How to measure the remaining HW in an unvented cylinder

[marshian]

19 hours ago, Lofty718 said:

1930's 190m2 end terrace with solid brick in existing house and cavity wall in some parts, old suspended floors uninsulated and no ewi (should of done these)

 

whole house heated 24/7 to 21.5 with setback to 20c at night gas bill for december worked out at £6 a day this includes cooking and hot water usage (cylinder is set to recover 24/7 too whenever hot water drops below 40c)

 

Just for comparison and I'm not knocking your costs v comfort I'd love to be able to heat my house to that level.

 

Early 80's 4 bed detached with a stupid shape (think T shaped where several rooms have 3 external walls it's 113 m2 total with 2 floors (~55m2 each floor)

 

Gas for CH (rads only no underfloor) al HW and we cook on a gas hob most of the time. Heat loss calcs say 4.5 kW at -2

 

Heating on 0630 to 0815 and 1545 to 2200 weekdays - 0900 to 2200 weekends - rooms not used are set to 18 rooms used are set to 19 - 21 depending on use (Bathrooms higher than living room).

 

Cavity wall insulation, 25 year old SUDG but we did recently replace both sets of french doors for more thermally efficient ones - 100 mm of loft insulation and a 14 year old Glow Worm Flexicom 24HX that has a min kW of 10kW

 

Gas for Dec was £3.23 per day & Jan was £3.05 per day (includes SC and VAT)

 

I'm around 3.9 to 4.1 kW/HDD (with a base line for HDD at 16.5)

[Adsibob]

8 hours ago, JohnMo said:

Get rid of the LLH and replace with a small volumiser say 20L that should fit in the same space as the LLH. The volumiser would be in the house heating circuit only.

Remove the big secondary circulation pump, as not needed anymore 

Thanks @JohnMo. So that I can understand the basis of this recommendation, can you please explain:

 

What the volumiser would do which the LLH can’t do? Is Volumiser another word for buffer tank, or are these completely different?

 

Why you think I don’t need a big secondary pump?

[Adsibob]

It’s a tricky one, on the one hand, I like the simplicity of @JohnMo’s idea, but at the same time I was coming around to the features of WC. I guess I will ask the engineer I enventually go with to design and price both options, then I can consider pros and cons.

 

 Query whether a half way house might be to go with JohnMo’s idea, but with one modification: leave all tados installed, set them all to 20C when we are out for the day, 21C when we are in for the day and 18C at night. Then pay their stupid £3 a month subscription for something they call active start, I think, which is a sort of approximation of weather compensation. It takes weather forecast data for your postcode and triangulates this against the responsiveness data on your heating and heat loss data of your house, and then uses all that data to predict when it should turn on and off your heating to achieve the target temps you’ve set. Far from perfect, but might be a good compromise.

[JohnMo]

30 minutes ago, Adsibob said:

Thanks @JohnMo. So that I can understand the basis of this recommendation, can you please explain:

 

What the volumiser would do which the LLH can’t do? Is Volumiser another word for buffer tank, or are these completely different?

 

Why you think I don’t need a big secondary pump?

The difference between a LLH and buffer is purely volume of water it contains, both provide hydraulic separation.

 

A volumiser is inserted in the flow or the return and is there to provide volume only, it does not provide hydraulic separation.

 

With hydraulic separation you have to have a pump either side of the buffer or LLH - one for the boiler and one for CH and/or cylinder side

 

The big pump is there because you have a LLH.  Remove the LLH and the boiler pump will do the pumping.

 

24 minutes ago, Adsibob said:

leave all tados installed, set them all to 20C when we are out for the day, 21C when we are in for the day and 18C at night.

Trouble with WC is they have a glacial reaction time due to the low flow temp.  You may be better setting to 20.5 except a set back period of 19.

 

[Lofty718]

1 hour ago, marshian said:

 

Just for comparison and I'm not knocking your costs v comfort I'd love to be able to heat my house to that level.

 

Early 80's 4 bed detached with a stupid shape (think T shaped where several rooms have 3 external walls it's 113 m2 total with 2 floors (~55m2 each floor)

 

Gas for CH (rads only no underfloor) al HW and we cook on a gas hob most of the time. Heat loss calcs say 4.5 kW at -2

 

Heating on 0630 to 0815 and 1545 to 2200 weekdays - 0900 to 2200 weekends - rooms not used are set to 18 rooms used are set to 19 - 21 depending on use (Bathrooms higher than living room).

 

Cavity wall insulation, 25 year old SUDG but we did recently replace both sets of french doors for more thermally efficient ones - 100 mm of loft insulation and a 14 year old Glow Worm Flexicom 24HX that has a min kW of 10kW

 

Gas for Dec was £3.23 per day & Jan was £3.05 per day (includes SC and VAT)

 

I'm around 3.9 to 4.1 kW/HDD (with a base line for HDD at 16.5)

Your costs sound quite reasonable, the cavity wall insulation all around in an 80's build makes all the difference. I lived in a 80's property previously (without CWI) and had similar running costs to you and it was a lot less leaky than something with solid brick and suspended floor. What flow temp are you running at? you should try and heat your house all day to 20c and see how much gas it will use, for our little research project here

 

Also worth pointing out with weather compensation you don't get huge savings on the cold days running costs won't be much different when the boiler is running full whack, but i've noticed when the weather is mild is where you save most of the money. September-October and March - early may. A better cost comparison would be a whole years usage.

Edited February 2 by Lofty718

[marshian]

49 minutes ago, Lofty718 said:

Your costs sound quite reasonable, the cavity wall insulation all around in an 80's build makes all the difference. I lived in a 80's property previously (without CWI) and had similar running costs to you and it was a lot less leaky than something with solid brick and suspended floor. What flow temp are you running at? you should try and heat your house all day to 20c and see how much gas it will use, for our little research project here

 

Also worth pointing out with weather compensation you don't get huge savings on the cold days running costs won't be much different when the boiler is running full whack, but i've noticed when the weather is mild is where you save most of the money. September-October and March - early may. A better cost comparison would be a whole years usage.

 

Flow temps I vary depending on outside temps low to mid 50's normally (never more than 60 so far this year - that cold snap we had) return temps High 20's to Mid 30's (very dependant on flow temps but I get just under 20 deg delta at the boiler once the circuit is up to temp)

 

The boiler has a 10 kW min and due to internal programming gives a 18kW hit for 8-10 secs on restart which is a pain - I have to have an extended POR and ACT settings to give the circuit time to cool as much as possible or it overshoots way to easily and it still cycles a fair bit this means mean water temps in the rads are low 30's this time of year

 

I know I could go ASHP but it's being replaced for a Viessmann 100 W heat only in the summer

 

Boiler is range rated to between 12 and 16kW (acts as my other manual weather comp assisting flow temp changes because we heat intermittantly so I need a reasonably responsive system and a quick warm up)

 

I could try to heat the house to 20 deg all day but the shape of it means those rooms with 3 external walls are my biggest contributions to my heat loss and we don't use 2 of them

 

My 3.9 to 4.1 kW / HDD I'm OK with when it's Autumn or Spring (or a mild day in winter) I can be anywhere from 5 to 9 kW per HDD - that's where I know WC would help because my manual weather comp is never as accurate as a well managed curve (I tend to have temps I know work for autumn winter and spring so miss out on the finer deg changes that weather comp would provide)

 

Annual usage (last 12 mths) 8,147 kW as at 31st Jan

[Adsibob]

2 hours ago, Adsibob said:

Then pay their stupid £3 a month subscription for something they call active start, I think, which is a sort of approximation of weather compensation. It takes weather forecast data for your postcode and triangulates this against the responsiveness data on your heating and heat loss data of your house, and then uses all that data to predict when it should turn on and off your heating to achieve the target temps you’ve set. Far from perfect, but might be a good compromise.

Actually, this is just more Tado marketing crap. Looked into reviews of the early start feature and seems pretty dumb. Reviews quite poorly on the Tado community forum.

[marshian]

11 minutes ago, Adsibob said:

Actually, this is just more Tado marketing crap. Looked into reviews of the early start feature and seems pretty dumb. Reviews quite poorly on the Tado community forum.

 

Wiser have a similar system called ECO mode - it learns your heating pattern and then uses the weather based on your location to bring the heating on to reach your target temp at the time you need it - used it for a week and it absolutely chewed thro the gas for no real benefit

 

I don't need the house at temp when I get up - I need it to be warming up - ie not fecking chilly just some heat added from the overnight off

 

I need the bath room up to 19 for a shower at 8am not 6am - I don't go near it till then

 

So in summary I probably needed to complete change the target temps and times to make it work for me and I couldn't be arsed

 

I've not tried it since

 

Other opinions may well be different

[JohnMo]

Early start early stop with UFH just doesn't work, the algorithm is really designed for radiators not UFH.  Same as load compensation useless with UFH. Never achieves the correct temperature at the right time. Tried it with Atag controls and Salus.

[SimonD]

22 hours ago, JohnMo said:

My suggestion is to keep it simple.

 

Leave UFH system as is, with thermostats etc

Move boiler to 4 port configuration

Get rid of the LLH and replace with a small volumiser say 20L that should fit in the same space as the LLH. The volumiser would be in the house heating circuit only.

Remove the big secondary circulation pump, as not needed anymore 

Run heating at a fixed flow temp (not WC), but run way lower flow temp than it's run now, say 35-40, but run for much longer. Nearly all the benefits efficiency wise, easier to implement, your wife will not be asking why you bought all those thermostats.

 

13 hours ago, Adsibob said:

It’s a tricky one, on the one hand, I like the simplicity of @JohnMo’s idea, but at the same time I was coming around to the features of WC. I guess I will ask the engineer I enventually go with to design and price both options, then I can consider pros and cons.

 

A big problem with this suggestion is that it doesn't deal with the different Delta Ts of the heating system. You need 20 at the boiler and about 7 across the UFH which means a significantly different flow rates!

 

Just one pump feeding the system is not going to cut it, I'm afraid. And with the mass flow rate calcs, you're very likely to still need a flow temp of around 50C at the boiler for this to actually work. There has got to be some form of mixing in there.

 

@Adsibob may I suggest that with the engineer/s you're speaking to, you focus on the principles of the system, not specific suggested solutions or products? So highlight the solar gain, modulation, efficiency, comfort etc. and of course your budget and if necessary be willing to junk existing controls and set aside your preconceptions etc. (although by the sounds of it, you're rather close to that point anyway - I personally would be outraged at a £3 per month subscription for control functionality that can be gotten more acurately with good system setup and a sensor plugged into the boiler itself). At the end of the day you're only really worried about a system that provides comfort, simple manageability and reliability without much regular input by you.

[Adsibob]

22 hours ago, JohnMo said:

My suggestion is to keep it simple.

 

Leave UFH system as is, with thermostats etc

Move boiler to 4 port configuration

Get rid of the LLH and replace with a small volumiser say 20L that should fit in the same space as the LLH. The volumiser would be in the house heating circuit only.

Remove the big secondary circulation pump, as not needed anymore 

Run heating at a fixed flow temp (not WC), but run way lower flow temp than it's run now, say 35-40, but run for much longer. Nearly all the benefits efficiency wise, easier to implement, your wife will not be asking why you bought all those thermostats.

@SimonD, re @JohnMo’s suggestion above, I’m a little confused by your comment:

17 hours ago, SimonD said:

A big problem with this suggestion is that it doesn't deal with the different Delta Ts of the heating system. You need 20 at the boiler and about 7 across the UFH which means a significantly different flow rates!

Or are you talking about something else? Wouldn’t the 4 pipe system give me two temperatures: high for heating the cylinder and the two radiators and low for the UFH?

[JohnMo]

30 minutes ago, SimonD said:

You need 20 at the boiler and about 7 across the UFH which means a significantly different flow rates!

How can you have 20 dT requirement when you are only flowing at low temps, the boiler would be expecting a return temp lower than room temp - that cannot happen. Example flow of 30 degrees how can you have a return of 10 when the room is at 20? A boiler capable of low flow temperature isn't designed like that. 20dT is old hat for high temp boilers only.

 

Example - My Atag never looked for 20dT would just modulate the pump the get the dT it wanted to see. At low flow temps would modulate the pump to around 7dT, that was the dT you had from the boiler.

 

37 minutes ago, SimonD said:

Just one pump feeding the system is not going to cut it,

Again not sure where you get one pump, there is one pump in boiler and one on each manifold. 4 manifolds and boiler pump.

 

Get rid LLH, no mixing going on there, flow around 32 into the floor, 42 from the boiler to allow for mixing manifold mixers. If you wanted to get dT20 you just run at dT 10 across the floor, boiler return is 22, efficiency about as good as it gets.

 

 

[Dan F]

44 minutes ago, JohnMo said:

there is one pump in boiler and one on each manifold. 4 manifolds and boiler pump.

 

44 minutes ago, JohnMo said:

mixing manifold mixers

 

My understanding was that the UFH pumps (after the mixing valves) need to pull from a buffer.  The UFH flow rate is consistent, but the flow rate to the manifold changes based on the position of the mixing valve.  Does this really work without hydraulic seperation?

 

You'd need a bypass valve I assume, but doesn't the lack of buffer/LLH impact the correct operation/mixing of the UFH circuits?

Edited February 3 by Dan F

[JohnMo]

38 minutes ago, Dan F said:

 

 

My understanding was that the UFH pumps (after the mixing valves) need to pull from a buffer.  The UFH flow rate is consistent, but the flow rate to the manifold changes based on the position of the mixing valve.  Does this really work without hydraulic seperation?

 

You'd need a bypass valve I assume, but doesn't the lack of buffer/LLH impact the correct operation/mixing of the UFH circuits?

UFH pump pulls through the mixer valve. Doesn't need a buffer in the system but can if you want.  The low loss header installed has a pump on the central heating side, so different to elimination of LLH and just using the boiler pump. I run with zero hydraulic seperation and mixer valve and pump on UFH without issue. Have also run direct from heat pump and boiler without mixer and pump, again no issues.

 

If you have all circuits of the UFH running with actuators, you need a bypass, or simply make some circuits always open whenever there is a call for heat, such as bathrooms which can never be too warm.

[Dan F]

35 minutes ago, JohnMo said:

I run with zero hydraulic seperation and mixer valve and pump on UFH without issue.

Not sure about with 1 manifold, but I was fairly sure that the theory says that if you have 2+ such manifolds like this hydrualic seperation is a must.

 

Direct from heat pump with no seperation, mixer, or additional pumps is defintily a workable and is the ideal approach, no question there.

[Adsibob]

45 minutes ago, Dan F said:

Direct from heat pump with no seperation, mixer, or additional pumps is defintily a workable and is the ideal approach, no question there.

So if that’s the ideal, what is stopping me implementing that? Is it the 2 towel heaters being on their own zone? If so, couldn’t I have some sort of diverter that diverts water from the loop which heats the cylinder to the towel rads when needed? Towel rads are used for maybe 15 min at a time, twice a day at the very most.

[Lofty718]

Regarding dT at the boiler, mine is nowhere near 20 and you will never get that on a boiler running low temperatures 35-40c. It's always less than dT 10, but my boiler is oversized so better could be acheived on a Viessmann with a better modulation raito.

 

 

[marshian]

1 hour ago, Lofty718 said:

Regarding dT at the boiler, mine is nowhere near 20 and you will never get that on a boiler running low temperatures 35-40c. It's always less than dT 10, but my boiler is oversized so better could be acheived on a Viessmann with a better modulation raito.

 

 

Agreed - lower the flow temp the lower the DT at the boiler

 

Heat Geek reckon a good guide to expected DT is flow temp x .7 to get your return temp

 

Obviously the temps below are guides for boilers supplying rads but UFH flow temps can be a lot lower and the return much closer to flow and DT much narrower

 

Flow Temp	Return Temp	Diff
80	56.0	24.0
75	52.5	22.5
70	49.0	21.0
65	45.5	19.5
60	42.0	18.0
55	38.5	16.5
50	35.0	15.0
45	31.5	13.5
40	28.0	12.0

[Adsibob]

On 01/02/2024 at 16:23, SimonD said:

Given 2 major things: 1, you typical lifestyle and usage of the system, and 2, the solar gain in certain rooms, I will go against the grain here.

 

So briefly, I'd go down the route of 4 pipe priority hot water with weather compensation BUT retain/or install new room based zoning controls to deal with intermittent use and solar gain. The weather compensation deals with heat distribution through the temperature of the system and the zones by controlling flow. To deal with potential low system volume due to closed zones, the buffer would counterbalance this and reduce short-cycling risks.

This is also my gut feel, and indeed why I have so many zones in the first place. The building regs encourage zoning, so I thought this was a good thing: only heat what you are using. But when I mentioned my zoning to the heating engineer you recommended, he explained (or rather his junior associate explained because the main guy is on holiday) that keeping rooms switched off is a false economy because you get heat loss from the rooms which are on into the rooms that are off. This Heatgeek article explains the maths, but using the example of a radiator setup. Not sure it’s still such a problem in a UFH setup, but the engineer thought it would be.

Edited February 3 by Adsibob

[SimonD]

14 hours ago, Adsibob said:

Or are you talking about something else? Wouldn’t the 4 pipe system give me two temperatures: high for heating the cylinder and the two radiators and low for the UFH?

 

Don't worry, we're talking about something different. However, the 4 pipe system isn't really designed to have towels radiators on the high temperature hot water circuit and if they were, they would only get heated when the boiler is reheating your hot water cylinder. If you want the freedom to heat the towel radiators at any time, they would need to be on the normal central heating circuit.

 

11 hours ago, Adsibob said:

So if that’s the ideal, what is stopping me implementing that?

 

Th ideal situation depends on the customer's specific needs, not a generic one size fits all solution. What stops you from implementing this is:

 

1. you both want and need zoning for comfort and due to solar gain. This requires a buffer in your system to reduce short-cycling risks due to the microzoning you have throughout your house.

2. you want a towel radiator circuit with some extra warmth. This would be fed either directly from the boiler, or a pre-heated buffer tank.

 

13 hours ago, JohnMo said:

How can you have 20 dT requirement when you are only flowing at low temps, the boiler would be expecting a return temp lower than room temp - that cannot happen. Example flow of 30 degrees how can you have a return of 10 when the room is at 20? A boiler capable of low flow temperature isn't designed like that. 20dT is old hat for high temp boilers only.

 

I'm sorry, but what are you talking about? Delta T 20 is a standard design figure for hydronic systems and it is usually specified by boiler manufacturers although Viessmann has reduced it to 15 degrees, but other high efficiency boilers, like the Ideal vogue Max spec Delta T 20. You comment about Delta T 20 being old hat for high temp boilers is misconceived and certainly not supported by current industry design guidelines.

 

But to get back to the actual issue that arose out of my questions about the installed system and suggested modification. The design of the system however is about how to get enough heat to the right parts of the house at the right time, so it's about moving energy in a way that works for the occupant.

 

In this sense, it is about finding a balance between function and efficiency, not merely optimising efficiency and using arbitrary figures that don't give any indication that they'll work for the required heat load of the house over the heating season.

 

Simply running a system for longer will not sufficiently heat a home if it doesn't supply enough heat energy into the space. Your solution may not do so unless there are high flow rates through the system which may potentially add unecessary resistance and noise to the system - but at the end of the day, neither you nor I know that as the flow rates need to be calculated based on the installed system.  This is one of the reasons I'm trying to suggest weather compensation and load compensation because they'll dynamically adapt to the heating loads of the building by increasing flow temperature where necessary while maintaining lower flow rates. It's also one of the reasons that against the consensus on here I supported keeping the zoning in place because @Adsibob has said the heating system works well for their comfort. And that's where the suggestion of a buffer originally came from.

 

As is so often the case, the pipework arrangement and set temperatures has become the distraction whereas the original issue highlighted was control of the system in a way that is consistent with the ops needs, original intent, and the balance of comfort and efficiency.

 

Fundamentally the problem resides with the original system design because the installer has followed the herd by installing UFH when actual real world use and the nature of the house actually indicate that a low thermal mass/inertia system with generous buffer would have been the way to go which may have run at a higher flow and/or mean water temperature, but would have been more efficient overall due to the context.

[Adsibob]

@SimonD thanks again for all the time you are putting into this thread. And thanks to everyone really, all contributions are helping me learn.

Just to clarify one thing further: we much prefer ufh to radiators. So I think that even if a survey by a properly qualified engineer had concluded in this:

15 minutes ago, SimonD said:

actual real world use and the nature of the house actually indicate that a low thermal mass/inertia system with generous buffer would have been the way to go

I wouldn’t have accepted it. 
 

But your idea has got me thinking. let’s say I install weather compensation, is there a way to vary the flow rates in different zones depending on usage, or would that be incompatible with WC? So rather than on/off controls to open and close zones, are there ways of having electronically controlled flow rates on the manifolds to deliver more or less heat? This of course could get expensive, as I guess I would have to replace my manifolds, but they are pretty budget ones (I don’t think you can get cheaper than the ones I have) so might be something I would consider.

[SimonD]

15 minutes ago, Adsibob said:

This is also my gut feel, and indeed why I have so many zones. But when I mentioned my zoning requirement to the heating engineer you recommended, he explained (or rather his junior associate explained because the main guy is on holiday) that keeping rooms switched off is a false economy because you get heat loss from the rooms which are on into the rooms that are off. This Heatgeek article explains the maths, but using the example of a radiator setup. Not sure it’s still such a problem in a UFH setup, but the engineer thought it would be.

 

I'm familiar with the Heat Geek article and I'm almost sure I've watched a video on the subject. I've also read a number of other sources on the topic, including one of the lead books on hydronic systems design.

 

The fact is that the calculations are incredibly complex to really work this out because it depends so much on the fabric of the building as well as partition wall structure, door open, open plan etc., but it also depends on external factors. The heat geek article sums are a serious simplification of the dynamics involved and they also use the extreme design temp of -3 C and a mean room temperature of 20C which typically represents a fraction of the heating season. But also, doesn't take into consideration solar gain, for example. 

 

But also, heating systems almost never function in their set design state, they're by their very nature dynamic

 

If you don't take into consideration things like solar gain and instead design only for the static figures, you risk ending up with overheating, especially during autumn and spring. This is why I think heating system design is always a bit of a compromise.

 

The reality is that you probably don't need as many zones as you have and I'm sure you could rationalise them somewhat and still have the same levels of comfort with improved efficiency. What you could probably also test is a set period of time where you don't zone your heating but keep everything open and see how you experience that. You can take meter readings to see what happens with your consumption.

 

[SimonD]

28 minutes ago, Adsibob said:

I wouldn’t have accepted it. 

😁

 

33 minutes ago, Adsibob said:

is there a way to vary the flow rates in different zones depending on usage, or would that be incompatible with WC?

 

ESBE make outdoor/indoor regulated mixing valves for multiple zones - the company you've spoken to will know about these. And Viessmann has some weather comp mixing functionality, but whether it is suitable for your needs, I don't yet know as I haven't got that deep into the Viessmann design guide.

[Lofty718]

15 hours ago, SimonD said:

😁

 

 

ESBE make outdoor/indoor regulated mixing valves for multiple zones - the company you've spoken to will know about these. And Viessmann has some weather comp mixing functionality, but whether it is suitable for your needs, I don't yet know as I haven't got that deep into the Viessmann design guide.

Viesmann design recommends mixed circuits with a divicon / esbe mixing valve

 

Viesmann sell these divicons but they are prohibitively expensive. compared to just using an esbe valve and pump

 

https://viessmanndirect.co.uk/Catalogue/Divicons-and-Mixers/Divicon/Divicon-with-Mixer-Extension

 

I would never live in a house with UFH that's not controlled by an electronic mixing valve😃 my esbe works very well

[JohnMo]

1 minute ago, Lofty718 said:

would never live in a house with UFH that's not controlled by an electronic mixing valve😃 my esbe works very well

Would agree, I just set mine to max likely temp (33), so it generally fully open with no mixed flow, unlike a normal mixer that generally mixes down 10 degs like it or not.  The heat pump really has no idea it's there as far as flow temps are concerned.  They can be controlled at two set points - have second setting (22) set, so it closes the valve when the pump is switched off.