Biomass Boiler and Evohome - Do I need to control the Boiler?

[nochexisking]

Hi,
this is my first post - so if this has been answered before I apologies in advance - Just point me to the answer please

OK, so I have a 30Kw biomass boiler. This heats a 500l buffer tank. These are both located in a separate building adjacent to the house. I have a separate 200l hot water tank in the house.

As far as I understand it, the hot water in the buffer tank, when instructed by the hot water timer in the house, sends hot water to a coil that is wrapped around the hot water tank, which heats the water that is INSIDE the tank. It doesnt use the water actually from the buffer tank.

The hot water for the heating DOES use the buffer tank water - as far as I understand, and is called upon by a separate central heating timer.

The central heating is configured to 2 zones. These are currently controlled by the central heating timer, which has 2 zone settings that can be set independently.

The Biomass boiler seems to work independently of any timers, and simply keeps the buffer tank water temperature between 50-70c, which is set on the biomass boiler controls.

The system is 18month old - the timers are all honeywell



So far so good...I think


I now want to use the Evohome system, and use the radiator valves to create zones within the house, and not use the current 2 zone system, which is too limited for me. We have installed a wood burner since the heating system was installed, so this keeps the room warm enough. We do however want the bathroom and bedrooms etc to not feel like a fridge when going to bed etc.
My thoughts are that since the boiler seems to be independent, would it just be a case of setting the central heating to continuous, and then using the thermostatic valves to dictate when I want the heating on? In other words, can I bypass having to do or pay for any installation?

My only concerns with this is whether or not the central heating pumps would be constantly working, circulating water around the radiator circuit, but not into the radiators themselves? or would the thermostatic valves shut them off? I dont see how they can?

Do I need something that tells the heating to stop?

Thanks for any help

regards

John

[paulockenden]

I think you could probably use Evohome to control your CH pump when there is a demand for heat, but leave both of the CH zone vales locked open.

The TRVs will close when there's no demand, so there wouldn't be any wasted flow around your heating zones of there was no demand.

This assumes that you have a conventional 'radiators in parallel' setup.

[nochexisking]

Hi Paul,
Yes, the radiators are all set up as they should be, feeding off a main loop, but I've just remembered that the hall radiator has no TRVs. I also seem to remember reading that one radiator always needs to be open so that the circuit can always flow. I guess this radiator would always be piping hot?

[paulockenden]

With evohome you don't need to leave one rad without a TRV. In your case I think you'd be better off if you did them all.

You /could/ put an automatic bypass valve in, just in case, but in theory your heating pump shouldn't run unless at least one HR92 is at least partly open.

[paulockenden]

Although your system sounds complex, I think it you just treated your heat store tank as an uncontrolled boiler, it then starts to look a lot like a conventional heating and hot water system.

Incidentally, what do you burn in your biomass boiler?

[nochexisking]

How does the pump know to stop if the evohome can't talk to it? Not knowing how this works I don't understand how a trv can tell the pump to stop?

I burn wood pellets. I signed onto the RHI scheme last xmas

[paulockenden]

The TRVs talk to the evohome controller. This aggregates the heat demand from all of them. It would normally control a boiler which in turn would control a pump, but in your case the heat demand just needs to fire the pump. I think.

Or so it seems from what you've said so far.

[nochexisking]

I think what I may end up doing is keeping the current timers for both zones, but extend their on times, so say 7-10am in morning and 5-11pm at night, then just use evohome to control the heat demand per room.
If it doesn't work out, I could always add other boiler or pump Controllers later.
Just gotta shell out for 12 TRVS now :-(

[paulockenden]

You won't need timers. Evohome looks after that side of things.

[top brake]

Hi,
this is my first post - so if this has been answered before I apologies in advance - Just point me to the answer please

OK, so I have a 30Kw biomass boiler. This heats a 500l buffer tank. These are both located in a separate building adjacent to the house. I have a separate 200l hot water tank in the house.

As far as I understand it, the hot water in the buffer tank, when instructed by the hot water timer in the house, sends hot water to a coil that is wrapped around the hot water tank, which heats the water that is INSIDE the tank. It doesnt use the water actually from the buffer tank.

The hot water for the heating DOES use the buffer tank water - as far as I understand, and is called upon by a separate central heating timer.

The central heating is configured to 2 zones. These are currently controlled by the central heating timer, which has 2 zone settings that can be set independently.

The Biomass boiler seems to work independently of any timers, and simply keeps the buffer tank water temperature between 50-70c, which is set on the biomass boiler controls.

The system is 18month old - the timers are all honeywell



So far so good...I think


I now want to use the Evohome system, and use the radiator valves to create zones within the house, and not use the current 2 zone system, which is too limited for me. We have installed a wood burner since the heating system was installed, so this keeps the room warm enough. We do however want the bathroom and bedrooms etc to not feel like a fridge when going to bed etc.
My thoughts are that since the boiler seems to be independent, would it just be a case of setting the central heating to continuous, and then using the thermostatic valves to dictate when I want the heating on? In other words, can I bypass having to do or pay for any installation?

My only concerns with this is whether or not the central heating pumps would be constantly working, circulating water around the radiator circuit, but not into the radiators themselves? or would the thermostatic valves shut them off? I dont see how they can?

Do I need something that tells the heating to stop?

Thanks for any help

regards

John

Quite hard to visualise your system from just a description.

As you have explained the biomass boiler heats the thermal store using its own controls. Great

Evohome will simply treat the thermal store as the heat source. How you setup the evohome will depend on what valves are connected to the thermal store.

If you can provide some pictures or a schematic I'll take a look at it for you. Thanks.

[DBMandrake]

With evohome you don't need to leave one rad without a TRV. In your case I think you'd be better off if you did them all.

You /could/ put an automatic bypass valve in, just in case, but in theory your heating pump shouldn't run unless at least one HR92 is at least partly open.

I would not rely on this as a reason not to fit an ABV for two reasons:

1) When HR92's are scheduled to close (for example using the off action) they close the radiator valve before they remove their wireless heat demand.

This is easily proven by turning off all zones except one which is turned on to a high temperature - then turn off the remaining zone by setting it to 5 degrees. You will hear the motor closing the valve over about a 20 second period, it's not until a few seconds after the valve finishes closing that you'll hear the boiler relay turn off.

This means the pump is potentially pumping into a dead end for up to 20 seconds every time you schedule the zones to all be off. This could easily be enough to trigger a lockout or even promote a leak in the system due to high pressure.

2) If the system has any pump overrun (as ours does) then by definition the pump will continue to run for a while after all the HR92's have closed.

In my opinion if you are going to control all radiators with HR92's (eg no bypass radiator) you must have an ABV to allow temporary flow when all valves are closed because it does happen, even if only for short periods of time.

The system as a whole will work a lot more smoothly with an ABV fitted and there is really no reason not to have one these days on any constant speed pumped system.

[paulockenden]

On your point 2), there should be no over-run. It's normally there to protect a boiler (to remove the heat from it). Quite the opposite is needed with a thermal store.

Good point about the HR92s closing before the demand is removed, though.

[The EVOHOME Shop]

OK, so I have a 30Kw biomass boiler. This heats a 500l buffer tank. These are both located in a separate building adjacent to the house. I have a separate 200l hot water tank in the house.

As far as I understand it, the hot water in the buffer tank, when instructed by the hot water timer in the house, sends hot water to a coil that is wrapped around the hot water tank, which heats the water that is INSIDE the tank. It doesnt use the water actually from the buffer tank.

The hot water for the heating DOES use the buffer tank water - as far as I understand, and is called upon by a separate central heating timer.

The central heating is configured to 2 zones. These are currently controlled by the central heating timer, which has 2 zone settings that can be set independently.

The Biomass boiler seems to work independently of any timers, and simply keeps the buffer tank water temperature between 50-70c, which is set on the biomass boiler controls.

The system is 18month old - the timers are all honeywell



So far so good...I think


I now want to use the Evohome system, and use the radiator valves to create zones within the house, and not use the current 2 zone system, which is too limited for me. We have installed a wood burner since the heating system was installed, so this keeps the room warm enough. We do however want the bathroom and bedrooms etc to not feel like a fridge when going to bed etc.
My thoughts are that since the boiler seems to be independent, would it just be a case of setting the central heating to continuous, and then using the thermostatic valves to dictate when I want the heating on? In other words, can I bypass having to do or pay for any installation?

My only concerns with this is whether or not the central heating pumps would be constantly working, circulating water around the radiator circuit, but not into the radiators themselves? or would the thermostatic valves shut them off? I dont see how they can?

Do I need something that tells the heating to stop?

Thanks for any help

regards

John

This setup will work very easily with evohome. I have exactly the same setup as you (although mine is slightly more complicated) but I have a Ground Source Heat Pump instead of the Biomass Boiler. When compared to other systems, your buffer cylinder is your 'boiler' and will use a BDR91 as a 'boiler control relay' to operate the buffer cylinders pump. The rest of the heating system can be treated the same as a normal evohome system - Hot Water Kit controlling the motorised zone valve on the hot water cylinder and the requirement for an Automatic Bypass Valve if the pump is a fixed speed pump and you are fitting HR92's to all radiators (an ABV will help to prevent water hammer on the radiator valves and increase the life of the pump).