2 DHW tanks, 2 heating zones, 1 set of controls

[Miek]

Hi Plumbers. 

 

I have a situation with 2 separate dwellings (one house split in two) one of which has a Y plan heating system running of an oil fired system boiler. 

 

I would like to use this boiler to run both dwellings if possible, so that means 2 DHW tanks, and 2 CH circuits.  

 

What's the best approach? 

The least complex the better as the house is inhabited by elderly technophobes. 

 

Thanks in advance

Mike

[dpmiller]

use a UFH controlbox to accept requests from each house (via it's 'stat inputs), with motor valves driven off the actuator outputs and the boiler driven by the boiler output. Heat or DHW request on any input will bring the boiler and it's circ pump on.

[ProDave]

Do it all with 2 port valves.  So there will be 4 of them, HW to each house, and heating to each house.

 

Each house can have it's own electrical controls and it's own programmer driving it's own pair of 2 port valves.

 

Then when ANY of the 2 port valves is activated, the boiler and pump will fire up.

 

How are they going to split the fuel bill for this arrangement?

 

 

[Ed Davies]

I'd agree with @ProDave, convert to S-plan. Keep the wiring for the two houses as separate as possible. It'd save some theological arguments about earthing, etc, if each house's pair of two-port valves were in their own house and the call-for-heat signal from the new-to-the-system house was passed to the old house via some wireless mechanism or other. Avoids having a wiring centre needing to be isolated from two separate supplies to be safe to work on. Remember that the two houses might not now, or in the future, be on the same mains phase.

[Miek]

2 hours ago, ProDave said:

Do it all with 2 port valves.  So there will be 4 of them, HW to each house, and heating to each house.

 

Each house can have it's own electrical controls and it's own programmer driving it's own pair of 2 port valves.

 

Then when ANY of the 2 port valves is activated, the boiler and pump will fire up.

 

How are they going to split the fuel bill for this arrangement?

 

 

OK, that sounds simple enough for me to do. 

 

If all four valves are open and asking for heat, will it be necessary to balance the circuits in some way? Obviously pipework will have different resistance to flow. Maybe a non issue... 

 

Re : oil usage. That's for then to decide thankfully, I don't think metering the oil is workable or worthwhile. 

 

51 minutes ago, Ed Davies said:

I'd agree with @ProDave, convert to S-plan. Keep the wiring for the two houses as separate as possible. It'd save some theological arguments about earthing, etc, if each house's pair of two-port valves were in their own house and the call-for-heat signal from the new-to-the-system house was passed to the old house via some wireless mechanism or other. Avoids having a wiring centre needing to be isolated from two separate supplies to be safe to work on. Remember that the two houses might not now, or in the future, be on the same mains phase.

 

Seperating the wiring would be sensible, but the pump and boiler are usually fed from the wiring panel, so how do I separate the two if there are 2 wiring panel on the new system? 

 

[Ed Davies]

Wire the old house up as normal for a 3 x 2-way valve S-plan system except that the third call-for-heat input comes from the paralleled-up microswitch connections on the new house's wiring panel, either directly or via a relay or wireless connection.

[ProDave]

Isolation is a good point.  The problem is having a live source from 2 houses at one of the wiring centres.

 

Make sure each house has it's own wiring centre to take care of the thermostats, time clocks and actuating the motorised valves.  Use a (probably modified) wireless thermostat system to send the "call for heat" from each houses motorised valves to the boiler from the 2 properties.

[Miek]

4 hours ago, Ed Davies said:

Wire the old house up as normal for a 3 x 2-way valve S-plan system except that the third call-for-heat input comes from the paralleled-up microswitch connections on the new house's wiring panel, either directly or via a relay or wireless connection.

I think I get what you mean.. 

 

House 1 is used to power the boiler and pump as normal. House 2 uses its call for heat to switch a relay on house 1 pump and boiler wiring. So the relay provides electrical  isolation of the two systems. Correct? 

 

Or, a wireless system such that either house 1 or 2 call for heat triggers the pump and boiler ON.

 

[Ed Davies]

Yes. House 1 (with the boiler in it) wouldn't actually need a wireless transmitter, it could be connected direct to the boiler, of course.

[PeterW]

Consider using Low Voltage ie 12v to connect the two houses. All off the shelf and gets you out of the hassle of having phase issues and so on. 

 

The zone valve micro switches will cope with it as it’s low current and you’re talking about running something like bell wire between house 1 and house 2. 

[Ed Davies]

I like that.

 

You don't even need to put the DC through the microswitches. OK, it's a tiny current so won't affect the contacts but it's still nicer to keep the wiring as separate as possible.

 

House 2 is a normal 2-zone S-plan except that the line (or switched line) which normally goes to the boiler instead goes to a socket with a 12V (or whatever) output wall wart. Wires from that go through to house 1 to the 12V coil of a relay. House 1 wiring is also standard 2-zone S-plan except that the normally-open contacts of the relay are wired in parallel with the valve microswitches.

 

A minor advantage of doing it this way is that the DC supply is only turned on when house 2 is calling for heat.

[Miek]

Thanks folks

 

A 12v relay sounds a simple solution, I like that.