opentherm advantages?

Hi topher, you will save something but your TRV's are limiting heat input too, assuming that they are not fully open.

The Strathclyde survey started with a property without TRV's so this is a relatively significant difference in upgrade.

Opentherm improves modulation, by starting the process earlier based on the load indicated by the room thermostat, so as it approaches set point or if the demand occurs when the start point is close to set point but still below it, it modulates the gas valve and controls the flow temperature between pre-determined bands to void overshoot and only consume the smallest amount of gas required to achieve air temperature.

In comparison your Vaillant starts at full rate and attempt to achieve the flow temeprature set on the manual boiler stat, it will then modulate based on flow and return temperature, but the thermal mass of water will react much slower than air in terms of rate of temperature change.

This means that if the load (room temp) is close to set point, it may well hit flow temp and potentially switch off before the room stat is satisfied, before then switching back on when the return temp drops, conversely when the load is high and large volumes of cold water are circulating it will then go to full rate and stay at full rate until the return drops or room temp is reached.

These effects will be influenced by the system design, presence of TRV's, speed of pump, type of building, start and set point temp etc.

Opentherm seeks to overcome some of the potential issues by effectively simmering the boiler to achieve room temp.

Brilliant JonG, many thanks. I have a lot to learn.

I have now got a temporary hybrid system. Boiler is still controlled by my old digital thermostat in the hall, but most rads have Honeywell Evohome wireless radiator valves. After one day messing about, it seems to be OK now. My main comments are -

1. One valve was not getting a signal. Valve and controller were at diagonally opposite points of the house. I moved the controller closer to its final position and it's OK now.

2. Binding, unbinding and factory reset have to be done frequently on the valves. I now know how to do it. Honeywell could have a much simpler menu system instead of short presses, long presses, and cancellation long presses. Still, I know how to do it now.

3. If you get error messages as I did from communications problems, the error log gets bigger and bigger. It can not be erased. You have to put the controller on battery power, remove the battery for a few seconds, and re insert. This is a reset, not factory reset. Data is retained, and the system takes ages to re-establish communications.

4. Honeywell supply an adapter to convert my RA style rad valves (the thing with the pin that is pressed down to control the flow). They can easily be wrongly fitted. After excellent support from the Evohome Shop, I was able to fit them properly. The trick is to open the split fully so that it sits right up against the shoulder.

In summary I think I made the right decision to start with a hybrid system. If I had done the boiler controls and rad controls at the same time, I think we would have a cold house and me rushing about to fix things late into the night.

How about overrunning the TRVs slightly so the room slightly overheats? Might be condensing more that way.

I love it, and it is one of those things that you don't realise you need until you have it! Definitely keep the optimum start and optimum stop enabled, it is a key feature of the platform.

What cyclical rate have you set up, with a condenser it should usually be 3 starts per hour and 5 mins min run time, this should prevent the TPI from screwing too much with the modulation rates in built into a condenser.

Check your flow and return temps to see if it is condensing and try and reduce the FT as low as possible and balance to suit.

JonG,

I contacted the boiler maker (Vaillant, premium rate call) about boiler starts per hour, and I understood him to say it didn't matter much as the boiler modulated the flame to suit the heat demand. I will take your advice and set to 3 starts per hour. I will leave optimum start and stop enabled.

Q1. I have the boiler temperature set to 70 degrees and the hot water to 45. When you say keep the FT as low as possible, how low?

Q2. I have a little hand gun with a red laser beam that measures temperature. If I put black tape on the pipes, could I use that?

Q3. I understand that the biggest temperature difference between FT and RT causes the boiler to condense. What values should I use to determine if it is condensing?

gravelld,

If I set to a slightly higher temperature, it would keep that slightly higher temperature for all the on-time, using more gas. What I could do, is set a higher temperature for say 10 or 20 minutes, then revert to normal, this would put a slightly higher demand on the boiler at start up. I believe with the central controller and the "learning" programme, there would be a critically damped rise, with no overrun.

I have set a lot of rooms to all come on at the same time in the morning. I have to do a similar thing for the evening start and going to bed events.

gravelld,

I agree. I don't know how well a TRV in the far corner of a big room can control the temperature.

I have ordered a separate room thermostat which will be linked by radio to the controller which then drives the TRV. It has the advantage of being portable - I can put it in different parts of the room to find the best position. It can also be fixed to a wall. Seems to me a cool idea, the trouble is the more I find out, the more expensive it gets.

JonG

Over the recent cold spell, I have learned that with my radiator sizes, I have to run the boiler at 70 or 75 degrees to get the house warm enough. When I have got the installation completed I will try and achieve that 20 degree delta.

Another matter that may be if interest - the firmware update that corrects bugs and shows radiator override settings on the controller and the app is now available. But you have to request it from Honeywell. I have made the request and will explain how it works here.

Yet another matter that may be of interest - for some unknown reason the app showed two rooms incorrectly. Both had the wrong name, but the temperature on both was 62 degrees. Honeywell advised me to delete my account on the server, delete the app, reinstall my account on the server and reinstall the app. This was a very tedious process because the server was very slow, but in the end the problem was solved.

Got everything back together and working. Have left the house for a week and set up the 'Away' setting. All rooms go to 13 degrees and HW to off. With the app, I can see the temperatures reducing from the remote location. I see that one room is dropping faster than the others. This is helpful as it encourages me to consider increasing the insulation for that room

I also see how slowly the hot water temperature is dropping. I am pleased that the HW cylinder has such good insulation.

One hairy problem just before leaving was loss of communications between the HW relay and the controller. I called the Honeywell customer support (00 44 1344 656 200) and was given excellent help by Ben who talked me through the button pressing sequence to cancel the binding and reset it. I need to spend some time learning the process because I have had a number of communications failures.

What is the room stat setting?

Sounds like something wrong with the hard wiring to me.

Check HW stat is working and in contact with cylinder

Posted By: topherBut the boiler controller is calling for heat. So the boiler is briefly on, and the HW is passing through the bypass.

What controls the boiler's demand for heat? If the boiler itself is just measuring the temperature of its water, that would produce the symptoms you see, for example.

Turned on either by the HW, or the heating, or both. But it should not come on when neither are calling for heat.