Extended S plan with 5 channels 2 pumps

[doitmyself]

presuming a room temp of 20 c

Agreed. I didn't want to make the examples too complicated.

 

[ToolGuy]

The house is just a large domestic one needing a new boiler. The plumbing has been in place about 17 years, originally with two zones DHW & CH. New building regs specify the CH has to be split into two zones. Two zones is of limited practical use so the idea of sub zones.


I had considered Honeywell's CM-Zone system, programmable trvs, “OpenTherm” and computer controlled lan ideas but all way too expensive. I know zones are normally independent but not entirely possible here while sub zones would give some reasonable user control.


Heating controls don't seem to have progressed much in 30+ years and with the fall in electronics prices haven't controls haven't followed the downward prices. With the new building regs and push for more controllability more complex systems really need to arrive at lower cost.


I'm attaching (or at least trying) a schematic of this system.

 

[doitmyself]

The house is just a large domestic one needing a new boiler. The plumbing has been in place about 17 years, originally with two zones DHW & CH. New building regs specify the CH has to be split into two zones. Two zones is of limited practical use so the idea of sub zones.

If all you are doing is replacing the boiler, there is no requirement to have two zones. TRVs are recommended as the system will be drained down, provided the pipework does not have to be altered.

I had considered Honeywell's CM-Zone system, programmable trvs, “OpenTherm” and computer controlled lan ideas but all way too expensive.

Opentherm should be much less expensive than the others. You will need an OT compatible boiler, but then you can use any brand of OT control.

I know you have thought of an open vented boiler (40CDi or 438), why have you discounted a system boiler? Have a look at the Remeha 39C. It is a combi boiler, which can be configured to act as a system boiler and can use Opentherm controls.

I don't see why you need a separate pump for the HW. Provided the pump is immediately after the boiler and is correctly sized, and an automatic bypass valve is incorporated into the system, only one pump should be necessary.

 

[ToolGuy]

If all you are doing is replacing the boiler, there is no requirement to have two zones.

My understanding of regs was:

The latest Building Regulations Part L1 specifies that in new houses with a total heated living space floor area of over 150m2 the heating circuit must be split into two, fully controlled, separate zones along with the fully controlled hot water zone.

OK, TRVs could be used throughout but then no separate time controls.

Separate pumps not NEEDED but quicker DHW recovery times when CH is also in use and separates out balancing in the DHW circuit with the heating circuits. doitmyself gave a good schematic wiring for multiple zones. It looks like some of the underfloor heating controllers have provisions to allow 2 pumps so I think we are about finished on this.

 

[doitmyself]

The revised Guidance, does seem to be very draconian, suggesting that all properties have to be divided into two heating zones. Under 150m² they only need separate temperature control;over separate temperature and time control. This also appears to apply to existing systems when a component is replaced. In many cases this will be virtually impossible with out major surgery to the pipework.

On the matter of temperature control, the Guide says:

When an individual system component - such as a boiler or room thermostat - is being replaced, it is not necessary to upgrade the whole system. However, while not essential for compliance with building regulations, in the case of a boiler replacement, because the system has to be drained down, it would be good practice to install thermostatic radiator valves (or equivalent) on all radiators other than in the room with the main thermostat, provided the radiators are suitable and pipe work does not need to be altered. (Domestic Building Compliance Guide, October 2010. page 24.)

There is no similar get out for time control in over150m² installations. However I would not be surprised if an amendment sheet were to be issued fairly soon - they brought one out for the last edition - correcting the inevitable errors.

I can see where you are coming from with the HW pump. It will probably need to be set to speed 1.

 

[ToolGuy]

First I would like to thank everyone who has made helpful suggestions, but particularly doitmyself and TheGasEngineer who took a lot of time understanding this system. Will soon have to go back to the actual system to do something. It looks like will have to simplify the controls and not give the desired flexibility as control systems are just not up to it unless going to rather more modern esoteric controls out of the home automation league.


With the (maybe OTT) current building regs two and three channel programmers should be the norm, almost no call should exist for single channel, four or more channels should be common. Boilers should be able to handle two pumps separately if they need overrun. Maybe if OpenTherm or similar ever catches on in the UK controlling heating will come into the 21st century.