How to measure the remaining HW in an unvented cylinder

[marshian]

18 hours ago, Adsibob said:

<snip> I didn’t realise boiler setups were that complicated. My boiler and heating system and tank was installed by an electrician and a gas engineer.

 

<snip>

 

 

4) I like tado.

 

<snip>

 

With retrospect, I should have got the system properly designed, as then proper insulation for the secondary return/loop pipe would have been specified, and we might have a more sophisticated HW heating system but given everything is working well, I’m not sure how much I would have saved in the long wrong by paying for a professional design.

 

I've sniped out a lot of your post just to focus on a few comments

 

Point 1 - they aren't that complicated but you really need to match the controls to your needs

 

Point 2 - Yeah I get that when you get used to a "smart" system you ar reluctant to change to something else and have to relearn every thing to do with set up and programing- trouble is a lot of so called "smart" systems are really just "Smart On and Off" and you can cause yourself issues by micro zoning

 

Point 3 - Not wanting to cause offence but - How much of the design was down to you already having an opinion already on what you thought you wanted or needed?

 

I'm just a guilty of Point 3 when I had my current boiler installed and very guilty of it when I installed a wiser system thinking that out of the box it would resolve my issues at the time - it's taken a long time to actually get the system and boiler settings to work well with Wiser - biggest thing is to stop unnecessary zoning

[marshian]

2 minutes ago, SteamyTea said:

When he drives a car does he accelerate in the lowest gear possible up to the red line, then hit the brakes, then does it over and over again.

I do the long journey up to Buckinghamshire every couple of weeks, always amazed me, on the motorway, the number of cars that have no traffic in front of them that keep apply the brakes, for no obvious reason.

 

Fortunately he doesn't but I get the "inference"

 

Problem he has is I'm just a lay person - I know nothing about boilers and I'm not a trained gas engineer or boiler installer - his Gas engineer is trained and therefore he knows what is best and much more than a lay person. I've made a suggestion on how he can reduce his gas bills (60% more than mine in the same size house) and if he ignores it I can't help that.....

[Adsibob]

1 hour ago, SimonD said:

 

Are you aware that this product does not do load compensation with the boiler, i.e. manage flow temperatures to get full benefit of your modulating boiler? It only does relay switching for both hot water and central heating?

 

I'm a bit of a critic of Tado given that in the UK and also from their professional installer's shop that ships from Germany, you can't get a controller that does digital control and modulation for system/heat only boilers (S & Y plan), only for the combi. And if you want modulation via Opentherm E-bus or Km-bus for a combi you pay a hefty premium, £200 versus about £89. I now always spec other controllers because of this. For single zones, as a contoller, the Honeywell T6R-HW is far better because Opentherm is supplied as standard, as is the process of setup compared to the Tado (IMHO).

 

If you want full efficiencies from your boiler and heating setup, I'd recommend you change your controllers. Your heating engineer really should have told you this given the importance you put on modulation.

Are you sure about this?  I wasn’t aware. If it’s true, that’s pretty cheeky of Tado. I kind of assumed that smart meant smarter than a bog standard controller. I’m not going to change the UFH tado thermostats, but if you think there is a benefit to changing the HW controller, I’m happy to consider it. Is there something that can be controlled away from the house that also meets the requirements you mention?

[Adsibob]

Other question I have is whether load compensation is that relevant for a house that is only heated by UFH? The boiler sends hw to the manifolds and its mixed there. There are very rarely higher deltas between desired room temp and actual room temp of 2C, 2.5C at most.

[Adsibob]

2 hours ago, SimonD said:

Are you aware that this product does not do load compensation with the boiler, i.e. manage flow temperatures to get full benefit of your modulating boiler?

If this is accurate, then this marketing piece is one of the most misleading adverts I’ve ever fallen for. Shame we don’t live in Australia or the US otherwise this would be a great class action.

 

 

[SimonD]

8 minutes ago, Adsibob said:

Are you sure about this?  I wasn’t aware. If it’s true, that’s pretty cheeky of Tado. I kind of assumed that smart meant smarter than a bog standard controller. I’m not going to change the UFH tado thermostats, but if you think there is a benefit to changing the HW controller, I’m happy to consider it. Is there something that can be controlled away from the house that also meets the requirements you mention?

 

I'm as completely sure about this as I can be, this is an excerpt from a complaint I made to Tado about receiving incorrect guidance from their technical team before buying the controller from Tado for a customer - all of which worked out to be somewhat embarassing for me, but no apology from Tado:

 

Quote

I really am not sure which agents you've spoken with earlier, I do not see any conversations with your email address.

With S/Y plan systems, they usually have a system boiler and a hot water cylinder. This type of system operates on zone valves and relays and is not capable of modulation.

In such instances, we do not support modulation. We don't have a device that has a modulating, digital connection for central heating and then a relay connection for hot water.

For that specific reason, we offer the Wireless Receiver UK, with Hot Water control, which has 2 channels, like a standard UK programmer/timer.

 

The situation is different for the combi option and there are rumours there's a european version that does support modulation, but I've been unable to source one and feels like a waste of time trying any further....

 

26 minutes ago, Adsibob said:

If this is accurate, then this marketing piece is one of the most misleading adverts I’ve ever fallen for. Shame we don’t live in Australia or the US otherwise this would be a great class action.

 

That's a interesting point. Tado have already come up for criticism for removing modulation from the controls they sell in the UK without telling anybody, particularly the combi version. But also, if you read more into the paper they use to sell the efficiency gains, you'll find that it does not appear to be based upon the modulation of the boiler. Here's a bit that I find quite laughable:

 

Quote

Aside from the chosen comfort setting, the
achievable energy savings primarily depends
on the amount of time the users are at home
each day, the chosen room air temperatures
during absence, and the level of the internal
heat sources (refrigerator, oven, etc.). The more
frequently the users leave the home and the
longer they are absent, the larger the system‘s
potential energy savings are, as this increases
the length and frequency of the periods with
reduced room air temperatures. I

 

The bold highlights are mine, but to me it seems fairly obvious that if you're not at home needing heating and the heating is turned off, you're going to save energy!

 

Link to the report for full reading: https://www.ibp.fraunhofer.de/content/dam/ibp/ibp-neu/en/documents/ibp-report/579.pdf

 

You might also note that Viessmann Direct don't appear to sell Tado, but only Viessmann controls...

1 hour ago, Adsibob said:

Is there something that can be controlled away from the house that also meets the requirements you mention?

 

As you're already in the Tado ecosystem, there's no point trying to swap out anything for just part of the system. Live with what you've got and only when it's time to switch the whole thing do you reconsider what you have as a whole.

[SimonD]

1 hour ago, Adsibob said:

Other question I have is whether load compensation is that relevant for a house that is only heated by UFH? The boiler sends hw to the manifolds and its mixed there. There are very rarely higher deltas between desired room temp and actual room temp of 2C, 2.5C at most.

 

It is totally relevant because it reduces the load on the boiler as well as bringing operating (flow) temperatures down to improve running efficiency. It's also likely to extend running times of the boiler.

[Adsibob]

36 minutes ago, SimonD said:

As you're already in the Tado ecosystem, there's no point trying to swap out anything for just part of the system. Live with what you've got and only when it's time to switch the whole thing do you reconsider what you have as a whole.

But the HW control is separate to the UFh controls. And whereas the UFh controls are zoned and use low temp water, the HW control doesn’t. So if you could recommend a smart controller for the Hw I’d be grateful.

[marshian]

2 hours ago, Adsibob said:

But the HW control is separate to the UFh controls. And whereas the UFh controls are zoned and use low temp water, the HW control doesn’t. So if you could recommend a smart controller for the Hw I’d be grateful.

 

How smart do you want the HW controls to be?? You want HW when you want it?

 

Ideally I want the boiler range rated to the cylinders capacity to transfer the heat and the flow temperature of boiler to be whats required for the end temp of the water in the tank to be what I want.

 

Pointless for me to bugger about trying to achieve condensing temps in my boiler when heating water. The coil in the tank is sized for a 3kW input - the boiler is throwing 10 kW min at it (12kW on start up because that's what I have range rated the boiler to be maximum)

 

Even if the tank is down to 16 deg (ie completely cold) in 36 mins (time not boiler run time cos it'll cycle a few times in that) at a set point of 82 deg the tank stat set at 48 deg setpoint will turn the HW off and it'll gain another few degrees during the pump over-run period

 

If there is any HW left in the tank say 40 deg at top and 16 at the bottom it'll heat it to target in 20 mins

 

If it's -2 outside the house doesn't lose temp in rooms in 20 or 30 mins - there is still heat left in the rads when the water is called for.

 

That's why I will be going DHWP with the next boiler because now I'm doing it manually and in this day an age I want stuff to work for me not require manual intervention and I can leave the boiler to sort out it's flow temps based on weather comp for when hot water isn't needed.

[SimonD]

3 hours ago, Adsibob said:

But the HW control is separate to the UFh controls. And whereas the UFh controls are zoned and use low temp water, the HW control doesn’t. So if you could recommend a smart controller for the Hw I’d be grateful.

 

Do you know if your boiler has been installed with the 4 pipe system or 2 pipe system? Take a pic of boiler and pipework below maybe?

[Adsibob]

1 hour ago, SimonD said:

 

Do you know if your boiler has been installed with the 4 pipe system or 2 pipe system? Take a pic of boiler and pipework below maybe?

From what I can see, it’s two pipes, plus a gas pipe:

I also have a low loss header, not sure if that impacts your views (see next post)

 

 

[Adsibob]

Just now, Adsibob said:

next post

[SimonD]

1 hour ago, Adsibob said:

From what I can see, it’s two pipes, plus a gas pipe:

I also have a low loss header, not sure if that impacts your views (see next post)

 

 

 

Yes, it's a 2 pipe install. For PDHW the two pipes between the outer flow and returns and gas pipe would be used to supply the DHW. So it is possible to modify your existing installation, but not without some work.

 

I can't quite make out all the pipework in your photos, but you'd need to run pipes from these boiler connections straight to your hot water cylinder and this can bypass your low loss header pipework completely. You'd then modify the existing pipework that currently goes through the motorised valves to your water cylinder and just cap it off.

 

Wiring wise, you could still use your existing cylinder stat, but wire in a Viessmann cylinder demand terminal box which converts the 230v call from the cylinder to low voltage to go into your boiler to run the 4 pipe PDHW. That way you can still control the schedule from your Tado app. Otherwise, you could rewire to hot water control using the low voltage DHW cylinder temperature sensor.

 

That should, in theory, work...

[Adsibob]

@SimonD thanks. Please could you explain what is wrong with my current setup and how much more efficient heating the cylinder would be if I did this work? Just trying to understand the cost benefit analysis.

[Adsibob]

To at to my previous post, my understanding is that for a boiler to go into “condensing mode” the return temperature should not be higher than about 55C and a low loss header can assist with this.

 

So I’m just trying to figure out if the benefit I’m getting from the low loss header might be cancelling out the efficiency deficit of not having PDHW.

[marshian]

29 minutes ago, Adsibob said:

To at to my previous post, my understanding is that for a boiler to go into “condensing mode” the return temperature should not be higher than about 55C and a low loss header can assist with this.

 

So I’m just trying to figure out if the benefit I’m getting from the low loss header might be cancelling out the efficiency deficit of not having PDHW.

 

 

Absolutely - the low loss header should not be needed if you have separate flow temp for UFH and having to run at a fixed temp is impacting efficiency

 

PDHW at a sensible temp for HW tank reheat and a really low flow temp for UFH is what you need

[Adsibob]

36 minutes ago, marshian said:

 

 

Absolutely - the low loss header should not be needed if you have separate flow temp for UFH and having to run at a fixed temp is impacting efficiency

 

PDHW at a sensible temp for HW tank reheat and a really low flow temp for UFH is what you need

Sorry Marshian, I’m not understanding your response. I (now) understand that PDHW is best design, but in the absence of this I’m trying to understand how much worse of my current setup is, given I had understood there were efficiency benefits of using a low loss header.

[TonyT]

You don’t add a low loss header for adding efficiency, generally used if you have more than one boiler or multiple pumps to provide hydraulic separation to the system.

 

you have a decent boiler I wouldn’t stress any more 

 

.

 

 

[JohnMo]

8 hours ago, Adsibob said:

To at to my previous post, my understanding is that for a boiler to go into “condensing mode” the return temperature should not be higher than about 55C and a low loss header can assist with this.

 

So I’m just trying to figure out if the benefit I’m getting from the low loss header might be cancelling out the efficiency deficit of not having PDHW.

Would suggest you are overthinking something here.

 

You system is what it is, low loss header no point, but you have one, unless really well designed specifically for your system they reduce efficiency. But you have what you have.

 

If you are concerned with running out of hot water allow more time slots for heating. I heat once in the morning and again in the afternoon (but it will only add heat if needed by the thermostat), you could just as easily allow it to heat anytime based on thermostat thermostat. If you aren't consuming the thermostat will get to temperature and stop the heat cycle.

 

Unless you are willing to pay a huge amount of money out, to get a plumber in and pull your house apart, just use your thermostat, the timer you have - done

[marshian]

9 hours ago, Adsibob said:

Sorry Marshian, I’m not understanding your response. I (now) understand that PDHW is best design, but in the absence of this I’m trying to understand how much worse of my current setup is, given I had understood there were efficiency benefits of using a low loss header.

 

LLH means 2 pumps two lots of electrickery being consumed - that's a cost to you.....

 

Unless your system is really heavily zoned then I don't see why the boiler couldn't supply the low temp water required for your UFH and the high temp for HW generation when set up with DHWP

 

What flow temp and return temps are you running at the boiler and what flow and return temps are you needing for your UFH

 

 

[SimonD]

10 hours ago, Adsibob said:

@SimonD thanks. Please could you explain what is wrong with my current setup and how much more efficient heating the cylinder would be if I did this work? Just trying to understand the cost benefit analysis.

 

So just to go back to my original conclusion that you're in the Tado sphere and may as well just stay there without changing anything and you specifically asked me to suggest a different controller for your hot water. I'm not trying to steer you down that road due to the upheaval required to do so.

 

My statements were more to explain that your system is not doing what you think it is doing, nor probably what you meant for your system to do when you employed your installer. You thought you had priority hot water and you thought your boiler/controls combo would modulate the boiler that you'd chosen for its ability to modulate and the installation you have does not appear to do either of those.

 

You currently have a fairly traditional system which is either a Y or S plan depending on which motorised valve you have installed, with the additional of a low loss header. This means that the flow temperature of the boiler going into your heating system has to run at a minimum temperature required to heat your DHW to sufficient set temperature and it will do so at all times regardless of the heat demand of the house. So if your hot water is set to 50C the flow needs to be at least about 8C higher, ideally more. At present, your boiler will only modulate in order to keep the flow temperature at that fixed temp. You can obviously get your system running as efficiently as you can by balancing it to mostly be in condensing mode.

 

It's difficult to find reliable data to provide specific figures on the savings, but what we do know is that with either load compensation or weather compensation based modulation provides savings in the region of about 10-16%. With the use of PDHW it's going to be a bit more because you can benefit from the efficiency advantages of lower flow temp & the boiler condensing at lower temps for space heating. But then this also depends on usage patterns and correct system setup.

 

If you are going to undertake further work, then to get the best out of the system you should also install modulating controls, that are either load compensating, weather compensating, or both. I'd probably also ditch the low loss header at the same time.

 

I'm also wondering whether you have some comeback on your installer depending on the nature of the contract and what this specified, bearing in mind that doing all the above mentioned stuff is not really a complex high cost design process.

[JohnMo]

@SimonD so maybe a daft question, and out of interest - is a 4 pipe boiler such as the Viessmann, basically a combi boiler with a pump on the DHW side? So instead of taking in fresh water, uses system water to heat the cylinder?

[marshian]

2 hours ago, JohnMo said:

@SimonD so maybe a daft question, and out of interest - is a 4 pipe boiler such as the Viessmann, basically a combi boiler with a pump on the DHW side? So instead of taking in fresh water, uses system water to heat the cylinder?

 

I thought they (System boilers which aren't combi boilers) had a valve inside to divert between Flow to Cylinder and Flow to CH circuit. The call for HW or CH determines the valve position and the boiler settings for either HW or CH

[SimonD]

3 hours ago, JohnMo said:

@SimonD so maybe a daft question, and out of interest - is a 4 pipe boiler such as the Viessmann, basically a combi boiler with a pump on the DHW side? So instead of taking in fresh water, uses system water to heat the cylinder?

 

No daft question, but yes, it pretty much is. The internal pump does both duties using an internal diverter that you'd see on a combi. I reckon it's the same hydraulic unit as used on a combi minus the plate heat exchanger and uprated pipe size for the DHW flow and return. The normal intake of fresh water becomes the return from the cylinder. All using the system water.

[JohnMo]

59 minutes ago, SimonD said:

 

No daft question, but yes, it pretty much is. The internal pump does both duties using an internal diverter that you'd see on a combi. I reckon it's the same hydraulic unit as used on a combi minus the plate heat exchanger and uprated pipe size for the DHW flow and return. The normal intake of fresh water becomes the return from the cylinder. All using the system water.

Makes you wonder if you could simply strap an external pump on the DHW pipes and charge a cylinder. Use a heat pump cylinder at 14 to 16l/min - same as 6kW heat pump. Then leave the CH on WC.