Extended S plan with 5 channels 2 pumps

[ToolGuy]

In a large old house with 22 radiators with pressurized system need to replace the boiler and install controls. Plan on installing Worcester Greenstar 40 CDi or Vaillant ecoTEC plus 438 boiler. Thinking of Danfoss Tp9000Si Programmable Room Thermostat upstairs, Sunvic Select 307XL 3 channel programmer downstairs.


It has Megaflow DHW with its thermostat and pump and due to the layout of the house the only sensible CH zoning will be to have three sub zones off one main heating one using S plan plus.


Plan is separate pump for CH then 2 port valve to all the heating with 3 other 2 port valves separating secondary zones off this. The 1st primary zone can provide general background on ground floor, 2 zones can independently add extra rooms on the ground floor, the 3rd zone add in heating for upstairs.


Plan a 2 channel room stat to control upstairs CH and DHW. Three channel programmer and 1 room stat to control the 3 zones (main background plus the extra rooms). Question is how to wire it to prevent feedback loops to zone valves and allow pump overrun for the correct pump (DHW or CH) while holding open only the correct valve.


None of the programmers seem to have enough sense built in to handle this sort of situation so suggestions on programmers also welcome.


Thanks.

 

[TheGasEngineer]

OK I received your layout drawing. Thanks. I'm amazed. The idea of zones is that they are independent. I understand this is a family home. You want controlled heating and to make it efficient as possible, capital cost permitting.

The DHW is a zone in its own right and will therefore look after itself. I suggest you use a simple timer linked to the cylinder stat and probably located in the airing cupboard. I find that people rarely advance the hot water unless there is an unusual demand or if it is badly designed but that's another issue.

Unless there is an unusual heat demand in the various rooms or areas I suggest you ignore all the valves and only control the pump via a rooms stat / timer / programmer so that makes life ultra simple for you. A system should be set up so that when the control room (as I call it - the one with the stat) gets to temperature the balancing has ensured all the other rooms have already reached temperature. You banance rads (with a condensing boiler) by setting the return to 55degC. I do it by gauging the temperature of cold side of the rad by hand. The aim to get the return to the boiler down to 55degC or so.

The problem in a big house, when one room (one stat) determins when the heating is on/off, is that small inbalances can result in cold rooms. To improve the degree of control you need separate zones, but you haven't so you can't.

However, and this is where capital cost applies; Honeywell's CM-Zone will give separately zoned areas but all on the same pipe (like yours) but at a cost. I've not looked to see whether any of the limitations would limit its effectiveness for you.

There is a boiler with a flow sensor (like the BAXI 100HE - but leave that one alone!) which does not need a room stat to give the pump interlock. That's provided by the flow switch. It runs the pump periodically and if there is flow it fires. If not it hibernates for a few minutes. This allows all TRVS to be off manually or off because rooms are at temperature. It must be possible to rig up an flow switch box with a timer to fit to a heating system where the boiler does not have this switch. A good project. I would try using the flow switch from the Baxi 100HE; it would work a treat.
HTH

 

[doitmyself]

You balance rads (with a condensing boiler) by setting the return to 55degC. I do it by gauging the temperature of cold side of the rad by hand. The aim to get the return to the boiler down to 55degC or so.

I hope you take into account the reduction in radiator output when the return temperature is reduced. A rad with a 75C flow and 55C return will produce about 80% of the quoted output. So rads have to be upsized by about 25%.

 

[oldplumber]

why not simplyfy things and use programable trvs that are now available, reducing the need for addl valves and stats over several floors and rely on a more normal/simple system
Irealise u need 2 zones for 150m2 areas but it might be easier to work out on an older layout

 

[TheGasEngineer]

why not simplyfy things and use programable trvs...

See CM-Zone CM Zone - Honeywell UK Heating Controls

 

[fuzzy]

what you are trying to achieve is bordering on light commercial , if you have room i would install a 54mm loop header in the boiler room with each zone branching off this controlled via individual programmable room stats and zone valves , with the header on its own programmer . this would give a constant temp and control.

can you post a sketch of this please

 

[fuzzy]

I hope you take into account the reduction in radiator output when the return temperature is reduced. A rad with a 75C flow and 55C return will produce about 80% of the quoted output. So rads have to be upsized by about 25%.

modern rad schedules take into account cooler flow and return rates so no need to do this

 

[TheGasEngineer]

I hope you take into account the reduction in radiator output...

Radiators only have to be upsized if their output is too low. The factor is (DTd/DTm)^1.3 where DTd= design temp diff; DTm= manufacurers temp diff which gives (45/50)^1.3= 0.87 ie at a DTd of 45degC the rads would give 13% less heat if reading values from a table based on a DTm of 50degC. This shows why it is so important to do the calcs. At least you know if the system stands a chance of performing.

 

[doitmyself]

modern rad schedules take into account cooler flow and return rates so no need to do this

That might be true of commercial installations and large new-build housing developments where the design of the heating installation will be sub-contracted to large H&V companies. But I doubt if many self-employed plumbers or small heating companies would know where to begin.

And if you are just changing the boiler, you are stuck with the in-situ rads. Hopefully they will already be oversized, due to generous sizing in the first place or improved insulation since they were installed.

 

[doitmyself]

Radiators only have to be upsized if their output is too low.

Agreed. But isn't that stating the obvious?

The factor is (DTd/DTm)^1.3 where DTd= design temp diff; DTm= manufacurers temp diff which gives (45/50)^1.3= 0.87 ie at a DTd of 45degC the rads would give 13% less heat if reading values from a table based on a DTm of 50degC.

Presumably you are referring to the difference between mean radiator temperature and room temperature. It assumes that the actual flow and return temperatures are irrelevant, which is not correct.

Take a rad whose output has been measured using the BSI standard temperatures of 75°C/65°C/20°C, ie rad mean of 70°C and differential of 50°C. If it is run at 75°C/55°C/20°C, ie, mean of 65°C and differential of 45°c the output will reduce to 85.7% of the manufacturers quoted figure.
If it is run at 70°C/60°C/20°C, which is still a 65°C mean and 45°C differential the output is now 87.1% of stated figure. If it is run at 65°C/55°C/20°C, mean of 60°C, differential of 40°C the output will be 74.6% of stated output.

The temperature table given in radiator catalogues assume the radiator temperatures stay constant at 75°C Flow and 65°C Return; only the room temperature changes.

The coefficient, which you have given as 1.3 is not constant. It varies with type and size of radiator. Using Stelrad Elite as an example, it varies from 1.23 to 1.34. I have used 1.3 in my calculations.

 

[fuzzy]

presuming a room temp of 20 c

 

[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.