Relay switches

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Please excuse my complete lack of protocol in this diagram. What this does is as follows:

CH and HW at the top refer to 240V outputs from my heating programmer. The CH and HW outputs go through relay switches which are connected to a zone valve which controls hot water coming in to the building and a pump signal which switches the export pump pumping that hot water on and off. The relays work in such a way that if either the HW or the CH (or both) are calling for heat the zone valve will open and the export pump will come on. It all works well. But...

I now want to add an extra condition to this setup. Basically, there is a buffer tank in the house which stores up hot water. It will charge up with a charge pump using excess heat when the VZ is open and the export pump is on, and then, when it is fully charged the charge pump will switch off and I want it the ZV to close and the export pump to switch off. The heat from the buffer tank will then be used up by circulating that water with separate circulating pumps (not show here for simplicity and controlled by the heating programmer). Once the buffer tank is fully discharged I want the zone valve to open and the export pump to re-start.

I'm happy wiring the buffer tank charging pump to stats at the top and bottom of the tank to switch the charging on and off. I am unsure though of how to wire this into the relay setup. I think I may need another relay switch?

ZV and export pump:
Opens / switches on when CH or HW calling for heat and top buffer tank stat is below temp
Closes / switches off when bottom buffer tank reaches required temp

Charge pump:
Comes on if ZV open and export pump is on
Switches off if bottom buffer tank stat reaches required temp.

Below is a picture of my relay switches:

//media.diynot.com/121000_120756_94611_11336986_thumb.jpg
 
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//media.diynot.com/121000_120756_94609_21610927_thumb.jpg

Please excuse my complete lack of protocol in this diagram. What this does is as follows:

CH and HW at the top refer to 240V outputs from my heating programmer. The CH and HW outputs go through relay switches which are connected to a zone valve which controls hot water coming in to the building and a pump signal which switches the export pump pumping that hot water on and off. The relays work in such a way that if either the HW or the CH (or both) are calling for heat the zone valve will open and the export pump will come on. It all works well. But...

I now want to add an extra condition to this setup. Basically, there is a buffer tank in the house which stores up hot water. It will charge up with a charge pump using excess heat when the VZ is open and the export pump is on, and then, when it is fully charged the charge pump will switch off and I want it the ZV to close and the export pump to switch off. The heat from the buffer tank will then be used up by circulating that water with separate circulating pumps (not show here for simplicity and controlled by the heating programmer). Once the buffer tank is fully discharged I want the zone valve to open and the export pump to re-start.

I'm happy wiring the buffer tank charging pump to stats at the top and bottom of the tank to switch the charging on and off. I am unsure though of how to wire this into the relay setup. I think I may need another relay switch?

ZV and export pump:
Opens / switches on when CH or HW calling for heat and top buffer tank stat is below temp
Closes / switches off when bottom buffer tank reaches required temp

Charge pump:
Comes on if ZV open and export pump is on
Switches off if bottom buffer tank stat reaches required temp.

Below is a picture of my relay switches:

//media.diynot.com/121000_120756_94611_11336986_thumb.jpg[/QUOTE]

Your original setup only needs one relay if the outputs from the programmer are relay contacts. They are both doing the same thing, albeit with different programmer outputs onto the relay coils. So you may have a spare relay anyway.

From your two bits of logic at the bottom of your description, the charge pump runs when the export pump/zone valve is ON? If so, just wire that in parallel with the EP/ZV.

Should the EP/ZV/CP stay on until both stats are over temperature?

Presume the stats each have a chageover contact?
 
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From your two bits of logic at the bottom of your description, the charge pump runs when the export pump/zone valve is ON? If so, just wire that in parallel with the EP/ZV.

Yes, I think that's it! A lot simpler than it seemed... I think there are two relays to stop the CH and HW feeding back into each other if only one of them is on.

Thanks for your help.
 
Thanks, I couldn't work out how to do that...
You're welcome. You nearly got there ... having successfully got the pics into your album, all you would have needed to do was to click on "Show my images" below the box in which you were typing your message and then clicked on the pics in question to put them into your post.

Kind Regards, John
 
From your two bits of logic at the bottom of your description, the charge pump runs when the export pump/zone valve is ON? If so, just wire that in parallel with the EP/ZV.

Yes, I think that's it! A lot simpler than it seemed... I think there are two relays to stop the CH and HW feeding back into each other if only one of them is on.

Thanks for your help.

If the programmer has relay contacts as outputs then one isnt feeding back into the other, even if only one is on. Its just two contacts in parallel driving 2 relays when one would suffice.

My educated guess is that you will only need one relay to keep your pumps n valves latched on once the top stat is over temperature, until the bottom stat switches.
 
Actually I'm not quite there...I just realised that there needs to be another condition.

If the water coming into the house via the export pump is below a certain temperature (so no excess heat available to charge the buffer) I don't want the charge pump coming on and taking away more heat from the house. I can fit a stat to the incoming pipe to switch off the power going to the charge pump if the temp is too low, but the zone valve needs to stay open (powered up) and Export Pump on if CH or HW is calling and cutting power to the charge pump will cut power to the ZV/EP as these are powered through the pump.

So I could use the changeover to switch power to the ZV/EP, but then the power would feed back to the charge pump as this is connected to the ZV/EP... Maybe this is where I do need to put in a relay?

Thanks.
 
In the main there is no need for any relays the zone valve has micro switches and all we do is open the zone valve then the zone valve starts the boiler and pump.

Central-heating.bmp


Not my design taken I seem to remember from Honeywell that is common with the older systems.

The advantage of using the zone valve to switch is that should it for any reason fail to open the boiler and pump will not be forcing water through the bypass valve.

Many years ago I also had to design extras I was lucky electronics workbench allowed me to simulate the system.
boilerC2.bmp


I am at the moment thinking about modifying a central heating system and today it is more complex. For a boiler to gather heat from the latent heat of evaporation the return water must be cool enough so today we have heat sensors both on outgoing water and return water.

The boiler has some software which is referred to as anti-cycle not every boiler is the same but one of the problems is if any radiator allows hot water to return prematurely then the boiler will reduce output before the house is warm.

In the main the cure is to use thermostatic radiator valves (TRV) which switch off the radiators in warm rooms forcing extra water to cold rooms and lock shield valves to limit the flow.

I talk about this as if you ever change your boiler it will likely be a condensate type and you clearly don't want to then have to re-design.

The TRV has also progressed with timers being built into the valves sounds good only heat bedrooms at night and only heat living rooms in the day but when the valve opens it will only heat radiator if the boiler is on and water being pumped and the anti-cycle software can be tricked by the new TRV with timer so can be a delay before you get heat.

So today the heat store is being used more and more allowing multi-heat sources but it does get complex.


In the old days the simple hot coil would not have transferred heat quick enough but today the water storage tank has progressed.

however from that diagram you can at least see the plumbing is as important as the electrics.

It would seem when you talk about a heat buffer you are doing something like shown above. With gas, oil, and electric boilers there is no need for buffer but with solid fuel, wind and solar there is.

So maybe if you explain your aims we can better advise. The system above has a very real problem. How do you know when the heat store is full? i.e. when water getting to heat where it may start to boil.

By the solid fuel fire one needs a heat store gauge so only lit when there is capacity to accept the heat. The towel rail in the example is used as a heat sink with sons boat we had a radiator pressed against the hull to get rid of excess heat.

but to control we got beyond the relay stage and used a PLC. Plus mutli-pumps in case one failed all 12 volt can't rely on mains.

So what are your aims and why did you not use micro switches in the motorised valves.
 
I wasn't including the whole system to try and make things a bit simpler. But possibly I have done the opposite...

Outbuilding: Log boiler with export pump to deliver water to house

House (existing):
- Programmer to control separate HW and CW pumps and circuits. Output from the programmer goes to both the HW and CH circulating pumps as well as the pictured relays, which then output to:
- Zone valve (V1, normally closed)and relay cable running back to export pump in outbuilding. When CH or HW calls from the programmer, V1 opens up and the export pump (EP) starts to run

House (proposed)
There is a 1500liter insulated buffer tank in the house left over from a now defunct log boiler that was in the same room as it. Currently it is on a dead leg of the system. Ideally it would be in the outbuilding with the other buffer tanks there, but moving it won't be so easy and neither would changing the pipework significantly. I would like to use this tank for extra storage. Having gone through all of the possibilities, and given the fluid dynamics of the system, I have come up with this as the best option:

A charge pump (P4) will be used to charge up the buffer tank. This buffer tank has two stats - T1 at the top and T2 at the bottom. Once the tank reaches full charge (as determined by T2), the zone valve and export pump will shut off and the circulating pumps in the house will then circulate the water from the buffer tank until it is empty, at which point the cycle will start again. An extra condition is that I do not want the buffer to charge when the temp of the water coming into the house is too low (as determined by a pipe stat (T3) attached to incoming pipe from outbuilding). There is also an additional zone valve V4 (normally open) that closes whenever the charge pump comes on. This is because there is a bypass loop in the pipework to allow the tank to discharge without back feeding through P4 So my conditions are:

V1 /EP
open / on if programmer (CH or HW) calls for heat and T1 <70deg C
closed /off if T2 >75 deg C

P4
on if T3 >70 deg c and ZV open / EP on
off if T2 >75 deg c

V4
open if P4 off
closed if P4 on

I thought I had the wiring for the buffer tank charging sorted, but I now realise that what I had planned won't work. P4 needs to switch off as soon as T2 is up to temp and not switch on again until T1 is below temp. I can't work out how to stop it switching on as soon as T2 goes below temp. I now feel truly stumped and my head is full of wires.

Attached (hopefully) is a schematic



I should add that all of my stats have changeover switches.
 
I can't work out how to stop it switching on as soon as T2 goes below temp. I now feel truly stumped and my head is full of wires.

A latching relay will provide the function

Live-------contact on T1-----------contact on relay------relay coil----Neutral

A contact on T2 is wired in parallel to the contact on relay.

With T1 closed the relay will energise when T2 closes. It will stay energised via its own contact after T2 opens.

It will de-energise when T1 opens.
 
A latching relay will provide the function

Live-------contact on T1-----------contact on relay------relay coil----Neutral

A contact on T2 is wired in parallel to the contact on relay.

With T1 closed the relay will energise when T2 closes. It will stay energised via its own contact after T2 opens.

It will de-energise when T1 opens.

Thank you, that sounds like what I need. I'm not completely sure from your post on how to wire it 'though?
 
Yes sequential logic as bernardgreen says latching relays can be used.
I have tried to get the sequence in my mind.
As bottom sensor switches N/C on it will start timer N/C across pipe sensor N/O to allow hot water to reach the sensor and top sensor N/C will already be closed so pump will run. The relay now bypass bottom sensor so top sensor and pipe sensor are all that is required to maintain the pump running. When either open then pump stops.

If no hot water is available then the timer will keep trying the only cure is a second timer to limit how long before it re-tries this is the problem as I see it with only a pipe sensor you have a problem.

Using a PLC one can write a program to increase the time before re-trying each time it fails to sense hot water on pipe sensor and to reduce time each time it does sense hot water. Same with Arduino or PIC.

The other option is a manual reset button which you press on re-lighting boiler in the shed.
Second timer shown with this version.

I wonder if an RF tank sensor would not be better than the pipe sensor as that seems to be the major problem?
 
This seems an ideal application for a PIC (or similar) micro-controller with relay ouitputs to control boilers, pumps, valves etc and, ideally, thermistors linked to its A/D converters to measure temperatures. Alternatively use conventional thermostats connected to logic level inputs.

Then the actual logic is a SMOP (simple matter of programing) and the possibilties are endless - functionality can be improved by modifying the code, not the hardware. There is a development environment call FlowCode which allow you to input a logic flow diagram and will generate the code for a variety of microcontrollers, including PICs.
 

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