UFH Buffer Tank Temperature control

[book_woorm]

Hi,
Does anybody know of a commercially available control system / thermostat that automatically raises the temperature of an UFH buffer tank when it starts to get very cold outside.

The UFH system in this house struggles when it gets very cold outside (I don't thing the designers realised that the property would be north facing on Dartmoor). Putting more insulation in the building envelope would be very difficult/expensive so raising the temperature of the water going round the pipes is the available solution. However as the UFH buffer tank and DHW thermal store are one and the same, having a higher temperature at the bottom of the store makes a mockery of trying to put heat into the tank from the solar thermal panels. I don't want to be adjusting the the thermostat manually every day and even that would not cope with an overnight cold snap.

I've seen one circut that achieves this with three Frost stats set at different temperatures 5deg apart connected to 4 separate thermostats inserted into the tank each set at progressively higher temperatures. As the outside temperature drops each frost stat cuts in inturn and connects to a different thermostat on the tank. I don't have enough thermostat pockets in the tank to do this and I'm not sure I like that many switches in the system as points of failure. I can see how to do this with some temperature probes electronics, OP amps and the like but it seams daft to reinvent the wheel if such a thing exists.

Regards Book_woorm:snow

[dhaslam]

What you need is a weather compensated heating controller.    Unfortunately they seem to be  either incorporated into boilers or  sold very expensively separately.

A search finds this alternative solution 

http://www.navitron.org.uk/forum/index.php?topic=16146.0

[book_woorm]

I saw that one, but it goes down the mechanical one step route.

I think I can achieve continuous compensation using a couple of thermocouples and some electronics. I'm not sure about analogue or digital just yet The former would be simpler to make  the latter far more adaptable, I just want to be certain there is nothing outthere be for I start on the DIY approach.

[woody]

try the HCC solec series Navitron are listed as uk suppliers

[book_woorm]

Cant seem to find 'HCC solec' on the web have you got a url please.