I heard some bloke at an energy efficiency company advising people to turn their boiler control UP (leaving their room and cylinder stats alone). ie: If the switch on the boiler went 1-6 and it was at 3, turn it to 4 or 4.5.
He said this is because the boiler gets hotter quicker, heats the tank quicker, and reduces cycling. Thus saving energy. But won't this mess with the condensing point of a condensing boiler?
His argument is: tank calls for heat, boiler and pump start, boiler reaches temp and turns off, tank still wants heat, pump still goes, primary side water and boiler cool, hence the waste.
That might be true with a conventional boiler if the cylinder is able to accept all of the boiler output.
There isn't a Holy Grail at the condensing point. Nirvana isn't achieved. All that happens is that the *rate* of increasing efficiency with reducing temperature increases - i.e. a knee in the curve.
It's a jumble.
If it's a modulating model (typically should be), a cool water cylinder will present a substantial heat load and the boiler will run balls out condensing heavily because the return water is cool.
For a radiator load with TRVs reducing flow, the boiler will modulate down to match the load.
During DHW is stored at high temperatures and at kleast 60C for the prvention of legionella. When re-heating the boier temperature has to be hot. You can't get away from it. Condnesing boier or not it has to be hot. The only boier know that condenses wt all tiomes when supplying DHW is the ACV Heatmaster, which has a unique combied tank-in-tank/boiler. A class act.
The heat exchanger has to take all of the boilers output. The best heat exchange is a plate heat exchanger and bronze pump using a direct cylinder Works out cheaper than a cylinder with a quick recovery coil in many cases. Glow Worm in their new Extramax and Ultramax boilers use this method to reheat an integral unvented cylinder. These plates extract so much heat from the boiler it can really lower the return temperature to condensing levels for most of re-heat time.
He is generally right. But, the cylinder coil has to take the boilers output. On re-heating from cold a Part L cylinder will take the output of the average boiler when set to 80C for the initial part of the re-heat, until the return temperature is raised.
The problem is having the boiler at the ideal temperaure for CH to promote condesning efficiency. An outside weather compensator can do this. Boilers are available that will re-heat water at full belt and switch to weather compensation on CH. Even so external waether compensators and the odd reply can do this too.
The best is a heat bank in which the bottom CH half is heated by a weather compensator. The boiler operates in a superior full flow through the heat exchanger hydraulic environment, as does the CH circuit too. Boilers last far longer when heating heat banks.
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