Three Port Plus Two Port

[NoSparks]

An extension of a heating system requires the flow and return to be connected BEFORE a three port control valve (similar to a by pass). The extension needs therefore to be controlled by its own two port zone valve. Where should the CH demand signal be taken from?

At first site the white wire on the three port valve would be the obvious point, but does this go up to 120 volts when the HW comes on? and what would the effect of this be on the 2 port valve?

Geoff

 

[Gasguru]

If you connect a 2 port valve (for the extension) before the 3 port, when the extension has a heat demand the water will still flow through the cylinder circuit.

Cut out the 3 port and use 3x 2 ports. I assume you are adding another timeclock/programmable stat for the new extension or upgrading the existing clock to 3 channels + room stat. You may also need an auto bypass valve.

 

[NoSparks]

That would be a whole new ball game!

No, what I was proposing was simply a two port valve that opened when the CH port of the three port valve was open. ie no additional room stat, etc.

 

[Gasguru]

No, what I was proposing was simply a two port valve that opened when the CH port of the three port valve was open. ie no additional room stat, etc.

So it's not an independent zone and can't be controlled by a timeclock/stat. What's the point then? Just stick TRV's on the new rads. Regulations only require additional heating zones over a certain sized floor area/conservatory.

 

[NoSparks]

Lets go back to the requirement.

We are adding two additional radiators which because of the topology of the system will be connected to the flow and return BEFORE the three port valve.

We do not wish these new radiators to come on unless the central heating is switched on. That is we do not want the radiators to come on when there is only a demand for hot water.

To control the new radiators we will be using a zone control valve. The question is

a) Is there any better point in the wireing to take the CH demand from other than the white wire of the three port valve.

b) The white wire of the three port valve will become half wave rectified and have some resistance in circuit providing a 120 volt signal of limited power when there is a demand for water only. What effect would this have on a zone valve? Possible answers may be
Nothing.
Drives the port open.
Burns out the zone vale motor.
it may also
Burnout the resisters and diode in the three port valve
Cause the three port valve to malfunction
and maybe others.

Does anybody have any experiance of trying this?

 

[muggles]

Surely what you're proposing will cause a bypass to the main system?

 

[D_Hailsham]

b) The white wire of the three port valve will become half wave rectified and have some resistance in circuit providing a 120 volt signal of limited power when there is a demand for water only.

It's not the white wire which has 120v but the orange. You need to read Mid-position valve working and Diagnostics

From what you say, both the 3-port and the new 2-port will be controlled by the same thermostat. The two port valve has four wires: brown and blue (neutral) control the motor, which opens and closes the valve; grey and orange are the internal switch, which closes when the valve opens. This switch normally supplies power to the boiler, but is redundant in your case as the boiler is controlled by the 3-port valve.

All you need to do is connect the white wire to the thermostat call terminal (same as white of 3-port valve) and the blue to neutral, the other two wires are redundant.

 

[D_Hailsham]

Surely what you're proposing will cause a bypass to the main system?

Not if the system is properly balanced; though I would not like the job as it may need balancing valves in the flow to each CH zone.

The OP is proposing a modified S-plan plus, but with a mid-pos valve in place of the two zone valves for the HW and one CH zone and with both CH zones controlled by the same thermostat.

 

[NoSparks]

Muggles: It would if it were not controlled by a zone valve, which is why I am investigating how to install one.

D_Hailsham: Your right, the system will need balancing, but I had assumed I could do this using the Lock Shield valves on the extension Radiators.

D_Hailsham: The reference I have been looking at is hhtp://www.gasheating.co.uk/Mid-Position-Valve.html which shows the internal interconnection. In the Water only position the Gray is disconnected and the Orange is made live (240v). The motor will not normally run because the power available via R2, and R1 is insufficient to drive the motor. However, a half wave rectified signal will be available at the White wire via R2 and D1. The problem is I have no idea of the relative values of R1 and R2 nor the power handling capacity of R2 and D1. It seems probable that they would be matched to their intended purpose which could mean that they burn out if another motor is added. conversely the value of R2 may be sufficiently large that they don't burn out, but in that case what will be the effect of the half wave rectified signal on the additional motor? will it become permanently magnetised (what the reference calls "magnetic stiction"?

I was hoping that somebody might have tried it and been able to advise me!

 

[simond]

Would your time not be better spent designing a two legged stool? You proposed solution is a lash up and the current leak will be insufficient to power the synchronous motor.

You simply add your two port and connect the red/grey switched output from this and the orange wire from the three port into a relay (contactor) to feed the boiler 'on'. This way either valve can create a demand.

The two port valve will need to be actuated via a room stat in the new extension area.

Your problem is a hydraulic one. The three port is always open in one direction at least, so when your two port is calling for heat, the tree port is going to get it too.

By far the best solution is to replace the valves with two ports and I cannot for the life of me understand why you would want to install such a cr*p system when the solution is staring you in the face.

 

[D_Hailsham]

The two port valve will need to be actuated via a room stat in the new extension area.

If you read what the OP has written it is clear that he wants both circuits controlled from the same thermostat. So the new zone valve will only be open when the MPV is in either the CH only or the mid-position. It will be closed when the MPV is in HW only position.

I cannot for the life of me understand why you would want to install such a cr*p system

Again the OP has given the answer to this. It is physically impossible to connect the new rads after the MPV. Why, I don't know. Presumably something to do with the layout of his house.

To the OP

If I am correct about the common thermostat, all you need to do is connect the Blue wire of the new Zone Valve to neutral and the Brown wire to the same terminal as the white wire of the MPV. The other two wires on the Zone valve will not be used.

If the Room stat is calling for heat, the White wire will always be live and so will the brown wire. The voltages on the Grey and Orange wires are not relevant. So, if the Brown wire of the Zone Valve is connected to the same terminal as the white wire, the motor on the zone valve will run and open the zone valve. When the Rooms Stat reaches the required temperature, or the CH is turned off, the White wire and the Brown wire will do dead, the Zone Valve will close and the MPV revert to the HW only position.

 

[D_Hailsham]

D_Hailsham: Your right, the system will need balancing, but I had assumed I could do this using the Lock Shield valves on the extension Radiators.

You may find that the LS valves on the new rads will have to virtually closed to have any effect. A balancing valve in the flow to the new rad circuit would increase the resistance in the circuit, making it easier to adjust the LS valves.

D_Hailsham: The reference I have been looking at is http://www.gasheating.co.uk/Mid-Position-Valve.html which shows the internal interconnection.

Bad diagram, bad explanation.

In the Water only position the Gray is disconnected and the Orange is made live (240v).

When HW ONLY is required, the boiler is provided with 240v directly from the HW stat. The fact that the orange wire reads 240 is irrelevant; it only happens because the orange wire is connected to the same terminal as the boiler and HW stat.

The motor will not normally run because the power available via R2, and R1 is insufficient to drive the motor.

These resistors are there to prevent the motor turning when the orange wire gets 240v from the HW stat.

However, a half wave rectified signal will be available at the White wire via R2 and D1. The problem is I have no idea of the relative values of R1 and R2 nor the power handling capacity of R2 and D1. It seems probable that they would be matched to their intended purpose which could mean that they burn out if another motor is added. conversely the value of R2 may be sufficiently large that they don't burn out, but in that case what will be the effect of the half wave rectified signal on the additional motor? will it become permanently magnetised (what the reference calls "magnetic stiction"?

This is not important.

View media item 4485To quote from the explanation in the link quoted

So the valve can be in three states, as follows:-

1. De-energised:- Where the spring pulls on the valve, closing off the Central heating port thus corresponding to a hot water only position, (correct!) If the power is off, all the wires are dead, if the power is on, but we are not calling for hot water or central heating, the gray wire will be live, via the controls as above.(correct!) When we are calling for hot water, then the controls energise the orange wire and de energise the gray, (correct!) thus firing up the boiler and pump (not correct! The boiler fires up because the HW stat is providing 240v direct to the boiler, NOT because there is 240v on the orange wire)The motor will get a small current, through both resistors, but the two resistances combined are enough to ensure the motor does not turn.(Correct, the purpose of the resistors is to prevent the motor turning when 240v is supplied to the orange wire from the HW stat)

2. Fully energised:- where the motor has wound up tight and closed off the hot water port, corresponding to the Central heating only position. The control arrangement makes the White live, the grey live and the orange off. The orange wire is only temporarily off however. As the motor opens the valve and throw the switches, first, sw1 changes over, from the white to the grey, Following the wiring diagrams, you will see the motor still gets full power via the grey wire, and hence continues on, tripping sw2 thus energising the orange wire, via the white. (correct! In this case the boiler is supplied with power via the Orange wire, NOT from the HW stat)

3. Mid position:-, (The CH and HW position) The controls make the white (correct!)and orange wires(wrong!) live and the gray off (correct!). If the valve is already closed (HW only ), then the motor will be fed power initially via the white wire, when it switches sw1 (at mid position), Power comes via the white supply through SW2, half rectified through the diode and reduced by R1 via the white wire, effectively stalling it at this mid point (correct!), corresponding to both heating and hot water.
(In mid position the boiler is supplied with power from the HW stat NOT from the orange wire)

 

[NoSparks]

I think your analysis of the original article is a little harsh. In the first instance where you "disagree" I believe you actually agree. Yes the power (current) is supplied from the Cyl Stat to the boiler, but it is also true that in the process the orange wire becomes live (240 volts) as in the article.

Exactly the same in your second disagreement. The orange wire is made live even if it is not the source of power for the boiler.

I do agree that the original article could have been presented somewhat better by following a proper state transition diagram.

I'm not sure that your statement that "These resistors are there to prevent the motor turning when the orange wire gets 240v from the HW stat. " Is entirely true since the same would apply if R2 were omitted entirely.

However I assume from your statement that the covert path from the orange wire via R2 and D1 to the white wire, and hence to my additional motor "is not important" means that it is safe to do so, so I'll give it a try.

Thanks for your help.

 

[D_Hailsham]

In the first instance where you "disagree" I believe you actually agree. Yes the power (current) is supplied from the Cyl Stat to the boiler, but it is also true that in the process the orange wire becomes live (240 volts) as in the article.

But what the author wrote, without my comments, is:

When we are calling for hot water, then the controls energise the orange wire and de energise the grey, thus firing up the boiler and pump

This implies that the boiler is fired because two things happen: the orange is energised and the grey de-energised. The events are true, but they are not the cause of the boiler igniting.

Exactly the same in your second disagreement. The orange wire is made live even if it is not the source of power for the boiler.

The only time the orange wire serves any useful purpose is when the valve is in the CH only position. It then is the only source of power to the boiler. Ideally the orange wire should be disconnected from the boiler, except when it is needed. I suppose a relay or something similar could have been used, but this would have added to the cost and complexity. The solution was to put a high resistance R2 between the lower contact of SW2 and the motor. The motor then does not get sufficient voltage to run from either the orange wire or from the white, when SW2 has switched over.

I'm not sure that your statement that "These resistors are there to prevent the motor turning when the orange wire gets 240v from the HW stat. " Is entirely true since the same would apply if R2 were omitted entirely.

Surely that would depend on the relative values of R1 and R2?

However I assume from your statement that the covert path from the orange wire via R2 and D1 to the white wire, and hence to my additional motor "is not important" means that it is safe to do so, so I'll give it a try.

You have raised an interesting point. The motor stalls in mid position because it is provide by half-wave rectified voltage via D1 and R1. The orange wire supplies voltage to the D1 via R2, but in the opposite direction, so the output, on the SW2 side of D1 will be much less. If this was not done there, the voltage on the white wire would be dirty, feeding back to the CH thermostat etc.

 

[NoSparks]

So are you now saying that you are uncertain if the "dirty" signal on the white wire may cause problems with the second motor or that the second motor could cause R2 / D1 to burn out? If so I am not prepared to spend £100 plus just to try it.