Evohome firmware 02.00.19.31 Beta Trial - Exclusive for Automated Home Members

[Andy the Minion]

Andy - sounds intriguing, can you elucidate? is there more to this algorithm than just what the temperature reads on the controller?

Well it was around Paul's comment on wind chill, i will be checking the office for bugs (Paul I'm looking at you ) We have another cunning plan that the device is prepared for but needs additional weather data .... and now we get into confidentiality issues and project planning so I will stop there.

[mtmcgavock]

This is exactly my thinking as well. If the pump keeps stopping every few minutes hot water sits losing heat in pipework without reaching the radiators, especially with a low TPI duty cycle where the one or two minutes on time might not even be enough for the slug of hot water to reach some radiators. Continous flow through the radiators while the boiler flame cycles on and off gives a more even distribution of heat around the system.

It also helps prevent kettling in the boiler heat exchanger as it's not forcing the entire flow to go through the ABV every few minutes. (Removing the boilers heatsink in the process)

However to make this work properly on a system like mine with a heating zone valve (and address the issue mtmcgavock raises about the heating zone valve closing) I have a nice little wiring hack for my heating zone valve that I've been using for the last couple of years:



In short, if the hot water relay is on, (hot water reheat) the heating zone valve follows the on/off status of the heating relay.

However when the hot water relay is off the heating zone valve will ignore the heating relay and stay on so long as the pump is running. (Even during overrun)

This allows water to continue circulating continuously through radiators throughout the TPI cycle except when there is a hot water reheat in progress which might otherwise cause the radiators to go over temperature. When a hot water reheat is in progress the heating zone valve will follow normal TPI control to reduce heat transfer to the radiators.

Surely with this though in the summer you get heat into any rads with no HR92s?

It is something i'm going to have to implement though, i'm just getting a lot of wasted heat - my rad in my garage acts as a bypass so all the heat is going into there.

[paulockenden]

i will be checking the office for bugs (Paul I'm looking at you )

There's no monopoly on good ideas. Especially when they are so bleedin' obvious!

[DBMandrake]

Surely with this though in the summer you get heat into any rads with no HR92s?

I don't have any radiators without HR92's anymore, so not in my situation no.

You're right though - if you did have a bypass radiator then at the end of a hot water reheat cycle in summer a small amount of latent heat from the boiler heat exchanger would be dumped into that cold bypass radiator, however that's a good thing for the boiler, and it would barely be enough to make the radiator luke warm and would only occur once at the end of each hot water reheat cycle. (The heating zone valve would stay closed until the hot water zone valve closed and the boiler stopped firing - then it would open when there was only latent heat remaining)

When I did have a bypass radiator it barely warmed at all from the heat dump due to the relatively high thermal mass of the radiator vs boiler heat exchanger.

Now that I have all HR92 controlled radiators I rely on a one minute hot water overrun to allow latent heat to dissipate at the end of the hot water reheat cycle.

[Andy the Minion]

This is exactly my thinking as well. If the pump keeps stopping every few minutes hot water sits losing heat in pipework without reaching the radiators, especially with a low TPI duty cycle where the one or two minutes on time might not even be enough for the slug of hot water to reach some radiators. Continous flow through the radiators while the boiler flame cycles on and off gives a more even distribution of heat around the system.

It also helps prevent kettling in the boiler heat exchanger as it's not forcing the entire flow to go through the ABV every few minutes. (Removing the boilers heatsink in the process)

However to make this work properly on a system like mine with a heating zone valve (and address the issue mtmcgavock raises about the heating zone valve closing) I have a nice little wiring hack for my heating zone valve that I've been using for the last couple of years:



In short, if the hot water relay is on, (hot water reheat) the heating zone valve follows the on/off status of the heating relay.

However when the hot water relay is off the heating zone valve will ignore the heating relay and stay on so long as the pump is running. (Even during overrun)

This allows water to continue circulating continuously through radiators throughout the TPI cycle except when there is a hot water reheat in progress which might otherwise cause the radiators to go over temperature. When a hot water reheat is in progress the heating zone valve will follow normal TPI control to reduce heat transfer to the radiators.

Simon i replied to your pm but was told you broke your mailbox and need to clear some space

[DBMandrake]

Years ago, @DBMandrake came up with the brilliant idea to have the CH Valve open with the pump, rather than be controlled by Evohome. Best mod I made. It allows the CH Valve to open and close and hence not seize but more importantly it circulates the heat through the loop in pump over run mode. it also takes care of boiler frost protection too. I love the idea, so simple and effective.

Did you wire in hot water priority as well ? Or are all you radiators HR92 controlled to prevent radiators heating during hot water reheat ?

While that original idea of mine is better than just mechanically locking the heating zone valve open, (it allows full flow and also occasionally exercises the valve to stop seizing) I prefer the scheme I show in the circuit diagram above, as it is equivalent to what you are doing except when hot water reheating is enabled, at which point it reverts to normal TPI to prevent radiators going over temperature. Of course if you have hot water priority this isn't needed.

The above circuit is a further logical progression from the original idea to run the heating zone valve from the pump.

[mtmcgavock]

I don't have any radiators without HR92's anymore, so not in my situation no.

You're right though - if you did have a bypass radiator then at the end of a hot water reheat cycle in summer a small amount of latent heat from the boiler heat exchanger would be dumped into that cold bypass radiator, however that's a good thing for the boiler, and it would barely be enough to make the radiator luke warm and would only occur once at the end of each hot water reheat cycle. (The heating zone valve would stay closed until the hot water zone valve closed and the boiler stopped firing - then it would open when there was only latent heat remaining)

When I did have a bypass radiator it barely warmed at all from the heat dump due to the relatively high thermal mass of the radiator vs boiler heat exchanger.

Now that I have all HR92 controlled radiators I rely on a one minute hot water overrun to allow latent heat to dissipate at the end of the hot water reheat cycle.

All my rads have HR92s too, so I think a timer on my Heating MV would just be sufficient for when there’s an overrun from a heating demand - any pointers for what timer you used?

I use a 2 minute overrun on HW, plus the bypass rad in the garage for when there’s no heat demand for the CH.

[DBMandrake]

Simon i replied to your pm but was told you broke your mailbox and need to clear some space

Just checked and I only had 28 messages in my inbox. Not much room on this forum! I've deleted them all so try again.

[DBMandrake]

All my rads have HR92s too, so I think a timer on my Heating MV would just be sufficient for when there’s an overrun from a heating demand - any pointers for what timer you used?

I use a 2 minute overrun on HW, plus the bypass rad in the garage for when there’s no heat demand for the CH.

I used an MRT16-REM:

https://www.cpelectronics.co.uk/ener...ches/mrt16-rem

It fits a regular protruding back box and has a blank front panel. A version with volt free contacts is availble but if you're just switching 240v AC the standard version is fine. The mode should be set to overrun mode and the delay can be configured anywhere from about 5 seconds to an hour, so it's quite versatile. Not sure how easy it will be to get hold of one in the current climate though!

My boiler is so old it didn't have any pump overrun at all - so this is my retrofit pump overrun. (An old boiler with no pump overrun really doesn't like TPI I discovered!)

[roydonaldson]

Just got up this morning to find Bedroom Zone set to 35C.......and Living Room set to 19C, reading 15.5C, zone says calling for 100% heat, and yet Zone Valves are off and not pumping at boiler....

Roy.20200404_072012.jpg