Boiler modulation with LLH

[HRP123]

Pretty much yes, Vaillant and Viessman controls are easy wired for hot water priority. WB also do weather comp but your boiler looks quite old so I'm not sure. Which model is it?

No it does not make it less efficient it makes it more efficient with these mixing valves because the electronic mixing actuators sit on top of a three way valve that sends the cool return water back into the system rather than the standard mixing manifold which just blends high temperatures down.

A low temperature efficient heating system is as open loop as possible, with all the UFH running at one flow temperature and same for the radiators, the trvs can be used to limit temperature overshoots in rooms and ufh can be adjusted by the flow setters at the manifold but zoning is bad for efficiency. This is how heat pump systems are designed, esentially with the setup i'm suggesting you are getting as close to heat pump efficiency as humanly possible with a gas boiler.

Thanks for that explanation!

Ah so if I understand correctly, in the mixing valves you are using the cool return water rather than wasting it.

I guess it is a bit of a worry for me that with a big house, if the calculations are not correct in any way, you could have rooms which remain cold. Before I installed the current 10 year old WB 40cdi boiler (playing with range rating though so at 30kw ish now), there was a Geminox 24kw boiler which also did HW priority, except that it took forever to heat up and the rooms always felt cold as a result. Hence we moved to this system which at the time wasn't too expensive to operate ... but is really hurting now with 75,000 kw annual gas consumption projected.

 

[Deleted member 281264]

The mixing valve and pumps create a loop within the circuit that sends cool return water back in to keep a steady temperature, this type of system will also likely be much more comfortable than what you have now.

This is how heating systems in Germany are designed we just haven't cottoned on here yet.

To do the job properly you would need a heat loss calculation done by a competent engineer to size the boiler correctly. The idea of these systems is to keep everything at a low comfortable temperature constantly rather than zoning things off and blasting heat into certain parts of the house. The theory is to tune it so that the exact heat being lost from the building is constantly being replaced which is where the efficiency comes from.

It's a whole different way of heating a property than what we have been taught in the UK. Before it didn't matter because gas was cheap, but with current prices the inefficiencies and lack of education are being exposed.

I am pretty sure your setup could be simplified and made to run much more efficiently, the installer probably saw the size of house and thought you were made of money, hence all of those pumps.

 

[HRP123]

The mixing valve and pumps create a loop within the circuit that sends cool return water back in to keep a steady temperature, this type of system will also likely be much more comfortable than what you have now.

This is how heating systems in Germany are designed we just haven't cottoned on here yet.

To do the job properly you would need a heat loss calculation done by a competent engineer to size the boiler correctly. The idea of these systems is to keep everything at a low comfortable temperature constantly rather than zoning things off and blasting heat into certain parts of the house. The theory is to tune it so that the exact heat being lost from the building is constantly being replaced which is where the efficiency comes from.

It's a whole different way of heating a property than what we have been taught in the UK. Before it didn't matter because gas was cheap, but with current prices the inefficiencies and lack of education are being exposed.

I am pretty sure your setup could be simplified and made to run much more efficiently, the installer probably saw the size of house and thought you were made of money, hence all of those pumps.

Actually the pumps were not too much of a cost and the plumber is someone we use regularly (we do house renovations). Yes our house is bigger and we used the current system to replace a French Geminox boiler which was designed on the principle above but wasn't sufficiently heating the house. I found at the time the cost of multiple pumps was not that much more than the one massive pump - the main cost was the LLH and electrical work with multiple pumps.

The problem (my concern) with these systems if the HW demand is not satisfied fast enough, or calls for heat throughout the day (secondary hot water circulation), the boiler keeps diverting to supply the hot water at the cost of heating.

I've done a Heat Engineer calculation (attached) for the heat loss and it came up with 20kw - which I'm not sure how to convert into a boiler sizing or for the right flow temps etc. I suspect though that with a house like this you would probably need the boiler to run at a low flow temp for about half of the day at least to keep whole house feeling sufficiently warm.

Thanks for your thoughts and help.

 

[vulcancontinental]

You can argue that the LLH is to ensure pumps do not conflict but actually it's main purpose is to ensure the boiler heat exchanger always has the correct flow rate across it no matter how the system flow rates changed. Highly restrictive heat exchangers such as those mentioned with low residual head would suffer otherwise with major changes in system requirements. Did you find an installer?

 

[Deleted member 281264]

20kw heatloss means you need a 20kw boiler (20kw of power when it's -2 outside)

However heatloss studies are rarely totally accurate especially if you have guessed a lot of it.

You have nothing to worry about with a hot water priority setup as long as it's done correctly with a good size cylinder and coil you could even buy a high gain cylinder used for heatpumps which have a huge coil, but if it is a concern to you then you could get 2 boilers plumbed into the LLH one for hot water and one for heating, this could be very efficient but ideally I'd rather just have one boiler.

 

[HRP123]

You can argue that the LLH is to ensure pumps do not conflict but actually it's main purpose is to ensure the boiler heat exchanger always has the correct flow rate across it no matter how the system flow rates changed. Highly restrictive heat exchangers such as those mentioned with low residual head would suffer otherwise with major changes in system requirements. Did you find an installer?

Thanks I see what you mean re LLH and it helps by providing a buffer (in layman terms) for different flows from the boiler.

I have spoken to an expert Viessman installer but just trying to make sure (1) it will actually reduce my gas consumption while (2) providing sufficient heat. The previous boiler which was a priority hot water one didn't work very well.

 

[HRP123]

20kw heatloss means you need a 20kw boiler (20kw of power when it's -2 outside)

However heatloss studies are rarely totally accurate especially if you have guessed a lot of it.

You have nothing to worry about with a hot water priority setup as long as it's done correctly with a good size cylinder and coil you could even buy a high gain cylinder used for heatpumps which have a huge coil, but if it is a concern to you then you could get 2 boilers plumbed into the LLH one for hot water and one for heating, this could be very efficient but ideally I'd rather just have one boiler.

Its worth considering this option of the two boilers, in fact I was just thinking about this myself. I was wondering perhaps keeping the existing 40cdi boiler but range rated down and dedicated to the hot water cylinders. And then having a smaller one, lets say 24kw which is for heating requirements with weather compensation controls etc. Or getting an ASHP just for the underfloor heat demand. But as you say, less complexity is better!