UKH

Hope this isn’t going over previous discussions, but I’ve searched on here and most relevant threads are going back a fair while and this is, I guess, a fast moving subject.

We at present have a 20 year old non condensing gas boiler for heating and hot water with a 12 panel solar array with a diverter to the immersion heater to utilise otherwise unused solar. We also have a log burner (4.5kw IIRC) which on full bore with internal doors ajar makes a fair fist of warming if not heating most of the house.

The boiler is pretty reliable and heating engineers tell us it could easily go on for another decade. The question is do we grasp the nettle and invest in ASHP?

Things we are considering:

What is the outlook for gas prices?

What will this or future governments do about grants?

What is the point of doing our green duty while our kids think nothing of jetting off to Ibiza for a weekend?

Is our house so far from being energy passive that it won’t be worth the expense and we shan’t be comfortably warm in our dotage? When we had solar panels fitted, to get the grant support, we had to have a house energy survey, the result of which was 4 (I think). We possibly could improve matters by lining the inside of more of the outside walls and maybe we could double the between rafter insulation in the attic. The house is 1845 and has 22inch rubble filled stone walls.

Although the outline quote we’ve had from a company yet to visit the house seems a lot of money, it is less than buying even a small brand new EV.

 I would be interested to hear what is the experience of others.

 

In reply to Rog Wilko:

Given the headache of retrofitting, it's madness that new houses aren't already being built a lot more eco friendly. Lots of detached 'aspirational' houses being built in Kendal still connected to mains gas, with no solar panels.

No easy answer I don't think. We've got a similar set up. Using as little energy as possible and perhaps supplementing winter hot water needs with electricity rather than gas and save on the standing gas charge? Really like our optimmersion : )

In reply to Rog Wilko:

If you have a boiler that works reliably, what is your motivation for the change?

To reduce regular expenditure? eg reduce your gas bill?  Or to get a warmer house? Or to feel that you're doing your bit for the environment?

If it's purely financial you might find the pay back on your investment could take a very long time.

In reply to Rog Wilko:

I'd wait until your current boiler dies, but you really need 300mm plus in the loft anyway. If the house is a life time buy with no plans to move, slowly improve other areas of insulation to the best available. Triple glazing, some wall and floor insulation, solar panels... then when you switch you'll be in a much better position and your immediate term heating bills will fall too. 

In reply to Rog Wilko:

For an ASHP to effectively heat a building, the building needs to be well insulated , and (perhaps even more importantly) well sealed.

The main difference in terms of output between a gas boiler and an ASHP is that the peak heating power of an ASHP is lower and the radiator flow temperatures are also lower.

A gas boiler with a peak output of, say 30kW and with rad temps at 75C will be able to heat up a cold, leaky building quickly and then settle down to a lower output until the heating can be turned off (e.g. at night or when the occupants to work).

A large ASHP has a peak output of 16kW and a flow temperature of 55C. The UK's traditional model of intermittent heating of cold, leaky homes isn't well suited to an ASHP. They work most effectively when the building is more or less constantly heated. In other words, putting an ASHP in the wrong building could result in it taking forever to warm up. Literally, some ASHP installations and buildings are so mismatched that the building will never get to 20C above outside temperature.

Another factor that works against ASHPs on cold days, is that the colder the outside air is, the less heat they can pull from it. You may have seen 'co-efficient of performance' listed in specs. Basically electrical power in x COP = heating power out. The COP is lower in colder air, so on an icy day, when you need the highest heating output, your 16kW might be reduced to 12kW.

My advice would be to keep your boiler for now and focus on improving your building's insulation and air tightness. This will give you reduced fuel costs, lower emissions and increased comfort and will make the building more suitable for an ASHP if you ever choose, or are forced to, install one in the future. Bearing in mind that you have rubble filled walls, there will only be so much you can do in terms of sealing up the house without risking increased dampness and / or condensation. It's worth looking into Mechnical Ventliation with Heat Recovery (MVHR).

In reply to Jimbo C: I agree with most of that but would suggest getting a new condensing boiler now to reduce gas costs and CO2 emissions by maybe as much as 30% through higher efficiency, more sophisticated control and losing the hot water tank (despite the solar PV dump). Batteries my be a viable alternative for the solar PV? I don’t see ASHP being viable for a house like yours for the foreseeable future.

In the real world ASHPs don’t really reduce CO2 emissions as much as you think. When you switch one on it doesn’t result in a wind turbine spinning up, because they are always doing as much as they can. The MARGINAL load from your ASHP will instead be borne by a combined cycle gas turbine power station (irrespective of the green credentials of your electricity retailer). CCGT power stations are around 46% efficient so an ASHP with a seasonal efficiency of 3.0 will use around 0.7 kWh of gas to produce 1.0 kWh of heat. A modern gas condensing boiler will have a seasonal efficiency of around 88% using around 1.1 kWh of gas to produce 1kWh of heat. 
The justification of ASHP is based on the AVERAGE emission factor of UK electricity, but as I’ve explained above I think this is disingenuous with the way the grid operates at present and for the foreseeable future. Nobody would be more pleased than me if there was a growth in renewable and non fossil fuel generation to greatly diminish the need for marginal gas fired generation, but that isn’t going to happen any time soon.  

In reply to kevin stephens:

Could carbon capture be retro fitted to gas power stations in the future? Thus making them a bit greener. 

We have an air to air heat pump, so yes depending on the weather a varying proportion of our electricity generation isn't green, we've just relocated the point that pollution is emitted. 

In reply to ExiledScot:

Possibly sometime in the distant future (and at substantial cost), certainly not within the expected lifespan of a new gas fired condensing boiler

In reply to kevin stephens:

Are you sure that your 46% isn't a bit pessimistic?  I thought CCGTs achieved in the order of 60%.

You're absolutely right about marginal load more or less always being taken up by CCGT, of course, except for the really shitty days when it's taken up by coal.  We need to build some more wind farms.  Pity Dave wanted to get rid of all the green crap, really.

In reply to Jamie Wakeham: OK a little pessimistic, actually 49% to 50% based on the higher or gross calorific value of natural gas, ie the kWh/m3 shown on our gas bills. 60% would be based on the lower or net calorific value commonly used by turbine and generator engineers/salesmen. The difference is latent heat of water vapour that can be extracted from combustion product gases. That is why you sometimes see efficiency of condensing boilers disingenuously quoted as more than 100% (based on net CV). 

In reply to Rog Wilko:

We are moving to a property with no mains gas and currently has an oil boiler, so obviously a different starting place for the heat pump decision. However, one thing we are planning to do is fit underfloor heating. It seems to make a huge difference to how well the lower heat output is distributed and therefore effectiveness. We have found a system which is effective as a retrofit. 

That is not to say it is right for you, but maybe worth looking into if you did go down that route. 

In reply to ExiledScot:

Longannet power station in Scotland had a trial carbon-capture-and-storage project in 2009, apparently the process captured 90% of the CO2 that passed through it. There was an agreement with Shell to pipe it back under the sea to a depleted well but the project needed £1.5 billion which was not forthcoming so it was wound up by 2011, just before I retired from the gas industry...

In reply to ExiledScot:

CCS can be retrofitted, however it would be at quite significant cost and it puts a huge parasitic load on the plant so you would use a huge amount more gas for the same electrical power output.

I don't know the economics of CCS retrofit against Small Modular Reactors, but I would imagine the balance would be in favour of nuclear (if they are able to operate at their targeted generating cost) over the life of a plant.

In reply to petemeads:

Ah..ok. i was just pondering as if you look at the grid I feel we'll be gas reliant for decades. Obviously no short cut, money needs investing sooner rather than later. We often appear to be importing about 10% of our needs too. 

In reply to Jimbo C:

ASHP now exist that can run at 70 C if you want to use existing setup.

When you size an ASHP you do it for the cold situation not the hot. So I have an 12 kW Nibe F2040. I've had it 8 years. It heats a EPC C house from 1980s with 100 m2 footprint, 2 floors.

What you write about output makes no sense. On a warm day (outside temp ~9C) it will have a lower demand - so it will only use ~1 kW and output 6kW. On a very cold day, say -7C, it will use 5 kW to output 10 kW.

You don't run out of heat as it gets colder. Look at the countries where these are popular.

I've run mine continuously for 8 years (heating blocked Jun-Aug). I maintain a steady 21C all year round for less than the cost of oil. 

But then when I had mine installed it was done properly. Thermal model of the house, right sized radiators based on delta of 25C. A little more upfront cost, but I had the benefit of RHI for 7 years.

In reply to Philip:

The idea of heating an entire house, constantly to 21C (or whatever) seems nuts to me. Most of a house is empty most of the time, so it's vastly profligate. A heating system that requires this (even if cheaper than other options) is an inherently poor design.

In reply to MG:

That's what a proper installation of an ASHP is designed to achieve. It does need to be paired up with a building that has a low heat loss though. If you have a building with a high heat loss then intermittent heating, and only heating the rooms being used, makes sense. 

In reply to Philip:

That's what I said. The CoP is lower at colder outdoor temps. If 6kW is needed to maintain 21C indoors with an outdoor temp of 9C, you will need 14kW when it is - 7C outside. So my point was that because of the drop off in CoP, undersizing a heat pump causes a disproportionate drop in indoor temp. Fortunately you are getting on well with your properly designed system. I fear for those who end up with a poorly designed one. 

In reply to Jimbo C:

I get that 

But why? A bedroom say is occupied <50% of the time. Heating it all the time is wasteful, even if done very efficiently.

In reply to spenser:

Yes the effect of CCS on the energy balance for the plant never gets mentioned does it?

I know we are talking about gas generation, but David MacKay* suggests for a coal fired station it would reduce the delivered electricity by about 25%.Compressing and moving flue gases needs a lot of power!

* in his Sustainable Energy Without the Hot Air book, page 157.

In reply to chris_r:

These are very good questions and they have been hovering in my head too without any real conclusions being reached. Rather foolishly at our age, we like to take the long view and do worry about carbon footprint etc. To be realistic if we have another 10 years in our quirky cottage with its 4 floors and 3 staircases it will be surprise. But I do suspect houses like ours will become less saleable and a viable ASHP system could help to increase its value (as if it matters to us).

In reply to kevin stephens:

Re fitting a new condensing boiler. I have had lots of experience in the past with combi gas boilers, none of it good. Awful (and expensive) reliability. Are condensing boilers also a continual pain the backside? My current boiler may not be as efficient but it’s cost me next to nothing in repairs (not to mention inconvenience) over 20 years. Also, getting rid of a well insulated tank of hot water has no appeal for me.

In reply to Rog Wilko:

My partners grandparents have had solar since the mid 90's, and solar thermal panels for nearly as long. They recently had an ASHP fitted as well, alongside some radiator upgrades etc, albeit in a more suitable house (big 70's bungalow with typical CWI and loft insulation).

Their logic is they can afford to put greener options in whether or not they pay for themselves, and therefore its their responsibility to do so as many people can't. The solar has more than paid for itself and now keeps the ASHP going with little input from the grid, despite them being told it would reach its end of life a decade ago.

In reply to Rog Wilko:

Condensing boilers are fine if you buy a decent one. There is one downside though, and that is the condensate drain line freezing up in cold weather. The boiler locks out if this happens. There are two solutions: fit trace heating or fit a diverter which allows you to drain the condensate into a bucket inside the house until the condensate line thaws out. 

In reply to DamonRoberts:

An in perspective with which I have sympathy.

In reply to MG:

Not if it's properly insulated. Gas systems are designed to over heated to compensate for a house leaking.

In reply to Rog Wilko:

Should be “interesting”, not “in”

In reply to ExiledScot:

Yes. I was going to add that it's to do with the response time of the heating system (which is what I think you're pointing to).

A leaky house needs a large amount of heating power for the times when the indoor temp is low and you want it to be warm half an hour after switching the heat on.

A well insulated house won't typically get that cold (I'm talking about the heating being off overnight or similar), so can have a lower powered heating system. Equally you don't want it to get too cold because you don't have the heating power to give you a fast response time.

However, 21C in every room seems a bit too hot.