Thermal storage tanks

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I am keen to use a thermal storage tank and can find no info on the control of a central heating [rads] system temperatures.

The tank will store water at 78C and I want to control the temperature in the rad circuit from say 40C to 75C

My first view is to use a mixer/blending vavle as used for UFH, but their temps are set at 60C max, I am told.

I have asked several tank suppliers without an answer.

I am considering a vented system, but the same query applies to a pressurised system
 
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do you mean you want to vary the radiator circuit temp? If so your talking commercial controls.
 
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I had a tank from DPS heatweb which came with two such valves, one for the rads and one for the boiler circuit. They were 28mm with reducers so perhaps they only come in this size - I did know what the brand was and manage to find some on line but I can't remember now and have since moved house.

Would this do it?

http://www.advancedwater.co.uk/prod-520-373-0616.html

Input temp range is fine but max output temp is only 50 degress tho.
 
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My first view is to use a mixer/blending vavle as used for UFH, but their temps are set at 60C max, I am told.

I have asked several tank suppliers without an answer.

I am considering a vented system, but the same query applies to a pressurised system

You can use a TMV (3-port mixing valve with a thermostatic actuator). They're mostly intended for mixing DHW and usually come factory set to about 42 degC with a means of increasing the outlet temperature. There are probably some that will go up to the temperature you require. All such valves will require manual adjustment to keep the outlet temperature adequate for the heat losses (& outside temperature).

If you want an automatic adjustment, then you'd need a motorized 3-port mixing valve with a compatible controller. Have a look for weather compensation systems (flow temperature gets turned up & down depending on outside air temperature). They're not 'commercial' controllers; few domestic plumbers/heating engineers have experience of them, those that have often obtained it in commercial practice. Honeywell do them, ISTR, but I'm not sure since I do commercial stuff mostly. :LOL:

PS Why do you want a thermal storage tank? It makes no sense unless you need to store heat (solar thermal, log burner, off-peak heat pump, etc..).
 
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Thanks Onetap.
My reasons; I have an old 42kW boiler, 20 Radiators, long 35mm heating pipes, poor DHW flow-long runs, old header tanks in roof.
I fear pressurising the Heating circuit for risk of leaks, I do want to pressurise the DHW. I prefer to remove the header tanks.
I am looking at a McDonald Therflow tank which stores water at 80C and gives DHW thro an exchanger coil. The tank at 80C is on the same circuit as the rads so I need to be able to vary the temp in the rad circuit
I first thought of a mixer valve similar to used on UFH but cant find one to give rad temperatures and take 42kW
 
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I have a thermal store system which uses a mixer valve on the DHW output to reduce the HW temp by mixing with mains cold water. I run the tank at 60-65C, which works fine. This system does allow you some control of radiator temperature. Varying the tank thermostat varies the radiator temperature although you can’t go much below 60C, otherwise the DHW is not hot enough.

What is your reason for wanting such a range of control over your rad temperature?
 
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Thanks Onetap.
My reasons; I have an old 42kW boiler, 20 Radiators, long 35mm heating pipes, poor DHW flow-long runs, old header tanks in roof.
I fear pressurising the Heating circuit for risk of leaks, I do want to pressurise the DHW. I prefer to remove the header tanks.
I am looking at a McDonald Therflow tank which stores water at 80C and gives DHW thro an exchanger coil. The tank at 80C is on the same circuit as the rads so I need to be able to vary the temp in the rad circuit
I first thought of a mixer valve similar to used on UFH but cant find one to give rad temperatures and take 42kW


I think you're going at it from the wrong way.

There is no need to run the boiler at 80 C, except possibly when generating hot water. Running at a lower temperature, if/when possible, will be more efficient. You need to plan for replacing the old boiler at some time with a condensing boiler which, given the size of your system, would probably have a short pay-back time, if the old boiler hasn't already expired.

If you put in a mixing valve, you need a device to maintain the old boiler return temperature (back-end protection). You won't have that problem with a condensing boiler.

You seem to have assumed there will be leaks from the heating circuit; why so? Copper pipework probably won't develop a leak, radiators would be dealt with as required. Is there a history of corrosion?

Pressurized mains water is overrated IMHO. Its main benefit is at a shower.

There's lots of 3-port motorized mixing valves that will handle 42kW at 80 degC, they just cost more.
 
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It is not so much wanting a wide range of control, or to adjust too frequently.
With a conventional system, I would normally set the boiler at say 2. Maybe at 4 if a cold spell, and full in the worst of winter.
I have 4 zones which each have a programmer. All rads have TRV's
To have no control would be like having the boiler on full in spring & autumn, which has to be a waste.
I am puzzled why we take for granted a mixer valve on UFH, but nothing on a rad circuit.
 
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I have a thermal store system which uses a mixer valve on the DHW output to reduce the HW temp by mixing with mains cold water. I run the tank at 60-65C...............

The OP is talking about a different system; he wants a thermal store holding primary CH water at 80 degC flow from the boiler, with a 3-port mixing valve blending CH return water to give a reduced flow temperature to the radiators.
 
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I have a thermal store system which uses a mixer valve on the DHW output to reduce the HW temp by mixing with mains cold water. I run the tank at 60-65C...............

The OP is talking about a different system; he wants a thermal store holding primary CH water at 80 degC flow from the boiler, with a 3-port mixing valve blending CH return water to give a reduced flow temperature to the radiators.
Indeed. I was just wondering why a ‘conventional’ thermal store system, as I understand mine to be, which does give some control over CH temperature would not do the job. It sounds like the OP has no room thermostat control so is relying on TRVs and manual adjustment of the flow temp. If so, I would suggest that adding thermostat control would aid efficiency more than varying the radiator flow temp.
 
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I would just add that the system now has 4 zones each with its own programmer and one room thermostat per zone. To reduce the heating circuit temp I vary the setting on the boiler
 
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I would just add that the system now has 4 zones each with its own programmer and one room thermostat per zone. To reduce the heating circuit temp I vary the setting on the boiler

I have an image of a floor-standing cast-iron job like a Kingfisher; last forever, nothing to go wrong with it. A prolonged low return temperature will cause acidic condensation of the flue gases in these and shorten its life.

Sontay do rotary shoe valves which are ESBE make (taken over by Danfoss now ISTR). They're good. The control signal is usually 0-10V, depending on the actuator, and any compatible controller will run it. You'd probably do better with several smaller valves, each with it's own secondary pump.

A thermal store (big cylinder) would serve as a low loss header and give minimize short-cycling of the boiler. You still want to plan for a modulating condenser at some point and these can control their output temperature without mixing valves.
 
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I am puzzled why we take for granted a mixer valve on UFH, but nothing on a rad circuit.

Cost. It is essential for UFH, an optional extra for radiators.

I had mixing valve & thermal store on my radiator circuit, a remarkably comfortable system (when I eventually worked all the bugs out of the control system :oops: ). The rads were rarely hot, usually warm, the house was always comfortable.

Now replaced with a modulating condensing boiler; not a combi, note.
 
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I had mixing valve & thermal store on my radiator circuit, a remarkably comfortable system (when I eventually worked all the bugs out of the control system ). The rads were rarely hot, usually warm, the house was always comfortable.

Thanks Onestep. This is exactly my objective!

I searched the ESEB route - what a chase, but got there. They seem to have the goods, will contact later
 
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Thanks Onestep. This is exactly my objective!

Onestep?

Yes I know, but I binned it in favour of a modulating condensing system boiler and a vented HW storage cylinder because;

1) the condensing boiler was more efficient;
2) I didn't need to store 100litres of 80 degC water
3) and I got rid of the 3-port valve ( can be a maintenance problem) because the condenser's controls could turn it's flow temparature down when possible;
4) available off the shelf, much less messing around trying to program a controller to do what you want.
 
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