New Gas Boiler

[Robin]

how long do you make it for a 180 L tank, 3 kW heater, incoming water at

10 C? (Losses from cylinder may be ignored.)

[John Rumm]

I suspect even the marketing wonks would balk at claiming a CoP of 8:1 for a ASHP.

[Robin]

+1

actually, no, make that +£60,000 - the ballpark cost of doing a proper job on this v modest Victorian terrace. (I do wish someone would force the CCC to show that their estimates of the costs of insulating such houses are realistic when full regard is had to things like the risks of rot.)

[John Rumm]

And given we use gas to produce large quantities of electricity directly (and probably waste loads more providing spinning reserve for all the wind farms!) it is likely to remain that way for the forceable future. It is only the presence of artificial constraints like price caps that will distort the economics.

[John Rumm]

Gas boilers are typically cheaper than oil ones, and require less infrastructure. There are probably more installers as well. Much of the cost of doing the work will depend on how much other stuff needs to changing at the same time.

When we moved in here there was a floor standing Ideal mexico, running a fully pumped vented system with conventional slow recovery DHW cylinder. There were DHW and CH header tanks in a cupboard in an upstairs bathroom (effectively built into the former loft space). So it was not particularly effective (lift a shower head more than 4' from the floor, and the water stopped flowing!), slow to reheat, and expensive to run.

So I gutted most of the system, got rid of both header tanks, new wall mounted Vaillant system boiler, and e bus controls. Two heating zones, one DHW. Installed a 210L unvented cylinder heated from the boiler but with immersion backup. I also replaced a bunch of rads and installed some new ones in places where there were none before. ISTR it was around £3k for the parts alone. It took the best part of 10 days of work all in, and I expect it might have been quite pricey to pay someone to do all that! However the results are very nice to live with. Decent mains pressure showers and fast bath refills. Quick recovery. Heating that "just works" with very little supervision, taking changes in season and weather in its stride.

[John Rumm]

as is the dry rot or other water damage that you are not aware of because the system is continuously topping up for you to compensate for the leaks. :-)

[Harry Bloomfield Esq]

John Rumm was thinking very hard :

The quieter operation obviously goes hand in hand with greater efficiency.

[John Rumm]

They mention a different design of HEX though (Ali rather than SS etc)

I just had a look at an installers manual:

See page 12 - radically different design from the Ecotec range for example.

[Theo]

You coordinate it so the immersion runs after the gas has got the tank up to whatever flow temp you've set. So the immersion is only taking it from 50 to 60C, not 10 to 60C.

Theo

[Theo]

One thing my ASHP does is it looks at the return temperature. If the return temp is hot, it knows all the emitters are throttled back (by TRVs etc) and there's no point pumping more heat into the system, given there's a buffer tank to keep the loop supplied with hot for a while. Do any gas boilers do that?

Theo

[Robin]

Ah, so. My mistake. I agree a couple of hours would deliver +20 C.

[John Rumm]

Yup all of em these days, its called modulation. Basically with will try and load match - throttling their output power to meet the current demand and no more. That keeps condensing efficiency high and gives a nice stable temperature control without big swings and overshoots.

[SteveW]

Plus a proper assessment of feasibility. We already have cavity wall insulation, so to get better, we need internal or external insulation for the walls.

One wall of the house is a wall between the two houses, so no problem.

The front and rear of the living room, the front of the hall and two of the bedrooms could be insulated inside or outside (although the latter would not fit in with surrounding buildings and would require the roof extending). Insulating inside the front bedroom would require the hot water cylinder to move, along with all the central heating piping - it is already crammed in tight and even a couple of inches would require a lot of re-work.

The bathroom could only be insulated outside, without ripping up the tiled floor and walls, re-plumbing, etc., and as it is a small bathroom, it would feel uncomfortably tiny with any lost space.

The kitchen could only be insulated along part of one wall inside, without narrowing parts too much for the appliances to fit in or moving appliances too close to doorways. External insulation (including for the hall) would require moving drains and the soil pipe and would narrow the drive enough to prevent (necessary) access to the garage in the back garden (it is already very tight).

The third bedroom is above the kitchen, so the same restrictions on external insulation apply, plus there is only enough space now to squeeze between the bed and the chest of drawers, so internal insulation is impossible.

[Theo]

This is the one I have:

SCOP=5.4 That's at 7C outside/35C flow.

While it's set for 55C for hot water, often the weather compensation throttles back the radiator output so it's in that 35C ballpark. It's only if you work it hard will it ramp up the flow temp to the max.

It doesn't display the COP so I don't know how it changes through the year or how many kWh of heat I get out of it, but the number of actual sub-zero days where I live is relatively few.

It was installed exactly 6 months ago, and since then has consumed 2140kWh for all heating and hot water - including the coldest months of the winter. If we assume the same again for the summer and autumn (likely a substantial overestimate), that's 4280kWh pa. Previously we were using 1200 litres of oil pa, which is 12420kWh. That makes (a substantial underestimate of) my SCOP=2.9.

On that measure at current rates we'll spend £1284pa on electricity, against £1140pa on oil (at current Boilerjuice prices). If the annual usage comes in at more like 3000kWh (little heat in summer, stormy but not cold Oct/Nov) that would cost £900 and be a SCOP=4.

That's with no extra insulation (EPC=D/E), just a new cylinder and larger radiators.

Theo

[SteveW]

It certainly can - but not for 8 zones (one per room), all running at different times and temperatures.

If I go the Arduino ebus route, I have already looked at working out a total demand, based on individual room temperatures, of the rooms that are timed to heat and individual weightings for those rooms, converting that to a single, overall, household demand and sending that to the boiler.

[SteveW]

I've just looked at comparisons and nothing exceeds 350% averaged efficiency, with the higher efficiencies only possible when we least need heating (20°C and above outside) and much lower efficiencies (down to 150 to 200%) are normal during cold periods, just when we need it most. On top of that electricity prices are around 5 times that of gas and normally stay within the 4 to 5 times range, whatever the prices are at the time.

We therefore have the massive, up-front cost of insulating (and likely re-plumbing and re-decorating) the whole house and installing a very expensive heat pump and then still paying more in fuel costs than if we'd stuck with gas!

[SteveW]

The figures I am seeing are that gas has doubled in price, while electricity has almost trebled.

[Harry Bloomfield Esq]

Theo used his keyboard to write :

They all do it. All modern gas boilers check the return temperature and adjust their output to some extent, by modulation.

[Harry Bloomfield Esq]

SteveW explained :

+1

[Harry Bloomfield Esq]

2017 I was paying 11.209 and 2.390 per Kwh

Now I am paying 27.358 and 7.280 per Kwh