Which timeclock/programmer?

[PeedOftec]

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I have an ACV 300SLME thermal store linked an Worcester oil boiler. The oil side has pumped flow and return.

http://www.acv-uk.com/slme.htm

The radiator circuit is pumped from the primary water in the ACV outer water jacket, the same water as goes through the oil boiler. (The oil boiler is NOT connected to the coil in the ACV tank).

The thermostat on the top of the ACV tank is in the secondary “potable” water and triggers the oil stove to come on, to heat the DHW, when the secondary water temp drops below the thermostat setting on the ACV.

The radiators have a room stat and when the room stat calls for heat it turns on just the radiator pump…… however the oil boiler will not fire up because the secondary water is “up to temp” as far as the ACV tank thermostat is concerned.

Only after the temp of the primary water drops, as it goes round the rads, pulling down the temp of the secondary water, does the oil boiler kick back in again.

What it means is the secondary water temperature is cycling as the radiators call for heat.

Ideally I would have liked to see the secondary water temp stay as constant as possible and when the room stat calls for heat, the oil boiler fires immediately and the primary hot water it produces goes straight round the radiators.

Do you have any recommendations as to the type of central heating timeclock that cold achieve this, or is this setup how it is normally done?

I have heard about “2 channel” and “single channel” programmers, are either these capable of controlling this way?
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(apologies if this should be in the "electrics" forum, could the moderator move it if needs be please.).
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[Boilerman2]

Thermal stores I have worked on have a HWS Store Stat (at the top), and a 2nd Thermostat (at the Bottom) which is wired to operate the boiler whenever a Heating demand occurs usually via a programmable Room stat pulling in a Heating Pump, or a UFH Zone opening, the lower half of the store then achieves a higher temeprature, this scheme works very well with UFH as ypou can set the lower part of the store to say 50'c therefore negating the need for a TMV on the UFH Manifold

 

[PeedOftec]

Thermal stores I have worked on have a HWS Store Stat (at the top), and a 2nd Thermostat (at the Bottom) which is wired to operate the boiler whenever a Heating demand occurs.........

There is a couple of sensor pockets in the bottom of the tank that may be useful?

7. Sensor pocket (coil)
8. Sensor pocket (lowest temperature tank)

http://www.acv-uk.com/slme.htm

Can a programmer take inputs for secondary water temp from one thermostat for DHW and primary water temp for the CH from another sensor?

Or do I need two programmers, both firing the oil boiler?
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[Boilerman2]

I would have thought that you would want the top of the store to be heated 24/7 to give instant Hot Water, my understanding of thermal Stores is that you use a much smaller boiler than would be required without the store, the store acts as an accumulator of heat, so switching Boiler off for a period of time could give a very slow recovery, most Thermal Store systems such as Gledhill Boilermate, Hot water On 24/7. with timed heating

 

[PeedOftec]

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I would have thought that you would want the top of the store to be heated 24/7 to give instant Hot Water, my understanding of thermal Stores is that you use a much smaller boiler than would be required without the store, the store acts as an accumulator of heat, so switching Boiler off for a period of time could give a very slow recovery, most Thermal Store systems such as Gledhill Boilermate, Hot water On 24/7. with timed heating

Yep, sounds about right, trouble is at the top of the store has a thermostat controlling the oil boiler, sensing secondary water temp, if it is up to temp it wont fire up.... until the CH pump has dragged the heat away round the rads, lowering the temp of the secondary ("drinking" water) and only THEN does the oil boiler kick in. As you rightly point out the top of the tank ideally is up to temp all the time and when the room stat calls for heat the boiler should kick in regardless of the temp at the top of the tank as the heat will be pulled off around the rads. Is this not possible?

Am I explaining myself clearly?
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[jackthom]

The only way I can think of doing this would be to have a relay which was energised by the CH room thermostat and whose (Normally Open) contacts were in parallel with the secondary thermostat to fire up the boiler.

 

[PeedOftec]

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The only way I can think of doing this would be to have a relay......... .

The ACV thermostat has NO and NC contacts... a relay in essence, albeit temperture controlled as opposed to electrically controlled...
When the DHW is "up to temp" could the other contacts on the stat be used to allow the oil boiler to fire up if there is a demand from the CH?

Just a thought, as you can see I'm not an electrician, nor a plumber...
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[jackthom]

Edit: If that is actually a relay where the coil is ON when the ACV thermostat is demanding heat, the COMMON contact goes to the boiler, the N/O contact is permanent live and the N/C contact is available to hook up to the room thermostat Switched Live you could be in business.


Otherwise........

I think it would have to be another independant relay. It mustn't interfere with the normal storage thermostat when the secondary water needs heating.

The only time an additional relay would have any effect would be when the room thermostat switched it ON and it would then short out the contacts of the ACV one and fire up the boiler.

The relay may have to be something like a 12V DC coil with a 12V "brick" power unit which gets power when the CH pump is on.