Very high 75,000kw per annum gas consumption

[HRP123]

How DIY capable are you? Three or four PIR sensor's and a bit of three core cable (L, N and SL) would not cost you much. Wire them in parallel, in series with the pump supply, to run set for say - ten minutes once triggered. You would be saving on both gas and electric bill.

Thanks, the issue with a large house is getting the PIRs to the 6 locations while concealing the wiring ... so it wouldn't easily be feasible to do this. Wireless PIRs could be unreliable due to beam/block floors and block walls.

 

[HRP123]

You should fit weather compensation and repipe the boiler to make it a hot water priority system

The UFH and the radiator pumps should also be seperated at the header and the UFH be controlled by an esbe mixing valve instead of the mixing valve on the manifold.,

This type of system will allow you to run 3 different flow temperatures on your system. One for the cylinder when it calls for heat as a priority which shuts off flow to everything else and then two seperate flow temperatures for underlfoor heating and radiators.

The only way to reduce gas consumption is to get lower flow temperatures, there may also be issues with the cylinders if there is secondary circuilation pumps or bad wiring somewhere for the UFH, you really need a professional in to sort this out

Actually I think a better setup for a larger house is to be able to do both hot water and heating at the same time which is why we originally put in a low loss header. The UF is already separate at the header as you suggest. Could you please explain the difference betwen the ESBE mixing valve versus the current JG Speedfit UF mixing valve which the plumber had fitted to the return? Does an EBSE valve work in a different way?

So in a sense the system is as you have described except that we are relying on the boiler to modulate up and down based on how many circuits are calling for heat. The problem is the way it is setup, I wonder if the JG mixing valve on the UF circuit is somehow distorting the flow temperatures to all the circuits, as I don't seem to be able to get the boiler flow temperature at the HW or radiator circuit - instead it is closer to the temperature set on the UF mixing valve.

Thanks for taking the time to put down your thoughts!

 

[HRP123]

What does the heat loss calculation come up with? The house sounds like it's bigger than average, but even so 40000 kWh/year is very high IMO, let alone 75000.

So I used the Heat Engineer heat loss calculation and it suggested based on my peak usage as assumptions (i.e. when guests are here) and with the lowest assumptions regarding insulation / glazing etc (i.e. I used Building Regs 2006 but I think my house is better than those) that the hot water is around 11,000kwh and the heating 51,000kwh. So this is high ! But in reality my guess is that this house based on being constructed 15 years ago with 100mm cavity insulation, brick/block/insulated floors and roof - should be around 40,000kwh if the system is setup correctly.

 

[HRP123]

How can this be true if you have such high gas usage!
if the demand rises dramatically when the temp falls this points directly to poor insulation and / or high leakage rates. Hot water return pumps use massive amounts of heat especially if the hot water circuit isn’t insulated. This can often be more then 1kw per hour when switched on.

Thanks - I think the high gas usage is due to the system somehow being inefficiently designed - i.e. due to the low loss header, multiple pumps and zoning we have the issues of getting the right flow temperature to the right circuit (whereas now I am suspecting this could possibly be distorted by the UF mixing valve and the low loss header), and making sure the boiler is actually modulating based on the amount of heat/HW demand... and a problem that cannot be easily fixed, which is in periods of low demand (say one UF zone coming on demaing 2kw) the boiler (WB 40cdi from 10 years ago) can only modulate down to 9kw instead of the lower required demand.

 

[HRP123]

Get a gas tightness test.

How many people in the house, water usage, corner baths, long showers?

40kW sounds ridiculous but even so, say the house loss is in reality 20kW, the house cannot absorb 40 so the boiler will be cycling a lot, you say yours is not.

Can the boiler be range rated?

Running a Worcester at condensing temps continually means the annual service will need to be a proper service and strip down rather than a safety check

www.Heat-Engineer.com, spend a tenner and a day, do it properly. There's a webinar this evening 28th Feb at 7pm, register for it.

Post photos front, back and sides of the house removing identifying marks if you like.

Your gas meter is not your enemy, it's your friend. Run heating over an hour or a cycle at a noted external temp and you'll know your heat loss by calculating gas used (don't roast a joint at the same time). Alternatively turn off a zone, run one zone reading the meter before and after.

These things you can do and are free other than a tenner for heat loss calc and you losing a day off.

Thanks for all the tips and information about the seminar (I missed it!).

I have paid for their heat calculation (see above).

What I am trying to work out is how the boiler is modulating based on the amount of heat demand. So I have range rated the boiler, now it is at 70% of the output. Max gas demand per hour seems to be around 25kw.

However I do not know how this is modulating down based on which circuit and sub circuit is calling for heat yet.

I can tell when the radiators circuits open because of my Nest on this circuit (with a day lag I can look at the history).

I cannot tell when a single or combination of underfloor zones open (just dumb battery powered room thermostats). So I'm about to connect wireless copper pipe temperature sensors to detect when the pipe temperature on the UF zone rises to then work out how long it has been open. However I cannot tell how many actual zones / actuators are open when the UF zone opens.

I know when my towel rails open because it is on a simple timer.

I cannot tell when the hot water cylinders call for heat. So again I am going to connect a temperature sensor here and try to work out how often this zone opens each day. If it opens and someone isn't showering it will be due to heat loss or the secondary hot water pump.

Then I need to correlate this to half hour gas usage to check if the boiler is modulating based on how many circuits are open. The problem as you indicate is to do this over a period of time I have to sit by the home hub display for a few days.

 

[oldbutnotdead]

What sort of volume is your low loss header?

 

[Friday round]

Have you reconciled the hot water estimated at 900-1000kwh monthly against your billing actuals for the periods when heatings off?

 

[Deleted member 281264]

Actually I think a better setup for a larger house is to be able to do both hot water and heating at the same time which is why we originally put in a low loss header. The UF is already separate at the header as you suggest. Could you please explain the difference betwen the ESBE mixing valve versus the current JG Speedfit UF mixing valve which the plumber had fitted to the return? Does an EBSE valve work in a different way?

So in a sense the system is as you have described except that we are relying on the boiler to modulate up and down based on how many circuits are calling for heat. The problem is the way it is setup, I wonder if the JG mixing valve on the UF circuit is somehow distorting the flow temperatures to all the circuits, as I don't seem to be able to get the boiler flow temperature at the HW or radiator circuit - instead it is closer to the temperature set on the UF mixing valve.

Thanks for taking the time to put down your thoughts!

With hot water priority and a high quality cylinder it's not an issue at all. If it is a problem you can fit 2 esbe mixing valves one for the radiator circuit and another for the underfloor heating circuit and on Vaillant controls this allows paralell charging of the cylinder.

ESBE mixers/actuators allow MUCH greater control and comfort than the rubbish mixing valve on your manifold, that is very outdated technology for creating a mixed heating circuit. Those mixing valves take 70c water and mix it down to 35-50c at the manifold where as an esbe will be piped into the return of the whole heating system attached to a 3way valve and will use the cool return water to feed back into the UFH system and create it's own loop rather than the bog standard manifold setup.

see this video it explains it better.

 

[oldbutnotdead]

So I used the Heat Engineer heat loss calculation and it suggested based on my peak usage as assumptions (i.e. when guests are here) and with the lowest assumptions regarding insulation / glazing etc (i.e. I used Building Regs 2006 but I think my house is better than those) that the hot water is around 11,000kwh and the heating 51,000kwh. So this is high ! But in reality my guess is that this house based on being constructed 15 years ago with 100mm cavity insulation, brick/block/insulated floors and roof - should be around 40,000kwh if the system is setup correctly.

Not meaning to be rude but 'thinking' your house is better insulated than building regs required at the time isn't exactly hard data. What were the requirements at the time, what can you point at and say 'yes this place exceeds that standard'.
The energy from the gas you are burning is going somewhere.
Silly question- has the boiler been serviced recently? Or could it be running stupidly rich.....
You reckon the flow temps are 55 odd so not a lot is going up the flue. You reckon the house is well insulated- I'm not convinced cos that's the only place the energy can be going. Even waste heat from dhw circulation and iffy mixing valves is going to stay inside the building and only leak away through the insulation. The modulation shouldn't be a big deal, your llh will be helping to reduce the cycling that must be occuring if the load is lower than your 9kw- not super-efficient but not usually disaster level

 

[fixitflav]

Have you reconciled the hot water estimated at 900-1000kwh monthly against your billing actuals for the periods when heatings off?

If it's any help, my gas consumption in the summer (HW only) is about 220 kWh per month. Old, probably well furred-up HW cylinder, estimated about 50:50 between heating the water and losses.

 

[old duffer]

At the size you have mentioned, this is commercial and should be treated as such so the idea of a single heat source on comparison to a normal domestic property has no meaningful comparison. The area of 464m2 over 3 floors makes each floor larger that the average modern detached.

You heat the air in the building so the figures become cubed, not squared so you have 1000m3 (assuming an average ceiling height of 2.3m).
Then you need to consider that air changes should be around 4 per hour so the property moves 96,000 m3 of air per day.
Let's assume you don't heat for 7 hours night then 8 hours day so for 9 hours each day you heat meaning the volume is 36,000m3 (air change over the time frame).
The night time heat loss vs daytime will be different so you need to capture this. Humidity has a very important role so you also need to measure these values

Then you need to examine the heat transfer method and its associated efficiency loses (rad size, location, delta T etc)
Then you need to measure the heat loss per room and match the rad size to the room (considering all factors)
Then you need to consider the heat phase time scale...pointless having a home that is comfortable just at the time the heating is switched off
Then you need to consider that when DHW is being used, the heating is not operational...

The energy required to raise 1m3 of air through 1 degree centigrade is linear so if you know the starting temp and the temp you want and the volume to heat, its simple maths.

A property this size should have separate DHW system.

You can do all of this with very simple maths but you need to collect a lot of data first

 

[HRP123]

At the size you have mentioned, this is commercial and should be treated as such so the idea of a single heat source on comparison to a normal domestic property has no meaningful comparison. The area of 464m2 over 3 floors makes each floor larger that the average modern detached.

You heat the air in the building so the figures become cubed, not squared so you have 1000m3 (assuming an average ceiling height of 2.3m).
Then you need to consider that air changes should be around 4 per hour so the property moves 96,000 m3 of air per day.
Let's assume you don't heat for 7 hours night then 8 hours day so for 9 hours each day you heat meaning the volume is 36,000m3 (air change over the time frame).
The night time heat loss vs daytime will be different so you need to capture this. Humidity has a very important role so you also need to measure these values

Then you need to examine the heat transfer method and its associated efficiency loses (rad size, location, delta T etc)
Then you need to measure the heat loss per room and match the rad size to the room (considering all factors)
Then you need to consider the heat phase time scale...pointless having a home that is comfortable just at the time the heating is switched off
Then you need to consider that when DHW is being used, the heating is not operational...

The energy required to raise 1m3 of air through 1 degree centigrade is linear so if you know the starting temp and the temp you want and the volume to heat, its simple maths.

A property this size should have separate DHW system.

You can do all of this with very simple maths but you need to collect a lot of data first

Thanks for explaining this. I've reread it a few times (just a novice myself) to understand.

Just a question for you here. So let's assume I am thinking just about one floor, the ground floor which has wet underfloor heating only. Assume this is 140sqm so cubed 280sqm. We have people at home all the time, so assume 4 air changes x 10 hours of heating per day = 11,200 - so does this equate to 11.2kw needed for this circuit for 1 degree temperature rise per day? Thanks for helping!

 

[HRP123]

Not meaning to be rude but 'thinking' your house is better insulated than building regs required at the time isn't exactly hard data. What were the requirements at the time, what can you point at and say 'yes this place exceeds that standard'.
The energy from the gas you are burning is going somewhere.
Silly question- has the boiler been serviced recently? Or could it be running stupidly rich.....
You reckon the flow temps are 55 odd so not a lot is going up the flue. You reckon the house is well insulated- I'm not convinced cos that's the only place the energy can be going. Even waste heat from dhw circulation and iffy mixing valves is going to stay inside the building and only leak away through the insulation. The modulation shouldn't be a big deal, your llh will be helping to reduce the cycling that must be occuring if the load is lower than your 9kw- not super-efficient but not usually disaster level

Yes I don't have hard data. I'm going by the fact that the house was built by a reputable niche builder - and that they used beam block on one of the intermediate floors plus a well insulated slab on the ground floor and pitched roof insulation.

Boiler is serviced annually.

I think the problem is as you hint with the LLH. My working hypothesis right now is that even though the boiler flow temperature is 65 degrees, the LLH is somehow distorting the flow temperature to the various circuits to attached the blending valve set temperature of the underfloor heating loop (which is set around 50 degrees). I don't know how to verify this aside from using an IR thermometer to measure the pipes going into the HW cylinders, which instead of being 60 degrees, are closer to 50 degrees.

Also when lets say four circuits are open (UF, HW, towel rails, radiators) - the boiler can burn at full (or currently range rated down to 70% as a test) power, however when only one circuit is open it is cycling too much. This can happen during the day with UF heating as slight temperature falls in individual zoned rooms start the boiler up, but then it cycles down because the UF loop cannot heat up that quickly due to the area it has to circulate. I have increased the UF pump from 1 to 2 speed but still, I think it cannot send 70% of 40kw so quickly, so the boiler modulates down and then eventually cycles.

I adjusted the anti cycling time from the default 3 mins to 8 mins yesterday to test how this impacts things.

Thanks

 

[oldbutnotdead]

Hmm. Do you have any pics of the JG blending valve fitted (it sounds like) at the LLH?
And was this valve part of the original install or a retrofit? If it was a retrofit, what was in place originally to regulate the water temperature in the UFH setup?
The 'usual' setup with UFH (as I'm sure you've discovered) is for the supply pipes to be at system temperature (55 upwards), at the UFH manifold there'd be a separate pump (circulating within the UFH pipework only) and a blending valve which keeps the UFH tubes at temperature by bleeding in heat as needed from the main loop.

EDIT I'm starting to think you might be onto something with your theory. If the blending valve is at the LLH there'll be a comparatively large (20-30 litres maybe) of low temperature water heading to the UFH and returning to the LLH and thus the boiler. If the blending valve is at the manifold, that 20-30 litres in the pipes of hot system water becomes part of your thermal buffer which will keep the UFH warm without firing the boiler incessantly.

 

[old duffer]

Thanks for explaining this. I've reread it a few times (just a novice myself) to understand.

Just a question for you here. So let's assume I am thinking just about one floor, the ground floor which has wet underfloor heating only. Assume this is 140sqm so cubed 280sqm. We have people at home all the time, so assume 4 air changes x 10 hours of heating per day = 11,200 - so does this equate to 11.2kw needed for this circuit for 1 degree temperature rise per day? Thanks for helping!

now you enter a different aspect of delta t. The method of heat transfer now depends upon the barrier to air (the top layer of flooring) and the heat loss you have downward. What is the total volume of liquid of liquid in the coil, what temperature is that, what are the loses....all this need collating to reach an answer. You also need to consider that the room has an even heat source which is rising (not falling as per wall rads) so you will feel more comfortable at a lower temperature. My daytime temp across the entire property of 5 levels (using oversized wall rads) is 16 degrees centigrade with 48% humidity, which is a comfortable "doing things" environment. This is achieved with flow temp of 35 degrees and I achieve a delta T of 10...yes 10
To lift the temp on an evening I up the flow to 45 to achieve 17 degrees and running at 50 degree for an hour lifts to a sweltering 18 degrees.

With such a huge ground floor and with underfloor heating, my approach would be to heat this space using a dedicated boiler to run low temp flow. The Japanese know all about this and have a range of combis that are perfect for your needs. They can even be fitted outside without the traditional flue and only need a cover if the temp is likely to drop to -20.
A 24kw multi function boiler with integrated IoT controller (as standard) is around £900 delivered.
Search Rinnai zen