Heat Pump vs Gas Boiler: Lifecycle Cost Comparison (UK)

[JohnMo]

Take a look at the efficiency and recorded flue gas temps at low flow temps.  Screenshot from the same manual.

 

 

[scottishjohn]

look at this lifted from an article onundefloor heating and gas boilers

 

Condensing boilers

A condensing boiler is another excellent option for underfloor heating as they recover as much waste heat as they can.

| They then reuse waste heat in the system, which would otherwise be put out into the atmosphere from the flue.

Unfortunately, most standard radiators do not work as well with condensing boilers as they cannot make the most of the available energy. Traditional radiators have a flow temperature of 70°C and output of 60°C, which is above the range of a condensing boiler which operates at around 53°C.

 

 

not 35c which was what someone was saying they were running thier boiler at 

 

 

Edited October 28, 2022 by scottishjohn

[JohnMo]

The idea is the flue gas passes through a heat exchanger, it condenses, gets drained away.  The process has a phase change from steam to water, the latent heat is captured by the heat exchanger and passed to water increasing efficiency.  The acidic water goes direct to drain after that and does not go through the flue.

 

A condensing boiler working correctly has no steam coming out the end of the flue.

 

My boiler is running at target flow temp of 26 to 29 degrees depending on outside temperature.  So they do go below 35 degrees.

Edited October 28, 2022 by JohnMo
Deleted word

[scottishjohn]

4 minutes ago, JohnMo said:

The idea is the flue gas passes through a heat exchanger, it condenses, gets drained away.  The process has a phase change from steam to water, the latent heat is captured by the heat exchanger and passed to water increasing efficiency.  The acidic water goes direct to drain after that and does not go through the flue.

 

A condensing boiler working correctly has no steam in coming out the end of the flue.

 

Mine boiler is running at target flow temp of 26 to 29 degrees depending on outside temperature.  So they do go below 35 degrees.

I presume you are heating a buffer tank and then only heating it when you go below target temp ?

 or are you directly conecting the boiler to the underfloor system 

 those are floor target temps --not temp of water coming from bioler?

Edited October 28, 2022 by scottishjohn

[JohnMo]

Yes running a buffer, but the buffer has no thermostat, so just floats at supply temperature, so is never hotter than target flow temp.  Plumbed as a 2 port buffer.  Boiler fires up when it sees the return temperature drop to a level where its happy to fire up, keeps firing until it's no longer happy.  On an average 10 degree day, fires for 10 mins, off for 2 hours.  -5 day, on for 30 mins off for 30mins.

[scottishjohn]

10 hours ago, JohnMo said:

Yes running a buffer, but the buffer has no thermostat, so just floats at supply temperature, so is never hotter than target flow temp.  Plumbed as a 2 port buffer.  Boiler fires up when it sees the return temperature drop to a level where its happy to fire up, keeps firing until it's no longer happy.  On an average 10 degree day, fires for 10 mins, off for 2 hours.  -5 day, on for 30 mins off for 30mins.

so as suspected the boiler is not running at 35c ,but 54+ where it will be happy and not cause ezxcessive corrosion to  flue +heat exchanger

[JohnMo]

Sorry you really need to read up on condensing boilers theory.  What you have been told is just wrong and applies to non-condensing boilers.

 

Not sure where your getting my boiler is running at 54+ degs from, last time I looked while the boiler was firing it had a supply temp circa 28 and return 23/24.  If it gets to 35 it is forced to cut out, by the settings.

 

Only time it goes above that is for DMW as its a combi.

[PhilT]

21 minutes ago, JohnMo said:

supply temp circa 28 and return 23/24.  If it gets to 35 it is forced to cut out, by the settings

It's a really interesting revelation I had no idea such low temp high efficiency gas systems existed. What's your annual gas kWh usage and size of property?

[joth]

18 hours ago, Radian said:

18 hours ago, JohnMo said:

Thought they all were these days.

I think there's quite a bit of diversity in production around the globe. The Daikin Manufacturing Germany Gmbh factory was set up to re-brand Rotex Products into Daikin for example. Viessmann, Kensa and Vailant all have manufacturing plants in the UK. What I was thinking of were the frequently re-badged generic ASHP's that come out of China. Nothing necessarily wrong with those, I've considered them for my own heating before, but I have seen some with pretty primitive circulators.

Mitsubishi also manufacture in the UK

https://www.hvnplus.co.uk/news/mitsubishi-electric-invests-15-3m-in-uk-heat-pump-manufacture-09-11-2021/

 

Kinda surprising how many manufacture here, given how much lower the install base is here vs rest of europe.

[Radian]

23 minutes ago, joth said:

Kinda surprising how many manufacture here,

That's what I thought too. Hopefully we'll see prices fall as a consequence. Transportation costs of bulky products like these is significant.

 

[JohnMo]

44 minutes ago, PhilT said:

It's a really interesting revelation I had no idea such low temp high efficiency gas systems existed. What's your annual gas kWh usage and size of property?

Only had the system running in this configuration during Oct (off at moment due to warm temperature).  But have consistently delivered an average of 0.5kW (based on actual gas consumption) heat into the floor over a 27 day time period.

 

House is 192m2, UFH pipes at 300mm centres big buffer. In NE Scotland. In the depth of winter hoping for a 2-3kW gas input, but time will tell.

[PhilT]

1 hour ago, JohnMo said:

Only had the system running in this configuration during Oct (off at moment due to warm temperature).  But have consistently delivered an average of 0.5kW (based on actual gas consumption) heat into the floor over a 27 day time period.

 

House is 192m2, UFH pipes at 300mm centres big buffer. In NE Scotland. In the depth of winter hoping for a 2-3kW gas input, but time will tell.

Impressive. Passive build?

[JohnMo]

1 hour ago, PhilT said:

Impressive. Passive build?

No, but seems to be performing well.  Last winter was a disaster for gas consumption, underestimated what low temp heating needs to support it.  Lots of short cycling, house way too hot, then too cold most of the time, didn't appreciate how to manage a thick (100mm) concrete slab, hoped smart thermostats would help, but they just messed things up even more, the floor response time was outside there logic.

 

So operate as a single zone, with loops balanced to set room temperature 

[Green Power]

Say Radian is right that under 20W - call it an even 20 - for a pump. We still have 35W for a fan, so we now have 55W total.

 

55W x 4 hours = 220Wh = 0.22kWh x 365 days = 80.3 kWH/year.

x  £0.34 /kWH = £27.30/year = £355 over the 13 years.

[Radian]

12 minutes ago, Green Power said:

Say Radian is right that under 20W - call it an even 20 - for a pump. We still have 35W for a fan, so we now have 55W total.

 

55W x 4 hours = 220Wh = 0.22kWh x 365 days = 80.3 kWH/year.

x  £0.34 /kWH = £27.30/year = £355 over the 13 years.

 

4 hours for 365 days isn't very realistic. Here's how much time my boiler ran yesterday (quite typical for 8 months of the year)

 

 

2hr 10mins for HW. Minus a bit for the last push up to 55^oC which always entails a couple of on-off cycles when the boiler can't modulate any lower.

[JohnMo]

1 hour ago, Radian said:

 

4 hours for 365 days isn't very realistic. Here's how much time my boiler ran yesterday (quite typical for 8 months of the year)

 

 

2hr 10mins for HW. Minus a bit for the last push up to 55^oC which always entails a couple of on-off cycles when the boiler can't modulate any lower.

So are you using 2 hours x 11kW or 22kWh per day for hot water?  That doesn't sound right?

[Radian]

54 minutes ago, JohnMo said:

So are you using 2 hours x 11kW or 22kWh per day for hot water?  That doesn't sound right?

The total daily consumption (load) is as is labelled in the plot: 11kWh. Someone had a very long shower at 10:30 and it wasn't me 🙄

[PhilT]

On 29/10/2022 at 11:54, JohnMo said:

Only had the system running in this configuration during Oct (off at moment due to warm temperature).  But have consistently delivered an average of 0.5kW (based on actual gas consumption) heat into the floor over a 27 day time period.

 

House is 192m2, UFH pipes at 300mm centres big buffer. In NE Scotland. In the depth of winter hoping for a 2-3kW gas input, but time will tell.

That puts a whole new perspective on the life cycle cost comparison, if my calcs are correct, at that rate it looks like you're going to use around 8k kWh gas for a full year. Before installing my ASHP my last full year gas consumption was 21k kWh for a 120sqm property. So on a per sqm basis your gas boiler consumes around 25% of mine. The cost comparison with my heat pump would be you = 8,000kWh gas x 10.46 + 365 x 26.84 = £935pa, = £4.87/sqm, me = 3,000kWh electricity x 34.23 + 365 x 42.77 = £1,183pa = £9.86/sqm, around double the running cost per sqm. The only mitigation for the ASHP is the CO2 and energy consumption which, given gas contributes less than half of grid generation, means my equivalent gas consumption is roughly 1,500kWh pa

[JohnMo]

I have managed to use a 1k kWh of gas since 01 June to the end of Oct, which followed a series of modifications to heating and DHW system. 

 

Summer DHW mostly being heated by excess solar PV.  

 

Overall I am hoping for a sub 5k kWh annual consumption.  During Oct we had a number of days from 3 to 7 degrees, so am hopeful.  The 2 to 3kW input is at -5 so hopefully won't have that many days at that temp.

[Ferdinand]

On 29/10/2022 at 11:28, joth said:

Mitsubishi also manufacture in the UK

https://www.hvnplus.co.uk/news/mitsubishi-electric-invests-15-3m-in-uk-heat-pump-manufacture-09-11-2021/

 

Kinda surprising how many manufacture here, given how much lower the install base is here vs rest of europe.

The UK Govt has been targeting heat pump manufacture in the UK for a couple of years now. My impression is that there was a slow target - 600k per year by 2026 rather than by say 2023 - partly to let UK manufacture ramp up more. In the context of our economic pivot away from the EU single market that makes sense.

 

There were announcements in the budget back in 2020 iirc.

 

They have a carrot - £5k grants and eg the £1.8m of support funding indicated for Mitsubishi in that piece, and a stick  - which is the new gas boiler ban. And security of policy I think. That latter gives manufacturers a point at which their new boiler business will turn into a pumpkin if they do not move forward.

 

Plus stuff like zero VAT-rating on energy improvement products.

 

I'd expect that to succeed to some quite significant extent. There's a way ahead and a kick up the Rs.

 

Obvs the media will whine and whinge like a labrador denied sausages, but our media could not write a fair story about a government policy if Mack the Knife was holding a stiletto wrapped in barbed wire to their backside.

 

And I think lobby and green political groups position themselves to say Mooaaaarrrr !!, not "here's a start; let's think about how far we can get".

 

The one thing we know when any groups is interviewed about anything whatsoever is that the interview will contain a large element of "we demand that we get even more taxpayers' money than this for our cause and our organisation". That unfortunately is just the poisonous nature of our political culture.  

 

F