Design For New Central Heating System

[milleniumaire]

I'm looking to expand my central heating system by adding a new bathroom UFH zone. I'm also changing the pipes feeding the loft radiators to 22mm, instead of 15mm.

Early discussions with my heating engineer talked about introducing a Low Loss Header and one or more additional pumps.

The existing layout can be seen here:

Here's my view of what the new design might look like:

The loft radiators have had flow issues and the plastic piping feeding them was completely blocked by silt so they were never warming up. I have now cleared the pipes and want to introduce a 22mm feed from nearer the boiler as they were previously feed from the last radiator on the first floor. I will also re-route the loft pipes so they are no longer in a "star" shape, but are connected in parallel. Hopefully, along with an additional pump somewhere, this will ensure the loft radiator pipes don't silt up again due to their increased flow.

The new bathroom UFH manifold will be connected by 22mm pipes and will require either an actuator on the manifold (only one of the ports will be used) or a valve, controlled by a VR 91 thermostat in the bathroom.

One issue I have is the running of TWO new sets of 22mm flow and return pipes from (near) the boiler to the bathroom and loft. There is a landing floor spanning from one end of the house (where the boiler is), to the other end of the house (where the bathroom and loft pipes are) along which 4 x 15mm pipes currently run, notched into the joists.

Notching in another 4 x 22mm pipes seems like a none starter as does drilling 4 x 25mm holes into each joist.

I was wondering if the loft radiator circuit and the bathroom UFH manifold could somehow be supplied by a single pair of 22mm pipes (supply and return). I think the difficulty doing this would be the valve control as they are both separate zones!

Also, I'm wondering if it is better to have a single additional pump after the LLH, or possibly a pump for each zone? Given that both UFH manifolds already have built in pumps, this seems like overkill. So, potentially, a pump after the LLH would improve the CH flow and get the water to the two manifolds, where the manifold pumps would get it around the UFH circuits.

I would appreciate any thoughts you might have on the considered changes.

 

[Stu-B]

You need more 22mm throughout, maybe even some 28 near the boiler depending on how big your house is, pipe as near as you can to each rad in 22 then branch off in 15 to increase the flow, I’d also look at zoning the 3 floors, better overall control.

 

[milleniumaire]

Hi Stu, thanks for your suggestions, they make perfect sense.

The house is 22 years old, so without major upheaval there are limitations to what I can do. I'm in the process of a bathroom refurbishment and as the loft CH feeds are via the bathroom it seemed like a good idea to try to fix the loft flow issues at the same time.
I have already bought a new Vaillant VR71 wiring centre and compatible thermostats, which will allow me to add one additional zone for the bathroom UFH, so putting each floor in a separate zone isn't possible without more expense. TBH having all three floors on the same CH circuit has never been an issue as each radiator has a TRV, so we can already control the temperature for each room.

 

[SJB060685]

I suspect part of your original problem is the boiler pump is not man enough to overcome the resistance of your index circuit.
Hydrolic separation is going to help but installing a LLH might not be necessary.
You could install CCT's and still achieve the same result for a fraction of the price.

 

[doitmyself]

I suspect part of your original problem is the boiler pump is not man enough to overcome the resistance of your index circuit.

That could be because the system has been balanced for a 11C drop. Vaillant 6XX system boilers are designed for a drop of up to 20C. If the system is balanced for a drop greater than 11C the flow rate drops and the resistance decreases at a faster rate (head= k.flow^1.75). This means the pump will not be working so hard.

Parameters d.40 and d.41 (d.040 and d.041 for newer boilers) will tell you the flow and return temperatures.

The only negative factor will be a slight reduction in output from the radiators.

 

[SJB060685]

That could be because the system has been balanced for a 11C drop. Vaillant 6XX system boilers are designed for a drop of up to 20C. If the system is balanced for a drop greater than 11C the flow rate drops and the resistance decreases at a faster rate (head= k.flow^1.75). This means the pump will not be working so hard.

Parameters d.40 and d.41 (d.040 and d.041 for newer boilers) will tell you the flow and return temperatures.

The only negative factor will be a slight reduction in output from the radiators.

Where have you got an 11°c drop from? Most modern boilers look for a 20°c drop across the system.

 

[milleniumaire]

I suspect part of your original problem is the boiler pump is not man enough to overcome the resistance of your index circuit.
Hydrolic separation is going to help but installing a LLH might not be necessary.
You could install CCT's and still achieve the same result for a fraction of the price.

I will certainly discuss Close Coupled Tees with my heating engineer, so thanks for that suggestion. I assume the use of CCT's is very much dependant on positioning and the advantage of a LLH is that this is designed into the product.

That could be because the system has been balanced for a 11C drop. Vaillant 6XX system boilers are designed for a drop of up to 20C. If the system is balanced for a drop greater than 11C the flow rate drops and the resistance decreases at a faster rate (head= k.flow^1.75). This means the pump will not be working so hard.

Parameters d.40 and d.41 (d.040 and d.041 for newer boilers) will tell you the flow and return temperatures.

The only negative factor will be a slight reduction in output from the radiators.

I tried looking for parameter d.40 and d.41 on my existing Vaillant VRC 430 controller, but this only has parameters C1 to C26, unless there's another menu I'm not aware of.

 

[gmartine]

Where have you got an 11°c drop from? Most modern boilers look for a 20°c drop across the system.

The UFH?

God damn the min number of characters. Sometimes less is more.

 

[doitmyself]

Where have you got an 11°c drop from? Most modern boilers look for a 20°c drop across the system.

If you don't know where the 11°C drop comes from you are giving your age away! It was the standard before condensing boilers. Orginally it was 20°F which is 11.1111°C.

Unfortunately many condensing boiler were installed into existing systems already balanced for a 10/11°C drop and the installer did not understand the need to rebalance (or couldn't be bothered).
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I tried looking for parameter d.40 and d.41 on my existing Vaillant VRC 430 controller, but this only has parameters C1 to C26, unless there's another menu I'm not aware of.

The d. parameters are set/read at the boiler. You will find the information in the Installation Instrutions. If you don't have a copy, post the GC No from the data tag on the boiler, and someone will upload a copy

 

[milleniumaire]

Is it possible to combine a single, new 22mm supply and return to feed both the new bathroom UFH and the loft radiators? I've tried to show this in the following diagram:

This shows the new UFH manifold and thermostat on the 1st floor and a new 22mm feed to this from the boiler. I've also continued that new 22mm feed to the loft, but included a new valve. This valve would need to work in sync with the valve between the boiler and the ground/1st floor radiator circuits. All radiators in the house are controlled by a single thermostat in the hallway (shown as VRC 700 on the diagram). As every radiator has a TRV fitted, it is possible to use the TRV's to control individual room temperatures. They have worked this way for 22 years, so I'm happy for this to continue. I guess to have two valves working in sync, it's simply a case of connecting them both up to the VR 71 wiring centre using the same connections?

Why would I want to share a 22mm feed to the new bathroom UFH manifold and loft radiators rather than running two lots of 22mm pipe i.e. 4 pipes in total? Mainly due to the need to take large notches out of the joists. It's still not ideal having to notch the joists for 2 x 22mm pipes, but this is better than having to do it for 4 x 22mm pipes. Notching joists is necessary to get the pipes from the boiler end of the house to the bathroom/loft feed end of the house. Of course, this assumes that copper pipe is used. If plastic pipe was used, the joists could be drilled, but this still presents problems when doing this for 4 x 22mm pipes, rather than 2.

 

[oz-plumber]

There will be enough capacity from 1 set of 22mm pipes to run the UFH & the loft radiators.
I wouldn't bother running 2 sets of pipes to service each system individually.

 

[milleniumaire]

There will be enough capacity from 1 set of 22mm pipes to run the UFH & the loft radiators.
I wouldn't bother running 2 sets of pipes to service each system individually.

Thanks, I thought that would be the case.

Thanks for all the answers. I'm still a little unsure about the use of a LLH and additional pumps, but have arranged for the heating engineer to visit so we can discuss the design and hopefully arrange a date for the work to be done.