Better way to control water UFH system?

[Munchincocopops]

Hi - I have a 12mx5m garden room with water based underfloor heating. It works well but I am always wondering if there is a better way to control this.

At a guess I think there is about 400m of pipe as 4 loops in this area.

 

My installation has a wall thermostat (no floor sensor) and I the normal mixer valve/manifold/pump arrangement and when stat calls for heat it opens a valve (water from boiler to underfloor manifold/mixer valve/pump) which in turn activates UFH pump and turns on boiler.

Obviously when stat reaches temperature everything turns off.

 

Now I'm wondering about 2 things:

1. Better control of boiler as a 32kW boiler running at 70 deg C will soon meet mixer valve requirement but the stat is still calling for heat until the room reaches temperature. So I wonder if I use a thermocouple/programmable thermostat to measure return water temperature on the UFH manifold and set this to 45 deg c (?) and if above this turn off the boiler.

 

2. To install a buffer tank, use thermocouples/programmers to turn on boiler if buffer tank temperature is below 45 deg C and turn off boiler when temperture is above 60 Deg C. Might have to play around with max temperature to achieve a workable value. 

 

There will be some plumbing to do between boiler/buffer tank/manifold and extra valves possibly and likely some wiring changes to suit.

 

There might be a better way than what I am thinking so any comments or advice is appreciated.

 

Edited 12 hours ago by Munchincocopops

[JohnMo]

What in the rest of the heating system, as I assume you are not using 32kW just to heat a garden room?

[ProDave]

Fundamental question:  Is this a boiler just for the garden room, or is the garden room close enough to the house to be fed from the boiler in the house?

 

WHY run the boiler at 70C,  First thing turn that down to 55 or lower.  You will probably have to run the heating longer but it will work out cheaper.

[Munchincocopops]

Its a system condensing boiler and heats the whole house which are radiators. 

Plumbed so all have their own thermostats and timers. Mostly we live in the garden room so usually house heating is off or turned down.

Bathroom radiators come on whenever boiler is on.

 

So 70 deg is for water heating. All showers use hot water tank water so no electric showers.

 

House is quite large and built late 80's hence 32kW.

 

There is a third option. UFH has its own boiler?

 

Thanks for the comments.

[marshian]

What make and model boiler - does it have the functionality to do DHWP (Domestic Hot Water Priority) if it does then you wouldn’t have to run the boiler at 70 deg all the time just to satisfy the HW tank recharge temp required 

 

you coud probably drop the boiler temp to 60 - 65 and still get a decent volume of HW at a slightly lower temp storage

 

[JohnMo]

1 hour ago, Munchincocopops said:

radiators. 

Plumbed so all have their own thermostats and timers.

Some simplification sounds the order of the day. A couple of radiators kicking a huge boiler into life for 5 mins isn't an efficient way to run a heating system.

 

Will wait for the additional information requested above.

[Munchincocopops]

Thanks for the replies. Will look at boiler model tomorrow but I know its a Baxi, 4 years old and I'm not aware of built in DHWP or at least no controls visible to me to alter or select. anything other than  on/off and temperature setting I recall.

Will turn it down to 62 deg or so as i thought it had to be above 60 for bacteria reasons.

 

Maybe I did not explain properly

UFH has own /timer stat and demand on boiler.

Radiator CH has its own timer and a room stat and demand on boiler.

HW tank has its own timer and stat and demand on boiler.

 

Separate boiler demands achieved via 3 relays (UFH, CH, HW) using volt free contacts wired in parallel connected to boiler demand. ( some additional wiring as demand to boiler comes from motorized valve for each heating circuit)

 

Living room has 5kW radiator, some 14 other radiators in the house with their own valve TRV's except for living room which uses room stat and no valve TRV's.

 

Garden room added recently (attached to house open plan kitchen) hence large boiler before that for CH but now we find we tend to live more in garden room with UFH that is normally on all the time over winter so less need for radiator CH other than keeping the chill off the house.

Hope that explains why I ask questions on UFH.

 

So back to my original questions.

Option 1 or 2? Option 3 I added later I think will not help.

Edited 3 hours ago by Munchincocopops

[JohnMo]

1. I wouldn't bother

2.Not sure what you will gain from this

3. That just makes stuff way more complex, and sure it will gain you much.

 

Read a few Baxi datasheets and manuals and they don't seem the most sophisticated of boilers and not the best output turndown. With this in mind, you need places to dump heat, as your summer house will struggle to a absorb the heat on offer and I would suspect your boiler doesn't run for long and has plenty of cycling, which will ultimately reduce life, but use way more gas than needed.

 

Turning down flow temp could lead to issues with cylinder heating, so do it small steps, you need to ensure the cylinder heats in one long boiler run, not lots of short cycling, which will be the result if you trim heat too much.

 

The ideal way to run UFH is low and slow, so I suspect the UFH mixer could be turned down.

 

To help the boiler out, need other parts of your heating system open.

8 hours ago, Munchincocopops said:

radiators. 

Plumbed so all have their own thermostats and timers.

This is basically a recipe for boiler short cycling, higher gas consumption than you could have.

 

So timings I would set all the same, run whole house a little warmer.

 

Next steps and questions 

Does boiler accept opentherm control?

You really need to run the heating system differently, so priority domestic hot water, opentherm is an easy way to implement this. So basically you run one flow temp for cylinder heating and another for central heating.

[Munchincocopops]

Thanks for that.

Option 2 I was thinking it would reduce boiler cycling and constant run to heat water from 45 deg to 60 deg or so then turn off. UFH uses buffer tank water temperature to run UFH on stat demand eventually cooling buffer tank water to below 45 deg which in turn demands boiler to reheat to 60 deg.

 

That was my thoughts anyway hence seemed a good idea.

 

Will look into opentherm as it looks good with Hot water and lower temperature for UFH and house heating.

Last winter UFH was on constantlyfor 6 months.

 

Sounds like I should simplify and skip CH timer and CH on with hot water demand or UFH demand and use CH stat to control CH need (i.e motorized valve)?

 

Option 3...is it a typo or are you suggesting its a good idea even if complex/costly.

20 minutes ago, JohnMo said:

and sure it will gain you much

 

Thanks again.

[JohnMo]

3 minutes ago, Munchincocopops said:

Option 2 I was thinking it would reduce boiler cycling and constant run to heat water from 45 deg to 60 deg or so then turn off. UFH uses buffer tank water temperature to run UFH on stat demand eventually cooling buffer tank water to below 45 deg which in turn demands boiler to reheat to 60 deg.

100L cylinder with a 32 kW boiler takes under 4 minutes to go from 45 to 60, as it's only 1.75kWh heating capacity in the cylinder. So to get a useful run time you would need several hundred litres.

 

Hence my recommendations

[marshian]

5 minutes ago, Munchincocopops said:

Will look into opentherm as it looks good with Hot water and lower temperature for UFH and house heating.

 

 

 

Really need to know "boiler model" to be able to find out if it can be configured in DHWP and Open therm or Weather compensated - gut feel having read a few Baxi install manuals over the recent years is it will be unlikely.

 

UK Boiler manufacturers are mainly still in the dark ages unfortunately - only thing that will bring them kicking and screaming into the 21st century is people buying better configured boilers from Europe where they've been facilitating low temperature weather compensated flow to maximise condensing efficiency and DHWP 

[Munchincocopops]

Blimy.....must go and stand next to my boiler as it runs UFH to count how many times it cycles in say 10 minutes.

 

Hope the opentherm is an option now.

[JohnMo]

33 minutes ago, Munchincocopops said:

Blimy.....must go and stand next to my boiler as it runs UFH to count how many times it cycles in say 10 minutes.

 

If you count is 1 full cycle in under 10 mins, you have issue to fix. Your boiler should start, modulate down and run for a prolonged period.

Edited 1 hour ago by JohnMo

[Munchincocopops]

Baxi Megaflo 32 System ErP Condensing Boiler.

[marshian]

26 minutes ago, Munchincocopops said:

Blimy.....must go and stand next to my boiler as it runs UFH to count how many times it cycles in say 10 minutes.

 

Hope the opentherm is an option now.

 

10 mins won't give you much of a clue most boilers have 3 min anticycle timer

 

Seriously if a boiler is running more cycles than 3 per hour it's likely to be losing efficiency

 

I did once count my old boiler doing 10 cycle in 1 hour it's one of the reasons it's now recycled into bean cans...................

 

If a boiler is running on a 70 deg flow temp it very unlikely to be gaining much at all in condensing efficiency 88 or 89% at best

 

Get the flow temp down to below 55 Deg for CH and it's going to be condensing all the time and in the 90's from an efficiency point

 

[Munchincocopops]

Thanks  - will look into this over the week end....dont fancy standing for a hour in the garage but its something to look into.

[marshian]

Well reading the manual it does appear that it's capable of running lower flow temps (Although it's not a low temp boiler)

 

10.6 kW min output is quite poor but if you have a big drafty house with very little improvements to insulation it would be fine on a whole house heating system..... Maybe not so much heating a small area

 

It looks like weather comp is available (as an in flue sensor) - that's something I've seen mentioned before with Baxi boilers but previously only with combi boilers.

 

Don't know if it can be range rated at all - couldn't see anything in the boiler manual - probably not as it's made in a range of sizes and it should have been sized to the property needs...

[JohnMo]

So your boiler has a minimum output of a out 10kW, which is pretty huge.

 

So you really need most of your radiators on, while you try to run the UFH. Bringing down your flow temp will help, as it will slow down the system and reduce radiator output, so thermostats cycle less.

 

Tell us more about what is controlling your radiators?

[Munchincocopops]

Thanks - house used to be drafty when built but I soon sorted that. No cavity insulation bar garden room extension. No fitted any any as advised as house is buit of sandstone....bar garden room.

House is cosy warm and quickly heats up in the coldest weather so really happy with 32kW. It used to be 24kW Viessmann which never seemed to turn off when really cold nor house really cosy. 32Kw turned out to slightly cheaper to run CH but I'm thinking its overkill now as we mainly live in garden room with UFH.

 

But must admit in no time house is cosy when full CH is turned on.

 

So will weather comp help to save cycling - does that control flow temp. I will have to google weather comp.

 

Looks like this boiler does not support Opentherm from what I read.....but I'm no expert.

[Munchincocopops]

Laptop battery is running out so last post of the night for me.

Radiators - not sure what else I can add over above. TRV's on all bar living room that is on full as radio thermostat is in that room.

 

Thanks for the comments and advice.

 

Will be back tomorrow night.

[marshian]

14 minutes ago, Munchincocopops said:

Thanks - house used to be drafty when built but I soon sorted that. No cavity insulation bar garden room extension. No fitted any any as advised as house is buit of sandstone....bar garden room.

House is cosy warm and quickly heats up in the coldest weather so really happy with 32kW. 

 

If your heating on demand (or to a schedule based on occupation times) then you need a powerful boiler to get it up to temp fast sounds like that's what you are doing

 

14 minutes ago, Munchincocopops said:

It used to be 24kW Viessmann which never seemed to turn off when really cold nor house really cosy. 32Kw turned out to slightly cheaper to run CH but I'm thinking its overkill now as we mainly live in garden room with UFH.

 

Viessmann boilers even relatively old ones have excellent modulation (or turn down) 

 

I have a basic 16 kW Viessmann that will happily modulate down to 4 kW - I run the heating 24/7 at low flow temps with weather compensation

 

The boiler typically fires 20 - 25 times a day

 

When it's cold outside it runs for 50 mins in the hour at no more than mid 30's flow temp

 

When it's warmer like today 20 mins in the hour at very low 30's flow temps

 

My energy usage is directly related to the outside temps (because I'm only ever replacing the heat lost and the heat loss is driven by the outside temps)

 

Problem is when you end up with a big boiler with a poor modulation ratio and you are trying to heat a small space it's unlikely to be happy with the situation 

 

14 minutes ago, Munchincocopops said:

So will weather comp help to save cycling - does that control flow temp. I will have to google weather comp.

 

Looks like this boiler does not support Opentherm from what I read.....but I'm no expert.

 

Weather comp controls flow temp however it's better suited to whole house heating and 24/7

 

I have used it for scheduled heating and it was OK but it's not really the point.

 

Open therm is weather comp via internet sourced local weather (or rather outside temperatures)