In another topic,
Bigburner said:
Yes, a good boiler with weather compensation is the key. Broag Avantaplus are well priced, excellent quality, and have excellent control systems - OpenTherm.
Fit a 3-way diverter valve on the system with quick recovery coil in the cylinder giving DHW priority. The Avantaplus control system will run the boiler to maximum temperature to re-heat DHW ASAP. When DHW satisfied it returns to weather compensation for CH control keeping the return temperature as low as possible.
Where did you get the information about the Avantaplus control system running at max temp when heating hot water and returning to weather comp for CH? There is nothing about this in their literature, although some of their wiring diagrams show diverter valves and others show the traditional Y-plan with a mid-position valve. What would happen if a mid-position valve was used instead of a diverter? Would the boiler run at max temp or at weather controlled temp?
I'm interested as I have decided to install an Avanta 18v, when my existing Apollo Fanfare boiler gives up, and want to maximise the investment by using weather compensation etc, but I don't want to spend money on a diverter valve if I can retain my existing mid-position.
Look at:
http://www.avantaplus.com/docs/Issue 5 -Avanta Schematics Booklet.pdf
AVANTA 18v System Only Option 5
Simple weather compensated Heating with 230v room thermostat override and Priority DHW
Also:
AVANTA 18v System Only Option 6
Simple weather compensated Heating with volt free room thermostat override and Priority DHW
A cylinder stat or cylinder temp sensor can be used. You program this via the boiler controls. The compensator slop is set in the boiler too. It come with a slope re-set which is fine for most rad systems.
Look at:
AVANTA PLUS System Option 19
System boiler - Internal time clock with simple weather compensated UF Heating and priority DHW
This has UFH. A high limit temp stat and diverter valve to ensure UFH pipe are not overheated. The flatter compensator slope can be set vi the boiler. This means the UFH can be ticking over at 35C and when DHW is called the boiler ramps up to max to reheat fast. When it reverts to UFH the boiler temp may be 70-80C, so the UFH high limit will cut in and send the hot water back to the boiler until the temp drops below the high limit and then compensator control again.
UFH invariably entailed complex controls, as boiler only gave one temperature at any one time. Few ran UFH from a boiler directly, unless it was a boiler assigned to UFH only. Weather compensation was a separate compensator unit. To have the one boiler do UFH & DHW the boiler had to run hot and a blending valve to reduce for UFH. Thermal stores were used and invariably run too hot, blending down for UFH via blending valves or weather compensation. However, I implemented thermal stores with a weather compensator set to a UFH slope heating only a UFH section of the store - no cycling and the correct temperature for UFH. But this was complex and few service men could understand it unless they specialised in UFH. I always left documentation and drawing of the system by the store, so they could understand. All this is extra expense.
This boiler can run UFH directly under weather compensation and still reheat the DHW fast - I prefer a DHW only heat bank. This was possible before with reasonably priced boilers. Ravenheat did have this facility except thee was weather compensation - and the reliability of this company's products meant this was not an option. This simplifies design and installation and reduces cost substantially. Only a low loss header may be used and an extra diverter vale. The header can be knocked up simply enough, or with an open vented system use a cheap 40 litre direct cylinder and the diverter valve eliminated just using a high limit pipe stat to the UFH zones. The cylinder will absorb any small amount of boiler water that is too hot - a nice CH buffer.
On some boilers with weather compensation you can get the same functionality out of the boiler but you have to frig it. Use relate to switch the outside sensor to a resistor to kid the boiler it is -5C outside and then it runs up to max temp. When DHW satisfied it will revert to the true outside temp sensor. Some makers do not like this, as their technical department don't understand what is going on - this is common in commercial systems.
The boiler has to be told in the many situations what the system is. Set via the boiler.
Some MAN boilers have similar control functionality, but these cost. The Keston and Broag now reduce the cost of UFH and the running cost too as UFH runs at very low temperatures. The Broag as far as I can see, has much better control configuration than the Keston - although the Keston I avoid until field feedback is positive on reliability. Many were bitten by the Celsius, while previous very simple models were very reliable.
