Dual Zone Heating dilema - advice sought

goodburger

Hi,
I have a house with electronic valves controling two seperate zones (Upstairs & Downstairs).
At the boiler, there's a standard mechanical timer and two seperate light switch type switches with neons. One turns on each valve for each zone.

I decided to add some more automation by changing the timer for an electronic one and in turn buying one that could seperately control each zone. I found it hard to identify a suitable product, but in the end decided to use a timer with 3 on/off points per day and with seperate control for heating and for hot water. The idea was to use the heating output as ZONE 1 and the Hot Water output as ZONE 2.

This all seemed fine until I went to wire it this morning. There MUST be another type of timer that I have failed to come across which can do what I need. The problem with the solution I have tried is to do with the boiler. The boiler needs to heat the water obviously, and it needs to do this in a situation of ZONE1 or ZONE 2 being on and in a case where both ZONES are on together. Therefore, a seperate third output is really required for the boiler.

Because the boiler is common, if I connect it to be powered whenever either zone is on, electricity being as it is, the boiler causes the whole circuit to become common and when only Zone 1 output is on, zone 2 becomes live too, and visa versa.

I can't leave the boiler on 24/7 and just use the timer to switch the valves for each zone on/off as this makes no economic sense.

The outputs are double pole, so I could create an arrangement with relays which fired the boiler but kept it electrically out of the equation regarding the zone valves, but this seems like too much trouble when there must be a product out there which does just what I need...

Has anyone heard of a suitable dual zone central heating timer that I could buy???

Many thanks.

the magician

Horstmann do a range of timers and controls.Am about to fit one myself, mother-in laws house has one and I't has 3 zones, downstairs,upstairs and water.http://www.horstmann.co.uk/ should have something suitable

Pete67

The usual way to do what you want is to use the timeswitches to switch the motorised zone valves only. Each zone valve has 2 auxiliary contacts that close when the valve is driven open. You use the aux contacts to switch on the boiler. If you have more than one zone valve, connect all the aux contacts in parallel so that any valve opening will enable the boiler, but not the other zones.

A nice refinement to the scheme is to put room thermostats on each zone, so that the heating is only enabled when the timeswitch is on and the room stat is calling for heat. You should probably add a third zone for HW controlled by another timeswitch and a thermostat on the cylinder set at 60C.

Programmable digital room thermostats are available which combine the function of timeswitch and thermostat simplifying cabling, and allow you to automatically have different temperatures in each zone at various times of the day.

JamesM

Normally with the system you have described, the 2 light switches would control the boiler and the water pump. Seperate thermostats would control downstairs and upstairs zone valves. The timer would switch on. If the 1st switch was on, only the water would heat. If both switches were on, the water pump would pump water to the rads.
The new timer you have seems to work the same way. The hot water setting will just bring on the boiler and the heating setting will bring on both the boiler and pump.
Do you not have thermostats for upstairs and downstairs ?
You can use a seperate timer for the boiler and pump, and other timers for the zone valves.
I am sure that there is a modern controler that will coordinate everything.
Jim.

goodburger

Thanks for the quick responses people, I'm shocked and pleased...

The two zones (upstairs and Downstairs) do have wall mounted thermostats which are in series with the valve on/off conrtrol switches. I had hoped to replace the function of these switches with the timer/controller.

Each rad on the system also has a thermostatically controlled valve, so it's a gem of a system, it's just the basic control that I want to upgrade by adding a digital timer, but at the same time retaining the flexibility of dual zones.

I'll investigate the suggestion of the magician, and consider the other ideas too, many thanks.

Pete67

If I understand correctly Goodburger wants to boiler to be enabled only when there is a demand for heat in either or both of the two heating zones. This is good practice and prevents wasting fuel due to the boiler cycling continuously when heating is not required.

To do this requires eithers some sort of basic control logic so that the following situations are catered for:

zone 1 valve open, boiler on
zone 2 valve open, boiler on
zone 1 and zone 2 valves open, boiler on
zone 1 and 2 valves closed, boiler off.

This requires the use of relay logic to prevent the situation where both zone valves open when the boiler is switched on. It is possible to use the aux contacts instead of relays for switching.

I'm assuming that the system is fully pumped, so the pump will be enabled with the boiler. Goodburger does not mention how the hot water heating is handled but it can easily be treated as a third heating zone. There are also electronic 3 zone controllers with seperate pump and boiler outputs which can do this type of control but they are not common in domestic systems, probably due to cost.

copper12

Boiler should have a permanent and a switched live
If you boiler’ only has a permanent live’ then any other controls; have to be wired from the boiler and not the insulation switch .
You seem to all ready have all the right controls; there should not be a problem’ to wire this up’ so you have your automation .
If your boiler has a switched live
3 amp isolation; switched on; permanent live to the boiler
There will most likely be another live taken from the isolation to the timer switched live
From there to your light switches; heating and hot water; and to the thermostats’ from there if there’s a call for heat to the boiler .
Works slightly different if you have it wire from the boiler but not much .
From what I can gather you all ready have the zone valves and thermostats in place.

10-10-20

I assume you have five wires coming from the valves? (mine didn't, I had to run the switched wires myself...)
Live, neutral and a switched pair or triplet?

http://content.honeywell.com/uk/homes/Catalogue/Heating%20Controls/2.19%20V4043.pdf

If so, the switched pairs need to be in parallel with each other. One end of these will connect into the switched-live section of the boiler, with mains-live on the other end.
Once you have that operating correctly, you then have the basis of control.

corkonian0110

Hi all -

I have a similar (ish) problem with heating control.
Basic set up is a pellet boiler + controller & pump located in garage. Time clock located in hot press upstairs. 7 under floor zones upstairs and 7 underfloor zones downstairs. One pump for hot water cyclinder, one pump of upstairs underfloor, one for downstairs underfloor. Stats control the actuators on the manifolds.

My time clock has 2 outputs, one for HW one for CH.
At present the boiler is controlled from the timeclock - basically when set time occurs the live feed out to sockEt in garage to power up the boiler.

So heating called for at 7am, power goes from TC to feed boiler and underfloor pumps.
or alternately hot water called for , power feeds boiler and hot water cyclinder pump.
since I have only one common feed to boiler adjacent to the timeclock, both underfloor heating and hot water cylinder pumps come on together.

Can this be solved by the use of relays of some description?

10-10-20

Yes, you can solve this with a few relays. I used one to isolate the hot water system while the heating is on.
You will first off need to separate the elements in the setup (pumps for heating, pump for hot water).
Then, figure out whether your boiler is using the feedback from the room stats to cycle (on/off), or is it just working off the temperature of the returning water (not ideal).
Then use the outputs of the TCs to drive corresponding relays, remembering that you may at some time need both heating a hot water on at some time.

Post up a diagram of the setup with the main elements and we may be able to assist further.

copper12

Normal set up for central heating and hot water
[Isolation switch] [timer control clock ][thermostat room and cylinder stat] switched live to boiler and pump in that order
This would be separate from the permanent live to the some boiler’s?
pump may need to be wired from this in order for the pump overrun to operate if it has one incorporated

fishdog

I did a drawing a while ago showing the wiring for a 3 zone heating system. You can find it here it is post #6

This can be easily adapted for similar systems. If you need it changed to suit your requirements feel free to PM me.