Zone Heating with 3-Port Valves very complicated

[deemoss]

Hi,

According to http://www.diyfaq.org.uk:

"If the idea of heating different areas of the house in different ways interests you then you'll need to look at 2-port valves for each zone. Doing this sort of thing with 3-port valves gets very complicated."

This is exactly what i want to do. Why is it very complicated?

I have 2 zones, radiators only - no cylinder for hot water. Zone 1 will be heated 80% of the time and zone 2 only 20% of the time. If I employ the traditional 2 x 2-port S-Plan any time the heating is on at least valve will be energised. It looks easy to implement but not very efficient.

The Y-Plan on the other, will have one port open (zone 1) by default, so 80% of the time it will not be energised. In this case the valve will consume power only if zone 2 or both zones call for heating. I see this implementation more elegant.

However, the 5-wire wiring schemes of the 3-way mid-position valves take into account the difference between the wiring of the room thermostat and the cylinder thermostat, i.e. the cylinder thermostat (which I don't use) supplies a signal to the 3-way valve when it calls for heat AND when it is satisfied.

Ideally, the valve would behave like this

Zone 1 calls for heating

• Valve Port A open by default (not energised)
  Boiler and Pump powered

Zone 2 calls for heating

• Valve Port B open (energised)
  Boiler and Pump powered

Zones 1 and 2 call for heating

• Valve Port A and B open (energised)
  Boiler and Pump powered

No call for heating

• Valve Port A open by default (not energised)
  Boiler and Pump stopped

Is it possible to wire or modify a standard 3-way mid-position valve to behave like this?

Thanks in advance

 

[twgas]

with no hot water to worry about a 3-port valve would be fairly simple to connect, both electrically and the pipework. However, if you have a combi the wring may be more complex due to the fact that a lot of combis use "volt free" room stat connections.

 

[doitall]

Why would an S plan be less efficient than a Y plan.

A Honeywell 2 zone kit, piece a cake. Job done.

 

[D_Hailsham]

Ideally, the valve would behave like this

Zone 1 calls for heating

• Valve Port A open by default (not energised)
  Boiler and Pump powered

Zone 2 calls for heating

• Valve Port B open (energised)
  Boiler and Pump powered

It's the other way round: Port B is open when valve is not energised; Port A only opens when power is supplied to two valve wires.

So zone 1 (80%) would have to be connected to Port B and zone 2 (20%) to port A.

But as twgas said, you can't do this if the boiler uses volt free connections.

Which boiler do you have (make and model)?

 

[doitall]

The end switches are volts free, or you could use volts free relays.

 

[dcawkwell]

The electric consumed by a 2 port valve is small and not worth
worrying about.

2 port valves. You can then wire these up to individual room thermostats
Job done. Why make life hard life is too short.

 

[Agile]

The OP imagines the 6 w consumed by the valve motor is significant when supplying 6000 w of heating.

He also imagines that 6 w is totally lost and does not contribute towards heating the property.

Tony

 

[deemoss]

6 w is totally lost and does not contribute towards heating the property.

But also, I guess one valve is more reliable than two...

 

[D_Hailsham]

The electric consumed by a 2 port valve is small and not worth worrying about.

It may be small but Honeywell do say:

Continuous operation of the valve motor at the fully open position is not recommended

If a valve is open 80% of the time it is, essentially, permanently open.

However the OP seems to have forgotten, or not realized, that a zone valve will open and close under the control of the room stat as well as the programmer. So the valve is not open 80% of the time.

 

[deemoss]

So zone 1 (80%) would have to be connected to Port B and zone 2 (20%) to port A.

Correct, I guess mechanically ports A and B are identical so I can switch sides.

But as twgas said, you can't do this if the boiler uses volt free connections.

Which boiler do you have (make and model)?

The only thing I know is that the boiler manages the pump, and is turned on by a 220v signal (so it's not volt free). At the moment there is gust one room thermostat connected straight to the boiler. It has been working like this for years.

 

[deemoss]

The end switches are volts free, or you could use volts free relays.

The boiler comes alive with a 220v signal from a single room thermostat.

So I guess my problem is: How to connect 2 room thermostats, instead of 1 room and 1 cylinder thermostats to a standard mid-position 3-way valve.

 

[Agile]

Using two zone valves is the standard way to provide two zones and they can be manually opened if they fail every eight years!

The ONLY advantage of a three port valve is its cheaper!

Tony

 

[doitall]

Easy use the right room stat, or a 3 port valve with a changeover switch.

 

[dcawkwell]

The electric consumed by a 2 port valve is small and not worth worrying about.

It may be small but Honeywell do say:

Continuous operation of the valve motor at the fully open position is not recommended

If a valve is open 80% of the time it is, essentially, permanently open.

However the OP seems to have forgotten, or not realized, that a zone valve will open and close under the control of the room stat as well as the programmer. So the valve is not open 80% of the time.

It will only be open while the boiler is heating until the room reaches temperature. It will then close. Only if the heating system is underspec
and cannot get to temperature would the valve be open. At most the valve will stay open a couple of hours and then close until the thermostat calls for more.

 

[D_Hailsham]

However the OP seems to have forgotten, or not realized, that a zone valve will open and close under the control of the room stat as well as the programmer. So the valve is not open 80% of the time.

It will only be open while the boiler is heating until the room reaches temperature. It will then close. Only if the heating system is underspec and cannot get to temperature would the valve be open. At most the valve will stay open a couple of hours and then close until the thermostat calls for more.

Isn't that what I said?