Heat loss over time (Vented Cylinder)

[marshian]

Rather than continue to threadjack another post

 

System info

Y plan system

Vented cylinder 112 Litres (Installed 2011 from memory)

Insulation on all the pipes around the tank - extending to loft and in loft to header tanks.

I still think my losses are too high 0.5-0.7 deg per hour

 

Lagging is good quality Turbolit (a considerable improvement on std DIY stuff - albeit that was better than bare copper pipes)

 

22mm copper pipes have 9.5 mm wall insulation

15mm copper have 12.5 mm insulation

 

I use a pipe lager pro mitre box to get neat joints and most are glued

 

But I think I might have a reason but I'd like an opinion on it

 

My three port valve is at rest on HW and powered to mid position or CH

 

At the end of every CH cycle the time runs the HW for a min to reset the valve to rest (if left in HW the motor body gets warm - warm = electricity - constant running = wear and tear on the valve head)

 

Hot moves to cold - water in the coil is heated back by the hot in the tank and convection currents move the water/heat back to the boiler - if I swapped the 3 port valve round (and the wiring) I could make the CH position the rest and it would block any flow back to the boiler - however the other end of the coil would still be connected to the boiler by the return pipe??

 

[OwenF]

I’m struggling to wrap my head around the perceived issue, but initial thoughts are that CH for ‘at rest’ position generally is not desirable as it doesn’t allow the pump to overrun in event all TRVs close (assuming no automatic bypass).

 

I switched my 3-port valve, but that was to retrofit PDHW using a relay demand box. This has same outcome of having CH on the NO side of the valve. I had two non-TRV towel rails to ensure path for pump overrun.

[marshian]

1 hour ago, OwenF said:

I’m struggling to wrap my head around the perceived issue, but initial thoughts are that CH for ‘at rest’ position generally is not desirable as it doesn’t allow the pump to overrun in event all TRVs close (assuming no automatic bypass).

 

I switched my 3-port valve, but that was to retrofit PDHW using a relay demand box. This has same outcome of having CH on the NO side of the valve. I had two non-TRV towel rails to ensure path for pump overrun.

 

The issue is I think my heat losses from the HW tank are a bit high and I'd like to lower the losses.

 

My thoughts are that having HW to NO is allowing the HW circuit to steal heat (via the coil) to the circuit thereby increasing my tank losses

 

I have Automatic bypass because all Rads are on TRV's

 

DHWP is NO to CH and that's the system I will go to when I replace the boiler in the summer

 

I'll let the 3 port stay at CH for a few days and see if that changes the HW heat losses

[OwenF]

I guess I can’t argue with your experience/perception that this is a significant source of losses.

 

However, an alternative observation is that nearly every DHW system is plumbed exactly the same way. So if you are experiencing it, so is everyone else.

 

I think the typical mitigation here is to insulate (as far as possible) the pipe runs at least 1m from your cylinder. Perhaps consider more cylinder insulation.

 

You mention changing the boiler in future. Make sure you get one capable of priority hot water, then any negligible losses back to circuit (if any!) will be moot as PDHW is quick reheat

[marshian]

4 hours ago, OwenF said:

I guess I can’t argue with your experience/perception that this is a significant source of losses.

 

However, an alternative observation is that nearly every DHW system is plumbed exactly the same way. So if you are experiencing it, so is everyone else.

 

I think the typical mitigation here is to insulate (as far as possible) the pipe runs at least 1m from your cylinder. Perhaps consider more cylinder insulation.

 

You mention changing the boiler in future. Make sure you get one capable of priority hot water, then any negligible losses back to circuit (if any!) will be moot as PDHW is quick reheat

 

Good point on other people in same boat - happy for anyone to share their losses and tank type

 

I plan to insulate the pipe work between boiler and tank (currently in ceiling void and un-insulated) as we need to replace the kitchen this year (apparently 28years is too long for the same kitchen according to SWMBO) so we will replace the ceiling in order to run the lighting ring round (for spot lights that she also wants) - hence boiler replacement at same time.

 

Boiler requirements are 12 - 14 kW,

High modulation (min of 3kW or better)

Flow Temp range 30 to 80 (ideally)

Capable of doing DHWP with weather compensation.

 

Current Boiler (14 year old Glow Worm Flexicom 24HX) 24kW (Range Rated to 12kW)

Modulation poor (10kW Min)

Flow temp Range 45 to 82 (38 deg is OFF)

Not capable of DHWP

Could work with weather comp (but the flow temp range and min kW make it pretty pointless)

 

According to the calcs I have done house heat loss is 4.6 kW at -2

 

If anyone thinks I've missed out something that I should consider let me know

[OwenF]

If your heat loss is 4.6kW at design outdoor temperature, you might consider better minimum modulation than 3kW.

 

Currently the only one I’m aware of capable is the Viessmann V200 (modulates to 1.9kW)

 

I’ve literally just had a V100 11kW installed (house demand is ~9kW) and in the last 24hours with outside temp of 11 degC it’s been on minimum modulation.

 

I’ve heard many people say that sub-10kW heat loss should be heat pump territory. Gas boilers just can’t operate efficiently at super low heat demand. At 4.6kW I’d be expected a boiler to be constantly on/off except on the coldest days.

 

p.s. I agonised over heat pump vs boiler and decided outlay was too high. I’d rather not think whether I’ve made the wrong decision!

Edited January 26 by OwenF

[marshian]

8 minutes ago, OwenF said:

If your heat loss is 4.6kW at design outdoor temperature, you might consider better minimum modulation than 3kW.

 

Currently the only one I’m aware of capable is the Viessmann V200 (modulates to 1.9kW)

 

I’ve literally just had a V100 11kW installed (house demand is ~9kW) and in the last 24hours with outside temp of 11 degC it’s been on minimum modulation.

 

I’ve heard many people say that sub-10kW heat loss should be heat pump territory. Gas boilers just can’t operate efficiently at super low heat demand. At 4.6kW I’d be expected a boiler to be constantly on/off except on the coldest days.

 

p.s. I agonised over heat pump vs boiler and decided outlay was too high. I’d rather not think whether I’ve made the wrong decision!

 

You raise some good points

 

I am going Viessmann but it will be 100-W at 50/30 flow and return it's 3.2 kW

 

I don't want a system boiler (or a combi) - I want a heat only with the outlets for Flow and return on the top of the boiler because that's where my pipework is routed thro the kitchen ceiling void

 

Also the 100-W fits inside a kitchen cupboard D=285mm, W=375mm, H=600 rather than being part of the cupboard frontage like the 200 would be D=360mm, W=450mm, H=700mm (SWMBO Rules)

 

I considered ASHP as I think I could do that but my reasoning for not going that route is

 

1. There are very few excellent installers and a lot of very poor ones (Especially due to the current grant arrangement which is not doing anything good for the ASHP reputation)

 

2. The technology will improve further in the next 10 years

 

3. I'd actually struggle to find a space for an ASHP that could be out of view (they aren't exactly pretty units) and if I did get one fitted it would be in a narrow alley between house and fence and there would be a risk of micro climate

 

4. I retire in 3 years and we will look to downsize in maybe 10 - 12 years (another HO boiler will do us just fine) and we also like to cook with gas so we'd lose that if we went ASHP with the grant.

 

There are a few other reasons but in a nutshell they are the main ones

[marshian]

1 hour ago, OwenF said:

p.s. I agonised over heat pump vs boiler and decided outlay was too high. I’d rather not think whether I’ve made the wrong decision!

SWMBO has issued statement that if we change the boiler this year she's not going to be happy if a few years later we swap out for an ASHP so on that basis I'm very sure it's the right decision to go with a gas boiler again

 

When we replaced the kitchen 28/29 years ago we had the original non condescending Glow Worm heat only boiler (fuelsaver 15/30 I think) previous owners of the house had painted it green to match the units or wall (can't remember which) so we built the new kitchen units around it (whilst still maintaining service access) to hide the ugly damn thing (also helped with noise as it was a pretty noisy thing)

 

When replaced the boiler in 2009 one of the selection criteria was she didn't lose any cupboard space so the new Glow Worm was selected to fit in the hole left by the previous boiler - the cupboard doors still close and hide it away despite it being slightly deeper.

 

Now apparently if you've had a gloss white kitchen for 28 years you can't have another gloss white kitchen - I don't understand the female logic - so it's very likely the new kichen will be absolutely anything other than white. 

 

If any boiler is on show it's very likely to be white and a white appliance in a coloured kitchen apparently won't do either so it has to fit in the same damn hole and be hidden from view.

 

My flow and return monitoring also shown with today's flow and return levels

[SimonD]

5 hours ago, marshian said:

I am going Viessmann but it will be 100-W at 50/30 flow and return it's 3.2 kW

 

I don't want a system boiler (or a combi) - I want a heat only with the outlets for Flow and return on the top of the boiler because that's where my pipework is routed thro the kitchen ceiling void

 

If you go for the heat only 100-W you lose the built in PDHW capability that comes with the system version which supports a 4 pipe installation and weather comp., plus it has better connected functionality out of the box. That way you also get the full benefit of the modulating pump working with the boiler where you wouldn't get that with the heat only.

 

A small bit of extra pipework is a small price to pay for the long-term benefits.

[marshian]

29 minutes ago, SimonD said:

 

If you go for the heat only 100-W you lose the built in PDHW capability that comes with the system version which supports a 4 pipe installation and weather comp., plus it has better connected functionality out of the box. That way you also get the full benefit of the modulating pump working with the boiler where you wouldn't get that with the heat only.

 

A small bit of extra pipework is a small price to pay for the long-term benefits.

 

The pipework I can cope with - However it's depth exceeds a std 300mm wall cupboard which means it's going to need to be on show - imagine if you can a line of lets say black wall units broken by a bright white boiler..........

 

I can live with that - SWMBO can't - life is full of compromises I know when I can win this isn't one of those times

[marshian]

I think I've answered my own question

 

Last two nights tank has been heated to 51 Deg (this is the lowest the tank stat will accomodate)

 

Note - I normally only heat to 45 deg (To minimise losses)  and do it based on a timed cycle with a set boiler flow temp (30 mins and 68 deg Flow normally sees it settle at 44-46 which is spot on)

 

Attached is the Tank Temps by Hour and Losses By hour over the two nights and a graph showing the difference

 

It's pretty clear to me with the 3 port valve open to the boiler (AK at rest) I lose temp from the tank far faster than with the 3 port valve closed to HW and open to CH

 

[TonyT]

Can the boiler not go in the loft?

 

or above the cylinder with vertical flue?

[marshian]

2 hours ago, TonyT said:

Can the boiler not go in the loft?

 

or above the cylinder with vertical flue?

 

Good question - really good question.......

 

I'd need a 5m extension to the gas supply and that would have to be run externally (not so keen on that) or internally in a boxed section thro kitchen and bedroom above - boiler is currently right above the gas meter box so the supply is just 15mm and less than 1m. I guess if you increase the length of the supply pipe you'd need to increase the pipe size but I've no idea what any of that would cost?

 

I'd have to brick up the existing flue inside and out but that's not a deal breaker as I already had to brick up the bloody great hole the original non condescending boiler flue left when I last changed the boiler in 2009

 

I'd need to have the flow and return pipes changed to suit the new boiler location but if I've got to run a gas pipe up inside the house in a boxed section I can run the flow and return back down the same or re-route and go straight to the airing cupboard where the tank is.

 

The question is do I want a boiler in the loft in order to gain a single cupboard space in the kitchen - I'm also pretty sure I'd need to move the cold water store and header tank as I don't really want a system boiler - Do I want a gas engineer to have to go into the loft every year when it needs a service and safety check as opposed to just having to grant access to the kitchen.

 

I think a few houses around mine have done it so it's an option for sure

 

Airing cupboard unfortunately is quite restrictive size wise and having boiler above the tank might be a pain for servicing - SWMBO definitely wouldn't be happy losing her towel warming area (despite the fact I've never had a warm towel from the cupboard ever!!!

 

She'd also whinge at the loss of her summer/autumn/winter duvet storage (in vacuum bags to get them into the space)

 

I could suggest we store them in the additional kitchen cupboard - that would be a fun conversation

 

The loft is certainly something to consider.......

[TonyT]

When I’m talking about loft, I also mean floored, lighting, safe working space not standing on trusses servicing boiler.

 

pipe boxes can easily, be made, painted to blend in.

not sure about gas pipes running inside, but you could run one parallel with a rainwater down pipe 

 

 

 

 

[TonyT]

You probably get more saving swapping the pump for a more energy efficient model, wrap some extra insulation around the cylinder too

[SimonD]

1 hour ago, marshian said:

The loft is certainly something to consider.......

 

18 minutes ago, TonyT said:

When I’m talking about loft, I also mean floored, lighting, safe working space not standing on trusses servicing boiler.

 

 

[marshian]

2 hours ago, SimonD said:

 

 

 

 

A comprehensive destruction of the loft advantage

[JohnMo]

On 25/01/2024 at 16:29, marshian said:

Rather than continue to threadjack another post

 

System info

Y plan system

Vented cylinder 112 Litres (Installed 2011 from memory)

Insulation on all the pipes around the tank - extending to loft and in loft to header tanks.

I still think my losses are too high 0.5-0.7 deg per hour

 

Lagging is good quality Turbolit (a considerable improvement on std DIY stuff - albeit that was better than bare copper pipes)

 

22mm copper pipes have 9.5 mm wall insulation

15mm copper have 12.5 mm insulation

 

I use a pipe lager pro mitre box to get neat joints and most are glued

 

But I think I might have a reason but I'd like an opinion on it

 

My three port valve is at rest on HW and powered to mid position or CH

 

At the end of every CH cycle the time runs the HW for a min to reset the valve to rest (if left in HW the motor body gets warm - warm = electricity - constant running = wear and tear on the valve head)

 

Hot moves to cold - water in the coil is heated back by the hot in the tank and convection currents move the water/heat back to the boiler - if I swapped the 3 port valve round (and the wiring) I could make the CH position the rest and it would block any flow back to the boiler - however the other end of the coil would still be connected to the boiler by the return pipe??

 

 

 

Just looking at the photo, your issue could be the vertical section of pipe from the cylinder coil to the 3 port valve. Very likely you have a nice internal current in that pipe. Ideal would be to take the pipe down 150mm then up to the valve. That would eliminate any likelihood of a thermosyphon.

[marshian]

20 minutes ago, JohnMo said:

Just looking at the photo, your issue could be the vertical section of pipe from the cylinder coil to the 3 port valve. Very likely you have a nice internal current in that pipe. Ideal would be to take the pipe down 150mm then up to the valve. That would eliminate any likelihood of a thermosyphon.

 

Very interesting - thanks for that observation

[Alan Ambrose]

>>> Now apparently if you've had a gloss white kitchen for 28 years you can't have another gloss white kitchen

 

You are not meant to understand, just observe the instruction .

 

[marshian]

Just now, Alan Ambrose said:

>>> Now apparently if you've had a gloss white kitchen for 28 years you can't have another gloss white kitchen

 

You are not meant to understand, just observe the instruction .

 

 

Oh that I do know

 

Anyway as stated earlier

 

I know the battles I can win,

I know the ones that are going to end up in a draw

 

This one ain't either and it's not worth fighting for a draw or a loss

[marshian]

15 hours ago, JohnMo said:

Just looking at the photo, your issue could be the vertical section of pipe from the cylinder coil to the 3 port valve. Very likely you have a nice internal current in that pipe. Ideal would be to take the pipe down 150mm then up to the valve. That would eliminate any likelihood of a thermosyphon.

 

Just to make sure I've highlighted the section in red on an old picture before I insulated it all and added the proposed amendment in green (Distance not to scale)

[JohnMo]

32 minutes ago, marshian said:

 

Just to make sure I've highlighted the section in red on an old picture before I insulated it all and added the proposed amendment in green (Distance not to scale)

 

That's the idea.

 

[marshian]

I know my HW outlet from the tank and vent pipe to the loft tank are contributing to the losses but they are a constant (they are well lagged all the way to the cold water tank - approx 5m away)

 

I guess it would probably not be a good idea to put a similar drop and return arrangement in that section?

[John Carroll]

On 28/01/2024 at 09:41, marshian said:

I think I've answered my own question

 

Last two nights tank has been heated to 51 Deg (this is the lowest the tank stat will accomodate)

 

Note - I normally only heat to 45 deg (To minimise losses)  and do it based on a timed cycle with a set boiler flow temp (30 mins and 68 deg Flow normally sees it settle at 44-46 which is spot on)

 

Attached is the Tank Temps by Hour and Losses By hour over the two nights and a graph showing the difference

 

It's pretty clear to me with the 3 port valve open to the boiler (AK at rest) I lose temp from the tank far faster than with the 3 port valve closed to HW and open to CH

 

 

That's interesting, some would like if the MPV allways returned to a unpowered default position of HW, especially overnight, some may think that this can be accomplishied by programming the HW (last) on for a few minutes but this will only work if the cylinder stat is also calling, otherwise the valve will stay powered up in CH as "its last port of call".                                                                                                                              I attach a modified schematic for anyone who's interested in making the MPV allways return to the unpowered HW position.

Edited February 20 by John Carroll