How to measure the remaining HW in an unvented cylinder

[Adsibob]

1 hour ago, Lofty718 said:

since he has only UFH in his house it seems to me the most efficient way of setting up his system would be to run two different flow temperatures one on hot water priority for the DHW and then the boiler at all other times providing flow direct to the UFH circuits.  This would mean boiler always condensing 100% of the time in CH mode

Thanks for this @Lofty718, but just to flag that I do also have two towel rads on their own zone, which will always need hotter water than the UFH temp water, but presumably they could be heated by the same water that heats the system boiler?

[SimonD]

4 hours ago, Adsibob said:

There are four UFH manifolds in total:

1. two on the ground floor (one for zones 00 and 03 which are on the upper ground floor; and one for lower ground zones 01 and 02)
2. one on the first floor
3. one on the second floor

 

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.

 

Now this would mean a compromise when it comes to the towels rads temperature, but they could easily be kept warm for good comfort.

 

There is a trend to opt for UFH as the default but I think there are situations where a low thermal inertia system is more appropriate due to occupancy patterns, system use, and building characteristics and I think this is such a situation, but the UFH is alreadsy installed.

 

3 hours ago, Lofty718 said:

can I ask why you think he needs a buffer? it's quite unusual.

 

It's just to do the requirement for zoning and if you have lots of zonesand youuse then, it's better to have a buffer in there.

 

 

[JohnMo]

7 minutes ago, SimonD said:

requirement for zoning and if you have lots of zonesand youuse then, it's better to have a buffer in there.

Or could that be a volumiser, and do away with hydraulic seperation and additional system pump.

 

Currently he has pump in boiler, pump the other side of the LLH, then one on each UFH manifold - lots of pumps.

[marshian]

12 minutes ago, JohnMo said:

Or could that be a volumiser, and do away with hydraulic seperation and additional system pump.

 

Currently he has pump in boiler, pump the other side of the LLH, then one on each UFH manifold - lots of pumps.

 

All nicely chewing away on his electrickery supply - nice if you can afford it

[SimonD]

39 minutes ago, JohnMo said:

Or could that be a volumiser, and do away with hydraulic seperation and additional system pump.

 

Currently he has pump in boiler, pump the other side of the LLH, then one on each UFH manifold - lots of pumps.

 

Yes, that's certainly an option. I have to admit that I initially incorrectly assumed the huge Grundfos circulator was in part for a large rad circuit.

[Dan F]

2 hours ago, Adsibob said:

Thanks for this @Lofty718, but just to flag that I do also have two towel rads on their own zone, which will always need hotter water than the UFH temp water, but presumably they could be heated by the same water that heats the system boiler?

 

IMO That gets complex having seperate zone just for towel rails.  Also in spring/summer impacts efficiency as boiler/ashp has to produce max(zoneTemp1, zoneTemp2) and mix down typically, so you loose out on advantages of weather comp.  Best to use electric towel rails and stick them on a timer so they are on for 1-2hrs after presense is my view.

Edited February 1 by Dan F

[Dan F]

16 minutes ago, JohnMo said:

Or could that be a volumiser, and do away with hydraulic seperation and additional system pump.

 

Currently he has pump in boiler, pump the other side of the LLH, then one on each UFH manifold - lots of pumps.

 

I have two mixed circuits that can at different temperatures (and follow their own heat curves). For this approach, each circuit needs a pump and mixer valve and you need hyraulic decoupling on the flow (a volumizer on the return doesn't help).   I'm not sure exactly what @Adsibob has installed, but i would argue he needs pumps on UFH manifolds (for mixed circuits) or the circulation pump after the LLH and no pumps on manfiolds (all circuits running at same temp), not both.

 

[JohnMo]

21 minutes ago, SimonD said:

huge Grundfos circulator

It is huge and running on speed 2, so not a small energy input.

[Lofty718]

I have towel rads running on weather compensation flow temperatures on two different circuits. One towel rail is on the UFH circuit and the other 3 bathrooms are on the radiator circuit, my bathrooms are always very nice and warm but I did choose 1800Hx500L  towel rails. Obviously this means towel rails won't be on in the summer but that's a bit wasteful regardless.

 

I did wonder about that huge pump he has on his circuit, it looks expensive and totally uneccessary i've only seen those installed in mansions lol.

 

@Dan F when you say you have mixed circuits do you mean you have electronic mixing valves? what curves are you running in your place? I'm on 0.4 for radiators and 0.35 for underfloor heating

 

A mixed circuit for each of @Adsibob manifold would be too costly you could run the whole system from one mixer or even better straight from the boiler.

 

I read back on a previous thread in April where we were discussing this and you said your house is split into 12 different zones... is this true? that's insane.. so you have 12 different thermostats?!

 

This is how my boiler is running today, constantly on at low temp. I recently range rated the boiler down to 8kw, meaning @ 30KW It's insanely oversized.

Edited February 1 by Lofty718

[Adsibob]

Thanks everyone for all the help with this, it really is appreciated.  A couple of points of clarification / feedback:

 

I’m really keen for the towel rads to have fairly high temp serving them when they are switched on. This is because we ONLY use them to heat towels, so they really only come on for short periods. Maybe 20 min at a time once or twice a day at most. I simply tell Alexa “switch radiators on for 20 minutes” and she does the rest. It works really well. We do not need to use these to heat the bathrooms themselves, we can do that with UFH.

 

2 hours ago, Dan F said:

Best to use electric towel rails and stick them on a timer so they are on for 1-2hrs after presense is my view.

This would have been a good idea, but I don’t have an easy way to retrofit that. I think my towel rails are water only ones, and one of them is mounted on tiles in a wet room area. Getting new ones and supplying them with electricity will be expensive and disruptive I imagine. I am much more relaxed about doing disruptive work in the utility room where the boiler and LLH is, and in the MVHR and cylinder room in the attic, and even where the manifolds are, as all of those spaces are hidden away from view and they are service areas really, rather than places with a lot of aesthetic expense.

 

Clearly pumps use electricity and I’m keen to save that too, but I query how much electricity is really consumed by all these pumps, given the manifolds aren’t all on all the time. I estimate we are running 3 of the 4 manifolds for about 3-5 hours a day on weekdays and 8hr a day on weekends, and one manifold (the top floor one) for 3-4 hours, once or twice a week.  There are obviously lots of issues with my current setup, and the number of pumps is one of them, but it’s not high up on the list.

Edited February 1 by Adsibob

[Adsibob]

2 hours ago, Lofty718 said:

I read back on a previous thread in April where we were discussing this and you said your house is split into 12 different zones... is this true? that's insane.. so you have 12 different thermostats?!

Yes, this is true. You can see them on the previous page of this very thread.

[Adsibob]

@Lofty718, the figures you posted for your boiler look impressive. How big is your house? What type of construction is it? What is your average monthly usage in winter?

[Adsibob]

I see Tado is listed second on a Viessmann article entitled "Which smart thermostat to buy: a buyer's guide". I think I will be preparing a letter of complaint asking them to compensate for the £1200 I spent on Tado garbage, though it's confusing because apparently there are "European" models, whatever that means these days, that are compatible with opentherm.

 

It really is quite shocking that the article concludes with the following (my italic emphasis) conclusion, which completely ignores the incompatibilities between most of the thermostats mentioned and the modulating features of some Viessmanns:

 

Which smart thermostat to buy

So there you have the top-rated smart thermostats currently available in the UK. But how on earth do you pick one?

It’s best to consider what exactly it is you want the thermostat to do. Do you want to be able to control multiple zones, save money on your bills or keep an eye on issues and problems? Your choice of thermostat will likely depend on which of these things is most important to you. It’s likely that you also have a budget in mind, so price will be a contributing factor.

Finally, it could also depend on the type of system you already have. Typically, the ViCare thermostat will work only with a Viessmann boiler. If you’re a British Gas customer, you may be able to get a discount on the Hive thermostat system. But you may wish to avoid the Hive if you want to control a heat pump, for example.

[SimonD]

42 minutes ago, Adsibob said:

though it's confusing because apparently there are "European" models, whatever that means these days, that are compatible with opentherm.

 

The European model refers to the combi controller, not 2 channel for s or y plan. See link here: https://uk.shop.tado.com/products/add-on-wireless-receiver-eu-version

 

This model has to be ordered specifically from Tado and is shipped from Germany. I have ordered these for installation. I have done one on a Viessmann combi too. The problem is that this model costs £199 from Germany whereas the combi model you get from a local UK supplier can be as little as £89, but which doesn't have Opentherm compatibility and there's no clarity about this either - although there was an apology from Tado on the Heat Geek website but only after they'd removed the functionality from UK models without telling anyone.

 

Regarding S or Y plan here's a recent thread from the Tado community confirming no modulation:

https://community.tado.com/en-gb/discussion/16937/opentherm-with-y-plan-setup

 

Basically combi is fine, lots of threads on the internet about Tado,opentherm and s/y plan and how to get it to work and general conclusion is get something else or go PDHW and weather comp.

[Lofty718]

2 hours ago, Adsibob said:

@Lofty718, the figures you posted for your boiler look impressive. How big is your house? What type of construction is it? What is your average monthly usage in winter?

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)

Edited February 1 by Lofty718

[Adsibob]

6 minutes 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 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)

Interesting. Your construction is very similar to mine, in that I'm 1930s semi, with some cavity walls where we've extended at the rear. Only difference is my insulation in floors and loft and EWI. My house is a bit bigger than yours and our gas bill was also about £6 a day for December. But we don't cook with gas, as we have induction. Do you have MVHR? 

What was your actual kwh usage for December and where in the country are you based?
 

[Lofty718]

The gas cooker costs peanuts relatively to heating and HW so doesn't add too much. Don't have MVHR either

 

UFH is only 45sqm of mine, the radiator circuit eats up a lot of gas (11 radiators inc bathrooms) I imagine if you can get your boiler running with modulation and low flow temperature your gas usage will be tiny. I'm quite happy with the gas usage of mine considering the comfortability and just leaving it on 24/7

 

Few fails on my install happened too, first being a 30kw boiler with minimum modulation of 5.8kw, where as yours is 1.9 or 2kw can't remember. Then also the UFH was 200mm centres in a big open space, which isn't so good. But lessons learnt

Edited February 1 by Lofty718

[Dan F]

15 hours ago, Lofty718 said:

@Dan F when you say you have mixed circuits do you mean you have electronic mixing valves? what curves are you running in your place? I'm on 0.4 for radiators and 0.35 for underfloor heating

 

Yes, with aroTherm+.  Each circuit has elecontric mixing valve, temp sensor and pump.  All controlled by a VR71 wiring center:

- 0.15 for UFH

- 0.4 for a garden room which I plumbed into main house heating.

- higher for comfopost which I hardly use anyway.

[Dan F]

15 hours ago, Lofty718 said:

This is how my boiler is running today, constantly on at low temp. I recently range rated the boiler down to 8kw, meaning @ 30KW It's insanely oversized.

 

Looks like you in perfect shape to move to a ASHP 🙂. Not make any sense in your case with £7.5k grant?

[JohnMo]

12 hours ago, Adsibob said:

I see Tado is listed second on a Viessmann article entitled "Which smart thermostat to buy: a buyer's guide". I think I will be preparing a letter of complaint asking them to compensate for the £1200 I spent on Tado garbage, though it's confusing because apparently there are "European" models, whatever that means these days, that are compatible with opentherm.

 

It really is quite shocking that the article concludes with the following (my italic emphasis) conclusion, which completely ignores the incompatibilities between most of the thermostats mentioned and the modulating features of some Viessmanns:

 

Which smart thermostat to buy

So there you have the top-rated smart thermostats currently available in the UK. But how on earth do you pick one?

It’s best to consider what exactly it is you want the thermostat to do. Do you want to be able to control multiple zones, save money on your bills or keep an eye on issues and problems? Your choice of thermostat will likely depend on which of these things is most important to you. It’s likely that you also have a budget in mind, so price will be a contributing factor.

Finally, it could also depend on the type of system you already have. Typically, the ViCare thermostat will work only with a Viessmann boiler. If you’re a British Gas customer, you may be able to get a discount on the Hive thermostat system. But you may wish to avoid the Hive if you want to control a heat pump, for example.

Not sure the open thermostat one would have worked for you, as you have so many zones and suspect most will be open and closing UFH manifold loops. An opentherm thermostat would really only be any good in a central area doing all the heat control - single zone.

 

Weather compensation

You have a bunch of thermostats already installed and connected to your manifolds and mixers and pumps. The mixers will limit the lowest flow temp from the boiler you can use as there will be around 10 degs of mixing going on inside the mixer.

 

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]

1 hour ago, JohnMo said:

An opentherm thermostat would really only be any good in a central area doing all the heat control - single zone.

 

This is a really good point. Most, if not all control systems that provide modulation, whether weather comp or load compensation are really best in single zones. I was talking to a technical person at Honeywell who was indicating that as Opentherm is designed as a heating protocol it doesn't really work very well with DHW (e.g. when using Opentherm to manage priority hot water) and it is not optimal when dealing with motorized valves -it doesn't like them that much.

 

When I've spoken to various boiler manufacturers and control manufacturers both the implicit and explicit message is the same. For example, with Worcester Bosch boilers, you can have modulation and pdhw without any zones, or you can have zones without modulation because as soon as you add motorised valves, the design of the control system means that the signal must be converted to 230v so relies on relay to work.

 

I do think there is a mismatch between control manufacturers and boiler manufacturers and I also think that some of the boiler designs are defficient in this regard - they are often limited by silly design implementations/limitations.

 

This makes it extremely difficult to design and install some systems that by their nature might need zoning, but especially when you consider the Building Regs Part L requirement for zoning.

[Lofty718]

3 hours ago, Dan F said:

 

Yes, with aroTherm+.  Each circuit has elecontric mixing valve, temp sensor and pump.  All controlled by a VR71 wiring center:

- 0.15 for UFH

- 0.4 for a garden room which I plumbed into main house heating.

- higher for comfopost which I hardly use anyway.

Identical setup to me just with a boiler instead, I have VR71 with two zones but one zone (radiators) is an unmixed circuit.

3 hours ago, Dan F said:

 

Looks like you in perfect shape to move to a ASHP 🙂. Not make any sense in your case with £7.5k grant?

I will consider in future, maybe running a hybrid system keeping the boiler for HW although you cannot get the grant with a hybrid system. I didn't fancy a heat pump initially after reading about a lot of people having issues with their installs and didn't fancy a huge unit on the patio lol I've got the whole heating setup tucked nicely in the loft.

 

 

 

I think @JohnMo suggestion is a good one. Will result in a low temperature system and efficient system without a ridiculous outlay.

 

I looked at the cost of the massive pump on his HW circuit and depending on the model it's at least £500ish. @Adsibob that is a grundfos magna pump right? I feel the installer has really taken advantage here with overspeccing the amount of equipment needed.

Edited February 2 by Lofty718

[SimonD]

5 hours ago, JohnMo said:

Run heating at a fixed flow temp (not WC), but run way lower flow temp than it's run now,

 

2 hours ago, Lofty718 said:

Will result in a low temperature system and efficient system without a ridiculous outlay.

 

The marginal cost of installing weather compensation alongside all the other suggested works is so minor and the long term benefits such that it would be silly not to install it if @Adsibob decides to modify the system. To me it's a bit like suggesting a shiny new efficient boiler but keep the old thermostat - oh, hang on, that's exactly what this suggestion is 😉

 

Remember, we're here because of the controls in the first place!

Edited February 2 by SimonD

[Lofty718]

 

1 hour ago, SimonD said:

 

 

The marginal cost of installing weather compensation alongside all the other suggested works is so minor and the long term benefits such that it would be silly not to install it if @Adsibob decides to modify the system. To me it's a bit like suggesting a shiny new efficient boiler but keep the old thermostat - oh, hang on, that's exactly what this suggestion is 😉

 

Remember, we're here because of the controls in the first place!

I agree, if it was me I would 110% install weather compensation but a lot of people are dubious about it and it's a step too far out of the norm of normal heating lol

 

To run his system on true weather compensation he needs to ditch all of the mixing valves on the manifolds and use an electric mixing valve, which I would highly recommend as they are brilliant bits of kit for controlling UFH.

[Dan F]

5 hours ago, Lofty718 said:

Identical setup to me just with a boiler instead, I have VR71 with two zones but one zone (radiators) is an unmixed circuit.

I will consider in future, maybe running a hybrid system keeping the boiler for HW although you cannot get the grant with a hybrid system. I didn't fancy a heat pump initially after reading about a lot of people having issues with their installs and didn't fancy a huge unit on the patio lol I've got the whole heating setup tucked nicely in the loft.

 

Efficient install like yours seems it is will actually be cheaper to run than gas, and thats without considering overnight tarrifs or PV.   As for the external unit,  you can have them further away if requied... and gotta think about the planet too 😄

 

Question though: Why would you want/need to keep a boiler for HW?