Design help required.

[PrenticeBoyofDerry]

After doing heat loss calc and correction factors on a property, with mixed heating emitters of rads (mainly upstairs) and UFH mainly down stairs a total of 42kW requirement (rads demand 17kW, UFH demand 18kW plus 3kW for hot water plus 10%)
My thoughts are that two room sealed boilers would be best required.
Would it be ideal to have rads controlled by one boiler and UFH by another, or a mixture on both with port valves, plus one selected boiler for hot water or the hot water split over the two?

 

[muggles]

Two boilers on a low loss header supplying everything, that way if one boiler fails the other can provide some heat to all systems while a repair is awaited

 

[ALEC1]

no benefit to two boilers if you can't cascade them properly, especially if are weather comoensating the install...

 

[Dan Robinson]

Two Intergas SB 24s with the cascade feature enabled.


LLH, you could even use one with hot water priority.

 

[AngelesPlumbing]

UFH 18kw wow!!!

 

[Dan Robinson]

That one you saw with me was about that Kevin.

 

[ALEC1]

What is the cascade feature on an intergas?

 

[Dan Robinson]

The feature that lets you cascade two boilers... you should pay more attention to my CC ramblings .


Details in the CCR.

 

[ALEC1]

Very helpful Dan, does it try to run both boilers at their most efficient load like viesmann's, or just switch between the two or more boilers on a timed basis...

 

[Richardthe3rd]

After doing heat loss calc and correction factors on a property, with mixed heating emitters of rads (mainly upstairs) and UFH mainly down stairs a total of 42kW requirement (rads demand 17kW, UFH demand 18kW plus 3kW for hot water plus 10%)
My thoughts are that two room sealed boilers would be best required.
Would it be ideal to have rads controlled by one boiler and UFH by another, or a mixture on both with port valves, plus one selected boiler for hot water or the hot water split over the two?

It depends on the property & it's use. Also, if it's oil for example you're sometimes better with a simple 'lead/lag' set up or have them dedicated, one for the UFH & the other doing the higher temperature radiators/hot water.

You have only allowed 3KW for Hot Water, so if it's a home of that size - with several bathrooms/shower rooms, it maybe a bit on the shy side?

An advantage of having two boilers on any fuel is location, what's the point in having miles of high temperature pipe work running through a property, just for the sake of having a boiler cascade??

If its natural gas boilers, with that size of UFH system is a big consideration. The 3 elements of the system are very different, if in a home, UFH even in winter will tick over when it's up to the target temperature, hot water will be at peak times - as will the radiators.

Be careful who's advice you take on here mate, most have never done any commercial heating & at best are combi kings.

 

[ALEC1]

tend to agree with Richard, except two boilers...you need to use a boiler manufactueres controls and valves to get a seamless system, viessmanns divicon, or vaillants vr61..

both designs have hot water priority, both would have an un mixed radiator circuit, and mixed UFH, you can also have multiple zoning with manufacturers boiler controls...

I don't know whether you can cascade two domestic vaillants, or even two small viessmans, but both have single 45 kw boiler...

 

[Dan Robinson]

Two boilers can modulate much lower than a single big one.

Not a bad thing with significant amounts of ufh.

You also get redundancy.

The interconnecting pipework on two boilers is not exactly a herculean task.

Alec, the IG cascade is pretty basic. But correctly setting up the boiler's is a 5 minutes task and a far superior boiler.

 

[ALEC1]

I think what worries my about IG for UFH is the mixing valve...unless that can create its own low temperature demand with its own curve for the floor, from the boilers which means it has some sort of bus feed back to the boiler, its a lacking design.

Its not that these things don't exist, putting inter gas on par with vaillant and viessmann but they are not in the UK, so you are stuck with fixed flow temps for the floor.

 

[Dan Robinson]

Not if you size the system properly.

I grant it is perhaps an issue on retrofit, but....

 

[PrenticeBoyofDerry]

no benefit to two boilers if you can't cascade them properly, especially if are weather comoensating the install...

Is the cascade system, similar to the low loss header method.
What if any would be the difference?